Measle Effect Rev 2

REPORT ON THE MEASLE EFFECT

FOR PRINTED CIRCUIT BOARDS

USED BY LANDIS & GYR (EM) TELFORD

AUTHOR : P. ROUSE CIRCULATION : J.HOWELL DIRECTOR OF MANUFACTURING J.NIELD TECHNICAL SERVICES MANAGER J.KING MANUFACTURING SERVICES MANAGER G.RUMMING CED DELEGATE D.WILLIAMS SUPPLY MANAGER P.ROUSE DESIGNER P. WARNER KCE EUROPE I.CURRY WELWYN SYSTEMS LIMITED

INDEX

DESCRIPTION PAGE TERMS OF REFERENCE........................................................................................................3

DEFINITIONS...........................................................................................................................4

INTRODUCTION......................................................................................................................5

BACKGROUND........................................................................................................................6

FINDINGS ................................................................................................................................7

CONCLUSIONS .....................................................................................................................10

Measle Effect ......................................................................................................................11

Dendritic Growth .................................................................................................................12

RECOMMENDATIONS ..........................................................................................................13

APPENDIX A.........................................................................................................................14

Letter and Memo. initiating investigation ............................................................................14

APPENDIX B.........................................................................................................................18

Specifications for tests to be done by ERA + Report from ERA .........................................18

APPENDIX C.........................................................................................................................29

Specifications for tests to be done by L & G Business Support..........................................29

Report from LGBS Lab .......................................................................................................29

APPENDIX D.........................................................................................................................34

Log. book entries for ERA 1st & 2nd tests..........................................................................34

APPENDIX E.........................................................................................................................36

Additional information on Solder resists and cleaning agents used in PCB manufacture and

by assembly subcontractor .................................................................................................36

PROBIMER 71....................................................................................................................38

PSR4000 ............................................................................................................................41

GRACE Electronic Materials...............................................................................................46

TAMURA.............................................................................................................................48

APPENDIX F .........................................................................................................................50

Test Results........................................................................................................................50

ENVIRONMENTAL CHAMBER TEST RESULTS ..............................................................58

Measle Effect Rev 2.doc Page 2 of 59 P.D.R.02/07/93

TERMS OF REFERENCE 1) To determine the cause of the Measle effect on printed circuit boards currently in production. 2) To establish the nature of the problem. 3) To Establish the chemical constituents of the substance causing the problem, with the use of external facilities. 4) To establish the effects of the problem on printed circuit assemblies, both in current production and in the field, over short and long term, including implication to the life and reliability of products such as Radio Telemeter, Gas Prepayment Meter ( ETM ). 5) To establish the size of the problem (via relevant statistics) and to make predictions of field failures with respect to time.


DEFINITIONS 1) The effect in question shall here, and after be referred to as the 'Measle Effect.' 2) Dendritic growth is the growth of lead crystals which have a 'fern like' appearance 3) 'SEM' is an abbreviation used for a Scanning Electron Microscope 4) EDX is an abbreviation for Energy Dispersive X-ray, which is equipment for analysing the chemical constituents of an object by covering it with an extremely thin coat of either Gold or Platinum. 5) PCA : Printed Circuit Assembly, i.e. printed circuit board with all the components on. 6) PCB : Printed Circuit Board. 7) Salt : Chemical name for reaction between an acid and a base electrolyte. 8) PTH : Plated Through Hole. A term to indicate a printed circuit board with copper pattern both sides, connected by holes which have been electolus copper and tin-lead plated. 9) Resist : Solder resistive film; lacquer or ink covering copper pattern to reduce short circuits during machine soldering process. 10) Tracking : This term refers to conduction of high voltages on the surface of a PCB between conductive lands. Not to be confused with copper tracks


INTRODUCTION This report has been compiled as a direct result of the discovery of the Measle effect, and has been necessitated due to the following reasons : 1) The possible seriousness of the problem relating to the reliability of all of Landis & Gyr's

products. ( See Memo dated 21/4/93 in Appendix A. 2) The difficulty in actually pinning down the cause of the effect and the chemical source. 3) The amount of money that the PCB manufacturer KCE has poured into chemical analysis on our behalf to establish whether or not the effect is as a result of a process problem in the manufacturing of the PCB, or due to chemicals or processes used by the subcontract assembly company Welwyn Systems Ltd. ( fair justification for ascertaining who is actually responsible for this problem ). 4) The need for an objective and unbiased analysis of the facts, with a reasonable number of statistic being available in order to achieve this. 5) The number of meetings which have been initiated in order to look at this problem, resulting from the Memorandum from Ruth Wainwright ( Dated 21/4/93 in Appendix A ) which showed the seriousness of the problem if indeed it is wide spread. This report is has the object of bringing together the analysis of affected boards ( with the aid of a Scanning Electron Microscope from a third party ), together with statistical information, to aid the decision as to whether this really is, or will be a large scale problem. The 'Conclusions' section will sum up the facts in such a way as to show : source; responsibility; implication for quality and reliability for affected products. The 'Recommendation' section will deal with actions which should be taken as a result of the conclusions.


BACKGROUND The Main issue brought out by this document is an effect which has come to be known as the Measle Effect. The part of this report called 'Findings' will show that there are two effects present which will be dealt with separately at that stage. In order to made it easier to understand what this report is about it is necessary to give some background to the main factors concerned. The following is a brief background on the types and usage of solder resist.

Solder Resist is a comparatively recent innovation in the printed circuit technology, i.e. in the last 30 years or so. Previously either the whole copper area would have been soldered if the PCA was Machine soldered, or if the PCA was hand soldered, only the component pads would be soldered. During the functional life of a PCA, any unsoldered copper would oxidise forming a protective layer ( since the oxidation in air is not progressive ), unless there was the presence of an electrolyte, e.g. aggressive flux and moisture; acid leaking from a battery or capacitor etc. The introduction of solder resist ( also referred to a protective lacquer ) during the mid 1960's, was to reduce the amount of solder deposited on the copper lands and tracks of the PCB and thereby reduce the number of solder short circuits common during machine soldering ( i.e. wave; dip or drag soldering methods ). A by-product of this was to protect the copper from oxidisation either by humidity or by electrolytes mentioned above. The loss of particles of solder resist is not a problem to the functionality of PCA's in itself, remembering that the main purpose of the solder resist is the literally resist solder during the assembly and soldering process. In terms of the type of PCB's which Landis & Gyr currently use, until recently the double sided PTH boards which we use have had all copper areas and tracks Tin-lead plated and then covered with solder resist. During the soldering of the PCA's it was often noticed that as the tin-lead plating under the resist was 'reflowed, there was a rippling under the solder resist, in some cases resulting in the loss of some of the solder resist, usually on large landed areas such as ground plains. For years this particular effect has been accepted in the industry as been not aesthetically good, but not affecting functionality. At present, and for the past 2 years now we have been using PCB's which have been selectively plated, i.e. the tin-lead plating is only deposited on the areas required, i.e. the plated holes and vias, and any areas required to be soldered. The implication of this is that there is now no Tin-lead plating under the solder resist. This means that there will be no rippling under the solder resist as hither to experienced, and it also means that we are back to the situation as with single sided boards where the resist is directly on top of the copper. This is seen as a step forward for both PCB fabrication in saving the saving of plating, and on the whole for the customer ( L & G ), who no longer experienced the unpleasant rippling.


FINDINGS As can be seen from the results of the two independent tests done by ERA and the LGZ laboratories (APPENDIX B and C) the following two area are high lighted : 1) The presence of sodium -hydroxide under the solder resist. 2) The clear presence of lead migration or dendrtic growth. It must be understood that there are clearly two different problems here and only the first causes the manifestation of what has already been referred to as the 'measle effect.' As a result the first part of this conclusion will deal with the presence of sodium-hydroxide. ADDENDA The following is some additional information supplied by KCE on what some other Assembly subcontractors do in regard to cleaning etc. 3 Cases Subcontractor from automotive industry This company has a no-clean policy. If there is a misregistration in the solder paste, the boards are disposed of. Alarm system assembly - Some problems experianced with flux resisdue so took on a non clean policy. Computer periferal assembly - has done work for Northern Telecom for 3 years. They had a problem with lead migration. Probem with in - house manufacture, changed to no clean except for conformaly coated assemblies. This company uses Alpha Metals LR701 or Multicore NC4U - non active and non corrosive solder paste. This was selected to burn off the active effects at the reflow stage. In addition they use flux : Multicore X33 When screen solder paste needs to be washed off they use Smart Sonic 440 Alkaline. Ultra sonic cleaning not generally recommended. Non corrosive flux, not recommended for extreme humidity applications - corrosive fluxes tend to be more moisture absorbent.


1) FAILURE MODE : MEASLE EFFECT It was first thought that the discoloration underneath the solder resist was some form of lead migration i.e. dendritic growth which was spreading underneath the solder resist and was causing it to blister and crack off if touched. Initial chemical analysis seemed to confirm this however it is now clear that the results initially released ( which were not clearly specified in their objective, and there was no accompanying report ) were asily misinterpreted. Nearly all of the tests were carried out on the top of the solder resist and found the second problem which will be discussed later. From the statistics on field returns, it can be seen that there is hardly any evidence of the presence of the measle effect in assemblies which have been in the field i.e. in an assembled state for up to six months. It has not been possible to determine how long these units have been in the field and therefore the type and duration of the environmental conditions of the field, if at all. The measle effect was first identified by the assembly subcontractor Welwyn Systems ( WSL ) on some boards which had clearly been through a process that only a minority of boards go through. This process was an additional cleaning process, which was applied when the solder paste, screen printed onto the boards was misaligned and therefore rejected by that quality process. When this problem was highlighted, a number of samples where put into the L & G environmental chamber for an accelerated life test to try and reproduce this problem. The test consisted of a 'damp / heat steady state' type test at 60'C @ 95% RH. The results of this test can be seen on pages 15 & 16. This test reproduced this problem dramatically on the first 6 samples from technology, but as the results show, other boards introduced at a latter stage were not so badly affected. Unfortunately ( due to the lack of proper documentation of the samples ), it is not possible to give the case for each board. Two of the boards which were unpopulated but wave soldered by another subcontractor ( not WSL ) have only shown small traces of the Measle Effect in the form of small dots. These boards were introduced about half way through the damp/heat steady state test. The third set of independent tests were carried out by ERA with very clear objectives ( see Appendix B ), to find out what substances were present under the 'dark staining' underneath the blistered solder resist areas and from this to suggest possible causes, and implications for the life expectancy of the functioning assemblies. As can be seen from the ERA report in Appendix B, there were traces of what was thought to be Sodium-Hydroxide, ( although it is not possible to detect hydrogen with the EDX method due to the low atomic number of Hydrogen ) were consistently found under the blistered areas. SOURCE AND EFFECT Sodium-hydroxide is a common chemical used in the manufacture of Printed Circuit Boards ( PCB's ). During Manufacture, Photo-imagable resists are used a number of times before the final solder resist is applied. These typically would be as follows : a) electroless plate resist b) etch resist c) solder resist Resists 'a & b' are 'process resists' for fabrication and are stripped afterwards using an aqueous alkaline solution, either a 2-5% aqueous sodium hydroxide solution, or a 5% aqueous potassium/sodium hydroxide solution depending on the recommendations of the resist manufacturer. ( examples of various types are in Appendix E ). After each process ( not all mentioned above ) the PCB is cleaned, so that there is no contamination during the next stage.


2) FAILURE MODE : DENDRITIC GROWTH The second problem area is the clear presence of lead migration or dendritic growth. As can be seen from the report from ERA, the first two sets of tests and results reflected this. As already stated these tests were mostly carried out on the top of the solder resist, and found traces of either SnPb ( Tin lead ) or just Pb ( lead ). The primary reason for dendritic growth appears to appears to be because L&G assemblies are specified as 'Non clean', i.e. the flux is not removed after soldering. There are always very small traces of SnPb where there are unwashed flux deposits on the PCB. Under normal conditions the lead and tin remain inert i.e. in the form of solder derivatives ( traces of SnPb ). However under the accelerated life conditions of elevated temperature and humidity, there is usually evidence of a whitish growth across areas of the surface of the board. This is degrdation of the flux deposits which show up in the form of swirl-patterns on the surface of the PCB, with some small fern like growths, usually from solder pads and areas where solder derivative have accumulated in the remaining flux deposits. The Dendritic or fern like ( crystalline ) growth is clearly on the top of the resist, and is promoted by the environmental conditions. This has not been found to spread under the solder resist due to the adhesion of the resist to the base material. As mentioned above Pb has been found in faults in the resist, in both cases, ( pictures 002; 003; 004 & 014; 015 ) these appear to be a ball of solder caught in the fault possibly during soldering. It should be emphasised that the field returns analysed in the statistics have not exhibited any Dendritic growth.


CONCLUSIONS


CONCLUSIONS The conclusions for the 'measle effect' and the 'Dendritic growth' will be dealt with separately as follows :

Measle Effect The measle effect has been established by both ERA and LGBS as being water soluble salts ( Sodium Hydroxide ) not being adequately removed from the copper surface of the PCB before the application of solder resist ( LGBS : Results 2.3; ERA page 7:(i)). In an environment of normal relative humidity, this would probably remain inert, however, under conditions of fluctuating and high humidity, such as encountered by gas and electricity meters in the field, e.g. a box outside a house ( in some cases the door is left open, and the relative humidity can reach up to 100% ), it is possible for the salt to be reactivated and cause the measle effect. So far very few field returns have exhibited this effect to any degree, for the most part boards witch are more drastically affected have only been produced from the PCA subcontractor and various environmental tests carried out in-house. It has been ascertained that when small amounts of moisture are able to penetrate the solder resist ( through in some cases imperfections in the surface ) and reactivate the salts to form an active alkaline solution. The alkaline has the effect of oxidising the copper over the period of several days/weeks depending on conditions. The dark staining under the resist is in essence copper oxide. At the same time, the solution ( which is of the sort used to remove various resist coatings used in the fabrication of the PCB ) breaks down the resist forming blisters over a period of time. This becomes very marked as the presence of moisture is allowed to increase dramatically as the blisters break. This then fuels the process of oxidation and resist breakdown. From the statistics and findings it can be seen that only 100 PCA's have been segregated by WSL with this effect. This may be supprising when considering the many thousands for PCA's which we receive from WSL, therefore 100 PCA's is a comparatively small number although in terms of unit cost they carry allot of value. It has been shown ( Failure mode 1.2 ) that as small quantity of boards go through an additional cleaning process to remove solder paste. This uses an ultra-sonic method which agitates the solvent at ultra-sonic frequencies. It seems possible that the 100 PCA's at some time went through this process. It is more than likely then that this level of agitation would increase the level of penetration of moisture and accelerate the process of breakdown of resist and oxidisation of the copper to the extent that drastic results would be seen as in the case of the 100 PCA's from WSL. It should be noted that in many cases the PCA's from this group are in a worse state than the PCA's that underwent accelerated ageing in the L & G humidity chamber. This would imply a more severe treatment than we have hither to been able to achieve through 'real' accelerated life testing. The main area of concern which leads me to my final conclusion is that the analysis of the resist removed from the blistered areas show that copper oxide has been removed with the resist and resides on the back of the flakes of resist ( ERA report page 7:(i) ). Landis & Gyr gas and electricity meters are all mounted in the vertical plain, and it is possible that flakes of resist falling off during the life of the product ( 20 years ) may catch on adjacent pads, i.e. below, and cause resistive coupling or shorting. The resistance of copper oxide has not been investigated but is likely to be in the order 100's of kilo ohms. Although field failures so far have not been traced to this problem, it is more than likely that during the expected life of our products, there will be a contributory factor (ERA


page 8 conclusions (i)). The policy of Landis & Gyr is to try and remove any potential quality problems before they occur.

Dendritic Growth It will be noted that from the statistics for the 100 WSL PCA's and field returns that there was no recorded presence of Dendritic growth except in units which has undergone environmental testing by exposure to elevated temperature and humidity. and were subsequently sent to ERA for analysis. As stated in the : Findings / Failure Mode, the presence of the lead ( Pb ) dendrites, due to the presence of swirls of solder derivative ( flux and Sn Pb ) on uncleaned boards, is likely to grow due to either the conditions brought about through accelerated ageing in our chamber or the long term effects of being in the field where there are likely to be wide fluctuations of both temperature and humidity in various combinations ( ERA page 8 Discussion 4.3 ).Quite rightly ERA pointed out that the L & G policy of Non-wash together with the conditions brought about by the testing are ill advised, since they bring about the conditions for dendrites to grow which can bring about short circuits between terminals. Steps have been taken by L & G to design our metering systems to allow water to drain out, but this does not prevent humidity in general. In the medium to long term, a functioning unit in fluctuating conditions over a period of years will provide both the electrolyte ( active flux deposits with solder derivatives on the PCA ) and the electrical potential ( low voltage and current ) which could cause dendrites to grow, which could cause both resistive coupling and short circuits ( ERA page 9: (iv) ). Further investigation would have to be carried out to predict percentage failure Vs time due to this problem. In the short term failure of units due to this problem will be a very small percentage of unit drop-out. In the long term, this may contribute increasing numbers, but this is difficult to predict without statistical evidence.


RECOMMENDATIONS RECOMMENDATIONS : MEASLE EFFECT 1) KCE Thailand should be asked to review their method of cleaning to remove resists and associated solvents prior to application of solder resist. 2) KCE Thailand should be asked to find a solder resist which is more resilient to ingress of moisture and resistant to sodium hydroxide and other alkaline stripping agents. 3) WSL to review the method of reclaiming PCB's where solder paste has been misregistered and has to be removed. It may be better in the long term for WSL to scrap these boards. 4) Aprox. 100 PCA's from WSL are for the most part in a very poor condition. I suggest that PCA's with a code of 2 and above be scrapped. L & G have paid for these PCA's, there may need to be discussions as to who should pay for writing them off. RECOMMENDATIONS : DENDRITIC GROWTH PROBLEM 1) Ascertain how aggressive or active the flux used by WSL and TI, and if WSL's flux could be changed to reduce residue of solder derivatives residing in flux remaining on the finished / uncleaned PCA. 2) Review : Non-wash policy, i.e. cost of washable components Vs possible field failure in short and long term. GENERAL RECOMMENDATIONS A meeting should be convened as soon as possible to discuss to issues raised in this document. The people included should be the people on the circulation of this document.


APPENDIX A

Letter and Memo. initiating investigation


InterOffice Memo To: John Howell From: Ruth Wainwright. Date: April 21, 1993 Subject: Lead Migration - KCE Boards ____________________________________________________________________ CC: Greg Dujon, Steve Hunt, Jim Nield, Tom White, Denise Williams Recent exhaustive investigations have demonstrated that there is a serious problem with the quality and reliability of possibly all PCBs supplied to us by KCE. ERA Technology have already demonstrated that the 'measling' we are currently experiencing on boards which have undergone some form of environmental testing or those which are from meters returned from the field, is lead migration. However, during further investigation at ERA Technology a display board from current WSL stock, flow soldered but not cleaned by Welwyn, was found to have traces of tin/lead beneath the solder resist. The area was seen as a defect proud of the rest of the resist and analysis of the tin/lead was achieved by directing the beam of X-rays through a small hole in the defect. Tin/lead was not detected on the surface of the defect. Whilst there was a small hole (approx. 20um) in the resist, my feeling is that the tin/lead was present on the surface of the copper before the solder resist was applied. Several control and display boards of varying date codes (mid '92 - 9310), have been shown to develop what appears to be lead migration after a few days in our environmental chamber at 35°C/95%RH. This leads me to believe that we are still using boards which may give serious reliability problems during the lifetime of our products. Welwyn have also been able to demonstrate problems with RTM boards, where the resist appears to affected by their cleaning process and indeed peels away from the board. The cleaning process leaving marks similar to the lead migration under the resist. It is understood however, that these boards were not current date codes. From the evidence I have seen both at Telford and at ERA, I believe that KCE may be experiencing severe processing problems. I am convinced that there is contamination trapped below the resist during board manufacture. The system will be time, temperature, humidity and current dependant, so any energy added to the system in the form of any subsequent processing etc., will only seek to exacerbate what is already a dangerous situation in a shorter period of time.


Lead Migration - KCE Boards 21/04/93 Page 2 The failure process i.e. the migration of lead and/or any other contaminants will then be dependant upon the environment and usage of the boards. Because of this we are unlikely to see the problem in production unless the failure mode has been mobilised by some external factor. I believe that we are likely to experience severe reliability problems in the future with product already installed and that current build may also be affected in the same way. I will, of course, be willing to provided any further assistance with this problem should it be required. Regards


Memorandum To: G. Dujon From: J.J Howell S. Hunt J. Nield Date: R. Wainwright Subject: T.A. White Lead Migrgation D. Williams k.C.E. Board. cc: J.E. King M.R. Pollock In response to R.Walnwright’s memo of 21st April l993, regarding the possibility of lead migration on PCBs suppied by KCE Europe. I can confirm that we are undertaking investigatlons into this but to date, we have no concluslve evidence for a major quality and reliability problem. However we are leeping an open mind on this subject and when the causes of the ‘measling’ phenomenon is fully understood we will take the necessary action. I have asked J.Nleld to oversee the activities which are in progress in several departments and to prepare sorting out the relevent statistics on the findings to date. It would appear that Ruth has expressed doubts about the long term reliabilitt of several of our products but until we have concluded that there is in fact a serious problem we must continue production with caution while carrying out the investigations. To that end, KCE has undertaken to arrange another set of Printed Circuit Assemblies to be analysed at ERA Tecrlnology. To support this activity we have provided a test specification for ERA to follow, thus ensuring that the bare copper on several samples of the PCB where blistering and discolouration has occurred is analysed and to also examine several points within a discoloured area. Work will continue in house until the environmental conditions are determined, and the effect of testing the boards at elevated temperatures and humidities for a 3 month period (to simulate an accelerated life of one year in the field). A report on the outcomes and findings should be forwared to me at the earliest opportunity afters the tests are concluded. A review of of the quality and legal positions for recommpence will be taken within 1 week of the test results being made available. John Howell Technical Director


APPENDIX B

Specifications for tests to be done by ERA + Report from ERA


ERA TECHNOLOGIES

Final Report

Commercial-in-confidence

INVESTIGATION INTO CAUSE OF FAILURE OF PRINTED

ERA Technology Limited Cleeve Road Leatherhead Surrey KT22 7SA England Telephone: 0372 374151 Tele Fax 0372 3475496 ERA Technology MATERIALS APPLICATIONS DIVISION P.J. Howard ERA Report No. 76-01-93-0380 ERA Project No. 0890/930404 Client: KCE Europe Ltd Client Reference: Order No. 9395 Report approved by: H. Greenwood Manager Materials Technology Department Date 10th May 1993 RESEARCH, DEVELOPMENT AND TESTING FOR INDUSTRY - WORLDWIDE DIRECTORS: Admiral Sir Lindsay Bryson KCB DSc FEng FRSE Hon FIEE FP^qS (Chairman) M J Withers MSc FEng FIEE (Managing) K. Sedgwick FCMA FCCA JDipMA (Deputy Managing) H W Cross FCA M P E Desvaux BSc PhD MlnstP J C Smith CBE Feng Approved to Nato Standard AOAP 1 and 13 Reg No 1LWE01 and British Standard BS 5750 Part 1 Reg No FM 1303 Registered in England No 170454.


2

SUMMARY

Printed circuit boards (pcb's) supplied by KCE Europe Ltd. were found to be failing electrical tests after going through a humidity chamber. On examination, these pcb's had areas of discoloration, apparently on the copper surface underneath the solder resist. A number of samples were brought to ERA for examination by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) analysis in order to determine the nature of this discoloration and whether this, or any other mechanism, could be deemed to be a probable cause of failure.

CONTENTS Introduction Page 6

Background Page 6

SEM Investigation Page 7

Discussion Page 8

Conclusions Page 8

Appendix I Micrographs and Spectra

Appendix 2 Leaflet describing SEM/EDX equipment


4

SAMPLE LIST

Board No.l: Rejected by Landis & Gyr, suffered electrical failure Board No.2: As above - only populated side examined Board No.3: Board obtained from second customer of KCE, after flow soldering Board No 4: Display board - not examined Board No.5: Control board, after washing in ultra-sonic cleaner, but having had no solder paste applied Board No.6: Control board, not washed, as received from KCE Board No.7: Control board, fault as in 1 and 2 plus excessive white deposit Board No.8: Display board, flow soldered by second customer, not cleaned Board No.9: Control board received from Landis & Gyr with similar fault to boards 1, 2 and 7 - examined with regard to copper discolouration only.


5

FIGURES LIST

Micrographs and spectra relating to the various boards studied are located at the back of this report in Appendix 1.

Board No. Page 1 - 11 2 12 3 13- 15 4 16 5 16 6 17, 18 7 19 8 20 - 34 9


6

INTRODUCTION

KCE Europe Ltd. supply printed circuit boards (pcb's) to a number of clients. These boards

are manufactured at factories in Thailand and distributed in the U.K. by KCE Europe in

Bramley, Surrey. One client - Landis & Gyr - reported considerable numbers of electrical

failures of these pcb's after humidity testing, and on examination found large areas of copper

to contain discolored patches under the solder resist. Landis & Gyr felt that this effect may

have been the cause of the electrical failures they were experiencing and suggested that

KCE Europe should have the pcb's examined.

Various pcb's were brought to ERA by KCE Europe on a number of occasions, examined in

the Scanning Electron Microscope (SEM) and analysed by Energy Dispersive X-ray (EDX)

analysis.

This report, as requested by KCE Europe, is a summary of these investigations together with

conclusions in relation to the elements found and suggestions as to how they may have

come to be present. The possible effects on long term usage are also discussed.

BACKGROUND

The following description of processes ~nvolved are as stated by KCE Europe. The pcb's

made by KCE Europe are composed of a patterned layer o£ copper on a resin board. This

copper layer has at one stage during manufacture had a tin/lead layer above it which has

subsequently been etched off. The solder resist is a thick layer of organic material containing

particulate fillers which is put onto the copper to prevent solder being deposited in the wrong

areas. The boards then go through a solder process at KCE before being dispatched to

clients.

Landis & Gyr send the boards to an external assembler (Welwyn) to be loaded with devices.

Here the boards experience a flow-soldering process in which a "non-active" flux is used.

The boards are not cleaned after flow-soldering. In some cases, the solder paste is put on

incorrectly, cleaned off with solvent in an ultra-sonic bath and re-soldered. It is not known

whether or not all the problem boards have experienced this additional procedure.

Landis & Gyr then submit the loaded boards to a humidity test and it is after this test that the

electrical failures occur. The discoloration can occur after flow-soldering at Welwyn or after

humidity testing at Landis & Gyr.

7


SEM INVESTIGATION

The boards selected by representatives of both KCE and Landis ~ Gyr were examined in the

SEM and various areas analysed by EDX analysis. The complete set of micrographs and

spectra taken during three separate investigation sessions are included in Appendix I of this

report.

The results of these investigations can be summarised thus:-

(i) Discoloration of the copper surface appears to have been caused by a sodium-rich

material being caught between the copper layer and the resist. This may well be sodium

hydroxide as oxygen is also present in the analysis (hydrogen is not detectable by EDX

analysis). In the first board studied - Board I - the copper itself had been affected by this

sodium-rich material to a small degree, forming a layer of copper oxide which pulled away

with the resist In the last board studied – Board

(ii) the copper had hardly been affected at all. A small amount of potassium was sometimes

present in these discoloured areas, but the main elements detected were undoubtedly

sodium and oxygen. The discoloured patches were often centred around a particle or

particles which may have penetrated the resist layer and allowed the ingress of the alkaline

material. In some cases, these particles were lead/tin compounds (presumably solder) and in

other cases they were calcium rich particles with a small strontium content.

(ii) The surface of all the boards examined which had suffered from the electrical failure had

large quantities of ~older derivatives in swirls across the surface of the resist - not between

the resist and the copper. This was explained by Landis & Gyr as being due to the boards

not being cleaned after flow-soldering, following the "green" policy currently adopted by that

company. The latter had felt that this was practicable because a "non-active" flux was being

used in the flow-solder process. Boards received directly from KCE and from another client

of theirs did not exhibit this phenomenon.

(iii) In addition to the effect in (ii) above, several instances of dendritic growths of a very

lead-rich material were found, such as those shown in photographs 1, 2, 15, 16 and 17.

These fern-like growths emanated largely from soider joints and followed the general paths

of some of the swirls of solder-derivatives on the resist surface. Some of these features were

several millimetres long and it would have been possible for such a growth to form a

conducting path across the surface of the resist between the solder joints. Dendritic growths

such as this have usually been found to form due to a combination of electrolyte and voltage.


8

These may well have formed here during the humidity tests carried out by Landis & Gyr, in the presence of the excessive amounts of solder-derived swirls and flux left from the flow solder process. 4 DISCUSSION It appears that the discoloration of the copper, while undesirable, is unlikely to have been the cause of any electrical failure directly after the humidity test at Landis & Gyr. Although the surface of the copper layer has been oxidised in some cases, the attack has not been nearly severe enough to cause a track to become open-circuit, for example. In the long term, the effects on the copper would become more marked, as the trapped alkaline material continued to cause oxidation of the copper. For this reason, it would be advisable to eliminate the possibility of any alkaline material penetrating between the copper and resist layers. In order to determine the source of this alkaline material, it will be necessary to go through the processing schedule at both KCE and Welwyn to discover at what stage such a material has been used. The swirls of solder derivative on the resist surface are probably not, in themselves, causing any electrical failure due to the flux itself forming insulating regions around the conducting metallic droplets from the solder. However, the dendritic growths of the lead-rich conducting material can lead to short circuits between terminals, and will have been encouraged to grow in the conditions left by the combination of the non-cleaning of the boards after flow-soldering and the humidity testing at Landis ~ Gyr. 5 CONCLUSIONS (i) The discoloured regions on the copper surface of the boards are due to the presence of a strong alkaline - probably largely sodium hydroxide - between the copper and solder resist layers. This in turn leads to oxidation of the copper surface which may, in the long term, prove undesirable. (ii) The "green" policy of not cleaning the boards after flow-soldering by the assemblers is leaving an undesirably high quantity of solder-rich material on the surface of the resist. (iii) Dendritic growths of a lead-rich conductor are being formed across the surface of the board which could lead to the electrical failures reported by Landis & Gyr. (iv) The policy of not cleaning a board after flow-soldering and then subjecting it to a humidity test is considered to be an extremely unwise practice. The flux on the board, when in the presence of moisture, will form an electrolyte, thus promoting dendritic growth.


VER 1.0 DATE : 19.11.93

URGENT TELEFAX

LANDIS & GYR ENERGY MANAGEMENT ( UK ) LTD. HORTONWOOD 30

TELFORD SHROPSHIRE TF1 2DX

TELE 0952 677661 FAX 0952 677591 REC. 0952 677606 PER.

TO : Phil Warner FROM : Paul Rouse EXT. 3451 KCE Europe Manufacturing Services CC : Denise Williams Dear Phil, Regarding recent samples of PCB's with ‘UV (Ultra Violet) Bumping’, you will have read my last two reports and seen that the samples with ‘UV Bumping’ were a very great improvement for preventing the Measle Effect, even though it is obviously not he total solution in its present form. As a result of this, I would like to see this process used on our PCB's until a better solution is found. Obviously there will be a cost involved so I would be grateful if you could advise Denise as soon as possible, so that we can make a discussion to go ahead. In addition I may have to add a note to any new drawing to specify this, can you confirm that this additional exposure is 100mJ/cm2.

Regards

Paul

THE TOTAL NUMBER OF SHEETS IN THIS FAX IS : 1 END


VER 2.0 DATE : 27.04.93

URGENT TELEFAX



TELE 0952 677661 FAX 0952 677591 REC. 0952 677606 PER.

TO : PHIL WARNER FROM : Paul Rouse EXT. 3203 K.C.E. EUROPE Design Services CC : MRS. PIPPA HOWARD E.R.A. TECHNOLOGY Dear Phil, Further to our telecon. today, I have now sent another ETM Control board assembly to ERA Technology which I would like to have analysed in the following way set out below. It is my belief that we do not yet have sufficient facts to come to a conclusion, either what the problem is, or what has caused the problem in question. It is also my belief that we all have certain prejudices as to what this problem is. After discussions with Jim Nield ( Technical Services Manager at L&G ) we believe that it would be right to request a formal report from ERA, so that we can get an objective and independent report both on the previous set of results and the set being currently requested. It would be appropriate to discuss the cost of this report when the two companies get together in the next week or so to discuss conclusions. I am sure that you will explain to Pippa that this report is to be reasonably brief due to cost, but clear in stating what we require to know. Can I suggest that the following might be a suitable 'Terms of Reference.'

1) Logbook entries and appropriate electron-micrographs or photographs 2) Detailed description of findings for each item analysed. 3) Conclusions in relation to elements found, and suggestions as to how they may have

come to be present. Comments on possible adverse effects of findings with respect to : intended usage i.e. Printed Circuit Assembly, subject to variations in temperature and humidity; also with respect to progression with time.

4) This report should be as brief as practical within the above requirements. The following is the specification for Pippa. OVER


SIDE 2 To : Pippa Howard ERA Technology TESTING REQUIRED : The board supplied is an ETM control board of the type already analysed. The board supplied has numerous areas where the resist has blistered and is fairly easy to remove as I have already done in one area near the 27 way connector. 1) Remove the resist from 3 areas on the board where blistering and discolouration has occured, and analyse the bare copper and state what the constituents of the discoloured copper are. If this analysis is on a 'point', it would be ideal to look at several points within the discoloured area. In the report, the elements found should be stated in full, and if possible, the proportion of the elements found. An electron-micrograph or photograph of both the area and the detail should be enclosed as before so that the relevant labelling is visible. 2) The solder resist which has been removed, should be treated in the same way as the above, i.e. the under side of the resist should be scanned to reveal what additional elements are present, Phil Warner should be able to supply the constituents of the Photo-imageable resist, so that it's elements can be eliminated from the list. If appropriate electron-micrographs or photographs should be supplied if it is felt that these will be useful. As with the copper, in '1', three samples would be ideal for repeatability, however your time limit may not allow this, please advise Phil Warner if this is the case. I hope that this concise specification will aid you in the direction of analysis. If you have any questions, please go through Phil.

Regards Paul THE TOTAL NUMBER OF SHEETS IN THIS FAX IS : 2 END


APPENDIX C

Specifications for tests to be done by L & G Business Support

Report from LGBS Lab


VER 1.0 DATE : 30.04.93



TELE 0952 677661 FAX 0952 677591 REC. 0952 677606 PER. TO : FROM : Paul Rouse EXT. 3451 Manufacturing Services

TECHNICAL SPECIFICATION

FOR TESTING Dear Sir, I enclose 3 printed circuit board assemblies which I would like to have exammined by your Scanning Electron Microscope (SEM). I have detailed the areas below which I would specifically like you to look at. In addition I would like a report on the findings under the following headings : 1) Logbook entries and appropriate electron-micrographs or photographs 2) Detailed description of findings for each item analysed. 3) Conclusions in relation to elements found, and suggestions as to how they may have come to be present. Comments on possible adverse effects of findings with respect to : intended usage i.e. Printed Circuit Assembly, subject to variations in temperature and humidity; also with respect to progression with time. This report should be as brief as practical within the above requirements. TESTING REQUIRED : The 3 boards supplied are an 'ETM Control Board Assembly,' which has been through environmental testing for 10 days at 60 deg. Celsius, and 95 relitive humidity. The boards supplied have numerous areas where the resist has blistered and is fairly easy to remove as I have already done in one area near the 27 way connector on board number '1'. 1) Remove the resist from an area on each board where blistering and discolouration has occured, and analyse the bare copper. State what the constituents of the discoloured copper are. If this analysis is on a 'point', it would be ideal to look at several points within the discoloured area. In the report, the elements found should be stated in full, and if possible, the proportion of the elements found. >OVER


SIDE 2 An electron-micrograph or photograph of both the area and the detail should be enclosed so that the relevant blistering is visible. 2) The solder resist which has been removed, should be treated in the same way as the above, i.e. the under side of the resist should be scanned to reveal what additional elements are present, If appropriate, electron-micrographs or photographs should be supplied if it is felt that these will be useful. As with the copper, in '1)', three samples would be ideal for repeatability, however your time limit may not allow this. I hope that this concise specification will aid you in the direction of analysis. If you have any questions, please call me.

Regards Paul Rouse END


Landis & Gyr Business Support AG Gubelstrasse 22 CH©6301 Zug Tel: 042 24 11 24 Fax: 042 24 35 22 Landis & Gyr Business Support AG, CH©6301 Zug LANDIS & GYR ENERGY MANAGEMENT (UK) LTD For the attention of Mr Paul Rouse, Ext. 3451 Manufacturing Services HORTONWOOD 30 TELFORD SHROPSHIRE TF1 2DX UNITED KINGDOM Please reply to Direct line telephone no. M Pisinger BAEM©T©F©MT3 2771 042/242771 Date Your ref Our ref Direct line fax no. 27 May 1993 PI/2771 042/244331 Re : Scanning electron microscope inspection of faulty circuit boards Dear Mr Rouse We have inspected the teardrop shaped discolourations, which according to your data resulted from a corrosion test of 10 days at 60`C with a relative humidity of 95%, on the 3 printed circuit boards you sent to us, using a scanning electron microscope, as requested in your order of 30.04.93. At the same time, in accordance with your wishes, we have made a photographic record of the appearance (see enclosed photographs) of selected discoloured points and tested for the elements present at these points (see enclosed spectrum analysis graphs). To establish the true appearance of the discoloured points, we did not scratch off the coat of lacquer prior to inspection but carried out the inspection directly on the boards in their original state. In our opinion this method proved to be correct. To assure adequate electrical conductivity of the specimens during inspection, the specimens were lightly coated with gold and so gold is present in all the specimens' spectrum analysis results. Individual results: 2.0 On all discoloured points inspected the coat of lacquer was damaged and this varied from individual cracks to a completely cracked and partly peeling coat, 2.1 The elements Si, S, O, C and Ba found on all specimens come, in our opinion, from the silicon base of the coat of lacquer ( resist ), which contains BaSO4, 2.2 The elements Sn and Br found on some specimens (activation from the soldering flux) originate in the soldering process and the quantities of these elements also correlate to the distance of the points inspected from soldered points,


2.3 The remaining elements Na, Cl, K and to some extent Ca found are in our experience typical residue after an inadequate (faulty) cleaning. The shape (teardrop©shaped) of the discoloured marks also corresponds with this, where the remains of the cleaning fluid has collected in drops and the salts present have become concentrated after the evaporation of the fluid. 2.4 The adhesion of the coat of lacquer applied on the contaminated points is considerably reduced depending on the quantity of salts and the occurrence of cracks due to water absorption (water soluble salts) is increased in high relative humidity. The prognosis with regard to further corrosion of the damaged points is greatly dependent on the relative humidity. Water absorption could also cause electrolytes on the copper surface (little protection from cracked or peeling coat of lacquer {resist }), which could accelerate corrosion considerably.

Yours sincerely

M Pisinger Encs: 9 pages with scanning electron microscope photographs and the corresponding spectrum analysis graphs for 3 circuit boards. LANDIS & GYR


APPENDIX D

Log. book entries for ERA 1st & 2nd tests


The following is a key to the SEM. pictures on pages - - Compiled by ERA technology, paid for by KCE Europe. Date 14.04.93 SEM start 9.45am a) Resist pulled off from above damaged patch on copper earth plane. Pt-wated (1/2) Some Cu, plus (Si; S; Ba; Ti) in resist?, also small k. b) Board (1) from which (a) was pulled. 01 000 x32 BS 10KV TET20* dendritic Pb across board 001 x10 BS " " low mag - solder all over ( tin rich ) 002 x7 See " " damage under resist 002 x21 BS " " detail ^ centre am..d 003 x200 See " " detail ^ ( Pb, Sn ) 004 x420 " 8KV " centre of damage on Cu " under pulled off resist 005 x210 " " " droplets on Cu (C; O {K;Si; Ca}) 006 x700 " 10KV " debris on u-side resist c) Board (3) From customer "2" after flow soldering 03 007 X10 BS 20KV " no Pb/Su evident on resist 008 X32 " " " detail ^ clean resist d) Board (2) - from customer "1" - populated side, crud on solder joints 02 009 x32 SEC " " contaminated joint due to non-cleaning of flux - ok. Finish 12.30pm ( spoke to Ruth Wainwright= customer "1" re this problem). ************************************************************************* 2nd SESSION DATE 19.04.93 PRESENT : PHIL WARNER / RUTH WAINWRIGHT Start 9am ( + Display board, same problem after W/S washing off paste ) 5 : Control " ,after W/S washing, no paste ? 6 : " " ,not washed, as red from KCE 7 " " ,problem + excessive white deposit flux ? 07 010 x6 BS Flux & solder deposit 011 x20 " " " detail & dendrites 012 x50 Xray Pb scan of detail ^ 013 x50 BS/See same area as ^ 8 : Display board : flow soldered by customer 2, but not cleaned 08 014 x20 See Selected defect in resist 015 x500 " " " detail 05 } < examined - no defect visible, no solder on board 06 } between joint SEM FINISH 12.15pm


APPENDIX E

Additional information on Solder resists and cleaning agents used in PCB manufacture and by assembly subcontractor


Additional information about resist : Concerning the insulating properties of the resist, although on the whole resist improves the tracking characteristic of a PCB, as long as its surface is free from contaminants, ( i.e. flux and solder derivatives and other conductive mediums and electrolytes ), it must never be relied upon to provide this facility. There are three basic types of solder resist which can be used on a PCB these days : 2 Pak; Photo-image and dry film. These are defined as follows : 2 Pak : This is a 2 part epoxy based ink which can be applied to a PCB by screen printing and hardened by a catalytic reaction causing polymerisation initiated by either by UV light or Infra Red. Dry Film : This is an epoxy based plastic film which is rolled onto the PCB and cured for adhesion; exposed with a photographic image by UV. which hardens the film by polymerisation except in the areas of the solder pads, and developed to remove the unhardened resist. Photo-image an ink which can be screen printed onto the PCB using a silk screen; cured and then exposed as with dry Film. The information above lays the foundation for understanding the effects which we are seeing on our PCA's and helps us to understand how serious or not the effects in question are.


PROBIMER 71 PROBIMER' 71 is a single-component, photoimageable insulating and solder mask. It is negative-working, and is developed in 1% aqueous sodium carbonate solution. Processing is carried out on existingPROBIMER plants. Special features Single-component system, ready-to-use, good storage stabiIity Short exposure and curing times which increase the total productivity of the process Processing carried out on existing PROBIMER equipment High resolution, allowing precise reproduction of the photographic master Outstanding electrical, physical and mechanical properties Processing parameters Pre-cleaning should be carried out in chemical, mechanical brushing, or pumice spray units. The application of adhesion-promoting oxide Pre-cleaning layers is not required with PROBIMER'U' 71. Holding times or intermediate storage prior to coating should be kept short, otherwise the adhesion of the resist can be impaired by the formation of oxides. The PROBIMER 120-HS 24 pre-cleaning unit is recommended for use in processing PROBIMER'~' 71. The unit is connected to the coating line, so there are no holding times involved. Only absolutely dry surfaces should be coated. Coating PROBIMER'U' 71 is supplied as a single-component system in ready-to-use form. Coating temperature: 25° + 2° C Conveyor speed under curtain: 90 m / min Viscosity (at 25° C): 95 sec DIN 4 cup Wet weight: 5,5-7,5 g / 600 cm2 Diluent: 1 -methoxypropylacetate (MPA) Solvent Flash-off PROBIMER'U'film must beflashed off undercontrolled conditions. The PROBIMER 230-(2) flash-off unit guarantees this uniform drying of the film as well as the safe handling of the evaporated solvents. Drying temperature (° C): 25 - 30 Time (min): 8- 12 Ignition temperature (° C, DIN 51794): 315 Flash point (° C, DIN 51755): 45


Drying After exiting the PROBIMER~ 230 unit, the coating has a tack-free surface, but requires final drying before exposure. The PROBIMER 250-(2) continuous dryer and the PROBIMER~ 530 batch ovens are adjustable within wide limits, to allow drying of the full range of allowable wet weights. After drylng, the boards are reslstantto operator handling and can be further processed. PROBIMER~ 250-(2) continous dryer Zone 1: 135° C, + 2 IR Zone 2: 135° C Board surface temperatures, outlet: 40 - 45° C PROBIMER 530 batch oven: 80° C, 10-15 min Exposure The spectral sensitivity of PROBIMER'~ 71 is in the range of 350-500 nm. Exposure units with a spectral emission between 350 and 400 nm and which have a high proportion of collimated light are recommended to acheive the highest resolution reproduction of the mask image. PROBIMER 330 unit: 500-800 mJ/ cm2, 15 - 20 sec PROBIMER 340 unit: 500-800 mJ/ cm2, 8 - 12 sec Stouffer Step (21-step, ~D = 0.15): 5 - 7 Both silver halide and diazo films are suitable working films for exposure. Care should be taken to ensure that the film density in the 350 - 500 nm range is sufficient. Holding time After exposure, there should be a holding time of at least 5 minutes before further processing. Longer holding times are not critical. Developing Developing is carried out in a 1% aqueous sodium carbonate solution at 30-35° C. Continuous spray developing machines with adjustable spray pressure and uniform spray pattern are recommended. Care should be taken to ensure sufficient rinsing after development. Neutralization is not necessary. Existing PROBIMER solvent developing equipment can be converted. Temperature: 30 -35° C Spray pressure: 2,0 - 4,0 bar Developing time: approx. 60 sec Inspection - Stripping After final curing, PROBIMER ~ films cannot be easily removed and in some cases not without damaging the printed wiring board at the same time. Therefore, a check for defects should be made after developing, which will allow the boards to be easily stripped and to be recoated. PROBIMER 71 can be stripped in 5% aqueous potassium/sodium hydroxide solution. It is advisable to inspect the stripped boards prior to recoating, to ensure that all PROBIMER ~ residues have been removed.


Curing Curing can immediately follow developing and UV post-exposure without any holding time. The following curing conditions must be observed to ensure optimal end properties: ;~ PROBIMER 530 batch oven: 60 min, 135 - 140° C PROBIMER 590 continuous oven: 60 min, 135 - 140° C Protective lacquers and Protective lacquers are used to preserve solderability until further conformal coatings processing takes place, while conformal coatings are used to completely encapsulate the printed wiring boards after soldering/testing. Both types of coatings usually have good to excellent adhesion to the PROBIMER~ resist. However, due to the large number and variety of materials used, preliminary tests are recommended. Tests before product Awide varietyoffluxes,solderingmachinesandtechniques,aswell as release various cleaning processes, are used in the assembly of printed wiring boards. The best overall results are acheived by adapting the processing parameters and construction guidelines for optimal use of PROBIMER insulating and solder masks. It is necessary to carry out individual tests before the product is released. Storage PROBIMER photopolymer resists are complex chemical compounds formulated to react with actinic light. To ensure that product quality is always constant, it is recommended to: store them in original packing drums at 8-25° C to practice a "first in-first out" inventory system. With the storage conditions described above, PROBIMER'U' 71 has a storage stability of 6 months. Ciba-Geigy maintains a vast network of delivery centers so that fresh products are always available to the consumer who cannot maintain large inventories of material in his own warehouse. Safety in the workplace Specific product safety data sheets and the brochure "Protection and protection of the of the environment and safety in the workplace are available to the environment user on request so that he can handle PROBIMER products safely. PROBIMER products contain combustible solvents. Contact with naked light or fire is not permissible while the plant is in operation. Before repair work is carried out, the area should be thoroughly ventilated and the plant cleaned.


PSR4000 TAIYO INK MFG. CO.

PHOTOIMAGEABLE SOLDER MASK SYSTEM ( Alkaline Solution Development )

REVISED MAY 20TH 1987

1. CATALIST MIXING Add 40 parts by weight of hardener CA-40 (white) to each 100 parts of PSR-4000 (Green). Mix sufficiently for at least 5 minutes in order to ensure that the Hardener CA-40 ( White) added, is properly dispersed. Improper mixing operation may, thence, cause a part of Printed coat, later, with such troubles like as : (a) a non-uniformity in development. (b) a curing incomplete 2. COATING Either of such coating operations like as Screen Printing, Curtain Coating or Roller coating is desirabIe. Thickness of the coat printed at approximately 20-5 microns is mostly suitable for this application purpose. For coating by screen printing operation, a polyester monofilament fabricated at 100-150 Mesh-counts ( 100-150 threads/inch ) is recommendable. Overall height of conductor circuitry, including thickness of metal plating deposited upon, which is suitable for the coating is leveled at approxi.nately 100 microns in maximum. 3. PRE-CURE Curing Equipment Side Temp. Time HOT-AIR CIRCULATION OVEN : 1st print 80°c l5-20 minutes Reverse 30-35 " Remark : For a double sided board with a high conductor circuitry at over-all 100 microns in height, which is cured by a Hot-air Circulation Oven : 1st printed side : 80°C 20 minutes Reverse side : " 40 " 4. COOLING INTERVAL : After Pre-curing operation finished, a cooling interval for a certain period until the board's temperature once heated up can come down to the room temperature level, is desired. 5. EXPOSURE


Exposing energy : 400-800 mJ/cm² Exposure time : 60 seconds Remarks For a such board with a high conductor circuitry fabricated at an over-all 100 microns in height, includlng the thickness of metal plating deposited, a recomrnendable. exposing energy is rated at 1,000 mJ/cm² or greater.


PSR-4000 6. DEVELOPMENT * DEVELOPER : Aqueous Solution 1% by weight of SODIUM CARBONATE * SPRAY PRESSURE ; 1 5-2.5 Kgs./cm2 * SPRAY TIME ; for 30-60 seconds. Remarks ; During this development process, the non-exposed portions of Printed-coat are just swelled by the developer, not be dissolved ; For dissolution & stripping a water spray at the next process does disolve it and then strip away. 7. WATER CLEANING After Development Process finished, board's surface must be treated with a water spray cleaning completely. 8. POST-CURE Curing Equipment TemP. Time _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ HOT AIR CURCULATION OVEN : 145°C 45-60 minutes 9. POT LIFE Before Hardener CA-40 added : 3 months from date of production After " : 12 - 24.Hours. 10. CAUTION In the stage of Pre-curing process, if cured at a higher temperature and also for a longer time too, which exceeds our recommended levels ; a degradation on photosensitibity or an incomplete development may partly be occured at these processes, when it would be operated respectively.


PSR-4000 OPERATI ONAL CONDITIONS

- 3 - PROCESS CONDITION 1. SURFACE PRE-TREATMENT : CHEMICAL : An acid solution, "METALEX P-5" (Nihon Oil & Fat ) or equivalent diluted at 20 times. MECHANICAL : A polishing with a brush roller, "BRUSHLON" or equivalent, and a water spray cleaning. 2. COATING - SCREEN PRINTING : A polyster screen fabricated at 100-150 Mesh-counts (100-150 threads/ inch) stretched. THICKNESS : Wet thickness : 20-25 microns Dry " : 15-20 " COVERAGE : Approximately 7-10 sauare-meters with 1.05 kgs. of PSR-4000 with Hardener CA-40 added.

Remarks ; During and also after coating operation, to ~revent a direct Sun shines which exp9se the live coating, is essential. No nec.esc,-.~y t~ .replace Flour~cent lamp with Yello.w one. After coating operation finis~ed, boards must be promptly .~u~jectecl hy the nex~ manufacturin~ process, ~ithou. any lon~ inte~val hel~.

3. RE-CI)RE; ~em~. T~me

~OT-A~R CIRCULATIO~ OVE~; · 80~C 15 min. (20 min.*)

4 . SUR~ACE PREPARATION ON REVERSE ( 21\~ PRI~Y~) SIDE 5 . REVER~E ( 21~1D PRINT) SIDE ; After serni-curing process finished a cooli~g interval for a certain period ~f hold time, until board's temperature once heated up can Corn down to the room temperature, is des ired 6. ~OATI~G O~ REvERSE S ~E ; See 2RO~ESS 2. stated a~ove . . SEMI-C~JR~; Tem~. Tllne HOT-AIR CIRCUEALIOI~; ovl;t~'; 80°C 30 min. (40 min.~) 8. COOLI~G INTER~'AL ; Board's ~e~perature once heated Up must be.cooled down to a level of the roo~ temperature.


- 4 -

PSR-4000 OPERATIONAL CONDITIONS EXPOSURE / SIMULTANEOUS DOUBLE SIDES.EXPQSING EQUIPMENT 5 KW/c~2 X 2 lamps attattached at each side, one to upper inside top

and another at lower bottom base respectively. ILLUMINANCE ; 15 mW/cm2 EXPOSURES: 600 mJ/~2 for 40 seconds. (1,000mJ/cm2 ~or 60 seconds *) 10. DEVELOPMENT: DEVELOPER dilutue alkaline solution. 1gm by welght of SODIUM CARBONATE. SPRAY PRESSURE: 1.5-2.~ K~s./cm2 TEMPERATURE OF DEVELOPER: +25C or above. SPRAYING TIME : 30-60 seconds t60 seconds *) For spraying, a such type of eyui~rnent, l~ke as a Delta-shaped ~la. h~ad nozzles at~ached inside of the ~hamber, is desirable. During this development process, the non-exposed portions on the printed-coat are just swelled by developer, and then be stripped away at the next stage by a water spray cleaning for dissolution. 11. SYMBOL-MARK PRINT: THE~A~Y ~URABLE TYPE s An Epoxy $~as~d marking ink is applicable. Even after Post-cure finished, it is also still applicable too. U.V. RAYS DURABLE TYPE: UVR-110W~ ~0.121, White, is reconunendable. This ink is also still applicable, even after Post-cure finished. 12. POST-CURE: Temperature: HOT-AIR CIRCURATION OVEN 145°C 40-60 min. (60 min. *) Remarks ; Figures s.ated in som~ parent~eses.~hown above like as ~ *) is intended for use~as a refQrencQ, in 8 C~S~ Of such boa~d as a hi~h condu~to~ circuitry of over-~ll 100 microns in the height, in~luding a thickness of met~l plcting deposited upon,.fabricated would be, applied.


GRACE Electronic Materials

VoLTAcuRE SR-332 Data Sheet

U.V. Etch Resist/Alkaline Etchants Alkali-Strippable Description

VOLTACURE SR-322 is a screen printable, U.V. curable photopolymer designed for the "print & etch" process. The resist provides very high printing capability, which makes it suitable for fine line printing. The cured film is resistant to ammonium-alkaline etchants. After the etching process, the resist is easily stripped by use of an alkaline stripper. Boards can be stacked without blocking problems directly after U.V. curing.

Surface preparation

The copper laminate should be cleansed of all grease, oxides and surface contaminants and be free from moisture. A light scrub followed by a thorough water rinse and drying is recommended.

Screen printing

Screen fabric Polyester, metallised polyester or steel. Mesh count 120-140 T/cm for polyester Squeegee material Sharp hard rubber or polyurethane squeegee with a durometer of 80-90 Shore A. Screening Equipment Hand-, semi-automatic or automatic presses. After use, the screen can be washed out in acetate-based screen cleaners such as ethyl glycol acetate (cellusolve acetate) or butyl glycol acetate.

U.V. Curing

VOLTACURE SR-332 cures upon exposure to high intensity U.V. light (200-400 nm). In a normal U.V. oven with two medium pressure mercury lamps, each with an output of 5000 W (80W/cm or 200 W/inch) we would anticipate a curing speed of 5-10 m/min.

Etching

The etching rate varies with the type and temperature of the etchant used. VOLTACURE SR-332 can be etched with most alkaline etchants.


Stripping VOLTACURE SR-332 has a very high stripping rate and can be stripped with : 1) Alkaline solutions (2-5% sodium hydroxide in water) pH 11-13/122-131F (50-55 C) 2) Methylene chloride Handling and Storage VOLTACURE SR-332 should be stored in a dry place at a storage temperature of 64-77 F (18-25 C). Under proper storage conditions, the shelf life is 9 months from the date of manufacture. For details of health and safety data, contact a Grace representative. VOLTACURE SR-322 is supplied in 5 Kg packages. Our products are covered by a warranty on material quality only and on condition that they are handled and stored according to given directions. As the properties of the inks depend on the user's production procedure, it is necessary to test them in advance in each particular case. W.R. Grace Limited, North Circular Road, London NW10 7UH Tel: 01 965 0611 Tlx: 25139 We hope the information given here will be helpful. It is based on our best knowledge and we believe it to be true and accurate. Please read statements, recommendations or suggestions herein in conjunction with our conditions of sale which apply to all goods supplied by us. We assume no responsibility for the use of these statements, recommendations or suggestions, nor do we intend them as a recommendation for any use which would infringe any patent or copyright.


TAMURA

PRODUCT I N F O R M A T I O N

FINEDEL DSR-2200 X-7 PHOTO-IMAGEABLE SOLDER MASK

FOR CURTAIN COATING APPLICATION

FINEDEL DSR - 2200 X - 7 is a photo-imageable solder resist specifically designed for curtain coating applications.

1. F E A T U R E S

- Two component type product with long working life. - Superior high resolution capability and side wall definition. - Uniform coating thickness - Excellent eleotrical properties

2. G E N E R A L S P E C I E I C A T I O N I T E M S D S R - 2 2 0 0 X - 7 Colour Green Viscosity 25ps at 25°C Specific gravity 1.3 _ Non-volatile content 60 wt. % Flash point 45°C Mixing ratio ~0 : 20 by weight Pot life Minimum 5 days after mixing Shelf life Minimum 3 months


3. TYPICAL PROCEEDURE Pre-treatment Scrub 3 ~et thickness 75 - 85 microns Drying 80~C - 30 mins ~0°C - 20 mins 3~wsunn~ 600mJ/cm2on I.0 ~t% Na2 COl . 30°C. 2.0kg/cm2 . 60 secs Post-curing 150 °C, 30 mins UV post-curing IOOO mJ/cm2 4. PREPARATION ~ix 80 parts Finedel DS~-2200 X-7 with 20 parts Finedel CA-2200 X-7 hardener. Stir thoroughly and allow to stand for 15 minutes before use. The pot life of the mixed ink will be a minumum of 15 days, providing the ink is kept cool. Thinner #311 can be added to dilute the ink and it is also recommended for cleaning of the coating equipcent. 5. STORAGE Finedel ~S~-2200 X-7 should be stored a~ay from light. Storage temperature should not exceed 20°C. but preferably in a refrigerator between 5 - 10~C. Currect storage should ensure the ~aximum shelf life.


APPENDIX F

Test Results


Test Results SAMPLE BATCH OF ETM CONTROL BOARDS The boards were examined and classified into 4 severity classifications to see if there is any correlation between severity and date code. Source : These boards were in the technology department, and originated from WSL Severity was classified into the following 4 relatively subjective grades : N = none found <1= very small traces visible, e.g. small dark dots 1 = low : small areas visible, low coverage. 2 = med : medium coverage on both tracks and ground plains 3 = bad : General coverage where affected areas have formed blisters some of which have broken. 4 = exceptionally bad : large area coverage, very large blistered areas, large areas of resist has flaked off. CONTROL BOARDS NO. DATE CODE SEVERITY 1 9232 3 2 9222 2 3 9232 1 4 9225 3 5 9225 1 6 9222 1 7 9225 1 8 9232 2 9 9232 2 10 9222 1 11 9228 2 12 9224 1 13 9225 1 14 9249 3 Been in env. test ( t ) 15 9224 1 16 9232 1 17 9225 1 18 9222 2 t 19 9232 3 20 9223 3 t 21 9225 4 22 9222 2 23 9224 3 24 9232 3 25 9232 4 t and conformal coated 26 9225 3 27 9232 3 28 9224 2 t 29 9224 2 30 9225 2 t 31 9232 1 32 9222 1 33 9225 4


DISPLAY BOARDS 34 9223 1 35 9224 2 36 9223 1 37 9224 3 38 9221 2 39 STEVENAGE N 40 9227 3 41 9232 N 42 9221 1 43 9223 2


Customer Return Analysis : Item Rejection App. Note : 11413 CONTROL BOARDS NO. DATE CODE SEVERITY 1 9222 N 2 9222 <1 3 9222 N 4 9224 N 5 9224 N 6 9222 N 7 9224 N 8 9224 N 9 9223 N 10 9224 N 11 9222 N 12 9222 <1 13 9224 N 14 9222 N 15 9222 N 16 9222 N 17 9222 <1 DISPLAY BOARDS 18 9223 N 19 9223 N 20 9224 N 21 9224 <1 Traces of SnPb in two holes in resist 22 9224 N 23 9224 N 24 9223 N 25 9224 N 26 9223 N 27 9224 N 28 9223 N 29 9224 <1 2 very small spots 30 9221 <1 A few small spots 31 9224 N 32 9224 N 33 9224 N 34 9224 N 35 9224 N


Customer Return Analysis : These boards were analysed top and bottom as previous investigation had found some boards with measling on top. DISPLAY BOARDS NO. DATE T/B SEVERITY IRAN12878 CODE 1 9223 T N CW00756/001 B N 2 9224 T N 002 B N 3 9224 T N CW00762/001 B N 4 - T N Stevenage 002 B N 5 - T N Stevenage CW00760/001 B N 6 - T N Stevenage 002 B N 7 9224 T N 004 B N 8 9224 T N 005 B N 9 9221 T ) Slight discoloration in B ) places but no measles CONTROL BOARDS NO. DATE T/B SEVERITY IRAN12883 CODE 10 9225 T N CW00762/002 B N 11 9225 T N U3 reworked CW00760/002 B <<1 2 Spots very small 12 9223 T N CW00760/005 B N IRAN12885 13 9223 T N CW00756/001 B N 14 9222 T N 002 B N 15 9224 T N 00748 B 1 Reworked in sev. places, some small patches present 16 9223 T N CW00760/001 B <1 Some small dots


Analysis of boards sent from Welwyn Systems. These boards were specifically segregated due to the presence of the measle effect, however there is no record of the processes that these boards have been through, so it is not possible to tell if the have had solder paste removed at any time and therefore been through the Ultra-sonic cleaning process. CONTROL BOARDS NO. DATE T/B SEVERITY NO. DATE T/B SEVERITY CODE CODE 1 9228 T 1 21 9228 T 3 B 4 B 4 2 9228 T 1 22 9228 T 2 B 3 B 2 3 9251 T 2 23 9228 T 2 B 4 B 2 4 9228 T 2 24 9228 T 2 B 2 B 2 5 9251 T 2 25 9228 T 2 B 3 B 2 6 9251 T 3 26 9228 T 2 B 3 B 3 7 9228 T 2 27 9228 T 2 B 3 B 2 8 9228 T 2 28 9228 T 2 B 3 B 2 9 9251 T 2 29 9228 T 2 B 3 B 2 10 9228 T 2 30 9228 T 2 B 3 B 2 11 9228 T 2 31 9228 T 2 B 2 B 2 12 9228 T 2 32 9228 T 2 B 3 B 3 13 9251 T 2 33 9228 T 2 B 2 B 3 14 9251 T 3 34 9228 T 2 B 3 B 3 15 9228 T 2 35 9228 T 2 B 3 B 2 16 9228 T 2 36 9228 T 3 B 3 B 3 17 9228 T 2 37 9228 T 3 B 2 B 4 18 9228 T 3 38 9228 T 2 B 3 B 3/4 19 9228 T 2 39 9228 T 2 B 2 B 3 20 9228 T N 40 9228 T 3 B 3 B 4+


CONTROL BOARDS CONTINUED NO. DATE T/B SEVERITY NO. DATE T/B SEVERITY CODE CODE 41 9228 T 3 61 9238 T 2 B 3/4 B 2 42 9228 T 2 62 9238 T 2 B 1 B 3 43 9251 T 2 63 9251 T 2 B 1 B 2/3 44 9228 T 3 64 9251 T 2 B 3/4 B 2 45 9228 T * 65 9228 T 2 B 2 B 3/4 46 9251 T 2 66 9228 T 2 B 3 B 2 47 9251 T 2 67 9228 T 2 B 3 B 3 48 9228 T 2 68 9228 T 3 B 2 B 3 49 9228 T 2 69 9251 T 2 B 2 B 3 50 9228 T 2 70 9251 T 2 B 3/4 B 3 51 9228 T 2 71 9228 T 3 B 4 B 4 52 9228 T 2 72 9228 T 3 B 4 B 3 53 9251 T 1 73 9228 T 2 B 1 B 2 54 9251 T 1 74 9228 T 1 B 1 B 3 55 9251 T 1 75 9228 T 1 B 1 B 1 56 9228 T 2 76 9238 T 2 B 1 B 3 57 9228 T 2 77 9238 T 2 B 1 B 3 58 9228 T 2 78 9228 T 2 B 2 B 1 59 9228 T 2 79 9228 T 3 B 2 B 4 60 9228 T 3 80 9251 T 2 B 3 B 2 * TOP SIDE COVERED WITH WHITE DEPOSIT


CONTROL BOARDS CONTINUED NO. DATE T/B SEVERITY NO. DATE T/B SEVERITY CODE CODE 81 9306 T 2 101 9228 T 2 B 2 B 3 82 9228 T 2 102 9228 T 3 B 3 B 3 83 9306 T <1 103 9228 T 3 B 2 B 3 84 9251 T <1 B 3 85 9251 T <1 B 3 86 9251 T 1 B 3 87 9251 T 1 B 2 88 9251 T 1 B 1 89 9251 T 1 B 3 90 9228 T 3 B 3/4 91 9306 T <1 B 2 92 9228 T 3 B 3 93 9228 T 3 B 4 94 9228 T 2 B 2/3 95 9228 T 2/3 B 2 96 9251 T 2 B 3 97 9228 T 2 B 2 98 9228 T 2 B 2 99 9228 T 3 B 3 100 9228 T 2 B 2


ENVIRONMENTAL CHAMBER TEST RESULTS Results of Damp / heat cyclic and damp / heat steady state tests carried out at Landis and Gyr. The test was carried out in 2 stages to see the effects of a severe damp / heat cyclic and a not so severe damp / heat steady state test on the progress of both the measle effect and the lead migration. Unfortunately the boards that were subjected to the first test were not recorded satisfactorily, i.e. appearance prior to test; or identified. During the test a number or boards have been removed and added to the chamber, also unidentified. It is possible that all of the original unit have been removed. Damp /heat cyclic : Start :........ Finish : 16.03.93 @ 09:32 Damp / heat steady state : Start : 16.03.93 @ 09:32 Finish : 12.05.93 @ 15:00 Entry from logbook : 19.04.93 time 13:52 ETM CONTROL PCB'S from Goods in, inspected, top shelf, possible growth, 6 PCB's No. Date type Top/ Finding Code C/D Bot. _______________________________________________________________ 1 9223 C T <1 Small dotts on track & ground plains. U6 flux left behind. B <1 Lots of small dots 2 9224 C T <1 B 1 3 9224 D T <1 B <1 4 9223 D T <1 B <1 small dots. 5 9222 C T <1 small dots on tracks and gnd plain. B <1 small dots and rings of dots. 6 9224 C T <1 small dots, some on tracks. B 1 small dots and rings of dots. 7 9225 C T N B 1 small dots and some larger areas. 8 9310 C T <1 B 3 9 9223 D T <1 B <1 very small dots 10 9222 C T N B <1 11 9224 C T 3 U3 reworked with flux residue evident and an apparent burn near PL1. B measles toward one end



No. Date type Top/ Finding Code C/D Bot. _______________________________________________________________ 12 9310 C T 2 2 points were previously marked BLACK B 2 6 points marked RED - general growth. 13 9310 C T..<1 Blank board (soldered @ another co.) Small dots on tracks & ground. B..<1 Small dots. 14 9306 D T..<1 Blank board (soldered @ another co.) Small dots on most tracks B..<1 Small dots A 9309 C T..<1 B.. 3 B 9310 C T.. 1 Single resist B.. 3 Double resist A 9307 D T..<1 Small dots visible on most tracks B..<1 B 9306 D T..<1 Single resist Small spots visible B.. N Double resist Some blisters between resists COMMENTS : Considering the severity of this test, the effects are not as bad as might be expected, when compared to the boards which came from WSL, which we are told have only been through the normal production processes.

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Measle Effect Rev 2