Section 8 - Achieving a PCB Cost Reduction Through Design.do

8/4/2019 Section 8 - Achieving a PCB Cost Reduction Through Design.do

http://slidepdf.com/reader/full/section-8-achieving-a-pcb-cost-reduction-through-designdo 1/9

Achieving PCB Cost Reduction Through Design

Introduction

As a manufacturer of Printed Circuit Boards spanning an extremely diverse range of technologies and volumes, Evolution Circuits are often asked the golden question;

“How can I reduce the cost of my PCBs? ”

Whilst the simple answer would be to make the boards as simple as possible, order the largest batch quantity and ship them using the cheapest method, there are amyriad of other considerations that can have an extraordinary effect on themanufacturing cost, and therefore buy-price of your boards.

Most people understand that PCB manufacture is a highly labour intensive industrythat is fundamentally driven by economies of scale, and most manufacturers use costcalculation software that will analyse the set-up times, processes involved/time inprocess and anticipated yield to dictate the final price.

However, there are external factors that significantly affect the price of PCBmanufacture which are not within the control of the factory, such as utilities (water and electricity specifically), material cost increases (laminate, copper and preciousmetals) and even the exchange rates when buying in US$ but selling in £GBP.

However, It is the expectation of many medium-to-large sized customers and

manufacturers to achieve year-on-year cost reductions with their PCB spend despitethese considerable price pressures.Due to the cost of raw materials rising sharply over the past 24 months and, thiscoupled with significant electricity and water charge increases, the general pricetrend of PCBs to the UK manufacturers is actually cost-up, not cost-down.

Consequently, there has been no better time to review the cost reduction potentialwithin your new and existing PCB designs to maximise your profitability.

As there is limited opportunity to positively influence a finished and fixed design, thebest way to achieve this is through open discussion and consultation with EvolutionCircuits in the early stages of the design and layout process.

Within this document, I have illustrated most of the key contributory factors thatinfluence cost within PCB design and manufacture.

With a greater understanding of these manufacturing cost influences and an inclusiveapproach to PCB procurement, it is possible to work towards achieving the mostaggressive PCB prices with little or no compromise to the performance of either theproduct or any subsequent assembly process.

Keith Wrigley - General Sales Manager, Evolution Circuits

Designing-in a PCB Cost Down



Evolution Circuits’ Cost Analysis of Printed Circuit Board Manufacture

In line with the cost down trend of electronic equipment, there is increasing

pressure on PCB manufacturers to offer cheaper and cheaper prices despitethe rising cost of raw materials, processes and the increased utilisation of precious metals to meet with lead-free legislation.

There are of course several key factors that radically affect the manufacturingcost of a PCB such as choice of base material and solder mask that mightreduce the manufacturing cost by 10%-50% but the consequence of utilisinglower grade materials might come at the expense of the increasing cost of assembling the resultant PCB, the long term reliability of the finished productand the potential for reduced yield that could actually increase the final realcost of the equipment.

As a highly labour & process based industry that leans heavily on economiesof scale, there are fundamental basic principles that dictate the cost of a PCB.

1. Manufacture batch volume2. Materials3. Technology (layer count)4. Track and gap tolerances5. Drilled hole and via complexity6. Delivery premiums for priority turnaround

The simple initial recommendations to reduce cost are to make more boardsin a single batch and utilise the cheapest method of shipping, but this doesnot give fundamental guidance at the design or concept stage.To truly design in cost-down into your PCBs you must understand the cost of each manufacturing stage/process and give consideration to the down-lineimplications of utilising lower quality materials and the potentially detrimentaleffect on manufacturing yield.

The following information explains the specification of materials andprocesses and then graphically explains the breakdown of manufacturing cost

of a PCB.

Material Parameters

There are 6 major different materials used to manufacture PCBS:- FR1, FR2,FR3, FR4, CEM-1and CEM 3 (FR=Flame Retardant and CEM= CompositeEpoxy Material).

All of the above are selected based on their performance criteria as follows;

-2-



Glass Transition Temperature (Tg Rating)

This is a maximum operating temperature rating expressed in oC. A high TGrating is very important to guard against barrel cracking and pad fracture

during the soldering operation, especially at the elevated temperaturesassociated with lead-free processes.

Coefficient of Thermal Expansion (Tce)

Surface Mount Device (SMD) assembly exposes a PCB to more temperatureshocks than conventional through-hole process. At the same time, theincrease in track/pad density forces designers to increase the layer count of the board thus making the board more susceptible to the problems associatedwith the base material’s Tce.This can result in particular problems with regards to Z-axis expansion of the

material since this induces stress in the copper plated holes and this canresult in reliability problems.

Dissipation Factor

This is a measure index of the tendency for an insulating material to absorbsome of the AC energy from electromagnetic fields passing through it.Low values are important for RF applications, but relatively unimportant for logical applications.

Electrical Breakdown Voltage (DBV)

The voltage per unit thickness of an insulator at which an arc may passthrough the insulator.

Water Absorption Factor (WA)

The amount of water an insulating material may absorb when subjected tohigh relative humidity expressed as a percentage of total weight.Absorbed water increases relative dielectric constant as well as reducing theelectrical breakdown voltage.

Material Grades

FR1 & FR2

Both grades are manufactured with phenolic resin binder and are virtuallyidentical with regards to chemical composition. The primary difference is thatFR 1 has a higher Tg rating of 130oC (FR2 has a Tg of 105 oC) and since thecost is very similar, many manufacturers choose to only use the FR1 and nothold stock of FR2.

-3-



FR3

Very similar in performance terms to FR2 but is manufactured using an epoxyresin binder rather than the phenolic resin.

FR4

This grade is manufactured with glass fibre epoxy laminate and is the mostcommonly used material (typically 1.6mm/0.062 inches thick) to manufacturePCBs.FR4 uses 8 layers of glass fibre material bonded together and the maximumconstant operating temperature will be 120oC to 130oC depending onthickness.

In the Far East, FR4 is significant the most widely used PCB base material

followed by FR1 and then FR2.The FR1 and FR2 grades are primarily used for single sided work, as they arenot well suited for through-hole applications.As FR4 offers superior manufacturing and operating characteristics for mostapplications ranging from single-sided right through to multi-layer work, it isthe favoured grade with volume manufacturers. Additionally the economy of standardising on the premium grade and volume purchasing bulk volumes of FR4 would often make it not only the most cost effective, but also the mostreadily available on short lead-times.

CEM-1 & CEM 3

CEM-3 (CEM= Composite Epoxy Material) is very similar to FR4 but ismanufactured using a composite powder material that gives a very smoothfinish with a milky-white colour.Although intended to be a direct replacement for FR4, it is not popular in theFar East and is therefore not purchased in volume, making it costuncompetitive.

CEM-1 Material is a paper based laminate with a single layer of glass fibre. Itis not suitable for through-hole applications and therefore utilisedpredominantly for low-cost, simple single-sided applications where quality is a

secondary focus to price.

Base Material Conclusion

Whilst there will always be applications that require physical characteristicsexhibited by FR1/2/3 and CEM-1/3 materials, FR4 is generally accepted asthe best material to use for the vast majority of PCB applications.

There are differing grades of FR4 that exhibit superior performance under heat and/or humidity but manufacturers will tend to utilise higher grades of

-4-



FR4 as the stability of the base material is higher, and consequently processand quality control is easier through the manufacturing processes.

Mass volume manufacture is greatly aided by the use of higher quality FR4

material and the resultant yield is consequently higher.Lower grades of FR4 tend to be used as an effective way of reducingmanufacture cost of small batches such as prototypes. Also where there isconsiderable price pressure on the manufacturer it may be deemed necessaryto utilise a lower grade of material to remain cost competitive. However, thiscan work out as a false economy as the resultant yield may be proportionallylower thus making the individual circuit cost effectively higher.

Cost Analysis

In order to design-in savings at the concept stage of your PCB, it is important

to break down the total manufacturing cost by process. By doing this, it shouldbe apparent where the greatest savings can be made.This must all be done with a sympathetic view to the down-line assemblyprocess so that any initial savings on material grades do not increase theprocessing costs.

If we breakdown the typical cost of a double-sided PCB manufactured in FR4material, it can be shown as follows;

Process %1. Base Material 15

2. Chemicals used within processes 43. Drilling 94. Plating & Finishing 355. Photo Etching 126. Solder Mask & Silk Screen 127. Test and Inspection 38. Managing cost 39. Profit 7

Base Material

15%

Chemical

4%

Drilling

9%

Plating &Finishing

35%

Photo Etching

12%

Solder Mask & Silk Screen

12%

Test & Inspection

3%

Managing Cost

3%

Profit

7%



-5-

Conclusion (2-Layer PCB)

As plating and finishing represents significantly the highest cost followed bymaterial and then solder mask/screening, these must be the most obviousareas of focus.By not using Solder mask or a screen-printed ident, the saving is considerable(12%) or alternatively, using a cheaper solder mask process could result in a5% saving.By reducing the complexity of the PCB it should be possible to reduce theoverall cost by the greatest amount. This can be achieved by more extensiveuse of surface mount components that could also reduce the overall boardsize and number of plated through holes thus saving on material cost.

You can compare this to the cost breakdown of a 4-layer PCB using the samequality of materials;

Process %1. Base Material 252. Chemicals used within processes 63. Internal Layers 204. Drilling 65. Plating & Finishing 176. Photo Etching 77. Solder Mask & Silk Screen 78. Test & Inspection 29. Managing cost 310. Profit 7

-6-

Base Material23%

Chemical6%

Drilling

9%

Plating &Finishing

17%

Photo Etching

7%

Solder Mask & Silk Screen

7%

Test & Inspection2%

Managing Cost3%

Profit7%

Internal Layers

19%



Conclusion (4-Layer)

With this manufacturing example, the extra cost of material is the highest at25% with internal layers next at 20% and plating & finishing at 17%.

Again reducing the complexity of the board design offers the most effectiveway to reduce overall cost, but the use of lower grade FR4 materials wouldnegatively impact the management of costs and manufacturing yield so thiswould not be recommendable for volume PCB manufacture.Any savings made on lower grade RF4 materials would usually be linked tolower Tg and higher Tce ratings that are likely to result in higher assemblycosts and therefore it would be inadvisable to cut corners here.

Process Considerations

There are ways to reduce the manufacturing cost of a PCB that would resultin savings down-line.

1 Routing Vs Scoring

Avoid complex rout paths as they are time consuming in manufacture and jobs are costed by time in process.If narrow rout gaps can be avoided, this will allow the factory to stack moremanufacturing panels together during the routing process and thereforereduce the overall time on the machine.Scoring is quicker and cheaper than routing but does require straight vertical

and horizontal lines and therefore is only suitable for square or rectangular boards.It may be possible to reduce the amount of routing on a board by using acombination of both methods.

2 Waste Strips / Scrap

When a PCB is panellised, all areas around the circuit are classed as wastematerial or scrap.This scrap area is utilised for machine holes, fiducial marks or they exist togive a suitable clearance around the board to allow for surface mount

assembly access around the periphery of the circuit.You pay for waste material and therefore it should be kept to a minimum.It is sometimes possible to have waste only on selective sides of a circuit or better still to utilise waste areas around complex shaped circuits to makeadditional small circuits of a similar technology (double-sided or 4-layer for example).

-7-

3 Colour of Solder Mask and Screen Printed Ident



The industry standard for PCB resist colour is Green and therefore processequipment is set up for this colour for the vast majority of time. Whilst it ispossible to select a number of different solder mask colours such as black,blue, red and yellow for example, this would require additional process timedue to cleaning and changeover. For small batches, it may be more

economical to change the method of applying solder resist to avoid thisinconvenience and there may be additional cost involved.

Similarly, most screen printed idents are white or yellow as a secondaryoption. As above, the request to use other colours might require additionalcleaning processes and the purchase of ‘non-standard’ inks in small volumes.All of these considerations are likely to be passed on to the end-user as extracost.

4 Volume Manufacture

A proportion of cost for PCB manufacture is linked to set-up time between partnumbers and therefore it is considerably more cost effective to manufacturelarger quantities in a single run rather than dividing the job over several weeksor months.With the elevated shelf life of PCBs (especially with the Gold finished RoHScompliant finishes) it is considerably more cost effective to ship in initialquantities as required and stock manage the balance either by Kan-Ban or fixed delivery schedule.

5 Manufacturing Lead-Times

As with all industries, there is a scale of cost that is linked prioritising themanufacture of PCBs.Most manufacturers will offer PCBs with lead times as short as 24 hours butthe cost of this would be exponentially more expensive than a standarddelivery schedule of 10 days for example.The reason for this is the necessity for factories to ‘set aside’ manufacturingcapacity to allow for rapid turn-around requests. This might result inequipment or resource lying idle during periods of low demand that needs tobe paid for in the premiums applied.There is no better way to actively reduce your PCB expenditure than to either plan ahead to give yourself the extra time, or to work with a flexible

manufacturer who can give you the optimum supply scenario to meet your initial lead-times with a balance of PCBs to follow in the most cost effectiveway.The premium for a 3-day manufacture over a 10-day price can easily be 100%more.

-8-

6 Off-shore Manufacture

The PCB industry is heavily labour dependant.



For this reason, there has been a steady shift of volume PCB work to the Far East where labour rates are lower and the manufacturing scale is larger.

The cost benefits for moving to the Far East can be considerable (20%-50%cheaper for multi-layer work) and the quality levels are generally comparable

or in many cases better than high-end UK manufacturers.The scale of PCB manufacture in China, Taiwan and Korea dwarfs thevolumes of the competitive European manufacturers and consequently thecumulative buying power of these companies will result in much lower material and chemical expense that would be passed on to end-users as acost saving.

With strategic local support, a stock managed supply of volume boards caneither replace or supplement a UK based PCB supply scenario to achievesizeable price reductions.

7 Off-shore Prototyping

Typically, prototypes are manufactured locally on short lead-times and the jobmay only be moved offshore at the point where volume manufacture wouldrealise a lower manufacture cost.If there is enough time to allow for prototypes to be manufactured in the samefactory that would manufacture the volume quantity, it would not only reducethe need for additional tooling charges, there would also be the additionalbenefit of continuity for any incremental changes or concessionaryamendments made to the board that would not be lost or omitted in thechange-over.

For final iteration production versions, it is sometimes possible to produce theprototypes offshore without cost, thus eliminating the considerable expense of UK prototyping.

Conclusion

There are many considerations during the design and subsequentmanufacture process that can generate considerable savings, and there is nobetter way to achieve this than to involve your PCB designer/manufacturer inclusively at point of concept.

All savings must be applied with a global consideration for the knock-on-effecton the total PCB manufacturing process and ultimately the quality and long-term reliability of the finished product.

Documents

Section 8 - Achieving a PCB Cost Reduction Through Design.do