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7"D-Ri3 LASE RUAN EL(rC mEIL ?oiTiumO E i F1E T ro i -TELECTRONIC DEYICESMU ISRAEL INST OF METALS NAIFA
Z AUAV ET AL. DEC 67 EOARD-TR-09-03 AFOSR-SE-0315'UNCLASSIFIED F/G 9/3 N
L 6
-S
MICROCOPY RESOLUTION TEST CHART
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MINISTRY OF INDUSTRY 101111114 I=I& TRADE "flflfllINDUSTRIAL R&D j 1D 7=11 V.ADMINISTRATION 'fl'VYfl 10191
ISRAEL INSTITUTE OF METALS. 1 1VI' 1113111" 11n1] I' ,
DVELAPMENT in(0. FOUNDATION LTD. 3113 flUD00 .
LASER AND ELECTROCHEMICAL STUDIES OF METALLIZATIONS
IN ELECTRONIC DEVICES
Second Annual Research Report
No. 504-591
1 Sep 86 - 31 Aug 87
J. Zahavi ,.M. Rotel
Israel Institute of Metals
B. Dobbs -.
WPAFB, MLSA, Dayton, Ohio 45433, U.S.A.
f:," C . E T -D ......
APRGI01988 bC' c
Technion City, Haifa, December 1987
. .C tII
UNCLASSIFIEDl~- . 7,SEC URITY CLA ."AION1 OP $HI$ PAGE
REPORT DOCUMENTATION PAGEIa. REPORT SECURITY CLASSIFICATION lb, RISTRICrIVE MARKINGS $
Unclassified
2a. SECURITY CLASSIFICATION AUTHORITY 3. DISTRIBUTIONJA~VAILABIL.ITY OF REPORT
Zb. ECLSSIICAIONDOWNRADNG CHEULEApproved for public release;2b. ECLSSIICATON DOWGRADNG CHEULEDistribution unlimited
A. PERFORMING ORGANIZATION REPORT NUMBER(S) S. MONITORING ORGANIZATION REPORT NUMBER(SI
64 AEO EFRIGOGNIAIN 1b FIESMO 7. NAME OF MO0NITORING ORGANIZATION
Israel Institute of Metals fi Aplicble European Office of Aerospace Research andI Development
6C. ADDRESS (Otr'. Stitt, end ZIP Cod.) 7b ADDRESS (CiMy State. and lip Code)Technion - Israel institute of Technology Box 14Technion City FP0 New York 09510-0200Haifa 32 000, Israel
Ba. NAME OF FUNOING/)ON RING Eb OFFICE SYMEOL 9. PROCUREMENT INSTRUMENT IDENTIFICATION NUMBERORGANIZATION AFIL terials (if applicable)
Laboratory and EOAR MLSA/LRP AFOSR 86-0315
Bc. ADDRESS (Crty. State. and ZIPCode) 10. SOURCE OF FUNDING NUMBERS
A7VAL/ML'lSA E CA DLRPF PTR5A IPROJECT TASK WORK UNITW.right-Patterson AFB, Box 14 V 6P 0 . NO. NO ACCE SSION NO.OH 45433-6533 FPO New York 09510 61102F 20 D 211. TITLE (include Security Clasubfcatiovt)
LASER AND ELECTROCHEMICAL STUDIES OF M{ETALLIZATIONS IN ELECTRONIC DEVICES
12. PERSONAL AUTHIOR(S)J. Zahavi and M. Rotel
l3a. TYPE OF REPORT 3ib. TIME COVERED 14. DATE OF REPORT (Yearat. a) S PAGE COUNTInterim Scientific FROMlI Sev S 8T031 AU9L8 ' 1987 December
16. SUPPLEMENTARY NOTATION
- -17. -COSATI CODES ~ 11. SUBJECT TERMS (Continue on reverse If nectuary and iden~tify by block num~ber) .--FIELD GROUP SUB-GROUP j~ Laser treatment, Pb-Sn coatinrg, corrosion, potentiodynamic
* .J.L ..... polarization. I ,~-7*-19. ABSTRACT (Continur on1 (rvers If necessary and identify Z, -block num.ber) .- - p-
* The research during this year was concerned with appl'cation of excimer laser (193nm,6 7 2
24 nsec, 1 1 watt/as pulse) to Pb-Sn surfaces. The laser induced mlting of the .
Pb-S co Ig resulted in bright area in which lead-rich zone were observed.
Ferferential dissolution of lead was observed during electrochemical potentiodynamfic
thlrat io ofe the as -deposited and laser treated surfaces. Calculation showed
thttelaser-treated. specimen had higher corrosion rates than as-deposited counter- .. ,
Part~6
_____
0. OISTRIRITION /AVAILABILITY OP ABSTRACT 21 ABSTRACT SECURITY CLASSIFICATIONCOUNCLASSIPIEDuJNLIMITED 0 SAME AS RPT M DTIC USERS Unclassified
22a. NAME OP RESPONSIBLE INDIVIOUAL 22b. TELEPHONE (Include Area Co.) 22c, OFFICE SYMBOLLARELL K. SMITH, Lt.:'Col, USAF (44 1) 409-4505 EDARD/LRP
DO FORM 1473, Ba MAR 53 APR edition m'ay be used unl exh'austed. SECIRITY CLASSIFICATION OP. 1415PAGEAll other edition, art obsoete. UNCLASSIFIED
i% 1xii
€..
EOARD"Th-8" 3
This report has been reviewed by the EARD Information Office and isreleasable to the National Technical Information Service (NTIS). At NTISit will be releasable to the general public, including foreign nations.
This technical report has been reviewed and is approved for publication.
LELK. -84TLt Col,' USAF-Chief, Physical Chemistry/Materials
PHILIP .CONRAN, Colonel, USAFCommande
.... ,,, :-
Vw
S
. N'
Technion Research Israel Institute
and Development Foundation of Metals
~~.,,e
LASER AND ELECTROCHEMICAL STUDIES OF METALLIZATIONS
IN ELECTRONIC DEVICES
Second Annual Research Report
No. 504-591
1 Sep 86- 31 Aug 87
J. Zahavi
M. Rotel
Israel Institute of Metals
B. Dobbs
WPAFB, MLSA, Dayton, Ohio 45433, U.S.A.
Technion City, Haifa, December 1987 % ..
%
! 'N' 1
: - -• nn na u ! u II mII m| n
1. INTRODUCTION .................................... 1
2. EXPERIMENTAL .................................... 1...'..
2.1 Laser Operation ............................ 1
2.1.1 Laser Conditions .................... 2
2.2 Polarization .............................. 4
2.3 Specimens ................................. 5
2.4 Electroplating .................................. 5
3. RESULTS AND DISCUSSION ............................ 7
3.1 Potentiodynamic Polarization .................. 7
3.2 SEM Observations ........................... 20 .
3.2.1 Laboratory Specimens ................... 20
3.2.2 Commercial Specimens ................... 23
3.2.3 Tin coated Specimens ................... 25
4. CONCLUSION .................................... 25
0
i .L.." .. ..
i *,,.... i::. :
D~st ;.''. %,
1-7i
, , i% I II
1. INTRODUCTION
The research during this year was concern~ed with application ~ -of excimer laser to Pb-Sn surfaces as a means of thermal
treatment of the coated area.
In this year the laser was used to produce large surfaces in
order to study the effect of laser treatment on corrosion
resistance of the Pb-Sn surfaces.
The treated and untreated surfaces were compared in terms of
electrochemical potentiodynamic polarization.
The corroded area morphology shows that the corrosion
proceeds primarily though preferential lead (Pb) disso-
lution.
The laser-treated surfaces had higher corrosion rates than
the as-deposited specimens.
The laser treatment may have produced a melted surface of
the Pb-Sn and of the Sn coatings, similar to surfaces
observed after the reflow process as noted in the previous
annual report.
%
2. EXPERIMENTAL
2.1 Laser Operation
The laser used in our experiment this year was excimer laser
manufactured by Lambda Physics Model 201MSC working at 193nmwith pulse duration of 24nsec. The activated laser material
is a mixture of Ar and F2 gases in which produces
activated molecules of ArF. The beam mode was rectangular |with a small hole in the center. The beam dimensions were
1 S|
o
0.8x2cm, and it was directed perpendicular to the specimen
surface by a 45* turning mirror after passing through an
aperture that cut the beam in half in order to eliminate the
hole in the center of the beam cross-section (Fig. 2.1).
Prior to irradiation, the beam cross-section area was
measured and the energy per pulse for this section was
monitored by power meter.
Specimen movements were controlled by a computerized x-y
table. The specimen was shifted during the treatment so as
to produce overlapping between the adjusted pulses.
Laser energy per pulse was calculated according to the
formula: *
watt/cm2 =W/R .R A tL,
where 7.
W - energy measured by heat-sensitive apparatus (watt)
R.R - repetition rate pulses per second
A - area of laser beam cross-section (cm')
t_, - duration of laser pulse (24nsec in our experiment)
The laser beam power ranged from about 0.4 to 1 Watt at 10
pulses per sec, while the beam cross-section area was
0.2cm2 to 0.5cm2 . Accordingly, the energy per pulse was
8- 106watt/cm 2 . *
2.1.1 Laser Conditions
The laser energy applied was calculated from the energy per
pulse and the overlapping between the pulses. Table 2.1
summarizes the laser conditions applied.
. . , , ,., , , , 2 I_~' p
0
| IV
%1, % 10
.
%
. .4=
% J I ,.
X-Y Table ' "
Fig. 2.1: Schematic set-up
3 ./ r"./ '
3S
% I
%
Table 2.1: Laser energy conditions
Exp. Sample Energy R.R I Over- No. of Energy -6
Table No. per IlappingjPulses Density I
No. I Pulse [Pulse/ I per II [Watt]I sec] I Area [Watt/cm ]1
3.1 all 12.9X10O 10 50% 10 5.9X10 I
3.2 all 3X10 6 10 50% 10 6X10
7
•73.3 1 12.5XI0 61 10 50% 1 0 1 5X107 I
1 2 11.5XlO 1 10 1 50% 10 3X10' I
1 3 11.5X10'1 10 1 50% 1 0 1 3X10 I
4 1.9X106 , 10 50% 1 0 1 3.8X10 73.4 all 3XI0 6 10 50% 10 6X10'
.4
2.2 Polarization?. ,
Potentiodynamic polarization was carried out in 10-'M NaCI
solution. The resulting polarization curves provided
information regarding the corrosion behavior of the Pb-Sn
coating in aqueous solution. Corrosion rates were
calculated in millinch per year (MPY) units.. "
The polarization curves were obtained with the aid of a
corrosion measurement system model 350A manufactured by
Princeton Applied Research. The detailed set-up of the
experiments was given in the previous report.
Polarization parameters were:
Scan rate: 0.5mv/sec
Initial potential: -1.0 Volt (versus S.C.E.)
Vfe-r tex poteontial : 0.0 Volt (versus S.C.E.)
Finil potential: -1.0 Volt (versus S.C.E.)
Init ial delay: 7)u mntes .N
These parameters, were used in .ill the exleriments with a
view to satisf.i tory comparability.
4 .' .
4!
2 3 Specimen
The polarized specimen types were:
A: As deposited laboratory prepared Pb-Sn coatings on copper
foil with varing coating thickness. %
B: Laser treated laboratory Pb-Sn coatings on copper foil
with varing coating thickness.
C: Commercial as deposited Pb-Sn coating on epoxy plated
with 70um electroless copper.
D: Laser treated commercial specimen.
E: As-deposited tin plated or copper foil.
F: Laser treated tin plated surfaces. .
2.4 Electroplat ijng.O:
Tin-Lead Alloy Platin was described in detail in the
previous report. The coating was plated from a fluoborate
bath supplied by Galvanocor which was built up according to
the following formula:
Lead fluoborate - 41 gr/l .
Tin fluoborate -120 gr/l
Fluoboric acid -140 gr/l
Boric acid - 10 gr/l
Additive LAI - 15 gr/l
Additive LA2 - 15 gr/1
Stabilizer LA5 - 15 gr/l
The coating thickness was varied by changing the plating
time. ,• '4" .
......... _. ,.W
04~
Tin plating was done from tin fluoborate bath which was ..
built up from6V
Stannous fluoborate 115 mli
Fiouboric acid 380 mI/I N*Boric acid 29.9 gr/1
LAI 15 mi/i
4- LA2 5 mi/i
LA3 11.5 mi/i
The coating thickness was varied by changing the plating
time. The current density was l5mA/cm2 . Tin foil was used
as anode.
. zPP
4'0
3. RESULTS AND DISCUSSION
3.1 Potentiodynamic Polarization
Potentiodynamic polarization was carried out in order to
assess the susceptibility of Pb-Sn alloy coating and tin .% \
coating to corrosion in chloride solution.
Corrosion rates of the various specimens in 10-2 M NaCl
solution are shown in Tables 3.1-3.4, Typical '-
potentiodynamic polarization curves are shown in Figs.
3.1-3.4.
According to the electrochemical theory of polarization (see %
previous report), the corrosion rates can be calculated by
two methods: (A) the polarization resistance technique; (B)
the Tafel technique.
According to method A a range of ±25mv around Ecorr is used
for determination of the slope of the line (Fig. 3.4A).
AE Rp J3A '-F = '__._____ ___
I P 2.31 corr ( A+c)
or I = C "corr 2 .3 (A+ 3C) RF P.
where0, - cathodic Tafel constant (volts)
0. - anodic Tafel constant (volts)
- corrosion current density (A/cm2 ).
I % I
---- can be determined from the slope of the line by
using equation (1). The calculated I.... can be used to
determine the corrosion rate according to equation (2),
which was derived from Faraday's law.
p.-':.I0"M ..
7 .~
0.131 o EW %corr
(2) Corrosion rate (mpy)= d
where 16NEW - equivalent weight (gr)
d - density of corroding species (gr/cm 3 ).
mpy - millinch per year
Fig. 3.4A shows an example of the curve obtained by the
linear polarization technique and the straight line
represents the calculated slope.
According to method B, the projection of the intersection of
the Tafel constant with Ecorr determines I ..... and this
Icorr is used to calculate the corrosion rate by using
equation (2). By this method, we can find I.-. from only tone of the Tafel constants. This is of advantage where the
Tafel constants differ widely. The cathodic Tafel constant
is usually selected for I..... determination because in the
cathodic mode the specimen is free from oxidation products
that can affect its behavior during polarization (Fig.
3.4B)
Tables 3.1-3.4 summarizes the calculations of the various -
polarization parameters by using the two methods described
above. Icorr was calculated through the linear polarization
method (R.) while I.,... through the cathodic Tafel
constant.
Figs. 3.5 and 3.6 show the correlations obtained by
regression between I .... and I/Re and between .
and 1/R., respectively. T ...- was calculated the
cathodic Tafel constant, as for many specimens the anodic S
Tafel constant was unobtainable. %
The correlation found by using both Tafel constants (Fig.
3.5) through the linear polarization (R,) method was: "
(3) I.,=...:0.02-10-6+4.42"10-2" I/Rip
r=0.94
8 IIII
*... .... -
where "
I.... in amp/cm2 *
R1 in Qcm2
r - correlation coefficient
I at 1/R.=0 is very small and can be neglected.
We can assume that _
' 4.42 - 10-2 12. 3 OBA+BC adp R'"
The correlation found by using the cathodic Tafel constant
was:
I....=1 .67- 10-6+1 .7.10-2 -1/R.
r = 0.47where
Icorr in amp/cm2 -
I/R in Q- cm-2
r - correlation coefficient e.-.
This second correlation was not very good and it seems that
we cannot use it for corrosion behavior estimation. The .
difference between the cathodic and anodic Tafel constants
rules out a linear relationship between Icorra and I/R...
(This difference may be a consequence of the corrosion type,
which was found to be more local and intergranular than the
general type). ,%
The first correlation was used to calculate the corrosioncurrent for specimens whose I---- could not be calculated
through both Tafel constants.
Tables 3.1+3.3 indicate that for most of the specimens -
I... was higher for the laser treated specimens than for
the untreated ones. For example, for coating thickness
12.7um (Table 3.2) the I_.._ found for the laser treated .
specimen was 1.046"10-amp/cm2 and for as-deposited
specimen 0.065"10-amp/cm'. The calculated values
obtained from the linear relationship were 1.37-10 - 1 and
9
a~j : _ : : 'V. : -77777 r-. IV n, rV9p ,
0.0510-6 amp/cm, respectively. %
Similarly, for the commercial specimen (Table 3.3) the
calculated I_.. of the untreated specimen was
0.92"10-amp/cm2 and for the laser treated specimen ",
2.64-10 -1 and 1.21"10-Oamp/cm2 . Higher I ....
values resulted in higher corrosion rates in accordance with
equation (2).
The same pattern was observed for the tin coating where the
I---, of the laser treated surface was
0.1036"10'n/cm 2 as against 0.1533"10nA/cm2 for
the as-deposited specimen. U
Figs. 3.1+3.3 indicate that the polarization curves obtained
were not the typical ones with equal anodic and cathodic
Tafel constants, but the anodic curve shows a similarity to
passivation behavior, i.e. potential increase without
current increase. This behavior interferes with the
corrosion rate calculaLions and can produce errors. The
unfavorable correlation between Icorr- and I/R. supports
this explanation. The corrosion morphology observed by
scanning electron microscope also supports this possibility.
VA
VN
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.,."'
Y1k TS SRi1PLE :3DATE 29 07TAPE
-0 IO FILEARE I :)Ev 50 C
-0. 300 mt/SEE 0 s0iECORR -0 4- 0
RESULTS. -- CTC 0 ?02%
- o.Soo Rp 3 2 1 EiICORR 1 4E
MPY 1 201
-0 '1r
-0.700
-O.90}
A1O 1Q 1 a10 O 0,Af 1
DRATE 29 07-0. O0 TAPE G
FILE 7AREA I.76GEI -,1.000Ej, 0.000
-0.300-,00o . %GEECORR - "' .E~RRESULTS
TC 0 20oATC 0 .292 . -
-0.50o Rp B oIoES 040ESCORR 6 527EI '%
MPY 0 07S .1,
ECO -0 Gc2
-0 700 --
-0 .930
I CI 161 162 10-2 t1i 165 IOENPLM2
Fig. 3.1: Typical cyclic potentiodynamic curves obtained for %
Pb-Sn coatings in 1O-2M NaCl. (Coating thickness
12.6im). A. After laser treatment. B. As-deposited
spec ien.
14
ua m I
% I- -- -a m-
&'U E '7-1
-0.1007
0. 900 -C "C
r L- • --. /'
-0 50 2 - ..- . ,e, .. ,.
-0.A
10# 161 6 ,, .00 1-ONR/CPL 2
fr0LT
DE S~c~
ELC
I '.. .
ETZ
D.Sat) Rp GE r
i E i .. %
-0 700
,S-0.900-h~~
10 10' 162 164 (6S 10 r4..L1C 0
Fig. 3.2: Typical cyclic potentiodynamic polarization in . .
1O-2 M NaCl of Pb-Sn coatings (coating thickness
8.1m). A. After laser treatment. B. As-deposited
specimen %
15 •
--. mm m . .ammamm m[ m man mmm •• ,' m
- - -. -- - , . 4
;0
VOLT 'RMPLE IDRTE os liTAPE
3.500 FILEARER 1 730Ev I 500E - 000
ECORR -0 452
RESULTSCTC 0 leiRTC 0 294
I SO0 'CORRE 2 S91E3tIPY GI
ECORR -C 435.- 03
o. snfo
-o .soo.•a*' k
A
lot I- b or, 107 NALm2
lid =
.500 E O -3 S -
C r- . 69
; -
16? ~ ~ ~ ~ ~ -10 14 6 16- 1b-i, M
Fig. ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ P 3.. Tyia"oetoyai plrzto u:so
commercial Pb-Sn coating 10-2M NaC1. A. After , -
~laser treatment. B. As-deposited specimen.
16 I
11 SSAMPLE 430DATrE [12 is
-0.4~7S REA 5 OfJO
j 0 520
E ~ R -0 ** 4 8 0
-93.48S R~ESULTSRP I 7S2EI
MPr 6 02OE2
-0.s - 4s
-~6a 2E6NFI/rM2
rYPICA POL&AALZATION RESISTANCE PLOT
ANODIC
DECEI DECADE %~
w%
.j
W.4
BAVS
K)r 1AIQAIOAA . %.LOG CURRENT %4.
TAFEL PLOT ....
Fig. 3.4: A. Typical linear polarization curve
B. Typical Tafel plot
17
I t. -U . . .... -
I corr 0.02' 10-6+ 4.42.10 - 2 I/R10 r 0.94
0 8-, 0
S6
0. ACL,// 0 without loser }-
4 * with loser oel0 A without loser...
- table 3.2A with loser
2 D Without loser
O A I with oser table3.3.
00 2
1/Rp (Xl cm- 2 x10-4)
* :-:-...
Fig. 3.5: Correlation obtained between IQo. and I/Refor polarization of Pb-Sn coating in 10-2 M NaCI
18 0
-S
I C167.0-6+1.7. 10 - 2 I/Rp O without laserC0 1 0 with laser table 3.1 t10 Arwith laser 0
A without laser -
Itoble3.3
IO [A with loser , AN"
. . without laser ',, CY with loser }table3.3
E..
94
(...1
0
0 20 I 2
R/Rp (S- cm-2 x10 - 4 )
%=',
Fig, .6: Correlation obtained between I=.. and I/R.
for polarization of Pb-Sn coating in 10-IM NaCI
19
,. , -',,
• I i I I0
3.2 SEM Analysis
The micrographs are grouped according to the Tables: Figs.
3.7+3.18 refer to Table 3.1, Figs. 3.19+3.26 - to Table
3.2, Figs. 3.27+3.29 - to Table 3.3, and Figs. 3.30+3.35
to Table 3.4. =
3.2.1 Laboratory Specimen
Fig. 3.7 shows the laser treated Pb-Sn coating with varying
coating thickness, and Fig. 3.8 - the same specimens after
polarization. EDS analyses of the various areas are given
in Fig. 3.9. .,
The specimens without laser treatment before and after
polarization are shown in Figs 3.10+3.11, respectively. The
EDS analyses of these specimens are shown in Fig. 3.12.
Comparison between the laser-treated and untreated specimens
revealed that the laser treatment resulted in morphology ., ..
changes. Separate brighter (Pb-rich) and darker (Sn-rich) 0
zones were produced probably through a melting process.
The corroded areas of the laser treated and untreated
specimens revealed similar phenomena of Pb-dissolution.
While from the laser treated surfaces (Figs. 3.8, 3.9)
Pb-rich zones were dissolved, Pb grains were dissolved from
the as-deposited ones (Figs. 3.11, 3.12). The EDS analyses
show the presence of Sn only at the corroded areas of both
laser treated and untreated surfaces. '.#
Figs. 3.13+3.18 are cross-sections of the specimens shown in
Figs. 3.57+3.1.1. Figs. 3.13 and 3.14 revealed dissolution
of Pb during polarization from untreated Pb-Sn coating. The .
elimination of the bright Pb-rich areas by the corrosion
process was characteri7ed by a pitting effect. (Figs. 3.14,3.15 ). *.. :
The cross-secti, .s of the laser-treated surfaces are shown ..A ,.
in Figs. 3.16+'.18. The development of differenit regions in %-%
200• . . S -
i i I .
the coating is seen clearly. Fig. 3.16 shows a Sn-rich grey' _
area and brighter areas with Pb and Sn content. Table 4.5
shows the concentration distribution over the depth of the
brighter region. The Sn content of the grey region remained
constant irrespective of depth.
Table 3.5: EDS analysis of the bright region shown in
the laser treated Pb-Sn coating cross-
section (see Fig. 3.16)
I IJ
IElement I Outer I Center INear Cu II Side I Ibasis I j.'. ]
I wt% Iwt% lwt%
Pb j 45 78.4 f 39.9Sn 49.6 11.8 j 21.7 fCu 5.4 9.8 38.4
Cl 0.0 0.0 0.0
Pb dissolution from the surface of the Pb-rich region was
possibly responsible for the smaller amount of Pb on the ?:
outer side of the coating in compared with the center.
The phenomenon of Pb dissolution which resulted in
exposed areas is seen in Fig. 3.17. The development of
various regions is seen clearly also in the unpolarized
specimen shown in Fig. 3.18.
Figs. 3.19+3.24 bring out the intergranular mode of the
corrosion process. Figs. 3.19 and 3.20 show the corroded 0
area of Pb-Sn coating with 2.7vm thickness. Although the
backgrounds of the corroded area differed, the
mechanism seems to be similar dissolution of Pb from the
grain boundaries spreading to the Pb-rich zone and further ,
to the tin-rich area. Table 3.6 which shows the EDS
analyses of the various areas support these observations. . .
21
U,
-JF '.W .A NK IF I P -%P.70 . _
0
Table 3.6: Comparison between EDS analyses of corroded
Pb-Sn coating specimen (2.7pm in thickness) with
and without laser treatment
I IUncorroded Specimens ( Corroded Specimens
(All Area I Bright (Dark regionlEdge Corr. lCenter
I Region I Area (Corr. Areal
wt% wt% ( wt% ( wt% I wt%
S II I I I I
Pb 152.0150.5 191.1 1 1 9 .7 * 1 3.8 114.7 1 3.61 8.4Sn (43.3146.8 1 5.8 ( 1 (87.5 * 174.3 177.2 136.7138.9 ICu 1 2.51 2.5 0.1 1 1 0 1 121.8 1 8.0 159.5152.6
cl 10.21 0.2 1 3.0 1 1 2.8 1 ** 0.1 1 0.1 1 0.21 0.1 1
* Laser treated specimen
** Untreated laser specimen .- ,-..
Not obvserved in as-deposited laser specimen
Figs. 3.21 and 3.22 and Table 3.7 show a similar pattern for
the Pb-Sn coating with 8.4pm thickness. -%.
Table 3.7: Comparison between the EDS analyses of the
corroded Pb-Sn coating specimen (8.4um) with and
without laser treatment
I Uncorroded Areal Corroded Area "
wt% ( wt%
1---- f t I -- ":-"-
Pb ( 53.6 I 51.1 7.4 ( 4.2 ( Si s4 46.1 I 48.6 ( 49.6 ( 44.2 -Cu ( 0.0 0.1 42.8 51.5 "CI 0.3 ( 0.2 ( 0.2 0.1 % %
* Laser tr(ited specimen
** As-deposited specimen.
22%N
The same corrosion mode was observed also for the coating
thickness of 12.7um (Figs. 3.23, 3.24). The "B" micro-
graphs show distinctly the boundary of the corroded area -6
as only Sn crystals remain on the copper base.
All experiments discussed above were conducted by
irradiation by unfocused laser. In order to achieve higher
laser energis, the beam was cofused and
6"10 7 watt/cm2 was applied per pulse. Figs. 3.25, 3.26
are SEM micrographs of these specimens. A very bright
surface was achieved with distinct separation between the
bright Pb-rich and grey Sn-rich areas, (Figs. 3.25, 3.26).
The surface obtained was smoother than its as-deposited
counterpart as can be seen by comparing Figs. 3.25B and
3.25D against 3.25E. Experiments will be conducted to study
the effect of high laser energy on the corrosion resistance
of Pb-Sn coatings.
3.2.2 Commercial Specimens 0
Figs. 3.27A through D are micrographs of the commercial
specimens treated at different laser energy, and Fig. 3.27E
the untreated specimen. Fig. 3.28 shows the same
micrographs at higher magnification. It is seem that a . .
melting process occurred, but there is only partial
separation between the bright and grey areas. The best
smoothing of the surface was achieved with higher laser
energy per pulse. Table 3.8 reveals this separation for
specimens (1) and (3) (Figs. 3.28A and 3.28C). The
composition of the as-deposited specimen is also inch 'led in
Table 3.8 (specimen 0 for which no separation was observed,
Fig. 3.8E).
. . . . m m m i I i 1
23%
. ,. ,,
Table 3.8: Comparison of different areas in Pb-Sn commercial
specimen after laser treatment
(1) (2) (0)
_ _ II ITotal IBright IGrain IBright I Grey I TotalI I (Area (Edge I Area I Area I II I IGrain I I I I II I ICenterI I I I II I I wt% Iwt% I wt% I wt% I wt%i I i I IIPb 50.9 176.9 25.6 1 78.7 1 22.1 1 48.6 1
I Sn 47.3 21.9 72.5 j20.6 76.9 49.6(cu( 1.8 1.2 I 1.91 0.7j 1.0 1.8(
Figs. 3.29 are the micrographs of the corroded commercial
specimen; Figs. 3.29A and 3.29B show the laser treated S' ,.
area, and Fig. 3.29C the as-deposited area after
polarization. Table 3.9 summarizes the EDS analyses of the
specimen after polarization.
Table 3.9: EDS analysis results of Pb-Sn coating after
polarization
-I IWithout laser treatmentILaser treated (I)l
I ISmall ILarger I Whole lWhole IBetween II Crystall Area I Area ICrystals I -I I wt% I wt% I wt% I wt% I wt%I ) I I I~t(Pb I 0.6 I 1.5 1 5.0 1 2.9 1 7.3 ,ISn I 21.4 1 88.8 1 47.2 71.0 1 57.3(Cu 1 73.9 1 7.16 I 46.0 1 24.1 1 1.2ICl 1 4.1 1 2.1 1 1.8 1 2.0 1 34.1 0
4.24Sd
• , i I I I I I I
These results and SEM observations show that the corrosion
process begins initially with Pb dissolution followed by
partial Sn dissolution. It was observed that the amount of
Sn remaining on the base was higher for the laser treated
surface compared with the as-deposited surface, 71% against
47.2%, respectively (Table 3.9).
This phenomenon can possibly be attributed to the laser
treatment.
3.2.3 Tin Coated Specimens
Figs. 3.30+3.35 are micrographs of the as-deposited tin
coating after laser treatment and after polarization. Figs.
3.30 show the coating (thickness-6.7um) before and after
laser treatment. The melting phenomenon is demonstrated
clearly by the transition from Fig. 3.30A to 3.38B. Higher
magnification of the laser treated area (Fig. 3.30B)
revealed the effect of cooling on the melted surface (C,D).
Figs 3.31-3.32 and 3.34-3.35 compare the corroded as-
deposited and laser treated surfaces for coating thicknessesof lm and 3.6Um respectives. It is seen that the corrosion
morphology of both surfaces has a circular symmetry.
Initially, the circular boundaries separated from the
background and afterwards tin dissolution occurred. The
corroded area composition shows a of small amount of Cl,
and larger amounts of Cu and Sn (Figs. 3.32A,C).
2g
,,, ia I I I I ''"0
4. CONCLUSION
Laser induced melting of the Pb-Sn coating resulted in 1bright area at energy levels of 106 watt/cm2 -
lOwatt/cm2 per pulse. The laser treated area produced
a lead-rich zone believed to be a solid grain as discussed
in the previous report. Formation of these zones possibly
prevents improvement in corrosion resistance and affects the
corrosion mode by producing larger anodic sites.
Perferential dissolution of lead was observed for both the
as-deposited and laser treated specimens, resulting in a
non-general corrosion mode closer to the intergranular type.
Calculations showed the laser-treated specimen had higher
corrosion rates than their as-deposited counterparts.
Analysis of the results revealed inconsistencies -
discrepancies, possibly due to deviation of the corrosion
mode from the general type.
The commercial Pb-Sn coated specimens revealed the same
corrosion behavior as the laboratory-plated ones. The
corrosion resistance of the as-deposit of tin coated
specimen was found also to be higher than for the
laser-treated specimen.
% %%
26.
26 ,
0Z+
- • m • | |
270
I LA
j -4
p -6c, "
~ A3 : ~ A~
A kj -. V
WkE
..%
CD~~~, 2.1 ,"*x100 50
A,B 4.39pm x 1000, x 5000.G,) 12.1 pjm x 1000, x 5000
Fi- M I. K. TIM -. A. -. .
28
'B
-~1w
Fig. 3.8 SEM observations of laser treatment Pb-Sn surfaces after % eIJpotentiodynamic polarization in 102M NaCi
A,B l.89iim x 1000, x 5000SC,D 2.1 V.m x 750, x 5000E,F 8.1 pm x 750, x 5000
29 0
. ......... ... . . ... ...... ......... ... .... J..,i...., .a...~....,....t. 1 .... i....i..
oil ..
II'
J!~i ~ III r.'i~:%
~6 - LT= 100 SECS.
Fi.39 ESaayi flsitetdsrae21mbfr n fe
A f II rN.% XN.
30
4--1
# r 10E VA*,tt-WTI:FIAL____ *1~A j ___
-,~ * -
'-"de
% -
IVV4 4V
~% ~ %
31
V IRm
%-
S - JR
*'.'A
Ott .h
A~:;~~ ~J%
j~t,
Fig. 3.11 SEM observations of corroded area of as-deposited Pb-Sn coatings%
with various after thickness polarization in 10-2M NaCl.A,B. 1.96 pm Pb-Sn coating thickness specimen.
x 750, x S000respectivelyC,D. 4.3 pim -Sn coating thickness specimen FT
x 750, x 5000 respectively
32
........ .........
1 I
... ... ... ... ..
L ~T= 100 SC~o O
0 0 .......... ....... L -. t !_. L ..........1-.4............. ... . ..............
IIt-
11
54-1 LT= 5 ES
Fig. 3.12 ESaayiofs-deposited Pb-Sn coating after polarization in 10-(see Fig 4.11)
A. Coating thickness 1.96um (Fig 4.1B). 1.%P,B. Coating thickness4.3im (Fig 4.11D)
33
_%,4
e WI
% 0
~' S
~-
-- a
.,~ ~
34* 5*5%
4
.. 5'S
5 p *.1* .~JSt. St~ 5~
SJ.
.i~ *J.'-p
5,5% ~&'*S.*S*' *U~~
--- St
* *U
N. S% .?.*
US. U~* .JU ~S*~*'~ ~'!
'US.
S5' 'S.-,'-* St *~ -
.5,.
S-~ -~
.'~ *5 *
*StS.S5 .%.;5,S. ~'.* N.
'-p..
Fig. 314 SEM observations of crc8s-~zUI:n of as deposited Pb-Sn coating after*5,~ ~*polarization in 102 M NaCi
A. Uncorroded area. x 5000B. Corroded area . x 5000
''.5%
0
5*.* .*.'.*,-*N.
35
3500 1 .91-P
IIN- 511 E:N- ~CL- CL0 -0
I I IICuK 8.00
I LI
II
I A
IJ~ 2.a :3, 5'6 -8
LL IL I l, II IIIi I A11I~j I IIIiu i I I I II li u iI II I II IIi
Rv V77.
U
Ij Ij I L LI
Fig. 3.15 EDS analksis of the area shown in Fig 4,14.--
A. Uncorroded area(Fig 4.14A)Sl. Uncorroded area bright region (Fig. 4.14A)C. Incorroded area grey region (Fig. 4.14A)D. Corroded area (Fig. 4.14B).
aI
* ~a -
366
hA~a L,- u.LA14-U I
4.Vi.
F; i
0-In-F T 1A 1 1 'T-7 I T-1 I P, (71~~~4 2 4: 5 ,r0 1 7
Fig. 3.16 S(31 observations of Pb-Sn (M2c&5-XctC( of laser treated specimen after-polairization in 10-2M. NaCl (cooting thickness 4.3vm)
A. Crossection observation x 5000B. Crosscction observation. x 2000C. r.. a nalysis of the grey area.D. r. 0 nlyi of the bright area.
* % le
S'%*
.* %
A. , .'
376
N.
04
Fig. 17 SI-'M observation,; of crns--tiLcti of laser treated Pb-Sn specimen,,:
- .. .
38
.,-...-
Fig. 3.18 SEM observations of crcss-sectfim of Pb-Sn laser treated specimen",S-,without polarization. (Coating thickness 12,7m) 0A. x 2000..
B.. x 5000 ',
"I.-
. i / l
39
ktI'
N.
Lc
''%
ES
Fig. 3.19 SEM observations of Pb-Sn laser treated specimen after polarizationin 10-2M NaC1(coating thickness 2.7pm).
A. Corroded area x 1000B. Corroded area x 5000C. Corroded area x 1000D. Corroded area x 1000 *E. Corroded area x 2000 %. I
40
Al..
~~4
'AF
Fig. 3.20~ SiM obevtosof corroded area of as deposited Pb-Sn coating after
polarization in 10-2M NaCI. (Coating thickness 2.9ijm.
A. Corroded area x 1000.R. Corroded area x 50000C. Corroded area x 2000
41
AtA
40-
A. Corodedarea 200
C. 2 bennin of corroded area of 2000sie bSncain fe
polaizaion n 1-2M a~l (Cotin thiknes 8. im
A. Corodedarea 20.
B. Elargent f crrodd ara x 000
C. Bginnng f corode ara x 000
42 I
A6A
%.*
C0
Fig. 3.22 SEM' observations of Pb-Sn corroded area of laser treated specimen afterpolarization in l0-2 M NaC].(Coating thickness 8.41irn).
A. Corroded area x 1000B. Corroded area x 5000C. Beginning of corrosion, Sn crystal x 2000.
dP % F
43
404
4~ A.
IE''
B 1
Fig-3.2 3 SEM observations of corroded area of as deposited Pb-Sn specimenafter polarization in 10-2M NaCl.( Coating thickness l2.7pim).A. Corroded area x 200.B. Beginning of corroded area x 1000.
44S
'4V
W,,
~~.1 -
Fi.32 E bevto flu coroe -b ae raedseie fepoaiztoni 1-M4 al
A.Croddaeax10
B. orrdedare x 500
45
Al"F
MR1,
a,,
*E
Fig. 3. 25 . -
SEM observations of high energy laser treated surface of Pb-Sn coating, !
A. Laser treated surface one line x 1000.9 .:B. Htigher~magnificance of. A. x 5000.C. To overlapping lines x 1000D. Higher magnificance of C, x 5000E. Without laser treatment x 5000,
46
I LA
E:NWr j UI. ED4VTTr -1 L7-r-- . r
r- m --I-t
B~~ A4 ,L
* 40
U-N
rryrri rT1m11ni~r1UrI~Tri~pTi~rn- 324
47
O-M-S
LN
-.E r-N 4-.1%-"INK~
Fi.3.7 EMosevton f omrca P-ncotn atrVae
* i g . 3 .2 7 : e m o b e r t i n o f c o mm.A . L a e r a P b -S n o a t i ng0 wa ft e r l s e r
B,C. Lsreer~y of 3.0.atc D. Laser energy of3.8.107 watt/cm .E. without laser treatment.
-V .
48
-A.
A B.
:%
C~
p
9%.
Fig. 3.28
SEM ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ * obevtoso omrca bS pcmn
Fig.3.2 at ighr manifcatin (SOOO. A Lasr eerg
of 5107wat/cm. B,. Lserenegy o 3.07 attcm0
D. ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ .Lae enryo .. 0-At/.. E ihutlsrtetet
IW
-' I
4 1%
Fig. 3.29 SF.MI observations of corroded Pb-Sn commsercial specimen after polarizationin 10-2M NaCl,(x 750).
A.~ ~ ~ Afe ae-ramnto .0 atcA. After laser trcatment of 5.107 watt/cm.'
C. With laser treatment
or
.- ,e
% %
50
-S
%
b ./* 'r
%
Fi. .0 E osrvton f i srac efr adafe lsr ratet catnthickess 67ijm)
Fig. CD 3.0 S A bevtoso tnsraebfr nfter laser treatment (oatinthickess 67Ire
A. Asdeposted x1000
51
Al,~
1w
ig
Ir 40Ka~
*.2
-ig 3.1 SN bevtoso9.rddtn pcmnatrplrzto 0 MN~
Pig. 3 C. SEnaobsetn of l corroded tirecie afe poarOtin10 NINi*
A. UCorroded area x 750.
*j Ir-W Ic. IV K1CI--%TXv- 1% P-N
52
~4 f
B
4" N
*g~ ~* 6j.
%.-.-:%
%-a'd
Fig. 3.32 SENM observations of corroded laser treatment tin specimen. (coatingthickness 0.96 pim).
A. Corroded area x 75.B. Elargentof te crrodd aea x500
C. Enlargment of the corroded area x 500.
D. Uncorroded area x 2000.
%ag~
*% %a
% %
A
.11 4
rT 7 r II" I-,- I,
0 2 4 5 E- 7 S, S. : 4 5 C-.-
Fig.908 3.3 EDSaayi fteaeasoni is .1336A.0 Corddaeiihu ae ramn Fg .4
B. Ucorode ara wihou laer reatent(Fi. 331)C. corddae ihutlsrtetetspcmn(i.33)
D. Ucorodedare, lser reamentspeime (Fi. 331)
54
p.-,V
Op %
Fig. 3.34 SEM observations of corroded tin area withoutlaser treatment.(Coatingthickness 3.6um).
v A. x 500B. x 5000C. Uncorroded area x 2000 'S
55
185
A 4 B
A
* 0 .
Fig. 3.35 SEN observations of corroded laser treated tin specimen. (Coating thickness3.6 jim).
A. Corroded area x 200.B. Enlargment of the corroded area x 2000. a aC. x 5000.
44
w wv w v w