J o u r n a l o f Electronic Mate r i a l s , Vol. 24, N o . 1, 1995 RegularIssuePaper

Solder Joint Reliability of Indium-Alloy Interconnection

KOZO SHIMIZU, TERU NAKANISHI, KAZUAKI KARASAWA,K A O R U HASHIMOTO, and K O I C H I NIWA

F u j i t s u Laboratories Ltd., 10-1 Morinosato-Wakamiya, A t s u g i 243-01, J a p a n

Recent high-density very l a r g e scale integrated (VLSI) interconnections inmultichip modules require high-reliability solder interconnection to enable us toachieve s m a l l interconnect sizea n d l a r g e n u m b e rofi n p u t / o u t p u t terminals, andto minimize soft errors in VLSIs induced by a-particle emission from solder.Lead-free solders such as i n d i u m (In)-alloy solders are a possible alternative toconventional lead-tin (Pb-Sn) solders. T o realize reliable interconnections u s i n gIn-alloy solders, fatigue behavior, finite element m e t h o d( F E M ) simulations, anddissolution and reaction between solder and metallization were s t u d i e d withflip-chip interconnection models. We measured the fatigue life of solder jo in t sand the mechanical properties of solders, and compared the r e s u l t s with acomputer simulation b a s e d on the FEM. Indium-alloy solders have b e t t e rmechanical properties for solder j o i n t s , and t h e i r flip-chip interconnectionmodels showed a l o n g e r fatigue life than t h a t of P b - S n solder in t h e r m a l shockt e s t s between l i q u i d nitrogen and room temperatures. The fatigue characteris-tics obtained by experiment agree with t h a t g i v e nby FEM analysis. Dissolutiont e s t s show t h a t P t film is r e s i s t a n t to dissolution into In solder, indicating thatPt is a n adequate b a r r i e rl a y e r material for In solder. This test also s h o w s thatAu dissolution into the I n - S n solder raises its m e l t i n g p o i n t ; however, Agaddition to I n - S n solder prevents m e l t i n gp o i n t r ise. Experimental r e s u l t s showt h a t In-alloy solders are suitable for fabricating reliable interconnections.

K e y w o r d s : Fatigue, flip-chip, In alloys, interconnection, solder

I N T R O D U C T I O NI n d i u m (In)-alloy solders, such as i n d i u m - t i n (In-

Sn) 1,2 and indium-lead (In-Pb)3,4 solders, are a pos-sible alternative to conventional lead-tin (Pb-Sn) sol-ders because they are reliable and have a relativelywide m e l t i n gp o i n t range. Step-soldering required forhigh-density packaging ofmultichip modules (MCMs)uses a n u m b e r of solders with m e l t i n gp o i n t s t h r o u g ha wide range. Lead-free solders such as In-alloy sol-ders are expected to decrease environmental pollu-tion and soft errors in very l a r g e scale integrated(VLSI) interconnections induced by a-particle emis-sion from the solder, because Pb generally containsimpurities such as U and T h element w h i c hrelease a -particle.~ Solder fatigue is caused by stress induced by

(Received March 25, 1994;revised September 16, 1994)

t h e r m a l expansion mismatch between LSI chip/com-p o n e n t and substrate d u r i n g t h e r m a l cycling. T oo b t a i n h i g h e r solder j o i n t reliability, solders must beable to w i t h s t a n d fatigue. The reliability decreaseswith the solder j o i n t s ize .6,7

Previously, the flip-chip interconnection technologyfor Si and GaAs chips operated in l i q u i dn i t r o g e ns wass t u d i e d because carr ier mobility in complementarymetal-oxide semiconductor9 and high electron mobil-ity t r a n s i s t o r1°,11 devices becomes h i g h e r t h a n that a troom temperature. This s t u d ys shows that In solder issuitable for flip-chip interconnections subjected to al i q u i d nitrogen environment. Thermal shock t e s t sbetween l i q u i d nitrogen and room temperatures ex-h i b i t t h a t In solder has a longer fatigue life than Pb-Sn solder. The reliability of flip-chip interconnectionsis also affected by the m e t a l used for the b o n d i n gpads.Metallization materials must have good compatibil-

40 Shimizu, Nakanishi, Karasawa, Hashimoto, and Niwa

Chip: Si, GaAs

Solder

Substrate(A1203)

Fig. 1. Close-up view of flip-chip interconnection model. This modelconsists of a GaAs chip and alumina substrate.

Neutral

A !iiiiiiiiiiii i!!i!i i! iii i!I iiiiiiii!i!iiiiiiiii !iiiiiiiiiiii!;a ; rai iiiiiii:Jiiii:i!i!!!iii':i s

Solder bump bump

I I

100pm

bFig. 2.The three-dimensional FEMmodel for interconnection: (a) thethree-dimensional FEMmodel (1/4 Mpartion model), and(b) the three-dimensional FEM model (single bump model).

ity with solders, i.e. good wettability and m i n i m a lchemical reaction. If the m e t a l s dissolve into thesolder, intermetallic compounds may form and soldercharacteristics such as m e l t i n g p o i n t may change.Dissolution and reaction characteristics between thesolder and metallization materials are i m p o r t a n tfactors to o b t a i n reliable interconnections.

In this paper, the reliability of flip-chip i n t e r -connections u s i n g In solder was s t u d i e d inclusive of al i q u i d n i t r o g e n environment. T h e r m a l fatigue life

was analyzed on the b a s i s of mechanical properties ofI n solder, elongation, and tensile strength. T o predictt h e r m a l fatigue characteristics of flip-chip solderj o i n t s , simulations were performed on the mechanicaldeformation behavior of In and P b - S n solderjo in t s bym e a s u r i n g stress-strain curves for each solder andcalculating plastic s t r a i n and Von Mises' equivalentstress by the finite element m e t h o d (FEM). Plastics t r a i n and Mises' equivalent stress are closely relatedto the t h e r m a l fatigue life of solderj o i n t s .

T o clarify the reaction between In-alloy solder andAu metallization, change in m e l t i n g p o i n t of I n - S nsolder with Au dissolution was examined. Silver addi-tion to I n - S n solder was t r i e d to p r e v e n tm e l t i n gp o i n trise with Au dissolution, because the m e l t i n g p o i n tincrease with Au dissolution in this experiment.

EXPERIMENTAL PROCEDURE

Fatigue Life of Solder J o i n t

Four different solder alloys were examined: In, In-48%Sn, In-40%Pb, and Sn-37%Pb. U s i n g v a p o r depo-s i t i o n technique, solder b u m p s were formed on both Siand GaAs model chips and a l u m i n a substrates too b t a i n high solderability. The alloy composition of thesolder b u m p s was controlled by correcting the compo-s i t i o n of the m o t h e r alloy m e l t e d in a crucible becausethe v a p o r pressure is different b e t w e e nthe elementalmetals. TM

The flip-chip interconnection s a m p l e we made iss h o w n in Fig. 1. The bump diameter was 200 ~m, thep i t c h was 400 pm, and the bump h e i g h t was 130 pm.The metallization film for the b o n d i n g pads was goldover p l a t i n u m with a t i t a n i u m underlayer (Au/Pt/Ti)both on the Si, GaAs/alumina, and b u m p s are electri-cally interconnected in series.

For the t h e r m a l shock t e s t , the flip-chip i n t e r -connection sample was immersed in l i q u i d n i t r o g e nfor 30 s, then exposed to n i t r o g e n gas a t room tem-p e r a t u r e (20°) for 30 s, then a g a i n immersed intol i q u i d nitrogen. The electrical resistance was mea-s u r e d a t room temperature (20°C). If a crack occursand propagates in the solder b u m p , the electricalresistance increases. 13 T o m e a s u r e the resistance, afour-point probe m e t h o d was u s e d .

Tensile TestU s i n g I n s t r o n universal tester, tensile t e s t s were

done a t -196 (liquid n i t r o g e n temperature), -70, 20,and 125°C. Tes t pieces were cas t with same coolingrate as the solder reflow process (l°C/s). The cross-head speed was 0.5 m m / m i n . This is approximatelythe same s t r a i n rate t h a t will occur in solder jo in t sd u r i n g t h e r m a l cycle t e s t s .14

SimulationFor the simulation, the three-dimensional solid

models s h o w n in Fig. 2 were u s e d . Since the sizedifference between the flip-chip bump and LSI (Sichip) or substrate is large, the plastic s t r a i n andMises' equivalent stress were calculated by two-step

SolderJ o i n tReliability of In-Alloy Interconnection 41

analysis. We examined the bump located farthestfrom the n e u t r a l p o i n t . This bump is significantlyaffected by the t h e r m a l expansion mismatch betweenthe chip and the substrate. Here , the chip is Si and thesubstrate is alumina. U s i n g A B A Q U S®15 FEM pro-g r a m , we calculated the elasto-plastic t h e r m a l stresswith the temperature dependency of the solder's me-chanical properties.

Dissolution

Dissolution in In SolderDissolution of m e t a l s into the In solder was ex-

a m i n e d by reflowing solder on a t h i n film of eachmetal, ofw h i c h measuring m e t h o d is s h o w n in previ-ous s t u d y .TM Two t y p e s of two-layer metallization filmwere studied: gold over nickel (Au/Ni) and gold overp l a t i n u m (Au/Pt). The film samples were 1000A thick.Metallization p a t t e r n s (3 x 3 mm) were vapor-depos-ited on glass substrates (10 x 20 x 1 mm). An In solders h e e t (3 x 3 x 2 mm) was placed on each film p a t t e r n ,then was m e l t e d with a m i l d l y activated r o s i n flux byh e a t i n g a t 220°C for 720 s. U s i n g flip-chip i n t e r -connection samples with metallization f i l m s ofA u / N i /T i and Au/Pt/Ti, the difference between t h e s e filmswas also examined by analyzing the element (Pt, Ni)distribution in the solder b u m p .

Dissolution in I n - S n S o l d e r

Both Au(0. 1 pm)/Ni(2 ~m) thin Au films and Au(2~m)/Ni(2 ~m) t h i c k Au f i l m s were examined. Thesefilms were electroplated on phosphor bronze p i n s . T odissolve the films into the I n - S n solder, the pin sampleswere dipped into the m o l t e n solder in a n a l u m i n acrucible a t 130°C for 3 min, and then they werewithdrawn. Dipping/withdrawing was repeated up to50 times, and e v e r y time the f r e s h pin sample wasd i p p e d into solder. The microstructures of solderswere examined u s i n g a microscope and e n e r g y dis-persive analysis by x-rays (EDX) together with scan-ning electron microscopy (SEM). The liquidus tem-perature (TL) of the solder was measured by differen-tial t h e r m a l analysis (DTA), and the solder composi-tion a f t e r Au dissolution was analyzed by atomicabsorption spectrometry.

RESULTS AND DISCUSSIONFatigue Life and Mechanical Properties

F i g u r e 3 shows the t h e r m a l shock test r e s u l t for aSi chip on a n a l u m i n a substrate. The resistance of Sn-3 7 % P b solder increases a f t e r 80 cycles, and t h o s e ofIn-48%Sn and In-40%Pb solders increase a f t e r 150cycles. The resistance of In solder r e m a i n s constanteven a f t e r 300 cycles. This indicates that In and In-a l l o y solders w i t h s t a n d fatigue b e t t e r than S n - P bsolder and are suitable for Si flip-chip interconnec-t i o n s in l i q u i d nitrogen. The resistance increase isa s s u m e d to be caused by the cracks formed in thesolder b u m p . Also, we supposed that the cracks c a n beobserved a t room temperature.

As s h o w n in Fig. 4, the t h e r m a l shock test r e s u l t fora GaAs chip on a n a l u m i n a s u b s t r a t e indicates t h a tthe resistance of Sn-37%Pb solder increases a f t e r 100cycles, and t h o s e of In-48%Sn and In-40%Pb soldersincrease a f t e r 200 cycles. The resistance of In solderr e m a i n s c o n s t a n t even a f t e r 300 cycles. As with Sichips, In and In-alloy solders are suitable for GaAsflip-chip interconnections in l i q u i d nitrogen. Ofcourse,the difference in fatigue life of solders is related tot h e i r mechanical properties.

The elongation a t fracture of each solder was mea-s u r e d in l i q u i d nitrogen. In and In-alloy solders havemuch h i g h e r elongation t h a n Sn-37%Pb solder ass h o w n i n Fig. 5. The h i g h e r elongation appears toincrease the fatigue life; however, the elongationvalues of In and In-alloy solders are a l m o s t the same .Hence , the difference in elongation does not explainthe fatigue life of In and In-alloy solders, b u t it may bea t t r i b u t e d to the alloy toughness.

Consequently, we p l o t t e d a new factor, e/G, of the

[] In - 4 8 % S n

15 - z~ Sn - 3 7 % P b

..-.. o In - 5 0 % P b l

ot -

"~ 5n"

RE

I I

0 100 2 0 0 3 0 0N u m b e r of c y c l e s

Fig. 3. Changes in resistance dur ing the therma l s h o c k test betweenl iqu id nitrogen and room temperatures fo r the flip-chip interconnectionmodel us ing a Si chip and an alumina substrate.

r r

dot "

ffl

r r

15

10

5

[] In - 4 8 % S n.z~ S n , 3 7 % P b ~o In - 5 0 % P b /

2/RE

Oo l 300N u m b e r of cycles

Fig. 4. Changes in resistance dur ing the therma l s h o c k test be tweenl iqu idn i t rogen and room temperatures for the flip-chip interconnectionmodel us ing a GaAs chip and an alumina substrate.

42 Shimizu, Nakanishi, Karasawa, Hashimoto, and Niwa

LN2

2.0

2O

10

0 In

m

In-5OPb In-48Sn

100

r • mSn-37Pb

Fig. 5. Elongation to fracture of In, In-48%Sn, In-40%Pb, and Sn-37%Pb so lders measured in l iqu id nitrogen.

1.513_

O4v

co

1.0

0.5

m M

In

LN2

o4v

t -O, B

c-oILl

In-5OPb In-48Sn Sn-37PbFig. 6. Elongation to tens i le strength ratio, d~, of In, In-48%Sn, In-40%Pb, and Sn-37%Pb solders measured in l iqu id nitrogen.

.£

I:1.

0.05

0.03

0.01

-0.01

-0.03

i i i i

...J

..... e ..... In . . ~

-o0s G s'o 16oTemperature (°C)

Fig. 7. Plastic strain (~p) of In and Sn-37%Pb solder in each tem-perature.

solders. We c o n s i d e r t h a t s is t h e fac to r showing a nabil i ty to r e l a xt h e s t r e s s induced in t h e s o l d e r bumpsa n d t h a t (~exhibits a possibility t o in tegra te t h e s t r e s sa n d strain a n d to init iate cracks a t t h e s t r e s s concen-t ra t ion position a n d w e a k e r s i tes like as t h e grain

80

v

t -O° m

t ~E)3t -O

UJ

l I I I

• In• Sn-

60

40

20

I I I I

-50 0 50 1O0Temperature (°C)

30

Fig. 8. Elongation of In and Sn-37%Pb in each temperature.

boundar ies o r defects in t h e solder . So d(~ is a s s u m e dt o be t h e measure o f toughness o f t h e s o l d e r a n d tocorrela te to fa t igue behav io r o f t h e s o l d e r bump.I n d i u ms o l d e r has a h ighe r d(~ va lue t h a n In-al loys o rSn-37%Pb as shown in Fig. 6. This resul t agrees wellwith t h e resul t s on t h e r m a l s h o c k t e s t r e su l t s .

F E M S i m u l a t i o n

The dependence o f t h e m a x i m u m plast ic strain a n dM i s e s ' equ iva len t s t r e s s on temperature In a n d Sn-37%Pb solders were ca lcu la ted . Both so lders showsimilar behav io ra t temperatures f r o m - 4 0 ° C to 125°Cas shown in Fig. 7. I n d i u m solder , however , has amuch wider e longa t ion range t h a n Sn-37%Pb s o l d e ras shown in Fig. 8. Figure 9 s h o w s M i s e s ' equ iva len ts t r e s s in 125°C for both solders. I n d i u ms o l d e r exhib-its a uniform s t r e s s d is t r ibu t ion a n d a low s t r e s sva lue . On t h e o t h e r h a n d , Sn-37%Pb s o l d e r indicatess t r e s s concentrations a t t h e top a n d b o t t o m interfacesa n d a h ighe r s t r e s s va lue t h a n In solder . From thissimulat ion resu l t , t h e fa t igue life o f In s o l d e rbecomeslonge r t h a n t h a t o f Sn-37%Pb solder . This agrees witht h a t o f experimental resul t s measur ing res i s t ance asa func t ion o ft h e r m a l cycles.

D i s s o l u t i o n

Dissolution in In S o l d e r

Nickel a n d Pt barr ier layer dissolution in to Ins o l d e r was observed t h r o u g h t h e b a c k o f t r anspa ren tg l a s s substrates. To form t h e samples , In s o l d e r wasreflowed fo r 720 s on t h e films. The Ni film appearspart ly leached a t t h e e d g e , whereas t h e Pt film s h o w st h a t dissolution o f t h e film is n o t a lmos t observed asshown in Fig . 10.

Figure 11 s h o w s element d is t r ibu t ion maps o f Nia n d Pt in t h e c r o s s sec t ion o f t h e flip-chip in-terconnection model. Most o f t h e Ni dif fuses in to t h eIn s o l d e r from t h e init ial c o n t a c t areas o ft h e chip a n ds u b s t r a t e dur ing hea t ing fo r s o l d e r ref lowing. Hence ,t h e Ni is widely d is t r ibu ted t h r o u g h o u t t h e In solder .

SolderJ o i n tReliability of In-Alloy Interconnection 43

a b

Fig. 9. Mises' equivalent stress contour line obta ined by FEM simulation for flip-chip interconnection: (a) In solder, and (b) Sn-37%Pb solder.

The Pt, however, diffuses only slightly into the Insolder, and most of it r e m a i n s a t the i n i t i a l contactareas. T h e s er e s u l t s suggest that Pt film is superior toNi film as a metallization material for use as a b a r r i e rlayer.

Dissolution of In-Sn SolderThe typical solder microstructure a f t e r our coated

pin experimental configuration was d i p p e d 50 t i m e sand the related quantitative chemical analysis re -s u l t s are s h o w n in Fig. 12. The t h i c k Au film sampleindicates precipitation of a new crystalline p h a s e ass h o w n in Fig. 12a. This crystalline p h a s e was identi-f ied as AuIn 2 intermetallic compound. On the o t h e rh a n d , the thin Au film sample exhibits the typicaleutectic microstructure as s h o w n in Fig. 12b, t h a t iscommonly observed in the original In-48%Sn solder.The thin Au film sample consists of both a Sn-richp h a s e and a n e a r l y eutectic composition phase. Theformation of the AuIn 2 intermetallic compound indi-cates that the Au l a y e r on the pin sample dissolvesinto the In-48%Sn solder.17

Effect ofAdding Ag to In-48%Sn SolderThe m e l t i n g p o i n t of In-48%Sn solder increases

with the Au content as s h o w n in Fig. 13. In a n a t t e m p tto p r e v e n t m e l t i n g p o i n t r ise, we t r i e d a Ag additionto In-48%Sn solder b a s e d on p h a s e diagram. 18Thechange in l i q u i d u s temperature (TL) with Au contentfor In-48%Sn solder was measured. As s h o w n in Fig.14, TLrise in In-48%Sn solder with 5 wt% Ag is a b o u thalf that in the original In-48%Sn solder. A f t e r dip-ping 50 times, the typical microstructure of the 5 wt%Ag a d d e d In-48%Sn solder is obviously different fromt h a t of In-48%Sn solder w i t h o u t Ag addition as s h o w nin Fig. 15. The EDX analysis r e s u l t s show t h a t solderwith Ag addition consists of I n - S n , InSn-Ag, and In-Sn-Ag-Au p h a s e s as s h o w n in Fig. 16 and Fig. 17. TheAuIn 2 intermetallic compound, w h i c h precipitates insolder w i t h o u t Ag addition, is not observed. The p h a s ediagrams 18 indicate t h a t In-Sn, In-Ag, and Sn-Ag

l mm I

a) A u / N i b) A u / P t

Fig. 10. Compar ison of (A) Au /N i and (B) Au/Pt films a f te r reflowing Inso lder for 720 s at 220°C. Samples were observedthrough the backof g lass substrates.

Fig. 11. Energy dispersion x-ray analysis results on the c r o s s sectionof the interconnect fo r Au/Ni/Ti and Au/Pt/Ti films.

alloys have the eutectic, suggesting t h a t In-Sn-Agt e r n a r y eutectic may be formed. The In-Sn-Ag alloyexhibits lower l i q u i d u s temperature if t e r n a r y eutec-tic is formed, and l i q u i d u s temperature may not riseso much even ifAu dissolves into the In-48%Sn solderwith Ag addition. Also, I n - A u and S n - A u alloys havethe eutectic, and Ag-Au is a solid solution type alloy.So, it is supposed that In-Sn-Ag-Au q u a r t e r n a r y eu-tectic may be created. This implies t h a t liquidustemperature may not increase so much when Au

44 Shimizu, Nakanishi, Karasawa, Hashimoto, and Niwa

@

In I 28.3

Sn 71.7

@ /O,,olIn 4 0 . 9

Sn 59.1

@ @ /o,,o/In 26.0

Sn 74.0

b

Fig. 12. Microstructures and EDX results for (a) thick Au film, and (b) thin Au film.

In 42.5

Sn 57.5

160 i i

~,oO Liquid o j_Liquidus temperature (TL)v• 140 , ~ ~

¢D d + SolidQ..

~ 120I--- © 0

- - I n - 4 8 % S n Solid

1oo o g {o 20Au content (wt%)

Fig. 13. Change in melting point of In-48%Snsolder with Au content.

160

140Oo

._1

I - -120

' g

100 ' ' ' '0 5 10 15 20 25Au content (wt%)

Fig. 14. Change in l iquidus temperature (T,) with Au content for Ag-containing In-48 %Sn solder.

dissolves into the Ag a d d e d In-48%Sn solder, becauseof formation of In-Sn-AgAu q u a r t e r n a r y eutectic. Onthe b a s i s of EDX analysis results, it is suggested t h a t

Au (In-48%Sn)d isso lu t ion In-48%Sn +5%Ag

None

20 w t %C ~

Fig. 15. Compar ison of microstructure a f te r 50 dipping t imes for In-48%Sn solder and Ag-containing In-48%Sn solder.

creation of InSn-Ag t e r n a r y eutectic a n d / o r In-Sn-Ag-Au q u a r t e r n a r y eutectic p h a s e s play a n i m p o r t a n trole in suppressing the liquidus t e m p e r a t u r e rise.

S U M M A R YT o fabricate reliable interconnections u s i n g In-al-

loy solders, we studied the fatigue life, finite elementm e t h o d (FEM) simulations, and dissolution and reac-tion between solder and metallization with flip-chipinterconnection models. The r e s u l t s are summarizedas follows.

• In and In-alloy solders show a l o n g e r fatigue lifet h a n conventional P b - S n solder for a flip-chipinterconnections w h i c h consisted of Si and GaAschips and a l u m i n a substrates cycled betweenroom temperature and l i q u i d nitrogen. I n d i u mand In-alloy solders have high r a t i o s of elonga-tion to tensile s t r e n g t h in l i q u i d nitrogen, w h i c hprovides a long fatigue life.

• The h i g h e r elongation improves the fatigue char-acteristics. The w i d e r elongation r a n g e of In-alloy solder increases a fatigue life. These r e s u l t s

S o l d e r J o i n t Rel iabi l i ty of In-Alloy Interconnection 45

agree well with t h o s e from FEM analysis.• P l a t i n u m film is extremely r e s i s t a n t to dissolu-

tion into In solder, suggesting good b a r r i e rl a y e rcharacteristics.

• I n d i u m - t i nsolder reacts w i t h A u and forms AuIn 2intermetallic compounds. Gold dissolution in In-Sn solders raises the m e l t i n g point. A d d i n g Ag,however, prevents the m e l t i n g p o i n t r ise. This isbecause In-Sn-Ag t e r n a r y a n d / o r In-Sn-Ag-Auq u a r t e r n a r y eutectic phases are formed in I n - S nsolder containing Ag.

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15 . ABAQUS, User's Manual Version 5.2, Vo1.1,2, (Pawtucket:Hibb i t t , Karlsson & 8orensen, Inc., 1993).

16. K. Karasawa, T. Nakanishi , M . Ochiai and K. Hashimoto ,Proc. 1992 IMC, June (1992), p . 136.

17. K. Hashimoto , E. Hor ikoshi , T. Sa te and K. N i w a , Z. Henmi,IEEE Trans. CHMT, vol. CHMT-8,No.4, (December 1985), p .541.

18. M . H a n s e n and K. Anderko, Constitution of Binary Alloys,(New York: McGraw-Hill Book Company, Inc., 1958).

! !

5t~m

In 56.9

Sn 11.9

Ag 31.2

(%)

In 47.8

Sn 52.2

Fig. 16. Energy dispersive x-rayanalysis results on Ag-containing In-48%Sn solder.

| I

5~m(%)

In

Sn

Ag

26.1 In 39.5 In 56.7

15.0 Sn 24.3 Sn 11.2

58.9 Ag 4.6 Ag 32.1

Au 31.6

Fig. 17. Energydispersive x-rayanalysis resultson Ag-containing In-48%Sn solder.