reliability studies μbga solder joints-effect of ni-sn intermetallic compound

IEEE TRANSACTIONS ON ADVANCED PACKAGING, VOL. 24, NO. 1, FEBRUARY 2001 25

Reliability Studies of�BGA Solder Joints—Effect ofNi–Sn Intermetallic Compound

Y. C. Chan, Senior Member, IEEE, P. L. Tu, C. W. Tang, K. C. Hung, and Joseph K. L. Lai

Abstract—This paper studies the bending and vibration effectson the fatigue lifetime of (ball grid array (BGA) solder joints. Thecorrelation between the fatigue lifetime of the assembly and theheating factor ( ), defined as the integral of the measured tem-perature over the dwell time above liquidus (183 C) in the reflowprofile is discussed. Our result shows that the fatigue lifetime of

BGA solder-joints firstly increases and then decreases with in-creasing heating factor. The optimal heating factor is found tobe 300–680 sC. In this range, the assembly possesses the greatestfatigue lifetime under various mechanical periodic stress, vibra-tion and bending tests. The cyclic bending cracks always initiateat the point of the acute angle where the solder joint joins thePCB pad, and then propagate in the site between the Ni–Sn in-termetallic compound (IMC) layer and the bulk solder. Under thevibration cycling, it is found that the fatigue crack initiates at val-leys in the rough surface of the interface of the Ni–Sn IMC with thebulk solder. Then it propagates mostly near the Ni–Sn IMC layer,and occasionally in the IMC layer or along the IMC/nickel inter-face. Evidently, the Ni–Sn IMC contributes mainly to the fatiguefailure of the BGA solder joints. The SEM and EDX inspectionshow that only Ni3Sn4 IMC forms between the tin-based solderand the nickel substrate. Moreover, no brittle AuSn4 is formedsince all the Au coated on the pad surface is dissolved into thesolder joint during reflowing. The formation of the Ni 3Sn4 IMCduring soldering ensures a good metallurgical bond between thesolder and the substrate. However, a thick Ni3Sn4 IMC influencesthe joint strength, which results in mechanical failure. Based onthe observed relationship of the fatigue lifetime with Ni–Sn IMCthickness and , the reflow profile should be controlled with cau-tion in order to optimize the soldering performance.

Index Terms—Cyclic bend, fatigue, intermetallic, -BGA, relia-bility, solder joint, vibration.

I. INTRODUCTION

T HE micro ball grid array (BGA) package has been suc-cessfully applied in many electronic products; hence the

reliability of BGA assembly is facing increasing interest. Forsolder ball-grid-array technology, solder joint reliability is oneof the most critical issues in the development of these technolo-gies [1]. The BGA structure includes a low stress die-attachelastomer between the silicon die and the solder bump array,which dissipates thermally induced stress caused by mismatchesbetween the silicon and the substrate, allowing good solder jointreliability under thermal shock and temperature cycling [2]–[9].

Manuscript received December 15, 1999; July 6, 2000. This work was sup-ported by City University of Hong Kong Grant Project 7 000 955 and Hong KongResearch Grants Council Project 9 040 212.

Y. C. Chan, P. L. Tu, C. W. Tang, and K. C. Hung are with the Department ofElectronic Engineering, City University of Hong Kong, Kowloon, Hong Kong.

J. K. L. Lai is with the Department of Physics and Materials Science, CityUniversity of Hong Kong, Kowloon, Hong Kong.

Publisher Item Identifier S 1521-3323(01)00563-9.

However, in normal use, portable products are always faced withvarious kinds of mechanical stresses such as bending and vibra-tion [1], [10]. By studying the initiation of failure and propaga-tion of cracks in LLCC solder joints exposed to a random vibra-tion environment, it was shown that the failure mode is consis-tent for vibration type loading [11]. Therefore it is important toevaluate the ability of these devices and assemblies to withstandmechanical stresses.

This paper studies the vibration and bending fatigue ofBGA solder joint reflowed in N with different tempera-

ture profiles. During the soldering process, the formation ofintermetallic compound (IMC) between tin-based solder andelectroplated Nickel substrate is inevitable [12]–[14]. Thegrowth of the Ni–Sn IMC can strongly affect the solderabilityand the strength of solder joints, which result in mechanicalfailure of the joint [12]. It is important to investigate in ordergain some insight of the potential reliability issues that maycaused by the growth of this IMC compound during reflowing.Little is known about the Ni–Sn IMC’s behavior onBGAsolder joint reliability under mechanical vibration, thereforethe effect of the growth of the NiSn under six differentreflow-profiles on mechanical fatigue is discussed in this paper.

II. EXPERIMENTAL PROCEDURE

A. Sample Preparation

1) Sample Details:Micro-BGA packages (CSP46T.75-DC24) with Sn/Pb-eutectic solder balls were mounted onFR-4 printed circuit boards (PCB). The board size was 110mm 120 mm, with a thickness of 1.2 mm. The PCB padsare of copper of 105 m thickness, plated with 15 m ofnickel and a less than 0.1m gold flash. The BGA packagescomprised a dummy die with metallization forming a daisychain in conjunction with the substrate metallization, designedto permit monitoring of critical solder joint regions by electricalcontinuity.

2) Soldering: CSP46 components were placed on thePCB by a high-precision automated placement machine(CASIO YCM-5500V) after printing of no-clean flux paste(#66-80 333E71). Then the boards were reflowed in a 5-zonereflow gas-forced-convection oven (BTU VIP-70N) with sixdifferent temperature profiles, as shown in Fig. 1. Duringreflowing, the nitrogen setting was 20 SCFH, with oxygencontent of 100 ppm in the fifth zone. The time-resolvedtemperature during reflow between the component and thePCB was measured using a wireless profiler of Super M.O.L.E,E31-900-45/10.

1521–3323/01$10.00 © 2001 IEEE

26 IEEE TRANSACTIONS ON ADVANCED PACKAGING, VOL. 24, NO. 1, FEBRUARY 2001

Fig. 1. Measured temperature profiles used to reflow�BGA assemblies.

3) Reflow Parameters:The 183 C melting temperatureof the eutectic solder is defined as the reference temperatureline—the liquidus (see Fig. 1). The length of time spent and thetemperature above this liquidus are important parameters forthe formation of a good solder joint. In this study, the integral ofthe measured temperature C in the liquidus temperature,with respect to time is used to approximate the term .This integral is given the name “heating factor” [9] and isconsidered to be the characteristic of the reflow profile. Theheating factor, peak temperature, and dwell time above theliquidus temperature corresponding to reflowing profiles aresummarized in Table I. Before the reliability tests, all sampleswere x-rayed to detect soldering quality for the evaluation ofinitial mounting reliability.

B. Reliability Test

In order to evaluate the influence of IMC thickness on solderjoint failure, samples reflowed at different profiles were sub-jected to vibration and bending fatigue tests. 8–12 samples perof each temperature profiles were tested for data statistical anal-ysis.

1) Cyclic Bending: The bending fatigue testing was per-formed by using an “INSTRON-mini 44” tension tester, withthe sample configuration illustrated in Fig. 2. The assemblyPCB is cut down into a size of 70 40 mm for all samples, andhas one edge fixed. During the bending test, a repeated bendingload is applied at the free edge of the PCB. Point “a” in thefigure is defined as the reference point, and is on the oppositesurface to the component, at the mid-point of the edge of thecomponent as indicated in the figure. The strain at point “a” isset to cycle between 1000 to 1000 , at a bending speed of320 mm/min. The dynamic strain at point “a” is measured andis continuously recorded by using a Model 3800 wide rangestrain indicator.

2) Vibration Cycling: A vibration simulator system (KingDesign 9363) is used to examine the fatigue lifetime of solder

TABLE IREFLOW PARAMETERS

Fig. 2. Schematic of the cyclic bending test.

joints. The PCB with BGA’s soldered on its surface was fixedto an electrodynamic shaker with four bolts positioned at eachcorner. A steel vibration stud of 56 g weight was bonded to topof every BGA package. TheBGA assemblies were verticallydriven by a shaker. The shaker was performed with a sinusoidalexcitation with an acceleration of root-mean-square (RMS) 10g, and a frequency 30 Hz, such that the peak to peak displace-ment is about 5.65 mm. The vibration cycling continues untilfailure occurs. Thus, RSM of sinusoidal load applied on solderjoints under one package is calculated by (packageself-weight stud weight) 5.5 (N).

CHAN et al.: RELIABILITY STUDIES OF BGA SOLDER JOINTS 27

Fig. 3. SEM micrographs of etched solder joints showing the Ni–Sn IMC layers resisted, reflowing under (a)Q = 33 C, (b)Q = 205 C, (c)Q = 307 C,(d)Q = 682 C, (e)Q = 864 C, and (f)Q = 2004 C.

TABLE IIRESULTS OFVIBRATION FATIGUE TEST OF THESOLDER JOINTS REFLOWED WITH SIX PROFILES

During the fatigue test, a computer monitoring systemequipped with AD/DA cards was used to monitor any electricalinterruptions in the current through a “daisy chain” network.The interruption is caused by a complete through crack,which creates an open circuit greater than 25 ms. Testing wasconcluded when significant number of failures had occurred.The number of cycles at solder joint failure is recorded, and isdefined as the fatigue lifetime of the sample. The failed solderjoints are then cross-sectioned and analyzed using a scanningelectron microscope (Philips XL40G) and stereo microscope.

III. T EST RESULTS

A. Ni–Sn IMC

During reflowing, all Au on the pad is dissolved into the joint(about 0.11-wt.%), so only Ni–Sn IMC is formed between thesolder and the electrolyzes Ni deposits [15]. The SEM of crosssection of the solder joints reflowed with different heating fac-tors is shown in Fig. 3. The thickness of Ni–Sn IMC is variedwith the different heating factors. Moreover, the thickness ofNi–Sn IMC layer is only approximately one-quarter as thick


Fig. 4. Mean Ni Sn layer thickness versus heating factor.

Fig. 5. EDX and ZAF analysis of Ni–Sn IMC layer.

as the Cu–Sn IMC formed at the interface between tin-basedsolder and BGA metallizing pad. And it is not appreciably af-fected whether it is in contact with the Pb-rich phase or Sn-richphase. Average thickness of the IMC layer with different heatingfactors are summarized in Table II. The thickness of theIMC increases linearly from 0.09m to 0.606 m with the in-creasing heating factor from 33–2004 C, shown as Fig. 4.The composition of the IMC layer, as verified by using the EDXand ZAF-4 analysis is shown in Fig. 5. It is found that the IMClayer forms between the solder and the substrate comprises onlyNi Sn brittle phase, and not NiSn and NiSn phases whichwill only be formed on a very rough surface or under reflowedtemperature of 240C for more time than 10 min [16]. Thefeature of Ni Sn layer also is not different with Cu6Sn5 IMCformed on copper pad. Cu/Sn IMC layer possesses smooth sur-face [17], yet Ni Sn layer is peaky and spiky NiSn whiskercomes into solder along Sn/Pb interface, as shown in Fig. 6.

Fig. 6. SEM of Ni Sn peaky layer in�BGA solder joint.

Fig. 7. Vibration fatigue lifetime as a function of the heating factorQ .

Fig. 8. Relationship between the average fatigue lifetime and the heating factorQ under cyclic bending.

B. Reliability Test Results

1) Vibration Cycling Test:The reliability of the solder jointsis examined with the aid of Weibull distribution method [17],[18]


Fig. 9. Cross section of initiate crack under vibrating: (a) crack in NiSn layer at the PCB side and (b) crack in Cu–Sn IMC layer at the component side.

Fig. 10. SEM of failed joint after vibrating 256 h: (a) propagation crack and (b) magnification of the circle in (a). The reflow is withQ = 682 s C (tupl-4).

wherecumulative distribution function of failure;

time to failure;

shape parameter;

scale parameter.

Applying the principles of least squares and ranking to the ex-periment results, the “best fit” Weibull parametersand arecalculated. The fatigue life of first failed sample (first failure),Weibull and are summarized in Table II. Furthermore, ananalysis of this test data was performed to statistically definethe number of vibrating cycles, that is the early failure 1% level

. The and are primary parameters to describe fa-tigue lifetime of solder joints, and were plotted in Fig. 7. Thefigure displays the quantitative relationship of the andwith heating factor and IMC thickness. The fatigue lifetime

and first increases and then decreases with increasingheating factor and thickness of the IMC layer. After the pointthat 682 s C, the Ni Sn thickness is about 1m, thelifetime decreases rapidly until 864 s C and then thelifetime decreases more slowly. When the heating factoris307–682 C, the solder lifetime h, almost is threetimes of other. The results reveal that the heating factor hasstrong influence on the solder’s fatigue lifetime.

2) Cyclic Bending Test:The average fatigue lifetime of thesolder joints is plotted against heating factor in Fig. 8 withstatistical result of the cyclic bending. The relationship betweenthe bending fatigue lifetime and is similar to that of the vi-bration test. It first increases and then decreases with increasingheating factor. The greatest lifetime occurs whenis near 500

Fig. 11. Cross section of cracked solder joint under cyclic bending.

s C. In the optimal range of 307–800-sC, the fatigue lifetimeof BGA solders is greater than 4500 cycles.

3) Optimal Profile: To sum up the results of both thevibration and bending test, the optimal range of heating factorfor reflowing the BGA assemblies should be between 300and 680 sC. Moreover, among the six reflow profile, namelyTUPL-1 to TUPL-6 (as shown in Fig. 1), the best temperatureprofile is “tupl-4” in which the solder joints possess the greatestfatigue lifetime. Evidently, solder joints can’t be formedsuccessfully if the heating factor is less than 200 sC becauseof the time requirement for fluxing reaction [19]. However, toolarge a heating factor results in thickening of the IMC layer [9].Such fatigue lifetime variation is attributed to the growth of theIMC layer. Additionally, too large a heating factor subjects thecomponents to a large thermal shock because the ramp rate inconjunction with peak temperature determine the total energyinput into the package during reflow.


Fig. 12. Fractograph of break solder joint by vibrating 100 h after removing component: (a) fracture and (b) fatigue striation. The sample is reflow with tupl-4,Q = 682 s C.

Fig. 13. EDX and ZAF analysis of vibration fracture.

C. Failure analysis

1) Cross Section Observation:By using the SEM, highmagnification micrographs of the failed solder joints subjectedto vibration and bending tests are shown in Figs. 9–11. Theresult of EDX and ZAF-4 analysis by scanning the regionlabeled “e” in Fig. 10(b) reveals that the top of the fracture isNi Sn IMC layer, shown as Fig. 5. During vibration cycling,the fatigue crack initiates mostly at valleys in the rough surfaceof the interface of the NiSn with the bulk solder, and propa-gates first in IMC layer toward the nickel/IMC interface, seeFig. 9(a). Then, it propagates mostly near the IMC layer, andoccasionally in the IMC layer or along the Ni/IMC interface, asshown in Fig. 10(a). By the way, the crack also initiates rarelyin Cu-Sn intermetallic compound of the solder reflowed by

2004 sC (tupl-6), see Fig. 9(b). Under cyclic bending,cracks always initiate at the point of the acute angle wherethe solder joint joins the PCB pad, then propagate nearly theNi Sn layer surface in solder, shown as Fig. 11.

2) Fractography: By investigating the failed samples sub-jected to vibration test, which theBGA package dismantlesfrom the PCB, it is found that about 40% of joints fail due tothe fracture inside the solder, while the others do by the de-

Fig. 14. Fractograph of failed solder joint by cyclic bending.

laminating of Cu pads from the polyimide base. Fig. 12 showsa fractograph of fracture region of solder joint after the com-ponent is being dismantled from the PCB after the vibrationtest. The sample has undergone 100 h vibration cycling. It isfound that the fracture surface is flat, and presents typical fa-tigue mode. The fatigue striation resulted by crack propagatingcan be seen from Fig. 12(b). The rate of crack propagation isapproximately 1 m per cycle. By using the EDX and ZAFanalysis on the fracture surface, as shown in Fig. 13, it is foundthat only nickel and NiSn IMC are detected. Evidently, thefracture has been occurred at the interface between Ni–Sn IMClayer and Nickel-plated on PCB pad. But for the bending test, acharacteristic of tough fracture is appeared, as shown in Fig. 14.The fracture dimple appears a sort of toughness micro-void. Byusing the EDX and ZAF analysis on the fracture surface, it isfound that only tin and lead are detected, so evidently, the frac-ture has been occurred inside the solder.

IV. DISCUSSION

Brittle Ni Sn IMC contributes mainly to the fatigue failureof solder joints and also it is the real root cause for fracturingnear the IMC layer. The Au concentrations tested did not pro-mote solder joint failures, unless concentration above 3.0 wt.%resulted in increase of void [19]. Also the parameters for elec-troless Ni/Au plating are not the real root cause for the brittleinterfacial fracture [20].


The phenomenon of Ni–Sn IMC induced solder joint failurecan be well explains by the volume shrinkage of the NiSnlayer. The thick NiSn layer poses potential reliability issuesdue to a 10.7% volume shrinkage during the transformationfrom solid phase Sn and Ni to the NiSn compound. By com-parison, the volumetric shrinkages to form Cu6Sn5 and Cu3Snare only 5% and 8.5%, respectively, which are smaller than thatof Ni Sn . As the thickness of the IMC layer increases, internalstrain and intercrystalline defects are formed and increase grad-ually in severity at the grain boundary of the NiSn IMC andthe IMC/solder interface. Especially at the valley of the Ni–SnIMC, the vibration fatigue strength is weaker than in solder andat Cu–Sn IMC on chip copper pad, so to result in initiation crackoccurs mainly in the region. And the brittle NiSn layer pos-sesses low dynamic ductility. In mechanical fatigue, strain ac-cumulation around the IMC results in crack initiating and prop-agating. Therefore, the thicker NiSn layer, that is, the largerthe heating factor, the shorter the fatigue lifetime of the solderjoint under mechanical stresses.

V. CONCLUSION

During reflowing, all the Au coated on the surface of the pad isdissolved into the solder joint, only NiSn phase IMC is formedbetween Sn-37Pb solder and PCB substrate. The average thick-ness of the IMC layer increases linearly from 0.4m to 2.1 mwith increasing heating factor from 33 to 2004 sC.

In reflowing the BGA assemblies in N, the optimal heatingfactor is found to be 300–680 sC. If the heating factor is lessthan 200 sC, solder joints can’t be formed successfully becauseof time requirement for the fluxing reaction. After exceeding theoptimal , the fatigue-lifetime of solder-joint decreases withthe increasing heating factor, because IMC layer growth withthe increasing .

In cyclic bending condition, the failure cracks always initiateat the point of the acute angle where the solder joint joins thePCB pad, at which the stress concentrates. It is recommendedthe solder-mask opening diameter should be greater than the paddiameter, and the flank of the pad should be plated with a goldantioxidation flash, to achieve improved reliability.

Undervibrationcycling, thefatiguecrackinitiatesmostlyat thevalleys in the roughsurfaceof the interfaceof theNiSn with thebulk solder. Then it propagates mostly near the Ni–Sn IMC, andoccasionally in the IMC layer or along the nickel/IMC interface.The bending fatigue cracks also propagate along the site betweenthe Ni–Sn IMC layer and the bulk solder. Therefore, the Ni–SnIMC contributes mainly to the fatigue failure of solder joints, andit is the real root cause for fracturing near the IMC layer.

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[3] J. H. Lau and Y.-H. Pao,Solder Joint Reliability of BGA, CSP, and FinePitch SMT Assemblies. New York: McGraw-Hill, 1997, pp. 297–328.

[4] C. Mitchell, “Assembly and reliability study for the micro-ball gridarray,” in Proc. IEEE/CPMT Int. Electron. Manufact. Technol. Symp.,1997, pp. 344–346.

[5] J. Fjelstad, “Chip scale packages,”Printed Circuit Design, vol. 5, no. 2,pp. 12–16, Feb. 1998.

[6] T. Koyama, K. Abe, N. Sakaguchi, and S. Wakabayashi, “Reliabilityof mBGA mounted on a printed circuit board,” inProc. 1995 SurfaceMount Int., 1995, pp. 43–56.

[7] J. Partridge, P. Boysan, and D. Foehringer, “Influence of processvariables on the reliability of MicroBGA™ package assemblies,” inProc. 48th Electron. Comp. Technol. Conf., Seattle, WA, May 1998, pp.518–524.

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[17] P. L. Tu, Y. C. Chan, and J. K. L. Lai, “Effect of intermetallic com-pounds on the thermal fatigue of surface mount solder joints,”IEEETrans. Comp., Packag., Manufact. Technol. B, vol. 20, pp. 87–93, Feb.1997.

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[19] N.-C. Lee, “Optimizing reflow profile via defect mechanisms analysis,”in Proc. 3rd Int. Symp. Electron. Packag. Technol., Beijing, China, Aug.1998, pp. 261–270.

[20] Z. Mei, P. Johnson, M. Kaufmann, and A. Eslambolchi, “Effect of elec-troless Ni/immersion Au plating parameters on PBGA solder joint at-tachment reliability,” inProc. IEEE, 49th Electron. Comp. Technol.,S04P3, San Diego, CA, 1999.

Y. C. Chan (SM’95) received the B.Sc. degree inelectrical engineering, the M.Sc. degree in materialsscience, and the Ph.D. degree in electrical engi-neering, all from the Imperial College of Scienceand Technology, University of London, London,U.K., in 1977, 1978, and 1983, respectively.

He joined the Advanced Technology Department,Fairchild Semiconductor, Los Angeles, CA, as a Se-nior Engineer, and worked on integrated circuits tech-nology. In 1985, he was appointed to a Lectureship inElectronics at the Chinese University of Hong Kong.

Between 1987 and 1991, he worked in various senior operations and engineeringmanagement functions in electronics manufacturing (including SAE Magnetics(HK) Ltd. and Seagate Technology). He set up the Failure analysis and Reli-ability Engineering Laboratory for SMT PCB in Seagate Technology (Singa-pore). He joined the City Polytechnic of Hong Kong (now City University ofHong Kong) as a Senior Lecturer in electronic engineering in 1991. He is cur-rently Professor in the Department of Electronic Engineering and Director ofEPA Centre. He has authored or co-authored over 100 technical publicationsin refereed journals and conference proceedings. His current technical interestsinclude advanced electronics packaging and assemblies, failure analysis, andreliability engineering.


P. L. Tu received the B.S. degree from the BeijingUniversity of Aeronautics and Astronautics, Beijing,China, the M.S. degree from the Nanking Universityof Aeronautics and Astronautics, Nanking, China, in1988, and is currently pursuing the Ph.D. degree inthe Department of Electronic Engineering, City Uni-versity of Hong Kong.

His research interests are in reliability study of areaarray solder joint, such as BGA, CSP, and flip chip,in degradation mechanisms of ACF and in adhesionstrengths of underfill.

C. W. Tang received the B.Sc. degree in mechanical engineering (with first classhonors) and M.Sc. degree (with distinction), both from the University of HongKong, Kowloon, and is currently pursuing the Ph.D. degree in advanced pack-aging of flip chip assemblies at the City University of Hong Kong, Kowloon.

His research interests are in advanced electronics manufacturing technologyand reliability issues of no-flow underfill and anisotropic conductive film (ACF)of flip chip assemblies.

K. C. Hung received the B.Sc. degree in applied physics from the City Poly-technic of Hong Kong in 1993 and the Ph.D. degree in physics and materialsscience from the City University of Hong Kong, Kowloon, in 1998.

He currently works in the Department of Electronic Engineering, City Uni-versity of Hong Kong, as a Research Fellow. He has authored or co-authoredover 30 technical publications in refereed journals. His current research interestsinclude the advanced electronics packaging technology, reliability engineering,failure analysis, and nondestructive testing.

Joseph K. L. Lai received the M.S. degree in physics (with first class honors)from Keble College, Oxford University, Oxford, U.K., in 1974 and the Ph.D.degree from the Department of Mechanical Engineering, City University ofLondon, London, U.K., in 1982.

From 1974 to 1985 he was employed as Research Officer at the Central Elec-tricity Research Laboratories, Surrey, U.K. In 1984, he was appointed ProjectLeader of the Remaining Life Study Group and a member of the Remanent LifeTask Force, Central Electricity Generating Board, U.K. He returned to HongKong and joined the City University of Hong Kong (previously called CityPolytechnic of Hong Kong) in 1985. He is now Chair Professor of MaterialsScience, Director of the Materials Research Centre and Associate Dean of theFaculty of Science and Technology. He has been very active in serving the localcommunity. He is the joint inventor of a novel temperature indicator called “Fer-oplug” which has been patented in the U.K., USA, and Europe with financialsupport provided by the British Technology Group. He has acted as consultantfor the Hong Kong Government and local industries on over forty cases of ac-cidents/disputes involving the failure of metallic components. He has publishedover 80 papers in international refereed journals.

Dr. Lai received the Applied Research Excellence Award from the City Uni-versity of Hong Kong in 1995 and the Teaching Excellence Award in 1996. Heis a member of the Vocational Training Council, the Consumer Council, the CityUniversity Council, the Research Grants Council’s Physical Sciences Panel, theCouncil and Executive Board of the Hong Kong Institution of Science, the Pres-sure Equipment Advisory Committee of the Labour Department, and the Elec-tricity Ordinance Disciplinary Tribunal Panel.

reliability studies μbga solder joints-effect of ni-sn intermetallic compound

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