Reliability Studies of BGA Solder Joints Effect of Ni Sn Intermetallic Compound

Transcription

1 IEEE TRANSACTIONS ON ADVANCED PACKAGING, VOL. 24, NO. 1, FEBRUARY Reliability Studies of BGA Solder Joints Effect of Ni 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 effects on the fatigue lifetime of (ball grid array (BGA) solder joints. The correlation between the fatigue lifetime of the assembly and the heating factor ( ), defined as the integral of the measured temperature over the dwell time above liquidus (183 C) in the reflow profile is discussed. Our result shows that the fatigue lifetime of BGA solder-joints firstly increases and then decreases with increasing heating factor. The optimal heating factor is found to be s C. In this range, the assembly possesses the greatest fatigue lifetime under various mechanical periodic stress, vibration and bending tests. The cyclic bending cracks always initiate at the point of the acute angle where the solder joint joins the PCB pad, and then propagate in the site between the Ni Sn intermetallic compound (IMC) layer and the bulk solder. Under the vibration cycling, it is found that the fatigue crack initiates at valleys in the rough surface of the interface of the Ni Sn IMC with the bulk solder. Then it propagates mostly near the Ni Sn IMC layer, and occasionally in the IMC layer or along the IMC/nickel interface. Evidently, the Ni Sn IMC contributes mainly to the fatigue failure of the BGA solder joints. The SEM and EDX inspection show that only Ni 3 Sn 4 IMC forms between the tin-based solder and the nickel substrate. Moreover, no brittle AuSn 4 is formed since all the Au coated on the pad surface is dissolved into the solder joint during reflowing. The formation of the Ni 3 Sn 4 IMC during soldering ensures a good metallurgical bond between the solder and the substrate. However, a thick Ni 3 Sn 4 IMC influences the joint strength, which results in mechanical failure. Based on the observed relationship of the fatigue lifetime with Ni Sn IMC thickness and, the reflow profile should be controlled with caution in order to optimize the soldering performance. Index Terms Cyclic bend, fatigue, intermetallic, -BGA, reliability, solder joint, vibration. I. INTRODUCTION THE micro ball grid array ( BGA) package has been successfully applied in many electronic products; hence the reliability of BGA assembly is facing increasing interest. For solder ball-grid-array technology, solder joint reliability is one of the most critical issues in the development of these technologies [1]. The BGA structure includes a low stress die-attach elastomer between the silicon die and the solder bump array, which dissipates thermally induced stress caused by mismatches between the silicon and the substrate, allowing good solder joint reliability under thermal shock and temperature cycling [2] [9]. Manuscript received December 15, 1999; July 6, This work was supported by City University of Hong Kong Grant Project and Hong Kong Research Grants Council Project Y. C. Chan, P. L. Tu, C. W. Tang, and K. C. Hung are with the Department of Electronic Engineering, City University of Hong Kong, Kowloon, Hong Kong. J. K. L. Lai is with the Department of Physics and Materials Science, City University of Hong Kong, Kowloon, Hong Kong. Publisher Item Identifier S (01) However, in normal use, portable products are always faced with various kinds of mechanical stresses such as bending and vibration [1], [10]. By studying the initiation of failure and propagation of cracks in LLCC solder joints exposed to a random vibration environment, it was shown that the failure mode is consistent for vibration type loading [11]. Therefore it is important to evaluate the ability of these devices and assemblies to withstand mechanical stresses. This paper studies the vibration and bending fatigue of BGA solder joint reflowed in N with different temperature profiles. During the soldering process, the formation of intermetallic compound (IMC) between tin-based solder and electroplated Nickel substrate is inevitable [12] [14]. The growth of the Ni Sn IMC can strongly affect the solderability and the strength of solder joints, which result in mechanical failure of the joint [12]. It is important to investigate in order gain some insight of the potential reliability issues that may caused by the growth of this IMC compound during reflowing. Little is known about the Ni Sn IMC s behavior on BGA solder joint reliability under mechanical vibration, therefore the effect of the growth of the Ni Sn under six different reflow-profiles on mechanical fatigue is discussed in this paper. A. Sample Preparation II. EXPERIMENTAL PROCEDURE 1) Sample Details: Micro-BGA packages (CSP46T.75- DC24) with Sn/Pb-eutectic solder balls were mounted on FR-4 printed circuit boards (PCB). The board size was 110 mm 120 mm, with a thickness of 1.2 mm. The PCB pads are of copper of 105 m thickness, plated with 15 mof nickel and a less than 0.1 m gold flash. The BGA packages comprised a dummy die with metallization forming a daisy chain in conjunction with the substrate metallization, designed to permit monitoring of critical solder joint regions by electrical continuity. 2) Soldering: CSP46 components were placed on the PCB by a high-precision automated placement machine (CASIO YCM-5500V) after printing of no-clean flux paste (# E71). Then the boards were reflowed in a 5-zone reflow gas-forced-convection oven (BTU VIP-70N) with six different temperature profiles, as shown in Fig. 1. During reflowing, the nitrogen setting was 20 SCFH, with oxygen content of 100 ppm in the fifth zone. The time-resolved temperature during reflow between the component and the PCB was measured using a wireless profiler of Super M.O.L.E, E / /01$ IEEE

2 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 temperature of the eutectic solder is defined as the reference temperature line the liquidus (see Fig. 1). The length of time spent and the temperature above this liquidus are important parameters for the formation of a good solder joint. In this study, the integral of the 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 is considered to be the characteristic of the reflow profile. The heating factor, peak temperature, and dwell time above the liquidus temperature corresponding to reflowing profiles are summarized in Table I. Before the reliability tests, all samples were x-rayed to detect soldering quality for the evaluation of initial mounting reliability. B. Reliability Test In order to evaluate the influence of IMC thickness on solder joint failure, samples reflowed at different profiles were subjected to vibration and bending fatigue tests samples per of each temperature profiles were tested for data statistical analysis. 1) Cyclic Bending: The bending fatigue testing was performed by using an INSTRON-mini 44 tension tester, with the sample configuration illustrated in Fig. 2. The assembly PCB is cut down into a size of mm for all samples, and has one edge fixed. During the bending test, a repeated bending load is applied at the free edge of the PCB. Point a in the figure is defined as the reference point, and is on the opposite surface to the component, at the mid-point of the edge of the component as indicated in the figure. The strain at point a is set to cycle between 1000 to 1000, at a bending speed of 320 mm/min. The dynamic strain at point a is measured and is continuously recorded by using a Model 3800 wide range strain indicator. 2) Vibration Cycling: A vibration simulator system (King Design 9363) is used to examine the fatigue lifetime of solder Fig. 2. TABLE I REFLOW PARAMETERS Schematic of the cyclic bending test. joints. The PCB with BGA s soldered on its surface was fixed to an electrodynamic shaker with four bolts positioned at each corner. A steel vibration stud of 56 g weight was bonded to top of every BGA package. The BGA assemblies were vertically driven by a shaker. The shaker was performed with a sinusoidal excitation with an acceleration of root-mean-square (RMS) 10 g, and a frequency 30 Hz, such that the peak to peak displacement is about 5.65 mm. The vibration cycling continues until failure occurs. Thus, RSM of sinusoidal load applied on solder joints under one package is calculated by (package self-weight stud weight) 5.5 (N).

3 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 II RESULTS OF VIBRATION FATIGUE TEST OF THE SOLDER JOINTS REFLOWED WITH SIX PROFILES During the fatigue test, a computer monitoring system equipped with AD/DA cards was used to monitor any electrical interruptions 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 was concluded when significant number of failures had occurred. The number of cycles at solder joint failure is recorded, and is defined as the fatigue lifetime of the sample. The failed solder joints are then cross-sectioned and analyzed using a scanning electron microscope (Philips XL40G) and stereo microscope. A. Ni Sn IMC III. TEST RESULTS During reflowing, all Au on the pad is dissolved into the joint (about 0.11-wt.%), so only Ni Sn IMC is formed between the solder and the electrolyzes Ni deposits [15]. The SEM of cross section of the solder joints reflowed with different heating factors is shown in Fig. 3. The thickness of Ni Sn IMC is varied with the different heating factors. Moreover, the thickness of Ni Sn IMC layer is only approximately one-quarter as thick

4 28 IEEE TRANSACTIONS ON ADVANCED PACKAGING, VOL. 24, NO. 1, FEBRUARY 2001 Fig. 4. Mean Ni Sn layer thickness versus heating factor. Fig. 6. SEM of Ni Sn peaky layer in BGA solder joint. Fig. 7. Vibration fatigue lifetime as a function of the heating factor Q. Fig. 5. EDX and ZAF analysis of Ni Sn IMC layer. as the Cu Sn IMC formed at the interface between tin-based solder and BGA metallizing pad. And it is not appreciably affected whether it is in contact with the Pb-rich phase or Sn-rich phase. Average thickness of the IMC layer with different heating factors are summarized in Table II. The thickness of the IMC increases linearly from 0.09 m to m with the increasing heating factor from C, shown as Fig. 4. The composition of the IMC layer, as verified by using the EDX and ZAF-4 analysis is shown in Fig. 5. It is found that the IMC layer forms between the solder and the substrate comprises only Ni Sn brittle phase, and not Ni Sn and Ni Sn phases which will only be formed on a very rough surface or under reflowed temperature of 240 C for more time than 10 min [16]. The feature of Ni Sn layer also is not different with Cu6Sn5 IMC formed on copper pad. Cu/Sn IMC layer possesses smooth surface [17], yet Ni Sn layer is peaky and spiky Ni Sn whisker comes into solder along Sn/Pb interface, as shown in Fig. 6. Fig. 8. Relationship between the average fatigue lifetime and the heating factor Q under cyclic bending. B. Reliability Test Results 1) Vibration Cycling Test: The reliability of the solder joints is examined with the aid of Weibull distribution method [17], [18]

5 CHAN et al.: RELIABILITY STUDIES OF BGA SOLDER JOINTS 29 Fig. 9. Cross section of initiate crack under vibrating: (a) crack in Ni Sn 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 with Q = 682 s C (tupl-4). where cumulative distribution function of failure; time to failure; shape parameter; scale parameter. Applying the principles of least squares and ranking to the experiment results, the best fit Weibull parameters and are calculated. The fatigue life of first failed sample (first failure), Weibull and are summarized in Table II. Furthermore, an analysis of this test data was performed to statistically define the number of vibrating cycles, that is the early failure 1% level. The and are primary parameters to describe fatigue lifetime of solder joints, and were plotted in Fig. 7. The figure displays the quantitative relationship of the and with heating factor and IMC thickness. The fatigue lifetime and first increases and then decreases with increasing heating factor and thickness of the IMC layer. After the point that 682 s C, the Ni Sn thickness is about 1 m, the lifetime decreases rapidly until 864 s C and then the lifetime decreases more slowly. When the heating factor is C, the solder lifetime h, almost is three times of other. The results reveal that the heating factor has strong influence on the solder s fatigue lifetime. 2) Cyclic Bending Test: The average fatigue lifetime of the solder joints is plotted against heating factor in Fig. 8 with statistical result of the cyclic bending. The relationship between the bending fatigue lifetime and is similar to that of the vibration test. It first increases and then decreases with increasing heating factor. The greatest lifetime occurs when is near 500 Fig. 11. Cross section of cracked solder joint under cyclic bending. s C. In the optimal range of s C, the fatigue lifetime of BGA solders is greater than 4500 cycles. 3) Optimal Profile: To sum up the results of both the vibration and bending test, the optimal range of heating factor for reflowing the BGA assemblies should be between 300 and 680 s C. Moreover, among the six reflow profile, namely TUPL-1 to TUPL-6 (as shown in Fig. 1), the best temperature profile is tupl-4 in which the solder joints possess the greatest fatigue lifetime. Evidently, solder joints can t be formed successfully if the heating factor is less than 200 s C because of the time requirement for fluxing reaction [19]. However, too large a heating factor results in thickening of the IMC layer [9]. Such fatigue lifetime variation is attributed to the growth of the IMC layer. Additionally, too large a heating factor subjects the components to a large thermal shock because the ramp rate in conjunction with peak temperature determine the total energy input into the package during reflow.

6 30 IEEE TRANSACTIONS ON ADVANCED PACKAGING, VOL. 24, NO. 1, FEBRUARY 2001 Fig. 12. Q = 682 s C. 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, Fig. 14. Fractograph of failed solder joint by cyclic bending. Fig. 13. EDX and ZAF analysis of vibration fracture. C. Failure analysis 1) Cross Section Observation: By using the SEM, high magnification micrographs of the failed solder joints subjected to vibration and bending tests are shown in Figs The result of EDX and ZAF-4 analysis by scanning the region labeled e in Fig. 10(b) reveals that the top of the fracture is Ni Sn IMC layer, shown as Fig. 5. During vibration cycling, the fatigue crack initiates mostly at valleys in the rough surface of the interface of the Ni Sn with the bulk solder, and propagates first in IMC layer toward the nickel/imc interface, see Fig. 9(a). Then, it propagates mostly near the IMC layer, and occasionally in the IMC layer or along the Ni/IMC interface, as shown in Fig. 10(a). By the way, the crack also initiates rarely in Cu-Sn intermetallic compound of the solder reflowed by 2004 s C (tupl-6), see Fig. 9(b). Under cyclic bending, cracks always initiate at the point of the acute angle where the solder joint joins the PCB pad, then propagate nearly the Ni Sn layer surface in solder, shown as Fig ) Fractography: By investigating the failed samples subjected to vibration test, which the BGA package dismantles from the PCB, it is found that about 40% of joints fail due to the fracture inside the solder, while the others do by the de- laminating of Cu pads from the polyimide base. Fig. 12 shows a fractograph of fracture region of solder joint after the component is being dismantled from the PCB after the vibration test. The sample has undergone 100 h vibration cycling. It is found that the fracture surface is flat, and presents typical fatigue mode. The fatigue striation resulted by crack propagating can be seen from Fig. 12(b). The rate of crack propagation is approximately 1 m per cycle. By using the EDX and ZAF analysis on the fracture surface, as shown in Fig. 13, it is found that only nickel and Ni Sn IMC are detected. Evidently, the fracture has been occurred at the interface between Ni Sn IMC layer and Nickel-plated on PCB pad. But for the bending test, a characteristic of tough fracture is appeared, as shown in Fig. 14. The fracture dimple appears a sort of toughness micro-void. By using the EDX and ZAF analysis on the fracture surface, it is found that only tin and lead are detected, so evidently, the fracture has been occurred inside the solder. IV. DISCUSSION Brittle Ni Sn IMC contributes mainly to the fatigue failure of solder joints and also it is the real root cause for fracturing near the IMC layer. The Au concentrations tested did not promote solder joint failures, unless concentration above 3.0 wt.% resulted in increase of void [19]. Also the parameters for electroless Ni/Au plating are not the real root cause for the brittle interfacial fracture [20].

7 CHAN et al.: RELIABILITY STUDIES OF BGA SOLDER JOINTS 31 The phenomenon of Ni Sn IMC induced solder joint failure can be well explains by the volume shrinkage of the Ni Sn layer. The thick Ni Sn layer poses potential reliability issues due to a 10.7% volume shrinkage during the transformation from solid phase Sn and Ni to the Ni Sn compound. By comparison, the volumetric shrinkages to form Cu6Sn5 and Cu3Sn are only 5% and 8.5%, respectively, which are smaller than that of Ni Sn. As the thickness of the IMC layer increases, internal strain and intercrystalline defects are formed and increase gradually in severity at the grain boundary of the Ni Sn IMC and the IMC/solder interface. Especially at the valley of the Ni Sn IMC, the vibration fatigue strength is weaker than in solder and at Cu Sn IMC on chip copper pad, so to result in initiation crack occurs mainly in the region. And the brittle Ni Sn layer possesses low dynamic ductility. In mechanical fatigue, strain accumulation around the IMC results in crack initiating and propagating. Therefore, the thicker Ni Sn layer, that is, the larger the heating factor, the shorter the fatigue lifetime of the solder joint under mechanical stresses. V. CONCLUSION During reflowing, all the Au coated on the surface of the pad is dissolved into the solder joint, only Ni Sn phase IMC is formed between Sn-37Pb solder and PCB substrate. The average thickness of the IMC layer increases linearly from 0.4 mto2.1 m with increasing heating factor from 33 to 2004 s C. In reflowing the BGA assemblies in N, the optimal heating factor is found to be s C. If the heating factor is less than 200 s C, solder joints can t be formed successfully because of time requirement for the fluxing reaction. After exceeding the optimal, the fatigue-lifetime of solder-joint decreases with the increasing heating factor, because IMC layer growth with the increasing. In cyclic bending condition, the failure cracks always initiate at the point of the acute angle where the solder joint joins the PCB pad, at which the stress concentrates. It is recommended the solder-mask opening diameter should be greater than the pad diameter, and the flank of the pad should be plated with a gold antioxidation flash, to achieve improved reliability. Under vibration cycling, the fatigue crack initiates mostly at the valleys in the rough surface of the interface of the Ni Sn with the bulk solder. Then it propagates mostly near the Ni Sn IMC, and occasionally in the IMC layer or along the nickel/imc interface. The bending fatigue cracks also propagate along the site between the Ni Sn IMC layer and the bulk solder. Therefore, the Ni Sn IMC contributes mainly to the fatigue failure of solder joints, and it is the real root cause for fracturing near the IMC layer. REFERENCES [1] J. H. Lau, Solder joint reliability of flip chip and plastic ball grid array assemblies under thermal, mechanical, and vibrational conditions, IEEE Trans. Comp., Packag., Manufact. Tehnol. B, vol. 19, pp , Nov [2] T. Koyama, M. Sasaki, and S. Wakabayashi, Advanced CSP and substrate technologies, in Proc Int. Symp. Microelectron. (SPTE Vol. 2920), 1996, pp [3] J. H. Lau and Y.-H. Pao, Solder Joint Reliability of BGA, CSP, and Fine Pitch SMT Assemblies. New York: McGraw-Hill, 1997, pp [4] C. Mitchell, Assembly and reliability study for the micro-ball grid array, in Proc. IEEE/CPMT Int. Electron. Manufact. Technol. Symp., 1997, pp [5] J. Fjelstad, Chip scale packages, Printed Circuit Design, vol. 5, no. 2, pp , Feb [6] T. Koyama, K. Abe, N. Sakaguchi, and S. Wakabayashi, Reliability of mbga mounted on a printed circuit board, in Proc Surface Mount Int., 1995, pp [7] J. Partridge, P. Boysan, and D. Foehringer, Influence of process variables on the reliability of MicroBGA package assemblies, in Proc. 48th Electron. Comp. Technol. Conf., Seattle, WA, May 1998, pp [8] R. Ghaffarian and N. P. Kim, Reliability and failure analyzes of thermally cycled ball grid array assemblies, in Proc. 48th Electron. Comp. Technol. Conf., Seattle, WA, May 1998, pp [9] P. L. Tu, Y. C. Chan, K. C. Hung, and J. K. L. Lai, Comparative study of micro-bga reliability under bending stress, IEEE Trans. Adv. Packag., vol. 23, pp , Nov [10] E. Jih and W. Jung, Vibration fatigue of surface mount solder joints, in Proc. Thermomech. Phenom. Electron. Syst. Intersoc. Conf., Piscataway, NJ, 1998, pp [11] S. Liguore and D. Followell, Vibration fatigue of surface mount technology (SMT) solder joints, in Proc. Annu. Reliab. Maintainability Symp., Piscataway, NJ, 1995, pp [12] H. D. Blair, T. Y. Pan, and J. M. Nicholson, Intermetallic compound growth on Ni, Au/Ni, and Pd/Ni substrates with Sn/Pb,Sn/Ag, and Sn solders, in Proc. 48th Electron. Comp. Technol. Conf., Seattle, WA, May 1998, pp [13] H. H. Manko, Solders and Soldering: Material, Design, Production, and Analysis for Reliability Bonding, 3rd ed. New York: McGraw-Hill, [14] W. Yujing and J. A. Sees et al., The formation and growth of intermetallics in composite solder, J. Electron. Mater., vol. 22, no. 7, pp , [15] J. Glazer, P. A. Kramer, and J. W. Morris, Jr., Effect of gold on the reliability of fine pitch surface mount solder joints, Circuit World, vol. 18, no. 4, pp , [16] K.-L. Lin and J.-M. Jang, Wetting behavior between solder and electroless nickel deposits, Mater. Chem. Phys., vol. 38, no. 1, pp , June [17] P. L. Tu, Y. C. Chan, and J. K. L. Lai, Effect of intermetallic compounds on the thermal fatigue of surface mount solder joints, IEEE Trans. Comp., Packag., Manufact. Technol. B, vol. 20, pp , Feb [18] J. C. Bobrowski and W. E. Murphy, Designing surface mount technology for operational service life, in Proc. Annu. Reliab. Maintainability Symp., Piscataway, NJ, 1993, pp [19] N.-C. Lee, Optimizing reflow profile via defect mechanisms analysis, in Proc. 3rd Int. Symp. Electron. Packag. Technol., Beijing, China, Aug. 1998, pp [20] Z. Mei, P. Johnson, M. Kaufmann, and A. Eslambolchi, Effect of electroless Ni/immersion Au plating parameters on PBGA solder joint attachment reliability, in Proc. IEEE, 49th Electron. Comp. Technol., S04P3, San Diego, CA, Y. C. Chan (SM 95) received the B.Sc. degree in electrical engineering, the M.Sc. degree in materials science, and the Ph.D. degree in electrical engineering, all from the Imperial College of Science and 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 Senior Engineer, and worked on integrated circuits technology. In 1985, he was appointed to a Lectureship in Electronics at the Chinese University of Hong Kong. Between 1987 and 1991, he worked in various senior operations and engineering management functions in electronics manufacturing (including SAE Magnetics (HK) Ltd. and Seagate Technology). He set up the Failure analysis and Reliability Engineering Laboratory for SMT PCB in Seagate Technology (Singapore). He joined the City Polytechnic of Hong Kong (now City University of Hong Kong) as a Senior Lecturer in electronic engineering in He is currently Professor in the Department of Electronic Engineering and Director of EPA Centre. He has authored or co-authored over 100 technical publications in refereed journals and conference proceedings. His current technical interests include advanced electronics packaging and assemblies, failure analysis, and reliability engineering.

8 32 IEEE TRANSACTIONS ON ADVANCED PACKAGING, VOL. 24, NO. 1, FEBRUARY 2001 P. L. Tu received the B.S. degree from the Beijing University of Aeronautics and Astronautics, Beijing, China, the M.S. degree from the Nanking University of Aeronautics and Astronautics, Nanking, China, in 1988, and is currently pursuing the Ph.D. degree in the Department of Electronic Engineering, City University of Hong Kong. His research interests are in reliability study of area array solder joint, such as BGA, CSP, and flip chip, in degradation mechanisms of ACF and in adhesion strengths of underfill. C. W. Tang received the B.Sc. degree in mechanical engineering (with first class honors) and M.Sc. degree (with distinction), both from the University of Hong Kong, Kowloon, and is currently pursuing the Ph.D. degree in advanced packaging of flip chip assemblies at the City University of Hong Kong, Kowloon. His research interests are in advanced electronics manufacturing technology and 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 Polytechnic of Hong Kong in 1993 and the Ph.D. degree in physics and materials science from the City University of Hong Kong, Kowloon, in He currently works in the Department of Electronic Engineering, City University of Hong Kong, as a Research Fellow. He has authored or co-authored over 30 technical publications in refereed journals. His current research interests include 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 of London, London, U.K., in From 1974 to 1985 he was employed as Research Officer at the Central Electricity Research Laboratories, Surrey, U.K. In 1984, he was appointed Project Leader of the Remaining Life Study Group and a member of the Remanent Life Task Force, Central Electricity Generating Board, U.K. He returned to Hong Kong and joined the City University of Hong Kong (previously called City Polytechnic of Hong Kong) in He is now Chair Professor of Materials Science, Director of the Materials Research Centre and Associate Dean of the Faculty of Science and Technology. He has been very active in serving the local community. He is the joint inventor of a novel temperature indicator called Feroplug which has been patented in the U.K., USA, and Europe with financial support provided by the British Technology Group. He has acted as consultant for the Hong Kong Government and local industries on over forty cases of accidents/disputes involving the failure of metallic components. He has published over 80 papers in international refereed journals. Dr. Lai received the Applied Research Excellence Award from the City University of Hong Kong in 1995 and the Teaching Excellence Award in He is a member of the Vocational Training Council, the Consumer Council, the City University Council, the Research Grants Council s Physical Sciences Panel, the Council and Executive Board of the Hong Kong Institution of Science, the Pressure Equipment Advisory Committee of the Labour Department, and the Electricity Ordinance Disciplinary Tribunal Panel.