Reliability of Lead-Free Solder Connections for Area-Array Packages

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1 Presented at IPC SMEMA Council APEX SM 2001 For additional information, please Reliability of Lead-Free Solder Connections for Area-Array Packages Ahmer Syed Amkor Technology, Inc Chandler, AZ Abstract Pb free solder for electronics assemblies is fast becoming a reality primarily because of market driven forces. This impacts the entire electronic manufacturing industry, from component supplier to equipment manufacturer. While the industry has identified possible alternates to Sn/Pb solder alloy, much work still needs to be done, especially in the area of component & board level reliability and assembly process development. One of the key factors in selecting the replacement for Sn/Pb solder is the board level reliability with an alternate alloy system used for a wide range of electronic components in the industry. While the initial selection is based on reliability evaluations using leadframe components, data is still lacking for BGA and CSP type components to finalize the selection. This paper seeks to fill this gap by providing the board level reliability comparison of Pb free alloys for area array (BGA & CSPs) type of components. Nine different Pb free alloy systems including three compositions of Sn/Ag/Cu alloy systems are considered, and their reliability is compared with Sn/Pb eutectic alloy for two BGA type packages. The packages were assembled with Pb free balls and were mounted on printed circuit boards in order to evaluate the board reliability during temperature cycling (using three cycling conditions). The data presented here suggests that the Pb free alloys being considered are as good or better in reliability compared to the Sn/Pb eutectic alloy currently in use. The data also indicates that the acceleration factor for the alloy systems from different cyclic conditions are significantly different compared to Sn/Pb eutectic solder. Introduction Finding a viable alternate to Sn/Pb solder alloy requires R&D effort involving materials and processes development and reliability evaluation. A number of industry groups and consortia [IDEALS, NEMI, JEIDA, IPC, NCMS] had and are working in these areas to identify the possible solder alloy replacement. During the last year or so, the industry has converged towards a Sn/Ag/Cu based alloy, although a consensus has not yet been reached on the exact composition. A variety of Sn/Ag/Cu alloy compositions have been recommended by the industry groups and consortia 1,2,3,4,5, with only a slight difference in actual composition. Although board level reliability is a major part of these evaluations, little data has been published comparing the reliability of this alloy with the Sn/Pb alloy, especially for area array packages such as BGAs and CSPs. Further, the effect of different Sn/Ag/Cu compositions and temperature cycle conditions on reliability is not clear at this point. Almost all of the on going activities on finding the viable and reliable replacement for Sn/Pb solder use some kind of accelerated test condition. For it to be considered as a potential candidate, it is generally assumed that the new alloy must perform as good or better than the Sn/Pb alloy in a reliability test. Certainly this would be a correct approach if all the solder alloys behaved the same during temperature cycling and the acceleration factor from the field level conditions were the same for all alloys. This, however, is highly unlikely as each alloy has its own high temperature deformation mechanisms and behavior, and therefore the acceleration factors from field to accelerated level can be significantly different. Since field condition experiments cannot be run in a reasonable amount of time, it is imperative that different accelerated conditions be used to determine the acceleration factors from one to another accelerated condition. This will help not only in understanding the expected behavior at field level conditions, but also in determining if a certain alloy can be used for the wide range of applications. With the above in mind, the work reported here had the following objectives: 1) Collect and compare board level reliability data for BGA type packages, 2) Investigate the effect of Sn/Ag/Cu composition on reliability, 3) Investigate the acceleration factors for different temperature cycle conditions, and 4) Select the Pb free Solder ball alloys for BGA type packages. The above objectives were met by partnering with industry groups such as NCMS and by conducting internal evaluations. Two different types of BGA type packages were selected for this evaluation in the initial phases. The packages were assembled with different solder ball alloys and were mounted on test boards for LF2-7 1

2 thermal cycle reliability evaluation. The following sections provide the details and test results. Selection Phase 1 s (NCMS Project) In early 1997, National Center of Manufacturing Sciences (NCMS) initiated a High Temperature Fatigue Resistant Solder Project. The projects focus was on finding an alternate to Sn/Pb solder for high temperature electronics applications. One of the primary objectives of this project was to identify a set of Pb free alloys that would exhibit superior performance at the operating range of 55 to 160 o C as compared to the Sn/Pb solder in the operating range of 55 to 125 o C. The project started with a list of 33 Pb free solder alloys which was later reduced to 7 alloys using down-selection criteria in various phases. The criteria included exclusion of highly toxic and radioactive materials, cost, oxidation, flux compatibility, thermal analysis, wetting balance, metallographic x-section, and thermomechanical fatigue behavior using Leadless Ceramic Chip Carrier (LCCC) packages. The final 7 Pb free alloy systems, shown in Table 1, are being used to compare their board level reliability for 55 to 160 o C temperature cycle condition (NCMS test). The package list for NCMS project included 0805 and 1206 resistors, LCCCs, PLCCs, TSOP, and QFPs of various sizes and lead counts. Initially the project did not include BGA type packages in the board level reliability evaluation phase, however, a 27mm-256 lead PBGA was later included when Amkor joined this consortium. In addition, Amkor also assembled 12mm-144 lead flexbga packages with the above Pb free alloys. While only the PBGA was used for 55 to 160 o C NCMS temperature cycle condition, both of these packages were evaluated by Amkor using the more mainstream temperature cycle conditions of 40 to 125 o C and 0 to 100 o C. While a full report on the NCMS project will be published early next year, this paper provides data for Amkor packages and test conditions. Phase II s The Pb free movement really picked up steam during the last year primarily due to environmental concerns in Japan. A number of Sn/Ag/Cu alloy compositions have since been suggested by different industry groups such as NEMI (Sn/3.9Ag/0.6Cu), IDEALS (Sn/3.8Ag/0.7Cu), and JEIDA (Sn/2-4Ag/ Cu.) Currently, there is also a heated discussion regarding the exact eutectic. Generally, the compositions being considered have Ag in the range of 3.0 to 4.0% and Cu in the range of 0.5 to 1.0%. It is not clear, however, if this slight change in composition will have any effect on reliability. Besides these Sn/Ag/Cu based alloys, IDEALS project has also recommended eutectic Sn/Cu composition for wave soldering applications, primarily in relationship cost. For the purpose of investigating the board level reliability of these alloys, additional evaluations were performed in Phase II. The alloys selected for this phase are listed in Table 2. Notice that eutectic Sn/Ag was also included in this phase, as this is the most common Pb free alloy used in the industry today. Table 1 - s for Phase I Study (NCMS s) Class Melting Point ( o C) A1 Sn/Ag A11 Sn/Ag/Cu A14 Sn/Ag/Cu A21 Sn/Ag/Cu/Sb A32 Sn/Ag/Cu/Sb/Bi A62 Sn/Ag/Cu/Bi A66 Sn/Ag/In B63 Sn/Pb Control 183 Table 2 - s for Phase II Study Class Melting Point ( o C) LF1 Sn/0.7Cu 227 LF2 Sn/3.5Ag 222 LF3 Sn/4.0Ag/0.5Cu ~217 LF4 Sn/3.4Ag/0.7Cu ~217 Sn/Pb Sn/Pb Control 183 Table 3 - Packages Considered for Pb Free Solder Reliability Evaluation Package Size I/O Substrate Ball Size Ball Pitch Die Size Type Material PBGA 27x27mm 256 BT 30 mils 1.27mm 10x10mm FleXBGA 12x12mm 144 Tape 18 mils 0.8mm 6.4x6.4mm LF2-7 2

3 Package Selection and Assembly The board level or solder joint reliability for BGA type packages depends upon a number of factors such as package construction, substrate type, die size, and ball size. The substrate materials most commonly used are BT or organic laminate, ceramic, and polyimide tape. Because of the different CTE of these substrate materials, solder joint reliability is a strong function of the substrate material. BGA and CSP type packages also come with various ball pitches using different ball sizes. Since the joint reliability is a function of standoff height, ball size can have a significant impact on reliability. With this in mind, the packages selected for this evaluation included different substrate material and ball sizes. The details of the packages selected are listed in Table 3. The packages were assembled using the standard assembly process until ball attachment. This is due to the fact that all of the alloys listed in Table 1 & 2 melt at significantly higher temperature than Sn/Pb eutectic alloy, and thus a significantly higher reflow temperature is required to attach the balls to the packages. As higher reflow temperature may result in delamination and package cracking, all the packages were baked for at least 4 hours at 125 o C before ball attachment to avoid package level failures. After baking, the ball attachment was done using standard ball attach equipment and processes, with the exception of the maximum reflow temperature. While most of the balls were attached using a maximum reflow temperature of 240 o C, the temperature was further increased to 250 o C for Sn/Cu alloy because of its higher melting point. It should be noted that a standard water soluble flux was used for ball attachment. Figure 1 shows the ball surface after ball attachment. All Pb free balls for Phase II alloys were significantly less shiny compared to Sn/Pb balls and showed a frosty surface. Some of the balls of Sn/Cu alloys also showed significant ridges on the ball surface, as shown in the picture. The x-sectional picture of Sn/Pb and Sn/Ag/Cu alloy balls after attachment to the package are shown in Figure 2, showing no significant difference in ball shape or any collapsed height. (a) (b) (c) (d) Figure 1 - Solder Ball Surface a) Sn/Pb, b) Sn/Cu, c) Sn/Ag, and d) Sn/Ag/Cu s Figure 2 - Cross-section of Solder Ball after Ball Attachment to the Package; a) Sn/Pb, and b) Sn/Ag/Cu PCB Design and Assembly A separate test board was designed for each of the packages listed in Table 3 to perform the reliability testing. Each board type had 15 locations for identical packages with a matching daisy chain pattern. All pads on the board were non-solder mask defined with the pad sizes slightly smaller than the pad size on the package. All boards were of 4-layer construction and were fabricated in 1.6mm thickness using FR-4 material and OSP surface finish. Prior to board mounting, reflow profiles were established using a setup board for each package type. Three different reflow profiles were developed dependant on the type of solder alloy with their varying maximum temperatures (220, 240, and 260 o C respectively). While the 220 o C profile was used for Sn/Pb alloy, components with Pb free alloys (except Sn/Cu) were mounted using the 240 o C profile. The 260 o C profile was used to mount packages with Sn/Cu alloy because of its significantly higher melting point as compared to other Pb free alloys in this study. The three reflow profiles used are shown in Figure 3. LF2-7 3

4 Temp (C) (a) Time (s) PCB Corner Top of Package PCB Corner Solder Joint PCB Center Top of Package PCB Center Solder Joint which showed slightly increased collapse over the other alloys. (a) (b) Temp (C) (b) Time (s) PCB Corner Top of Package PCB Corner Solder Joint PCB Center Top of Package PCB Center Solder Joint (c) (d) Figure 4 - Solder Joint Cross-section; a) Sn/Cu, b) Sn/Ag, c) Sn/Ag/Cu, and d) Sn/Pb Temp (C) Time (s) (c) PCB Corner Top of Package PCB Corner Solder Joint PCB Center Top of Package PCB Center Solder Joint Figure 3 - Reflow Profiles Used for Surface Mounting ; a) 220 o C Maximum Temperature, b) 240 o C Maximum Temperature, and c) 260 o C Maximum Temperature Being that this study involved a number of different solder alloy systems and not all alloys were available in paste form at the time of board assembly, it was decided to use a flux only process when mounting the parts on the boards. Although flux only assembly is not generally recommended, it was used here because of the comparative nature of this evaluation and to avoid logistic issues, especially with a very low volume assembly. It should be noted that previous studies have shown that the flux only assembly does not typically result in degradation of fatigue life. The high temperature flux (Heraeus F369) was applied on the board surfaces and the parts were placed on the boards using standard placement equipment. Finally, the parts were reflow soldered to the boards using the appropriate reflow profiles. Figure 4 shows a representative x-section of solder joints for the alloys in Phase II after package to board mounting. All joints looked very similar except for joints with Sn/Cu alloy Reliability Testing A number of accelerated test conditions are being used in the industry to evaluate the thermal cycle reliability of solder joints. These cyclic conditions vary in ramp rates, dwell times, and frequency that have a significant effect on reliability. In order to compare and establish the reliability of one alloy system, it is important to use as many different conditions as possible. This is also important as the relative comparison and acceleration factors from one to another condition may actually depend on the type of test condition used. Due to high homologous temperature (ratio of melting and operating temperature in absolute scale) and highly strain rate dependent behavior of solder alloys, it is entirely possible that an alloy performing better in one cyclic condition may perform worse in another condition. To cover the range of cyclic conditions and to investigate their impact on relative reliability, three different accelerated temperature cycle tests were used in this study as noted below. TC1: -40 to 125 o C, 15 minutes ramps and dwells, 1 cycle/hour, single zone chamber cycling, TC2: -55 to 125 o C, 2 minute ramps, 13 minutes dwells, 2 cycles/hour, dual zone chamber cycling, and TC3: 0 to 100 o C, 10 minute ramps, 5 minute dwells, 2 cycles/hour, single zone chamber cycling. While TC1 and TC3 cycling conditions were used for Phase I alloys, packages with Phase II alloys were also thermally cycled using TC2 condition. LF2-7 4

5 Results and Discussion Reliability Comparison for flexbga Package The flexbga package was used to evaluate the reliability of Phase I (NCMS alloys) as well as Phase II alloys. While only TC1 and TC3 conditions were used for the Phase I solder alloys, TC2 condition was added for evaluating the board level reliability of Phase II alloys. Although typically a sample size of 30 to 45 parts is used for evaluating the 2 nd level reliability, a sample size of 15 units was used here because of the comparative nature of this study. It should be noted, however, that because a flux only process was used for surface mounting, as many as 3 parts on some boards resulted in zero hour opens or very early (<100 cycles) failures. These data points are removed from the results reported below. Phase I s, TC1 Condition The boards with Pb free solder ball packages were temperature cycled between -40 and 125 o C until all units failed for every alloy system. As the actual data for all the alloys cannot be shared at this time because of contractual requirements from NCMS project, a relative comparison for first failure and mean life (50% failure point) is provided in Table 4 with respect to Sn/Pb control alloy. A full report on NCMS project will be published in early next year, containing the actual cycles to failure. The data in the table indicates that all alloys performed better than Sn/Pb eutectic alloy with the exception of Sn/Ag based alloy. Comparing the mean life, 5 of the 7 alloys resulted in 25 to 33% better fatigue performance than Sn/Pb alloy with no significant difference between the Pb free alloys. It should be noted that the two Sn/Ag/Cu compositions resulted in similar performance. This is further shown in the plot in Figure 5a comparing the two compositions with Sn/Pb eutectic alloy. With the exception of two earlier failures for A14, both compositions tracked each other very closely in failure distribution. Table 4 - Relative Comparison of Phase I s (TC1 Cycle, flexbga Package) Relative Fatigue Life Number on Test Number Failed By First Failure A A A A A A A B By Mean Life One surprising result was the significantly lower life for Sn/Ag based alloy. However, analysis for this alloy, shown in Figure 5b, indicated a dual failure mode. The failure analysis of the on samples failed earliest showed no evidence of solder cracking but the exact cause of failure could not be identified. The early failures are possibly due to surface mount process which did not use any paste for parts mounting. (a) A11 A14 B63 A1 B63 (b) Figure 5 - Comparison of Solder Joint Failure Distribution (Phase I, TC1, flexbga package); a) Sn/Pb vs Sn/Ag/Cu, and b) Sn/Pb vs. Sn/Ag Phase I s, TC3 Condition About 9000 cycles have been completed in this test conditions at the time of this writing. While all the packages with Sn/Pb alloys have failed starting at ~3400 cycles, some of the the Pb free alloys have not shown any failures at this point. A relative comparison of failure data is provided in Table 5. Although A32 and A62 are performing the best with no failure to date, all the other alloys are performing significantly better compared to Sn/Pb eutectic alloy in this test LF2-7 5

6 condition. Note that A1 alloy, which did not perform as well in TC1 conditions (dual failure mode), is performing about 2X better in this test compared to Sn/Pb. Regarding the Sn/Ag/Cu alloys (A11 & A14), both of them are performing about 2X better than Sn/Pb alloy with A11 slightly out performing A14. Figure 6 shows the plots for these alloys compared to Sn/Pb eutectic alloy. Table 5 - Relative Comparison of Phase I s (TC3 Cycle, flexbga Package) Relative Fatigue Life # on Test # Failed By First Failure By Mean Life A A A A A N/A N/A A N/A N/A A B A11 A14 B63 Figure 6 - Comparison of Solder Joint Failure Distribution for Sn/Pb and Sn/Ag/Cu s (Phase I, TC3, flexbga package) Phase II s, TC1 Cycling As of this writing 4000 cycles have been completed for this combination with more than 50% failure for all alloys, except Sn/3.5Ag. While Sn/0.7Cu and Sn/4.0Ag/0.5Cu alloys resulted in a similar performance as Sn/Pb alloy, the packages with Sn/3.4Ag/0.7Cu alloys showed about 10% reduction in reliability as shown in the plots of failure distribution in Figure 7. The data also indicates that Sn/Ag alloy is performing much better than Sn/Pb alloy for this cycling condition in this Phase with no failures so far. This further confirms that the early failures in Phase I testing for this alloy were not due to solder cracking. β1=20.61, η1= , ρ=0.90 β2=19.06, η2= , ρ=0.96 β3=10.40, η3= , ρ=0.98 Sn3.4Ag0.7Cu Sn4.0Ag0.5Cu Sn-Pb Sn-0.7Cu β1=7.27, η1= , ρ=0.96 β2=10.40, η2= , ρ=0.98 Sn-Pb Figure 7 - Comparison of Solder Joint Failure Distribution for Sn/Pb and Pb Free s (Phase II, TC1, flexbga package) Phase II s, TC2 Cycling The test was stopped after 3700 cycles were completed, with more than 50% failure for all alloys except Sn/Ag. All Pb free alloys showed a much better performance when compared to Sn/Pb eutectic with a more than 20% increase in reliability for Sn/Cu and the two Sn/Ag/Cu alloy compositions. The plots are shown in Figure 8. As apparent from the figure, the two Sn/Ag/Cu compositions showed similar performance in this test also. Only three failures were observed for parts with Sn/Ag alloy with the first failure at 3680 cycles. This was LF2-7 6

7 about 2X higher than the joints with Sn/Pb alloy which started to fail at around 1900 cycles. Sn3.4Ag0.7Cu Sn4.0Ag0.5Cu Sn-Pb Failure Analysis The failures reported above were analyzed with dye and pry and cross-sectioning techniques. Overall, it was found that solder joint failure for all of these Pb free alloys occur at the package side of the joint as is the case for Sn/Pb alloy. A representative x-section of joints with Sn/Pb and Sn/Ag/Cu alloys is shown in Figure 9. While Sn/Pb joint showed cracking very close to the package interface, the joint cracked through bulk solder in the case of Sn/Ag/Cu alloy. More detailed analysis of cracked joints is underway at this time. β1=16.07, η1= , ρ=0.98 β2=19.28, η2= , ρ=0.91 β3=15.16, η3= , ρ=0.99 Sn-0.7Cu β1=9.52, η1= , ρ=0.97 β2=15.16, η2= , ρ=0.99 Sn-Pb Figure 8 - Comparison of Solder Joint Failure Distribution for Sn/Pb and Pb Free s (Phase II, TC2, flexbga package) Phase II s, TC3 Cycling A total of 7280 cycles have been completed in 0 to 100 o C cycling at the time of this writing. Again, all Pb free alloys are showing much better performance compared to Sn/Pb alloy in these cycling conditions. While packages with Sn/Pb alloys started to fail at ~5100 cycles, no failures have been observed for Sn/Ag and the two compositions of Sn/Ag/Cu alloy. 2 of the 15 units with Sn/Cu solder have also failed, the first at 6130 cycles. Although sufficient data is not available at this time, the data that has been gathered indicates that the reliability of Sn/Ag/Cu alloys is at least 1.5X better than Sn/Pb alloy for this temperature cycling condition. Sn/Pb Sn/Ag/Cu Figure 9 - Cracked Solder Joints for Sn/Pb and Sn/Ag/Cu s due to Temperature Cycling Reliability Comparison for PBGA Package The PBGA package was used to evaluate the reliability of Phase I (except Sn/Ag) and Phase II solder alloys. Although only the TC1 and TC3 conditions were used for Phase I solder alloys, TC2 condition was added for evaluating the board level reliability of Phase II alloys. Again, a sample size of 15 was used for this evaluation and some of the very early failures (< 100 cycles) have been removed for data analysis. Phase I s, TC1 Cycling The test has completed 6700 cycles with only a few alloys (A11, A21, A66) showing close to 50% failure point. Table 6 provides a relative comparison of different alloys in relation to Pb/Sn alloy. As can be seen from the table, all alloys are performing much better than Sn/Pb alloy at this point. Also, between the two Sn/Ag/Cu compositions, A14 (Sn4.0Ag0.5Cu) is performing better than A11. Table 6 - Relative Comparison of Phase I s (TC1 Cycle, PBGA Package) Number on Test Number Failed Relative Fatigue Life By First Failure A A N/A A A N/A N/A A N/A A B By Mean Life LF2-7 7

8 Phase I s, TC3 Cycling About 9800 cycles have been completed on this test without any failures on any of the alloys, including Sn/Pb eutectic. The test will continue until at least 50% of all packages for each alloy fail. Phase II s, TC1 & TC3 Cycling A total of 3200 and 6200 cycles are completed on packages with these alloys in TC1 and TC3 cycling. No failures have been observed thus far. 2X Sn_Pb_TC3 Sn-Pb_TC1 Phase II s, TC2 Cycling About 4500 cycles have been completed at the time of this writing. While packages with Sn/Pb, Sn/Cu, and Sn/Ag solder balls have just started to fail, no failure has been observed on the packages with two compositions on Sn/Ag/Cu alloy. The test will continue until 50% of all devices fail. Effect of Temperature Cycle Conditions As mentioned earlier, the results from accelerated tests using different temperature cycle conditions help in not only indicating the alloy behavior under different temperature extremes, but also in determining if a certain alloy is acceptable for different applications. In order to gain some more insight, the above data is compared for different cycling condition in this section. Figure 10 compares the acceleration factor for eutectic Sn/Pb and Sn/4.0Ag/0.5Cu alloys from 0/100 o C to 40/ 125 o C temperature cycle conditions. While this acceleration factor is about 2 for Sn/Pb alloy, Sn/Ag/Cu alloy resulted in about a 3.15X reduction in life when tested at 40/125 o C cycle. A similar acceleration factor was also found for the other compositions of Sn/Ag/Cu alloy evaluated here. This is a very important result as this indicates that the Sn/Ag/Cu alloy does not need to be better than Sn/Pb alloy if both are tested using 40/125 o C and if the normal field level conditions are more benign and closer to 0/100 o C cycle. A summary of acceleration factors from 0/100 o C cycle to 40/125 o C cycle for the alloys in Phase I study is shown in Figure 11. The data clearly shows that all the Pb free alloys considered here have resulted in higher acceleration factors compared to the Sn/Pb (B63) alloy when comparing 0/100 o C cycle to 40/125 o C. β1=12.95, η1= , ρ=0.97 β2=10.40, η2= , ρ= X β1=9.55, η1= , ρ=0.93 β2=6.43, η2= , ρ=0.97 SnAgCu_TC1 SnAgCu_TC3 Figure 10 - Acceleration Factor Comparison for Sn/Pb and Sn/Ag/Cu s for TC1 and TC3 Cycling Acceleration Factors from TC3 to TC1 Cycle A1 A11 A14 A21 A32 A62 A66 B63 Figure 11 - Acceleration Factor Comparison for Sn/Pb and Pb Free s for TC1 and TC3 Cycling Summary and Conclusions The reliability of 9 different Pb free solder joints is compared with the Sn/Pb eutectic solder using two types of BGA packages. Three different temperature LF2-7 8

9 cycling conditions were used and all Pb free alloys performed better than Sn/Pb alloy for these packages. Three slightly different compositions of Sn/Ag/Cu alloy were evaluated as part of this study. Generally all three alloys showed similar behavior and with no significant difference in reliability. The data supports the general industry recommendation that this alloy can be used as a possible replacement for Sn/Pb alloy. Finally, a comparison between two different cyclic test conditions indicates higher acceleration for the Pb free alloys over a wider temperature range, implying significantly higher reliability at field level conditions for Pb free alloys. Based on this study and supporting data from the industry, Sn/4.0Ag/0.5Cu alloy has been selected as the preliminary replacement for Sn/Pb alloy for BGA type packages. Further studies are underway to finalize this selection. Acknowledgments The author wishes to thank all the people who have helped in carrying out this study. Special thanks are due to: Jeff Cannis and S. Y. Ryu for overall support of this project; Steve Hand and Al Santos for their help in sample preparation; and Larry Barker, W. J. Kang, Y. H. Ka, and Ezekiel Buchheit for carrying out the actual testing. References 1. Challenges and Efforts Toward Commercialization of Lead-free Solder-Road Map 2000 for Commercialization of Lead-free Solder-ver 1.2, The Japan Electronic Industry Development Association (JEIDA), February 2000; bfree/roadmap.html. 2. A Guide for Assembly of Lead Free Electronics, IPC Roadmap, Draft IV, June NEMI Group Recommends Tin/Silver/Copper as Industry Standard for Lead-Free Solder Reflow in Board Assemblies, Press Release, January An Analysis of Current Status of Lead-Free Soldering, UK Department of Trade and Industry Report, Warwick, M., Implementing Lead Free Soldering European Consortium Research, proceedings of the SMTA International, September J. Bath, C. Handwerker, and E. Bradley, Research Update: Lead-Free Solder Alternatives, Circuits Assembly, May 2000, pp LF2-7 9