Papers by Dr. Weiping Liu
by Jeffrey Chan, Scott Chen, Dr. Min Ding, Adriana Porras, Austin Huang, Anthony Gallagher, Dr. Weiping Liu, Dr. Ning-Cheng Lee
Chinese version of Achieving High Reliability Low Cost Lead-Free SAC Solder Joints Via MN or CE Doping.
CHINESE LANGUAGE, lead-free, Reliability, thermal cycling
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Posted on 6 May 2011
by Dr. Weiping Liu, Dr. Ning-Cheng Lee , Adriana Porras, Dr. Min Ding, Anthony Gallagher, Austin Huang, Scott Chen, Jeffrey Chan
In this study, the reliabilities of low Ag SAC alloys doped with Mn or Ce (SACM or SACC) were evaluated under JEDEC drop, dynamic bending, thermal cycling, and cyclic bending test conditions against eutectic SnPb, SAC105, and SAC305 alloys. The Mn or Ce doped low cost SAC105 alloys achieved a higher drop test and dynamic bending test reliability than SAC105 and SAC305, and exceeded SnPb for some test conditions. More significantly, being a slightly doped SAC105, both SACM and SACC matched SAC305 in thermal cycling performance. In other words, the low cost SACM and SACC achieved a better drop test performance than the low Ag SAC alloys plus the desired thermal cycling reliability of high Ag SAC alloys. The mechanism for high drop performance and high thermal cycling reliability can be attributed to a stabilized microstructure, with uniform distribution of fine IMC particles, presumably through the inclusion of Mn or Ce in the IMC. The cyclic bending results showed SAC305 being the best and all lead-free alloys are equal or superior to SnPb. The reliability test results also showed that NiAu is a preferred surface finish for BGA packages over OSP.
thermal cycling, Reliability, lead-free
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Posted on 2 Mar 2010
by Dr. Weiping Liu, Dr. Ning-Cheng Lee , Simin Bagheri, Blake Harper, Polina Snugovesky, Russell Brush, Jason Bragg
Assembled BGA/CSP devices with SnAgCu (SAC) solder joints are vulnerable when dropped due to the fragility of solder joints. Although reducing the Ag content of SAC alloy does help, the crack resistance when dropped is still considerably poorer than the eutectic SnPb system. Therefore, a new alloy with improved drop test performance is greatly desired. In this work, SAC105 doped with Ti (SAC105Ti) as a BGA/CSP sphere was studied for its drop test reliability. Four different solder combinations were evaluated: 1) SnPb solder paste with SnPb balls, 2) SnPb solder paste with SAC105Ti balls, 3) SAC305 solder paste with SAC105Ti balls, and 4) SAC305 solder paste with SAC105 balls. The number of completely fractured interconnects was counted for each type of component after a total of 100 drops. The cell with the fewest number of fractured joints was the pure SnPb cell, followed closely by SAC305 solder paste/SAC105Ti ball, then SAC305 solder paste SAC105 ball and lastly SnPb solder paste/SAC105Ti ball. This trend is consistent with the trend observed by measuring the electrical resistance. The combination of SAC305 solder paste with SAC105Ti balls was the best solder joint structure tested in terms of the lowest number of partial interconnect fractures and outperformed the other three combinations.
drop test, lead-free, solder sphere, SAC, SAC105Ti, solder paste, SAC305
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Posted on 14 Oct 2011
by Paul Bachorik, Dr. Ning-Cheng Lee , Dr. Weiping Liu
SAC-Ti alloys exhibited significantly improved drop test performance over not only SAC alloys, but also 63Sn37Pb for ENIG/OSP, NiAu/OSP, and OSP/OSP surface finish systems. The superior performance is attributed to (1)the increased grain size and dendrite size, therefore reduced hardness of solder, (2) inclusion of Ti in the IMC layer, and (3) reduced IMC layer thickness. DSC data indicate that the melting temperature and range were not affected by Ti, but the undercooling was almost completely suppressed. The creep properties of SAC-Ti alloy were comparable with those of SAC alloy, strongly suggesting the gain in drop test performance was not achieved by compromising the thermal fatigue performance. SAC-Mn alloys were also found to outperform SAC alloys and Sn63 for the X/OSP finish combinations studied. In general, SAC-Ti performed equally to or better than SAC-Mn alloys.
fragility, drop test, SAC, tin-silver-copper, lead-free, solder
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Posted on 10 Mar 2010
