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October 2017 • SMT Magazine 69 value and avoid its negative effect on reliability. A higher gold thickness will increase dwell time in the gold bath resulting in nickel corrosion under the palladium layer. This investigation addresses the reliability from an assembly perspective and more realistic thermal cycles and aging environmental condi- tions. ENEPIG is yet to be widely accepted for high-reliability applications with tin-lead solder assembly. First, technology trends for LGA are discussed followed by an example of the diffi- culty of reflow for HASL with PCB surface finish compared to ENEPIG finish. Then, briefly dis- cussed is assembly on a PCB with ENEPIG fin- ish using two advanced area array packages, one an LGA with 1156 solder joints and the other one with CLGA 1272 (ceramic LGA) LGAs. The LGAs were subjected to 200 thermal cycles (-55°C to 125°C). Optical and SEM photomi- crographs showing solder interface conditions after 200 thermal cycles (TC) are presented and were compared to samples that were subject to additional 324 hours of aging at 125°C. Further- more, these were compared to those that were subjected to an additional 100 thermal shock cycles (-65°C to 150°C). The article concludes with a summary and recommendations for the next steps of investigation. LGA and Advanced Packaging Trends This article focuses on the second-level (board-level) solder joint reliability and inter- metallic formation of LGA1156. Figure 1 cat- egorizes single-chip microelectronics packaging technologies into three key technologies 7,8 : • Plastic ball grid arrays (PBGAs) including flip-chip die version (FCBGA), land grid array (LGA) with solder balls, quad flat no lead (QFN) and new versions • Ceramic ball grid array (CBGA), ceramic column grid arrays (CGAs), and ceramic LGA version 9 • Chip-scale packages, smaller footprint versions of BGA, and wafer level packages (WLPs) RELIABILITY OF ENEPIG BY SEQUENTIAL THERMAL CYCLING AND AGING Figure 1: Single chip packaging technologies covers three main categories. LGA exists in all three categories.