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Analysis of BGA Solder Joint Reliability for Selected Solder Alloy and Surface Finish Configurations
Keywords: BGA, solder joint reliability, surface finish
New challenges for the electronics industry are being incurred as a result of the recent global adoption of Pb-free initiatives. The microelectronics packaging sector is particularly impacted by these events as a result of changes to design, material requirements and assembly specifications. Solder alloys and surface finishes for package substrates (and PWBs) must meet the Pb-free requirements without resulting in any decrease in reliability. As a result, many designers, fabricators, assemblers and OEMs are facing challenges in terms of ensuring the reliability of these assembled packages while still maintaining their competitiveness in the market. The presentation summarizes the findings from part of a major ongoing project to evaluate the performance of several combinations of surface finishes and solder ball alloys for wire-bond and flip chip BGA package applications. High-speed ball shear testing was used as the primary methodology for examining 2nd level solder joint reliability in this phase of the evaluation. The solder alloys tested included eutectic SnPb, SAC305 and SnAg. Surface finishes included electrolytic nickel/electrolytic gold as the process of record (POR) and electroless nickel/electroless palladium/immersion gold (ENEPIG). Determining the shear speed (a key parameter) for each solder alloy involved use of a concept known as “point of inflection” (POI), including a failure analysis screening process that was also performed. The evaluation included high-speed shear testing conducted after solder ball attach, as well as after extended storage at high-temperature conditions. Results of the high-speed ball shear testing include analysis of total energy, shear strength and failure mode. SEM and FIB investigations are also included for examination of pre- and post-test conditions, including formation of intermetallic compounds in the solder joint during ball attach and subsequent extended thermal storage. Findings are discussed and conclusions are presented, summarizing the performance of the various surface finish/solder alloy combinations and the resultant reliability of the respective solder joints under the specified test conditions.
Hugh Roberts, Global Manager, OEM/EMS Technology Exchange
Rock Hill, SC

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