SMTA International Conference Proceedings


LEAD-FREE SOLDER ASSEMBLY FOR MIXED TECHNOLOGY CIRCUIT BOARDS

Authors: David Suraski and Karl Seelig
Company: AIM
Date Published: 9/24/2006   Conference: SMTA International


Abstract: For SMT applications, the electronics assembly industry has migrated to Tin/Silver/Copper alloys, and within this group the industry has narrowed its focus to the SAC305 (96.5% tin, 3% silver, 0.5% copper) alloy. However, it is well known that SAC305 can cause negative results in wave soldering, hand soldering and selective soldering applications. Because of this, the industry is looking for alternative alloys for non-SMT applications. The common alternative alloys are SN100C™, SAC-LOW, and SACX™.

The issue of choosing a wave/selective solder alloy is more complicated than choosing an SMT alloy because not only must these solders form a reliable solder joint, but they also are used in a molten solder bath, where various interactions can impact manufacturing and reliability. This paper will provide an in-depth discussion of several issues related to lead-free solder alloy selection for mixed technology circuit board assembly, including: how these alloys react to molten solder baths; copper corrosion and appearance; “hot tears/shrink holes”; voiding; surface cracking; crosscontamination characteristics (the compatibility of these alloys with SAC305 and tin-lead); thermal cycling and shear testing characteristics.



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