Abstract:

This paper describes the interaction of the NEMI recommended lead-free solder for reflow assembly (Sn3.8Ag0.7Cu) with different commercial printed wiring board (PWB) platings. It also discusses the effects of plating type and manufacturer on the strength of the lead-free solder joints. PWBs from two different manufacturers with the same four types of plating were examined. The platings were organic solderability preservative over bare copper (OSP), immersion tin (ImSn), immersion silver (ImAg), and immersion gold over electroless nickel (ENIG). Hot air solder leveled (HASL) boards with Sn37Pb plating from one manufacturer were also studied. The bulk and interfacial microstructure were examined immediately after reflow, and then after high temperature aging for up to 1000 hours and the microstructure was correlated to the strength of the solder joint.

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