Effect of Bi Content on Properties of Low Silver SAC Solders
Authors: Mehran Maalekian, Ph.D., Yuan Xu, and Karl Seelig Company: AIM Metals & Alloys Date Published: 9/27/2015
Abstract: Since the adoption of RoHS and REACH regulations for electronics manufacturers, Sn-Ag-Cu (SAC) alloy systems have largely replaced the Sn-Pb solder alloys with Sn-3Ag- 0.5Cu (wt%) (SAC305) the most widely accepted. This high silver content SAC alloy (greater than X percent) has a major deficiency however, the relative fragility of the solder joint. This is due to the formation of primary Ag3Sn platelets crystals in the solidified structure leading to poor drop-shock performance causing major concerns for portable devices. Lowering or eliminating Ag content of SAC has been proposed as a solution but with limited success. In this work, a systematic study is presented to address the effect of Bi content on soldering and mechanical performance of low silver SAC alloys. Thermal behavior (melting and solidification), wetting and spreading performance, and tensile and hardness properties of alloys are compared and a promising lead-free SAC-Bi solder alloy that also demonstrates tin whisker mitigation properties is recommended.
Lead-free solder, electronic assembly, wettability, mechanical properties, melting, tin whisker