ICSR (Soldering and Reliability) Conference Proceedings

Low Silver SAC-Bi Lead-Free Solder for Reliable Applications

Authors: Mehran Maalekian, Ph.D., Karl Seelig
Company: AIM Metals & Alloys
Date Published: 6/6/2017   Conference: ICSR (Soldering and Reliability)

Abstract: The conversion to RoHS-compliant lead-free assembly has brought a challenging task to the electronics industry due to process compatibility, cost and reliability considerations. The Pb-free alloy SAC305 emerged as the industry standard during the RoHS transition because of its reasonable thermal fatigue reliability and compatibility with the mixed metals supply chain that would combine lead on the components and PCBs with lead-free solders. However, there are issues surrounding SAC305 implementation, for example; poor drop shock performance, unstable mechanical performance by aging, tin whisker growth, and high cost of silver. The solder industry is innovating to address these challenges. New options and new understandings are emerging to meet the demands of multiple markets as RoHS exemptions expire.

Bi-containing alloys and other micro-alloys are emerging as the next generation of enabling technologies. Bi has a long history in the solder alloy market. It lowers the solder melting point, improves wetting, improves mechanical performance and is relatively inexpensive. These characteristics address the major shortcomings of many of the lead-free solders in the market today. Hence, in this paper we study the effect of Bi on microstructure, mechanical performance and soldering properties of a low silver SAC alloy. It is demonstrated that adding Bi (<3wt%) would improve soldering and mechanical behavior of low silver SAC alloy. The reliability and stability of this Bi-containing low silver SAC is presented and compared with SAC305.

Key Words: 

Lead-free solder, reliability, electronic assembly, mechanical properties

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