ALTERNATIVE LEAD-FREE ALLOYS FOR SMT ASSEMBLY

摘要

As OEM and EMS PCB assemblers gain experience with lead free/RoHS compliant practices, many are pursuing alternatives to the SAC305 family of lead-free alloys in wave and selective soldering. Cost savings, aesthetic improvements, and the reduction in copper dissolution, have encouraged the use of these alloys. The alternative alloys investigated in this study show potentially successful outcomes with no measurable adverse impact on reliability. In fact, in some cases, there have been reliability improvements. Conversely, implementation of alternative alloys for SMT assembly has not moved as quickly. This is mainly due to the perceived need for increased reflow temperatures commonly compared to the low SAC305 reflow temperature of 217°C. This paper will examine the risks involved when changing alloys, including tin whisker growth, head in pillow (HiP) mitigation, drop shock performance, and flux compatibility. Mechanical data and testing procedures will be included, providing the user with valuable insight into initial alloy composition versus the alternative.