Optimizing Solder Alloy Composition for Low Temperature Assembly
Authors: Keith Sweatman, Tetsuro Nishimura, Tetsuya Akaiwa, Pavithiran Naraynanan Company: Nihon Superior Co., Ltd Date Published: 9/22/2019
Abstract: Pressure to reduce process temperatures is forcing the electronics industry to identify solder alloys that can deliver the required productivity and service reliability in assembly processes that expose substrates and components to temperatures even lower than those required with tin-lead solders. As with the search for lead-free solders, the elements available for formulating low process temperature alloys are limited to the relatively few in the periodic table that, as well as contributing beneficially to properties required in a solder, are non-toxic, readily available and reasonably priced. Since assessing reliability by accelerated life testing of assemblies designed to simulate representative electronic circuitry is expensive and time consuming, it is useful, for screening purposes, to have a simple test that measures at least some of the properties that are known to affect reliability in service. One such method is the ball shear test and in this paper the results of such testing are reported for a short list of alloys that emerged from a preliminary evaluation of larger number of experimental alloys as potential candidates for low temperature solders. A tin-bismuth alloy with small additions of copper, antimony and nickel was identified as having the performance in ball shear testing that indicates that it should have good reliability in service as well as a process peak temperature under 200°C.
Low temperature soldering, Lead-free, Tin-Bismuth, Ball shear test