Microstructural stability of Sn-Bi/copper and Sn-Bi-Zn/copper soldered joints under high temperatures.

Abstract

The increase in the density of integrated circuit components resulting from the continuous miniaturization of electronic devices that populate modern life presents a series of Engineering challenges. Among these challenges, the optimization of alloys intended for soldering of integrated circuit components remains very important. In this context, some alloys from the Sn-Bi system exhibit a set of mechanical properties and adhesion characteristics to Cu substrates that make them excellent alternatives among Pb-free alloys. Sn-Bi alloys have suitable wettability and heat transfer capability. However, mechanical performance and interface layer stability still need improvement. Zn is one of the candidates. Another aspect to be considered in these applications is the effect resulting from the contact of these alloys with the Cu substrate of electronic circuits over time at temperatures higher than ambient. It is known that Sn alloys in contact with Cu under favorable time and temperature conditions give rise to the Cu6Sn5 phase layer formed at the interface region. Depending on Cu6Sn5 morphological features and volume can lead to region embrittlement and consequently compromise the reliability of the solder joint. Thus, the present study aims to contribute through the analysis of the influence of Zn (at two different levels: 2 and 10 wt.%) on the mechanical properties, adhesion to Cu substrate, and morphology and volume of resulting phases in the Sn-40 wt.% Bi alloy.