On the factors affecting the dissolution of copper in molten lead-free solders and development of a method to assess the soldering parameters

摘要

Purpose - The purpose of this paper is to investigate the various factors that influence the dissolution of copper in molten solder, paying particular attention to important parameters: temperature, solder composition and flow rate. Design/methodology/approach - To determine the dissolution rate of copper in lead-free solders, a simple and automated technique is developed. This methodology provides repeatable measurements that allow the various experimental parameters to be isolated. Factors that greatly affect the dissolution rate of copper, such as soldering temperature, flow rate and solder composition, are taken into account. Particular attention is paid to the flow rate of the molten solder. In fact, different alloys at the same temperature can have considerably different flow rates, owing to their different viscosities at that temperature. The dissolution rates of copper in seven lead-free alloys and the Sn-Pb alloy are compared at 255, 275 and 300℃. Findings - It is observed that generally the samples with a thicker intermetallic layer are those that exhibit a longer dissolution time. Originality/value - The transition from tin-lead to lead-free increases the tendency for copper dissolution in molten solders, clearly representing a serious risk to circuit reliability. This paper presents the many advantages of a method for comparing the dissolution rate of copper with different solder alloys.