An investigation into the use of lead free solders in the electronics industry

Abstract

Tin-lead solder is the most common material used to join conductors in electronic assembly and has been used in electronics assemblies since the earliest days of radio. After many decades, highly engineered systems have developed. The mechanical, electrical and thermal properties of tin/lead solder, combined with its low material cost, have made it the material of choice for joining active and passive components. However, well publicised environmental and toxicity concerns have led to increased controls and legislation which aim to eliminate the use of lead. The major continuing use of lead is in automobile batteries. Lead used in electronic solder represents only 0.6% of the total use. In Europe, the EU Waste Electrical and Electronic Equipment (WEEE) Directive will eliminate or severely restrict the use of lead in electronic manufacturing. The environmental concerns and the new legal restrictions relating to the use of lead have initiated the search for acceptable alternate joining materials for electronics assembly. This dissertation reviews the physical, mechanical and potentially hazardous properties of lead-free solders compared with tin/lead solders. The performance of lead-free solders in electronics assembly is assessed and compared to common tin/lead solders. Fatigue testing results are reported for thermal cycling electronics assemblies soldered with lead-free compositions. The dissertation also includes a discussion on substitution availability and supply.