Developing new joining materials for low-temperature electronics assembly

New regulations due to environmental and health concerns including the European RoHS (Restriction of Hazardous Substances) and WEEE (Waste Electric and Electrical Equipment) directives have led to a shift towards tin-based, lead-free solders in electric and electronic equipment. For the assembly of electronic devices on printed circuit boards (2 nd level packaging), the most widely used lead-free alloy is near eutectic tin-silver-copper (Sn-Ag-Cu or SAC). Compared to tin-lead based solders, the higher melting points of SAC solders can result in additional stress, accelerated ageing and a global decrease in reliability for components and polymer-based printed circuit boards during reflow processing. These recent concerns have led to new research and development in lead-free solders area [1]. Numerous new alloy compositions are being investigated as well as new approaches like manufacturing alloy nanoparticles or improving mechanical properties with nanoparticle reinforcements in conventional micrometre-sized solders.