Lead-free Tin Surface Finish for PCB Assembly

The use of lead in electronics assembly operations has come under scrutiny due to health and environmental concerns associated with lead exposure. Lead is one of the most useful metals in modern industry; however, lead has the dubious distinction of being one of the most toxic of metals. Increasingly restrictive government regulations on the use of lead are hastening the search for feasible alternatives to tin-lead solder alloys. From an electronics assembly standpoint, there is a desire to replace lead bearing HASL (hot air solder levelling) coatings with a metallic, lead-free alternative. To answer these needs, Motorola have developed a lead-free, immersion plating technology for the surface finish of PCB printed circuit board bond pads. The Motorola development work has focused on the metallurgical system of tin-bismuth, which is a simple eutectic system similar to that of tin-lead, featuring a minimal number of phases and a wide operating window.