The microstructure and properties of solder joints

Solder joints in microelectronic devices consist of low-melting alloys that wet and join metal contacts and are, ordinarily, used at high homologous t emperatures in the as-solidified condition. Differences in solidification r ate and substrate interactions have the consequence that even solder joints of similar composition exhibit a wide range of microstructures. The differ ent microstructures have different properties; for this reason, the high-te mperature creep properties that govern much of the mechanical behavior of t he solder may differ significantly from joint to joint. The modern trend to ward ultrafine-pitch solder joints raises new questions as the joints take on dimensions that are commensurate with the scale of the microstructure an d the dimensions of common interfacial flaws.