Effects of reflow on wettability, microstructure and mechanical propertiesin lead-free solders

Solder joints used in electronic applications undergo reflow operations. Su ch operations can affect the solderability, interface intermetallic layer f ormation and the resultant solder joint microstructure. These in turn can a ffect the overall mechanical behavior of such joints. In this study the eff ects of reflow on solderability and mechanical properties were studied. Nan oindentation testing (NIT) was used to obtain mechanical properties fi om t he non-reflow (as-melted) and multiple reflowed solder materials. These stu dies were carried out with eutectic Sn-3.5Ag solders, with or without mecha nically added Cu or Ag reinforcements, using Cu substrates. Microstructural analysis was carried out on solder joints made with the same solders using copper substrate.