Study of height reduction of Sn99Cu1/Cu solder joints as a result of isothermal aging

Sn99Cu1/Cu solder joints were investigated after isothermal aging at 175°C for different lengths of time under vacuum conditions. The results revealed height reduction of the solder of approximately 1.2 μm after aging for 1132.5 h. This was primarily attributed to growth of a layer of interfacial intermetallic compounds. The reduction was measured by use of a copper block containing a recess filled with solder, which was reflowed then polished flat. Height reduction of the solder joint during aging was found to obey the parabolic law \(\Delta h = -\!\!\hbox{ }0.031\sqrt t\), and was in excellent agreement with theoretical calculation.