Solder joints provide mechanical and electronic connections between solders and components for various levels in microelectronic package. However, due to different thermal expansion coefficients and elastic modulus of the associated materials, solder joints are susceptible to fatigue degration, microcracks and fracture. The solder joint reliability is, therefore, critical in the evalution of the joint quality. Recently, the employment of lead-free solder is attractive due to the environmental concern of the Pb-containing solder. Hence, the investigation on the unleaded solder joint is of practical importance in the field of microelectronic package.
Intermetallic compounds (IMC), which form and grow between solders and metallizations, are considered to be a source of mechanical weakness for its brittleness and different coefficient of thermal expansion from the metallization or the solder.