Intermetallic growth studies on Sn-Ag-Cu lead-free solder joints

Solid-state intermetallic compound (IMC) growth behavior plays an important role in solder joint reliability of electronic packaging assemblies. The morphology and growth of interfacial IMC compounds between 95.5Sn-3.8Ag-0.7Cu Pb-free solders and nickel/gold (Ni/Au) surface finish on BGA solder joint specimen is reported. Digital imaging techniques were employed in the measurement of the average IMC growth thickness. The IMC growth behavior subjected to isothermal aging exposure at 125degreesC, thermal cycling (TC), and thermal shock (TS) with upper soak temperatures of 125degreesC are compared. An equivalent isothermal aging time is proposed for comparison of IMC layer growth data. It was noted that IMC layer growth under thermal cycling and thermal shock aging gives an acceleration factor of 1.4 and 2.3 based on the equivalent isothermal aging time.