Reliability test and IMC investigation of lead and lead free solder joints on different surface finish processes

In this study, lead free (Sn-4Ag-0.5Cu (SAC)) and lead (62Sn-36Pb-2Ag (SP)) solder joint on various surface finished of ball grid array (BGA) pad, such as Immersion Tin (ImSn), Organic solderability preservatives (OSPs), Ni-P/Pd/Au (ENEPIG), and Ni-P/Au (ENIG) was investigated by its interface morphology and its physical properties. To evaluate the mechanical and physical properties of BGA pad with lead and lead free solder joint, it was tested by bonding strength measuring, shear force test and interfacial microstructure. The IMC (Inter metallic compound) of SAC and SP solder with these finishes were also studied by using Focused Ion Beam (FIB) microscope to observe the crystal grain, morphology and size. It was found that the IMC crystal lattice is dependent on solder material and the solder joint reliability is dependent on both the solder material as well as the surface finish. Moreover, the shear test results show that the shear strength of solder joints could not be significantly influenced by the thickness and morphology of the interfacial IMC.