Evaluation of mechanical properties of low-Ag ball grid array solder joints using a high-speed ball shear test

Solder joints of Sn-1.0Ag and Sn-1.0Ag-0.1Ce on electroless nickel/electroless palladium/immersion gold (ENEPIG) were studied and mechanically evaluated using a high-speed shear test. The effect of Pd thickness in ENEPIG on the reliability of solder joints was evaluated after multiple reflows. Microstructural observations of the solder joint interfaces and fractures after shear tests are shown. For comparison, conventional SAC305 Pb-free solder was also mechanically evaluated under the same conditions. By adding a thin Pd layer in ENEPIG surface finish, the intermetallic compound (IMC) layer's morphology of SAC305 change from needle type (as Pd thickness = 0 μm) to scallop type (as Pd thickness = 0.1 μm). While the intermetallic compounds (IMCs) layer's morphology of 1.0Ag solders change from facet type (as Pd thickness = 0 μm) to needle type (as Pd thickness = 0.1 μm). ENEPIG with thicker Pd layers was suitable for 1.0Ag solders during high speed shear test whereas conventional SAC305 showed the highest shear strength with an ENIG surface finish.