Interfacial Reaction and Mechanical Property of BGA Solder Joints with LTCC Substrate

摘要

The effects of aging time on the microstructure and shear strength of the Low Temperature Co-fired Ceramic (LTCC)/Ag pad/Electroless Nickel Immersion Gold (ENIG)/BGA solder joints were investigated through isothermal aging at 150 deg C for 1000 h with conventional Sn-37Pb and Sn-3Ag-0.5Cu. Ni_3Sn_4 intermetallic compound (IMC) layers was formed at the interface between Sn-37Pb solder and LTCC substrate as-reflowed state, while (Ni,Cu)_3Sn_4IMC layer was formed between Sn-3Ag-0.5Cu solder and LTCC substrate. Additional (Cu,Ni)_6Sn_5 layer was found at the interface between the (Ni,Cu)_3Sn_4 layer and Sn-3Ag-0.5Cu solder after aging at 150 deg C for 500 h. Thickness of the IMC layers increased and coarsened with increasing aging time. Shear strength of both solder joints increased with increasing aging time. Failure mode of BGA solder joints with LTCC substrate after shear testing revealed that shear strength of the joints depended on the adhesion between Ag metallization and LTCC. Fracture mechanism of Sn-37Pb solder joint was a mixture of ductile and pad lift, while that of Sn-3Ag-0.5Cu solder joint was a mixture of ductile and brittle (Ni,Cu)_3Sn_4 IMC fracture morphology. Failure mechanisms of LTCC/Ag pad/ENIG/BGA solder joints were also interpreted by finite element analyses.