Shear Fracture Behavior on Ball Grid Arrayed Tin–Silver–Copper Solder/Pure Copper Pad Joint Interface

Abstract

Shear strength of Sn–0.39 mass%–3.9 mass%Ag–0.5 mass%Cu lead free solder joint interface on non-resist pure Cu pad were measured to evaluate the true joint strength. Shear test was carried out under the shear speed, V_s=0.14 mm/s and the shear height, Z=0 μm from the non-resist substrate surface. Shear fracture generated and propagated complicatedly on the joint interface. The shear strength using the non-resist pure Cu pad was lower than that using the FR-4 print board. The reaction layer was composed of Cu_5.6Sn and Cu₆Sn₅ intermetallic compound with column shape on the joint interface. Reaction layer thickness, t, column space, s and column width, w have been investigated to analyze the layer structure morphology. Silver composition in the solder influenced on shear strength but not on reaction layer structure morphology. Shear crack propagated intricately in the solder side and the reaction layer side. Shear fracture had the ductile deformation area of the solder and the brittle fracture area of the intermetallic compound.