Mechanical reliability of transient liquid phase bonding of Au–Sn solder with Ni(Cu) substrates

Abstract

Mechanical reliability of transient liquid phase (TLP) bonded Au–Sn/Ni(Cu) joints was investigated in this study. The results show that the TLP bonded Au–Sn/Ni(Cu) joints have excellent mechanical performance, even after exposed at 400 or 450 °C, especially in Au–Sn/Ni–30Cu and Au–Sn/Ni–40Cu systems. The shear strength could reach 75 MPa in TLP bonded Au–Sn/Ni–40Cu joint and increased to 87 and 97 MPa after exposed at 400 or 450 °C for 24 h, respectively. It was found that during TLP bonding at 350 °C, ordered AuCu, Ni₃Sn₂, and α(Au) phases formed in the Au–Sn/Ni–Cu joints, then the ordered AuCu phase transferred to disordered (Au,Cu) phase and a new Ni₃Sn phase appeared between substrate (Au,Cu) and the Ni₃Sn₂ layers after exposure at 400 or 450 °C. However, only Ni₃Sn₂ layer formed after TLP bonded and new Ni₃Sn layer appeared near substrate after exposure at 400 or 450 °C in the Au–Sn/Ni bonding system. The ductile Au–Cu [ordered AuCu or disordered (Au,Cu)] layer releases local stress concentration in joint under shear stress, which improves the mechanical reliability. Moreover, the maximum stress in Au–Sn/Ni(Cu) joints decreases with the increasing thickness of Au–Cu layer. As a result, the Au–Sn/Ni joint presents lower shear strength as brittle Ni₃Sn or Ni₃Sn₂ layer formed near substrate, whereas the shear strength of Au–Sn/Ni–Cu joint increases with thicker Au–Cu layer.