Bonding strength of Cu-to-Cu joints using Cu cold spray deposition by an oxidation and reduction process for power device package

Abstract

Reliable die-attach bonding is critical for high temperature electronic packaging. A Cu-to-Cu bonding was attempted by using an in stiu nanocrystallized surface on commerical microscale Cu cold spray deposition without using organic solvents. During sintering at 300 °C, Cu2O nano particles were formed on the surface of the cold spray deposition and then were reduced into Cu nano particles by formic acid. The shear strength reaches 20.7 MPa under applied pressure of 5 MPa and was increased with an increase of applied pressure. The formation of nanoparticles lead to a much higher shear strength compared to the joint fabricated by using microscale Cu particles. Cu2O would be further oxidized at higher temperature transferring into CuO and consequently CuO would be firstly reduced to Cu2O gradually. Subsequently, Cu2O can be reduced into Cu finally. Controlling the oxidation temperature could achieve Cu-to-Cu bonding quickly. An economical approach to implement Cu-to-Cu bonding was established.