Copper Sintering Pastes for Die Bonding

Recently, Ag sintering die bonds has attracted as die bonding materials in automotive inverters due to their high bonding reliability and high thermal conductivity. In this study, the bonding reliability of copper sintering die bonds was evaluated using the power cycle test and FEM simulation. Power cycle lives using the Weibull method were compared between pressure-assisted copper sintering (Cu sinter [P]), pressureless copper sintering (Cu sinter [N]), pressure-assisted silver sintering (Ag sinter), and high-Pb solder. The characteristic lives of the Cu sinter [P], Cu sinter [N], Ag sinter, and high-Pb solder were 215480, 77394, 41948, and 5450, respectively. The breakdown points of the samples bonded by Cu sinter [N], Ag sinter, and high-Pb solder after power cycle tests were at the interface between the chip electrode and the die bonding layer in the chip edge area. By contrast, the sample with a Cu sinter [P] was broken in the Schottky barrier diode (SBD) chip. The superior bonding reliability of Cu sintering [N] is explained by a finite element method (FEM) simulation. The Cu sinter [N] showed a smaller maximum thermal strain range compared with Ag sinter and high-Pb solder because of its smaller CTE and higher Young’s modulus. This smaller thermal strain range can suppress cycle fatigue and cause a superior power cycle life of the Cu sinter [N]. The less porous sintered Cu layer from Cu sintering [P] obtained a higher Young’s modulus, which consequently increased characteristic life. Sintering conditions such as pressure, temperature, and time can control the porosity of the sintered Cu layer, which means they also control the bonding reliability and breakdown location.