Development of sinter paste with surface modified copper alloy particles for die-attach bonding
Copper sintering is a potential alternative to silver sintering and transient liquid phase bonding. In this paper, an innovative approach for copper sintering is investigated using brass powder, which is etched by HCl. Due to the acid biting action, Zn is selectively removed from the binary copper-zinc system. The dissolving of Zn causes a modification of the brass particles and an efficient increase of the exposed surface area, which enhances the sinterability. The focus of the work is to investigate the effects on sinterability of the initial zinc concentration in the powders. Two commercial brass powders, from the same supplier, with equal particle size and shape but different zinc concentration, i.e. ca. 10 wt% Zn and ca. 30 wt% Zn, were selected. Polyethylene glycol 600 (PEG600) was used as reducing binder for the sinter paste. Paste composed of particles realized by etching brass with a maximum of 10% Zn in the starting material show 15% higher shear strength after sintering compared to the shear strength of the paste composed of particles realized by etching brass with a maximum of 30% Zn in the starting material. XRD analysis of the particles before and after etching and microstructure analysis of the sintered interconnects were conducted to provide scientific insights into the occurring phenomena.