A multi-pronged approach to low-pressure Cu sintering using surface-modified particles, substrate and chip metallization

High temperature power electronics based on wide-bandgap semiconductors have prominent applications, such as automotive, aircrafts, space exploration, oil/gas extraction, and electricity distribution. Die-attach bonding process is an essential process in the realization of high temperature power devices. Transient liquid phase (TLP) bonding and Ag sintering has been on the forefront of research over the past decade as suitable replacements to high-Pb solders. However, brittle intermetallics in the case of TLP bonded interconnects and high cost of Ag coupled with challenges of high electromigration in Ag, warrant the development of reliable substitutes. Cu offers to be a promising alternative to Ag, especially because of thermal and mechanical properties on par with Ag and a cost advantage by being a factor 100 cheaper than Ag. However, high tendency of Cu to be oxidized poses a major challenge in realizing stable interconnects. For this purpose, in this contribution, we present the use of poly-ethylene-glycol 600 as reducing binder in the formulation of the Cu sintering paste. Moreover, with the aim to achieve a low-pressure Cu sintering process, a low cost wet chemical etching process is developed to selectively etch Zn from brass to create nano-porous surface modifications to enhance sinterability, enabling sintering with low bonding pressure of 1MPa and at temperatures below 300°C. Finally, we propose a multi-pronged approach based on three crucial factors: surface-modified substrates, nanostructured surface modifications on micro-scale Cu particles and use of a reducing binder in the Cu particle paste. Results of sintering experiments under N2 atmosphere are discussed and compared with sintering results using non modified materials.