Copper sinter paste that can sinter without pressure in nitrogen

Abstract:
In this study, we develop a Cu sinter paste for pressure-less sintering in a nitrogen atmosphere. The bonding process of the developed Cu sinter paste involves printing, chip mounting, drying, and sintering. The Cu sinter paste was used for bonding in a nitrogen reflow oven at a sintering temperature of 260 °C for 60 min without pressure; it achieved a die-shear strength of 47 MPa. Stencil-printing and screw-dispensing methods are employed in the printing process. A die-shear strength of 40 MPa or higher is obtained for a sintering temperature in the range of 260 °C or higher. The sintering process requires a non-oxidizing atmosphere (e.g., nitrogen or vacuum), and the maximum bondable chip size is 5 mm  5 mm. Chips that are 7 mm  7 mm or larger cannot bond stably because of the generation of large voids and cracks. Copper, silver, palladium, and platinum are used as adherents, and their die-shear strengths are greater than 40 MPa. The results confirm that the developed Cu sinter paste can be sin-tered using conventional bonding equipment used for soldering, which offers the potential to achieve high bonding reliability and high thermal conductivity as copper sintering bonds.