Pressureless Sintering Process of Ag Sinter Paste Bonding Ag Si Die on Bare Cu DBC Using Convection Reflow Oven in Nitrogen for Die Attach

Ag sintering has been paid considerable attention to an alternative to soldering in die attach for decades, especially for high power electronics packaging because of its high melting temperature (962°C), highly thermal and electrical conductivity of the sintered silver joints, and low process temperature that is normally less than 275°C. Ag sintering reported in literature and currently used in industry, however, is long time process, especially for pressureless sintering process, which would takes an hour at sintering temperature in air so as to achieve strong bonding. Though air is good for organic capping agents to be burnt out during sintering process, it would cause the oxidation of air-sensitive components in power electronic package during assembly. We recently developed a series of silver sinter pastes that can fast sinter at the peak temperature range from 240°C to 275°C, with a shortest sintering time of 2min, in nitrogen using a conventional reflow oven like BTU oven, to form strong sintered Ag joints on Ag and bare Cu DBC substrate, and/or bare Cu coupon with Ag Si or bare Cu dies. In the present paper we will present silver sintering process conditions, shear strength, microstructure of the sintered Ag joints, and preliminary reliability tests. Thermal shock test with a profile of -55 to 155°C, 10min of dwell time was employed to evaluate thermomechanical reliability of the sintered Ag joints bonding Ag Si die on bare Cu DBC substrate made in air and nitrogen by BTU reflow oven. Scanning electronics microscopy (SEM) was utilized to characterize cross-section microstructure of the sintered Ag joints. Influence of sintering process conditions on shear strength and cross-section microstructure of the sintered Ag has been investigated extensively.