Development of a Ag/glass die attach adhesive for high power and high use temperature applications

The increasing power densities of certain semiconductor devices such as SiC and GaN require higher continuous use temperatures and high thermal properties. For example, one application is for a continuous use temperature of 300°C with SiC devices, with a die attach process at about 370°C. This paper describes development of an Ag/glass die attach paste which demonstrates high performance and reliability, for high temperature continuous use. The Ag/glass paste contains a unique crystallizing glass having a crystalline re-melt temperature of greater than 300°C and less than about 370°C. During the die attach process with Ag/glass paste, the crystallized glass component melts at about 350°C and wets the die and substrate surfaces. During the cool down of the die attach process, the glass crystallizes creating a robust structure having a re-melt temperature greater than 300°C. Therefore, die adhesion remains high for a 300°C continuous use temperature. Another key requirement of a die attach adhesive for use with SiC devices is power dissipation; i.e., heat dissipation. High thermal conductivity and very low interfacial thermal resistance for die attach parts have been demonstrated in this paper. Thermal resistance measurements (laser flash method) were consistently as low as 0.01Kcm
²
/W, while the bulk thermal conductivity was about 100W/mK. An inherent advantage of glass as the adhesive agent is its wettability on oxide or metal surfaces. This allows the option to use bare dies and substrates in lieu of metalized surfaces in certain applications, leading to the potential for significant cost savings. This new technology replaces the higher cost solder alloys and provides a high reliability option that meets the requirements for SiC device packaging.