Gerhard Palm

SiC-Die-Attachment for High Temperature Applications

In this paper a die-attachment technology for high temperature applications based on the Low Temperature Joining Technique (LTJT) is presented. The present challenge is to fit the thermal expansion as well as the mechanical properties of the die-attach layer to the characteristics of chip and substrate. While the classic LTJT is based on sintering a sub-micron silver paste at temperatures between 150°C and 300°C to bond an electronic device to a substrate, the modified procedure employs a powder mixture consisting of silver powder and special filling powder material. Type and amount of the filling material is dependent on the application and the used substrates. Considering a low thermal expansion and high electrical as well as thermal conductivity we chose SiC, TiC, and BN as filling materials in this work.

Die-attach for high-temperature applications using fineplacer-pressure-sintering (FPS)

A new joining technique called “Fineplacer-Pressure-Sintering” (FPS) for die-attach of small electronic components (e.g. LEDs and photodiodes) is described. Using a modified Flip Chip Bonder, bare dies could be bonded onto substrates with high positioning accuracy. For the FPS process a 50 tons press, which is conventionally used for pressure sintering, is no longer required. Very high average shear strengths (63 MPa) were achieved on molybdenum substrates (metallization: Ni/Au). With the help of silver powder of micro-to-nanometre grain size the electrical and mechanical properties of the compound layer could be further increased. The bond strength of metalized GaN-LEDs on Al2O3 substrates with a Ti/Pd/Au metallization is twice as high as with standard micro-powder and the process temperature could be reduced to 200° C. Finally the applicability of FPS was demonstrated by an optoelectronic module consisting of two commercial InGaN -LEDs and GaP -photodiodes on a metalized Al2O3 substrate. Successful function was found with prototype modules at temperatures up to 250° C.