Thermostable porous Ag die-attach structure for high-temperature power devices

Abstract

In this work, efforts were made to prepare a thermostable die-attach structure which includes stable sintered porous Ag and multi-layer surface metallization. Silicon carbide particles (SiCp) were added into the Ag sintering paste to improve the high-temperature reliability of sintered Ag joints. Presence of SiCp in the bonding structures inhibited the coarsening of the porous Ag network during high temperature storage (HTS) tests, and the morphology remains similar to that of the as-sintered state. In addition to the Ag paste, on the side of DBC substrates, the thermal reliability of various surface metallization such as Ni, Ti and Pt were also evaluated by shear strength, cross-section morphology and on-resistance test. The results indicated that Ti and Pt diffusion barrier layers played an active role in inhibiting the oxidation of Cu and inter-diffusion between Cu and Ag at high temperatures exceeding 250 °C. While Ni barrier layer showed a relatively weak barrier effect due to the generation of thin oxide layer between Ag and Ni. The changes of on-resistance indicated that Pt metallization has a relatively better electrical property comparing to that of Ti and Ni. Ag metallization which lacks of barrier layers showed a severe growth of oxide layer between Ag and Cu, however, the on-resistance showed less changes, which needs further studies.