The Pressure Balance Effect of the Polytetrafluoroethylene Buffer Film in Pressure-Assisted Sintering Bonding

Bonding pressure is one of the most important process parameters in pressure-assisted sintering bonding of the SiC power chips. The buffer film, placed between the pressure indenter and the chips, is essential to balance the pressure during the simultaneous bonding of multiple chips. However, the pressure balance mechanism, optimization, and enhancement of the buffer film have been rarely studied. In this study, a simulation model for the pressure balance effect of the polytetrafluoroethylene (PTFE) buffer film was established and verified by experimental results. The mean relative error (MRE) between the simulation and experimental results was merely 1.06% and 1.98%, regarding to the compression ratio and porosity of the joint. It was found that the pressure balance ability peaked at an optimal pressure for the first time. The optimal pressure value was negatively correlated with the sintering temperature regardless of the film thickness. To improve the pressure balance effect at lower pressure, drilled buffer films were proposed to enhance the pressure balance ability of the PTFE film. With a drilled film, the joint porosity difference between two chips with a 60- $\mu $ m-height difference was reduced by 44%. The combination of films with different removal rates could further eliminate the influence of a specific height difference. This work is promising to deepen the understanding of the pressure balance mechanisms of the buffer film and pave the way for low-cost and low-pressure sintering bonding.