Cu Sinter Pastes for Pure-Cu Die-Attach Applications of Power Modules

In this study, we investigate Cu sinter pastes consisting of coated and dispersed nano- and micro-particles for pure-Cu die-attach applications of Si dies on Cu-plated DCB. The sinter pastes are deposited on wafer level by stencil printing prior to thermal pre-conditioning and die separation. We show the required process conditions for die-attach formation by pressure sintering of Cu pastes in reducing atmosphere at elevated temperatures. We evaluate the quality of the sinter interconnect by mandrel bending, Scanning Acoustic Microscopy (SAM), Scanning Electron Microscopy (SEM) and thermal shock testing (TST). Using a linear regression analysis and putting the results into context with the SEM and SAM analysis, we can show that sinter force and sinter duration are highly influential process parameters, while Cu thickness and a HCOOH pre-cleaning step do not show any significant effect on the joint formation. We further show that on DCB level, the Cu sinter joint can withstand dynamic temperature loading between $-40^{\circ}\mathrm{C}$ and $+150^{\circ}\mathrm{C}$ up to 500 cycles without showing any significant signs of degradation.