Effects of Die-Attach Voids on the Thermal Impedance of Power Electronic Packages

Thermal runaway is among the major failure mechanisms of power semiconductor packages. Thermal dissipation of power electronics depends on the quality of the solder die-attach, any defects such as voids, and delamination-impede heat dissipation that results in hot spots that can cause thermal runaway and/or a premature device failure. Therefore, investigation of thermal impact due to die-attach defects is indispensable for improved device performance and reliability. In this paper, transient dual interface measurement is used to characterize the thermal path of a power electronic package consisting of an insulated gate bipolar transistor (IGBT) and copack diode. The die-attach defects were identified by X-ray imaging. The impact of voids on thermal dissipation was quantified by junction-to-case thermal resistance and structure function analysis. The junction-to-case thermal resistance (IGBT) values were found to be increasing with the increase in void%. The largest void% instead of the total void% has a greater impact on the thermal dissipation of the devices. However, die-attach voids under the IGBT die have no impact on junction-to-case thermal resistance (diode), suggesting that the copack diode heat path is independent of the IGBT heat path.