Package Design of a Double-Side Cooled 20-kV Gallium Nitride Diode Module With Improved Insulation by Nonlinear Resistive Polymer-Nanoparticle Coating

Packaging of medium-voltage wide-bandgap power devices is challenging because the insulation requirement for these devices pushes the common packaging materials to their limits. In an effort to develop packaging technologies for a 20-kV gallium nitride vertical diode, a nonlinear resistive polymer-nanoparticle composite was considered in the package design for improving the insulation capability without trading off the thermal performance. The package has a “sandwich” structure with multiple diodes connected between direct-bond-copper substrates. The package's parasitic inductance per diode is 9.8 nH, thanks to its wirebond-less design. Thermal simulations of the double-sided package resulted in a junction-to-case thermal resistance about 41 % lower than that cooling from one side. The design also included sintered-silver interconnects for higher joint reliability. To reduce electric field stress at electrode triple points on the substrates, which significantly lowers the partial discharge inception voltage of the package, the triple points are coated by the nonlinear resistive composite. It was verified experimentally that the coating increased the partial discharge inception voltage of both the alumina and aluminum nitride substrates from 15.6 kV to 30.6 kV or by 96%.