The University of Arkansas High-Density Electronics Center has been engaged in power device and power electronic module research and development efforts for more than 10 years. HiDEC has complete processing, packaging, and assembly facilities for developing state-of-the-art power device and power electronic module packages. These facilities are also available for use by industry partners. In 2009, the University of Arkansas, along with Arkansas Power Electronics Inc, Rohm Inc., (Japan) and Sandia National Laboratory, won an R&D 100 award for the world's first 50-kVA, 1200V, SiC-based vehicular inverter drive capable of continuous operation at 250oC shown in Fig. 1. This module utilized SiC power devices on direct-bond aluminum (DBA) and high-temperature silicon-on-insulator (HTSOI) gate drive and control circuitry on our low-temperature co-fired ceramics (LTCC) board. The entire module was fabricated using HiDEC facilities.
High temperature operation enables significant size and weight reduction of power electronic converters. Emerging wide bandgap power devices based on SiC enable the operation of the power electronic module at high switching frequencies as well as temperatures greater than 200 oC. Fig. 2 shows a switching position module consisting of an 8kV SiC SGTO and a 10-kV SiC diode in a Teflon housing for evaluation of a fault-current limiter project funded by the Department of Energy. The multiple 10-mil bond wires needed for carrying the 60 A current are clearly shown along with the five power input/output connectors. Fig. 3 shows the process sequence for the fabrication of a power electronic module. All processing was performed at HiDEC facilities. Besides the direct-bond copper (DBC) substrate, other substrates such as direct-bond aluminum (DBA), and active brazed metal (ABM) ceramics were also investigated. Low-temperature co-fired ceramic substrates were also investigated for very high current (>150 A) power module integration by leveraging full-tape-thickness features and high density vertical interconnect within the LTCC. Figure 4 shows an example of an eight SiC power electronic module for a high-voltage (6 kV) and high current (450 A) application. The eight SiC devices were paralleled to increase its current handling capabilities. At HiDEC, power modules with up to 48 SiC devices (24 paralleled SiC devices each) on a single substrate were designed and fabricated. Both wire-bonded and wire-bondless power electronic modules were investigated . Several material systems were investigated to enhance the thermal and electrical breakdown characteristics of the power electronic modules [2-7].
To ensure a properly designed power electronic module, the module is first simulated using several FEM simulation tools to evaluate their electrical, thermal, and mechanical properties. Fig. 5 shows an example of the thermal simulation for a wire-bondless power electronic module and the electrical breakdown simulation of a SiC device on a package.
Reliability evaluations of the package and module are also performed at HiDEC. These evaluations include thermal shock and thermal cycling from -55oC to 225oC.