Within a few years time, silicon carbide (SiC) and galium nitride (GaN) power devices will be used in a wide-range of applications for both industrial and military purposes. The ability to operate in harsh environments makes the technology immediately attractive for military motor drive applications (electric-hybrid vehicles, jet turbine units, electric actuators, etc.), industrial deep earth geological exploration (such as deep well seismic sources and on-site instrumentation), and commercial electric vehicles (in conjunction with advanced fuel cells and battery sources). Beyond these applications, cost will become the driving factor behind the use of wide bandgap power electronic drives. Any electrical motor that would see improvement in performance through the integration of the electronics and motor into a single assembly would benefit. Higher temperature, harsher environment electronics means wide bandgap devices integrated with motors would improve reliability, reduce cost, reduce weight, reduce complexity, and reduce size. The potential commercial benefits are enormous. All of these applications require the development of multichip power modules (MCPMs).
APEI, Inc. leads the state-of-the-art in high density power electronics research design, evidenced in part by our patented MCPM technology, protected by U.S. Patent #6,462,976. The MCPM approach is a power electronics packaging strategy which extends the concept of multichip modules (MCM) to high power electronics assemblies, with the core idea that the control and power circuitry components are integrated together into a single compact power module.
The MCPM is built in two major stages. The first stage consists of the direct bond-copper (DBC) power substrate, where thick copper plates are directly bonded to either side of a ceramic substrate. The metallization traces on this power substrate are designed specifically for the capability to conduct large amounts of current at high voltages. The high power bare-die SiC devices used above are mounted with a high temperature die attach method directly to the DBC substrate providing an excellent thermal path to the heat spreader. The second stage is the control board. Because of the demanding power and thermal requirements, the power substrate metallization traces cannot be tightly patterned for high density control electronics. Instead, the control board is fabricated from a high temperature multilayer polyimide substrate. The metallization traces on these layers are flash gold plated for improved reliability. The control components are bare-die devices wire bonded with gold wire, surface mount passives, and magnetic components. The control board is mounted to the high power substrate by a high temperature adhesive. The heat spreader of the MCPM is a metal-matrix-composite material), which is a ceramic matrix injected with a metal. These heat spreader materials offer excellent thermal conduction capabilities while simultaneously providing a close CTE match to the DBC ceramic substrate (thus reducing stresses and the chances of thermal cycle / thermal shock failures).