Multichip Modules (MCM) for high current applications are increasingly requested by the industry for applications such as power amplifiers, inverters and DC-DC-converters. The use of traditional thin and thickfilm hybrid substrates for high current applications is limited due to thin metallization layers and relatively high electric resistance of the conductors. Using the DEC (Direct Bond Copper) technology thick copper foils (0.125mm - 0.7mm) are cladded to Alumina or Aluminumnitride. The patterning of the copper is done by a technology similar to processing conventional PCBs. The thick copper conductors provide excellent current carrying capability and heat spreading of power dies attached onto it. The strong adhesion of the copper to ceramic bond reduces the thermal expansion coefficient in the plane to values only slightly higher than those of the ceramic itself (7.2 - 7.6 x 10(-6)). This allows direct die attach of large dies without using TEC controlling layers. As the DEC technology is using copper foils, integrated lead offs can be realized. This technology has been developed by curamik (R) electronics over the last years and is now in volume production. A new via technology combined with integrated leads allow the design of low weight hermetic packages with improved thermal performance. As the resistance of these vias is < 10(-4)Omega, there is practically no current limitation in comparison to glass sealed feed throughs of conventional hermetic metal packages. High end multichip modules with extremely low thermal resistance (<0.03 WW) can be achieved by the integration of 3-dimensional micro channels for liquid cooling underneath the power circuit area. This is potentially a future solution for high speed microprocessor systems also.
