High-density interconnect substrate with low thermal resistance for GaAs LSI multichip modules

A copper-polyimide multilayer sunbstrate developed for high-density and high-speed application was confirmed to have a great advantage for high power-dissipating GaAs LSI chips through thermal resistance evaluation. 5-mm-square GaAs specimens and the authors´ original chip surface temperature measurement technology based on the diode drop method were utilized to examine the thermal resistance. In spite of the low thermal conductivity of the polyimide, thermal vias formed in the substrate were most effective in keeping the surface temperature of LSI low. The expectedly low junction-to-case thermal resistance of 4.8°C/W was obtained for the substrate having 2.6% thermal vias in the die-attach area. Face down bonded specimens by flip chip interconnect technology, which is the most suitable assembly technique for high-speed multichip modules, were also investigated. Consequently, thermal vias combined with thermal bumps were clearly proved to have a sufficiently positive influence upon decreasing the thermal resistance