A novel active area bumped flip chip technology for convergent heat transfer from gallium arsenide power devices

Superior low noise amplification characteristics have made gallium arsenide power amplifiers attractive for consumer electronics applications, e.g., cellular phones. To reduce the cost of their introduction, many new technical approaches are being pursued in the areas of device design, fabrication and even packaging. The difficulty in dissipating heat from conventionally die-bonded/wire-bonded gallium arsenide power amplifiers forces thinning of finished wafers. There are both yield and environmental issues associated with this operation. A novel lead-free bump technology for active area flip chip bonding of GaAs power amplifiers has been developed (patent pending) in which the heat transfer path from the hot zones in the active area of the device to the heat sink has been shrunk and the bulk of the GaAs itself has been bypassed. Bumped amplifier flip chips bonded to aluminum nitride substrates can dissipate heat fluxes up to 300 watts/cm² with an acceptable rise in junction temperature. By employing this active area bump technology, the junction to substrate thermal resistance has been kept equal to or lower than the conventional wire-bond/die-bond route using wafer thinning. Therefore the requirement for thinning of finished wafers can now be eliminated