Thermal Design Considerations on Wire-Bond Packages

摘要

Due to their excellent microwave behaviour (low or moderate dielectric loss, highly conductive inks) and theirrnhermeticity, LTCC materials are being widely used for MM1C packaging. The latter is often required to protectrnbare dies against the impact of harsh working conditions on the field. Several applications, such as front endrnmodules for mobile communication or transmit modules for point-to-point systems, require packages with veryrnlow thermal resistance, since up to 70% of the supplied power is converted into heat.rnAlthough glass ceramic materials have a better thermal conductivity compared to organic boards, it is stillrninsufficient. Thermal vias are one way to locally improve the thermal conductivity. However, their dimensions,rnbulk material, arrangement and number of layers have a strong impact on the resulting performance. Heatrnsources (hot spots) on the MMIC, the MMIC thickness and optional heat spreaders need to be included in thernevaluation as well. Previous simulations showed that as many thermal vias as possible should be placed belowrnthe heat source. In addition, thermal vias should be directly located under the hot spot.rnThe whole system with the environment from the bare die to the heat sink has to be taken into account, as wellrnthe heat path in the package. In this investigation various constructions are considered. The principal build-uprnconsists of an Al-plate as heat sink (thermal ground) with a glued PCB on the top, the mounted package and thernbare die as the heat source in the package. A simulation model of a power amplifier TGA9083-SCC fromrnTriQuint was used as a bare die to realize a realistic scenario.rnThe paper considers different thermal concepts by means of simulation. Variables in the studies are LTCCrnmetallization materials, PCB designs and mounting materials for wire-bond packages.rnThe optimal system for lowest thermal resistance is a LTCC-housing with an inserted MoCu-plate which isrndirectly mounted onto the board heat sink.