High Aspect Ratio Through-Glass Vias as Heat Conductive Element

In this work metallized Through Glass Vias (TGVs), manufactured by Laser-Induced Deep Etching (LIDE), will be presented as a means to modify the thermal conductivity of glass wafers. Glass, compared to silicon, exhibits superior electrical properties like for e.g. dielectric loss. It has been shown to be a suitable material for hermetic packaging of devices such as microwave emitters. However, the low thermal conductivity of a glass package proves a challenge for high power and continuous operation of active devices due to temperature buildup. The heat which is generated can not be dissipated through the glass as good as silicon (Thermal conductivity of: Silicon 150W/mK; Glass 1,2W/mK). To increase the thermal conductivity of glass packages and to solve issues regarding the operational temperature of ASICs inside a glass package, arrays of copper metallized TGVs can be used as thermal head spreader. Copper has a superior thermal conductivity of about 400W/mK. Aside of using TGVs for signal transmission, high dense TGV arrays are utilized for local increased thermal heat transfer. The benefit of these local heat transfer solution is the avoidance of any thermal cross talk in case of a multi-chip package which is beneficial for temperature sensitive devices like photodiodes, VCSEL or DRAM. Here, we demonstrate how an array of solid-copper-filled TGVs improves the thermal conductivity of a glass wafer both in simulation and experiment. The manufacturing process of the TGVs is illustrated swiftly with reference to prior publications on the subject. The method of copper-filling using a combination of physical vapor deposition and electroplating is explained in more detail. We present the results of our heat transfer simulation and compare them to the obtained experimental results.