Large, High Conductivity Direct-Fill Copper Thermal Vias for High Power Devices

Ultra-large-scale integration of multifunctional high-power-electronic devices place rapidly increasing demands on the heat dissipation capabilities of their high-density packaging that can no longer be accommodated with current thermal management designs and materials. A novel copper thermal via technology is presented that allows the direct formation and integration of large mm-size thermal vias into Printed Circuit Boards (PCBs), ceramic and glass substrates, thus maximizing heat dissipation. Modeling indicates that such a design can achieve a heat transfer coefficient exceeding 3000 W/cm2*K. The novel ActiveCopper material presented here allows for rapid prototyping and the process can be fully integrated into PCB manufacturing. It can be applied via direct dispensing or large area-type stencil printing. The ActiveCopper material exhibits multiple unique features: 1) it comes in a paste form that flows easily allowing for rapid filling of holes of any shape, size and thickness; 2) it sinters to bulk Cu in air at normal reflow temperatures of 200–235°C but can operate at temperatures exceeding 300°C. It can be processed using typical hot-pressing conditions as employed in standard FR4 PCB manufacturing. 3) After fusion, the resulting large via is filled with copper. No other binders are left behind resulting in very high thermal conductivity currently at 364 W/m*K. 4) The material is fully RoHS compliant, safe to handle in air and stored at room temperature. This new materials system enables many new applications and overcomes the limitations of electroplating. One can directly bond and solder to the material; it exhibits high reliability having passed nearly 3500 thermal shock cycles at -55 to +125 °C already.