Materials selection issues for high operating temperature (HOT) electronic packaging

Currently, there are two major drivers for high operating temperature (HOT) electronics in the 135-200°C range. Products with significant heat generation such as power electronics or small portable electronics without space for cooling mechanisms provide a large market segment in the low end of this temperature range. The upper end of the temperature regime is represented by products that are placed into a HOT environment such as distributed sensors and control systems. Use of polymers for packaging in these applications is typically hampered by the low thermal conductivity and thermal degradation resistance of polymeric materials used in low-cost laminate PWB technology. Also, HOT applications generally require exposure to rigorous thermal cycling for power up and down and environmental exposure. Classes of polymeric materials appropriate for the various aspects of electronic packaging at high operating temperatures and -55°C-225°C cycling are discussed. Also, a new electronic packaging technology which uses some elements of laminate, except that circuits are directly deposited on insulated metal substrates, is presented. This packaging has several-fold better thermal conductivity than conventional ceramic or polyimide glued-to-heat-sink HOT packaging, is more mechanically robust than ceramic, is lightweight and compact and can be deposited on 3D surfaces to minimize space requirements. Multilayer circuits with dimensions as small as 50 μm lines and spaces and 75 μm vias are possible, as well as large dimension circuits for power applications. This approach is also more cost effective than conventional HOT packaging