An Improved Thermal Conductivity Polyurethane Composite for a Space Borne 20KV Power Supply

This effort was designed to find a way to reduce the temperature rise of critical components of a 20KV high voltage power supply (HVPS) by improving the thermal conductivity between the component heat sources and a heatsink external to the encapsulated modules. Three strategies were evaluated by developing complete procedures, preparing samples, and performing tests. The three strategies were: 1) improve the thermal conductivity of the polyurethane encapsulant through the addition of thermally conductive powder while minimizing impact on other characteristics of the encapsulant. 2) Improve the thermal conductivity of the polyurethane encapsulated assembly by the addition of a slab of thermally conductive, electrically insulating material, which is to act as a heat spreader. 3) Employ a more thermally conductive substrate (Al ₂O₃) with the existing encapsulation scheme. The materials were chosen based on the following criteria: high dielectric breakdown strength; high thermal conductivity, ease of manufacturing, high compliance, and other standard space qualified materials properties (low out-gassing, etc.). An optimized cure was determined by a statistical design of experiments for both filled and unfilled materials. The materials were characterized for the desired properties and a complete process was developed and tested