Highly Filled Polymers for Power Passives Packaging

This paper presents a packaging technology for passive devices and characterization results of a demonstrator. Due to high demands on weight, cost and size this demonstrator was chosen to show the potentials of highly filled polymers for packaging solutions in power electronics especially for automotive and aerospace applications. As a demonstrator a choke for a high power multiphase 100kW DC/DC converter was chosen. A highly filled thermal conductive thermo-plastic polymer (TC-polymer) was used to package the choke with high demands on the cooling. The TC-polymer was used to cover the total surface of the ringcore and the copper windings in one injection molding process and to realize an improved heat transport through the polymer towards the water cooled heat sink. Thermal simulations of the power losses prior to the experimental test setup showed the enormous potentials of TC-polymers. Based on these simulations different compounds of highly filled polymers with different filler fractions of 40vol.%, 50vol.% and 60vol.% Al2O3 filler were produced and used to house the choke in an injection molding process. The high filler fraction and the thermal conductivity, which is one order in magnitude higher than unfilled polymers, lead to changed process conditions, compared to standard injection molding, especially with respect to temperature and pressure conditions during the molding process. The research results show restrictions and challenges in the over-molding of chokes with thermal conductive compounds, as well they revealed the viability of solution strategies. After optimizing the process, using non destructive analysis methods for the choke, it became possible to produce inductive devices with a TC-polymer package. An experimental setup with one phase of the power converter was built up to verify the simulation results. The temperature distribution of the inductive device was investigated and documented. The experiments show the extensive potentials of TC-polymers in power electronic applications.