Thermally Conductive MgO-Filled Epoxy Molding Compounds

The use of magnesium oxide (MgO) as a filler in an epoxy molding compound (EMC) was considered to identify the maximum thermal conductivity that could be achieved without compromising rheological or processing control and processing flexibility. MgO is an attractive candidate filler for EMCs used in automotive and other applications because MgO is inexpensive, electrically insulative, has relatively high thermal conductivity, is nontoxic, and is a relatively soft filler material meaning it will be less abrasive to surfaces it contacts during its processing and shape molding. A maximum bulk thermal conductivity of 3 W/mK was achieved with a 56% volume fraction of MgO filler. This 56 vol% MgO-filled EMC has a thermal conductivity approximately twice that of traditional silica-filled EMCs with the same volume fraction of filler and has equivalent electrical insulative, thermal expansion, and water absorption characteristics. It is concluded that if a thermal conductivity greater than 3 W/mK is needed in an EMC, then a much more expensive filler material than MgO must be used.