Design Constraints for the Use of Insulated Metal Substrates®

Power electronics used in consumer product assemblies require thermal management. Several current products rely on ‘printed wiring’ designs. These have copper patterns separated from a metal substrate by a performance dielectric. The acceptance of this design concept ensures the availability of insulated metal substrates (IMS) for these applications. Available design guides do not describe the design constraints forced on these assembly designs by the physical characteristics of the materials in use. The following three design issues are discussed in this paper: — Dielectric strength testing does not relate to the proof stress testing required for product agency approval. — There is a special case for conformal coating or the use of potting compounds when IMS assemblies are used. — The choice of the metal substrate is based on quantity, thermal coefficient of expansion and thermal conductivity, often in that order.