Evaluation of a Novel Dielectric Material for Aluminum Substrates

Thermal management of high heat flux devices such as wide band gap devices, concentrated photovoltaics (CPV), and light-emitting diodes (LEDs) remains a major area of concern. Increases in power density mandate the need for packaging with low overall thermal resistance. This is especially true for light-emitting diodes (LEDs), an industry which many expect to eventually overtake incandescent and fluorescent lighting. Chip-on-board assembly provides minimal thermal resistance as long as a highly thermally conductive substrate is used. Aluminum is a very good heat sink material for this purpose due to its high thermal conductivity (up to 220 W/m-K) and low cost. In order to electrically isolate the substrate, a dielectric base layer must be placed on the aluminum. This material must exhibit good thermal conductivity and breakdown voltage, and must be a close match to the coefficient of thermal expansion (CTE) of aluminum (~25 x 10-6/°C).

This paper compares the performance of a lead-free thick film dielectric material on different aluminum alloys. The reliability of several dielectric properties will be examined, as well as the materials thermal conductivity and bowing deflection.