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A New Alumina Multi-Layer Substrate for Power Control Unit
Keywords: power circuit, thick conductor, CTE
Kyocera has developed a new alumina multi-layer ceramic substrate called ¡§Power Control Substrate¡¨. With this new technology, both power and control circuits can be combined into one substrate, which will provide a unique substrate solution for automotive power control applications. Typically, power control units are made of two separate substrates. The first substrate is the control, or logic, circuit and the second substrate is power circuit. In many instances, the control substrate is a printed circuit board and the power substrate is a copper-bonded ceramic substrate. With the Kyocera Power Control Substrate, these two separate substrates can be integrated into one ceramic substrate, with the resulting footprint smaller than the two substrates it replaces. To achieve high power handling capability, the Power Control Substrate has a thick conductor called a ¡§Trough¡¨. The trough is composed of tungsten and copper, and it has the same thickness as one ceramic layer, which can range from 0.15mm to 0.20mm thick. To prevent cracking at the ceramic/metal interface, the CTE of the Trough has been matched to the CTE of the ceramic by creating an composite conductor comprising of 55 vol% tungsten and 45 vol% copper. The Trough can be placed either internally, or on the surface of the substrate, and at 0.20mm thick, the Trough can have conductivity as low as 0.25 mƒÇ/sq. Furthermore, with a thermal conductivity as high as 150 W/mK, the Trough provides an effective means of thermal dissipation for power devices. This paper will demonstrate the reliability of the power control substrate after component assembly. The substrate will be exposed to temperature cycling ranging from ¡V40 to 125C, and we will confirm that the Trough will experience no resistance variation, nor lack of adhesion between the metal and the ceramic.
Masamitsu Onitani, Research and Development
Kyocera Corporation
Kirishima, Kagoshim 899-4312,
Japan


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