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16 The PCB Magazine • December 2017 ly by etching), a metal baseplate that enhances the thermal performance of the substrate, and a dielectric layer that insulates the circuit foil electrically from the baseplate. The IMS baseplate is typically either cop- per or aluminum. Selection can depend on factors such as the required thermal capacity and conductivity, which can affect size, weight, and cost. Copper has higher thermal conduc- tivity and a lower coefficient of thermal expan- sion (CTE) than widely used aluminum alloys (Table 1), but is also heavier and more expen- sive. An aluminum baseplate may be deemed more suitable for a cost- or weight-conscious automotive use case, although, if a thin copper baseplate is acceptable then weight and cost can both be lower. New techniques that are important in the automotive and LED-lighting industries, for purposes such as saving space, complying with existing standard form factors, or saving assem- bly costs, include forming IMS assemblies by machining the metal substrate to allow bending into various shapes. Figure 3 shows some of the novel forms that have been produced to solve complex design challenges without requiring multiple boards and the associated fixings and connectors. Compatibility with machining pro- UNDERSTANDING THERMAL MANAGEMENT AND MATERIALS TO BOOST POWER ELECTRONICS RELIABILITY Table 1: Properties of widely used aluminum alloys and copper, as IMS baseplate material. Figure 3: Creative design with IMS allows forming in three dimensions to streamline product assembly while maximizing thermal performance of the circuit board.