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A High-Temperature, Wide Bandgap Discrete Plastic Package
Keywords: Power Packaging, Silicon Carbide, Plastic Encapsulation
Higher temperature rated electronics are typically limited to ceramic and metal packages. These package formats are, however, more expensive than plastic encapsulated packages due to the higher cost of these materials. Plastic packages are normally limited to 125 to 150 °C due to the lower operating temperature limits of the packaging materials, such as ordinary electronic molding compounds and tin plating. Historically, these temperature ratings are perfectly suited for most silicon devices. More recently, higher operating temperature silicon devices have become more widely available. In addition, other semiconductor materials that can operate at elevated temperatures, such as silicon carbide are able to benefit from high temperature packaging. Low-cost, high temperature plastic packages allow for a higher market penetration of these devices due to the lower cost materials and reduction in assembly time. In this work, a low-cost, high temperature TO-247 format plastic package is presented for 1200 V rated silicon carbide semiconductor devices. The packaged device performance is demonstrated up to 200 °C using these devices. MOSFET and diodes are prescreened, packaged, and then electrically tested after packaging to characterize any effect the packaging has on the device performance. Screening and performance tests included reverse bias voltage blocking, on-state IV curves, gate leakage, on-resistance, transconductance as a function of temperature, and thermal resistance. The performance of these plastic encapsulated devices was compared to typical performance of the same devices in TO-254 metal packages. The discrete device packages were also temperature cycled from -55 to 200+ °C for hundreds of cycles and retested to verify reliability of the packaged devices. These packages utilize nickel plated lead frames and high temperature polymer resins to meet these higher operating temperature ratings. An injection molding press was setup in-house and molds were designed and machined to meet JEDEC standards. Molding profiles were developed for resin candidate materials and parts were injection molded. Important material considerations were the glass transition temperature of the polymer, molding temperature, and voltage blocking and leakage current characteristics of the polymer at temperature. Various polymer resins were evaluated for performance to determine the best material for this application. The result is a plastic package that can house silicon carbide devices up to 1200 V, 50 A, and 200+ °C that can be sold at a much lower price point than metal packaged devices while simultaneously offering equivalent performance.
Chad B O'Neal, Senior Research Engineer
Arkansas Power Electronics International Inc.
Fayetteville, Arkansas

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