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This paper proposes a novel, low-cost high-thermal dissipation molded package. In the structure, power chips are soldered on a Cu plate, which is placed on a newly developed resin sheet. The Cu plate size is designed by FEM to improve heat dissipation. The heat resistance value satisfies the package requirement for thermal dissipation. This paper also focuses on the reliability of the power module. The goal of the thermal cycling test (287 K to 398 K) is 1000 cycles. The maximum size of the power chips is 15 mm×15 mm, and the solder layer fatigue life between the power chips and Cu plate is discussed. By FEM, it is suggested that the mold compound supports the power chip and the strain of the solder decreases to one fourth. In the case when cracks are generated at the interface between the Cu plate and the molded compound, the effect of distortion control decreases. The cracks are found in the interface by acoustic microscope scanning after the thermal cycling test. In order to prevent cracks, many dimples are formed on the Cu plate. As a result of the experimental study, it is confirmed that the reliability of the package is more than 3000 cycles.