Thermal-mechanical considerations of a novel power module with high junction temperature

Abstract

Mechanical and thermal analyses are performed for a power module with target junction temperature of 220°C. The initial design of the package consists of six silicon carbide dies with electrical connections traditionally made by wires being replaced by copper clips and flip chip joints. From mechanical simulations, it is found that compliance of the copper clips affect the stress level at the attachment layer. Several clip designs were investigated and results shows that the design with the greatest flexibility will result in the lowest stress at the attachment layer. For properties of the molding compound, the higher the coefficient of thermal expansion (CTE), the larger the attachment stress whereas for molding compound modulus, the attachment stress can increase or decrease, depending on the corresponding CTE. From thermal simulations, it is found that voids at the attachment layer marginally affect the thermal characteristics while thickness and properties of the thermal interface materials (TIM) greatly affect the thermal performance. The findings suggest that when a metallic attachment material is chosen, dimensional parameters and material choices of the attachment material is less critical to the thermal performance. From power cycling analyses, it is observed that the rise in temperature is largely concentrated around the dies which are powered-up.