Parameter Optimization for Unstable Pin Bonding

Abstract

Abstract Plastic frame power modules with press-fitted or molded pins create challenging bonding conditions. Pin stability variations, from relatively stable to unstable within a single power module, makes it difficult to find process parameters that fit to all pins equally well. Also, tight space, full utilization of the pin surface for bonding and a large number of pins per module makes clamping solutions difficult or impractical. Therefore, we used process optimization to find optimal process parameters for the unstable pin bonds and active process control feature to reduce deformation variance in bonding. The study revealed the importance of the cleaning phase optimization for both sides of the pin stability variations. We found that ensuring a good cleaning phase, typically within first 10ms of the process on the unstable pins, significantly improved the quality of the bonds. Unstable pins tended to lift after bonding with traditional parameters, but demonstrated good shear strength with optimized parameters. Active process control ensured that all bonds reached optimal deformation, regardless of the pin stability. Generally, the best approach to reach good bond quality is to ensure an optimal bonding environment, including clean and stable bond pads. However, when it is not possible or practical to stabilize the bond pad, this study shows that carefully executed process optimization combined with the active process control can lead to robust bonding on unstable pins.