Finite Element and Experimental Analysis of Spacer Designs for Reducing the Thermomechanical Stress in Double-Sided Cooling Power Modules

This article addresses the role of metal spacer design in reducing the thermomechanical stress of solder joint in automotive double-sided cooling power electronics modules. The performance and reliability of power modules are becoming increasingly important in electrified vehicles. A double-sided cooling structure has dual heat sinks placed on the top and bottom of the module and is the most promising solution for improving the thermal reliability of power modules. One of the unique components of this structure is its metal spacers, which are responsible for both electrical and thermal conductions via the connecting embedded power semiconductor dies and their top-side substrates. Reported spacers are typically cuboid in shape, providing a relatively large solder-contact area with the power dies. This large contact area is beneficial in reducing the electrical and thermal resistances, but it increases thermomechanical stress and may accelerate the deterioration of die-bonded solders. This article explores the role of three new spacer shapes in reducing the thermomechanical stress of the solder. Their performances are validated using both the finite-element method (FEM) simulations and thermal cycling experiments. In this article, an octagon-surface spacer demonstrates the best solder reliability compared to the two other designs and the conventional cuboid spacer.