Thermal Interface Selection Criteria for Prismatic Battery Modules
Optimal prismatic module thermal interface selection balances bulk conductivity against rheology and compliance to accommodate swelling without dielectric rupture.
Interface Shear Stress
Meaning
Frictional or resistive force per unit area acts parallel to the contact plane between two bonded materials when they experience relative displacement. In thermal management assemblies, interface shear stress arises due to the mismatch in coefficients of thermal expansion between the silicon die and the metal heatsink. This localized stress can degrade the mechanical bond and the thermal path.
It represents a primary driver of mechanical failure in stacked electronic layers.
Stress Generation
Thermal cycling generates varying expansion rates in adjacent assembly layers. When the temperature rises, the metal heatsink expands more than the silicon chip, forcing the intervening adhesive or thermal pad to deform sideways. This deformation creates a shear gradient across the thickness of the joint.
The magnitude of this effect is proportional to the temperature delta and the stiffness of the bonded materials.
Interface Failure
Exceeding the cohesive or adhesive strength of the interface material leads to delamination or pump-out. In grease-like materials, the continuous shearing action forces the compound out of the joint, creating air gaps that increase thermal resistance. For cured adhesives, the stress can cause micro-cracks to propagate along the bond line.
This physical separation disrupts the cooling path and leads to thermal runaway in high-power applications.
Stress Minimization
Selecting low-modulus materials or highly compressible gap pads helps mitigate these shear forces. These flexible compounds accommodate the relative motion without generating high stresses.