Gap Pad TIMs for Variable Stackup Heights

Thermal pads are solid, elastomeric sheets designed to accommodate significant variances in stack-up height. Their inherent compressibility allows them to conform to uneven surfaces and fill gaps effectively. Typically ranging from 0.5mm to several millimeters in thickness, thermal pads provide a straightforward solution to bridging larger gaps without compromising mechanical integrity.

There are four important things to remember when selecting pads for stackup variations.

1.?????? High Compressibility: Select thermal pads with high compressibility to manage large variations in stack-up height. Compressible pads can fill larger gaps and adapt to different component heights effectively. The tradeoff for higher compressibility will be higher thermal resistance. Care must be taken during assembly so compression rates don’t exceed maximum PSI ratings.

2.?????? Surface Conditions: The surface finish of the mating components determines how well the TIM wets the surface. Those with rougher microscopic surface irregularities require softer, more compressible gap pads. Again, the trade-off is reduced thermal conductivity. Machining, grinding, or lapping are secondary operations that improve surface conditions, allowing more thermally conductive TIMs to be used.

3.?????? Material Selection: Choose materials like silicone-based pads or phase change materials that can handle the required height variations while maintaining good thermal performance. For some applications, such as optics, silicone outgassing from the TIM will be a problem with certain TIMs. In these cases, silicone-free pads such as those using polyurethane should be considered.

4.?????? Testing and Validation: Test the thermal pads under real-world operating conditions to ensure they can handle the expected stack-up height variations. Validate their performance in terms of thermal resistance and mechanical stability.