Thermal Interface Materials Reliability and Evaluation

Today’s electronics and modern microdevices generate large amounts of heat. In order to preserve electronic systems so that they operate within their specifications, heat must be spread and dissipated. Proper temperatures are essential to sustain peak performance and reliability.

Thermal interface materials (TIMs) are designed to minimize contact resistance at the interface site. TIMs can be made of many types of material and can be permanent or removable.

Reliability of TIMs

The ideal TIMs have high thermal conductivity, require small contact pressure, have no leakage from the interface, do not deteriorate, and are easy to apply and remove.

When selecting a reliable thermal interface material, several factors must be considered:

Thermal Conductivity and Bond Line Thickness

Thermal conductivity should be considered, but also the possibility of degradation when exposed to harsh environments over long periods of time. Low bond line thickness is often targeted and requires TIMs with low viscosity.

Thermal Contact Resistance

Low thermal contact resistance can be achieved when the TIM has good wetting with the surfaces.

Adhesive Strength

Reworkability and shock/vibration reliability are reliant on the adhesive strength, especially over temperature ranges.

Reworkability

Due to the possible need to remove a heat transfer device for rework, TIMs resilient to stress need to be considered. A TIM with a high adhesive strength may cause deformation during rework.

Apparatus for Evaluating TIMs

Delamination or cracking can take place in a thermal interface material during shock or vibration. Damage to the TIM will result in increased thermal impedance. While visual inspection for damage is needed, the thermal performance must also be tested for reliability.

Although a test performed on the electronic assembly before and after shock does not precisely determine thermal impedance change, it does determine if the TIM’s performance will remain within acceptable reliability levels.