This is because the thermal tapes do not fill gaps as well as liquids, and thermal joints made with tapes will normally include considerable interstitial air gaps. For the most part, the quality of the two joining surfaces will determine the amount of contact that can be achieved and the thermal performance that can be expected. The high shear strength of these thermal tapes means that reliable joints between heat sinks and semiconductors can be achieved, even with poor surfaces and no mechanical fasteners. Thermal greases and compounds will provide the lowest interface resistance, but they are pastes and require care in handling. Elastomers eliminate handling problems but they sometimes require high compressive loads even with well prepared surfaces.
Thermal tapes offer great convenience but their gap filling properties are limited.
The success of any particular combination of heat sink, interface material and heat sink will depend on the thoroughness of the design, the quality of the interface material and its proper installation. 1 Thermal greases and compounds generally are not electrically conductive. However, they do flow from a thermal joint and allow the joining surfaces to make electrical contact.