Abstract :
The thermal stability of polyol-ester-based
thermal pastes is evaluated by weight loss, viscosity and
thermal contact conductance measurements. A high
degree of thermal stability has been attained by using a
half-hindered phenolic primary antioxidant and a
thiopropionate secondary antioxidant. By using either
carbon black or boron nitride particles as the solid
component, a thermally conductive paste with a high
degree of thermal stability has been attained. The antioxidants
cause the residual weight (excluding the
solid component) after oven aging at 200 C for 24 h to
increase from 36 to 97 wt.%. They cause the viscosity
not to increase upon heating and they reduce the
thermal cracking tendency. They do not affect the
thermal contact conductance measured across mating
surfaces that sandwich the paste. The use of a fullyhindered
phenolic primary antioxidant is less effective.
Both carbon black and boron nitride serve as antioxidants
in the presence of either primary antioxidant or
secondary antioxidant at 200 C, though, in most cases,
they degrade the thermal stability in the presence of
both primary and secondary antioxidants, particularly
at 220 C. Below 180 C and in the presence of primary
and secondary antioxidants, boron nitride is particularly
effective in promoting the thermal stability. Boron
nitride paste shows an estimated lifetime of 19 years
at 100 C, compared to 1.3 years for the carbon black
paste, and 0.10 year for commercial polyol-ester-based
Arctic Silver 5. Carbon black paste has a lower tendency
for cracking after heating than boron nitride
paste, due to the low volume fraction of the solid
component.
