The
key to maximizing the thermal interface performance
of a system is eliminating as much ambient air
as possible from the interface gap. Filling the
gap with a highly conformable, thermally conductive
material is one of the most effective means of
accomplishing this. Using a highly conformable
material can minimize the negative effect of contact
resistance generated by microscopic peaks and valleys
along the heat sink surface while compensating
for surface concavity.Determining
the height of the interface gap is critical, since
maximum thermal efficiency requires that interface
material completely fill the gap to eliminate any
air voids.
However,
when the interface material is thicker than necessary,
the heat is forced to flow through this excess
material to reach the heat sink. This contributes
unnecessary additional thermal resistance to the
system. The effect of interface gap on the interface
thermal resistance is illustrated in the diagram.
This diagram illustrates that the thermal resistance
increases linearly with interface thickness. In
addition, it indicates two important aspects of
thermal interface performance of a system:
1. The plot’s slope is inversely proportional to the
thermal conductivity of the interface material.
2. The plot’s y-intercept is proportional to the contact
resistance of the system.
