Figure 1. Low-resolution scanning electron micrographs of the exfoliated
graphite platelets for the production of the thermal interface material.
The moderate-resolution scanning electron micrographs of the exfoliated
graphite platelets are illustrated in Figure 2 for the production of the
thermal interface material. It is well known that many electronic
components, and especially power semiconductor components such as
transistors and microprocessors, are more prone to failure or
malfunction at high temperatures [57, 58]. Consequently, the ability
to dissipate heat often is a limiting factor on the performance of the
component. Heat dissipation may be affected by the direct mounting of
the electronic component to a thermal dissipation member such as a cold
plate or other heat sink or spreader. The dissipation member may be a
dedicated, thermally-conductive ceramic or metal plate or finned
structure, or simply the chassis or circuit board of the device [59,
60]. However, beyond the normal temperature gradients between the
electronic component and the dissipation member, an appreciable
temperature gradient is developed as a thermal interfacial impedance or
contact resistance at the interface between the bodies [61, 62]. The
thermal interface surfaces of the component and heat sink typically are
irregular, either on a gross or a microscopic scale [63, 64]. When
the interfaces surfaces are mated, pockets or void spaces are developed
therebetween in which air may become entrapped. These pockets reduce the
overall surface area contact within the interface which, in turn,
reduces the heat transfer area and the overall efficiency of the heat
transfer through the interface. To improve the heat transfer efficiency
through the interface, a thermal interface material may be used to fill
the gap between the heat sink and electronic component to fill in any
surface irregularities and eliminate air pockets. The thermal interface
material may be a pad or other layer of a thermally-conductive,
electrically-insulating material. Even in a direct contact, however, the
processor and the attach block do not transfer heat efficiently, because
the quality of contact between two non-conforming solid surfaces is
typically poor. A thermal interface material may therefore be inserted
between the processor and the attach block in order to enhance the
thermal contact between the two surfaces. Under mechanical pressure, the
soft thermal interface material conforms to the microscopic surface
contours of the adjacent solid surfaces and increases the microscopic
area of contact between the thermal solution surface and the silicon die
surface and therefore reduces the temperature drop across this contact.
The quality of the contact between the processor and the attach block,
or thermal interface material performance, depends on the quality of the
thermal conduction through the thermal interface material and the
quality of contact between the thermal interface material and the two
surfaces. Consequently, a precise material tester capable of providing
precise measurements of thermal interface material performance may be
useful to improve overall thermal solution designs for notebooks and
other devices.