Figure 7. Effect of pressure on the bond line thickness of the thermal interface material for smooth surfaces for graphite platelets and carbon black.
The effect of pressure on the bond line thickness of the thermal interface material for rough surfaces is illustrated in Figure 8 for graphite platelets and carbon black. Typically, information handling systems include a plurality of thermal conducting members such as, for example, processors, integrated heat spreaders, heat sinks, heat transfer dies, and a variety of other thermal conducting materials. As the heat production of thermal conducting members, for example, processors, increases, the transfer of heat between thermal conducting members, for example, the processor, an integrated heat spreader, a heat transfer die, and a heat sink, raises a number of issues. Conventionally, a thermal interface material such as, for example, a thermal grease, a phase change thermal interface material, and a variety of other thermal interface materials, is used between a plurality of thermal conducting members such as, for example, a processor and a heat sink, an integrated heat spreader and a heat sink, a heat transfer die and a heat sink, and a pair of heat sinks, in order to fill air gaps in the thermal conduction path between the two thermal conducting members. It is optimum to apply an amount of thermal interface material to the interface surfaces between the thermal conducting members such that the thermal interface material engages approximately 100 percent of the interfaces surfaces between the thermal conducting members and completely occupies an interface volume between the thermal conducting members. However, when pressure is applied to engage the thermal conducting members the thermal interface material and then heat is transferred between the thermal conducting members, the thermal interface material thins and spreads across the interface surfaces between the thermal conducting members. This can cause the thermal interface material to flow out of the interface volume between the thermal conducting members and migrate onto, for example, a silicon substrate or a printed circuit board that the thermal conducting members are coupled to. This phenomenon is known as pump out and is accelerated by expansion and contraction of the thermal conducting members during heating and cooling cycles, which results in the loss of the thermal interface material from the interface volume between the thermal conducting members. This can be particularly problematic in some chipsets and processors that include power input pads located adjacent the chipset or processor on the base substrate, as the thermal interface material can migrate out of the interface volume between the thermal conducting members and onto the power input pads, resulting in excessive heating and part failure at the power interconnect. As the thermal interface material spreads in the volume between the first thermal conducting member and the second thermal conducting member, the excess of thermal interface material becomes housed in the channel, preventing the excess of thermal interface material from migrating off of the first thermal transfer surface and onto the sensitive top surface and the electrical contacts. The method then proceeds to the step where heat is dissipated from the heat producing component. The heat producing component is operated and produces heat, which is conducted through the first thermal conducting member, the thermal interface material, and the second thermal conducting member. The fins on the second thermal conducting member allow the heat to be dissipated to the ambient. Consequently, an apparatus and method are provided that allow excess thermal interface material being used to help dissipate heat from a heat producing component to be housed such that the excess thermal interface material does not engage sensitive surfaces in the system that could cause failure in the system.