Category Archives: Thermal Science

One of the basic concepts of electronics cooling is effective transfer of heat from semiconductor devices to the ambient using heat sinks or other cooling technologies. The effectiveness of this approach depends on a systems total thermal resistance, which is composed of discrete thermal resistances on the path of heat from the source to the ambient. One of these resistances is spreading resistance.

Spreading resistance occurs whenever a small heat source comes in contact with the base of a larger heat sink. The heat does not distribute uniformly through the heat sink base, and consequently does not transfer efficiently to the fins for convective cooling. Figure 1 shows a CFdesign^® simulation solution for such an occurrence. The spreading resistance phenomenon is shown by how the heat travels through the center of a heat sink base causing a large temperature gradient between the center and edges of the heat sink.

Figure 1: CFdesign solution showing temperature distribution
at the base of a heat sink

Spreading resistance is an increasingly important issue in thermal management as microelectronic packages become more powerful and compact and larger heat sinks are required to cool these devices. In high heat flux applications, spreading resistance can comprise 60 to 70% of the total thermal resistance.

A good estimate of spreading resistance is required to manage heat effectively using conventional air-cooled heat sinks. There have been a number of theoretical and experimental studies to estimate spreading resistance. Two of the most notable methods belong to Yovanovich et al. [1] and to Gordon N. Ellison [2].

While these extensive studies cover all aspects of spreading resistance, they involve cumbersome infinite series and complicated coefficient terms.  (click the link to read the rest of our article here on our electronics cooling blog)

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