Two control experiments were also performed: 1) replacing the densified polyimide foam with a more thermally conductive (2×) polyurethane foam; 2) removing the insulating layer using only the graphite heat spreader 14 with a 1 mm air gap between the display plate and heat spreader 14. In all three cases (invention concept vs. control cases), only a slight reduction in the surface temperature of the display plate was observed (<1 C). The chief difference was the impact the treatment had on the reference temperatures of the heat sources 18. Using the case of the 1 mm air gap as the untreated, baseline, the graphite+air gap control sample increased the average resistor temperature by +2.4 C, while the graphite+PU foam case showed a ?0.9 C drop. However, for the case of the graphite+Solimide foam, an 8.5 C temperature drop was observed. These tests were repeated and the findings were consistent.

Typical results demonstrate the change in average resistor temperature vs. time for the different configurations as an indication of the heat spreading performance. Though only a small reduction in temperature was observed, the more interesting result is the larger reduction of heat source temperature when using the polyimide insulating layer 12 vs. heat spreader 14 only w/ an air gap. The additional 8.5° C. drop in temperature comes with no change in the electrical input voltage or current to the heat sources, implying that the heat spreader 14 performs better when backed with the polyimide insulating layer 12.