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32 SMT Magazine • March 2015 higher in-plane thermal conductivity of CFCC layer the topside Cu weight has less of an ef- fect on the FR4 case, but more effect on the high-k base material cases. Note that Tmax for the FR4 case dropped dramatically with the addition of the 4.5mil thick layer of CFCC but that Tmax for the high-k base materials are about the same. The composite layer greatly improved the performance of the low-conduc - tivity material. Another interesting feature is shown in Fig- ure 6. Here we see that regardless of the CFCC layer thickness, Tmax remains about the same. This implies that a very thin layer of the com- posite core is all that is needed to provide en- hanced heat removal. Increasing thickness of the layer does not affect thermal performance, but will increase mechanical stability and CTE control. Figure 7 is a summary of the data with ½ oz. topside copper and 50 µm dielectric thickness. The base thickness increases along the X-axis. The Y-axis is Tmax. One-half oz. copper is the worst case coverage, approximating patterned topside metal of higher weight. The chart shows a comparison of the materials with and with- out the CFCC materials inserted. The most dra- matic effect is seen in the FR4 case, where the addition of the composite layer reduced Tmax by 35°C. For higher conductivity base layers of aluminum, copper and graphite, the addition of the CFCC layer increased Tmax by 2–5°C. TImE TO DITch hEavY mETaL FOr SOFT rOck? continues Feature Figure 4: Standard stackup. Figure 6: Stablcor ® thickness. Figure 5: Stackup with Stablcor ® . figure 7: Comparison.