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July 2016 • The PCB Magazine 69 From the above, • Specific heat capacity for 1080 is given by: C p = 825.6 + 3.001T (J kg -1 K -1 ) with T in Celsius. • Specific heat capacity for 106 is given by: Cp = 825.6 + 2.8683T (J kg -1 K -1 ) with T in Celsius. With density ρ, • volumetric heat capacity for 1080 (at 30°C) is ρC p = 2.058 x 10 6 (J m -3 K -1 ) • volumetric heat capacity for 106 (at 30°C) is ρC p = 2.005 x 10 6 (J m -3 K -1 ) Step 2: Z Thermal conductivity by flash method Note: To perform such an optical flash meth- od measurement, one side of the sample has to be black. To do that, one side is covered with an appropriate black paint instead of the carbon sputtering. It was verified by a separate complex method (simulation under COMSOL software) that this black paint does not affect the results. Step 3: XY Thermal diffusivity by transient fin method As described previously, the copper track designed on the sample is connected to a gen- erator to produce a linear heat flux. An infrared camera is placed to measure the temperature of the two distant points and of the sample. Iden- tifying the transfer function allows to compute the thermal diffusivity. Sample preparation Using a standard PCB fabrication process, the samples were manufactured with the rele- vant 1080 or 106 prepregs. A stack-up approxi- mately 200μm thick was built. Hereafter is a picture of the realized sample. Thermal Conductivities Determination The transient fin method is used to deter- mine XY thermal diffusivity. The thermograms (recorded by the IR sensor) give the temperature variation at and distances from the heating Figure 9: Example of theoretical and experimental thermogram by flash method. Figure 10: 106 and 1080 test samples for transient fin method. Table 4: Z thermal diffusivity measurements by flash method. The measured Z thermal diffusivities have been extracted in the following table. Figure 11: Example of thermograms at x 1 and x 2 distances. A THERMAL CONDUCTIVITY MEASUREMENT METHOD, ADAPTED TO COMPOSITE MATERIALS