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July 2016 • The PCB Magazine 67 per track in the middle, and power supply bars on one side. There is no other specific treat- ment required. Temperature variation can be recorder on front side or rear side. In order to ease the centering of the optical sensor on this opposite side, fiducials can be added by etch- ing (photolithography). In that case, the re- sulting copper fiducials should be far enough of the analyzed zone, not to disturb the mea- surements. The transient fin sample has to be connected to a current source, and placed in front of an IR sensor, which will record temperature over time variations, at defined distances from the copper track. To make the measurement easy and repeti- tive, an apparatus is suggested on the next figure. Method to Get XY and Z Thermal Conductivities Step 1 Density and specific heat have to be mea- sured first. Specific heat is measured by differ- ential scanning calorimetry (DSC). Together, density and specific heat give volumetric heat capacity ρC p , considered as isotropic. As this is quite standard, and measuring equipment is commercially available, this will not be de- veloped here. For DSC and density measure- ment, depending on the equipment and speci- fied method for DSC and density measurement, no specific samples are required, usually only a small piece of material. Figure 5: a) Example of experimental and opti- mized theoritical curves T 2 (t); b) Reduced sensi- tivities of T 2 (t) to a (blue) and h (red). Figure 6: Transient fin sample design. Figure 7: Transient fin sample method apparatus example. A B A THERMAL CONDUCTIVITY MEASUREMENT METHOD, ADAPTED TO COMPOSITE MATERIALS