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62 The PCB Magazine • July 2016 As represented on the figure above, the XY plane is the plane of the woven glass fibers, while Z is the axis of the thickness of the base material. When examining various datasheets of major dielectric base materials (typ. high Tg glass-epoxy materials), it appears that base ma- terial suppliers use a wide range of methods to measure the thermal conductivity of their prod- ucts. In most cases, it is also visible that anisot- ropy of materials is not considered. Figure 1: Thermal transfer representation in a glass-reinforced material. Table 2 : Some supplier's datasheet extract. A THERMAL CONDUCTIVITY MEASUREMENT METHOD, ADAPTED TO COMPOSITE MATERIALS