Determination of the glass transition temperature of electrotechnical prepregs by differential scanning calorimetry (DSC)

Electrotechnical prepregs are used as gluing gasket in the manufacture of multilayer printed circuit boards. These materials are obtained by fiberglass impregnation with a mixture of modified epoxy resins. The glass transition temperature ( T g ) of the cured prepreg is determined by differential scanning calorimetry. This universal approach provides a wide range of instrumental parameters and does not contain numerical values of metrological characteristics. We present a methodology of T g determination taking into account the requirements of GOST and experimental conditions and assess the metrological characteristics of the technique. Cured samples of prepregs produced in Russia and aboard were studied. Thermograms were recorded for two samples of each prepreg. T g was calculated from the transition on the curve of second heating at a rate of 20 °C/min. It has been shown that the relative total error of the method is ±4%. Since in some cases the visible glass transition was not recorded on the thermograms of cured prepregs, a linear approximation of the T g dependence from a high heating rate at which the glass transition is more pronounced to the value of 20 °C/min was carried out. Control of the correctness of the determination was carried on samples for which T g can be confidently determined by extrapolation and traditional experimental-calculation methods. It is shown that both extrapolation and calculation methods lead to the same results within the limits of the analytical error. The obtained results can be used for determining T g of electrotechnical prepregs and incoming inspection of the corresponding product.