Determination of Glass Transition Temperature of Electrical Prepregs by Differential Scanning Calorimetry (DSC)

Abstract—Prepregs for electrical purposes are used as an adhesive layer between individual layers in the production of multilayer printed circuit boards. They are materials obtained by impregnating fiberglass with a mixture of modified epoxy resins. The glass transition temperature (Tg) of the cured prepreg is determined by differential scanning calorimetry. This approach is universal, provides for wide boundaries of instrumental parameters, and does not contain numerical values of metrological characteristics. The paper presents a methodology for determining Tg taking into account the requirements of GOST and the conditions of the experiments and an assessment of its metrological characteristics. Cured samples of prepregs of Russian and foreign production were studied. Thermograms were recorded on two samples for each specimen, Tg was calculated based on the glass transition on the second heating curve at a rate of 20°C/min. It is 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 dependence of Tg on high heating rates was done, at which the glass transition is expressed noticeably better to the value of 20°C/min. The control of the correctness of the determination was carried out on samples for which it was possible to reliably determine Tg by the extrapolation and classical experimental-calculation method. It was established that both calculation methods lead to the same results within the limits of the analysis error. The results can be used in determining Tg of prepregs for electrical purposes and incoming inspection of the corresponding products.