Thermal Properties Evolution of PCB FR4 Epoxy Composites for Mechatronic During Very Long Ageing

摘要

Very long ageing times, up to 8000 h at 110 °C, were achieved on printed circuit boards PCB FR4 Laminate commonly used in automotive design. This composite is fabricated from glass fiber embedded in a flame retardant epoxy resin. Ageing is performed in an oven under air atmosphere at a temperature lower than the glass transition temperature, thus physical ageing must take place. Thermogravimetric analysis indicates that during heating, the flame retardant interacts first with O2 atmosphere for temperature higher than 180 °C. Fourier transform infrared spectroscopic analysis shows that chemical degradation of the samples due to oxidation occurs after ageing at 110 °C for time longer than 940 h. From thermally modulated differential scanning calorimetry analysis, two different modifications of the epoxy resin are evidenced: one fraction for which oxidation modified drastically the molecular structure and one fraction which is not yet oxidized. These two fractions had different molecular mobilities leading to different molecular relaxation processes at the glass transition.