Effects of X-Ray Radiation on Solid Insulating Materials

In the present work an attempt has been made to study the effects of ionizing radiation such as X-ray irradiation on the electrical properties of solid insulating materials such as FR4 laminates and relate these to concurrent changes in the physical and chemical properties of the above material. FR4 laminates find extensive use as an insulating material in PCB's where HV power supply components are mounted in X-ray generators. In the present work samples of FR4 laminates were irradiated in ambient air with X-rays to different absorbed doses of up to 6.3 times 104 rad. The post irradiation effects on the material shows deterioration in electrical properties such as dielectric strength, dissipation factor, volume resistivity and surface resistivity. Analysis by FTIR indicates that when samples are irradiated in air, it exhibits increase of hydroxyl groups and decrease of all the characteristic infrared bands of the initial chemical functions. SEM photographs show newer defects generated in the irradiated sample. There is also a change in color of the material when exposed to X-rays and this is due to the fact that X-ray initiated free charge gets trapped by the defects/impurities and changes the absorption characteristic of the material. In addition, the decrease in crystallinity and increase in surface roughness was monitored by Differential Scanning Calorimetry and contact type profilometer.