Damage of Flexible Printed Wiring Board Associated with Lightning Induced Voltage Surges

Damage produced on flexible printed wiring boards (PWB´s) while in service has been found, and examination of them suggests that the damage was caused by flashover from lightning pickup surges. Laboratory simulation of lightning pickup surges on printed wiring circuits produced similar damage, whereas simulated ac power crosses did not. Blackened area between conductors are not burnt but are shown to be due to the presence of a multitude of submicron-sized particles from the discharge site, which are scattered between the copper lines due to the high pressures encountered in the discharge region. Voltage breakdown distributions of some flexible printed wiring circuits have been obtained at various stages of processing (nonbonded and bonded) and with various electrical prestresses (1 kV and 2 kV pulses). The breakdown voltage as a function of the number of discharges was also obtained.