Effects of low pressure on tracking failure of printed circuit boards

Abstract

In general, printed circuit boards (PCBs) used in power devices and system operation in low pressure environments are more susceptible to damage from surface discharges. Additionally, repetitive operation of power systems is an important factor leading to tracking failure. Whether the tracking phenomenon at low pressures is different from that at atmospheric pressure needs better understanding to ensure reliable applications. In this paper, studies of tracking failure of PCBs in a low-pressure chamber, are reported for an electrode configuration comprising a pointed end of track close to the side of a track. Test samples were made by printing these tracks onto a glass-cloth epoxy-resin laminate. Experiments were carried out using repetitive unipolar pulses to simulate voltage surges. The ambient pressure was reduced from atmospheric pressure to a very low pressure (0.6 kPa). The time to failure and the cumulative charge passing before failure were recorded as function of the pressure, temperature, pulse interval and insulation distance. The results obtained indicate that the low pressure enhances the breakdown endurance of PCBs and the breakdown phenomena at low pressure are different from those at atmospheric pressure. With the decrease of the pressure, the cumulative charge is increased but the tracking failure is delayed. At low pressures, increasing temperature has little effect on the cumulative charge, but has significant influence on the time to tracking failure.

Surface breakdown of printed circuit board under magnetic field with reduced pressure

“…It results in the increment of the discharge energy that can accelerate the formation of carbonized conductive path [3] . On the other hand, the reduction of the oxygen content strongly inhibits the ignition hence the deposition of the carbonized compounds is delayed [10,11] . It should be mentioned that the discharge energy and the ignition simultaneously contribute to the formation of the path, and the result is determined by the dominant one.…”

Electrical tree characteristics of XLPE under repetitive pulse voltage in low temperature

“…When the temperature decreases to -90 °C, the chemical reaction between oxygen impregnated from air during the fabricated process or produced by the degradation of the XLPE and carbonized products is reduced [41]. More carbonized products are left in the channels, which make the tree channel conductive.…”

Tracking failure of gamma-ray irradiated polybutylene polymers under magnetic field

“…The tracking failure is considered as one originated from the surface discharge [4]. Due to heat energy from the discharge current, molecular chains of the polymer tend to be broken [20], which gives rise to the formation of decomposed carbonized compounds on the surface [1]. Since free carbons of conductive nature are involved in such compounds, they act as an extended electrode that enhances the local field and encourages more intensive discharge [2].…”

“…Once electric field applied between electrodes reaches the breakdown strength of gas, discharge can be introduced onto polymer surface [1]. As sufficiently intensive discharge lasts for a considerable time, the decomposed carbon products, with some parts of the channel carbonized, are progressive and rapidly deposit on the surface [2].…”