energies Article Study on Insulation Breakdown Characteristics of Printed Circuit Board under Continuous Square Impulse Voltage Quan Zhou 1, Mingqian Wen 1,* , Taotao Xiong 2, Tianyan Jiang 3, Ming Zhou 1, Xi Ouyang 1 and Lai Xing 1 1 State Key Laboratory of Power Transmission Equipment & System Security and New Technology, School of Electrical Engineering, Chongqing University, Chongqing 400044, China; [email protected] (Q.Z.); [email protected] (M.Z.); [email protected] (X.O.); [email protected] (L.X.) 2 State Grid Chengdu Power Supply Company, Chengdu 610000, China; [email protected] 3 School of Electrical and Electronic Engineering, Chongqing University of Technology, Chongqing 400050, China; [email protected] * Correspondence: [email protected]; Tel.: +86-136-784-20200 Received: 22 September 2018; Accepted: 23 October 2018; Published: 25 October 2018 Abstract: The widely distributed interconnects in printed circuit boards (PCBs) easily couple with high voltage under the action of electromagnetic pulses, which leads to insulation failure. In this study, the dielectric breakdown characteristics of four typical PCBs are studied under continuous square impulse voltage conditions. First, the electric field distribution in the four electrode models is simulated with the ANSYS software (ANSYS Maxwell 17.0). Electric field simulation results show the weak area of electric field distribution. On this basis, the possible breakdown patterns of PCB are analyzed. Second, the influence of factors, such as temperature, pulse duty ratio, interconnect insulation distance, and air pressure, on PCB breakdown voltage is studied through a breakdown test on the PCBs. Results show that the discharge between the single-layer electrodes of the PCBs is surface discharge, and the breakdown is that of a “gas–solid composite medium”. Meanwhile, the breakdown of a double-layer PCB is solid breakdown. Finally, scanning electron microscopy (SEM) produced by Tescan (Brno, Czech Republic) is performed to study the carbonization channel after PCB breakdown. SEM results reveal that the PCB carbonization channel is influenced by temperature and pressure in varying degrees. Keywords: PCB; continuous square impulse voltage; electric field simulation; breakdown test; SEM 1. Introduction With the development of high-density, high-integration, multi-function power electronic equipment, the insulating medium between metal tracks and layers on printed circuit boards (PCBs) is facing increasingly severe insulation problems [1]. Moreover, on PCBs in spacecraft power systems, microwave weapons, and other fields, the insulating medium is affected by severe external factors, such as high temperature, low pressure, and electromagnetic pulse interference. Research has shown that high-power electromagnetic pulses can easily couple the metal interconnects in PCBs with high voltages, which can reach nearly thousands of volts, resulting in insulation failure [2,3]. Thus, the influence of PCB insulation design, external environment, electric field form, and other factors on the insulation characteristics of PCBs should be studied systematically to provide theoretical guidance for insulation design and protection. The waveform of electrostatic discharge (ESD), which causes PCB insulation failure in actual operation, is randomly formed. This waveform includes sine, saw tooth, and attenuation sine waves. The insulation damage caused by ESD is thus difficult to simulate Energies 2018, 11, 2908; doi:10.3390/en11112908 www.mdpi.com/journal/energies Energies 2018, 11, x FOR PEER REVIEW 2 of 13 Energies 2018, 11, 2908 2 of 13 tooth, and attenuation sine waves. The insulation damage caused by ESD is thus difficult to simulate directly. At present, the method of device damage threshold in the National Army Standard [4] injects squaredirectly.-wave At present,pulses into the device methods. ofReference devices damage [5,6] show thresholded that in the the breakdown National Army characteristics Standard of [4 ] integratedinjects square-wave electronic devices pulses into under devices. ESD and References those under [5,6 ]continuous showed that square the breakdown-wave pulse characteristics voltages can beof equivalent. integrated electronicIn addition, devices continuous under s ESDquare and-wave those pulse under voltage continuous can be used square-wave to simulate pulse the voltagesimpact ofcan PCB bes equivalent.caused by ESD. 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The ANSYS effects software of temperature, to analyze pulse the weakduty insulationratio, interconnect area and insulation possible breakdown distance, airpatterns pressure of, the and PCBs. breakdown The effects times of on temperature, the breakdown pulse voltage duty ratio, of the interconnect four electrode insulation models distance, were studiedair pressure, through and experiments breakdown times in view on theof the breakdown practical voltageinsulation of the problems four electrode caused models by severe were exte studiedrnal factorsthrough in experimentscomplex environments in view of the. Then practical, the change insulation in the problems morphology caused of byinsulating severe external polymer factors media in betweencomplex PCB environments. electrodes Then,on the the surface change was in the observed morphology and analyzed of insulating through polymer scanning media electron between microscopyPCB electrodes (SEM on) theto explain surface the was formation observed mechanism and analyzed of throughthe carbon scanningization electron channel microscopy in the process (SEM) of PCBto explain breakdown the formation. mechanism of the carbonization channel in the process of PCB breakdown. 2.2. Electrode Electrode Model Model Design Design and and Simulation Simulation Analysis Analysis TheThe designed designed PCB PCB electrode electrode model modelss are are shown shown in in Figure Figure 1.1. 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