正极性重复脉冲电压下有机硅凝胶-PI界面的沿面放电特性

Surface Discharge Characteristics of Interface Between Silicone Gel and PI Under Positive Repetitive Pulse Voltage

高压大功率绝缘栅双极型晶体管器件(insulated gatebipolar transistor,IGBT)器件封装绝缘问题已成为高压大功率IGBT器件自主研制的关键制约因素之一。由于器件内部芯片终端钝化层处场强较高,导致钝化层最外层的聚酰亚胺(polyimide,PI)与封装材料有机硅凝胶的界面之间易于发生沿面放电,此位置是弹性压接型IGBT器件封装绝缘薄弱的环节。为此面向IGBT正常运行时所承受的正极性重复方波电压工况,建立了有机硅凝胶-PI界面沿面放电特性试验平台,同步采集放电过程中光脉冲信号以及放电脉冲信号,试验中发现有机硅凝胶-PI界面沿面放电在方波上升沿以及方波的高电平区出现了多次正向放电,同时在方波下降沿以及低电平区出现了多次反向放电。基于测量得到的光电倍增管中检测到的光信号与沿面放电脉冲一一对应关系,提出了提取重叠于方波电压上升和下降过程中的位移电流波形中的沿面放电脉冲的方法,实现了沿面放电脉冲的准确提取。在此基础上,分析了沿面放电脉冲的波形参数及放电瞬时电压的统计特性,结果表明,不同电压周期中的沿面放电脉冲时间参数具有统计独立性,即各个周期的沿面放电过程相互独立,随着外施电压升高,放电次数以及脉冲幅值均增加。最后,结合放电脉冲特性,给出了正极性重复方波电压作用下有机硅凝胶与PI材料沿面放电特性的定性机理解释。

One of the key constraints for the independent development of high-voltage high-power insulated gate bipolar transistor(IGBT)devices is high-voltage IGBT device package insulation problem.The interface between the outermost polyimide(PI)of the passivation layer and the encapsulation material,silicone gel,is prone to surface discharge since the high field strength inside the device exists at the terminal passivation layer of the chip,and this location is the weak point in the insulation of the compliant press-pack IGBT device encapsulation.In this paper,an experimental platform of surface discharge characteristics of silicone gel-PI interface is established for the positive repetitive square voltage condition that IGBTs are subjected to under normal operation,and the light pulse signals and discharge pulse signals are collected simultaneously during the discharge process.It is found that the surface discharge of the silicone gel-PI interface shows several forward discharges at the rising edge of the square voltage and the high voltage plateau of the square voltage,and several back discharges at the falling edge of the square wave and the low voltage period.Based on the one-to-one correspondence between the detected optical signals in the photomultiplier and the surface discharge pulses,a method of accurate extraction of the along-plane discharge pulses is achieved,which can be adopted to extract the surface discharge pulses and to overlap the displacement current waveforms at the rising and falling edges of the square voltage.On this basis,the current waveform parameters of surface discharge pulses and the statistical characteristics of discharge instantaneous voltages are analyzed.The results show that the time parameters of surface discharge pulses in different voltage cycles are statistically independent,i.e.,the surface discharge processes in each cycle are independent of each other,and the number of discharges and the pulse amplitude increase with the increase of voltage.Finally,in combination with the discharge pulse characteristics,this paper gives a qualitative explanation of the surface discharge characteristics of silicone gel and PI material under positive repetitive square voltage.