【作者】 熊涛涛；

【导师】 周湶；

【作者基本信息】 重庆大学 ， 电气工程， 2018， 硕士

【摘要】 印制电路板(PCB)作为电子产品的核心元件,其绝缘水平直接影响电子产品的安全稳定运行。随着电子设备的高密度化、高集成化、多功能化,PCB互连线线宽、线间距、层间距越来越细微,给PCB线间、层间的绝缘带来了严峻地考验。另一方面,航空电子类产品中的PCB还面临这诸如电磁辐射、高温、低气压等恶劣的外界环境影响。因此,有必要对PCB的绝缘问题开展更深入的研究,为PCB的绝缘设计及防护提供一定的理论依据。论文主要内容有:(1)根据PCB的物理结构及布线方式对PCB线间及层间的绝缘问题进行了分析,设计了四种PCB电极模型,模型包含PCB平行互连线模型(模型a)、PCB互连线拐角模型(模型b)、PCB互连线与焊盘模型(模型c)、PCB相邻层互连线正交模型(模型d),并对这四种电极模型进行了Ansys电场仿真分析,仿真结果表明,模型a、d的电场畸变最大值出现在梯形铜电极片底边夹角处,模型b的电场畸变则出现在电极拐角处的梯形电极底边夹角处,模型c中焊盘边缘处的场强畸变明显大于电极互连线边缘的场强畸变。(2)对PCB的短时耐受电压特性进行了研究,研究结果表明,模型a、b、c、d的击穿电压随互连线间距的增大而增大,随脉冲占空比、脉冲重复率的增大而减小。另一方面,模型a、b、c的击穿电压随温度的增加而减小,且随着气压的降低,三种PCB电极模型的击穿电压均先降低后增大,且对其进行多次击穿试验时,其仍保留一定的绝缘能力。对于模型d来说,其击穿电压随着温度的增加先基本保持不变,后出现线性下降,且其击穿电压不随气压的变化而变化,重复击穿试验时,其在第一次击穿后就基本丧失绝缘能力。(3)结合扫描电镜及能谱仪对PCB击穿后的表面碳化通道进行了定性及定量的分析,分析表明,PCB电极模型a、b、c电极间的绝缘击穿包含两个过程,分别是电极间沿面空气放电击穿和电极间绝缘聚合物碳化析出形成碳化通道。放电过程中产生的热能以及电子发射的撞击作用均会在一定程度上切断PCB绝缘聚合物电介质的分子链,从而加速PCB的绝缘破坏过程,其中热能的积累占据主导作用。另外,温度、气压、电极类型等因素对于PCB电极间的绝缘击穿破坏均有着较大的影响。(4)在常压及低气压下分别对PCB电极模型a进行了电热双应力绝缘加速寿命试验,统计检验中,PCB的电老化失效数据能够很好地符合双参数威布尔分布,采用极大似然估计对威布尔失效模型的形状参数和尺度参数进行了估计,得到了PCB的威布尔特征失效时间。基于此,进一步采用多元线性回归分析得到了PCB的Fallou、Ramu、Crine寿命模型,试验验证表明Fallou模型对电极模型a在常压及低气压下的绝缘寿命均具有优越的拟合性能。更多还原

【Abstract】 The insulation reliability level directly affects the safe and stable operation of the printed circuit board(PCB).With the high density,high integration and multi-function of electronic devices,the line width,line spacing and spacing between PCB interconnects become more and more subtle,which brings severe test to the PCB interline and interlayer insulation.On the other hand,PCB in avionics products always faces harsh environment such as electromagnetic radiation,high temperature,low pressure and so on.Therefore,it is necessary to further study the insulation characteristics of PCB,so as to provide some theoretical basis for insulation design and protection of PCB.The main contents are as follows:(1)This paper designed four PCB electrode models according to the actual insulation problems of PCB.The model includes PCB parallel interconnect model(model a),PCB interconnect corner model(model b),PCB interconnect and pad model(model c),and PCB adjacent layer interconnect orthogonal model(model d).Then,the simulation analysis of the four model are conducted by Ansys,the simulation results show that the model of the electric field distortion of a and d reached the maximum at the bottom angle of trapezoidal copper electrode film,and the distortion of the electric field in the model b appears at the angle of the electrode bottom at the corner of the electrode,what’s more,the field intensity distortion at the edge of the weld plate in model c is obviously larger than the field strength of the electrode interconnects.(2)The short-time durability characteristics of PCB is studied,the results show that the breakdown voltage of model a,b,c,and d increase with the insulation distance and decreases with the pulse duty ratio,pulse repetition frequency.On the other hand,the breakdown voltage of model a,b and c decrease with the increase of temperature,and with the decrease of air pressure,the breakdown voltage of the three PCB models were first decreased and then increased,when repeat the test on same PCB,it still retains the insulation ability.The breakdown voltage of model d changes little with the increase of temperature at first and then decreases linearly.Moreover,the breakdown voltage does not change with the change of air pressure.After repeated breakdown test,the insulation capacity is basically lost after the first breakdown for model d.(3)The surface morphology after PCB breakdown is analyzed qualitatively and quantitatively by SEM and XPS.The analysis shows that the insulation breakdown between the electrodes of PCB electrode model a,b and c consists of two processes,which are the surface discharge and the carbonization of insulating polymers to form carbonization channel.The heat energy produced in the discharge process and the impact of electron emission will cut off the molecular chain of the PCB insulated polymer to a certain extent,and the accumulation of heat energy occupies the leading role.Moreover,the factors such as temperature,air pressure and electrode type have great influence on the breakdown of insulation between PCB electrodes.(4)The accelerated life test of the PCB electrode model a is carried out at standard atmospheric pressure and low pressure,respectively.In the statistical test,the failure data can well accord with the double parameter weibull distribution,then,the weibull characteristic failure time of PCB is obtained by the maximum likelihood estimation.Based on this,the Fallou,Ramu,and Crine life models of PCB are obtained through the multiple linear regression analysis.The experimental verification shows that the Fallou model has superior fitting performance to the insulation life of the electrode model a both at standard atmospheric pressure and low pressure.更多还原