Study On The Effects Of The Representative Substances Of Dust On Failure Mechanism Of The Electrochemical Migration Of Printed Circuit Boards

As the integration density of electronic devices continues to increase,the spacing between the wires of printed circuit boards(PCB)becomes smaller and smaller.The potential risk of PCB insulation failure due to electrochemical migration(ECM)is rising.At the same time,China's air pollution is serious.The dust particles in the air can be attracted to the electronic equipment by gravity and static electricity.The failure mechanism of the ECM becomes complicated.Therefore,studying the mechanism of the representative substances of dust on the ECM failure of PCB has important guiding significance for the design of high-density PCB and the formulation of reliability evaluation schemes.In this paper,the mechanism of ECM failure of PCB caused by dust representative substances is studied.Firstly,the ECM phenomena of PCB under different ion concentration were studied by water drop experiment.At the same time,the components of ECM products were detected.The failure mechanism of ECM of high-density PCB under the influence of soluble salt was obtained,and was verified by experiments using natural dust solution.Secondly,the distribution density of insoluble particles is divided into high and low intervals.Orthogonal experiment and range analysis are used to study the effect of insoluble particles,temperature,humidity and bias voltage on the insulation failure time of circuit board surface.Finally,the experimental method of interaction between soluble salts,insoluble particles and environmental factors was explored,so as to simulate the ECM failure of PCB under dust.Under the influence of soluble salt(NaCl),Cu and a small amount of Ag are the main components in the dendrites produced by ECM.The role of Cl-in droplets is to destroy the oxide film on the surface of the anode and promote the dissolution of the anode metal.The increase of solution concentration makes the failure mechanism change from ECM failure to ionic conduction failure.At this time,metal ions react with anions to form precipitation,which consumes metal ions migrating to the cathode.When the anion is consumed completely,the metal ions of the anode continue to migrate to the cathode to form dendrites.In the case of insoluble particles(SiO2)with low distribution density,temperature increases the electrochemical reaction and saturated vapor pressure,which accelerates the failure of ECM,so temperature has the greatest influence.The significance is temperature>voltagedistribution density>relative humidity.In the case of high distribution density,the barrier effect of dust particles with higher distribution density on water is greater than that of water adsorption,and the effect of relative humidity is the most significant.So the order of significance is relative humidity>distribution density ≈ temperature ≈ voltage.In addition,the dielectric properties of insoluble particles change the electric field distribution between the two poles,which results in the relationship between the failure time and the voltage no longer conforming to the Ahrrinius equation.Finally,by dropping a certain concentration of soluble salt solution on the circuit board and drying the circuit board,the surface of the circuit board is evenly distributed with soluble salt.The insoluble particles are then dispersed freely on the surface of the circuit board through a sieve.The temperature,humidity and voltage are provided by the temperature and humidity box and the voltage regulator respectively.This method can control each variable separately,and has certain feasibility.