The Investigation Of Dust Impact On High Density Circuit

Printed circuit board (PCB) used as electronic components supporting body and electrically connected to the provider has been playing an extremely important role in electronic products, along with the increase of integrated density, device size and pacing becomes smaller and smaller, more and more failures due to electrochemical migration appear. At the same time, the pollution of China’s environment become more and more serious, the sandstorm is more and more frequent, So as to the effect of dust on circuit board has to be taken seriously. This paper studies the influence of dust on the surface humidity and the electrochemical migration of the PCB.Dust consists of two kinds of components:the soluble salt and the insoluble particles. Firstly, the influence mechanism of reduction of PCB’s surface critical relative humidity which caused by soluble salts and delay of water off which caused by insoluble particles was studied by temperature humidity bias (THB) test. Secondly water drop test was used to research the effect of soluble salt concentration on electrochemical migration, and then THB test was used to verify that. Finally, In order to study the influence of natural dust on electrochemical migration, we obtain the PCB samples by using two methods of spraying collected natural dust and natural deposit. Then we complete the water drop test and the THB test at last and it come to a conclusion of the influencing rules of natural dust on PCB.According to this study, we can make the following conclusions:the solubility of the soluble salt has a great influnce on the surface critical relative humidity of PCB. The greater solubility of soluble salts, the easier it is to reduce the critical relative humidity of PCB. The shape of insoluble salt also has great effect on the surface moisture of PCB. The result of water drop test shows that with the increase of salt concentration, the time to failure firstly increased and then decreased. There are two special concentrations at the point of Ca, Cb. Ca is the salt solution concentration when electrochemical migration failure time is the shortest, and Cb is the salt concentration when electrochemical migration just stopped whose calculation method was given in this paper. The natural dust has a comprehensive effect on the electrochemical migration of PCB, it promotes the electrochemical migration, especially the part of soluble salt.