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The Effects of Soluble Salts in Dust on Insulation Failure of Printed Circuit Boards
Pages: 114-119
Year: Issue:  11
Journal: Transactions of China Electrotechnical Society

Keyword:  Insulation failuredust contaminationelectrochemical migrationion concentrationwater drop test;
Abstract: With the miniaturization of the electronic devices,the spacing of the circuit patterns on the printed circuit board( PCB) becomes smaller. So the failure of the electrochemical migration( ECM) between lines gets easier. Meanwhile,due to the severe air pollution,dust can be absorbed and deposited on the PCB.The soluble salts in the dust can change the ion concentration in the water film condensed on the PCB,so the insulation failure mechanism and the time to failure( TTF) can be changed. In this paper,the immersion silver finished Y pattern PCB is adopted to study the insulation failure characteristics and the change rule of TTF by the method of water drop( WD) tests,in which the Na Cl solution and the dust solution with different concentrations are prepared. It is found that the insulation failure mechanism on the PCB changes from ECM to ion conduction and the TTF of the insulation failure shows a first decrease,then increase,and at last sharp drop trend as the ion concentration in the salt solution or the dust solution increases. There are three salt concentrations. The soluble salt concentration Capushes ECM of anodic metals to from quickly on PCB; the critical salt concentration Cb transfers the dendrite conduction caused by the ECM to ion conduction on PCB; and the concentration Ccrestrains the ECM fully.
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