Study on Corrosion Failure Mechanism of Ceramic Optocoupler Under Thermal Stress

摘要

The scope of this paper is to study on corrosion failure mechanism of ceramic optocoupler under thermal stress. With this regard, a failure case for current transfer ratio (CTR) deviates is analyzed. Scanning electron microscopy (SEM) and energy dispersive X-ray microanalysis (EDX) are used to detect the failure position. The SEM study revealed that the passivation layer is the critical factor of chip corrosion by blocking the impurity ions and water vapor into the chip. To find out the weakness of ceramic optocoupler, ANSYS method is used to analyze distribution of internal thermal stress and deformation of material. According to thermal analysis results, the deformation on the passivation layer is higher than surrounding material. Then the failure mechanism of CTR reduction was analyzed. When the passivation layer was destroyed, both SO_2 and vapor in the air entered into device, resulting in corrosion of A1 electrode. By studying optocoupler's failure mechanism, the factors that are affecting the performance electrical parameters under thermal stress for optocouplers are identified.