| WEI Xiao-qin,ZHANG Lun-wu,XIAO Yong,WANG Yan-yan,ZHAO Fang-chao,WANG Shi-wei.Corrosion Behaviour and Mechanism of Delay Circuit in High Temperature and Humidity Environment[J],47(7):197-202 |
| Corrosion Behaviour and Mechanism of Delay Circuit in High Temperature and Humidity Environment |
| Received:January 19, 2018 Revised:July 20, 2018 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2018.07.028 |
| KeyWord:Kovar alloy delay circuit high temperature and humidity environment accelerated aging test corrosion behavior corrosion mechanism |
| Author | Institution |
| WEI Xiao-qin |
Southwest Technology and Engineering Research Institute, Chongqing , China |
| ZHANG Lun-wu |
Southwest Technology and Engineering Research Institute, Chongqing , China |
| XIAO Yong |
Southwest Technology and Engineering Research Institute, Chongqing , China |
| WANG Yan-yan |
Southwest Technology and Engineering Research Institute, Chongqing , China |
| ZHAO Fang-chao |
Southwest Technology and Engineering Research Institute, Chongqing , China |
| WANG Shi-wei |
East China Institute of Photo-Electron IC, Bengbu , China |
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| Abstract: |
| The work aims to improve adaptability of delay circuit to storage environment. Laboratory accelerated aging test of delay circuit was carried out at 80 ℃ and 90% RH, and sampling was done on 0, 97th and 133rd day to test electrical properties, analyze outer surface corrosion damage characteristics, test internal defects and extra material, check sealing of shell, locate faulty parts, observe internal chip corrosion damage characteristics and detect corrosion products, and further analyze mechanism of action of high temperature and humidity on delay circuit outer lead - glass interface sealing failure and Kovar alloy substrate corrosion. There was no output waveform at output 3 on the 133rd day of wet-heat aging. With the extension of wet-heat aging time, crevice corrosion at on outer lead - glass interface gradually worsened, Helium leak rate increased monotonically, and shell sealing gradually reduced and even failed. External moisture entered into the delay circuit, the internal chip was defect-free throughout the aging cycle, but extra material appeared in circuit cavity on the 133rd day and lay on lead post edge of the 14th pin which was the failure point of conduction test positioning. Under the action of high temperature and humidity, a corrosion cell was formed due to potential difference between the Kovar alloy substrate and gold-plated layer thereon. Kovar was electrochemically corroded by moisture and oxygen as a cathode, and corrosion products formed and covered the gold-plated surface, which resulted in open circuit between the 14th pin and gold bonding wire, and the delay circuit failed. Therefore, the moisture entering into the circuit can be delayed by reducing humidity of circuit storage environment, while improving production process and forming a layer of dense oxide film transition layer of appropriate thickness on the metal-glass sealing interface. Thicker Kovar alloy gold-plated or nickel-plated layer can reduce probability of occurrence of electrochemical corrosion of the substrate, and improve adaptability of delay circuit to storage environment. |
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