低壓電容器之陽極鋁箔腐蝕製程研究

Chemical and Electrochemical Etching of Aluminum Foil for Low-voltage Electrolytic Capacitor

高純度鋁箔（99.989%）經腐蝕或化成過程後，常被用來作為鋁電解電容器的電極材料，而電容量主要是受到鋁箔有效表面積所影響。本研究針對低壓電容器中的陽極鋁箔作電化學與化學腐蝕來擴大表面積增加電容量，並在鹽酸、磷酸、硝酸與硫酸混合液中探討採用不同的電解參數，諸如電流密度、波型、頻率和化學溶液參數，諸如前處理、溶液的濃度和溫度，對低壓化成後之電容量及表面蝕孔分佈的影響。
經研究發現，適當的前處理及電解方式，雖能提高鋁箔表面蝕孔密度，但對低電壓化成後靜電容量的提升卻不明顯。而採取多段腐蝕處理，對鋁箔的表面做發孔、擴孔及衍孔處理後，卻可提高在18.4 V化成10分鐘後的靜電容量到60μF/cm2以上，並達到市場規格。電解過程中，若前段採用高於市頻的600 Hz發孔處理，更能提升表面的蝕孔密度。

High purity aluminum foil after proper etching and forming treatments has been extensively used as the anode of electrolytic capacitor whose capacitance is largely affected by the effective surface area of aluminum foil. In this study, electrochemical and chemical etching treatments were employed to enlarge the surface area and increase the capacitance of aluminum foil. The fabrication parameters included the pretreatment (the kind, composition and temperature of the solution), the electrolyte for chemical and electrochemical etching (single acid vs. mixture of several acids), and the current waveform (current density, frequency and the type of waveform).
Experiment results show that proper pretreatment followed by one-stage electrochemical etching enhanced the population density of the pits. However, the capacitance of the foil after lowvoltage forming treatments was still much lower than that of the commercial foil. In contrast, the foil fabricated by a multistage etching process consisting of the treatments for pit nucleation, growth, and propagation, respectively, had a capacitance of 60μF/cm2, which is comparable to the commercial foil. Finally, the AC current with frequency of 600 Hz was more effective for pit nucleation.