Aluminum bulk micromachining through an anodic oxide mask by electrochemical etching in an acetic acid/perchloric acid solution

• A new aluminum bulk micromachining through an anodic oxide mask was developed.
• Laser irradiation of anodized aluminum results in the formation of a locally exposed aluminum pattern.
• The anodic oxide acted as a resist mask during electrochemical etching.
• A hemicylindrical microgroove with a flat surface was fabricated by electrochemical etching.
• Free-standing oxides formed by an undercutting were easily removed by ultrasonication.

A well-defined microstructure with microchannels and a microchamber was fabricated on an aluminum plate by four steps of a new aluminum bulk micromachining process: anodizing, laser irradiation, electrochemical etching, and ultrasonication. An aluminum specimen was anodized in an oxalic acid solution to form a porous anodic oxide film. The anodized aluminum specimen was irradiated with a pulsed Nd-YAG laser to locally remove the anodic oxide film, and then the exposed aluminum substrate was selectively dissolved by electrochemical etching in an acetic acid/perchloric acid solution. The anodic oxide film showed good insulating properties as a resist mask during electrochemical etching in the solution. A hemicylindrical microgroove with thin free-standing anodic oxide on the groove was fabricated by electrochemical etching, and the groove showed a smooth surface with a calculated mean roughness of 0.2–0.3 μm. The free-standing oxides formed by electrochemical etching were easily removed from the specimen by ultrasonication in an ethanol solution. Microchannels 60 μm in diameter and 25 μm in depth connected to a microchamber were successfully fabricated on the aluminum.

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