Why do chemical alumunium etchants (acidic/alkaline) exists? Chemical aluminum etchants were developed for the photo resist masks for ciruciut boards and decorative application on aluminum surfaces. In the photo resist masks primarily acidic etchants were created since alkaline etchants on aluminum are not suitable due to their high alkalinity pH. This resulted in the traditional more common acidic aluminum etchants known as Keller's Etch (mixture of DI Water, Nitric Acid, Hydrochloric Acid , and Hydrofluoric Acid with immersion time of 10 - 30 seconds), Kroll's Reagent (mixture of DI Water, Nitric Acid, and Hydrofluoric Acid with immersion time of 15 seconds), and NanoFab Aluminum Etchant (mixture ratio of 16:1:1:2 of Phosphoric Acid, Nitric Acid, Acetic Acid, and Water) by the University of Alberta, Canada.
The acid etching can be done without heavy smut challenges, particularly on aluminum diecastings. The chemical etch is quicker, safer, and better controlled than traditional milling techniques resulting in better economy of scale. The advantages are many; no surface burrs, application of complex geometries, smooth edge profile, no-heat-affected zones, tight tolerances possible (±10% of Material thickness), and 1:1 apperture aspect ratio possible. The advantages in this paragraph noted above apply to Alkaline Aluminum Etchants as well, which is suitable for precision engineering and light-weight applications in aerospace, automotive and EV sectors.
It should be noted that acid aluminum etchant with an "etch-only" finish is not suitable for enhance corrosion resistance and surface hardness. This is where alkaline etchant role shines. Alkaline etching is commonly used for aluminum treatment especially in applications such as; anodizing, painting, powder coating, and plating. It reduces or eliminates surface imperfections such as scratches, nicks, and extrusion die lines. The process removes the natural oxide layer from the aluminum substrate to create a clean, virgin surface for subsequent treatments. Alkaline etching is essential before anodizing, painting, powder coating, or plating to enhance bonding, corrosion resistance and surface hardness. The subsequent process just mentioned increases the thickness of the aluminum oxide layer, improving its protective properties. Thus by crucial monitoring the dissolved aluminum and sodium hydroxide (NaOH) concentrations during alkaline etching one is able to achieve consistent results.
Spotless™ Al-Etch is an excellent alkaline etchant for aluminum and aluminium alloy substrates. It produces a uniform etch on clean surfaces. The degree of etching can be changed by adjusting time, concentration, and temperature through precision engineering. It has good draining and rinsing properties; reducing drag-out losses and contamination of subsequent processes. For further information on process, equipment, and analysis see TDS and SDS in the document section.
