How is it possible that, when you dunk a part with an etching mask in a bath of etchent, that the etchent can “know” which direction to work in? Surely, if you already have a pit in a part and it’s filled with somethign that wants to etch the metal, it will etch in all directions equally, because there’s no chemical difference between the side-walls of a pit and the bottom of the pit. Obviously this isn’t the case because anisotropic etching is something that’s used all the time in industry, but I cannot for the life of me understand the process.
In: Chemistry
Anisotropic etching isn’t just bathing the masked material in an etchant. It’s a form of plasma etching, where a pair of electrodes are used to create ions that attack the unmasked material, eroding it away. The ions are created above the material and propelled down onto it. Think of it like standing under and awning while it’s raining; the awning is the mask, and the rain is the ions. It would get you wet if it touched you, but you’re shielded from it.
The current flows between the electrodes, from one to the other. The movement of ions in the solution caused by this current is what etches the line between the two electrodes.
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