Can Anodising be used as a Dielectric?
There are several ways of creating alumina. Some are intended for mechanical applications; Nanotherm is designed specifically for electrical use. That requires a very dense layer of alumina, using fine-grain nanocrystals to create an electrically impervious barrier.
Another form of alumina coating is anodising. This has always seemed attractive to developers of thermal applications, but it forms an extremely porous layer, made up of needle-like crystals. This is ideal to provide basic wear resistance and mechanical hardening – which is why it is used on the casing of many electronic devices, such as many of Apple’s iPhone and iPod products. However, that porosity renders is useless for electrical applications, as the porosity creates electrical hazards between the base aluminium and the circuits implemented on the alumina.
As a result, anodising has proven to be a “fool’s gold” in that it has consumed years of development and a fortune in research dollars – but the underlying electrochemical principles make it highly unlikely that such a treatment will ever be cost effective and reliable in electronics.
The contrast with Nanotherm is clear.