Page 40 - PCMI Journal July 2018
P. 40
David Allen | Emeritus Professor | Cranfield University | UK Photochemical Machining of Aerospace Materials
5/31/18
Mineral acid etchants for aluminium
Typical formulations include:
• Hydrochloric acid solutions: Concentrated HCl : H2O
(1 : 4 v/v ratio) at 22-65°C
• Hydrochloric / nitric acid solutions: Concentrated HCl : Concentrated HNO3 : H2O (10 : 1 : 9 v/v ratio) at 49°C
Commercially-available etchants for etching aluminium thin films
e.g. Microchemicals Aluminium Etchant
Mixtures of
• nitric acid ( to oxidise the Al to Al2O3),
• phosphoric acid ( to solubilise the Al2O3 formed),
and (optionally)
• acetic acid (to act as a wetting agent and buffer for HNO3) and water are effective
but etch rate is typically 0.1μm/min at 28°C (usually too slow for general PCM applications)
Issue 131 July 2018 PCMI Journal 39
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