Page 50 - PCMI Journal July 2018
P. 50
David Allen | Emeritus Professor | Cranfield University | UK Photochemical Machining of Aerospace Materials
Issue 131 July 2018 PCMI Journal 49
5/31/18
Standard photoresist processing
• Standard processing is usually not good enough to prevent lifting of the resist and a subsequent very poor (low value) etch factor.
• The fluoride (F-) ion is very small and is able to penetrate through the resist surface and attack the underlying material!
• The ion also seems to attack the material fastest at its interface with the resist layer.
Fundamental requirement: Excellent adhesion of the photoresist to the material to be etched
• PCM of thicker materials implies longer immersion times in the aggressive HF etchant.
• Thicker resist coatings increase resistance to permeability but can also reduce image resolution.
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