Page 49 - PCMI Journal July 2018

David Allen | Emeritus Professor | Cranfield University | UK Photochemical Machining of Aerospace Materials
5/31/18
Limits of exposure to gaseous HF
• Irritation to nose and throat occurs at 3ppm.
• OSHA (Occupational Safety & Health Administration) PEL
(Permissible Exposure Limit) = 3ppm (for an 8 hour shift)
• OSHA STEL (Short Term Exposure Limit) = 6ppm (for 15 minutes)
• IDLH (Immediately Dangerous to Life and Health) = 30ppm
Technical challenges
The aggressive nature of HF etchants means that
challenges exist in the PCM process, namely:
• Chemical resistance of an HF-compatible photoresist
• Excellent adhesion of such a resist to the material to be
etched
• Use of HF-corrosion resistant materials in etching machines
• Additional safety features in etching machines intended for use with HF
Issue 131 July 2018 PCMI Journal 48
5