Page 24 - PCMI Journal July 2018

David Allen | Emeritus Professor | Cranfield University | UK Photochemical Machining: Where has it come from, and where is it going?
And large companies with in-house production facilities such as:
• Philips (The Netherlands)
• Buckbee-Mears (USA) and
• RCA (USA)
All of which were prominent in the manufacturing of colour TV shadow masks by PCM, together with smaller companies supplying materials (especially photoresists) and etching equipment.
Potential PCM technology of the future: The Future for Etching and Resists
As PCM is developing rapidly in many fields such as device miniaturisation, medical, automotive, aerospace and electro-optical applications, it is important to understand that the process has a viable future and that further technological advances will extend the process capability for applications in new markets including high-tech products.
Questions need to be asked as to how such advances might be made, such as
• Will the metal cleaning processes remain the same?
Perhaps not! Is it essential for the metal cleaning process to be carried out in PCM companies? PCM companies need closer relationships with metal suppliers in my opinion. Why can’t the metal suppliers provide pre-cleaned metals? They are responsible for putting the oils and greases on the metals in the first place! I also believe that there will be an increase in the use of very thin materials. Unfortunately, this can present problems through damage by manual handling and automated transportation in exposure and etching machines. Reel-to-reel PCM could be of immense benefit in damage limitation but the volumes etched need to be substantial for economic success.
• What types of photoresists will be used in practice in the future
Negative-working DFRs are now almost exclusively aqueous-processable to reduce environmental impact by eliminating VOCs from the atmosphere. The availability of both old and new formulations for liquid resists suggests that they still play important roles in PCM applications where very thin materials suffer from traditional stripping (when positive-working resists can be used to advantage) and very high resolution cannot be obtained with negative DFRs.
I believe that corrosion-resistant materials such as titanium will be etched in larger quantities in the future as they are crucial to advance bioengineering and aerospace applications. These metals and alloys can only be etched in aggressive etchants such as hydrofluoric acid (HF). Several new resists (both liquids and DFRs) have been developed based on epoxy chemistry that are particularly resistant to aggressive chemical etchants but, unfortunately, stripping the resist after processing can be challenging.
Issue 131 July 2018 PCMI Journal 23