Page 27 - PCMI Journal July 2018

David Allen | Emeritus Professor | Cranfield University | UK Photochemical Machining: Where has it come from, and where is it going?
A calcium carbonate concentration of 150-300ppm has been suggested as the optimum hardness by [Wilson] and may be modified by additions of Epsom salt.
It can be seen from the above that to make small, but important improvements in imaging quality the use of bespoke water can be a critical factor.
Conclusions
PCM is a manufacturing technique that has developed from the printing industry and not the PCB industry. However, it should be acknowledged that the technique has benefitted from technology applied to the manufacture of PCBs especially with regards to applications of photoresists and the provision of processing equipment such as etching machines. In summary, PCM has had a very interesting history derived from photoengraving and the next few decades of progress should yield an even more cost-effective process for new technology part production and applications that require high resolution at low cost.
Acknowledgements
I wish to acknowledge useful discussions on PCM history with Bob Crutchley (ex-Precision Micro, UK), Peter Engel (Newcut Inc., USA), Bill Fox (Conard Corporation, USA), Alan Gosling (Attewell Ltd., UK), Marcus Heather (Precision Micro, UK), Kirk Lauver (Chemcut Corporation, USA), Ken Marino (Orbel Corporation, USA), Hugh McCallion (ex-Photofabrication (Services) Ltd., UK), Chester Poplaski (ex-Newcut Inc., USA) and Yasuhiro Ueda (ex-Hirai Seimitsu Kogyo Co. Ltd., Japan).
References
Allen D.M., Photochemical Machining and Photoelectroforming, ISBN 978-1-5262-0188-1, 2016, Frontispiece.
Allen D.M., Photochemical Machining for Micro Parts, Chapter 3.21 in Design for Advanced Manufacturing: Technologies and Processes, (Ed. LaRoux Gillespie), McGraw-Hill Education, ISBN 978- 1-259-58745-0, 2017, 353-9.
Borth P., Photoengraving, on-line Encyclopædia Britannica, accessed 2017. Bridges K., Optimising the Dry Film Process, PCMI Journal, 109, June 2008, 15-18.
Bridges K., “Imaging of Photoresists” lecture in “Understanding Photochemical Machining: Part 1”, a Cranfield University Short Course directed by Prof D.M. Allen, July 10th-12th, 2007.
DeForest W.S., Photoresist Materials and Processes, McGraw-Hill, ISBN 0-07-016230-1, 1975.
Hepher M., The Photo-Resist Story – from Niépce to the Modern Polymer Chemist, The Journal of Photographic Science, 12, 1964, 181-190.
Issue 131 July 2018 PCMI Journal 26