Interesting question. The obvious problem with Nano coatings is that they are very thin. You are scraping a sharp metal blade over the surface every time you print, so there will obviously be some ware. This will inevitably lead to the coating being removed. I suppose, if you have not seen an increase in defects, then either the coating is still present or the process is robust enough for it to work on the worn stencil. It would be virtually impossible to identify if the coating is worn down unless it imparts a lower surface tension on the stencil. You could then try to observe the relative wetting of a liquid to see if it spreads in the same way as on a fresh stencil. Anyway, if there are no issues keep using it. If there are issues, it may be worth trying a new one.
Richard Boyle
Global Product Champion, Henkel Electronics
Richard Boyle is a Global Product Champion at Henkel Electronics. He has over 25 years experience in the electronics assembly industry and is responsible for the global technical service of all of Henkel's solder materials.
Good questions I know of no way a user can measure the nanocoat thickness since some nanocoats are only nonometers thick. A reasonable test to see if the stencil still has a nanocaot, is to mark the contact side of the stencil with a magic marker. If you can't easily wipe off the mark the nanocoat may be showing signs of wearing off.
Bill Coleman
Vice President Technology, Photo Stencil
For over 18 years, Dr. Coleman has been the vice president of technology for Photo Stencil, working closely with customers to understand their printing requirements. His efforts have resulted in several new stencil products.
The best way to characterize how the nano-coating degrades over time is by measuring the print transfer efficiency of the stencil over time. To do that, you need to measure the volume of solder paste deposited onto the PCB. By tracking that over time you will know whether the stencil (or print process) has changed in any way. That is the critical data, rather than measuring the nano-coating thickness. Also, even if it was feasible to measure the thickness of the coating (without destroying the stencil), changes in coating thickness that do not effect transfer efficiency probably aren't a concern. I would suggest periodically collecting data on print transfer efficiency and monitoring it over time.
Brook Sandy
Technical Education Program Manager, IPC - Association Connecting Electronics Industries
As manager of IPC’s technical educational program, Sandy-Smith will be responsible for content development and successful execution of IPC’s educational programs and technical proceedings for conferences, webinars, workshops, tutorials and professional development offerings for the electronics industry. She will lead the development and execution of the technical program and professional development curriculum components of the organization’s trade show events, specialty conferences and professional development events.
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