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May 23, 2011

Nano Coated Stencil Wear

With Nano Coating on stencils evolving over the past few years, what is the best method to measure the Nano Coating thickness and how to determine if it degrades over time?

R. W.

Experts Comments

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
Product Support Specialist
Indium Corporation
Brook is Product Support Specialist for PCB Assembly Materials at Indium Corp. With a background in Chemical Engineering and previous experience with conductive adhesive new product development, she provides expertise in choosing the right materials and processes to optimize PCB assembly operations.

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.

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.
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