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stencil epoxy debonding

#4367

stencil epoxy debonding | 25 April, 2000

We have quite a few stencils that either are debonding, have debonded, or we suspect will debond when we can least afford for it to happen.

The epoxy is coming loose from the foil, but remains attached to the webbing. All the stencils that are coming apart are from one manufacturer, but they insist that it's our process, i.e., an exceedingly high rinse temp (~110F max., ~75F min., please don't make me explain why). We wash all our stencils @ 75F in a Smartsonic model 5000 for 90 secs., and rinse for 15.

My question on all of this is this: Are there really EPA regulations that allow some stencil manufacturers to use a more high temperature tolerant (but more hazardous) epoxy because of their hazmat controls, and others must use less hazardous (and less temperature tolerant) epoxies because they don't have adequate control of their hazardous material issues? This is what I was told by someone that isn't currently a stencil vendor of ours, but I'm sure he'd like to be.

Is anyone else experiencing this problem, in this fashion, iow, with some vendors but not others?

Thanks, guys.

Steve

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Eric Chua

#4368

Re: stencil epoxy debonding | 26 April, 2000

Hi Steve,

What type of chemical used for washing stencil. Must be take note.

Thanks.

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#4369

Re: stencil epoxy debonding | 26 April, 2000

I knew I was forgetting something. We use Smart Sonic 440-R, a mildly alkaline (ph 12.4 in the concentrate, we dilute to about 10%) detergent that they obviously recommend for use.

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JP

#4370

Re: stencil epoxy debonding | 28 April, 2000

I had a similar problem. We wold begin to notice the debonding within hours after recieving the stencils. As it turned out, our stencil vendor, located in CA, was shipping the stencil to our facility, located in ND, before the epoxy was fully cured.

Under nomally conditions, this wouldn't have caused a problem, but the sub-artic temps we see on ND winter nights was causing the epoxy to freeze during shipping, before it fully cured. The result was very brittle epoxy.

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Joe

#4371

Re: stencil epoxy debonding | 1 May, 2000

I have the same equipment and the same chemicals and have had the same problem. The part of the stencil which is glued to the mesh is being destroyed by the ultra sonics in the equipment. The only solution I found is to seal the glued part of the stencil with a coating which can keep those ultrasonic particles out.

good luck.

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Bill Schreiber

#4372

Re: stencil epoxy debonding | 2 May, 2000

There are two primary causes of epoxy adhesive bond failure, heat and over exposure to moisture. Ultrasonic cavitation is a only a mechanical "scrubbing" action on a microscopic level. However, if the adhesive bond is week or has small areas of detachment, ultrasonics will manifest this weekness by driving cleaning solution into this week area.

Please refer to the article on our web site which is written by a leading stencil manufacturer, Richard Clouthier, titled "Improving Print Screen Yields" published by EP&P. He states that wash or drying temperatures above 110 degrees F (43 C)will debond the adhesive because the adhesives are heat cured and the expansion / contraction of the stencil metals will "pull" the scheen away from the frame and metal etched foil. These adhesives are also hygroscopic (absorb water). Long cycle times or "soak" times will swell and weaken the adhesive bond.

Mr. Clouthier's article can be found on the following Web Site: www.smartsonic.com Click on the "Recommended Reading" button.

Hope this helps.

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#4373

Re: stencil epoxy debonding | 2 May, 2000

As I understand it, though, a 90 sec. 75F wash and a 15 second rinse (plus the lift cycle, another 10 secs., perhaps) at a MAX. of 110F isn't supposed to be nearly enough of a swing to swell that epoxy or expand the foil. According to my contacts at SmartSonic, that is. ;-)

Perhaps we have what one would refer to as a secondary cause, for example a less than pristine surface on the foil when the epoxy is applied, or???

Still no comments on the old vs. new epoxy, driven by agency hazmat concerns, grandfathering, and the like, eh? Hmmmm.....

The saga continues....

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