Peter: This is not unusual, depending on what type of adhesive you are
using. The isopropyl alcohol can react with the adhesive partially
polymerizing it. This results in a hard pretty much insoluble residue in the
stencil apertures. The same is true if you use it to wipe down a misprinted
board surface. You will end up with "locked in" adhesive on the board.

There are chemicals that will remove the hardened adhesive residue but they
are expensive and a bit hazardous. Dynalloy Inc carries a variety of
stripping chemicals. However unless you have many stencils to clean and are
set up for it, I would recommend just replacing the stencil.

As far as normal cleaning in production, there are a large number of
proprietary solutions available both from the adhesive suppliers and
manufactures of cleaning products. I think you will find that the
manufactures of cleaning products typically have the lower costs but they
will not be as cheap as the IPA. We have used a Petroferm product with good
success. Without knowing exactly what adhesive you are dealing with I'm a
bit hesitant to recommend a particular product.

You should contact a variety of suppliers, I think you will see the cost can
vary significantly from one to another depending on what type of cleaning
chemistry you use. Bottom line is do not use isopropyl alcohol for this
application.

                                                                Regards

Michael Barmuta

Staff Engineer

Fluke Corp.

Everett WA

425-446-4076

-----Original Message-----
From: Peter L. [mailto:[log in to unmask]]
Sent: Thursday, July 31, 2003 9:28 AM
To: [log in to unmask]
Subject: [TN] Stencil Cleaner for SMT adhesive


Technet,

We have been using IPA to clean SMT adhesive off the stencil during the
build and ultrasonic wash after the build. Over time we started noticing
residues of adhesive around the inside walls of the stencil appertures. The
adhesive appeared to be cured and hardened and we tried many ways but were
unsuccessful in removing it (brush with more aggressive solvent, ultrasonic
clean etc.)

We were informed that a specific proprietary cleaner solvent has to be used
to clean the adhesive off the stencil effectively. The down side is a 5X
cost compared to IPA and a 2-5 times slower evaporation rate.

Does anyone have similar experience with cleaning SMT adhesive off the
stencil? What is the common cleaning interval applied during adhesive
printing? (we clean every 5 prints) Any suggestion in methods to
recondition the stencil appertures?


Rgds,
Peter

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