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February 2001

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Subject:
From:
Bill Schreiber <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 22 Feb 2001 11:36:41 -0600
Content-Type:
text/plain
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text/plain (191 lines)
On Tue, 20 Feb 2001 10:24:31 -0600, [log in to unmask] wrote:

>Ahne,
>
>1.  We run the stencil cleaner at room temperature - maybe colder when
>water is changed
>
>2.  we use smartsonic 440-R smt detergent made for the cleaner
>
>3.  We use a standard smartsonic ultrasonic stencil cleaner
>
>4.  Production told me they change the detergent when the boards are not
>clean after the cleaning cycle is done.
>     I am not comfortable with this method.  What does everyone recommend
>for changing the cleaning solution?
>
>Tenison Stone
>
>
>
>
>
>"Ahne Oosterhof" <[log in to unmask]> on 02/20/2001 10:06:48 AM
>
>Please respond to <[log in to unmask]>
>
>To:   "'TechNet E-Mail Forum.'" <[log in to unmask]>,
>      <[log in to unmask]>
>cc:
>
>Subject:  RE: [TN] Stencils with glue releasing
>
>
>Good morning Tenison,
>We are in the business of making stencils and have learned a few things
>about glue and how well it holds up.
>The major reasons why glue may let go:
>1) The cleaning temperature is too high. Most glues and epoxies used to
>attach stencil plates to the mesh and mesh to the frame is chosen to
>release
>at temperatures over 140F. I suggest you try to keep your cleaner
>temperature below 120F.
>2) Using a cleaning solution that attacks glues and epoxies. Several brands
>of these materials will dissolve glues, especially when used at high
>concentrations. Never use these materials at concentrations higher than
>recommended by the manufacturer and try to stay well below them if
>possible.
>3) Ultrasonic cleaning ( and sometimes high pressure cleaning) may have an
>impact on glue attachment and may cause a slow, progressive release of some
>glues.
>4) Over time and use the solution in your tanks may change drastically due
>to the addition of the residues you are removing from the stencils. Keep
>track of the contents of the tanks.
>
>Please give me a call to discuss your specific problem and how you can
>resolve it.
>
>Regards,
>Ahne Oosterhof
>A-Laser, Inc.
>(503)641-9428
>
>
>-----Original Message-----
>From:     TechNet [mailto:[log in to unmask]] On Behalf Of
>[log in to unmask]
>Sent:     Tuesday, February 20, 2001 05:35
>To:  [log in to unmask]
>Subject:  [TN] Stencils with glue releasing
>
>Hi everyone!
>
>My problem today has to do with stencils for solder paste printing.
>
>We are having a lot of problems with the glue releasing when we go to use
>the stencil.   Packing tape will hold through the end of the job.  The
>temperature is OK and the time in cleaner is acceptable according to the
>stencil vendor.
>
>We have checkout our stencil cleaner and the parameters on the various
>printers.
>
>We have had our stencil cleaner for many years and only had the problem in
>the last year.'
>
>We have had no luck with the problem and the stencil vendor is also
>confused.
>
>Has anyone had this problem before and found a solution?
>
>Tenison Stone
>Telex Communications
>
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Dear Tenison,

Smart Sonic's 440-R SMT Detergent will last almost indefinately when
cleaning solder paste because the chemisty is not consumed during the
cleaning process like a saponifier is consumed.  However, we recommend the
440-R SMT Detergent be changed every 2 or 3 weeks on a regular schedule.
The reason is for preventative maintenance purposes.  An ultrasonic bath is
a standing pool of water.  Just as if you placed a glass of water on your
desk and checked it 4 - 5 weeks later, the water would be contaminated.  To
prevent outside contamination, or when the wash water is used for cleaning
other applications such as post solder flux from pallets or oven radiators,
the wash water should be changed.  Regular maintenance is more practical
and less expensive than attempting to titrate the concentration or analyze
the solution for contamination.  You only have 2.5 gallons of 440-R SMT
Detergent invested in the bath at a total cost of approximately $45.00. It
is easier and cheaper to just change the wash water and replace it with
fresh solution.  If you are only cleaning solder paste, you will probably
be reluctant to change the wash water after 2 - 3 weeks because it will
look just as fresh and be cleaning just as well as when you started.
However, remember PM is only $22.50 per week if changed biweekly.

As for the release of the adhesive bond, my gress would be someone is
allowing the stencil to "soak" in the wash water.  The adhesives used to
bond the screen to the metal foil and frame are not only heat-sensitive,
they are also hygroscopic (absorb moisture).  A big advantage of the Smart
Sonic Stencil Cleaning Process is that the cleaning time is so short. The
stencil is exposed to moisture for only a couple of minutes.  If a stencil
is allowed to remain in water for long periods of time (more than 10 or 15
minutes is all that is takes sometimes) the adhesive will absorb moisture
and swell.  When dried, the adhesived bond is weakened and will eventually
release.

Rules of thumb: 1) Don't expose stencils to wash water or drying air
temperatures above 120 degrees F. (49 degrees C.) 2) Don't expose stencils
stencils to long wash or rinse cycles and 3) Never allow a stencil
to "soak" in any liquid.

There is an article on our website by Mr. Richard Clouthier (a stencil
manufacturer) "Improving Screen Print Yields", EP&P, July '96. Mr.
Clouthier discusses the various factors affecting a stencil's integrity and
performance.  Go to (www.smartsonic.com) and click on the "Recommended
Reading" button.

If you should have any other questions, please do not hesitate to contact
me.

Best regards,
Bill Schreiber, President
Smart Sonic Corporation
E-mail: [log in to unmask]
Tel: 1(818) 909-6400

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