Hi Steve,
I had a similar problem with some diodes, and used the "flood" print
option on our DEK printers - don't know about other printers. Have you
tried this? In case you haven't, the flood print will perform two prints,
the first being a normal print with the squeegees in contact with the
stencil to the pressure set in the program. Then, the second print raises
the squeegees a user programmed distance off the stencil, which gives you
a film of adhesive that will provide more adhesive height. This occurs
because adhesive releases quite well from apertures. Effectively, you can
vary the height of the adhesive with one stencil by varying the flood
print height. Note that you will have this increased height on all the
apertures, so you have to watch your 0805's. You may notice some very
peaked deposits from the small apertures.
This process works well with stainless steel stencils - I'm not sure why a
polymer stencil would be recommended. Good luck!
Howard Watson
SMT Manufacturing Engineer
AMETEK/Dixson
Grand Junction, CO
Steve Gregory <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
05/12/03 03:00 PM
Please respond to "TechNet E-Mail Forum."; Please respond to SteveZeva
To: [log in to unmask]
cc:
Subject: Re: [TN] Stencil printing SMT Adhesives...
Hi Joyce!
Went to that link and there really wasn't anything about printing SMT
adhesives there. I did find a Loctite article that describes the process
of printing variable dot heights from a single thickness stencil...from
reading it, it looks very similar to the Cookson article from a while
back.
http://www.loctite.com/electronics/tp_multipoint.html
In that article it also recommends using a polymer stencil. KJ Marketing
in Canada makes polyimide stencils, I tried calling them, but it must be
quitting time already there...I'l try again tomorrow.
Anybody ever try something like this?
-Steve Gregory-
http://216.203.210.37/GregM/S02_Shea.doc
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Monday, May 12, 2003 3:40 PM
To: [log in to unmask]
Subject: [TN] Stencil printing SMT Adhesives...
Hi All!
I've stencil printing adhesives for a while now, but I've run into a
problem with this one assembly. The problem is that on the backside of
this board there are about 30 or so MELF diodes with square endcaps (A
JANTX part), and these parts stand-off the board enough so that the part
doesn't contact to epoxy.
Cookson used to have a good article about stencil design when stencil
printing adhesives, if I remember the article correctly, it stated that
with proper design, you could get the adhesive height taller than the
stencil thickness...I think they took it off their web page because the
article was saying you could get variable dot heights by stenciling the
epoxy, and thus you don't need a Camelot dispenser B^D
I can't increase the stencil thickness, because I'm stenciling epoxy for
0805's, and I'm afraid if I go thicker on my stencil, the epoxy won't
release with the small openings. Does anybody still have that *.PDF? Or
possibly give me some insight to increase the dot height?
I sure would be appreciative...
-Steve Gregory- ---------------------------------------------------
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