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
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.
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.
-----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?
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