Richard,

I have done this in a former life with good results on a variety of
boards. And it can be done without a glue dispenser, however you will
then need two screen printers. You first print your paste using a 4 mil
stencil, then print your glue. The glue stencil will be 8-10 mil, with
underside cavities ~6 mil deep to allow clearance of the glue stencil to
the pasted pads. Due to the thickness of the glue stencil, you will
require smaller than normal glue apertures. You also need a glue that
does not string to prevent paste contamination during glue stencil
release. You can then run the board through a standard place and reflow
process, the reflow preheat ramp cures the glue before reflow.
Afterwards, a standard laminar wave will be fine for both your through
hole parts and bottom side discretes.

Mike

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Richard Lepa
Sent: Monday, October 20, 2003 4:35 PM
To: [log in to unmask]
Subject: [TN] SMT Glue and Paste with Wavesolder


Hello Technetters,

We have a very challenging board that has quite a high quantity of SMT
parts on the bottom side, both Rs and Cs and SOICs.  The problem is that
I cannot use the chipwave on the soldering machine because there are
large open areas on the topside of the boards where the solder will
flood through.  Since I can't use the chipwave I get a lot of solder
skips in addition to bridging.


The question is:  Has anyone ever used the glue/paste/place/reflow
process and then used the wavesolder to re-solder the bottomside SMT
parts and solder the thru-hole parts?  Are there any inherent problems
with using this process?  Would this process reduce reliability of the
parts due to increased stress levels and intermetallics.  Your help will
be greatly appreciated.

Thanks,

Richard Lepa
Manufacturing Engineer

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