We have been using the injection method successfully for several years
(had the exact same problems as you when trying to bond first). We
use a 1/16" hole under the center of the part (2 holes for rectangular
parts). Injecting material (using a 16 ga. needle with the tip cut
off) until it shows on all four sides gives you about 80% coverage.
We use Uralane 7762 (one part adhesive that requires storage at -40°C),
but there are other adhesives that would work. Our PWB packagers
keep complaining about having to route circuitry around the holes, so
we are looking at other options. One of our other divisions deposits
a pattern of spots of bonding material, places the part and reflows.
I don't know the details yet on their process, but they claim that it
works.
Ed Knowles
Materials Engineer
Lockheed Martin Astonautics
_____________________________________
__________________________________________
From: [log in to unmask] on Sat, Feb 15, 1997 2:36 AM
Subject: Re: Assembly
To: Knowles, Ed; [log in to unmask]
You might try Loctite 3609 or Ciba Geigy 7275. We have had some
success with these products curing before reflow in a similar
situation as yours.
Linda Kenison
Vicor
(508)749-7570
______________________________ Reply Separator
_________________________________
Subject: Assembly
Author: [log in to unmask] at Internet
Date: 2/12/97 10:40 AM
I have an application where we are bonding leaded SMT parts (Ceramic &
Plastic QFP and Flatpacks) using a contact adhesive (double-sided)
tape
because it is easy to apply and doesn't require a heat cure.
Unfortunately, the tolerance stack up causes conditions where bonding
cannot be assured. Also, when these adhesive are subjected to the
high
temperature of the convection reflow oven the thickness increases
temporarily causing the part to lift, the solder soldifies, and the
tape
thickness returns to it's original thickness.
We tried changing to a film adhesive, but have not been able to find
one
that could be cured during the reflow solder process. The temperature
profile is not sufficient to cure these materials and we can't subject
the assembly to an oven cure because of the solder paste that has
already been deposited.
Does anyone have an adhesive material that has been demonstrated to
cure
during a typical reflow solder profile, that comes in eather a preform
or a dispensible paste/liquid? Also, does anyone have a similar
situation in which they solder the parts first and then inject
adhesive
through an access hole later, followed by a cure step? If so, how has
it worked out. We don't like to add secondary processes, but I don't
see much alternative.
Thanks, Peter H. Cote
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