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December 2012

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Subject:
From:
Joyce Koo <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Joyce Koo <[log in to unmask]>
Date:
Tue, 11 Dec 2012 21:19:25 +0000
Content-Type:
text/plain
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SMT adhesive is not immediate cure. But reflow cured (provide tack for the stuff you want bond, but no stress prior to hit reflow).  UV delay cured adhesive is almost immediate cured. But you will need good light source (possibly, a pair of light guides) and good process control to ensure accurate placement (you can not move a thing after UV zap).  No self centering, leveling etc.  One shot deal if you have guts to deal with it (any warpage issues, or adhesive shrinkage issues on the side- different topic).  I'll go for standard SMT adhesive.  It is more forgiving process and cheaper. My 2 cents. 
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----- Original Message -----
From: Robert Kondner [mailto:[log in to unmask]]
Sent: Tuesday, December 11, 2012 03:35 PM
To: [log in to unmask] <[log in to unmask]>
Subject: Re: [TN] Sugestions for Pre Reflow Component Adhesive

Steve,

 The specified tooling holes are a little loose. I guess I could close up
the holes but the posts do cock slightly. Problem is these will mate into
another board so I want them to be straight. Just a slight cock and the long
pin ends are really out of position. Worse yet they go on an aluminum based
PCB so doing rework takes a lot of heat and is difficult.

 I have used thermosets before but was hoping there was a high temp
"Instant" adhesive.

Thanks,
Bob K.


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Tuesday, December 11, 2012 2:43 PM
To: [log in to unmask]
Subject: Re: [TN] Sugestions for Pre Reflow Component Adhesive

Hi Bob,

I have a question; what are the dual row connectors that you are using that
rock during reflow? Dual row SMT headers usually have no problems sitting
flush and perpendicular to the surface of the board as long as the footprint
is correct. Is it the locating pin that they are pivoting on?

I will agree with everyone about using Loctite chipbonder. I've used 3609 to
keep components from moving during reflow. For instance there were some
D-paks where the lay-out of thermal (or ground pad) wasn't correct for the
part, and the part would center itself over the thermal pad during reflow,
which would pull the leads off their pads and result in no heel fillets. A
dot of 3609 was hand dispensed so that it contacted the body of the part and
the PCB, and it would cure enough before the solder went liquidous during
reflow to overcome the surface tension of the solder and keep the part where
it was placed. The board was later spun to fix that footprint and some
issues.

Steve

-----Original Message-----
From: Robert Kondner
Sent: Tuesday, December 11, 2012 1:04 PM
To: [log in to unmask]
Subject: [TN] Sugestions for Pre Reflow Component Adhesive

Hi,



Can anyone make suggestions on an adhesive to hold down components while
they go through the reflow oven?



I plan on using some SMT dual row .025 posts. I get them with locating pins
but they still rock some. I was thinking of placing a drop of cyanoacrylate
(Super Glue Gel) but that stuff gives off terrible odors at high temps. I
don't think it was designed for reflow temps.



Any Suggestions?



Thanks,

Bob K.







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