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March 2004

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Subject:
From:
Collins Graham <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 4 Mar 2004 15:22:36 -0500
Content-Type:
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text/plain (172 lines)
Hi Cal
Is it a peelable mask, or how are you removing it?

Anyway, you can get fixtures a lot cheaper than that.  I will contact
you off-net with some recommendations.  Don't know of any universal type
fixtures, every board is different...

regards,

Graham Collins
Process Engineer,
Northrop Grumman Canada Corporation
Halifax
(902) 873-2000 ext 6215

>>> Cal Driscoll <[log in to unmask]> 03/04/04 03:56PM >>>
Graham-
Thanks for your reply
I left out some information...this is a No clean Soldering operation.

We went from Gluing to Double sided reflow as the resistor networks
(+50 of
them) were having many many solder short. Our Wave is not a top notch
system...more of a batch system;

A pallet conveyor with a foam fluxer and dual wave.....Not much for
adjustments...Non the less it is what we have at the moment.

I love the idea of a fixture...and had actually started research on
this.....One quote we got was for $1,500 for a single dedicated
fixture.

This is a fair amount of cash for one board type...as we have many many
that
we run.

If you could recommend a universal fixture (if they exist) that would
be
great.


Again Thanks
Cal


-----Original Message-----
From: Collins Graham [mailto:[log in to unmask]]
Sent: Thursday, March 04, 2004 2:39 PM
To: [log in to unmask]
Subject: Re: [TN] Removable masking/ Double sided reflow


Chris
The concerns I'd have would be:
1) any moisture sensitive parts on the bottom side that are getting
stressed by the heat of the wave?
2) what is that quantity of solder masking material doing to your
cleaner?  I'd guess it's clogging your filters if you re-circulate the
media, at best you are dumping a fair bit of material down the drain.
It might make sense to do for a few, but not in any quantity...

I'm sure it's a lot faster, so I can understand why the operator would
want to try it (although we would be unhappy they tried it without
proper pre-checks).

A couple of alternatives that might work better:
 - get fixtures made to mask the bottom side SMT stuff - we do this
and
love it.  No masking, the SMT is paste attached, good times on
building
the boards.
 - or glue the parts on and simply wave 'em so long as there are none
that will suffer from the heat

have fun!

regards,

Graham Collins
Process Engineer,
Northrop Grumman Canada Corporation
Halifax
(902) 873-2000 ext 6215

>>> [log in to unmask] 03/04/04 03:22PM >>>
Hello All-
WOW !!! two postings from me in two days...

Here is the case:
We run a double sided reflow process.
We Print, Place, and Reflow the bottom of the boards..

Then

Print, paste, and reflow the top side.

Since the bottom side is mostly discrete and Resistor networks (unlike
the
one pictured on Steve's Site) it works well.

For the through hole components we hand insert and solder them.


I just went down to the wave soldering room and found the
operator...........

Covering  the bottom side components  with removable masking material
(Chemtronics Brand) and sending the boards through wave.

Once Soldered...he removes the masking and all looks well.


Question(s);
1) Is this an acceptable practice?
2) What documentation is available to support or disclaim this?
3) What reliability issues are there due to any thermal mismatch?
4) Any leaching of masking material into the solder join causing poor
joint
integrity?

Please advise,

Cal

P.s. Steve be a fountain; not a drain...keep up the excellent work

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