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Date: | Thu, 21 Sep 1995 09:00:38 GMT |
Content-Type: | text/plain |
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Steve,
We, at GenRad, have just started using a double sided refolw with selective wave
solder with great success. We had the priviledge of stipualting the layout of the
PCB so it was suitable for the process we had in mind.
This involves the same process you use (I assume) but instead of wave soldering
the whole of the underside of the PCB we use a board carrier with appertures
exposing only the through hole components to the solder wave, negating the need
for gluing the SM components. Using this method also closes the process window on
the wave solder process as you only have to solder through hole devices.
If your PCB is well down the design route then this may be of no use whatsoever
but with teamwork and gentle(!) persuation we have managed some major advances in
DFM.
Andy Richardson
Manufacturing Engineer
[log in to unmask]
GenRad UK
From: MX%"[log in to unmask]" 21-SEP-1995 01:08
To: MX%"[log in to unmask]"
CC:
Subj: Solder balls....
From: [log in to unmask]
Date: Wed, 20 Sep 95 11:37:27
Good Day!
I've got a question that is kinda' peculiar that maybe someone can
help me with. We're building products that are double-sided, and due to a
number of reasons (design mostly) we print solder paste on the bottom and
dispense glue as well. The reason we do that is to ensure that we get
good solder fillets on the locations that do not wave well either because
of orientation to the wave direction, or that the locations are shadowed
by other components.
Our customers supplier quality engineer has a concern with solder
balls that are embedded in the glue dots beneath the components...this is
mostly prevalent on 0805 components that I feel is occurring because of
the hot slump that occurs during reflow and the spacing between 0805
pads. We also see it on 1206 components, but not bad as on the 0805
chips.
My question is, should this a really be a concern?...The balls ARE
glued, they ain't going anywhere, and they're not big enough to short any
conductors anyway.
But the quality engineer fears that it could lead to cross-talk if
there is enough of them in one spot that's close to a trace...is he
right? I'm not knowledgeable enough about that stuff to know...BTW, the
board operates at 100mhz...
Thanks in advance!!!
////
| @@ / Steve Gregory
C ) Process Training Engineer
////
\_o Pragmatech Incorporated
| @@ / 101 Nicholson Lane
C ) San Jose, California 95134
\_o ////
[log in to unmask]
| @@ / Phone:(408) 943-1151
C ) Fax:(408)943-1461
\_o
-------------------------------------------------------------
....the views expressed above are my own, not my employers...
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