----- Original Message -----
Sent: Monday, April 14, 2003 8:32
PM
Subject: [TN] An apology, and a
question...
It seems sometimes that what I post opens a big can of
worms...open mouth, insert foot. I've received some emails directly, that have
put me in my place.
I want to apologize to everyone, and I promise to
leave the list moderation up to the moderator; Jack Crawford.
My hope
is, that my occasional indiscretions can be forgiven. I try to support this
distinguished list with whatever I can do. I just want to say I'm sorry to
everybody.
Now on to my question. I've just recently been confronted
with a big, thick, lots of copper back-plane. It's the same one I posted about
wave soldering just recently. BTW, I was able to get satisfactory topside
fillets by baking the assembly at 100 C., whisking out of the oven to the wave
machine, fluxing the top-side, and hitting it with both the turbulent and
laminar waves.
The next big challenge is rework. Wished we could have
built them without having to rework anything, but we have a few SIP resistor
networks that were put in with the wrong polarity, and it seems almost
impossible to rework these guys without lifting a pad on the bottomside. The
pads have no traces connected to them on the surface layer, and the barrel
looks fine...it's just the annular ring pad is gone. I have a AIR-VAC PCBRM-12
and I've tried to "Pre-heat" things by just placing the area into the nozzle,
for a few seconds, then remove it, multiple times, so as to drive heat into
the laminate, before I attempt the actual removal.
I'm thinking I
probably need to pre-heat the assembly over a fairly large area around where
I'm trying to attempt rework, because the thickness of the PCB, and the way it
sucks heat away from the rework location. I'm learning there is no-way to
rework the PTH on a AIR-VAC the same way we do with .062" boards. I'm thinking
of a laboratory hot plate to pre-heat (that's because I have one
here).
Any tips or help that anyone can share would be greatly
appreciated...
-Steve Gregory- ---------------------------------------------------
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