Hi
Steve,
I'm afraid you've
got me dead to rights here. After thinking about this, I can't point to
any real problems caused by exposed copper. And
I've carried this idea around for long enough that I don't know how I originally
justified it. In any case, this fear of exposed copper appears to be
outmoded, as IPC-6012, in section 3.5.4.6 allows exposed copper on areas not to
be soldered amounting to 1% of copper area for class 3 and 5% of copper area on
classes 1 and 2. Vertical edges of conductors are allowed to be exposed,
apparently without limit.
So I guess I owe you
a debt of thanks for killing off an old dogma of mine. Maybe we should
just say, "That dogma just won't hunt!".
Regards,
Seth Goodman
Goodman Associates,
LLC
tel 608.833.9933
fax 608.833.9966
Hi
Seth!
The "exposed copper monster" raises it's head again...I'm just
asking, is exposed copper REALLY a bad thing? I've seen many differing
opinions...if it's such a bad thing, how do OSP coated boards survive? How did
the Statue of Liberty survive for 100-years in the elements, acid rain on the
east coast, etc..or the uninsulated telegraph wires strung over the
USA?
Just asking; is exposed copper (other than solderable surfaces
that were intended to be plated and didn't because of dewetting or some other
reason) a REAL problem?
I might think that if the assembly were
subjected to a corrosive enviroment it could be a problem, but then the
assembly should be protected with a conformal coating because the tin/lead
plating is going to suffer as well.
From my understanding about copper
oxidation, copper will oxidise to a certain point and then stop, the oxidation
actually prevents further oxidation. That's the desirable green patina that
one sees on old sculptures. Am I wrong about this?
-Steve
Gregory-
It's too easy for a small scratch to expose
copper and that's
not a good thing. My two cents worth,
anyway.
Regards,
Seth Goodman
Goodman Associates,
LLC
tel 608.833.9933
fax
608.833.9966