TECHNET Archives

February 2002

TechNet@IPC.ORG
Options: Use Monospaced Font
Show HTML Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
Re: BGAs on alternative finishes
From:
Seth Goodman <[log in to unmask]>
Reply To:
[log in to unmask]
Date:
Wed, 6 Feb 2002 00:42:26 -0600
Content-Type:
multipart/alternative
Parts/Attachments:
text/plain (2187 bytes) , text/html (3729 bytes) 
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

  -----Original Message-----
  From: TechNet [mailto:[log in to unmask]]On Behalf Of [log in to unmask]
  Sent: Tuesday, February 05, 2002 9:33 PM
  To: [log in to unmask]
  Subject: Re: [TN] BGAs on alternative finishes


  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

ATOM RSS1 RSS2