TECHNET Archives

April 2000

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text 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:
From:
James H Moffitt <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 5 Apr 2000 21:04:23 EDT
Content-Type:
text/plain
Parts/Attachments:
text/plain (46 lines)
Steve/Alcon:
- Re exposed copper.  Not a problem per 600, A-610.  Exposed copper just
turns green and as soon as the surface is protected from the environment by
the coating, the oxidation/tarnishing stops.  There has been some conjecture
that exposed copper would lead to metal migration, but as far as I know
neither DOD or anyone else has found a smoking gun to indicate that this has
ever caused or contributed to a field failure.
- History Lesson:  Once upon a time DOD had a bad problem with exposed
Kovar/Alloy-42 (it kept oxidizing and eventually would result in an open
circuit when the lead rusted away from the solder (bad things happen to a
Naval or Marine Corp. airplane and onboard systems in a perpetual salt-fog
environment).  Consequently, DOD prohibited exposed Kovar/Alloy 42.  During
one revision of the Mil-Specs the DOD contractors cried hard times and got
the requirement for optimum inspection lighting (centered at 3000K, e.g.
quartz halogen) deleted (cost too much to have a good light).  Without the
broad color spectrum available with optimum lighting it is difficult or
impossible to differentiate between exposed Kova/Alloy 42 and exposed copper,
so DOD simply said "no exposed basis metal", and didn't really worry about
exposed copper.  For a while industry standards/specifications mimicked the
DOD requirement for no exposed basis metal.  Eventually someone figured out
why the Mil-Stds said no exposed basis metal and then the requirement was
dropped.   Recent industry specifications and standards require neither
optimum lighting or (in some cases) magnification aids.
- Exposed copper (on lead ends and the vertical sections edges of circuit
traces/pads/etc.) should not be considered a problem (as far as I know no
failure mode is/has-been associated with exposed copper).   Exposed copper
due to mechanical, thermal, or chemical attack is another kettle of fish and
must be examined on a case-by-case basis to determine if it constitutes a
defect.
Cheers, Jim Moffitt, Technical Director, Electronics Training Advantage,
Indianapolis IN

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Keach Sasamori at [log in to unmask] or
847-509-9700 ext.5315
##############################################################

ATOM RSS1 RSS2