I do love it when someone asks a question that we are real knowledgeable on.
Thank you.

Tarnish on Copper after stripping is endemic to resist stripping.  It is made
much worse by buildup of Copper in the stripping chemistry.  In other words,
most strippers will not tarnish when new, but begin to tarnish as they are
used, and Copper builds in the sump.

The problem is cureable by using a  resist stripping chemistry with the
proper anti-tarnish in it.  Most resist stripping chemistry has 250 ppm of
Copper when the stripper is dumped.  It is possible to get resist strippers
that will not build up more than 30 ppm of Copper for the same number of
panels stripped, and average less than 2 false defects per 18" X 24" panel.
This has a nice added benefit of keeping the Copper in the rinse waters so
low that they usually do not have to be treated, and can legally be put right
down the drain.

Many stripper chemistry vendors have resolved this issue by simply going to
high volume feed and bleed, thus turning the sump over often, and keeping the
dissolved Copper levels low.  This is great for the chemistry vendor, but
expensive for the PCB fabricator, and not required with the proper
anti-tarnish chemistry.

As you probably have surmised, we are one of the vendors who can supply
resist strippers with the proper anti-tarnish properties.

Rudy Sedlak
RD Chemical Company
[log in to unmask]

##############################################################
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 Gayatri Sardeshpande at [log in to unmask] or
847-509-9700 ext.5365
##############################################################