TECHNET Archives

November 1997

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:
Robert Welch <[log in to unmask]>
Reply To:
TechNet Mail Forum.
Date:
Thu, 20 Nov 1997 17:17:03 +0000
Content-Type:
text/plain
Parts/Attachments:
text/plain (44 lines)
Roger,

What you undoubtedly are seeing, is the distinctive color of cobolt
used as a hardener in conjunction with the nickel.  Many years ago in
the time of tin/lead IR reflow and poor materials this cobolt stain
would raise it's ugly head.  At another large OEM we had this
condition tested and verified that 1; it was cobolt and 2; that it
created no functional problems other than cosmetics.

The root cause never was fully understood.  It seems to to have been
a combination of over scrubbing the laminate, low resin material
i.e.;  it was particularly prone to attack cheap double-sided work,
and poor rinsing  after gold.  The # one cause seemed to be low gold
bath efficiency, and/or high brightener/hardener levels.

To complicate matters you knew for sure if it was'nt there until
after reflow.  Perhaps the high temp in combination with the
chlorides in the fusing fluid reduces the cobolt from an invisible
valence state down to it's common purple one. I have been able to
make the purple go away in a HOT (175)  STRONG CAUSTIC SOLUTION.
But even this was probably just oxidizing it back to some invisible
state and ruining the material.  Perhaps one of these real chemists
can tell us what the actual states are.

Welcome  Mr. Hamilton and your Quazillion years of
valuable experience.
Robert E. Welch
Process Specialist
Email: [log in to unmask]
Modem: 804-239-9120
Fax:   804-237-3048

##############################################################
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.
For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311
##############################################################


ATOM RSS1 RSS2