Purple discoloration on gold plated boards is due to the formation of
'purple of Cassius', which yu should be able to find out about in your
chemistry books. I believe that it is due to some contamination absorbed
into the resin of the laminate. I remember this problem 15 years ago,
and a change of laminate supplier had the problem go away.

Dougal
Dougal Stewart
Product Development Manager
Viasystems Selkirk Ltd
Selkirk, Scotland, TD7 5EJ
Tel: +44 1750 21601
Fax:+44 1750 22513
email   [log in to unmask]

> -----Original Message-----
> From: [log in to unmask] [SMTP:[log in to unmask]]
> Sent: Tuesday, May 19, 1998 7:00 AM
> To:   [log in to unmask]
> Subject:      [TN] DISCOLORATION
>
> HI ! EVERYBODY
> I HAVE A PROBLEM.
> AFTER I/R REFLOW PROCESS, PCB WAS DISCOLORED AROUND
> GOLD PLATING, ESPECIALLY EXPOSED EPOXY AREA CHANGED
> LIGHT VIOLET.
> THE PCB WAS APPLIED A HASL PROCESS AND EDGE CONNECTOR
> GOLD PLATING. WE TESTED MANY TIMES AND ONLY PCB WHICH
> WAS APPLIED THE HASL PROCESS AND GOLD PLATING PROCESS.
>
> THERE IS LOW PEAK OF Sn BY SEM ANALYSIS ON THE DISCOLORED
> SPECIMEN ONLY.
>
> THE GOLD PLATING CHEMICAL MAKER SAID :
> IF AMINO-COMPOUNDS WHICH IS USED HARDNER OF EPOXY
> MATERIAL JOIN WITH A CYANIDE, PCB CAN DISCOLORATION AFTER
> THERMAL SHOCK.
>
> PLEASE HELP ME WHY THE PCB WAS DISCOLORED AS SOON AS
> POSSIBLE.
>
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