Zoran,

Two things about Au over Ni to note. First of all, over time, Ni will 
diffuse thru gold (mostly along the grain boundaries) and get onto the 
surface where it will oxidize. Enough Nickel oxide on the surface can 
give you solderability problems.  A strong flux may help. The time it 
takes for this to happen depends on the thickness of the gold.  I 
don't have any numbers but 6 months does not seem like a very long 
time.

Secondly, the quality of the gold plating is just as important. If the 
gold has a lot of porosity, Cu and Ni can diffuse to the surface. Try 
a Nitric acid vapor test (gold porosity test) to ensure that porosity 
is not a problem.  Hope this helps. Perhaps others can give you some 
advice on what, if any, flux would work.

Regards,
Paul Terranova
[log in to unmask]
Phone: 508-467-3109
FAX: 508-467-6796


DIGITAL's Analytical and Environmental Test Services Lab
Digital Equipment Corporation
M/S: MRO1-3/D2
200 Forest Street
Marlboro, MA  01752


-----Original Message-----
From:	"MRMTS::MRMTS::MRGATE::\"DASMTS::PMDF::ipc.org::TechNet-request\"  
"@sandz.mro.dec.com 
[SMTP:"MRMTS::MRMTS::MRGATE::\"DASMTS::PMDF::ipc.org::TechNet-request\"  
"@sandz.mro.dec.com]
Sent:	Wednesday, May 28, 1997 11:45 PM
To:	Paul Terranova
Subject:	ASSY:Au/Ni Coated Boards
From:	NAME: Raich, Zoran <[log in to unmask]@PMDF@INTERNET>
To:	NAME: [log in to unmask] <[log in to unmask]@PMDF@INTERNET>


Dear Technetters
We have some printed circuit boards with gold over nickel coating 
which   are experiencing solderability problems, ie very poor wetting. 
I have   heard that this may be due to nickel migration through the 
gold over   time. The boards are approximately 6 Months old. Is there 
a particular   shelf life for this type of coating before we need to 
dump the boards?.
Regards
Zoran Raich
Process Engineer
NetComm (Aus) Ltd
(+612) 9878 7394
[log in to unmask]

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