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December 2006

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Subject:
From:
Guy Ramsey <[log in to unmask]>
Reply To:
Date:
Fri, 29 Dec 2006 07:37:34 -0500
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30 micro inches of gold cannot be achieved through ENIG plating. From
Coombs' Printed Circuits Handbook; 

"In this finish a layer of electroless nickel with a thickness of 120 to 240
micro inches is deposited on the copper surface. This is then followed by a
thin coating (2-4 micro inches) of immersion gold. The nickel is a diffusion
barrier to copper and is the surface to which the soldering occurs. The
function of the immersion gold is to protect the nickel from oxidation or
passivation during storage."

Your specifications would require gold electroplate. The nickel thickness
seems to be an order of magnitude too thin. 200-300 micro inches nickel
plated with 30 micro inches of gold would seem to be a compromised gold
thickness intended to have reasonable wear resistance and still allow for
acceptable soldering process results. 

A word of caution. The gold would be too thick for most solder paste -
surface mount applications, resulting in brittle solder connections. We
worked out a rule of thumb some months ago, here on the TechNet. I think the
number was 5 mil stencil - 10 micro inches max gold thickness. I am sure the
thread is in the archives.

This causes some problems in practice because it is difficult to protect the
nickel with a 10 micro inch max on gold electroplate. It is a process thing.

 
 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David Harman
Sent: Friday, December 29, 2006 1:09 AM
To: [log in to unmask]
Subject: [TN] Questions on ENIG VS gold plating

I need some help in understanding.

 

Are specified requirements are emersion gold plate per

Mil-G-45204 type 2, gold plating thickness maximum of .00003 inches (30

micro inches) over minimum of .00005 inches (50 micro inches) nickel for our
PCB

 

Is this a standard that is used widely, any other recommendations? 

 

My supplier has indicated the following.  

The specifications you listed in your e-mail do not apply to the ENIG finish
(Immersion Gold, electroless nickel)

Mil -G- 45204 refers to Electroplated Gold, Type 2 is 99.0% purity

 

IPC 6012B Table 3-2 requirements for ENIG are 1.97 u" minimum immersion gold
and 118 u" minimum of electroless nickel.

 

 

Which is a better specification? What would give better quality /
reliability?  Is there anyway to correlate the two different specifications.


 

Can I correlate ENIG specs, to that of gold plating.?

 

Dave

 

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