Well, now that Jeff has told you about the standard here is a little more.
As Paul says, "it depends"
Though ENIG is a great finish for today's designs there are some definite issues with the latest IPC standard.
Depending on the type of design you may want to modify the callout to fit your requirements.

1. Use standard as a reference for digital designs (remind your fabricator that "black pad" is not acceptable)
2. Reduce the nickel thickness for RF designs as more nickel creates a bigger barrier for the RF to flow.

Personally I callout 3 to 8 microinches of Immersion Gold over 50 to 150 microinches of Electroless Nickel.
But then I am doing high powered, low loss required RF.
Good Luck and have a Happy Holidays
Hope it helps,
FNK

Frank N Kimmey CID+
Principal PCB Designer
Powerwave Technologies Inc
Office 916-941-3159
Fax 916-941-3195
Cellular 916-804-2491

-----Original Message-----
From: Jeffrey Bush [mailto:[log in to unmask]]
Sent: Thursday, December 23, 2004 10:10 AM
To: [log in to unmask]
Subject: Re: [TN] Immersion gold specification


The current ENIG standard is IPC-4552.  The spec on thickness for all
classes is 2 uinch minimum for gold and 118-236 for nickel. 

Jeffrey Bush
Director, Quality Assurance and Technical Support

VERMONT CIRCUITS INCORPORATED
  76 Technology Drive - POB 1890
    Brattleboro, Vermont 05302
      Voice: 802.257.4571.21 Fax: 802.257.0011
           http://www.vtcircuits.com
 

-----Original Message-----
From: David Harman [mailto:[log in to unmask]] 
Sent: Thursday, December 23, 2004 1:01 PM
To: [log in to unmask]
Subject: [TN] Immersion gold specification

Hope the network out here has a great holiday and successful new year.
 
 
I have one last question for this year regarding plating standards and
specifications.  
 
 
I am trying to call out gold immersion specification over nickel on my
PCBA.   My understanding is Mil-G-45204 type ll is no longer a valid
specification. 
 
Is the industry standard  3 micro inches max - 1 micro inch min.  (As
long as the process can be controlled you should not have any nickel
migration.)  Is this correct.
 
 
 
Can some one tell me how I would spec this out on my drawing and what
standard is used in the industry for gold immersion over a an absolute
minimum of .00005 nickel.
 
 
 
 
 
Thanks

David Harman

 

 

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