Ryan,
Nickel is a barrier to RF and increases loss.
The thicker the Nickel the thicker the barrier even on soldered joints.
Also, many RF Engineers prefer to leave the RF path exposed (uncovered by soldermask).
So we see large runs of exposed ENIG surfaces after processing (assembly).
Also, (again) some houses will do Soldermask after ENIG due to the corrosive (probably not best wording) effects of the ENIG chemistries (if you use a lower quality mask material then it may not survive the ENIG process).
Bottom line is more Nickel means more loss and loss is bad so we use less Nickel.
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: [log in to unmask] [mailto:[log in to unmask]]
Sent: Monday, December 27, 2004 7:53 AM
To: [log in to unmask]; Frank Kimmey
Subject: RE: [TN] Immersion gold specification
Hi Frank,
Why is the Nickel thickness reduced for RF designs? Immersion Gold is
typically done after soldermask, so the traces are still copper, and the
gold pads become covered with solder after assembly. Therefore, the
skin affect wouldn't apply to the nickel.
Ryan Grant
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Frank Kimmey
Sent: Thursday, December 23, 2004 11:31 AM
To: [log in to unmask]
Subject: Re: [TN] Immersion gold specification
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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