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January 2002

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Date:
Thu, 31 Jan 2002 08:36:50 -0600
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Good Morning TechNet! Rick, I have a very different perspective on ENIG
than Peter so here is some food for thought. There is a specification for
ENIG  - IPC-4552 - which is in final ballot and should be release in the
March/May timeframe. I recommend getting a copy.  It's my opinion that the
specification is quite useful considering there is no other specification
available for industry use. The ASTM B488 specification is not a workable
solution for electronics applications. There was a great deal of committee
discussion on the electroless nickel plating thickness. The nickel
thickness is very much viewed as application specific, for example,  RF
designers desire minimal thickness (30-50 uinches) as opposed to connecting
applications which use 200 uinches. Rockwell Collins is successfully using
2-5 uninches for the immersion gold thickness and 50-150 uinches for the
electroless nickel thickness in avionics applications and we intend on
using the IPC-4552 specification in our documentation. Additionally, 50
uinches of electroless nickel is very adequate as a diffusion barrier as
both the nickel/copper and nickel/gold phase diagrams demonstrate a wide
range of immiscibility The only instances I have seen a 50 uinch
electroless nickel thickness not be adequate was for pwbs which were
subjected to repetitive thermal excursions (e.g. lots of rework, or 4
reflow passes). Using an immersion gold thickness of 6 uinches will not
guarantee you solderability - the 4552 committee demonstrated that (by
conducting testing) that 2 uinches of immersion gold can be steam
conditioned and still provide expected solderability coverage. Teaming with
your ENIG vendor, understanding their plating process control practices and
requiring some level of solderability testing is the best way of insuring
solderability.  Good Luck.

Dave Hillman
Rockwell Collins
[log in to unmask]




[log in to unmask]@ipc.org> on 01/30/2002 09:03:53 PM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
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Sent by:  TechNet <[log in to unmask]>


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Subject:  Re: [TN] ENIG Thickness Standard?


Rick,

I went through this pain a while ago, and got a lot of tremendous help from
Ingemar Hernefjord in particular. I believe there is no released standard
for ENIG, though there is an empirical spec IPC-4552. It does not contain a
lot of useful detail, though. I specify 5 microinches (0.12 microns) of
Gold over minimum 235 microinches (6 microns) Nickel for my boards, after
reading a number of studies and failure reports. In fact I was recommended
to use 250 microinches of Nickel, but this would have made our boards too
thick. The thicker gold layer minimises porosity and therefore oxidation to
the underlying Nickel layer.

Older thinking was for around 100 to 120 microinches Nickel, but studies by
Eriksson and others concluded that with the growth of gold flashing through
the Nickel from one side and Cu/Ni intermetallics on the other side of the
plating, that a thicker Nickel layer would offer the boards a longer
solderability shelf life and greater solder joint reliability.

Hope this helps a bit. Certainly, I haven't experienced any problems with
soldering or mounting of components on boards to this spec.

Peter




                    Rick Thompson
                    <rthompson@VENTURAELECTR        To:     [log in to unmask]
                    ONICS.COM>                      cc:     (bcc: DUNCAN
Peter/Asst Prin Engr/ST
                    Sent by: TechNet                Aero/ST Group)
                    <[log in to unmask]>               Subject:     [TN] ENIG
Thickness Standard?


                    01/31/02 08:36 AM
                    Please respond to
                    "TechNet E-Mail Forum.";
                    Please respond to Rick
                    Thompson






Is there a standard for the plating thickness of the ENIG surface
finish?  I've searched the archives and didn't find anything.  Based on
a customer request we had increased the requirement for the electroless
nickel to 200u inches. A couple of our board vendors are telling me that
that is excessive and that anything over 100u inches is overkill. I've
seen references in the archives for anything from 120u inches to 200u
inches.  What (if anything) is considered standard for this finish?

Thanks for your inputs.


Rick Thompson
Ventura Electronics Assembly
2655 Park Center Dr.
Simi Valley, CA 93065

+1 (805) 584-9858   x-304  voice
+1 (805) 584-1529 fax
[log in to unmask]

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