Dave,

We do dual plating here all the time.  You'll find that ENIG plating
cannot always be plated thick enough to withstand the number of cycles
that you need for the connector fingers - 30u-inches minimum.  (And it
takes longer to get it that thick.)  And if you try to plate everything
with that thickness, the assembler will have a very difficult time
soldering your parts!  

Even if you don't "plan" to disconnect them very often, the requirements
for connectors on most Class 2 products are (roughly) 500-1000 cycles
per year that you guarantee the product. (Your company may have a
different or specific requirement.)  For that you need the thicker gold
plating.

Another thing we found out was mixing Hard Gold with ENIG runs the risk
of the hard gold flaking off - not setting properly.  If a thin coat of
Hard Gold is applied to everything and then a thicker coat of Hard Gold
is applied to the fingers (or other features), you get great adhesion.
Each fabricator is a little different and it's a good idea to discuss it
with them.

Here's the very generic note we use (huge tolerances on the nickel
here...)

GOLD PLATING:
	GOLD PLATING ON SOLDERABLE SURFACES:
		0.076-0.38 um (3-15 u-inches) OF GOLD OVER
		3.8um - 20.3um (150-800 u-inches) OF NICKEL.
	SELECTIVE GOLD MASKED AREAS PLATING SHALL BE:
		0.76 um - 2.28um (30-90 u-inches) OF HARD GOLD OVER
		3.8um - 20.3um (150-800 u-inches) OF NICKEL.

We also create a selective gold mask GERBER file that identifies all the
pads that require the hard gold.

Cherie

-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Dave
Schaefer
Sent: Tuesday, June 16, 2009 2:05 PM
To: [log in to unmask]
Subject: [DC] Gold Fingers - ENIG or Hard Gold

Have a product that would be considered low insertion cycle that makes
connection to a back panel via "gold finger" edge connection.

I would prefer to specify ENIG finish for the entire PCB.

Is ENIG suitable for this application, or is Hard Gold required?

Are there any specifications which outline the requirement?

Thanks,
Dave

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