We have been using Immersion gold in press-fit applications for two 
years with excellent results.  The mating connectors have both gold 
and Solder finish on the press-fit leads.  There is a lot of 
immersion gold press-fit going on in Europe for the past 4 years or 
so with excellent results.
	With any solder finish, you will find a lot of variability in hole 
sizes.  HAL doesn't help this much as it has the same problem and the 
hole size change varies by the hole diameter.
	I suspect that you never did get good hole diameter control, but it 
was not detected!
	With immersion gold we are able to spec a +- .002 on very thick 
boards and this is what we received!  This is on a .155 thick board!
	Note:  the extra solder probably will not give you a problem with 
press-fit as it is displaced when the press-fit connector is 
inserted.

	There is no way to control HAL, or reflowed solder for good hole 
diameter control!  The only way I have seen is to put so little 
solder on the board that the normal
spec for solder thickness is violated!

	[log in to unmask]

	
 ----------
From: Michael Branning
To: [log in to unmask]
Subject: FAB:Electroless Ni/Immersion Au & press-fit connectors
Date: Thursday, November 21, 1996 2:28PM


Our principle product uses a 14"x17", .125 thick, 8 layer backplane 
with 48
press fit connectors. Its currently specified as SM over reflow 
solder. Our
PCB supplier has performed wonderfully in the past, but we are now
receiving
some boards with out of spec finished holes (spec .033 +.002/-.003). 
Cross
sectioning shows the problem to be extra, irregular solder buildup in 
the
holes. They are suggesting we should spec SMOBC to help the problem.
Another
new vendor we are talking with is recommending a Ni/Au process. My 
feeling
is the original vendor produced very satisfactory product for 3 yrs, 
and
should be able to continue to do so. However, I'd like to take this
opportunity to do some investigation. I have a few questions:

1. Is anyone out there using Ni/Au on boards with press-fit 
connectors?
2. Would anyone venture an opinion on impedance differences that 
would
exist
between the three processes?
3. Does our current spec seem unreasonable or difficult to 
manufacture?
4. What about if the hole was specified as .033 +/- .002?

Thanks!
Michael Branning
Avtec, Inc.
4335 Augusta Hwy
Gilbert, SC 29054
(803) 892-2181
(803) 892-3715 FAX
[log in to unmask]

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