Tenison

I agree with Gerard. The best solution is to simply use a silver
contact. This has been done with great success; the data however has not
been published, at least to the best of my knowledge. I will contact a
source and see if the might reveal the information to you. They also
supply this technology.

If you elect to use a carbon contact with silver I see little risk
overplating the silver with carbon. The cure should not present a
problem since silver will withstand multiple reflow operations with no
degradation in assembly performance.

Best regards

Lee


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gerard O'Brien
Sent: Friday, January 21, 2005 9:38 AM
To: [log in to unmask]
Subject: Re: [TN] IAg and carbon pads

Tenison - the problem is the protection of one surface from the other
process. If you run carbon first then it will require a dryfilm to
protect
it from plating up with the silver. When you remove the dryfilm there is
a
chance of staining the Ag surface and thus impacting solderability. If
you
run Ag first, then the thermal exposure for curing the Carbon and the
outgassing of the ink may also impact solderability.
The best method I have tried to date is to use a peelable mask over the
carbon but the cost/labor involved is prohibitive to the point that
supplying ENIG in its place is an actual cost saving.
Another option is to use the Ag as a switch pad. The 4553 document
covering
I Ag has data to 1 million cycles for membrane type switch pads,
recommended
for class 1 and class 2 applications only.


Regards

Gerard O'Brien
Photocircuits Corporation
Co-Chairman 4-14 plating committee.


-----Original Message-----
From: Stone, Tenison (MN10) [mailto:[log in to unmask]]
Sent: Friday, January 21, 2005 9:04 AM
To: [log in to unmask]
Subject: [TN] IAg and carbon pads

I would be curious to hear answers to this question asked yesterday:

Question for anyone: Has anyone used IAg as a board finish with carbon
ink
over any desired areas?  Seems like it might work for a keypad with
parts on
one side and contacts on the other...


Looking at lead free - can we replace HASL with IAg and have carbon pads
on
the opposite side?  What should be tested to prove a design using IAg
and
carbon pads?

Tenison Stone
Sr. Process Engineer
Honeywell, International
1985 Douglas Dr. N
MN10-2471
Golden Valley, MN  55422
Tel: 763-954-4925   Fax: 763-954-4447
[log in to unmask]

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