In a message dated 2/6/01 9:02:00 AM Eastern Standard Time,
[log in to unmask] writes:

<< We have a couple assemblies that have solder on the gold fingers. >>

Hi Rich,

I'm sure you'll get an abundance of excellent references on the How-To's for
removing solder from gold (and sources for solder wick, etc.). So I'll
instead write to share a proactive idea for future-thinking.

Have you considered substituting a polymer thick film coating (PTF) for the
gold coating? PTF coatings (think "conductive inks") have the advantage of
providing a conductive finish to your card edge connectors without the
liabilities of electro-deposited Ni/Au. Points to Ponder (in no particular
order):

Solder Resistivity
PTF coatings are generally as resistant to solder adhesion as the solder
mask. Thus there is no taping and, consequently, no opportunity for solder
seepage.

Electrical Performance
Most inks today are available in varying resistance formulas, down to 1-ohm
per square. Contact resistivity is typically @ or below 1-ohm. Unless you're
running very heavy current there's likely no loading problems to anticipate
at the connector.

Mechanical Performance
PTF coatings are the clear winner over gold. The same ingredient that makes
the ink conductive  -  graphite  -  also acts as a lubricant, so that there
develops a self-lubricating relationship between connector and connector
fingers.

Shelf Life
PTF coatings have virtual unlimited shelf life.

Cost
A PTF finish on card edge connectors should impart a cost adder slightly
higher than an additional silkscreen; likely less than the cost adder for
electro-deposited card edge connectors.

Solvent Resistivity
Expect robust performance comparable to FR-4 resin systems and polymer solder
masks.

Organic Liability
PTF formulas are completely non-nutritional and do not promote organic growth.

There's more to be said, but my point is that you may have a viable option
that will satisfy the connector function without the liability of solder on
gold and, most likely, for less money than your currently paying.

In the interim, good luck getting your solder removed.

Bob Lazzara
Circuit Connect, Inc.
Tel:    +1 706.245.4232
Fax:    +1 706.245.4299
Web:    www.CircuitConnectInc.com

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