Pat:

Some of your message can be interpreted in different ways... is the plating you are having a problem with Tin plating, or "solder" (Tin/Lead) plating?

Tin/Lead can be plated from a number of electrolytes, and traditionally it was plated from a fluoborate bath, which gave the highest quality plating.  Within the last 15 years, another electrolyte has come into use... methane sulfonate, which is a much less forgiving electrolyte, and tends to give poorer quality plating.

Pure Tin is plated from either a sulfate, or methane sulfonate bath, and both these suffer from the same malady...and are not as good as fluoborate..

My suspicion is that if the plating is Tin/Lead, the original vendor used fluoborate, and the new vendors are using methane sulfonate.

There are other problems relating to Tin/Lead plating, which need careful attention, even in the fluoborate bath... but the above issue is probably central to the problem.

Rudy Sedlak
RD Chemical Company

"Diamond, Pat" <[log in to unmask]> wrote:
Hi Technetters,

we have a potential problem, after our connector manufacturer went out of
business, we tried an alternative approved company who manufactured some
evaluation samples.

The samples we received showed evidence of missing/contaminated plating in
the bottom of the solder cups. After soldering and cross sectioning some of
the cups, there was evidence of non-wetting and flux entrapment in the
bottom of the cup. When we contacted our supplier, they stated that due to
the configuration constraints and the plating method, they cannot guarantee
to produce 100% plated parts every time (we have also had this confirmed by
alternative sources).

We have devised an alternative manufacturing method which will correct the
problem but will not receive part for approximately 3 months!

Some background information on the product:

The unit the connectors are used on, is an aircraft fuel density sensor
which sits in the fuel tank and measures the amount of fuel on board say a
747.

After assembly, the connectors are potted with an epoxy and then electron
beam welded to the sensor which has been previously evacuated to 3 E-4 Mbar.

My question is; given that the solder has wetted fully on the outside (and
most of the inside) of the cup and that the connectors are in a vacuum, will
the flux entrapment cause corrosion etc. with the passage of time?

A few bits of further info:

* The cup is made from 1.02mm Diameter Nilo 50 and the plating is 2.5
microns of electro-tin, flow brightened over a copper undercoat
* The solder used is HMP- 93.5%Pb/5% Sn/1.5%Ag
* The flux used is Ersin 362 Rosin activated
* The operating temperature spec is -55 +125 degrees C

The other unfortunate problem is that we cannot change the cup material or
the plating method!

Any help/advice you can offer would be appreciated.

Pat Diamond


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Pat Diamond
Senior manufacturing Engineer
Weston Aerospace Tel: +44 (0)1252 868122
124 Victoria Road Fax: +44 (0)1252 370298
Farnborough, Hampshire, GU14 7PW Web www.westonaero.com>
England Email mailto:[log in to unmask]

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