Gregg,

I have been through a lot too. For some years I was responsible for all
connectors for radar systems, radiolinks and such things. I got circular
multipin connectors from Pakistan coasts, cadmium coated connectors that
were so corroded that they could hardly be handled without crushing them.
And other examples. So, when as worst, even cadmium doesn't stop. These were
extreme environments (beacons at sea).

I investigated and tested new series for our today's radar, e.g. the ones
that you might have seen with a long body mounted on top of a medium size
jet. That system has hundreds and hundreds of circular connectors. They are
all nickel plated and mounted on aluminum chassis. And we have no corrosion
problems despite everything is drowned in condensed water when shifting from
ground to high altitude and vice versa.

In fact, electroless Nickel has an activated oxide which is extremly
corrosion resistant. The mistake many do,  is to torque the receptacle with
steel nuts and washers. THAT is no good. I can't tell you what we use, but
not steel. It's important to make as large a physical contact as possible
against the chassis. Spot contacting means sometimes return current
constraints.

You use conversion chromate, you say. Hmm....we don't. That treatment is
sensitive to mechanical damage. It's enough with scratching your screwdriver
against it, and you got exposed aluminum (little exaggerated, but you get a
picture of what I mean).

/Inge



On 16 September 2011 00:19, Temkin, Gregg <[log in to unmask]>wrote:

> Anyone ever had any negative experiences with mounting nickel plated
> connectors to an aluminum chassis.
>
> We're using Nickel plated composite connectors (D38999/20M) against 5541,
> Type II, Class 3 coated sheet aluminum and having to meet 2.5 mohms or less
> of bond resistance.
>
> I've been through plenty of bond resistance wars and I'm particularly
> concerned with the galvanic couple of Aluminum and Nickel especially since
> we're not sealing the interface and having to go through salt fog testing as
> part of our qualification.  We must maintain less that 5 mohms after salt
> fog exposure without re-torqueing screws, which seems to be the common
> hidden factory way of sweeping the problem under the rug.
>
> I've been told we have lots of experience with silver colored connectors in
> aluminum housings, but a further look-see shows all those connectors are
> actually Cadmium over Nickel plating which is a much nicer galvanic match.
>
> If this is truly a risk, then our options appear to be:
>
> 1. Seal the interface with a conductive gasket (the interface is
> inaccessible for a goop application sealing)
> 2. Plate the Aluminum with Nickel to eliminate dissimilar metals
> 3. Use a washer of intermediate material to reduce the galvanic span
>
> Are there other suggestions or experiences anyone can relate?
>
> Thanks,
>
> Gregg
>
> Gregg Temkin
> Principal Manufacturing Engineer
> [Description: Description: clip_image002]
>
>
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