Dave,
Thank you for the reply. As usual an excellent reply. In this application, the impact of nickel would a non-issue, but I will forgo it and specify the copper. If this was a PB I would have no problem, but  I'm speculating on a copper plating spec and thickness. I'm hoping my cross-section of the pin will give me a target. The silver finish will be per ASTM B 700 with minimum thickness of 200-300 micro-inches (more for the durability end then a soldering concern). It's good to hear that standard solder and soldering process is acceptable. I wouldn't feel comfortable trying to specify what and how to solder.
Does this mean I have to be nice to Doug?
Dewey


From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Friday, March 28, 2014 2:40 PM
To: TechNet E-Mail Forum; Whittaker, Dewey (EHCOE)
Subject: Re: [TN] Pins and Needles

Hi Dewey - for what its worth, here are some thoughts. Silver is a very common contact material so that's no surprise. You can solder to silver over BeCu but having a copper underplate would make it more solderable. Also keep in mind that silver and copper love each other so the solderability will only be a short term function. BeCu is a very common pin material for contact applications so also no surprise. Using a nickel barrier is a big question as it would improve the contact characteristics in terms of both wear and solderability. However, sometimes nickel causes functional problems with the overall circuit characteristics. As for soldering, use Sn63, Sn60 or Sn62 as all three would work just fine (I don't see leaching being an issue as long as the soldering process is typical). What you really need is an old pin that you can do both XRF and then a cross section so you can backwards engineering what the original plating stackup looked like. Good Luck.

Dave Hillman
Rockwell Collins
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From:        "Whittaker, Dewey (EHCOE)" <[log in to unmask]<mailto:[log in to unmask]>>
To:        <[log in to unmask]<mailto:[log in to unmask]>>
Date:        03/28/2014 09:39 AM
Subject:        [TN] Pins and Needles
Sent by:        TechNet <[log in to unmask]<mailto:[log in to unmask]>>
________________________________



Dear Technet,
For the record I'm looking for a special talent. Old, old product that has beryllium pins ultrasonically bonded in a plastic switch housing. The pin is silver plated prior to installation. The spec  and materials have been obsolete for 25-30 years. They asked me to write a new one, so my first question was why silver? Watching too many Lone Ranger episodes as a child or hooked on oxides?
One end of the pin rubs on the sliding switch plate (proprietary finish) which is probably silver. The other end
of the pin is installed in a PBA and flow soldered .
So the pin has to be conductive, solderable and let's say hard. There is  no specific information on the beryllium pin, so how do I help them without knowing how I helped them. My questions are as follows:

*         Do I apply a copper plate on the pin first

*         Do I apply  a nickel barrier layer over the copper plate

*         What nickel plating spec (ASTM B 700) do I use and what minimum thickness (200-300 micro-inches) when one end needs to be soldered

*         Should the solder in the flow solder bath be 2% Ag
I would not have designed this  is and what I want to change it may not be possible, I'm open to suggestions to try anyway. Whole new pin with one special surface finish, would be my reply.

Dewey

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