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    Gold sockets, tin tube pins - a no-no?

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    deepee99

    Posts : 1260
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Gold sockets, tin tube pins - a no-no?

    Post by deepee99 on Sat Aug 29, 2015 7:24 pm

    A electronics engineer friend (and a a tube junkie in his own right) who worked for John Fluke and then at Intermec said it was "received wisdom" at both shops that gold and base metals should not mix in a tube or IC connection.
    I pass along his thoughts after asking him to put them in writing:

    "I can't tell you what happens metallurgically in the contact zone, but it was received wisdom at Fluke that you never use a gold pin in a base metal socket or vice versa. Tin on tin is good, gold on gold is best, but gold on tin is worse than tin on tin. I heard the same thing when I worked at Intermec.

    "The issue seems to be not so much with connectors that are regularly plugged in and out but with permanent connectors and particularly with ICs in sockets. Over time, the base metal would oxidize and make a noisy connection (some of these thin films of base metal oxides and intermetallic compounds even have semiconductor properties).

    "Perhaps tin on tin was okay because there were no dissimilar metals with different electromotive potential (obviously a big problem if there's moisture) or maybe it was that the tin was soft enough that the platings on each part actually smooshed together.

    "The issue wasn't that the connections totally opened up to where they'd overheat or fail to carry high currents, but that small-signal connections would get noisy. It may well be that in a tube amplifier the thermal cycling creates enough wiping action to keep the connection good, or that the voltages are high enough to destroy oxide films. But if I was designing that sort of thing, to be on the safe side, I'd stick with nickel-plated sockets. Of course it might also be that your "gold" tube sockets have just a thin decorative whiff of gold on them and it wipes right off of the contact area after a couple of insertions, leaving you with the underlying nickel plating at the actual point of contact."

    At any rate, food for thought.
    Cheers,
    Dave


    arledgsc

    Posts : 330
    Join date : 2012-11-30
    Location : SF Bay CA

    Re: Gold sockets, tin tube pins - a no-no?

    Post by arledgsc on Sun Aug 30, 2015 11:11 am

    The Tin Commandments from  TE Connectivity (formerly AMP)
    http://www.te.com/documentation/whitepapers/pdf/sncomrep.pdf

    1.  Tin coated contacts should be mechanically stable in the mated condition
    2.  Tin coated contacts need at least 100 grams contact normal force
    3.  Tin coated contacts need lubrication
    4.  Tin coating is not recommended for continuous service at high temperatures
    5.  The choice of plated, reflowed, hot air leveled, or hot tin dipped coatings does not strongly affect the electrical performance of tin or tin alloy coated contacts
    6.  Electroplated tin coatings should be at least 100 microinches thick
    7.  Mating tin coated contacts to gold coated contacts is not recommended
    8.  Sliding or wiping action during contact engagement is recommended with tin coated contacts
    9.  Tin coated contacts should not be used to make or break current
    10.  Tin coated contacts can be used under dry circuit or low level conditions

    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Gold sockets, tin tube pins - a no-no?

    Post by Bob Latino on Sun Aug 30, 2015 12:02 pm

    Also check out our forum post from December of 2013 on "tin whiskers" .. The ability of tin under certain circumstances to grow crystalline threads and cause a short between two connections ..

    Tin whiskers thread ..

    Bob

    deepee99

    Posts : 1260
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: Gold sockets, tin tube pins - a no-no?

    Post by deepee99 on Sun Aug 30, 2015 12:33 pm

    Bob Latino wrote:Also check out our forum post from December of 2013 on "tin whiskers" .. The ability of tin under certain circumstances to grow crystalline threads and cause a short between two connections ..

    Tin whiskers thread ..

    Bob

    Bob, that NASA paper is a fascinating read. Thanks; I'd missed it.
    What are the most common metals used for tube pins, anyway? I've seen gold plating on some novals (obviously they're not solid gold or the pins would collapse trying to insert them into a socket). What do modern tube-makers use? I've got some NOS tubes from the 50s whose pins are pretty ratty, so I'm guessing not nickel.

    sKiZo

    Posts : 1287
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Gold sockets, tin tube pins - a no-no?

    Post by sKiZo on Sun Aug 30, 2015 2:12 pm

    ANY dissimilar metals can cause corrosion. Best bet is to apply a thin coating of D5 to seal the metal every now and then. Bonus is increased conductivity.

    Same holds true for most any mechanical connection. That gray stuff on your RCA jacks? That's NOT dust ...

    PS ... whiskers are more of a problem with the newer "green" lead free solders and surface mount components where the leads are close. Stuff's also a PITA to work with on the home bench as it's difficult to get consistently good connections. Good old 60/40 lead is still popular for a reason. I use Cardas Quad myself. Pricey, but worth it.

    deepee99

    Posts : 1260
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: Gold sockets, tin tube pins - a no-no?

    Post by deepee99 on Sun Aug 30, 2015 2:24 pm

    sKiZo wrote:ANY dissimilar metals can cause corrosion. Best bet is to apply a thin coating of D5 to seal the metal every now and then. Bonus is increased conductivity.

    Same holds true for most any mechanical connection. That gray stuff on your RCA jacks? That's NOT dust ...

    PS ... whiskers are more of a problem with the newer "green" lead free solders and surface mount components where the leads are close. Stuff's also a PITA to work with on the home bench as it's difficult to get consistently good connections. Good old 60/40 lead is still popular for a reason. I use Cardas Quad myself. Pricey, but worth it.

    Yes, avoid any solder that has RoHS anywhere on the label. Skizo, what's the charm of Cardas Quad over plain old Ace Hardware 60:40? And I wouldn't dream of a tube-roll or swap without a little goosing of D5.

    sKiZo

    Posts : 1287
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Gold sockets, tin tube pins - a no-no?

    Post by sKiZo on Sun Aug 30, 2015 3:58 pm

    Eutetic solders like Cardas Quad are either solid or liquid ... little or no in between state that can fool you and give you a cold joint. Once it puddles, you're good. It also sets faster, making it easier to seat the components with nary a wiggle that can weaken the bond.

    Cardas Quad goes an extra step by including copper and silver to upgrade the conductivity. If I had a complaint, it'd be the small diameter of the solder which doesn't leave a lot of room for flux. Not an issue, as I always pre-flux the tip and keep it well tinned anyway.

    I love my Cardas Quad!



    PS ... you DO need a hot iron for the stuff - I run mine at around 725F.

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