Metal finishing Q&As since 1989

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Problems with de-wetting while "Tin / lead" dipping Alumel and Chromel contact pins

November 3, 2009

Hi
I am trying to tin / lead (63/37) dip 3 types of contact (later to be fitted to a connector) The portion of the contact to be dipped is 0.215" with a diameter of 0.033"

1. Gold plated - As you would expect no problems here !
2. Alumel - 95% Nickel, 5 % Aluminium - de-wetting of up to 50%
3. Chromel - 90% Nickel, 10 % Chromium - de-wetting of up to 50%

We have plated both 2 and 3 with a copper flash (120 ± 30 micro inches) and found an improvement but it still isn't by any means a perfect process with about 50% success

In addition my main concern is that of course I must not change the thermocouple properties of these contacts (2 and 3)

Related questions !
I now have a large box of contacts which I can not use is, can any one recommend a way of removing the tin / lead and copper flash with out any damage to the base material ?

Does any one know of a method to plate these contacts as opposed to hand dipping them ?

Is copper the best plating to use prior to the dip ?

Sean Keating
product designer - London, UK