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April 2010

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Wed, 14 Apr 2010 15:19:47 -0700
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Jack,
like you say, it's more to it....gold thickness is not the one and only 
parameter.  Other factors are contact asperity, contact geometry, contact 
area vs. current, wipe pressure, switch slide coefficient, underlying 
plating, life expectancy and at least half a dozen more parameters. I was 
specialist on electromechanical and manual switches decades ago, don't 
remember all details, but I can tell you this: if you count on gold 
thickness only, you don't know what you are shipping.  93.7% Au? We did not 
name that Gold at all. We talked about maximum 0.1% impurities.  The more 
impurities, the higher the friction coefficient. Well, I don't know what 
level of quality you speak for. I was in the HiRel, so maybe I'm too 
demanding. Anyway,  My advice (which you will probably frown at) is
basic metal ?? your wiper
300 uinches of pure Nickel
25 uinches of Rhodium over Nickel
5 uinches of soft gold (gold works as 'lubricant')

The above based on a qualified switch mechanism.  If that is not the case, 
not even 160 uinches of gold  will work for a very long life.  160 uinches! 
Never heard of such a lot of gold. When extrem current switching is actual, 
one use to work with mercury switches, microswitches or like.

Don't listen to me, I'm from an era when we dismantled switches and relays 
and measured all contact parameters and stored the  test data for minimum 10 
years. And all our own test equipments were sent to a qualfied reference 
lab. Madness?

Inge

--------------------------------------------------
From: "Jack Olson" <[log in to unmask]>
Sent: den 14 April 2010 14:14
To: <[log in to unmask]>
Subject: [TN] Question for "Old-Timers" about Gold

> ya know, every time I think I know enough about a particular subject,
> something comes along to make me realize there is more to it....
>
> I need to order some boards using a fabrication drawing that hasn't been
> updated in over fifteen years.
> We need Hard Gold Electroplating for a rotary switch contacts.
> One of the notes calls for gold knoop hardness 200-300, thickness 130-230
> uin. 93.7% purity
> The last FAI report showed gold thickness of 160 uin. All other historical
> records are lost in the shifting sands of time
>
> Our vendor has knoop hardness 150, 99.7% purity and says gold requirement 
> is
> too thick.
>
> IPC says knoop 150, gold minimum 31.5 uin. for edge connector fingers, 
> which
> I assume is the same for contacts (doesn't seem to be addressed)
>
> Printed Circuits Handbook says knoop 150,  thickness 25-50 uin for
> non-military, 99.8% gold purity
>
> Has gold plating changed that much since then?
> Is there a danger of wear-out if I get 50uin. gold plating when our old
> boards were 160 uin.?
>
> surfin' the learnin' curve,
> Jack
>
>
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