Jack,
Last time I had to do it was in 1998, 12 years ago, I went by IPC-2221 Class 2 and the vendor didn’t whine.
IPC-2221, page 20, Table 4-3 delineates the different usages of gold, and for your switch, I imagine one of these two is correct:
Class 1 and 2 Gold (min) for edge-board connectors and areas not to be soldered = 0.8um (31.5uin)
Class 3 (MIL-SPEC and med-spec) calls for 1.3um (51.1uin)
Gold (max) on areas to be soldered = 0.8um (31.5uin) for Class 1,2,3
Table 4-4 (Gold Plating Uses) on the same page specifies minimum purity 99.0%, Knoop hardness 130-200 and a letter “S” signifying “suitable” for Contacts.
Other arcana in the MIL-SPEC may be of use. I believe MIL-G-45204 in my old IPC-2221 became MIL-DTL-45204D in 2007.
Dunno about your last two questions. I don’t have a current copy of IPC-2221.
Dunno if anybody’s gonna pay to grind out a cross-section to send to the x-ray or the beta-backscatter to measure how thick the gold *really* is, or make the vendor issue a CofC for the purity of the gold – in the Class 3 world when it’s mission-critical they sometimes do both.
Anyway it’ll be interesting to see what others say about this.
Gary
Designing since 1975
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Jack Olson
To: [log in to unmask]
Sent: Wednesday, April 14, 2010 5:14 PM
Subject: [DC] 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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