Gold edge connectors.

On 31 Aug 2005 15:11:37 -0700, "Glenn Gundlach" wroth:

Most all gold plating is so thin that it will be rubbed off of the microscopic high points that constitute the interfaces between connectors regardless of whether the mating surfaces are gold-gold or gold-tin and leave the connection to be made via the substrate material. Gold plated contact surfaces are 99 percent cosmetic and only 1 percent functional.

Jim

Plating material and thicknesses are specified by the designer.

Requirements are determined by the application, (insertion count spec).

Don't mix connector mating materials in equipment designed for use in the field.

RL

*VERY* wise words of advice !

Graham

So you can put a gold pin in a gold socket.

"SIMM devices with gold contacts should NOT be placed into SIMM sockets with tin-lead contacts or vice-versa. Mixing dissimilar metal contact types has been shown to result in unreliable memory operation. "

OTOH, I wouldn't worry about it if using it only for occasional servicing on an extender card.

I read in sci.electronics.design that legg wrote (in ) about 'Gold edge connectors.', on Thu, 1 Sep 2005:

In particular, be VERY cautious about gold with tin. It's OK if your extender cards are just for maintenance and repair, but don't leave them in contact for more than an hour or so. An intermetallic compound forms, which is not at all nice.

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

On Thu, 01 Sep 2005 04:32:13 +0100, Pooh Bear wroth:

It sounds like a knee-jerk techno-myth to me. Where is the supporting evidence? What are the boundries of the problem? Do you know how many different surface materials there are in use today? How can you ever avoid mixing materials without knowing the exact composition of each material you expect to use?

Jim

Are you talking about SIMMS or PC board fingers?

The risk to a big, gross (by micro-component standards)

40-year old circuit board seems minimal at this point.

In this case the SIMMs and mating sockets are designed differently. Tin plated sockets typically have a higher insertion force because the socket has to wipe through the oxidation on the contact. Often there is a barb on the socket to cut through the mating surface. A higher retention force is also needed to maintain the gas-tight contact.

Gold connectors have a lighter spring and no barb, since there isn't any oxide to cut through. Mixing them causes either the heavier wiping force (or barb) of the tin contact to cut through the gold plate or the tin surface not being wiped clean/sealed by the gold contact.

A tin contact may still damage a gold finger.

--
  Keith

On Thu, 1 Sep 2005 11:39:04 +0100, John Woodgate wrote in Msg.

I've frequently used gold-plated IC sockets with no ill effects although the IC pins are tinned. Of course the fact that I didn't have trouble doesn't mean I couldn't get some one day, but why do gold-plated sockets exist at all if the contact starts deteriorating as quickly as you say?

robert

I read in sci.electronics.design that snipped-for-privacy@nowhere.net wrote (in ) about 'Gold edge connectors.', on Thu, 1 Sep 2005:

No.

Look up any decent works on electrochemistry and intermetallic compounds.

There is a table in IEC/EN 60950 that goes some why to indicate bad combinations from electrochemical considerations. But it's inadequate, because it relates to rather idealized conditions. For example, chloride ions (which are everywhere outside the chem. lab) cause corrosion in combinations where the table doesn't predict it.

The gold/tin thing arose years ago when transistor leads were gold plated and soldering proved difficult. It's OK if there is enough tin, but if not the unnsolderable, hard intermetallic compound forms and the joint fails, maybe quite a while later.

Question 37 at

is instructive, and the page is helpful in other ways as well.

Finding 3 at:

is also relevant.

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Where's my hanky! Someone covered my screen with coke.

--
  Keith

I read in sci.electronics.design that Robert Latest wrote (in ) about 'Gold edge connectors.', on Thu, 1 Sep 2005:

The deterioration doesn't start after an hour, it takes a long time to develop. But enough tin contamination may be there after about an hour, depending on contact design.

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Yes. Though I haven't noticed barbs on PC edge connectors, they do have a different contact pressure and wiping action.

I'd tend to agree. I wouldn't abuse the boards, but a couple of insertions shouldn't hurt.

--
  Keith

Since it is only an extender card for servicing, you can safely use tin plating or hot air level lead/solder on the edge connector. Gold is used because it does not corrode or tarnish and that goes while it is in contact with other metals too. You can even use plain copper board as well, just keep it clean and untarnished.

Furthermore, the early 70's gold plating was about 100 times thicker that today's gold flash plating of a few micron. In fact, if you recycle those old connectors. you will end up with quite a bit of gold (relatively speaking).

What will damage the connector is:

1: Your pcb/edge being too thick 2: Your edge having a sharp end - bevel it with a file or sanding paper. 3: Very many insertion cycles. 4: Lots of sideways movements of your extender while it is plugged in.

Good luck, Ben

I read in sci.electronics.design that Keith Williams wrote (in ) about 'Gold edge connectors.', on Thu, 1 Sep 2005:

I thought it was a bond that terminally damaged a gold finger.

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

!!!!! Only if you want to contaminate the contacts and make the unit unreliable.

Graham

The gold may indeed be 'damaged'. See the other posts

Tell them you need the card edge gold plated ?

The fingers should actually be a little longer than the board profile. Also you'll want to connect all the fingers together with little tracks so they can all be plated. The excess rubbish gets removed whren the board is profiled.

Graham

...and do no forget the "purple plague" from gold and aluminum...