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Gold edge connectors.

G

Glenn Gundlach

Jan 1, 1970
0
I'm working on some old ('70s) Ampex 2 inch videotape machines. I
haven't located any extender boards and I'm ready to make my own. The
original cards all have gold plating.
2 questions
1: Can I use plain tin plate for the connector or will that damage the
gold in the female connector?
2: what special processing is needed at my end on the PCB files to have
gold plating?

Thanks
Glenn Gundlach
 
I'm working on some old ('70s) Ampex 2 inch videotape machines. I
haven't located any extender boards and I'm ready to make my own. The
original cards all have gold plating.
2 questions
1: Can I use plain tin plate for the connector or will that damage the
gold in the female connector?
2: what special processing is needed at my end on the PCB files to have
gold plating?

Thanks
Glenn Gundlach

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
 
L

legg

Jan 1, 1970
0
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.

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
 
P

Pooh Bear

Jan 1, 1970
0
legg said:
Don't mix connector mating materials in equipment designed for use in
the field.

*VERY* wise words of advice !

Graham
 
B

Ben

Jan 1, 1970
0
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
 
J

John Woodgate

Jan 1, 1970
0
Don't mix connector mating materials in equipment designed for use in
the field.

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.
 
*VERY* wise words of advice !

Graham

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
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that [email protected] wrote (in
It sounds like a knee-jerk techno-myth to me.
No.

Where is the supporting
evidence?

Look up any decent works on electrochemistry and intermetallic
compounds.
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?

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 http://www.npl.co.uk/ei/news/faqs.html is instructive,
and the page is helpful in other ways as well.

Finding 3 at:
https://www.reliabilityanalysislab.com/FailureAnalysisFindings.asp

is also relevant.
 
R

Robert Latest

Jan 1, 1970
0
On Thu, 1 Sep 2005 11:39:04 +0100,
in Msg. said:
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.

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
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Robert Latest
On Thu, 1 Sep 2005 11:39:04 +0100,


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?
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.
 
R

Richard Henry

Jan 1, 1970
0
Robert Latest said:
On Thu, 1 Sep 2005 11:39:04 +0100,


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?

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

Richard Crowley

Jan 1, 1970
0
jmeyer wrote ...
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?

"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. "
http://support.intel.com/support/motherboards/desktop/archive/professionalgxwork/vendors.htm

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

Keith Williams

Jan 1, 1970
0
jmeyer wrote ...

"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. "
http://support.intel.com/support/motherboards/desktop/archive/professionalgxwork/vendors.htm

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

A tin contact may still damage a gold finger.
 
K

Keith Williams

Jan 1, 1970
0
I read in sci.electronics.design that Keith Williams <[email protected]>


I thought it was a bond that terminally damaged a gold finger.
<splaattt> Where's my hanky! Someone covered my screen with coke.
 
P

Pooh Bear

Jan 1, 1970
0
Ben said:
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.

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

Graham
 
R

Richard Crowley

Jan 1, 1970
0
"Keith Williams"wrote ...
A tin contact may still damage a gold finger.

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.
 
K

Keith Williams

Jan 1, 1970
0
"Keith Williams"wrote ...

Are you talking about SIMMS or PC board fingers?

Yes. Though I haven't noticed barbs on PC edge connectors, they do
have a different contact pressure and wiping action.
The risk to a big, gross (by micro-component standards)
40-year old circuit board seems minimal at this point.
I'd tend to agree. I wouldn't abuse the boards, but a couple of
insertions shouldn't hurt.
 
P

Pooh Bear

Jan 1, 1970
0
Glenn said:
I'm working on some old ('70s) Ampex 2 inch videotape machines. I
haven't located any extender boards and I'm ready to make my own. The
original cards all have gold plating.
2 questions
1: Can I use plain tin plate for the connector or will that damage the
gold in the female connector?

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

2: what special processing is needed at my end on the PCB files to have
gold plating?

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
 
R

Robert Baer

Jan 1, 1970
0
John said:
I read in sci.electronics.design that [email protected] wrote (in



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 http://www.npl.co.uk/ei/news/faqs.html is instructive,
and the page is helpful in other ways as well.

Finding 3 at:
https://www.reliabilityanalysislab.com/FailureAnalysisFindings.asp

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