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Gold coated spring contacts

#6485

Gold coated spring contacts | 6 May, 2001

Can someone point me in the right direction (with a standard) as to how much gold you should specify for spring contacts - there is a huge variation available in thickness (and price!!).

thanks

Steve

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#6498

Gold coated spring contacts | 7 May, 2001

No specification, but a little help, maybe.

Consider selecting the thickness of gold [price] based on the number of insertions you expect.

Let me expand by describing an experiment done by Norm Einarson. [Mr. Einarson is a very famous board design guru. His book "Bare Board PBW Design Manual" published by Printed Circuit Technology ph.617-272-0938 is a very good approach to board design for manufacture. You may be able to buy it from SMTA http://www.smta.org also.]

The experiment was to determine insertions from a gold plated board into a connector. Same thickness boards (0.062"), with 100 m base nickel. � 100m gold => 500 insertions � 50 m gold => 300 insertions � 30 m gold => 50 to 75 insertions � 20 m gold => 10 insertions.

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genny

#6587

Gold coated spring contacts | 14 May, 2001

> The experiment was to determine insertions from a > gold plated board into a connector. Same > thickness boards (0.062"), with 100 m base > nickel. � 100m gold =_ 500 insertions � 50 m > gold =_ 300 insertions � 30 m gold =_ 50 to 75 > insertions � 20 m gold =_ 10 insertions.

Dave, can you clarify your dimensions? Does 'm' mean microns or micro inches?

Thanks

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#6589

Gold coated spring contacts | 14 May, 2001

You're correct. The units should be micro inches.

By the by, this gold always should be a hard gold (99.96%-99.97% pure) with a Knoop hardness range of 130 to 200 (optimum 170).

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#6660

Gold coated spring contacts | 22 May, 2001

Again not quite what your looking for, but close, consider IPC-2221, Generic Standard On Printed Board Design, Para. 4.4.4 for minimum requirements for edge board connectors, as a baseline.

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genny

#6710

Gold coated spring contacts | 29 May, 2001

Dave, Sorry to drag this out some more. When I saw this thread I realized that we often get PWB's fabricated with a gold plated edge connector tab. However we have not ever given any specs to the fabricator regarding the gold plating - all we say is "gold plate this area". (I know, I know, sloppy...) I would like to add a spec into our files for this.

So I asked one of the fab houses we use what they do when we ask for gold plating. He said they nickel plate 50-75 microns and then gold plate hard gold onto that, 15-25 microns. I found these numbers incredibly high, according to your little table, when I converted them into micro-inches. 50 microns is almost 0.002" of nickel, and 15microns is almost 600 microinches. According to your numbers I could probably insert this board 1000's of times without a problem. Am I missing something here? Do you see an error in my calculations or is your table really referring to microns? I can't see a fab house doing way more than they need to when given no guidelines. Human nature tends more to doing the minimum possible.

Regards,

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#6711

Gold coated spring contacts | 29 May, 2001

Sorry guys but you missed the point - I am looking at thicknesses for SPRING contacts - such as the ones used in the telephone plugs that fit into the wall socket, I cannot find a telecom standard - hence thought some PCBers might be able to shine a bit of light on the subject?.

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#6718

Gold coated spring contacts | 29 May, 2001

Well, no fault with your calculations from here. They appear to be correct. [Logic doesn't appear to be off to far off base, either. An epiphany, eh?]

As mentioned in an earlier posting on this thread, consider following the recommendations of IPC-2221, Generic Standard On Printed Board Design, Para. 4.4.4 for minimum requirements for edge board connectors, as a baseline. The IPC folk have done a wonderful job of creating the documents of this series and it's really "shame on you", if you continue to ignore them.

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#6719

Gold coated spring contacts | 29 May, 2001

I never heard anyone say anything about looking for telecom wear surface spec, what point did I miss?

Have you contacted the folk at old Bell Labs [http://www.bell-labs.com Er, whatever they're called now a days?]

From a different perspective, we understood that you weren't specifically seeking PCB edge connector conversations, but as Mick used to say: "you can't always get what you want, but if your try sometime, you get what you need (er, words to that effect).

Please explain the difference in the wear effects between: * Gold surfaces of telephone plug & jack rubbing together * Gold surfaces in a PCB edge connector & board fingers rubbing together.

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genny

#6723

Gold coated spring contacts | 30 May, 2001

I couldn't find that standard free on the IPC website and was looking for a quicker answer (hang my head in shame...) Sometimes my company's a little frugal, and to get them to buy a standard can be like pulling hen's teeth... I will see what I can learn about that standard.

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#6732

Gold coated spring contacts | 30 May, 2001

You are correct. IPC wants you to pay for that standard, regardless if you get a hard copy or download it. Generally, it�s pretty boring stuff for production types. [Although, you will recognize some of the goofy things your designers have done to you.] Design types should get it tattooed to their bodies. On that note, what a surprise it would be if your design types already had a copy that you could borrow. [While you�re rooting around the design library, you may be able to find D-275, as an alternative. 2221 and 2222 replaced D-275 for rigid organic boards in March 1998.]

I appreciate what you�re saying about buying specifications. My boss [the owner of a previous company where I worked] felt IPC-A-610A was fine and would not buy Rev B, when it came-out. So, everyone in operations chipped-in to buy the new standards. So, he ended-up buying Rev B to save face, blaming me for his lack of fore-sight, and being too lazy to take the time to understand the business; and developed an unvarnished dislike for my internal organs. He�d be scratching, adjusting his toupee, and going-off on something eruther about "blue tick hounds, hunting-down, treeing, and killing a Yankee". And me being a Redbone fan [dang Blues er so cold nosed, anywho], I never could get a fix on what he was mumbling about. Some of which may help explain why that company is out-of-business.

Consider this: * Many fabs publish on-line "PCB Fabrication Guidelines". Do a net search, download some, and use the portions of each that you like. Hadco's was particularly good, as I recall. * Discard all of your notes on your fabrication drawings and just note "According to IPC-2221, Generic Standard On Printed Board Design and IPC-2222, Sectional Design Standard For Printed Board For Organic Printed Boards unless otherwise noted." [Then tell your boss you have to buy the standards, because they�re written into the fab drawings.] * IPC-2221 says something like ... For edge connectors and areas not to be soldered: nickel - 2.5um min [Class 2 & 3]. For edge connectors and areas not to be soldered: gold - 0.8um min [Class 2], 1.3um min [Class 3]. [Yagot me why there would be a difference in the gold for the two classes. More must be better!!!]

One, hopefully, final point: Think about leaving things just the way they are right now. Move on to something that�s broken. You will not save very much money messing around on this. In fact, you�ll probably not even recover the cost of the time you�ve spent so far. [Of course that assumes you earn the same level of chicken scratchings that I do, which is probably a reasonable assumption given your earlier comments.] And it may even end-up costing more, once your fab reprices your board, as part of your drill to determine the wonderfulness of reducing the gold on the board fingers.

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genny

#6741

We're gettin' the standard! | 31 May, 2001

Good news! I put in a request to purchase the spec and it was approved! And then I found out that we recently renewed our IPC membership (I didn't know we ever had one) so we don't even need to pay the nonmember price! Good reading ahead...

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#6743

We're gettin' the standard! | 31 May, 2001

See, all those bad thoughts we had ... The guilt, how do we live with it?

3 Spec Fir Tree General Technical Specification 3a Design/Layout: IPC-2221 IPC-2222 3b PCB Fab: IPC-6011 IPC-6012 IPC-4101 IPC-A-600 3c PCB assembly: J-STD-001 IPC-A-610

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