PCB Edge Clips

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PCB Edge Clips

Postby kurth » Thu Jan 15, 2009 7:33 am

I need to build small modules in a 40-pin DIP form factor. I want to use edge clips for the pins (like the Parallax BASIC Stamp), but I can only find edge clips available from metal stamping companies that have $5K minimum buys. Does anybody know of a smaller quantity source of edge clips? Has SparkFun ever considered stocking them?
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Postby leon_heller » Thu Jan 15, 2009 9:27 am

I use SIL turned pins for modules like that.

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Postby VStar650CL » Thu Jan 15, 2009 9:34 am

I'm not very familiar with the BASIC Stamp stuff, but you might want to visit the Mill-Max and/or Keystone websites. Both carry a lot of "oddball" pins and interconnects and their products are both available from Mouser and DigiKey.

http://www.mill-max.com/
http://www.keyelco.com/
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Postby lyndon » Mon Jan 19, 2009 2:50 pm

What do you mean by "edge clips?" Card edge connectors?
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Postby FartingMonkey92 » Mon Jan 19, 2009 2:54 pm

Those little pins that can be soldered on the sides of PCB's...
Google image search "BASIC Stamp" or "Individual DIL-style pins" and have a look...
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Postby TheDirty » Mon Jan 19, 2009 8:28 pm

They look kinda cool, but I don't see any real advantage over standard pin headers and I can't figure out how each individual pin can be put on with such exact placement. You would have to have a jig of some kind, or maybe they come with a temporary jig to hold them in a row.

I guess the benefit would be that it would fit in a chip socket.

http://www.robotshop.se/catalog/images/bs2-ic.jpg
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Postby Sputnik » Thu Jan 22, 2009 1:07 am

A socket itself would work for the soldering jig!!!!!! Or just a hole pattern drilled in a PCB.
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Postby NleahciM » Thu Jan 22, 2009 6:05 am

Seems like a lousy design to me - think about how easy it is to rip one of those off of the PCB. Not only are they surface-mount (thus the only thing holding them on is the epoxy from the lamination process holding the copper pad to the FR4), but they're not connected together so they can't rely on the group strength of the row of pins.

Just awful - I see very little benefit to such a design.

If you really wanted to shave off space from the PCB you could do a castellations (see here if you aren't familiar with that term) on the edges of the PCB and solder normal through hole pin headers into those.

If you must use these surface mount pins at least put some vias on the pad to hold it down some.
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Postby VStar650CL » Thu Jan 22, 2009 7:56 am

Suggested it to him already, but I didn't know the proper term was "castellation." Learn something every day. Thanks!
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Postby macegr » Thu Jan 22, 2009 10:59 am

They're actually forked (bifurcated) and soldered on both sides of the PCB. In the tens of thousands of modules using these pins we ship every year, none have ever come back with a pin ripped off the PCB. That's because these devices are pushed and pulled vertically in sockets or breadboards, side or twisting forces are just not going to happen.

The pins are fragile enough to break after a couple of bending cycles, but in that there is no difference from normal DIP leads.

It saves a bit of space (especially with more than 2 layers) and some FR4, and won't destroy an IC socket like normal square pins would.
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Postby NleahciM » Thu Jan 22, 2009 11:46 am

macegr wrote:They're actually forked (bifurcated) and soldered on both sides of the PCB. In the tens of thousands of modules using these pins we ship every year, none have ever come back with a pin ripped off the PCB. That's because these devices are pushed and pulled vertically in sockets or breadboards, side or twisting forces are just not going to happen.

The pins are fragile enough to break after a couple of bending cycles, but in that there is no difference from normal DIP leads.

It saves a bit of space (especially with more than 2 layers) and some FR4, and won't destroy an IC socket like normal square pins would.

Ah - I didn't realize they were soldered to both sides. So that means you have to be sure to get the right size pin for your thickness of PCB. It does however mean that they'll have some strength - still a fraction of that that you'd get with a through hole pin, however.

I wonder how these are soldered in production environments... They can't be pick and placed - and they have to be soldered in with a jig of some sort to ensure proper pin spacing. Maybe there's some specialized tooling for them? I'd be really interested to hear.

As far as I can tell they actually use more board real estate than a through hole pin (the SMT pads are as big as a through hole pad and then they take up space on the side of the board where the actual pin sits) and force you to put them on the edge of the PCB - but the savings I suppose come from when you want to run tracks on the inner layers. I don't buy that they protect IC sockets as you can get pin headers with any size pins and even round pins.

I'm still having a lot of trouble figuring out why anybody would design these things in to a product. Seems like they add cost, reduce options, reduce strength, and make assembly more difficult. I supposed if you need the connectors to have a specific pitch, they allow you to make the PCB slightly smaller. But that's all I can really think of...
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Postby leon_heller » Thu Jan 22, 2009 11:53 am

It comes down to cost. They are much cheaper than turned pins and can be assembled much quicker. Special tooling is needed, so they are only suitable for large-scale production.

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Postby macegr » Thu Jan 22, 2009 2:46 pm

I posted a picture of them in the *other* thread about these. They come on a strip spaced 0.1" apart. Ours don't have a top strip, but many do, for even better alignment. If you push a strip of leads onto the edge of PCB, they clamp on and maintain alignment until you solder them. So production work does require a jig, but you would not have difficulty doing these by hand.

Through-hole pins depend on solder fillets for axial strength, edge pins are mechanically reinforced with tabs. Therefore a through-hole pin requires a solder pad to extend out beyond the centerline of the pin, increasing the required width of .6" pitch DIP-compatible PCB to at least .7" or .8". A 25% increase in PCB area is significant over large production runs. I would not trust a square header pin soldered into a half-round castellation, all axial forces are now translated into twisting forces on the copper adhesive and the un-reinforced solder fillet which is only wetting one side of the pin.

So I think the edge clip pins do have some immediate advantages if you've committed to this type of design. But for occasional hobbyist use, it may not have enough of an advantage to justify the effort in locating a source, when normal 0.1" headers are so widespread.
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Postby VStar650CL » Thu Jan 22, 2009 3:43 pm

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