Square peg in a round hole

We've just received some PCBs back from fab, and there's a problem. The boards have an PC motherboard-style power connector which is to take a significant current (10A or so). The footprint will take either a straight-through or a right-angle connector, and was prototyped with the straight-through version which have flat pins. The holes are plated-through, and the plating is electrically necessary.

We need to use right-angled versions. The only R/A connector available has square pins. Our holes are the same diameter, but round. D'oh.

So how might I go about making a large number of square pins fit in round holes? There's hundreds of pins to do, and a PCB respin is awkward. It's a tight enough fit that simply hammering it in isn't going to be a great idea, and filing the holes out is a no-no because of the plating. Filing the pins with a flat file is going to be hard work (especially since they're quite close together and can't be removed from the connector).

I did wonder about getting a die to cut a thread on the end of each pin (ie make it round), but 1mm diameter dies don't seem to be easily available. Is there something similar around?

Any other ideas?

Thanks Theo

Reply to
Theo Markettos
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HI Theo

I use diamond hole drills for glass-work. They consist of a hollow tube, with diamonds bonded to the 'business end' of the tube.

Might it be possible to use one of these as a sort of 'auto-file' - just to grind off the corners from your square pins ?

When used on glass, they need water-cooling - don't know if they'd need that for metal-cutting.

Alternatively, can you find somebody who can drill a 1mm hole into the end of a dremel-style mounted abrasive drum - that you can use to re-form the end of the mains socket pins.

Don't know what the effect might be of removing material from the pins - they might be plated to aid solderability, so you'd need to know that whatever's under the plating will solder OK - also that you're not affecting the current capacity of the socket (are there approvals issues, perhaps ?)

Regards Adrian

Reply to
Adrian Brentnall

How about drilling out the holes then soldering the connector pins on both sides to remake the electrical connection of the plated hole - or are these multilayer (ie not just double sided) pcbs?

Reply to
DavidM

Are there holes pre-drilled (I assume so) in the PCB for mounting the connector body?

cheers

Jules

Reply to
Jules Richardson

Are there holes pre-drilled (I assume so) in the PCB for mounting the connector body?

cheers

Jules

Reply to
Jules Richardson

Hmmm... there's an idea. I could laser cut a small piece of glass to the appropriate size with a hole in it, and then epoxy that in the end of a pen or similar (tolerances between pins are quite tight, so the tool has to be pointy). I'm only cutting copper, so it should be reasonably soft and amenable to glass. However if this goes wrong it sounds like a recipe for blood.

I'll see if there's any Dremel fittings lying around I can abu^H^H^Hexperiment upon...

No approvals issues, and taking off 0.4mm off the corners of the pins won't do too much harm to the current capacity (the straight-through connectors have smaller pins and the same current rating).

Now rummaging in the kitchen to find glass jars small enough to laser cut...

Theo

Reply to
Theo Markettos

Yes, I assume they've come from a standard footprint as neither of the connectors use them. Why?

Theo

Reply to
Theo Markettos

It's possible - it's only double sided, and there is access to the component side pins on the R/A connector, though I don't know if I can get a fat enough bit in to transfer sufficient heat. I'll try.

Theo

Reply to
Theo Markettos

Theo Markettos wrote: SNIP

Apart from looking for a different connector, which you couldn't find, but may nonetheless exist somewhere at a price, is there room for a tiny auxiliary or piggy-back adaptor board to take the connector and wire links or pins to the main one?

Reply to
Martin Crossley

Oh... hmm. Well, I was wondering if you could solder round vertical pins to the PCB, then solder a square-pinned connector to those - it'd hardly be elegant, but better than re-doing a bunch of PCBs (and quick, too).

My concern would be mechanical strength, though (even if power cabling was plugged in and supposedly never removed), so I really wouldn't trust it unless there was also a way to physically anchor the connector to the PCB.

As a second possiblity, maybe an off-board, in-line connector with short flying leads to the PCB?

cheers

Jules

Reply to
Jules Richardson

Just as an aside, the OP hasn't actually said what these PCBs are for.. if its military or medical stuff then most of the solutions proposed would be unacceptable. It should be noted that we used press fit connectors that had square(is) pins and it may be the case that this is the case here, if so insertion tools should be available to fit them.

If its a bit of consumer stuff then drilling it out and soldering both sides appears to be pretty obvious if the pads are big enough to form a good joint without the through plating.

Another possibility is to square the holes with a square pin in a press if its just a small error.

Reply to
dennis

What pitch are the pins? Could you modify a pair of suitable pliers by drilling a hole in them to act as a crimp to change the pins from square to round?

Reply to
Dave Plowman (News)

Make some sort of crimping device that forces the square pins round. You may be able to modify heavy pliers or small bolt cutters by creating flat meeting jaws and drilling a round hole of correct size in the meeting faces.(if you can understand my ramblings)

Reply to
F Murtz

OOPS did not see the same idea proposed earlier.

Reply to
F Murtz

How about redrilling the holes larger, and hence loosing the through plating. Then soldering in a slightly longer than board thickness length sleeve - this can be soldered top and bottom on the outside to remake the through board connections. The RA connector pins then drop through the sleeves, and can be soldered like normal.

Reply to
John Rumm

That sounds like a good idea. Or at least mangling the pins with pliers sufficiently might work. Pins are 1.14mm square on 4.2mm pitch.

For now I've soldered them by pushing in the pins as far as they'll go, then putting solder paste in the other side of the hole. Heat the solder paste and it surrounds the pin and drops through to the inaccessible component side of the pad (paste has a lot more flux than solder wire, and is a bit more mobile). Then fill up the hole with wire solder.

It's electrically good and isn't mechanically too bad. It'll probably do the job until we can respin the boards.

Theo

Reply to
Theo Markettos

I'd say that's wide enough to get strong enough square nosed pliers in. You might need a tungsten drill, though.

Reply to
Dave Plowman (News)

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