Square peg in a round hole


T

Theo Markettos

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
 
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A

Adrian Brentnall

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
 
D

DavidM

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
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?
 
T

Theo Markettos

Adrian Brentnall said:
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.
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...
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 ?)
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
 
T

Theo Markettos

Jules Richardson said:
Are there holes pre-drilled (I assume so) in the PCB for mounting the
connector body?
Yes, I assume they've come from a standard footprint as neither of the
connectors use them. Why?

Theo
 
T

Theo Markettos

DavidM said:
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?
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
 
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D

Dave Plowman (News)

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?
 
F

F Murtz

Theo said:
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
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)
 
F

F Murtz

F said:
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)
OOPS did not see the same idea proposed earlier.
 
T

Theo Markettos

Dave Plowman (News) said:
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?
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
 
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D

Dave Plowman (News)

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