SMT Nut, need to guessestimate the max torque

Another example is the one on page 5:

Technical data on page 17, so maybe I have answered my question myself :-)

Cheers

Klaus

Press-in and solder-in nuts and bushings and such are pretty common. The important part is to use them in tension, through the board, where possible. And back that up with some stiff wave or cone style washers.

I'd be less trusting of a bolted connection, secured with solder and foil alone. Especially if stiff, heavy wires are involved. (Low-number-of-strands wires, solid-core or flat strapping, or Litz if it's unusually stiff or the soldered end is too crunchy and bears a lot of leverage on the lug. Although straps and brackets tend to be formed to shape, so can be much better than anything.)

If you're already doing the intuitive thing, then, I'd expect they'll take as much torque as you care to crush the PCB with!

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website:

Hi

I have a project where I need very high current from a wire on a PCB, and a connector wont cut it

So, I have looked into SMT nut designs/SMT fasteners:

The nut is reflow or wave soldered to the PCB, and the production people mount a spade lug/ring to the nut with a machine screw and a spring washer

But, I am worried about the force applied when tightning the screw might damage the solder, and I cannot find information on the SMT nut max torque

Anyone used these before and have first hand knowledge?

This one has 0.5Nm force, maybe that's the maximum torque?:

Cheers

Klaus

It's much more complicated than that, probably over your head:

How much current?

Pressed in PEMs work fine in PCBs.

We also like to use faston lugs to connect wires to boards. Sometimes we use a u-shaped double faston, and run two wires, which equalizes current a bit. We also use multiple wires in AMP/Molex type connectors, again to balance the currents some.

Klaus Kragelund schreef op 08/04/2015 om 11:52 PM:

How much current do you need to handle? I have been using these in several designs up to 20A:

For a very high current design (160A) I put a busbar over the board (gold plated) and used nickel plated brass standoffs + bolts to get the power where it needed to go.

Wurth also has press-fit nuts in various shapes. These don't need to be soldered but pressed into the board. A press-fit connection is more reliable than a solder joint (especially long term). Backplane for telecom equipment are often using press-fit connectors for this reason.

Nm=torque

Thank you for the links, but I do not think we are over our head, we are used to use special/custom parts and performing the relevant tests

Funny about the Lugsdirect site, they talk a lot about precautions etc, but their soldering is amateurish, really crappy, along with bad pictures and ugly looking website. I wouldn't use them as a supplier for sure.

Cheers

Klaus

About 30A rms, but we need either double the current for derating - or special tests to confirm that we can violate derating rules

We are currently using pressfit THT parts, but they are a nightmare for the production (very high insertion force)

Like these: (but with 3 times more pins)

Cheers

Klaus

I couldn't find a pressed in for 1.6mm PCB

Found the microPEM which looks nice on Page 8:

Cheers

Klaus

Oh, I like those with tabs that go into the pcb. We use PEM nuts into sheet metal, but not into pcb. I'd give them (or Wurth) a call and talk to an engineer. The PEM nuts will need a strong insertion force too. The ones for metal have a knurled shoulder that deforms the metal it's being pressed into.

George H.

Wurth does a lot of weird stuff!

30 amps, or especially 60 amps, could cause serious PCB trace current crowding and heating. FR4 cold flows when it gets hot, which can loosen things up and increase resistance and make things hotter, which can be a runaway situation. So soldering is better than pressfit here.

I like to use several wires into several PCB contact points or connector pins, so that the external wire resistance equalizes the currents at the PCB connection points. I'd expect that the current per pin of those Wurth things would be badly balanced.

Beware FR4 cold flow!

Den tirsdag den 4. august 2015 kl. 23.52.41 UTC+2 skrev Klaus Kragelund:

does it have to be smd or pressfit?

-Lasse

Worry, too, about the forces on such a wire;; if it flexes the printed wiring board, your surface mount components will achieve their breaking stresses, one at a time...

Laptops often show component failures near connectors, because of the cable-induced strains.

Yes, we have in mind to use flexible wire, for the sake of stress relief

Cheers

Klaus

It can be either. The SMD is attractive, since we do not add a process to the production line

Cheers

Klaus

if you can use though hole digikey has quite a few regular screw/spring terminals rated for +30A

-Lasse

Klaus - mount one of the nuts on a piece of scrap board and use a torque wrench to find the breaking point. Divide the result by three & consider that the max operating force.

Hul

Klaus Kragelund wrote:

Yes, that's allready in the works, ordered some parts

Cheers

Klaus

and a connector wont cut it

YY9yCh3Yawnm

ple mount a spade lug/ring to the nut with a machine screw and a spring was her

ght damage the solder, and I cannot find information on the SMT nut max tor que

used to use special/custom parts and performing the relevant tests

ut their soldering is amateurish, really crappy, along with bad pictures an d ugly looking website. I wouldn't use them as a supplier for sure.

Like I said, you're over your head, and judging from your response, WAY ove r your head. Even your question is completely backward. The required tighte ning torque, as a function of material and hardware size, is independent of what your soldered nut can withstand. To give you an idea, for steel hardw are:

1/4 in screw -> 80 in-lb 1/2 in screw -> 480 in-lb 3/4 in screw -> 1050 in-lb It gets even worse for Al. Torques less than these get a substandard connection that ignores nearly 10 0 years of field experience. Now THAT is something that can be called "crap py."