Solderable PCB standoffs?

Michael hath wroth:

What you're looking for might be a hex or round standoff. The brass ones are solderable. Most are nickel plated and solderable. Be careful not to get something where the plating can't be soldered such as cadmium plated. See:

Of course it's insane. All good ideas are deemed insane until proven otherwise. Just assume that it's an insane idea and blunder onwards. You'll be yelled at by production at the appropriate time if you need confirmation of insanity.

No, that won't be the problem if you use a through hole and a screw to maintain mechanical integrity. For small tin boards, something like a

2-56 thread might be appropriate. If you're relying on the copper ground plane to support the standoffs, it can be done. However, the last time I did that, I had to use 2-oz copper on 0.062" G10/FR4 (due to high currents). The much thinner 0.5-oz copper on 0.032 board would never have worked, so we used screws and plastic spacers for those.

You may also have a problem soldering it without destroying the board. If you use a vapor reflow or IR heating to solder the surface mount board, the large mass of the standoff will absorb enough heat to burn the board. If not burned, it will warp it due to uneven cooling. It may also be too big to handle, too close to the edge to clamp, and too difficult to rework (if soldering fails). However, if you install the standoffs as a post soldering operation, you could probably control the heating and simplify the fixturing effectively.

Is there some reason you need to solder the standoff to the board? Wouldn't a small screw do just as well? If you're worried about breakage, don't put the hole too close to the edge, use washers, and assemble it in a fixture.

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I wonder if there's such a thing that is shaped like a SOJ-4 (or SMT DIP-4, like optocouplers are) but has a 2-56 thread in it? That could be reflow soldered like everything else, and still provide a lightweight mechanical fastening.

heve you considered PEM nuts?

al

They also have SMD standoff's

I'm about to use them for a product, but haven't actually tried them yet. Will have to do some trials.

Dave.

IME these are a lousy idea. Depending on the mechanical strength of solder as a fastener is dumb. Trying to solder them (and especially to REsolder them) was a PITA. The FR4 didn't like all the heat and the copper got damaged a lot.

SCREWS are the way to fasten a standoff.

I'm not sure.. but check

They have lots of bits and pieces.. D from BC

The knurled press-in PEM spacers are great. You pop them in after everything else is soldered. But be careful not to run traces too close to the holes, and fixture the press operation properly, and don't make the fit too tight, or you'll fracture traces.

John

Also,

As other have suggested, use PEM fasteners. I used them back inthe

90's and they proved the best method of attaching standoffs to pcb's.

How about something like this :

This is where using a decent iron like a metcal with a big tip helps a lot - if you can get the heat in quickly it reduces the risk of damage.

That's almost what I was thinking of. Just bend the legs out to make it an SMT gull-wing. Not much mechanical strength, but very light-weight.

Now that I know what to look for, here's another example:

Although those are 6-32 screws, if you imagine the legs bent out 90 degrees, it's the shape I was thinking of. I don't think you'd want something like that with more than a 2-56 screw's worth of load, though.

Do PEM nuts in FR-4 loosen at high temperatures the way eyelets and lockwashers do? I've always been much happier soldering stuff on if the board might see high temperatures for any length of time.

Cheers,

Phil Hobbs

I've never seen one come loose. Those puppies are *tight*. You'd think things might cold flow, but we haven't seen it. I'd be hesitant to use one for a high-current electrical connection, though. But that's always hard to do on a pc board.

What I hate is a spacer secured by a screw on the bottom of the board, inaccessable, that comes loose when you unscrew something on the other end. That makes me SO MAD.

John

standoff's

That seems like almost exactly what I wanted. It looks like you still have to put in a hole for those, but otherwise that's just about right. I'll check them out.

Thanks!

-Michael

That is the more traditional standoff - would be hard to surface mount the buggers!

We do small enough volume here that not only am I leading electronics design on this project, I also am leading electronics production! I get to yell at myself!

I was hoping to avoid putting a screw through the board. This is a very, very high density board and space is at a premium - hence why I'm hoping to find a surface mount standoff.

I hadn't thought about that - but that's a very good poitn. We typically hand everything to a board assembly house and have them do it - I'll call them ahead of time and see if they're worried.

Soldering will make it more permanent - less parts that fall out when disassembled. Also, hopefully if we can find a surfacemount one we don't have to put a hole all the way through the board.

Apologies if this gets posted twice.

Thanks,

-Michael