Solderable PCB standoffs?

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Greetings dudes and dudettes of the SED:

I feel like I've seen various PCB standoffs over the years that you
could solder on to a PCB. Heck - I feel like I have even seen some
surface mount ones. Anybody know where I can find these buggers? Also,
do you think using a surface mount one would be completely insane?
(I'd be somewhat scared about it ripping up nearby traces if it was
tugged on too hard)

Thanks,

-Michael


Re: Solderable PCB standoffs?

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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:
<http://www.keyelco.com/products/sprod09.asp?CategoryID11%>
<http://www.keyelco.com/products/prod31.asp?SubCategoryID94%>

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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.

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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.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Solderable PCB standoffs?
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That is the more traditional standoff - would be hard to surface mount
the buggers!

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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!

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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.

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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.

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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


Re: Solderable PCB standoffs?

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.

Re: Solderable PCB standoffs?

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How about something like this :

http://www.toby.co.uk/content/catalogue/products.asp?series=PCB%2D1

Re: Solderable PCB standoffs?

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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:
http://www.keyelco.com/products/specs/spec68.asp

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.

Re: Solderable PCB standoffs?
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heve you considered PEM nuts?

http://www.pemnet.com/comp_lit_files /

al


Re: Solderable PCB standoffs?
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They also have SMD standoff's
http://www.pemnet.com/fastening_products/pdf/smtdata.pdf

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

Dave.


Re: Solderable PCB standoffs?
On Mon, 01 Oct 2007 16:49:30 -0700, "David L. Jones"

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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


Re: Solderable PCB standoffs?
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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

Re: Solderable PCB standoffs?
On Tue, 02 Oct 2007 13:13:27 -0400, Phil Hobbs

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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




Re: Solderable PCB standoffs?
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standoff'shttp://www.pemnet.com/fastening_products/pdf/smtdata.pdf
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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


Re: Solderable PCB standoffs?
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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.


Re: Solderable PCB standoffs?

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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.



Re: Solderable PCB standoffs?

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I'm not sure.. but check

http://www.keyelco.com/

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

Re: Solderable PCB standoffs?

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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.
http://www.pemnet.com/fastening_products/pdf/kdata.pdf

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