Using standoffs to mount PC boards

[jefe]

I prefer to mount my PC boards with standoffs, as opposed to taping them to the pots, or board mounted pots that suspend the board, etc. After many years of inspecting the wiring of passenger trains and aerospace harnesses, and being somewhat familiar with mil-spec methods, I'm convinced that the most reliable long term method to mount PC boards is with standoffs, and to use only panel-mount jacks, pots, etc.

Unfortunately for me, I seem to be in the minority. Most of the pedal PC boards I find for sale don't have holes (or space) for standoffs. Take this guitarpcb.com muff board, for example:



There might be some room in the ground plane areas for me to add some holes, but just barely.

Why no love for standoffs?

[jefe]

Tonepad includes mounting holes:

[bassmannate]

I wish I knew, also. I really prefer standoffs with panel mounted pots. That being said, some of the really small layouts have such a light board that you can get away with pcb mounted pots to hold them in place.

[jefe]

I suppose that's true. I've never built anything that small myself, but I suppose I might some day.

[ayayay!]

I just put a dab of hot glue on the back of each pot.   

[jefe]

I just put a dab of hot glue on the back of each pot.   

One of the main problems I see with this: What if you ever want to mod something, or need to change a faulty pot? Now your board is glued in place, and I imagine it's gonna take some twisting and prying to get it off. And generally speaking, twisting and bending a PC board is a good way to break a trace or solder joint.

[amptramp]

I think the problem with standoffs is that they either have to attach to the top of the box where they are going to spoil the smooth surface or they are attached to the bottom lid where you need a longer harness just to open the unit up.  You may be able to bend a sheet of aluminum so that it is mounted securely between the pots and the chassis and has screws sticking up that would hold the standoffs.  Other people have used JB Weld or some similar epoxy to hold the standoffs.  The standoffs are mounted to the board and the board is offered up to the chassis with the standoffs sitting in puddles of epoxy.

BTW, I also have experience with avionics, spacecraft and railway wiring and I cringe at some of the things I have seen thrown together and subjected to the abuse of a tour.

[jefe]

I think the problem with standoffs is that they either have to attach to the top of the box where they are going to spoil the smooth surface or they are attached to the bottom lid where you need a longer harness just to open the unit up.  You may be able to bend a sheet of aluminum so that it is mounted securely between the pots and the chassis and has screws sticking up that would hold the standoffs.  Other people have used JB Weld or some similar epoxy to hold the standoffs.  The standoffs are mounted to the board and the board is offered up to the chassis with the standoffs sitting in puddles of epoxy.

That's how I've done it a few times, but I'm probably going to start mounting them with countersunk screws through the top of the box. Then maybe some JB weld or bondo to hide the screw, and a label to cover that.

BTW, I also have experience with avionics, spacecraft and railway wiring and I cringe at some of the things I have seen thrown together and subjected to the abuse of a tour.

Yep. The engineer in me simply can't throw things together that way.

[StereoKills]

This is why I use tonepad PCB's when doing projects they have available. Use in conjunction with any of the adhesive mount standoffs available from small bear, pedal parts plus, etc......

[jefe]

adhesive mount standoffs

I'm considering those as well, but I still worry about the durability of the adhesive. Nothing beats a hardware-mounted standoff.

But then again, maybe I just worry too much. I need to keep reminding myself that I'm not building an airplane.     

[liquids]

I totally hear you on this issue!

I'm no engineer, but I am always trying to build as cleanly and reliably as I can - or at least more than I did on all previous builds.  I always use standoffs for mounting my boards.  I would never want to do it any other way.  

That being said, I do use the plastic stuff.  It was the first thing I tried, and I've gotten used to it.  I also got a mistake order from smallbear of some 20 or so of them at one point which didn't hurt    I thought that junk would not be very reliable or sturdy, but it turns out they stick better than I wish they did.  As in - put them down once, and that is that, no forgiveness or mercy.  It's done.  I've tried to get them off, and some of the adhesive or whatever junk remains.  I usually have to scrape them off the metal they adhere to via screwdriver or knife or something.

Planning a board with spaces for standoff holes in good places takes extra planning. I use these standoffs: http://www.smallbearelec.com/Detail.bok?no=76


They are 3/16" or something, but they still put the board a fair bit off the bottom of the enclosure you mount them too.  The bigger taller one's are useless for me.  It's hard to see from the pictures but they have a little 'tab' in the middle to keep the board down, requiring you to push the tab inward to take the board off the standoff.    Even after hours of bread boarding and pondering, and rarely solder up my own designs/variations in the same season I started working on them, I still fully anticipate working on the build down the road. So I actually cut that part off, since the shape of the standoff works at keeping the boards down just fine, and it makes it far less work and force to take the board off the standoff, particular in a tighter enclosure.

I dream of metal standoffs, but I don't want more screws showing on the outside of my enclosure, and I don't want the look of JBweld adhering the metal standoffs to the inside of the enclosure.  In the end, I CAN get the plastic adhesive mount standoffs out of the enclosure should I need to if disassemble the build and re purpose the box, but I would abandon ship if the standoffs were epoxied down.

[StereoKills]

Yeah, from my experiences, you have no worries about them coming off.

[~arph]

Those adhesive ones I used, the tape dries out within a year and your board will rattle around. You need something better to keep them in place.

EDIt: So I have a different experience with them

[bassmannate]

Sounds like 3M twin stick...I HATE that stuff! I work on a Best Buy Project Team (I build displays/do special functionality stuff in several different stores) and every store has this ENORMOUS roll of 3M twin stick. More than the store could use in a million years. It's darn near impossible to get cleanly off and it's the first thing that sales people turn to if they need to stick two things together. I've even seen store employees stick temporary signs to walls with this stuff and it ends up pulling the paint off.

To make matters worse, you end up with what arph experiences in that it dries out and crumbles after a while. Maybe the adhesive on some of these is different though.

In short, I wouldn't use this stuff to stick two things together unless they were both temporary items.

[deadastronaut]

ive used the plastic standoffs, but i put a little blob of epoxy on the edges when its stuck down..., i dont trust the sticky to last...


i agree though.many pcb designs have no such holes...take it into photoshop and add them..or

when i cut my pcbs  i try to leave a space at the sides when i cut them....if possible...

[jefe]

In somewhat of a defense of the adhesives used on plastic standoffs... I'm not 100% sure, but I believe some 3M adhesives are meant to be permanent, and if the surface is properly prepared & cleaned, they won't come loose unless you pry off the standoff & scrape off the remnants, as liquids described above. I've used some very tough "industrial grade" dual lock velcro, where the adhesive stays put for several years, with no signs of drying up or anything.

[jefe]

when i cut my pcbs  i try to leave a space at the sides when i cut them....if possible...

I haven't gotten in to etching my own boards yet.. but yeah, I do this when I use perfboard.

[Philippe]

One of the main problems I see with this: What if you ever want to mod something, or need to change a faulty pot? Now your board is glued in place, and I imagine it's gonna take some twisting and prying to get it off. And generally speaking, twisting and bending a PC board is a good way to break a trace or solder joint.

I use standoffs to secure the PCB but some folks use velcro for the same application.

[Maudibe]

Heres a piece, more suggestions always welcome...

http://doctortweek.wordpress.com/2010/08/25/mounting-the-pcb/

[Toney]

Here is one method that may help.
When the PCB has absolutely no room left for mounting, a couple of small blocks of wood and flanges cut from pretty much any hard plastic  can do the trick.
This is window trim which can be bought be the meter/yard for a dollar or two from most hardware stores. It glues easily with a decent sized footprint to the aluminium - using a two-part epoxy adhesive.
I dug out a few millimeters to fit the edges with a hobby knife to fit the board exactly.
The board is sitting snugly in place and the flanges just cover the edges.
Does the trick.