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DIY Stompboxes => Building your own stompbox => Topic started by: sliberty on October 30, 2017, 09:37:17 AM

Title: PCB Insulation
Post by: sliberty on October 30, 2017, 09:37:17 AM
When building a pedal using PCB mounted pots, how do you insulate between the back of the PCB and the back of the pots? Is there some non-conductive plastic sheet material that I can get and cut to size for this purpose, or is there some other technique that you recommend?
Title: Re: PCB Insulation
Post by: EBK on October 30, 2017, 10:25:28 AM
There are special dust covers you can buy that insulate the back of the pots.  Here is an example:
http://www.smallbear-electronics.mybigcommerce.com/dust-cover-for-16mm-alpha-pots/

However, I personally just use either gaffers tape or double stick foam tape.
Title: Re: PCB Insulation
Post by: bluebunny on October 30, 2017, 10:26:08 AM
I often use the trimmed plastic pouches that are sometimes (still) used to package guitar strings.  Saves throwing them in the ocean.  Or a bit of card.  Or else buy the pots wearing condoms (the pots, not you):

(http://www.taydaelectronics.com/media/catalog/product/cache/1/image/211x211/9df78eab33525d08d6e5fb8d27136e95/V/o/Volume_1-2_32.jpg)
Title: Re: PCB Insulation
Post by: GGBB on October 30, 2017, 10:42:49 AM
The Alpha 16mm PCB mount pots RV16AF-41 have enough space so that under normal circumstances they won't contact the solder joints, but it all depends on whether or not the board can move around (and how big the solder joints are). You should generally make sure the board won't move so that the pot joints aren't stressed. When I use lugged pots mounted with solid core wire, I leave a little room using a plastic ruler as a spacer. Even then I normally use electrical tape for insulation if I don;t have any dust covers. I don't really like the dust covers as they seem to be a little deeper than the space allows so the pots need a little force to sit level which stresses the joints. It's probably possible to trim the covers, but that seems like unnecessary work.
Title: Re: PCB Insulation
Post by: merlinb on October 30, 2017, 11:17:21 AM
The double-sided sticky pads are enough insulation for me:

(https://s1.postimg.org/2ohcpgcly3/wes.jpg) (https://postimg.org/image/2ohcpgcly3/)
Title: Re: PCB Insulation
Post by: Groovenut on October 30, 2017, 12:00:13 PM
When I use 16mm right angle pots, I usually use this

https://www.harborfreight.com/4-fl-oz-liquid-electrical-tape-36821.html

works well for the peace of mind in case the other mountings should fail.

It peals off easily so you could put it on the pcb or the back of the pots

 :icon_eek: :icon_eek: goop :icon_eek: :icon_eek:
Title: Re: PCB Insulation
Post by: mimmotronics on October 30, 2017, 02:04:28 PM
I've personally used the double-sided sticky tape in the past, but might not be a viable long-term solution..would the adhesive lose its grip over time? The liquid insulating goop sounds like an interesting alternative!  :icon_mrgreen:
Title: Re: PCB Insulation
Post by: sliberty on October 30, 2017, 02:33:24 PM
That liquid electric tape looks like a cool solution. I'll have to pick up some of it. Thanks for the tip.
Title: Re: PCB Insulation
Post by: bloxstompboxes on October 30, 2017, 02:48:07 PM
When I use 16mm right angle pots, I usually use this

https://www.harborfreight.com/4-fl-oz-liquid-electrical-tape-36821.html

works well for the peace of mind in case the other mountings should fail.

It peals off easily so you could put it on the pcb or the back of the pots

 :icon_eek: :icon_eek: goop :icon_eek: :icon_eek:

They have a spray on version I have used as well. It was advertised on the package as being good for boats and resisting the salt water/air. I still have it, but use it much anymore since I try to use board mounted pots with the condoms or double sided foam, or velcro.
Title: Re: PCB Insulation
Post by: ElectricDruid on October 30, 2017, 03:30:16 PM
I use PCB-mounted right-angle Alpha pots a lot, and I find that the pot condoms push the pots away from the board. It wouldn't be so bad if the back of them was flat, but they seem to have a little peak on them - probably a moulding flashing or injection mark or something?

My personal favourite solution is overhead transparency plastic. In this age of laptops and projectors, I don't suppose many people use it any more, but there's probably still a lot of it kicking about. I have a pack of A4 sheets that has been keeping me going since the nineties sometime! It's stiff enough that a little bit of sharp wire won't poke a hole in it. I've seen similar plastic sheets used for covers for spiral bound documents, so I'm sure you can still get it. Way cheaper than pot condoms.

HTH,
Tom
Title: Re: PCB Insulation
Post by: J0K3RX on October 30, 2017, 04:38:33 PM
Use this and you can goop your boards at the same time  :icon_lol:

https://www.flexsealproducts.com/product/flex-seal-liquid/
Title: Re: PCB Insulation
Post by: rockhorst on October 30, 2017, 05:29:34 PM
I'd suggest the thick, foamy white double sided tape used to hang up mirrors and stuff, available at the hardware stores. I've tried the pot condoms, dislike them personally.
Title: Re: PCB Insulation
Post by: sliberty on October 30, 2017, 06:58:56 PM
Thanks for all of the replies.

I don't think I want to buy pot condoms for every pot for every build for all of eternity. Plus, one of the responses was that they might stick out too much.

The double stick take thing bugs me because of the risk that it might stick to the PCB and be hard to remove. I suppose I could leave the paper on that side, but who knows if it will stay on for the long haul.

The business card solution might work on some projects. The current one I am working on has the pots oriented in such a way that I would have to use two smaller pieces, and its not clear that they would stay where I put them.

The liquid tape solution sounded cool to me, so I went out and bought a bottle. I am going to give it a try, and will report back in a few days. This whole problem didn't occur to me until I had already solder the pots onto the board. So I'll need to remove them, give their backs two or three coats, let them dry fully (package says 10 minutes between coats, and at least 4 hours to dry), confirm that they are not conducting by using my ohm meter, and then re-solder them onto the PCB.

Stay tuned....
Title: Re: PCB Insulation
Post by: amptramp on October 30, 2017, 08:32:04 PM
You could use Gorilla tape on the back of the pots.  This stuff is much stronger than duct tape and it is difficult to cut through.  Don't use it on the circuit board - if you have to take it off, you may rip components off the board.
Title: Re: PCB Insulation
Post by: sliberty on October 30, 2017, 08:35:04 PM
Hmmmmm....never heard of Gorilla tape until now. I may get a roll just to check it out.
Title: Re: PCB Insulation
Post by: J0K3RX on October 30, 2017, 10:00:42 PM
Could try hot glue stix.. you can get them in all different colors and it peels off fairly easy if needed..
Title: Re: PCB Insulation
Post by: rockhorst on October 31, 2017, 04:28:18 AM
The double stick take thing bugs me because of the risk that it might stick to the PCB and be hard to remove. I suppose I could leave the paper on that side, but who knows if it will stay on for the long haul.
Quite simply put: it will...also, you stick it too the pots back side but not to the pcb. It may touch the tip of solder joint that are sticking out, but it's only 1mm thick (1/25th of an inch) so there's still separation between the pcb and the pot. You're making a fuss over something none existing ;).
Title: Re: PCB Insulation
Post by: italianguy63 on October 31, 2017, 06:35:58 AM
I use double stick tape... The cheap stuff-- the paper falls off too easy.  So, I started using 3M brand-- it is red.  And, too expensive, but luckily you don't use much of it.  It comes in a roll.

MC
Title: Re: PCB Insulation
Post by: EBK on October 31, 2017, 06:38:19 AM
If the backing falls off of your double stick foam tape, simply remove it and add a bit of gaffers tape in its place.  I'll often do that preemptively if I'm after single stick foam tape.

(Unless the backing is falling off while the tape is still on the roll...)
Title: Re: PCB Insulation
Post by: rockhorst on October 31, 2017, 06:42:37 AM
I'll post a picture of the tape and how I use it later. Maybe I'm missing something here, but these problems are alien to me.
Title: Re: PCB Insulation
Post by: EBK on October 31, 2017, 07:02:13 AM
I'll post a picture of the tape and how I use it later. Maybe I'm missing something here, but these problems are alien to me.
Sometimes fear of problems is the problem.   :icon_wink:
Title: Re: PCB Insulation
Post by: italianguy63 on October 31, 2017, 07:39:49 AM
I'll post a picture of the tape and how I use it later. Maybe I'm missing something here, but these problems are alien to me.
Sometimes fear of problems is the problem.   :icon_wink:

Like politics.
Title: Re: PCB Insulation
Post by: EBK on October 31, 2017, 07:46:06 AM
Like politics.
You had to mention the scariest thing possible on Halloween, didn't you?
Title: Re: PCB Insulation
Post by: anotherjim on October 31, 2017, 02:25:02 PM
If you want something that looks more professional than gunk or sticky tape, buy hard plastic sheet, or cut it from packaging. Clear acetate sheet looks good and can be bent up to make locating tabs if you don't want to glue it.
Get it from craft/modelling suppliers. Heat resistant is available.
Example...
http://www.stix2.co.uk/a4-clear-heat-resistant-acetate-sheets
Title: Re: PCB Insulation
Post by: marcelomd on October 31, 2017, 02:58:22 PM
Kapton tape is widely used for this kind of stuff. Also heat resistant.
Title: Re: PCB Insulation
Post by: Groovenut on November 01, 2017, 11:43:18 AM
Here's how it looks applied. It does have some self leveling properties. This is just one coat. (https://uploads.tapatalk-cdn.com/20171101/2694771209e246b4cb000ec8c6f8790a.jpg)


Sent from my iPhone using Tapatalk
Title: Re: PCB Insulation
Post by: ElectricDruid on November 01, 2017, 04:09:15 PM
If you want something that looks more professional than gunk or sticky tape, buy hard plastic sheet, or cut it from packaging. Clear acetate sheet looks good and can be bent up to make locating tabs if you don't want to glue it.
Get it from craft/modelling suppliers. Heat resistant is available.
Example...
http://www.stix2.co.uk/a4-clear-heat-resistant-acetate-sheets

Yep, that's stuff I was talking about! I guess it must be the same as the old overhead transparency sheets, since those projectors used to get really hot.
My solution for holding it in place is to drill holes in it for the pot legs to go through rather than making tabs. I use the PCB for a guide before I put the components on it - draw around it or at least mark a bit big enough to cover the pots, and then poke a pin through the PCB holes to mark the drill holes.
Title: Re: PCB Insulation
Post by: amptramp on November 01, 2017, 06:47:29 PM
I still have a sheet of fishpaper, the grey cardboard material that used to be used as a spacer and insulator in consumer electronics decades ago.  It always seemed to do the job.
Title: Re: PCB Insulation
Post by: blackieNYC on November 01, 2017, 07:14:27 PM
Could try hot glue stix.. you can get them in all different colors and it peels off fairly easy if needed..

I like hot glue to hold down ICs and socketed components BUT I've found you have to make sure a little glue gets under the IC socket, thus wrapping around the component on 3 sides. If I don't do this they come off quite often. You just pick at it a little and you can get it all off quickly.

Insulating a PCB, I use electrical tape BUT I fold it over on itself so there is no stickiness.  And for this one I put a ground plane inside (foil):
(https://i.imgur.com/tFGe0LU.jpg)
Title: Re: PCB Insulation
Post by: PRR on November 01, 2017, 11:48:55 PM
The home store has felt pads for furniture feet, if you fear having two sticky-sides.

"Fishpaper" is (for this purpose*) same-as "paper gasket" stock at the auto parts store. When you fix a 1929 Chevy in a hurry, and do not have the carb gasket, you cut one out of gasket paper. It comes in small and large sheets, thick and thin; start with the smallest thinnest one. Maybe $7? (A rip-off price but still barely profitable to keep in stock.) It does not self-stick, use dab of glue. (*If you have to insulate high-voltage motors, even 120V switches, the auto-parts stock may leak electrons. There is a starter motor repair shop on the industrial side of town which has electrical fishpaper, and may toss you a scrap no-charge.)