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Here's how it looks like

enter image description here

The small board with potentiometer is mounted above another board.

enter image description here

I used Connfly 1.27 pitch headers with 1.7 mm body height, cutting its body to approximately 1 mm.

enter image description here

But unfortunately I made a mistake in this design: 1 mm is too much, and boards must be closer than that. Both boards are having vias and pads, and while I cut all the through-hole pins (of potentiometer) so nothing protrudes, it is still bad idea to couple boards together for risk of shortage and capacitance, thus I need about 0.5 mm clearance. The headers are required for electrical connection, so they serve not only as mounting, but also for conducting.

Unfortunately I can not find any headers less than 1 mm height (and these are only on order). I am not sure I will be able to cut 1.7 mm thick header to 0.5 mm - it will simply broke during processing.

What would be a hack for this situation? What can I put between boards, preferably around the header pins, non-conducting and with least capacitance, to serve as a base for boards?

How would you approach this problem with minimal effort and in minimal time, given all the parts are already on the table?

Update: thank you very much for your answers. The plastic spacer solution would be great, except... my thought is that board will be subject to the physical force stress in its plane (when pressing and rotating the pot), and thus this stress will fully apply to the pins and then copper. Not sure how damaging it will be, but putting and leaving the spacer between boards where pins are located will make some relieve for these boadr-copper tensions. Would you agree to this point of view?

The material on hand from the defective power supply I was mentioning is ITWFormex, 0.45 mm thickness. It does not list the exact type of plastic, but looking to all the datasheets I see dielectric constant of no more than 2.22, therefore small spacer of 3 sq. mm with 0.45 mm thickness on the pins gives about 0.14 pF capacitance, which is tolerable within the design.

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    \$\begingroup\$ Do you need the spacing between the boards to be precisely controlled? What is your tolerance for the spacing? \$\endgroup\$
    – Elliot Alderson
    Apr 20, 2021 at 18:45
  • \$\begingroup\$ Can't you simply find some piece of flat plastic of the desired width and cut to the shape? Well, unless it is supposed to be production solution.. \$\endgroup\$
    – Eugene Sh.
    Apr 20, 2021 at 18:49
  • \$\begingroup\$ @ElliotAlderson Ideally all 4 must be of same height so that boards be parallel and potentiometer wheel goes out of chassis properly. \$\endgroup\$
    – Anonymous
    Apr 20, 2021 at 18:54
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    \$\begingroup\$ What value of stray capacitance will be unacceptable? Reducing the space between boards will increase capacitance between adjacent conductive parts. \$\endgroup\$
    – Theodore
    Apr 20, 2021 at 19:33
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    \$\begingroup\$ I think you might be over-estimating the mechanical strain relief the plastic body of the pin headers would provide. \$\endgroup\$
    – spuck
    Apr 23, 2021 at 14:36

4 Answers 4

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I would not try to make headers with a 1 mm body, I would simply put a plastic spacer between the boards, and use bare pins to make the connection.

  • cut a bit of plastic card or cardboard of the required thickness. Make it smaller than the board so it doesn't cover the header holes (more or less the size of the potentiometer footprint). You can glue it in place or you can use it as a soldering guide and remove it after assembly
  • push (hard) the plastic body down to one end of the headers pins, but do not slip it off completely so they're easier to handle during soldering
  • insert the headers from the top and solder the bottom
  • remove the plastic body completely and solder the top (or vice versa, whatever order is most convenient)
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    \$\begingroup\$ Agreed. A couple of layers of Kapton tape is a good alternative to a plastic shim. \$\endgroup\$
    – pericynthion
    Apr 20, 2021 at 22:15
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A thin spacer for this as a hack or refit and not a mass production method would be kapton or similar tape. Non conductive and high temperature. And a fixed height.

For mounting and conductivity your are better off skipping the headers and use Castellations. Plated half holes soldered to matching pads on your board.

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I agree with the other answers that a piece of insulator between the boards is the best option.

For the insulating material, you can use another PCB.

0.6 mm thick PCBs are available from most PCB manufacturers. And you can get it manufactured to the correct shape and with the required holes for the pins to get through.

The FR4 PCB material is a very good insulator as long as you don't place any conducting copper traces on it.

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    \$\begingroup\$ How about making the PCB carrying the potentiometer out of extra-thick material? No spacer, just two PCBs sandwiched directly together. \$\endgroup\$
    – spuck
    Apr 21, 2021 at 19:33
  • \$\begingroup\$ @spuck OP mentions that there are vias and plated-through pads on the potentiometer board, so those could short-circuit. \$\endgroup\$
    – jpa
    Apr 22, 2021 at 4:05
  • \$\begingroup\$ it should not be difficult to lay out the potentiometer PCB to make sure any vias on it do not line up with any exposed copper on the larger board. The vias can also be "tented" with solder mask. \$\endgroup\$
    – spuck
    Apr 23, 2021 at 14:34
  • \$\begingroup\$ True, but depends totally on application. Usually solder mask is not regarded as a reliable insulator, but perhaps it is acceptable for low voltage use. \$\endgroup\$
    – jpa
    Apr 23, 2021 at 16:02
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Assuming you will be hand-soldering in limited quantity:

Cut a sheet of insulating material the same shape and hole pattern as the potentiometer board. You might use thermal interface sheets since they have a known insulation value and thickness, and can be purchased with adhesive to make assembly easier. (You could use something less expensive too.) Attach the sheet to the main board.

Align the two boards together and solder bare wire or individual bare pins through the holes.

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  • \$\begingroup\$ Yes, hand soldering and in limited quantity. I have old defective power supply, it has relatively big sheet of plastic between PCB and chassis (covering its electronics). What this material is, and do you think I can use it? I think it is fire retardant. Not sure about its electircal capacity resistivity... I can cut small bases for pin connections, no nessesity to cover whole space of the pot board (and dry air is anyway better dielectric constant than anything else). \$\endgroup\$
    – Anonymous
    Apr 20, 2021 at 19:56
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    \$\begingroup\$ You only need the spacer in order to solder it, so cut up a cap’n crunch box and make a calibrated spacer. Solder board. Remove spacer. \$\endgroup\$
    – Kartman
    Apr 20, 2021 at 22:02
  • \$\begingroup\$ @Kartman updated the question \$\endgroup\$
    – Anonymous
    Apr 21, 2021 at 10:22
  • \$\begingroup\$ I wouldn't be too concerned about strength - you’ve got more than enough pins methinks so it will be unlikely you’d be able to break it. The pot will fail before the solder/plate throughs. \$\endgroup\$
    – Kartman
    Apr 21, 2021 at 12:52

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