4
\$\begingroup\$

I have soldered several small PCBs, and I want to stack them together (using hex spacers).

However, since lack of (vertical) space it could be that some components (on the top) might touch the wires/solder junctions (on the bottom) of the PCB above.

What is a good way to prevent this?

I was thinking about thin wooden or plastic plates between the layers, however, this will cost some (vertical) space, especially where the wires/solder junctions from the above PCBs are lower than the top components of the PCB below.

So another way I thought was to use two 'layers' of electrical tape, stick together (with the 'glue' sides towards each other). So it is like a flexible 'plate'.

Would such a thin (< 1 mm electrical tape 'layer') be enough to isolate signals around 5 V, and very low current (DMX512 signals)?

\$\endgroup\$
  • 5
    \$\begingroup\$ Why not just buy bigger spacers? \$\endgroup\$ – MCG Nov 6 '18 at 11:55
  • 1
    \$\begingroup\$ Is this a through hole PCB or surface mount? i.e. do you have pointy clipped-off legs sticking out of the board? Are the PCBs populated both sides or just one? \$\endgroup\$ – Jack B Nov 6 '18 at 11:59
  • 2
    \$\begingroup\$ In that case, can you not change the PCB layouts so that the components do not clash? A bit of care taken in the layout stage could easily fix this \$\endgroup\$ – MCG Nov 6 '18 at 12:09
  • 3
    \$\begingroup\$ If it is a one off project, then go with the Kapton take as mentioned in the answer by BenAdamson. If you are planning on doing more, redesign the PCB and make sure to consider these things in future \$\endgroup\$ – MCG Nov 6 '18 at 12:16
  • 2
    \$\begingroup\$ You shouldn't just worry about shorts. Mechanical stress can also break parts. And adding a layer of tape without separating the boards will only increase the stress. So I'd say don't do this, find a way to physically separate the boards. \$\endgroup\$ – The Photon Nov 6 '18 at 17:47
14
\$\begingroup\$

Kapton tape is a widely available industry standard product for this scenario. You can view the specs here - from table 3 you can see that it has a dielectric strength of over 100kV/mm, plenty strong enough for your purposes. It comes in different thicknesses but any standard 'off the shelf' kapton tape will suffice.

I'd recommend it over electrical tape as electrical tape tends to leave a sticky residue and is thicker, which may be undesirable given your height restrictions.

\$\endgroup\$
  • \$\begingroup\$ I will check into it; the stickyness is not a problem, since I want to stick two layers of electrical tape between each layer, one up, one down, so the sticky sides are stick together. \$\endgroup\$ – Michel Keijzers Nov 6 '18 at 12:11
  • 2
    \$\begingroup\$ Cut-off component legs may puncture Kapton tape. Especially if it's pressed onto them by other components. If you're going this way, I would go over the bottom of the PCB with end-cutters and trim the ends of the legs carefully first. Use a wide Kapton tape, and overlap it a bit to make sure it sticks well. \$\endgroup\$ – Jack B Nov 6 '18 at 12:22
  • 2
    \$\begingroup\$ Use Kapton sheets, not tape - you can get a variety of sizes. \$\endgroup\$ – Jon Custer Nov 6 '18 at 16:43
  • 1
    \$\begingroup\$ @JackB I've seen some boards use a thin flexible layer of foam covered by plastic on one or both sides to avoid the puncturing issue. \$\endgroup\$ – user71659 Nov 6 '18 at 18:20
  • 2
    \$\begingroup\$ If the height is really close enough for different types of tape to matter, then you probably want something more abrasion resistant. \$\endgroup\$ – Chris Stratton Nov 6 '18 at 18:47
3
\$\begingroup\$

As people have pointed out, you need mechanical strength against puncture and abrasion as well as insulation.

"Press Paper"/"Elephantide"/"Insulation Paper" is ideal for this task and is available in many thicknesses/grades.

Mylar film is also commonly used if you need something really thin. It is not quite as mechanically robust and has an increased cost though.

\$\endgroup\$
  • 3
    \$\begingroup\$ +1 We always called this stuff "fish paper", perhaps wrongly. \$\endgroup\$ – Spehro Pefhany Nov 6 '18 at 19:13
  • \$\begingroup\$ I think it is a bit too thick for my project, but I upvoted because I didn't know this existed and may be handy in future projects. \$\endgroup\$ – Michel Keijzers Nov 6 '18 at 19:41

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.