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Is there a reliable way to etch a PCB(from working product) so as to be left with the surface without the substrate? Sometimes an existing PCB product which wasn't designed with weight, size or flexibility in mind is to be reworked.

Looking for a good process to address that aspect of existing PCBs for ultralight weight application projects(air water etc)

Mechanical approaches have serious drawbacks as most PCBs are dual sided but perhaps I am wrong?

Once left with the thinest possible layer of all active components it will be replaced with flexible PCB type base .

Edit : Would 'Aqua regia dissolve the copper/tin as well as the epoxy holding the fibreglass? That is about the only way of doing away with substrate sandwiched in dual sided PCB design

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  • \$\begingroup\$ You're going about this backwards. Start off with a PCB made from something thinner/lighter and work up from there. \$\endgroup\$ – brhans Aug 10 '16 at 17:00
  • \$\begingroup\$ If you erode the PCB, the copper layer will fall off! \$\endgroup\$ – pjc50 Aug 10 '16 at 17:54
  • \$\begingroup\$ There are cases where an existing product comes assembled but I need to shave off the PCB substrate and place the active layer(s) on thin- 'strong' film of some kind. Goal is maximum weight reduction on assembled products. \$\endgroup\$ – Nick Aug 10 '16 at 18:00
  • \$\begingroup\$ Ha ha ha , yes I guess it will fall off :). Should be laid out bare on something flat to address that but the question here is how do you safely remove the substrate? \$\endgroup\$ – Nick Aug 10 '16 at 18:12
  • \$\begingroup\$ If there are wide enough spaces between the tracks on the PCB you could grind/cut/drill all the way through and leave big air gaps... \$\endgroup\$ – brhans Aug 10 '16 at 21:04
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You really, really, want to assemble the circuit on a thinner (or flexible) PCB. If you have gerbers or similar for the PCB, just send them off to a PCB manufacturer and get some thin PCBs made.

If you already have (or are buying in) a small number of single-sided PCBs and need to reduce their weight then you could try grinding down the back. Use a metalographic polisher/grinder to remove the fibreglass - go slowly and use flood cooling. If you're careful, you might get down to 0.1mm or so. You'll also be grinding away most of the legs of any through-hole components so you'll need to check that they haven't come loose afterwards. That won't work on a double sided PCB, obviously.

Most PCBs are a mixture of epoxy resin and glass fibres. You could probably find a strong acid to dissolve the epoxy. The only thing which would dissolve the glass would be HF. Both of those will destroy most components, and getting even a few drops of HF on your hand will kill you.

I very much doubt you'll find a chemical agent which will remove the fibreglass and leave the copper and components undamaged. And even if you did, the end result would probably fall apart before you got it onto the new substrate.

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Generally you will go with a thinner substrate (FR4 or something more esoteric) or simply mount your components directly on a flexible substrate.

Fiberglass isn't really something you want to grind away so you use as little of it as possible :-)

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  • \$\begingroup\$ How about a PCB with the components in place? \$\endgroup\$ – Nick Aug 10 '16 at 17:02
  • \$\begingroup\$ You really want to cut through fiberglass as little as possible. There's a reason why PCB drill bits are carbide and not just titanium nitride-coated. \$\endgroup\$ – Ignacio Vazquez-Abrams Aug 10 '16 at 17:53
  • \$\begingroup\$ True that yet it must be possible to dissolve the substrate and leave the active layer(s) untouched. \$\endgroup\$ – Nick Aug 10 '16 at 18:04
  • \$\begingroup\$ Anything that can dissolve fiberglass can dissolve the components. \$\endgroup\$ – Ignacio Vazquez-Abrams Aug 10 '16 at 18:18
  • \$\begingroup\$ Sorry, I did not mean dissolve the fiberglass but rather the epoxy(or whatever bonds the fibers) holding the fibers. With the bond gone the fibers should just come off on their own. That is my reasoning ... \$\endgroup\$ – Nick Aug 10 '16 at 18:34
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I think a thinner substrate would be the only way to go. The flexible material they sell is close to paper weight and only a couple of mils thick. A little costly. I have seen it on Ebay.

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  • \$\begingroup\$ I have some Kapton tape and can buy the overpriced eBay flexi PCB stuff but the issue is regarding a method of extracting the PCB substrate from existing(working) PCB boards. \$\endgroup\$ – Nick Aug 10 '16 at 18:07

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