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I know why silicon is used for ICs and transistors in general due to its doping features. But I don't know why we use silicon as a PCBs, all we need is to isolate pins from each other in a PCB, right? So, will any insulating material work? Such as wood?

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    \$\begingroup\$ Where did you see a silicon PCB? Can you think of any reasons why wood would be a poor substrate for a PCB? (I can think of several.) \$\endgroup\$ – Transistor Mar 5 at 13:50
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    \$\begingroup\$ yes wood based PCB's exist (paper impregnated with a binder) \$\endgroup\$ – Tony Stewart EE75 Mar 5 at 13:54
  • \$\begingroup\$ trolling much ? \$\endgroup\$ – Maple Mar 5 at 14:28
  • \$\begingroup\$ PCB "FR4" is essentially fibreglass (same material used for contemporary boat hulls), other laminates and substrates are possible, as Tony points out, wood to save cost or kapton for high temp use. Solder resist is effectively a type of epoxy that is painted on. The copper parts, for the most part , are glued on as well. \$\endgroup\$ – crasic Mar 5 at 14:33
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    \$\begingroup\$ im interested where it was believed silicon was used? \$\endgroup\$ – JonRB Mar 5 at 14:46
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PCB's are NOT made of silicon!

PCBs are made from coated paper (coated to make it somewhat fire resistant), this is the cheap option.

Better PCBs are made from epoxy coated fiberglass, a common material is FR4.

Reasons not to use silicon for PCBs:

  • Silicon is only a good isolator when it is very pure (no contaminants). For making semiconductors extremely pure Silicon manufactured. This is expensive to make but not much of it is needed per transistor / IC so the total material cost per device is quite low.

  • Silicon is very brittle it is simply unsuitable to make a strong PCB that can withstand some mechanical force.

Reasons not to use wood for PCBs:

  • Wood is flammable

  • Wood is not strong when it is thin.

  • Wood can bend over time due to aging and moisture.

Coated paper and FR4 do not have the disadvantages mentioned above. Also, it is easy to coat them with copper to make the connections. It is easy to drill holes in the material. These materials are cheap.

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  • \$\begingroup\$ FR4 suffers from changing properties due to absorption of moisture just as wood does. Maybe not as much, but in certain applications it is noticeable. \$\endgroup\$ – Arsenal Mar 5 at 14:42
  • \$\begingroup\$ Coated paper --> paper impregnated with phenolic resin is a better description. \$\endgroup\$ – Mattman944 Mar 5 at 16:05
  • \$\begingroup\$ Good answer, but a couple of caveats about silicon: Silicon is a very good insulator if you oxidize its surface, turning it into silicon dioxide (glass). This is the same insulator that keeps the tiny charges on EPROM gates from leaking away for tens of years. And sometimes silicon is used as the substrate for multi-chip modules precisely because it has the same thermal expansion properties as the dice mounted on it. And the interconnects on that substrate can be fabricated using the same processes used for making the chips. \$\endgroup\$ – Dave Tweed Mar 6 at 1:35
  • \$\begingroup\$ @DaveTweed Silicon is a very good insulator if you oxidize its surface, turning it into silicon dioxide (glass) I agree but then it is the silicon oxide (SiO2) that does the isolating, not the silicon itself. In an SOI chip fabrication processes one can even isolate every transistor individually on a single die. This allows for high voltage use and/or benefits for RF applications. SOI is unfortunately more complex and therefore more expensive than non-SOI processes. \$\endgroup\$ – Bimpelrekkie Mar 6 at 12:40
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After some research, silicon pcb does exists and there is an industry doing them.

As this publication shows https://www.eejournal.com/article/20130723-siliconcirc/

"Silicon circuit boards (SiCBs) are similar to printed circuit boards (PCBs) but made with a silicon substrate rather than FR-4."

They allow pad pitch of 30-40 micron. Or 3 micron according to the second link.

The main purpose as advertised is ultra high density,for micro scale systems.

This company manufactures them http://www.sbmicrosystems.us/what/silicon-pcbs/

One can see the use, with specific miniaturized ICs into small devices as wearable glasses, health monitoring ring, or substrate interconnect for CPUs/cache memory, nano robotics...

It's a very specific use and they are not meant to replace Pcbs.

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  • \$\begingroup\$ A nitch market. That's what I thought. \$\endgroup\$ – SteveSh Mar 5 at 16:38
  • \$\begingroup\$ Exactly what I was alluding to in my comment. Thanks for doing the research! \$\endgroup\$ – Dave Tweed Mar 6 at 21:10
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Never seen a PCB made from Silicon, for the reasons others have mentioned. Or for wood for that matter.

Materials I have used in designs include FR-4, Polyimide, Duroid (PTFE), Megtron, and ceramics.

Silicon as a substrate material actually does make some technical sense in that if you attaching bare Si chips to the substrate (using flip chip or bump pad technology), the fact that the CTE of the substrate matches the CTE of the chips means that you are much less likely to have cracked interconnects. But, except for some R&D activities, I've never seen that actually used in a product.

Would be interesting to hear anyone else's experience in this area. Maybe I should just make this into a new question.

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