For purely aesthetic reasons1, not for heat dissipation, I am contemplating using MCPCBs for these two applications:

  • Audio frequency circuits, such as a Baby 8 sequencer, Atari Punk console, synthesizer filters, audio effects, etc., and;
  • MCU circuits, such as so called "barebones" Arduino projects, where an ATmega328P-PU is employed, and a clock frequency of 8-20 MHz is used.

Would I encounter any adverse effects (capacitive or otherwise) due to the higher frequency ranges used (when compared to DC, or 50 Hz AC, high power LED applications)? I initially assumed that the metal substrate would act as a PCB wide ground plane, and therefore not cause any problems. However, after thinking about it a bit, I am not so sure.

I have seen MCPCB applications for audio amplifiers, so I assume that, for the former, there aren't any issues. For the MCU applications, would the several orders of magnitude higher frequency of the crystal/clock be an issue?

FWIW, the metal substrate would be of the thicker variety, 3.2 mm or higher, ideally 5 - 10 mm. MCPCB dimensions would be limited to a maximum of 120 x 500 mm, but typically 100 x 200 (or less) mm.

Here is an example of an MCPCB used for an LED:

LEDs on Metal-Core PCBs

1 For live performance of Chiptunes, ByteBeat, and the such like.

  • \$\begingroup\$ I'm confused: MCPCB: Metal core PCB. How does your audience even see the core? it's hidden below a thick layer of lacquer, typically. \$\endgroup\$ – Marcus Müller Apr 20 at 12:55
  • \$\begingroup\$ Very small bars, clubs and gatherings, intimate and close environment... People can quite easily see the equipment and examine it and ask questions. It's not that confusing really, and besides the point which I am asking. \$\endgroup\$ – Greenonline Apr 20 at 12:59
  • \$\begingroup\$ yeah, but I'd need a magnifying glass to tell a normal opaquely lacquered FR4 PCB from a metal core PCB, so what do you expect your audience to bring to your club? Can you point to a photo of what you're looking for? \$\endgroup\$ – Marcus Müller Apr 20 at 13:00
  • \$\begingroup\$ Maybe you are going to the wrong clubs? Along the lines of this \$\endgroup\$ – Greenonline Apr 20 at 13:01
  • \$\begingroup\$ Might be the case! I've never seen anyone run around with a magnifying lens! \$\endgroup\$ – Marcus Müller Apr 20 at 13:02

Generally, you're right: That metal plane is typically nothing but a big ground plane.

There's one electrical difference: That thick ground plane is typically only the thickness of some isolating paint away from the trace, which is far less than the 0.8mm – 1.6 mm of the average fiberglass substrate thickness of two-layer PCBs.

That makes a difference for high-frequency circuitry, where the wave impedance of a trace matters, and the signal isn't actually carried by the conducting trace, but as wave in the isolator.

However, that's RF, not 20 MHz digital – you should be fine.

Note that MCPCBs are typically a pain to solder by hand (exactly the reason you use them – they carry heat away fast), and that you can't have vias through them – and that really limits their usefulness!

  • 1
    \$\begingroup\$ Note that if the track width to MCPCB dielectric thickness ratio were 10:1 the impedance is 15 Ohms and digital with 5ns risetime is 60MHz BW This means you can use the smallest tracewidth that the Mfg can support to raise the impedance. FR4 is the oppposite problem where you want thinner dielectric. \$\endgroup\$ – Sunnyskyguy EE75 Apr 20 at 13:16
  • \$\begingroup\$ @SunnyskyguyEE75 - thanks \$\endgroup\$ – Greenonline Apr 20 at 13:27
  • \$\begingroup\$ Thanks Marcus, useful answer... :-) \$\endgroup\$ – Greenonline Apr 20 at 13:33
  • 1
    \$\begingroup\$ higher W/h ratio is lower Zo and 0.1mm prepreg over MCPCB is 1/8th thick of a 32 mil FR4 so Zo reduces to 20% of FR4 Zo. Ask for 0.3mm prepreg or how to get 25 Ohm Zo for ATMega with trackwidth/thickness ratio ~5. I have never tried but Saturn PCB.exe tells you Zo on Conductor Impedance. MCPCB thickness is not the issue. It is the extreme thin dielectric coating that gives very low Zo \$\endgroup\$ – Sunnyskyguy EE75 Apr 20 at 13:38
  • \$\begingroup\$ then you can spray paint it Candy Apple Red. ☺☻♥­ after you raise the Zo \$\endgroup\$ – Sunnyskyguy EE75 Apr 20 at 13:43

Apparently they can. From Metal Core PCB (emphasis is mine):

Metal Core PCB applications:

  • Lighting : LED Light is the biggest user of Aluminum PCB
  • Power module: Power Converters ,Inverters, solid state relays, power rectifier bridges
  • Power supply: switching regulator, DC / AC converter, SW regulator
  • Communication electronic equipment: high-frequency amplifier, filter appliances, transmitter circuits
  • Audio equipment: input, output amplifiers, balanced amplifiers, audio amplifiers, preamplifiers, power amplifiers
  • Computer: CPU boards, floppy disk drives, power supply devices Office automation equipment: motor drives…
  • Power module: Inverters, solid state relays, power rectifier bridges
  • Car: Electronic regulator, ignition, power controllers…

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