Thoughts on single PCB modules where the faceplate doubles as circuit?

I’m not sure if those have a proper name, but if you’re not sure what I’m talking about, here’s a great example by @jkb:

I know that @HAGIWO also runs exposed copper rails of +12V and GND on the back of blank PCBs used as faceplates, for ease of wiring up components. I’ve seen it done a few more times but can’t readily find a link.

How safe are they? How reliable are they? Why isn’t it more common? Any practical concerns?

Size is at a premium in Eurorack, but not in Kosmo, so why not do this more? It would also be possible to use SMD (maybe with JLC’s assembly service), to ensure capacitors and transistors can’t risk being bent, and to conceal it on the back if you are ashamed to put your components on display.


Largely a matter of taste, I suppose. I’m not a fan personally. It’s also impractical for many modules that need panel space for several knobs and switches.


Rich said all that needed to be said. I’ve felt it’s less like something I would use and more like a demonstration that things can be in inappropriate places, like filling a Nintendo 64 controller with Heinz baked beans.

-Fumu / Esopus

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I could see a use case with capacitive touch controls and where the electronics would be surface mounted on the back side, including reverse mount LEDs shining through the PCB.


I like the look, but I’m a geek…

I have bad patch cable hygiene, I often just pull out one end of a cable and leave it dangling. Sometimes I worry that I might short it out against something inadvertently and I guess having those +/- 12v pin headers sticking out might slightly raise the risk of that happening?


I like it because it saves on the costs of boards and I’m super cheap. But I’m also rowdy and inconsiderate, so I’d put the components on the other side to keep them from being knocked around. It also opens up the possibility of finger-based circuit bending, if you’re into that.

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I definitely think there’s great beauty in an instrument that’s not ashamed to expose its internals, takes pride in its handmade nature, and ruthlessly reduces unnecessary costs!

I’d also greatly simplify the mechanical design not to be concerned with making multiple boards stack up properly.

But I’m definitely concerned about the safety aspect, accidental shorts and the like.

(disregard the deleted post above, Discourse UI is confusing and made me post in the wrong thread)


Main issue I see with it is PCB is flexible and there’s a reasonable amount of force involved in plugging and unplugging. Solder is not a fan of such mechanical stress and neither are most surface mount capacitors.

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Thanks for the reactions everyone.

I am either way working on a terrible idea.

I will try to shove that board full of experiments about techniques I’m curious about.

I’m curious specifically about this one! How would this be done? Have the LED in the center of the area to light up and just remove the solder mask and copper around it? Does it yield good results?

This is exactly how I have an STM32 Black Pill mounted on my quad LFO. It’s not on the faceplate though, but it was a bit of a game to wire up. properly.

Thank god for the years of snake played on the old Nokia phones as a kid.

I haven’t done it or even seen it in person myself, but do I want to experiment with that technique someday.
It has been mentioned a couple of times in this forum.
A search of “back mounted LED” leads to links to these articles which could be good starting points.

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I had mentioned it a while ago, but for sandwiched PCBs!

Following a comments in the Hackady post shows a project that has a picture making it very clear how to do it:

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Never done it for synths but in many of the projects ive done for schools i keep components exposed so i can point and talk about what’s happening.
It looks fun and different which always draws me in.
Front, back, on show or crammed in an intricate latice of dead bug wiring and no pcb at all.
Your projects, so you decide.
Grand stuff, im interested to see how far you take this.
Some of the worst instruments in history show their guts… As do some of the best. Crack on sir!


I think it would look kind of cool to have traces running on the front panel of the module, but I wouldn’t want to put components there, or even the solder points of THT components–I feel like it presents too big a risk of shorts/damage to components. If I was going to do it in order to save costs I’d do the circuit in SMD on the back, wire the jacks and switches through somehow (probably a pain in the ass), and then just use traces and silkscreen to make the design and text on the front of the panel. It’s slick, and seems efficient/cost saving, but I think it creates its own issues.