PCB Trace Width

[alexisdroso]

Hi, I can not really decide what the width of the traces in a guitar pedal should be. R.G.Keen in a similar post mentioned 0.635 mm for signal traces. Given the fact that I will be not making the pcb myself and I'll have it done for me by a manufacturer is there any reason for the traces to be that big? For example I'm currently designing a fuzz face-like circuit. I know for a fact that the current draw will be no more than a few mA. With such a low current draw 0.635mm trace width seems a bit of an overkill to me. 0.254mm seems much more logical for signals and 0.635 for power, for instance. Am I missing something?

[GGBB]

Why do you feel you need to minimize trace width? For the vast majority of solid state analog guitar effects, it just isn't really that important as far as the circuit goes (extremes excluded). For the layouts I create for etching, I use ~1mm traces because I like how they look. Also, very fine traces are more prone to have problems due to etching inconsistencies.

But for fabbed boards I use .635mm .04mm - again because I like how bigger traces look, and because they give a feeling of assurance that they are better (which probably isn't completely rational). There is nothing gained by finer traces unless you are trying to solve difficult layout challenges and need to fit multiple traces in a small space (such as two between adjacent dip pads). Finer traces risk damage from circuit failures that cause over-current situations, and from overheating while soldering or reworking. Bigger traces make repairs and mods easier.

You of course need to check minimum sizes and clearances etc. for the fab's DRC, but otherwise I say bigger is better.

[alexisdroso]

What about the parasitic capacitances when using wider traces?

[italianguy63]

I usually use a pretty thick trace as a general rule.  If I run into cramped space due to trace routing problems, then I will thin out certain traces to get them to all fit on the PCB.  Lately, I have been doing 1590A work mostly, and things get hairy. 

MC

[alexisdroso]

When you say pretty thick, how thick?  For example if you use 0.635mm for signal traces, what are you using for power signals, 1mm? Are you etching the pcb yourself or send it to a pcb factory to do it? I have etched a few pcbs myself and in that case yes having bigger traces can really help, but when you get the pcb professionally manufactured, where there is far greater precision, I don't understand how bigger traces will help. Yes, heat dissipation is important, but for power mostly, the audio signals don't draw that much current to begin with.

[bartimaeus]

If you're worried that 0.254mm will be too small why not just split the difference and use ~3.5mm?

[GGBB]

I don't understand how bigger traces will help. Yes, heat dissipation is important, but for power mostly, the audio signals don't draw that much current to begin with.

Use the biggest trace width that does not introduce any new problems (layout, clearance, ...)* - why would you use a finer trace when there is nothing gained by doing it and all of the following gained by using bigger traces?

Not just for power - as I said - soldering, rework, mods, repairs, and not burning when something goes wrong. Bigger is better.

*I would add parasitic capacitance except our solid stated analog pedals circuits aren't really affected - clearances are usually large enough and traces not wide or long enough to affect < 10k guitar response.

[italianguy63]

When you say pretty thick, how thick?  For example if you use 0.635mm for signal traces, what are you using for power signals, 1mm? Are you etching the pcb yourself or send it to a pcb factory to do it? I have etched a few pcbs myself and in that case yes having bigger traces can really help, but when you get the pcb professionally manufactured, where there is far greater precision, I don't understand how bigger traces will help. Yes, heat dissipation is important, but for power mostly, the audio signals don't draw that much current to begin with.

I looked at my last project...

The "stock" thickness I used was .8128 mm.  The thin ones where spacing was cramped was .4064 mm.  Typically, I'd say I use ~.6.

I have my boards fabbed.  And, I tend to use heavier traces for GND and PWR.

MC 

[italianguy63]

And, by no means am I an EE or a pro at this.. just my .02.

I am just a DIY hobbyist.  MC

[merlinb]

Why are you people using millimetres?
15 thou (0.015 inch) is a good standard these days, although I prefer 25 thou when possible. Thicker the better really, since it is less likely to rip up when you remove components. Most houses can do smaller, but some might start sending you difficult messages if you want to go much below 12 thou.

[alexisdroso]

Personally, I'm European so I usually use metric, not imperial, just like most of the planet does. Come one guys, imperial system is just a bug 😂 I guess I'll get the traces as big as they can be.

[merlinb]

Personally, I'm European

So am I, but PCBs are designed in imperial. Pin spacings are 0.1 inch, fab houses expect dimensions in imperial...

[GGBB]

I don't use mm - I was translating because the OP used mm. I use 40mil for etching and 16mil for fabbed.

[alexisdroso]

@merlinb Not entirely accurate. I know for a fact that jlcpcb uses metric. I had no problems whatsoever with a couple of boards that I had printed there with the gerber files being in metric. @italianguy63 Although the black silkscreen looks quite neat it makes reverse engineering quite difficult cause you can not clearly see the traces. Other than that cool board man 

[italianguy63]

@merlinb Not entirely accurate. I know for a fact that jlcpcb uses metric. I had no problems whatsoever with a couple of boards that I had printed there with the gerber files being in metric. @italianguy63 Although the black silkscreen looks quite neat it makes reverse engineering quite difficult cause you can not clearly see the traces. Other than that cool board man 

Thanks.. I got in the habit of doing all my boards black.  I just like it.

The Banshee is a reverse-engineered Tube Screamer.

MC

[Rob Strand]

How thin you can go depends on the who is making the boards.   Home made stuff benefits from wider traces since they will still conduct despite pits and over-etching.   Thin traces could become broken.

Also when re-working and tinkering at home the wider traces are less likely to be damaged and peel off.

There's many specific cases for choosing a trace size but current and voltage drops are probably the most common reason to choose fat traces.

[alexisdroso]

That's why it seemed odd to me that wider traces were suggested. I clarified from the very beginning that I would no be etching the pcbs myself, so there shouldn't be any reason for wide traces based merely on the current and the voltage, as the current draw will be only a few mA.

[Rob Strand]

That's why it seemed odd to me that wider traces were suggested. I clarified from the very beginning that I would no be etching the pcbs myself, so there shouldn't be any reason for wide traces based merely on the current and the voltage, as the current draw will be only a few mA.

At the end of the day it boils down to what your manufacturer can do reliably.  If you don't push their capabilities you shouldn't see any issues.

[GGBB]

That's why it seemed odd to me that wider traces were suggested. I clarified from the very beginning that I would no be etching the pcbs myself, so there shouldn't be any reason for wide traces based merely on the current and the voltage, as the current draw will be only a few mA.

What are the drawbacks of wider traces?

[alexisdroso]

Other than making the laying out process more difficult none that I know of.