Self etched PCBs: what trace width and spacing should I use?

[Bricolo]

Hi all,


I wanted to know what was the minimum trace width and spacing I could use with DIY PCBS. The printing is done on a laser printer.

And, what's a good trace width for line level audio use?


Thanks
Alex

 

[Bricolo]

Eagle's default setting is 16mil tracks with 8mil spacing

Isn't this a bit small?

 

[chris ma]

Help needed?

If you care to sign an oath with a lawyer and a witness to promise you are not going to produce this PCB for commercial gains or groupbuys then our senior citizens may entertain you.
Otherwsie I think you may be on your own due to no fault of your own of course!

The Butcher

 

[Bricolo]

It's for a personnal project, nothing to sell

 

[pinkmouse]

I have never used the laser method, but I suspect you might want to make up a test sheet for minimum line spacing, lots and lots of lines at different pitches and see what works with your toner and paper.

 

[Bricolo]

ok I'll try that

and what about the trace width? what's a good size?

 

[chris ma]

Hi,

I am not so sure about the size of the tracks and spacing if you have doubts regarding the software's default setting then go overkill for safety by manual setting if it is an option.

Let me share my experience with laser prints and iron onto the copper. I like to set the print to BOLD to ensure enough toner but when you have spacing too close to each other then there is a danger of BOLD would make a short! As pinkmouse stated try and experiment. At this stage you are not going to ruin the copper board since you can wipe it clean and start printing again..

hope this help

The Butcher

 

[Bricolo]

Now I'm not sure I understoor your advices, Al and Chris


Did you mean, printing and etching a test pcb, or only printing it and see the result on the transparency?

 

[pinkmouse]

I would print and etch, just to make sure. You only need to use a scrap of cheap phenolic board, doesn't need to be anything special.

Use a group of lines of one size, not just a pair, though, that will average out any inconsistencies in etching.

 

[TroelsM]

My experience

I have made a lot of PCB's with trackwidth: 15mills and track-to-track spacing: 12mills without any errors. The biggest source of error is usually the poor quality of the PCB that are available to me.

If there is the smallest scratch in the protective foil you'll get an error in you design. But the same goes for the quality of your print-work.

HP's Laserjet 4 (and maybe 5) are some of the best. They will print perfekt every time even for smaller trackwidths.

TroelsM

Denmark

 

[Mike Gergen]

Keep any spacings between hi voltage and signal lines at least 4 mm. This means between anything over 40V peak and signal or ground level.

This is a UL standard for safety spacings.

I do 15 mil tracks all the time on home made boards.

 

[Bricolo]

it's not for high voltage

ps will be +-15V, and signals aroung 2V rms

 

[Bricolo]

Does this look acceptable?

Spacing is eagle's default setting (8mil), but I changed the trace width to 1mm

http://roulz.free.fr/DIY/board.pdf

 

[pinkmouse]

I'd leave a bit more spacing than that, otherwise soldering will be a real pain...

 

[Bricolo]

I'd leave a bit more spacing than that, otherwise soldering will be a real pain...

OK.
For soldering, so just arounf the pads, or also for the tracks?

This spacing allows me to have a full groundplane, going nearly everywhere since it even goes between the pads.

Are the traces ok, or too thick?

 

[Bricolo]

Here are 2 others:

http://roulz.free.fr/DIY/board-12.pdf (12mm spacing)

http://roulz.free.fr/DIY/board-16.pdf (16mm spacing)

 

[acenovelty]

HP4 Laser will print very cleanly down to 1/64 inch, both trace and spacing (.3969mm for the rest of the world.)

Prosit

 

[Bricolo]

So, only down to 16mil??

I printed the first pdf (8mil) on my canon bubble jet, on a sheet of paper
and the result is ok (except at one 45° trace)

so a laser printer on a transparency will do better, I think

 

[peranders]

I have made pcb's with 13 mil traces but this is something you must test yourself. I have made pcb's with traces between IC pins.

 

[Bricolo]

13mil? That seems small

what's a reasonable width for line level audio signal?