PCB Tracks - What can I get away with?

Paul Beard 2 years, 1 month ago

Hi all, this is my first PCB layout, so please forgive any naivety!

What is the approximate current capacity of "Thin", "Standard", "Thick" and "Extra Thick" tracks in the Fritzing PCB layout view?

How close do I dare place tracks, to other tracks and pads, assuming low voltages (<= 12V) and frequencies (<=500KHz)?

Assume I am planning to use Fritzing Fab or some other commercial manufacturer, rather than etching my own board.

For example, using thin tracks (16mil), and a grid of 0.025", I can place a track to run between two pads of a DIP package, and they don't seem to be touching. Will I get away with that, or is the etching process not that precise?

Thanks,

Paul

Jonathan Cohen 2 years, 1 month ago

Hi Paul,

Here is a thread with some useful pointers about current. For Fritzing fab, leave a minimum of 6 mils (a mil is .001 inch) between pads and traces or other pads. Other fab specs here.

- j

Paul Beard 2 years, 1 month ago

Cheers Jonathan.

So, some approximate, safe, conservative and easy to remember figures would be:

Thin: 1A

Normal: 1.5A

Thick: 2A

Extra thick: 2.5A

On the question of running tracks close to pads, how can I measure the gap to check its more than 6 mils? Will the ruler tool go that small?

Sorry, another question about Fritzing fab  that I could not see explicitly answered on that page: would the board I receive have all component holes drilled for me, and if so, are they through-plated, so I could run tracks from the hole on both sides of the pcb?

 

Thanks again, 

Paul

Jonathan Cohen 2 years, 1 month ago

For measuring, I would use the mouse position indicator in the status bar at the bottom of the window. Click on it to change the units (I think the default is inches). Zoom your view way in, then move the mouse to each edge of the feature for which you're trying to measure distance. The position indicator shows three decimal places for inches, so the last digit is mils. Subtract one position from another to get the distance.

Alternatively, export to Gerber (since this is what eventually gets used for the actual fabrication) and open the exported files in a Gerber viewer--most of these have some facility for measurement.

All holes/pins with non-zero ring-thickness will be drilled and through-plated.

- j

 

Paul Beard 2 years, 1 month ago

Excellent, thanks Jonathan.

Paul Beard 2 years, 1 month ago

Unfortunately, I can't get thin tracks (16mil) between the pads on DIP packages. There only seems to be about 4 to 5 mil clearance, using the mouse to measure the gap at 1000% magnification. Can someone confirm this please?

Thanks,

Paul

Jonathan Cohen 2 years, 1 month ago

Hi Paul,

I would suggest using a thinner trace--you can type directly into the trace-width combo box in the Inspector--any value from 8 to 128 (just type in the number, the units are assumed to be mils).

As of Fritzing 0.7.5, if your DIP comes from a Generic IC, you could also consider shrinking the ring-thickness of the pins you are trying to pass between, but thinning the trace is the more usual option.

- j

Paul Beard 2 years, 1 month ago

Thankyou Johnathan, I did not realise I could type a thickness. That will make some tricky bits of routing a lot easier!

Jonathan Cohen 2 years, 1 month ago

Hi Paul,

Are the values "extra thin" and "super fine" not visible on the trace width popup?

- j

Paul Beard 2 years, 1 month ago

Hi Jonathan, there is nothing  smaller than thin 16mil in the dropdown list, but I was able to type in 8 and my track now passes between dip pads with just over 6mil to spare either side. Think I am already a version of Fritzing behind.

Cheers,

Paul

Jonathan Cohen 2 years, 1 month ago

Hi Paul,

Thanks, that explains it--we added those dropdown menu items fairly recently.

- j

 

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