Internal and external tracks?

[ants]

I'm using a track width calculator for a circuit board. It gives two results one for internal tracks and one for external ones. What is the difference?

The calculator is here:

https://www.desmith.net/NMdS/Electronics/TraceWidth.html

Thanks.

 

[keith1200rs]

Surface tracks can dissipate heat into the air easier than internal tracks.

Keith

 

[ants]

Ah I see, so internal ones are sealed in come way. Thanks.

 

[keith1200rs]

Yes, clad with an insulating layer of fibreglass.

Keith

 

[ants]

I won't be using internal ones so that is good.

Do you think I could get away with traces at 0.3mm for 1 Amp? The website I've been using says 0.15mm would be ok at standard 35 micron thickness, it just seems very narrow to me.

 

[bdsplexus]

What temperature rise are you designing for? Is 35um your finished trace thickness, or are your traces plated up thicker than that? IPC-2221 indicates 0.3mm for a 10C rise in 35um copper at 1A, or 0.15mm for a 30C rise in 35um copper at 1A. This standard is widely accepted and generally agreed to be conservative. If you want a more aggressive estimate you might try referring to IPC-2152, published last year. That would allow you to obtain a more accurate estimate, but requires more information about your design such as indication of the substrate thickness, substrate material, whether you have planes present, whether you are running an array of parallel conductors, etc.

 

[keith1200rs]

Bear in mind that the widths you are calculating are looking at heat and voltage drop. If it was an analogue circuit or switching regulator then you also need to consider the effect of the inductance.

Keith.