[SI-LIST] Re: PCB tracks

  • From: Alan Hilton-Nickel <ahilton@xxxxxxxxxxxxx>
  • To: PhilippeR@xxxxxxxxxxxx
  • Date: Thu, 08 Aug 2002 15:03:39 -0700

Phillipe,

Far be it for me to not weigh in on the recurring topic of 90/45/curved pcb
traces.

I will agree with the posters so far that there is no signal integrity reason to
use anything other than 90 degree bends, except perhaps for high-voltage
circuits. My reasons for using 45 degree bends are mechanical. 

The process of pcb manufacturing involves several cycles with wash operations
between cycles. The 90 degree bends are harder to clean, retaining leftover acid
and bubbles more readily than 45 degree bends(*). The results can be
over-etching or cracking in the trace, or contamination of the board surface
leading to leakage currents in more sensitive analog circuitry. Since most CAD
packages can do 45 degree chamfers automatically, it costs nothing and results
in what is arguably a more reliable board. 

Since your router can do curved corners, the same logic may apply. Then again,
maybe your board house should be able to do a better job of cleaning between
processes.

But boy, I hate it when those darn electrons go flying off the bends! :-)

Regards,
Alan Hilton-Nickel


Philippe Robert wrote:
> 
> Hi there,
> 
> I am currently in the process of doing a new PCB, at the routing stage. In
> the router that I am using, there is an option to have 90-degree or
> 45-degree angles on the tracks. I know that it is better to have the option
> set to 45 to avoid changing too much the impedance of the tracks. I designed
> few board using that option.
> 
> In the router, there is an other option to have curves instead of angles on
> the tracks. Theoretically, it should be better in terms of impedance as the
> width of the track vary even less.
> 
> Could someone tell me if curves are better than 45-degree angles and why ?
> 
> Best regards.
> Philippe.
> 
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