It’s standard practice to avoid joining small PCB traces at 90 degrees, but instead to join them at an angle. But does it matter for thick traces?
Above and below are some 0.020″ or 0.024″ traces. Is it really going to matter, with a pad-size trace, what angle the joining trace hits the other one?
Convention would have you do something like the alternative layout below. Either like “A” or like “B.” But, is it really necessary and worth the extra time required to do that?
Part of me really wonders and another part of me says, it shows attention to detail and implies that the entire design was produced with the same care. It’s that elegance in design thing.
The other question I have relates to “B,” in the bottom image. Does it matter which direction the 45 degree trace intersects? Does it matter based on the direction of current flow or does it matter at all?
Which of the three illustrated techniques do you prefer and use?
Duane Benson
Winslow Leach says hi.
http://blog.screamingcircuits.com/
I would use “A”. “B” leaves an acute angle which is a no-no, especially with narrow traces. I always try to avoid T-junctions.
Agree with Bruce.
Acute angle generally equals “acid trap” (causing poor consistency in the eching process) .. though on a “fat” trace unlikely to cause any real problem (break in trace).
Thin traces with “90 degree Tees”?…. not aware of any problem with that…per se.
However ,
A 90 degree Tee in a thin trace … too close a pad… creates another type of acid trap (bad).
and
A 90 degree Tee too far from a pad… on high speed bus signals, creates signal issues (electrical stubs… creating reflections).
For this situation .. better to route the signal “through” the pad… or something similar to example A above is fine… (B is “no-no”)
RF signals.. another “kettle of fish”…
Depends. You talking commercial or defense/medical/auto application?
– Commercial. Do whatever you want, and do it FAST! Acid traps – ha! This product would be in a landfill long before the ol’ acid could eat its way all the way through the copper.
– Defense, Medical industry, Automotive (long-term product). Their design guidelines do not allow you to make these issues. Acid traps are bad, not having proper sized traces for power are bad, etc. You’ll also have many, many more design reviews, and someone will question this.
Me? I don’t create acid traps as a matter of habit, much like I commonly use rules-o-thumb because I’m dyslexic. 🙂 Nah! I even love to do 90 degree routed boards with my newbie engineers so I can educate them to what they’re not learning in schools. (then I go back and clean the routes up, just so we’re all happy)
Good day.
I agree with both John and Mitch above. Acute angles make for acid traps and the copper being etched under the resist therefore thinning the track.
Also a 90 degree bend can peel at the outer corner if adhesion is marginal or stressed.
It is a case of horses for courses, but I always use the 45 degree approach. It looks more professional, not like it was laid out by an ten-year-old. It really comes down to the designers preference, pride and satisfaction levels.