People tend to be lazy when judging something a PCB technically, so they go
for the appearance. An aesthetically pleasing PCB gives the impression that
who ever layed it out is intelligent enough to lay it out correctly.
Jason
Very true, but for some circuits, even at low frequencies, it makes
a difference. I will attempt to illustrate why the details matter in
electronics with a couple examples. One directly topic related, and
one closely related, but more toward workmanship in the industry.
Take a small HV supply, and lay out two PCBs, one with right angle
traces, and one with curved transitions or 45s utilized. Both PCB
assemblies get potted, so corona at the corners will not be an issue
here.
Testing the two boards will indicate noise characteristics in the 90
degree PCB that are greater in amplitude than the other two PCB
choices for the second board.
The reason is crosstalk. Another would be trace path lengths.
Either way, the 90 degree board will exhibit poorer, noisier
performance. If it is a regulated circuit, the likelihood of that
noise getting injected into the control loop(s) of the circuit are
high, causing poorer operation.
Another example of why the details matter:
A tester could not determine why he had higher leakage currents on
an assembly after it was potted than before.
Our chief engineer said "That's easy... Clean the board."
The guy couldn't believe it. I said that so much as breathing
"coffee breath" onto an HV assembly can cause failure modes and
particularly leakage (I learned it from the master tho). After
utilizing a vapor phase degreasing method for cleaning the unit in
question, the leakage currents read pre and post pot were reported by
him to be identical. He was "flabbergasted" (whatever/wherever that
comes from). I knew it, as I too didn't believe them to be so
sensitive some years back in my early HV realm experiences.
It is always important to clean PCB assemblies that involve high
impedance control or monitoring loops as it is quite easy to introduce
stray flows into places where they are not desired. Merely touching a
1G Ohm resistor with one's finger will render it useless.
SMD assemblies are of particular importance in control loops. Make
sure any resistor changes are followed by thorough spot cleaning with
a dabber, then a solvent, then forced air. One can spend hours trying
different value resistors, wondering why the math isn't working.
One only wants the electrons to flow in only the desired places, and
only in the desired ways. :-] *THEN* the math works... (mostly).
Anyway, today's PCB plot methods use round spots such that corners
even at right angles have a radius on the outside edge that matches
the trace width usually. 90 degree corners would probably not suffer
the same etch process problems, but would most assuredly still posses
many of the electrical gremlins associated with such structural shapes
where current flow is concerned.
I have taken the time to lay out boards with curved transitions all
around, yet still following the shortened path 45 methods for the most
part. Absolutely no sharp inside or outside corners were on it
though.
Great for HV stuff. Don't forget to "Bump Solder" all of your cap
and diode nodes on your HV multiplier boards! Round solder ball
shapes are a good thing. :-]