In 1980s, my country used a national standard to describe how thin PCB traces and how small via diameters could be. The rules were rather contrived and mostly covered THT boards with DIP packages. There were several categories from coarse to fine, which could be roughly translated as "PCB precision class":
When I started to use commercial PCB fabs around 2003, most local ones used much simpler "precision classes" which were more suitable for SMT. Basically, every class allowed trace width, clearance and via ring thickness of the same value, from 0.4 to 0.1 mm. And of course, the higher the class, the costlier the PCBs were to produce:
They mentioned these values come from IPC-A-600 standard (revision D), so I just assumed they're universally true and I had been using them ever since. But I came across the standard (revision G) a few days ago and I noticed there actually are no recommended "precision classes" in it. And it seems there never were:
http://www.vipcircuit.com/download.php?mod=down&id=9I also noticed some fabs use "precision classes" that use significantly different values than the pics above:
So my question is: is (or was) there an international standard or recommendation for such "precision classes"? Or is it basically anarchy and every PCB fab sets them arbitrarily according to their production capabilities?
IPC 751 IPC2221 and so on. Those are the 'standards'
but really trace width is determined by current and/or impedance requirements. Same for via size.
As for thru hole pads : that is determined by the size of the wire going in.
get the saturn pcb toolkit. it knows all the formulas.
Manufacturers will have to build there processes around what kinds of machines they have, at some point in the past those tables may have applied to some specific manufacturer for what they would quote
Even if you quote in imperial, almost all fabs only stock a range of drill bits in 0.1mm increments, I believe around 10mm holes and larger they switch out for routed holes. mainly due to how many different tools they can keep in the tool carousel, things like hole positioning tolerance and minimum drill size are a function related to there CNC machines, how accurate / precise they are, and how often drill bits are replaced. a 0.1mm drill bit is so flexible that it needs to be drilled at high RPM (more expensive machines), and wears out very quickly
Trace width / clearance comes down to there chemical baths and process, for most of them its pretty easy to say that they can pull off 0.3/0.3 with no issues, but when you get much below 0.15/0.15 things need much better controls, cleaning, etc to make sure etching is just right, this usually decreases the yeild.
If you have certain requirements in mind, Its probably better to just look over common manufacturers, you can push the specs of the cheap fabs occasionally, but they will get angry if you really push it (e.g. a 0.1mm trace snuck in on a 0.15mm pcb was fabbed correctly with no questions, but a whole complex design would be shot down)