this post was submitted on 08 May 2024
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And they aren't kidding around, modern high speed signals are so fast that a millimeter or less of difference in length between two traces might be enough to cause the signals to arrive at the other end with enough time skew to corrupt the data.
Edit: if you ever looked closely at a circuit board and seen strange, squiggly traces that are shaped like that for seemingly no reason, it's done so that the lengths can be matched with other traces.
A millimeter is huge in these situations. USB3 requires 5 mil tolerances, just over 0.1 mm. This scales with the inverse of data rate.
Electronics are so fast that we gotta take the speed of light into account. God help you if you put too sharp a bend in a trace, too ...
What is a mil in this context? I'm genuinely curious.
A millimeter i.e a thousands of a meter.
edit: I was wrong, confusingly enough it is a thousands of an inch
5 mm isn't 'just over 0.1 mm'. That can't be right.
Well, it depends on your margin of error.
In the design and manufacture of PCBs (aka circuit boards) a "mil" is a one thousandth of an inch, so it makes sense that's what is being used in this context.
Also the maths check out: 0.005 inches is equal to aprox 0.12mm, "just over 0.1mm".
I stand corrected, and I see I didn't read the comment thoroughly enough either.
Colloquially as a non-pcb maker I would use and hear the term "mill" as short form millimeter so I assumed it was that.
so TIL :)
Yeah, I found it wierd too when I started designing PCBs (as hobby) that "mill" actually stood for thousanth of an inch.
Probably for historical reasons, there are tons of things in the older domains within electronics that are based on inches rather than metric units: for example the spacing between the legs of a microchip in the older chip package formats (so called DIP, the ones with legs that go into holes) is exactly 0.1"
The sizes in more modern electronics isn't usually based on inches anymore, but circuit boards are old tech (even if done with new materials) so there are still a number of measures in there which are based on inches.