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When doing PCB layout, you're basically forced to think in thousandths, but work in millimeters... You end up memorizing multiples of 2.54mm (0.100in)
by synack 4y ago
When doing PCB layout, you're basically forced to think in thousandths, but work in millimeters... You end up memorizing multiples of 2.54mm (0.100in)
- seniorsassycat 4y agoWhy is that? Common components use thous but tooling moved to mils?
- synack 4y agoEssentially, yes. Older components tend to have imperial footprints, newer ones metric.
- klodolph 4y agoThere's something even worse... 0201, 0402, 0603 are all codes for SMT component sizes... and they mean something different depending on whether they are metric or imperial. 0201 imperial is 0603 metric. Most parts were imperial IIRC until at some point they started selling parts that were too small (smaller than 0201) and switched to metric. I can understand wanting to switch to metric, but reusing the same goddamn size codes is too chaotic for my taste. Come up with different numbers. You'll still use metric, but you'll just end up seeing lots of 2.54 or 0.254 everywhere.
- 0_____0 4y agoMy sophisticated wild-ass guess: Film and sheet thicknesses are often specified in mils, and PCBs are essentially fancy sheets of stuff laminated together. My unsophisticated wild-ass guess about why they persevere: Like Fahrenheit, it so happens that mils as a scale intuitively correspond to sizes of trace we care about. A 5 mil trace is pretty run of the mill for signals. 20 mils for most IC supply traces. 3 mils is small and expensive to make (last I checked! capabilities have changed rapidly in my decade of experience)
- stephen_g 4y agoPeople in metric countries just learn to be comfortable with decimals. So you end up with trace widths like 0.5mm or 0.3mm and you just get used to it. I think the intuition argument is often just a post hoc assumption for things that we are actually just familiar with.
- deleted 4y ago[deleted]
- 0_____0 4y agoThe intuition argument is pretty weak. Thinking about it a little harder, I think the reason is simply institutional inertia, same as for every other industry that retains inch-pound-second based systems.
- marcosdumay 4y ago> A 100µm trace is pretty run of the mill for signals. 500µm for most IC supply traces. 50µm is small and expensive to make The numbers get even better on the metric system. I was expecting them to just not get much worse, since they were picked on the imperial on.
- russdill 4y agoA lot of tooling and tolerances still uses thousands of an inch as well, complicating the use of a metric grid.