SV: Re: [sdiy] Altrium Designer/Protel mm versus mils

[Vesa Lahteenmaki]

>From: karl dalen <dalenkarl at yahoo.se>
>
>Speaking of going off grid, how many of you have
>switched into designing PCB's in mm instead of mil??
>
>Yes, there has been a change, all new PCB's shall be
>designed in mm thesedays as they say!
>
>KD

At least the better cad software lets you select which units to work with, 
mm or mils.
So you can work with either one as you please.
Metric units are now gaing more popularity even in old inch countries ( UK, 
US ) because ic packages keep shrinking and are based on the metric system. 
Leg pitch is now often 0.5mm, compare that to the old DIP pitch 2.54 mm ( 
100 mils ).

I remember in very early 90's I had to design a pcb with 0.5mm pitch 256-pin 
QFP. The problem was that we only had Dos version of Cadstar, which used 
mils ( windows version which had mm units wasn't released until 1994 ). Just 
integer mils, no desimals so I just couldn't create the footprint using 
19.685 mils pitch directly. So I had to use values 19,20,20,19,20,20,19... 
etc trying to minimize the error. Those were the good old days :-)

Vesa Lähteenmäki,
currently busy designing one of the PCBs for Galileo project ( European GSP 
system)

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