Confusion with passive SMD sizing


#1

Hello,

I am actually having a difficult time figuring this out with certainty. I am relatively new to KiCAD. Metric units have been selected in my preferences.

I have selected various 0603, 0805, etc., sizes for my passive components from the KiCAD component libraries. I have even soldered such components before by hand, but never paid much attention to their actual dimensions.

But I need clarification if these sizing references are in metric or imperial units. The component library in KiCAD does not seem to offer a clear answer, and I am having trouble figuring this out, because I cannot even find a simple specification for a 0603 footprint (metric or imperial) via Google search.

If someone could set me straight, I would appreciate it. I am using KiCAD 4.0.2 (stable) on a PC running Ubuntu.

Thanks


#2

In the kicad 4 lib only imperial size codes are included in the v5 lib we will also include the metric one. For reference see the relevant section of the KLC: http://kicad-pcb.org/libraries/klc/F3.1/ (It also includes a table that relates both size codes to the body measurements)


#3

The KiCad 4.x libraries use Imperial sizes. The KiCad 5.x libraries will use both metric and Imperial. (i. e. R_0805_2012Metric.)

Wikipedia has a table:


#4

Thanks! I wouldn’t have given it a second thought, but my fabricator asked for clarification. Then, to my horror, I realized that I live in a world where metric and imperial codes can appear the same, but mean entirely different things.


#5

You’re not the only one:
https://en.wikipedia.org/wiki/Mars_Climate_Orbiter

One of the American presidents (a smart guy) signed an agreement to phase out those silly inches, but the agreement was “voluntary” and “advisory” only. That was somewhere back in the '70s…


#6

I am very pleased to see that component sizes have been made much clearer in the V5 libraries and should help avoid these difficulties

I always find it interesting that US ‘Customary Units’ (Imperial) have, in any case, been defined in terms of the metric system since 1893. An obvious solution - standards are expensive but one that most staunch defenders of Imperial units seem unaware of.

From NIST;

In 1893, metric standards, developed through international cooperation under the auspices of BIPM, were adopted as the fundamental standards for length and mass in the United States. Our customary measurements – the foot, pound, quart, etc. – have been defined in relation to the meter and the kilogram ever since.

:slight_smile: