kicad-lib-committers team mailing list archive

[Rene Pöschl <poeschlr@xxxxxxxxx>]

This is because 0805 has larger tolerance ranges when compared to 0603.

For 0603 the tolerances are body length 0.2mm, "lead" length 0.25mm
For 0805 they are body length 0.3mm, "lead" length 0.5mm

I verified the tolerance ranges by checking 20 random resistors on 
farnell. For both 0603 the components fall into the tolerance ranges 
given by this ipc document. (I even found some 0805 parts that would 
require increasing the tolerance ranges even further.)

You can look at the old IPC-SM-782 [1[ standard and check for your self. 
That one still gives a suggested footprint. (The new IPC-7351B standard 
does no longer do that. It gives equations how do derive the pad sizes 
from the part sizes.)
The suggested footprints in that old standard use the same pad to pad 
clearance for both 0603 and 0805. As that old standard gives no 
explanation of how they derived that size i can only speculate that 
their rounding base was larger.


There will however be some minor improvements to some of these 
footprints. IPC-7351B uses slightly different equations compared to 
IPC-7351. The pull request that updates this can be found at [2]

A very similar question arose over at the forum [3] (The later part of 
the discussion is about footprints. The first part is a misconception on 
how kicad works.)

[1] http://www.tortai-tech.com/upload/download/2011102023233369053.pdf
[2] https://github.com/KiCad/kicad-footprints/pull/689
[3]
https://forum.kicad.info/t/v5-heads-up-devs-dont-explain-here-the-upcoming-changes/11123/22 
<https://forum.kicad.info/t/v5-heads-up-devs-dont-explain-here-the-upcoming-changes/11123/22?u=rene_poschl>



On 26/06/18 15:12, Wayne Stambaugh wrote:
> Recently the SMT capacitor and resistor footprints where changed to use
> rounded rectangular pads.  It looks like something may have gone wrong
> with the Capacitors_SMD:C_0805_2012Metric footprint.  The spacing
> between the pads is less than the 0603 footprint which doesn't make any
> sense to me.  I looked at a few datasheets and I couldn't find a single
> manufacturer where the 0805 spacing was less than the 0603 spacing.
> Would someone please confirm that this is correct before I file a bug
> report?  If this is correct, please include the reference document that
> contains this information.  I want to understand how this is possible.
>
> Thanks,
>
> Wayne