kicad-developers team mailing list archive

[Lorenzo Marcantonio <l.marcantonio@xxxxxxxxxxxx>]

On Sat, Apr 26, 2014 at 09:55:06PM -0400, Carl Poirier wrote:
> I originally thought the libraries were concerned when it came to units in
> eeschema. Thanks for the clarifications. So, why can't a 2.5mm grid be
> added, in the end?

Mostly because eeschema works in decimils and there would be rounding
issues.

Other than that because AFAIK the road map already calls for logical
units.

> Which one is used more widely? IPC-7351 Level A (pin one upper left) or
> IEC-61188-7 (lower left) ?

Most of the wizards in other EDA packages build components using the IPC rules.

> -Using a 100mil grid, pin ends and origin must lie on grid nodes (IEC-60617)

You have an ugly situation centering even-sided parts, but the idea is
that, yes. I position on 50mil but keep the distance at multiple of
100mils, as explained before. Just move the origin to fix it (and break
all the existing schematics:D)

> -Pin must have a length of 100, or 150mil if number needs more space
> (IEC-60617)

I don't remember a rule on pin length, however these values seems
reasonable to me. 150 mil often happens for rounding the edges to the
grid, too.

> -Pin 1 must be in quadrant 1 (IPC-7351), if not possible quadrant 3 (
> IEC-61188-7)

Ah, we switched to PCB modules...

Maybe we have a different idea of numbering quadrants:P The usual
definition (from trigonometry) is this:

    T
  2 | 1 
L---+---R
  3 | 4
    B

Left, right, top, bottom are the terms used by IPC.
The IPC rules for SMD zero orientation are these:

                        Pin 1
- Chip components       Left (1 is + in general, 1 is K for diodes)
  Molded capacitors     
  Molded inductors
  Alu capacitors
  (two pins components in general)

- SOT, TO, SOIC, TSSOP  Upper-Left (quadrant 2)
  Chip arrays
  (two sides of pin components in general,
   so DFN, SON, JSOP, CFP and so on, too)

- QFP, BQFP, CQFP, QFN  Upper-Left (quadrant 2)
  (four sides of pin, with number 1 on a corner)
  
- PLCC, LCC             Top-Center
  (four sides of pins, number on on center side)

- BGA, LGA              A1 on Upper-Left
  (area pin array)

So 99% of the origin is in quadrant 2 or on the left side (you don't see
a lot of PLCCs these days)

>  -Origin is placed in the middle with respect to device leads (IEC-61188-7)

Yes, to be exact the middle with respect to the outer boundary of the
device leads (because otherwise the sink on the DPAKs can give the wrong
solution).

For, ahem, legacy reason (I liked them better) I have the two-sided
component with pin 1 on lower left, by the way. You'll have to turn them
to get to the standard orientation.


-- 
Lorenzo Marcantonio
Logos Srl