KiCad

Bug #1466857
Comment #8

Comment 8 for bug 1466857

Revision history for this message

Wayne Stambaugh (stambaughw) wrote on 2015-06-20: Re: [Bug 1466857] Re: PCBNew does not update footprints after modification in the library

On 6/19/2015 6:11 PM, Adam wrote:
> You _do_ want to change a footprint if you have used an incorrectly designed one.
> You should at least get a notification of the modification and have the option to use the new footprint.

How do you define an "incorrectly" designed footprint? I'm constantly
tweaking "correctly" designed footprints to improve design layout and
ease of manufacturing. How do you know when a footprint is changed that
it actually corrected anything that would cause manufacturing issues? I
could be something as insignificant and changing the silk screen
thickness. Do we really want something like this to trigger a warning
(nag ware) every time there is a change?

>
> Everything that is defined as a constant feature of the footprint should be compared.
> This includes: pads, lines, texts, predefined solder mask clearance, 3D model, etc.
> I think that only parametrized texts (those defined on the schematics) should be excluded.
> In other words: those which identify the component (designators) on the PCB or assembly
> drawing (here also the name of the footprint and its value), as well as any user-defined texts.

These constants are not constant. It is not (at least for me) uncommon
to make local modifications to one or more pads or silk screen graphics
for design and manufacturing specific purposes.

>
> Perhaps the FPID could contain a "magic number" calculated based on the compared elements.
> Like a CRC calculated for the file, having discarded the "volatile" features.

This would be only way I know to do this and it would require a change
in the board file format. This would not happen until after the
upcoming stable release.

>
> If it is desired to prevent updating a particular footprint, in my opinion it is better to explicitly "lock"
> the footprint, just like you can do to prevent changing its position.
>
> BTW it would be nice to have the "update footprint from library" option in the right-click context menu.
> (or did I give up searching too easily?)
>

There is no context menu entry for this feature but I doubt it would be
terribly difficult to add to the footprint sub-menu.

How do you define an "incorrectly" designed footprint?  I'm constantly
tweaking "correctly" designed footprints to improve design layout and
ease of manufacturing.  How do you know when a footprint is changed that
it actually corrected anything that would cause manufacturing issues?  I
could be something as insignificant and changing the silk screen
thickness.  Do we really want something like this to trigger a warning
(nag ware) every time there is a change?

> 
> Everything that is defined as a constant feature of the footprint should be compared.
> This includes: pads, lines, texts, predefined solder mask clearance, 3D model, etc.
> I think that only parametrized texts (those defined on the schematics) should be excluded.
> In other words: those which identify the component (designators) on the PCB or assembly
> drawing (here also the name of the footprint and its value), as well as any user-defined texts.

These constants are not constant.  It is not (at least for me) uncommon
to make local modifications to one or more pads or silk screen graphics
for design and manufacturing specific purposes.

> 
> Perhaps the FPID could contain a "magic number" calculated based on the compared elements.
> Like a CRC calculated for the file, having discarded the "volatile" features.

This would be only way I know to do this and it would require a change
in the board file format.  This would not happen until after the
upcoming stable release.

> 
> If it is desired to prevent updating a particular footprint, in my opinion it is better to explicitly "lock"
> the footprint, just like you can do to prevent changing its position.
> 
> BTW it would be nice to have the "update footprint from library" option in the right-click context menu.
> (or did I give up searching too easily?)
>

There is no context menu entry for this feature but I doubt it would be
terribly difficult to add to the footprint sub-menu.