Re: gEDA-user: size of 0402 footprint

[Dan McMahill <dan@xxxxxxxxxxxx>]

Kai-Martin Knaak wrote:
> My next project will take into the realms of the barely visible: 
> PCB estate is at premium. So I decided to bite the bullet and switch to 
> 0402 sized SMD parts, rather than 0805 I use by default'. Now, what size 
> should the footprint be? The one supplied by the default lib of pcb seems 
> to be real small (/pcblib-newlib/geda/0402.fp). John Luciani's 0402 
> footprint is about twice the size. 
> 
> The majority of parts will be populated by a third party in a reflow 
> oven. I guess, they are ok with the small size footprint. They even told 
> me not to choose large footprints as this would encourage tomb stoning. 
> However, I will need to manually rework some of the more sensitive 
> resistors. Would that be possible with the small size footprints?
> 
> Any recommendation? 

{CAP,IND,RES}C1005{L,N,M}
are IPC-7351 conforming footprints for capacitors, inductors, and 
resistors under least ("L"), nominal ("N"), and most ("M") material 
conditions.

the '0402' one lands about in the middle of the nominal case for 
CAP/IND/RES.

If it were me, I'd probably use the "N" ones because "M" seems to add 
too much copper for my liking (after all, I'm using small parts to take 
up small amounts of room with small parasitics) and the "L" is more 
aggressive.

You can place for example RESC1005L, RESC1005N, and RESC1005M to see the 
difference.

If you want to double check the sizes, you can download a no-charge (but 
not open source) IPC landpattern viewer and see what they recommend. 
That is always the safe thing to do because you're using some standards 
that have been shown to work in the real world.

I'm pretty certain (but not 100%) that I've used the RESC1005L 
footprints and hand soldered them without too much pain using a far from 
modern soldering station.

-Dan


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