Dear Designer Council,

In the early years, I used simple rectangular pads for all my surface- mount
parts -- because that's all my software could handle.

Now that I've upgraded to software that can draw just about any shape I can
imagine, what is really the "best" shape for 0603 and 0805 chip resistors and
capacitors ?

Say I'm doing infrared reflow, and I'm not gluing anything down. (I know the
footprints for wave-soldered surface-mount components should be different).

I've seen some people basically add a half-circle to both ends of the footprint.
 I've seen marketing literature for some software packages babble on about "home
 base" shaped footprint pads, although it doesn't seem consistent on whether the
 chamfer should be towards the center of the part or towards the ends of the
part.

Now that I *can* make all these non-rectangular shapes, *should* I ?

I seem to be spending way too much time on these picky details. You'd think
someone would have run some experiments and come up with an authoritative answer
 by now.

I suspect the little decorations done above are merely to show off what *can* be
 done, rather than best practice of what *should* be done.

Has best practice changed since 1995 ?

_Surface-Mount Technology for PC Boards_ book by James K. Hollomon (1995)
p. 414-415
Ceramic chip capacitors and resistors: lands for reflow soldering * the gap
between the lands
should essentially match the space between terminations (bare body) on the
component (to minimize tombstoning).
* the land width = chip maximum width + 0.25mm ( 10 mil ).
* each land should extend about 0.64 mm ( 25 mil ) beyond the end of the part
for maximum resistance to thermal cycling stress.
(i.e., total copper extent is 50 mil longer than the physical length of the
resistor).

--
David Cary

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