[sdiy] square pads

David G. Dixon dixon at interchange.ubc.ca
Thu Oct 14 19:17:04 CEST 2010

> > Concerning orienting ICs, I line them all up straddling the power rails,
> > so I always orient them with the +V pin on the same side.  This means
> > that most quad opamp chips are upside down relative to most other chips.
> You use quad opamps? Heretic! :-)

Yes.  I don't know how I've avoided the stake thus far!

> Seriously, if all IC of the same type get the same orientation that's

In my experience, using my layout technique for analog circuits, it's always
the 14-pin DIPs which are turned around, as these are mostly quad opamps.
8-pin DIPs (typically dual or single opamps) and 16-pin DIPs (typically dual
OTAs and quad VCAs) are almost always right-side up.  There actually aren't
too many other ICs involved in my circuits -- the odd comparator (right-side
up 8-pin DIP) or voltage reference, perhaps.  Digital circuits are another
matter entirely, because they usually require a completely different layout

> Instead of centering the parts over the two rails you could maybe slightly
> shift them depending on orientation, that would also make it easier to
> "line up the dots" after stuffing.

Nah!  I'll keep doing it my way, because it allows me to build the bulk of
my synth circuits on boards 2.1" wide (which I can actually cut 2" wide,
thus getting the maximum number of boards out of a single sheet of blank
material) -- I'm cheap, remember?  Particularly complex circuits (like my
2164 4P LPF) are "double-wide" and thus require boards 4" wide (they share a
single GND trace down the centre-line, thus eliminating 0.1" from the width
requirement).  I've got this layout thing down to an exact science!

> >  Hence, the desire to use square pads for some clarity.
> You don't see them from the component side and from the solder side the
> pins
> all look the same anyway. :-P
> And don't make people look under a board that's stuffed, but not soldered
> yet. :-)

Ah, but I DO see the underside of the board when I'm stuffing (or, at least,
I CAN see it if I want to), because I clamp the board in a PCB vice, and I
can shine my desk lamp on the underside and see the pads and traces through
the board quite clearly.  Of course, I suppose many boards are made with
material which is not as translucent as the material I use, so this may not
apply generally.

In any case, I wouldn't really need to refer to the underside of the
physical board to make use of the square pads, since I'm referring to a
graphical representation of the stuffed board (with the printed circuit
showing faintly in the background, just as if it were being illuminated from
underneath) while stuffing.  Hence, the square pads on the graphic image are
just another way to ensure not getting the ICs (or, in my case, the IC
sockets) in backwards.

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