Re: gEDA-user: IPC standard SMT footprints (0603, 0402 vs. RESC0603N etc.)

[Colin D Bennett <colin@xxxxxxxxxxx>]

On Wed, 25 May 2011 16:56:46 +0200
Gabriel Paubert <paubert@xxxxxxx> wrote:

> On Wed, May 25, 2011 at 07:11:49AM -0700, Colin D Bennett wrote:
> > On Wed, 25 May 2011 06:41:26 -0700
> > Colin D Bennett <colin@xxxxxxxxxxx> wrote:
> > 
> > > (1) Why is RESC0603L/N/M much smaller than '0603'?
> > > (2) Why is there no similarly named set of RESC0805L/N/M for 0805
> > > size? (3) Why does RESC1608M nearly match the '0603' footprint?
> > >     Is there an imperial/metric naming confusion happening?  I
> > > thought 0603 was a standard name for this size.
> > 
> > I think I've answered some of this for myself... from Wikipedia's
> > âSurface-mount technologyâ article:
> > 
> >     01005 (0402 metric) : 0.016" à 0.008" (0.4 mm à 0.2 mm)
> >     0201 (0603 metric) : 0.024" à 0.012" (0.6 mm à 0.3 mm)
> >     0402 (1005 metric) : 0.04" à 0.02" (1.0 mm à 0.5 mm)
> >     0603 (1608 metric) : 0.063" à 0.031" (1.6 mm à 0.8 mm)
> >     0805 (2013 metric) : 0.08" à 0.05" (2.0 mm à 1.25 mm)
> >     1206 (3216 metric) : 0.126" à 0.063" (3.2 mm à 1.6 mm)
> > 
> > So the source of the confusion over footprints is that '0603' is a
> > valid name for both a metric and an imperial size.. both
> > different?  Whoever decided to name the packages that was must have
> > been on crack.
> 
> Indeed. I found a set of recommended footprints that distinguishes
> resistors from capacitors: 
> 
> http://www.ibselectronics.com/pdf/pa/walsin/smt_notes.pdf
> 
> I have used it quite successfully, including for long edge
> capacitors (0612 or 1632 metric) and 4 resistors in a single package 
> (4x0603 or 4x1608 metric). I also took into account the
> recommendations on page 10 when ordering the stencil, shrinking a bit
> the solder paste apertures generated by PCB.

Thanks for the note.  It is a curious coincidence that I was actually
reading this very PDF at the moment I read your message!  I had just
found it on Google.

Have you found the Walsin-recommended footprints for SMD chip resistors
and capacitors to be useful, and an improvement over other footprints
such as the pcb default "0603", "RESC1608N", etc.?

My fairly uniformed understanding is that the IPC standard specifies
the one set of footprints for use both resistors and capacitors.
(e.g., 0603-least, 0603-nominal, 0603-most.)  But is differentiation
between device types useful?  At least the package height differs (MLCC
is square along the X axis, while chip resistors are flatter, having a
height H much less than the Y dimension), but I don't know how this
would affect placement and soldering.

Regards,
Colin


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