I use 0805 and 1206 as standard, but then some of my boards will
eventually be wave soldered ;-)
On some boards I use 0603, but they have relatively large lands and
the space saved compared to 0805 is minimal.
I actually prefer QFN over leaded packages with small pitch. The QFN
is much less prone to shorts between the pins because the epoxy case
fills that gap. The trick is to extend the lands well outside the case
then you can drag-solder them easily and inspection is also easier.
This doesn't seem to affect reflow soldering at all, they still center
nicely.
Making power supplies and chargers, there are often constraints in
downsizing, like power dissipation. And if you need a number of large
components anyway, it does not make much sense to shrink only a
portion of them to a miniscule size, driving up production cost.
The same seems true for homebrew stuff - why increase your effort in
working with tiny resistors unless there really isn't enough space for
a 0805 component?
ST
On Sun, Jul 26, 2009 at 5:06 AM, Adam Seychell<a_seychell@...> wrote:
> Following the recent posts on BGAs, I'm curious what people consider the
> lower size limit for SMD to when doing home brew PCBs and projects. I
> used to use 0805 but found soldering 0603 parts wasn't that much more
> difficult, and so its my preferred choice for a new project. I
> experimenting with some 0402 on scrap motherboards and found it way to
> tedious to be practical. A big problem I see with 0402 is an inability
> to run a trace between pads.
>
> I found the no-lead chip scale packages (QFN) are somewhat more
> difficult to solder than corresponding leaded TQFP of the same pin
> pitch. Without reflow soldering, the pins of a QFN rely in wicking of
> solder applied from soldering iron tip located on the pad just external
> to the package. Its difficult to know if solder as wicked between pad
> and pin.
>
>