Homebrew PCBs

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.

0402 is my standard size. Especially for decoupling caps, but also resistors.  I use 0603 or larger if I need the extra power dissipation. 

I have done a few 0201's as well, but those are a little trickier. Sometimes just the static buildup on the vacuum pickup tip makes it hard to get an 0201 to detach and stick to the solder paste. 0201's have a tendency to tombstone more often as well.

There are now 01005's out there, but I have not had a chance to try them yet.

I figure as long as I have the resolution to make the boards I could go to the diffraction limit of my microscope. :)



--- In Homebrew_PCBs@yahoogroups.com, 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.
>

Adam Seychell <a_seychell@...> writes:
> 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 use 0603 by default; I see 0805 as "big".  I don't usually use 0402
but I don't find it difficult.  I've done 0201 and 01005 with
home-etched boards, just to see what each size is like:
http://www.delorie.com/pcb/smd-challenge/

The nice thing about 0603s is that you can put the pads on 100x50 mil
grids.  Likewise, SOT-323s fit on 100 mil spacing.  See the LED raster
board at http://www.delorie.com/electronics/usb-gpio/

I do 0.5mm pitch TQFP's all the time, no problem.  I've done 0.4mm
pitch too.

I just finished a board with 0.65mm and 0.5mm QFNs on it: 
http://www.delorie.com/electronics/powermeter/

The 0.65mm were easy.  The 0.5mm all worked, but usually required some
touch-ups after reflow.  I.e. flux pen along the edges and wipe an
iron over them, which cleans up all the connections.  The hardest part
is placing them accurately over the paste.  I think you can only
hand-solder the ones where the pad extends up the side of the chip,
but the ones where the pad is *only* on the bottom, I think reflow is
the way to go.

I did some 0.5mm CSPs as a test: http://www.delorie.com/pcb/inkjet/
(view the last picture)

Other than forgetting that they're lead-free (longer reflow time), I
was able to solder them.  The problem I had is that the connections
are "brittle" - flexing the pcb popped the chip off, leaving the
solder balls behind.  Of course, my boards are much more flexible than
stock PCBs.

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.
>
>

----- Original Message ----- 

From: "Adam Seychell" <a_seychell@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Sunday, July 26, 2009 4:06 AM
Subject: [Homebrew_PCBs] smallest practical SMD for homebrew ?


> 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.

I don't find 0603 to be difficult.

QFN isn't hard. I extend the pads a little for manual soldering, and 
drag-solder them.

Leon