Homebrew PCBs

I have done some detailed thinking about fastest assembly for prototypes.

I have still yet to find something better than Zeph paste in a syringe
+ hot air.  There's a video here for a QFP:
http://www.zeph.com/zephpaste.htm

Hot Air Operations:
i) Paste 4 sides of chip, 10seconds per side

Total Time: 40 seconds and no cleanup.

If I have more than 5 chips, it would be faster to use a stencil
instead of syringe.  I have a laser cutter and cutting the stencil is
about 5 minutes but I still don't use it all the time because stencil
use requires clean up of the stencil and application tools.

However it's still 5 minutes + 2 minutes to align/tape the stencil + 5
minutes to cleanup = 12 minutes + disposables.

I still use my hot air gun to do the stenciled parts because my hot
plate takes 40 minutes from heatup to cool down.  If I had a push
button oven, I'd use that.

I'm impressed with the ability to solder fine pitch QFP devices.
However, soldering n pins requires n+1 glue operations where solder
paste is only 4 operations per chip.

Hot air guns are cheap : $50-100 off ebay.  $15 of solder paste in a
syringe has lasted me several months for the limited prototype
assembly I need to do.

On Thu, Mar 11, 2010 at 2:11 PM, William Laakkonen
<worldradiolabs@...> wrote:
> Yipes- seems like a lot of work.
>
> I've been working with QFP (Atmega2580, AD9951) and 0603, 0805, 1206- hand
> soldering is no problem using 0.015" solder and standard iron- but then
> again with over 900 parts on one board, the oven approach is not practical
> for one-offs. I wonder why so many are doing solder-paste screens, etc for
> small lots. Faster to hand solder them IMO. Of course, if you want to spend
> the time making it more complicated than it need be...
>
> Use a Loctite mini-fluxer and regular solder and regular solder. If you want
> to see how to solder a QFP I have some photos here:
>
> http://picasaweb.google.com/worldradiolabs/PicastarComboBBDSPCodecDDSSections#
>
>
> Best regards,
>
> Bill