Hand Soldering any QFP requires:
1. Apply flux from mini-fluxer pen or similar
2. Position chip
3. tack solder opposite corners
4. glob solder across all pins, shorting most
5. lay a ∗good quality (E.G. M.G.Chemical) Solder Wick across the globbed
solder on one side and drag the iron across the wick, lifting nearly all the
solder, repeat this for other sides.
It may be scary to consider globbing solder on a $20 chip- I've done it
hundreds of times on QFPs now and have yet to lose a part.
Elapsed time for an Atmega2560 (100 pin TQFP) about 5 minutes and no oven,
paste, etc. Mind you I ∗have∗ used paste, hot air, solder mask.-, etc. I've
used the above method successfully also with .35mm pitch parts since about
1992 and have done it hundreds of times. No special skill or tools needed,
other than a good magnifier which you should have working with small items
anyway. I'm not a young guy either, so I must work with the magnifier lamp.
After soldering many thousands of SMDs, my conclusion is in most cases,
solder paste is a wasted effort unless your in production. If you can see
it, you can solder it with a (good) pen, solder, and wick. I use 0.015
solder for 0603 and up. I use .022 or 0.035 for QFP or SOIC devices and wick
up excess. I only see hot air and paste useful for things which you cannot
reach with an iron (flexible kapton boards with blind connects, BGA, ETC)-
and what hobbyist(s)) would use such parts unless they were free? I do see
"homebrew" in the title, which to me evokes a sense of doing more with less
and experimenting with new techniques.
Loading and soldering is only one side of a homebrew_PCB.
Regards,
Bill
On Fri, Mar 12, 2010 at 1:28 AM, Henry Liu <henryjliu@...> wrote:
>
>
> 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@... <worldradiolabs%40gmail.com>> 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
>
>
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