[Amps] X-TRA TUBE DAYS

[Ian White, G3SEK]

Dr. David Kirkby wrote:

>I do wonder with the increased use of surface mount components, this is 
>going to become more and more difficult in years to come. Many chips 
>are now only available surface mount. Some of them having spacing 
>between the connections of under 0.3 mm, making hand soldering a 
>complete impossibility.
[...]
>
>The precision with which electronic components can be automatically 
>placed by robots has increased dramatically in the last 15 years, but 
>the fingers don't seem to have developed much during the same period.

Both of those statements are too pessimistic. The key is to use a good 
magnifier to see what you're doing. Then the miracle of eye>brain>hand 
feedback kicks in, and the soldering iron tip becomes steady and 
controllable.

I don't believe that my hands are any more or less steady than most 
people of my age, and I've never had good natural fine-motor 
coordination. Even so, with magnification and a good iron I don't find 
it at all difficult to solder individual SMD IC leads at 1.25mm (0.05in) 
pitch. I use an ordinary Weller TCP iron with the sharpest-pointed 
cone-shaped tip.

For 0.6mm (0.025in) pitch, change to a different method: flood solder 
along all one side of the IC, and then use fine solder-wick to remove 
the excess. Then inspect it *very* closely for shorts. If in doubt, 
simply do it again.

I haven't tried 0.3mm, but would give it a go with that technique - if 
someone else had made the PC board. The board is also a difficulty with 
the ball-grid ICs, and I agree that it's very difficult for amateurs to 
go there (or even professionals making prototypes for short runs).

The magnifier, the sharp-pointed soldering tip and the thin solder-wick 
are your three best friends... but most of all, the magnifier. Going 
round an Agilent development lab recently, I noticed that although some 
benches didn't have a soldering iron, they all had a binocular 
microscope!

Good magnifiers are expensive, and good binocular microscopes even more 
so - but we are amateurs, so we find ways to make do. For SMD soldering, 
I use a pair of the strongest non-prescription "half-moons", balanced on 
my nose in front of the bottom (most magnifying) edge of my normal 
vari-focal glasses. For final inspection, I use a hand-held magnifying 
glass as well! My neck and shoulders pay for it later, but it does work.

Of course, I still covet a really high-quality binocular microscope that 
would let me sit comfortably at the bench without crouching over the 
board... or perhaps a pair of the expensive flip-down complex lenses 
that my dentist uses so he can sit completely upright and still see what 
he's doing in there.

So SMD isn't quite the end of the world after all.


-- 
73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
                            Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek