I have personally "welded" wires onto a SMT device using a sort of
"tweezers" built from two different bits of spring steel (actually a regular
tweezers that I cut into two) with a battery (6v lantern) connected across
the sides. I applied paste, positioned the wire against the pin, held it
down with one side of the tweezers, then got my solder ready, and made
contact with the other side of the tweezers against the pin. I would get a
little arc sometimes, but usually it just got damn hot, melted the solder,
and did the job. Very quick. I would just break the connection on the pin
side and continue to hold down the wire with the other as the solder cooled.
Really slick, however...

After completing the job, the device failed to function. All the connections
looked perfect, and it was easy to work in the limited space, but some of
the power must have traveled through the device and fried it. Maybe. Maybe
not; the chip was just on an adapter with none of the pins connected to
anything so how the juice would manage to flow through the chip is beyond
me. Anyway, it wasn't worth risking another chip, so I went and paid for a
new soldering iron with a fine point.

I've often wondered if using a different material at the tip of my
"tweezers" would have solved the problem. E.g. a little block of nichrome or
something like that so the power would flow from tip, through that sort of
resistive element and to the other tip, and the resistive element would
couple the heat to the wire and pin. The element could be really tiny and
have almost no mass making it easy to get in and out of cramped quarters.
The tweezers tips could always be connected and the power switched from
somewhere else, or one "tip" could be cut short and fixed just above the
element so that pressing down would close the circuit.

If anybody tries it, let me know.

---
James.
 
 

> -----Original Message-----
> From: piclist-bounces@mit.edu 
> [mailto:piclist-bounces@mit.edu] On Behalf Of Martin McCormick
> Sent: 2005 Feb 28, Mon 06:18
> To: Microcontroller discussion list - Public.
> Subject: Re: [OT] The Cold Heat Soldering Irons Recently on 
> the Market 
> 
> "Howard Winter" writes:
> >Yes, I bought one just to see what it was like.  The "tip" 
> is actially 
> >a pair of pieces with a gap in the middle, and it almost 
> seems to use 
> >the target to bridge of the gap.  You often  get a small 
> spark as you 
> >press the button (they tell you that's normal) and this, 
> combined with 
> >not-very-smal l tip size means that I don't think it's suitable for 
> >electronics.  I certainly won't be using it on anythin g with 
> >semiconductors in it!
> 
> Ben Hencke writes:
> >I also have one of these. The gap is huge! possibly 1/10th 
> of an inch 
> >or more, making it uselss for soldering most stuff, even 
> through hole.
> 
> 	Thanks to both of you!  I seem to remember the iron is 
> around $20 or so which does not make it a major purchase in 
> the over all scheme of life, but if I bought it with the idea 
> of soldering component leads on through-hole perforated board 
> which is what most of my electronic projects are built 
> around, and discovered what both of you described, I would be 
> annoyed.  It isn't a good deal if it doesn't do what you 
> bought it for.
> 
> 	I can also imagine what it could do to a PIC or any 
> other solid-state electronics if the two halves of the tip 
> fed the roughly 6-volt power in to the circuit rather than 
> shorting through the target and solder.  It wouldn't be pretty.
> 
> 	Howard Winter also mentioned the problem of orienting the tip.
> If everything else was perfect and this was a must-have tool, 
> I could probably mark the correct spot, but there are too 
> many gotcha's.  If I were designing such a tool, I would give 
> it a setup mode in which a Sonalert module could be switched 
> in series with the tip to whistle when contact was made.  
> Then one would know that it was ready to go.
> 
> 	Again, thanks for saving me time and money.:-)
> 
> Martin McCormick WB5AGZ  Stillwater, OK OSU Information 
> Technology Division Network Operations Group
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