On Thu, 21 Jan 2010 17:27:41 -0800 (PST), Jim Wilkins wrote:
On Jan 21, 1:11*pm, Frnak McKenney
wrote:
On Wed, 20 Jan 2010 10:33:10 -0800 (PST), Jim Wilkins wrote:
On Jan 20, 11:25 am, Frnak McKenney
Or you can use two irons, or with practice one iron moved quickly from
side to side. It works for me, at least. Resistors stand this abuse
better than capacitors.
With my eyesight and dexterity a fast-moving iron is a health and
environmental hazard. grin!
Oh, you are an engineer.
No, but my father and sister are. I started fixing radios and TVs
during high school, but I'm a Math major (New College didn't offer a
degree in any kind of Engineering); then during my college years I
got seduced by the Dark Side (software). grin!
For example, here are a few from a magazine ad:
$80 Sirocco SMD Rework Unit
http://www.circuitspecialists.com/prod.itml/icOid/9445
[...] (other CS items clipped)
I have a plethora of options (possibly two plethoras grin!); it's
just hard to sort through them to find a low-ish priced unit
suitable for learning and occasional use.
I'm tempted to try building one of the homebrew units I listed in a
previous post.
Frank McKenney, McKenney Associates
In the early 90's I checked out several larger units for my lab at
MITRE. We needed a heater underneath for multilayer boards with inner
power planes and thought we needed a wide selection of nozzles for
large parts like these:
http://en.wikipedia.org/wiki/TQFP
usually with 0.5mm lead pitch.
After many demos and a field trip I found out that
* I could use the machines better than the salesmen, meaning that
their recommendations and performance claims meant little. OTOH I'm
not a good salesman.
* If the board wasn't designed with some clearance around large parts,
removing them often wrecked the board. I used dead Mac hard disk
controller cards, not meant to be repaired and thus more of a test.
Understood. I've got some old (and presumably dead) motherboards
and adapters I'm keeping for the same purpose. I suspect I'll need
_lots_ of practice. grin!
* Hot tweezers were better for 2-lead components. Some of the parts
are little bigger than salt grains and they blow away.
http://en.wikipedia.org/wiki/File:Soldering_a_0402.jpg
* Manual dexterity and vision are more important than details of the
desoldering tool, except that a stiff clumsy cable can make hand-held
use almost impossible. Those have a stand and more heat and air,
though.
I'm still working on that one. It's the irregualr (uncorrectable)
astigmatism that causes the most problem, but if I magnify what I'm
working on enough that compensates.
That leaves SOT-23 transistors which a single nozzle can remove.
Nozzles for SOICs would probably be useful too.
http://en.wikipedia.org/wiki/Small-o...grated_circuit
Yup.
I've only had to remove large ICs because they had died, and then
cutting the leads with fine-pointed flush cutters worked better.
A vacuum pickup is nice if it seals well but needle probes are enough
to flip the part away. I like the manual eyedropper type better than
the vacuum hose ones for the lighter feel. YMMV
That's useful to know. Thanks.
If you can't remove a resistor with two irons you might find those
tools hard to use as well. No hot air rework tool I've seen was really
easy to operate. You can't tell when the last pin has melted and can
easily overheat the board or lift a pad.
The BK5000 unit he
$100 (sale) BlackJack SolderWerks Hot Air System w Soldering Iron
& Mechanical Arm
http://www.circuitspecialists.com/prod.itml/icOid/9752
offers both an iron and hot air. There's a one-day HAM fest coming
up here in Richmond in a few weeks (
www.frostfest.com), so I'll see
if there are any really good deals there before deciding.
Thanks for all the advice.
Frank
--
A science is any discipline in which a fool of this generation can
go beyond the point reached by a genius of the last generation.
-- Max Gluckman
--
Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all)