bz said:
There is no reason to go about 225 C (437 F), for any normal solder,
and, if you remember the book title by Robert Heinlein, paper
doesn't burn till you get to 451. [correction, Ray Bradbury, not RH. Sorry!]
I disagree. In order to get the solder to acquire melting temperature
in any reasonable length of time, the heat source has to be far above
the temps you mention. It is tedious to hand solder with a tip that
is less than 800 F, and desoldering requires similar temps. The
problem lies in heat transfer and loss.
You mistake the transfer of heat (calories) for temperature.
This is a common mistake.
I don't believe I'm mistaking the two, but I'm willing to be corrected
if you'll point out my error more clearly.
If the explanation that I gave was not clear, enough, I suggest the study
of thermodynamics and heat transfer.
http://en.wikipedia.org/wiki/Heat is
a good place to start.
The raising of the temperature to the melting point of the solder requires
the transfer of a sufficient number of calories to the component. This does
NOT require a high temperature, it just requires efficient heat transfer.
I keep thinking that you speak from theory, not practice.
Incorrect. I soldered my first connections in the late 50's. When I was 8
years old.
First connections were made with 50/50 solder. Well I remember trying to
hold the lead perfectly stationary while my fingers burned.
I was first licensed as a ham in 1961 as WN5DQP at age 16.
I built Heathkit TVs and Scopes in the early 60's. Using 60/40 solder.
I worked on a resistor/capacitor production line in the late 60's, early
70's.
First as a Process Technician then as a Process Engineer for Sprague
Electric Co. I WROTE process specifications for Sprague's production line
for soldering capacitors to their leads in the early 70's.
After the 'mini recession' in the early 70's I went into consumer
electronic service. I owned a consumer electronics repair shop in the
70's. Got a bit of practical experience there.
In 74-76, I fixed radars and electronics on ships on the Mississippi. Got
a bit of practical experience there also.
I did board repair on DEC and DG computers in the late 70's. Component
level repairs on PCBs.
A couple of years ago, I built an Elecraft K2/100 ham transceiver.
Recently, I built several SoftRock RXTX SDR radios, using SMT components.
I think that qualifies as a bit of practice to go with a bit of theoretical
knowledge, a BS in Chemistry, 1970.
It is
virtually impossible to solder with a 500 F iron,
I don't find that to be true. All one needs is a good clean iron properly
tinned, good 63/37 solder, and a good flux pen, clean, pretinned leads on
the components, a clean, pretinned PCB and proper technique.
Of course, ANY oxide (and solder does oxidize rapidly) on the tip of the iron
and you have just added thermal resistance. The iron tip MUST be freshly
cleaned and tinned.
yet many components
supposedly can't stand even that for more than 5 seconds.
Many components CAN'T.
We disagree quite strongly on this point
As I said originally, there are two philosophies.
, and I wonder on what you base
your perspective? Many, many years ago, the military presumed to insist
on 600F, and that proved to be woefully inadequate for hand soldering.
This is true, IF the iron is not clean or is underpowered. The point at
which a temperature controlled iron measures the temperature is also
important. The nearer the tip, the better.
Now, a solder bath, having an immense thermal mass, as well as providing
virtually total joint immersion, can solder well at 500.
Correct.
If I recall correctly, our 95/5 (tin/silver) solder pots ran at
495F(257C). The 62/36/2 pots ran considerably cooler but I don't remember
the numbers. There was a layer of hot wax on top of the solder to 'preheat'
the parts and protect the solder from oxidizing.
But hand
soldering with any measure of expediency requires *at least* 700, and in
my experience, 800 is far better.
Once you get the joint above the melting point of the solder, there is no
need for higher temperature. Proper heat transfer is the key.
Hot air guns are much, much hotter than the melting point of solder.
Depends on the settings of the gun. My 'CSI Hot air gun 2'
<
http://www.web-tronics.com/hotairgunwdi.html>
solders and desolders quite well at temperatures not much greater than the
melting point of the solder.
I have soldered and removed 48 lead SMT ICs without damaging the
surrounding SMT components. I have removed and later reused 8 lead SMT
ICs. This was done without badly charing the paper dams around the parts.
The paper WAS heated to a light brown so I believe the digital read out on
the hot-air gun.
Why
would that be, if the very low temps you advocate are actually
sufficient?
My hot air gun WILL go hotter, but after playing around with it for some
time, salvaging parts from old PCBs, I found that I could work quite well
with much lower temperatures than I had first tried. Nozzel size and air flow
rate are very important. The nozzel must be large enough to heat the area and
the flow rate must be sufficient to do so quickly.
True. And they needn't be exposed very long. Through-hole ICs and
transistors may need approx. 1 second per lead. With a typical 16 pin
surface mount IC, three seconds is plenty to skate down one side and
solder all 8 pins, at 800F.
Or even at 440 F, with 63/37 solder, and then to 'mop up' with clean, well
fluxed solder braid.
One 48 lead component I worked with recently has an absolute max of
300C(572F) for 10 seconds.
Your 800F is 427C. There is a very good chance of damaging such an IC at
that temperature.
And we had a discussion here not long ago, begun with the question of
why anyone would use anything other than 63/37, assuming a leaded
formulation. As I recall, no one offered any very plausible reason to
use anything else.
A small percentage of silver helps prevent leaching of silver from some
components and is vital for the mounting strips in some Tektronix scopes.
A small percentage of copper helps prevent leaching of copper from PCB
traces.
--
bz 73 de N5BZ k
please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.
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