Smitty Two wrote in
news
In article 39,
bz wrote:

Smitty Two wrote in
news
In article 39,
bz wrote:

.....
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.

It isn't your explanation that lacks, only your suggestion that I'm
confused on the topic.

Sorry. I didn't intend to imply that I could read your mind, just that many
people confuse temperature and heat. Many of those that confuse the two
think that a higher temperature is better for soldering.


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 agree. Unfortunately, efficient heat transfer is difficult to
impossible in many hand soldering applications. The excess temperature
to a small contact area makes up for that.

A clean iron, well tinned, clean circuit board and component lead, fluxed.
Clean the iron just before you bring it to the joint to be soldered.
Clean it by plunging it into a tangle of stainless steel shavings (a pot
scouring pad) and twisting as you remove it. The shavings do NOT cool the
iron like a sponge would.

Use thin solder. Put the solder against the component lead and board.
Touch the iron to the solder, board and component lead, all at the same
time.

Feed enough solder to wet the surfaces and encourage good heat transfer.
For leaded components, move the solder wire around to the other side of the
joint and make sure all wets well and you get a good solder fillet.

1/2 second should be enough.

The rate of heat transfer depends on TWO things: the difference in
temperature and the heat conductivity. In soldering there are other
important factors that often comes into play, the heat capacity of
the soldering iron and the power of the heating element.

Contact area is the holy grail of efficient heat transfer.

EXACTLY CORRECT! [for conductive heat transfer].
CLEAN contact area is vital.
.....

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.

How long does it take you to make one solder connection on a 1/4 watt
through-hole resistor on a typical board two-sided board with plated
through holes, at 500F? I ask because in production, 3 seconds is far
beyond unacceptable.


In production, the board is preheated before it reaches the solder fountain
and spends a couple of seconds in the fountain. It is then cooled at a
controlled rate to avoid temperature shock.

Or the solder paste is silk screen printed onto the board, the parts are
robot applied.
The board is then preheated for several minutes, the temperature is quickly
ramped up to the melting point of the solder and back down.
The board is then cooled and cleaned. This is done as the board is carried
by a belt through the different temperature zones.

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.

Then why do you assert that with low temps, component damage is
impossible?

I certainly didn't mean that component damage is impossible.

Let me restate my opinion:
It is easier to solder without damaging components using a clean, high
wattage, controlled temperature iron set at a temperature slightly above
the melting point of the solder
than it is when using a low wattage, high temperature iron.

With practice, either method can be used, but I have tried both and prefer
high wattage, with a lower, controlled temperature.

Given good heat conductivity (clean and tight joints in the iron)
and sufficient heat capacity (plenty of watts), a temperature
controlled iron is much better. The iron temperature should be set
slightly higher than the melting temperature of the solder. There is
no need for dozens or hundreds of degrees in excess of the melting
temperature.

We disagree quite strongly on this point

As I said originally, there are two philosophies.

And one of them works in practice!

BOTH work, in practice.

With proper [different] techniques, both can be used.

.....

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.

See above.


.....
Your 800F is 427C. There is a very good chance of damaging such an IC
at that temperature.

We do it all day long every day. Less than 1/2 second per lead. No
damage.

Yep. And I have seen what happens when the iron stays on the joint 1/2
second too long.
I have had to change ICs that failed because of overheating.

I have also had to work with non temperature controlled irons, even battery
powered ones.

I would ALWAYS prefer to have a high wattage (150W) temperature controlled
iron set to 500 or so degrees rather than a 15 W 900 degree iron.
You are, of course, welcome to use what you prefer.
As I said, BOTH methods can be made to work.

Best regards. I suspect that we have exhausted the subject for now.



--
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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