[Elecraft] Soldering Iron Temperature

[Ron D'Eau Claire]

The answer is in how fast the solder flows on  the joint. With most good
irons and tips appropriate to the size of the solder joint, 700F to 750F is
typical. 

Once you put the iron to the joint, solder should flow freely in about 3
seconds, not much longer. Dwell times (time the iron is on the joint)
greater than 5 seconds means you don't have enough heat, no matter what the
iron temperature says.

One can produce a FB solder joint even if the iron has to be on the joint
much longer, but you're in serious danger of damaging components or
de-bonding traces from the pc board. It isn't the temperature that destroys
the components so much as it is the length of time they are kept hot. It's
much easier on most components to be subjected to higher temperatures for a
short period of time than to be subjected to 100 degrees less for a longer
time. So a "hotter" iron is a safer iron around sensitive components. 

Some builders like to keep their irons below 700F. That's fine IF they get
enough heat fast enough to flow solder in 3 seconds or so, but, in addition
to damaging components, cooler irons are one of the most common reasons for
poor, "cold" solder joints in which the solder covers the pad and leads, but
doesn't actually bond to them, leaving a mechanical connection that will
oxidize and become intermittent over time. Cold solder joints used to be
easy to spot because they had a satin sheen to the solder when it cooled.
Unfortunately, the new solder formulations that reduce or eliminate lead may
produce that sheen even when soldered correctly. That means proper technique
is more important than ever to produce safe, reliable solder connections. 

If you have to use iron temperature settings above 750F to keep the dwell
time down to about 3 seconds for pc board work, look at the tip you're
using. Tips aren't terribly critical, but a tiny tip on a relatively big
joint simply won't transfer heat fast enough. Also, make sure you're using a
wet tip with a tiny film of solder that greatly helps heat transfer. I
generally touch the wire solder to the joint and set the iron on the edge of
the solder so it melts a tiny bit of the end on contact. That provides the
transfer medium. On most pc boards, melting off 0.5 mm or less of very thin
wire solder is plenty to provide good thermal contact. That's where using
appropriate size solder comes in too. Very fine solder is needed to work
easily on small pads. 

Another place to pay attention is the condition of your iron. Every few
years I disassemble my Hakko 936 to clean out any black oxidation that is
accumulating between the heating element and the tip. The Hakko has a
wonderful tip heater that really pour on the calories to keep the tip hot.
You don't have to worry about tip "temperature droop" with it unless perhaps
you're using it on a production line soldering SO-239 coaxial connector
shells <G>. But it needs to move that heat from the heater to the tip
efficiently, and to do that it needs to be clean inside as well as outside. 

Ron AC7AC


Hi guys,

  My Hakko 936 with several T-1 for surface mounted tiny components arrived
today.  It is not warm yet.  I have been using an Antex 15 Watt iron since
1971, and
I built my K2 #4962 with it.   Now, variable temperature is,
well, a variable that I have never had to consider.
So,  my questions:
 What temperature do you set with 60/40 solder on such as
a K2, and perhaps a different temperature when soldering
an AD9851?

73,
Ian, G4ICV, AB2GR, K2 #4962, LP-100 #278
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