[Elecraft] Soldering iron tip temperature for KPA100

[Lyle Johnson]

The point has probably already been made, but there is a big difference
between HEAT and TEMPERATURE.

Many times people will use a too-high TEMPERATURE to make up for inadequate
HEAT (related to the wattage of the iron).  They use the thermal mass of the
soldering tip to store extra thermal energy, and allow the heat to flow from
the resulting heat reservoir (which quickly lowers the tip  temperature,
hopefully to a safe value)

The idea of a temp-controlled iron is that it limits the tip temperature,
but provides heat to the joint as required up to the limit of the iron.

You could argue that for large joints that require a lot of heat, you can
use a small, low-wattage iron at 1,000 degrees F - but I wouldn't recommend
it.

One must be careful when soldering that the temperature does not exceed the
ability of the PC board or the component to absorb the thermal shock that
occurs when the iron is brought to the junction of the part(s) and board to
make a connection.

An extreme case is charring of the board.

A more common case is "lifting the pad" which occurs when the copper+tin
plating on the board expands and overcomes the adhesive bond which holds it
to the board.  This results because the pad was allowed to reach too high of
a temperature.

Another danger is cracking the plating between the plated-through hole in
the board and the pad on the surface of the board.  This can occur even when
the pad doesn't appear to have "lifted" and cause an unreliable connection
which won't fail until Field Day.

I have used systems where a part was soldered and desoldered from a board
hundreds of times with no damage to the board/pad adhesive or the part.

And I have used systems where one or two applications of the iron and the
pad was ruined.

In both cases, the difference was in controlling the temperature of the
iron, the board and the components.

As a result of these experiences, I never use an iron temperature of more
than 700 degrees.  If I need more heat, I use two irons, or a larger iron,
but never a higher temperature.  Solder melts at the same temperature
regardless of your iron.  If you are using more than 700 degrees, you have a
heat problem, not a temperature problem.

In the case of the KPA100, I used two small irons (Hakko 936 + Edsyn 951SX)
in the steps soldering Q1 and Q2 emitter tabs to the ground plane because I
don't have a higher heat capacity iron and didn't want to buy one.

IMHO, YMMV.

72,

Lyle KK7P