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+44(0)1822
613555 |
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+49(0)77
24 934 125 |
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info@aci-ecotec.co.uk |
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info@aci-ecotec.de |
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| Automatic iron soldering |
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| The soldering
tool |
An automatic iron soldering first requires a
suitable heat transfer medium. This heat transfer medium normally
consists of one heating element in conjunction with a soldering
tip and one or more temperature sensors. In addition to the
heat transfer medium, the soldering tool
principally has a solder feeder. The solder, often cored solder
with integrated flux core has to be fed to the soldering point
at an exact moment with a certain velocity and in exactly reproducible
quantity. The activation of the solder feeding therefore must
be freely programmable within the running process. It is a matter
of course, that on a soldering tool which is automation-capable,
different cored solder diameters and the standard supply units
(rolls) can be mounted. |
| The thermodynamic
behavior |
The contacting heat transfer during the iron
soldering follows the law of thermodynamics. A heat transfer
from a body with higher temperature (soldering tip) to a body
of lower temperature (soldering point) is concerned here. The
classic spot soldering by using eutectic solder is done within
a temperature range of 200 to 300 °C. The heat transfer
medium is normally adjusted to 320 to 400 °C. Decisive for
the correct functioning of a soldering of good
quality is the thermodynamic process. This process, however,
is not only determined by the temperature of the heat transfer
medium. Rather, a number of factors play an important role.
Beside the difference in the temperature of soldering tip and
soldering point, the mass ratio of soldering tip and soldering
point, the transitional section respectively the appearance
of the interfacial surface, the heat required for deposition
of the solder and the heat that flows from the soldering point
into the surrounding, determine the temperature curve in the
soldering point. The following diagram (Fig. 8) shows the temperature/time
course on a miniature soldering point with eutectic solder.
The melting point of this solder is at 183 °C. The topmost
line shows the temperature curve on the soldering tip. |
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| Fig 8: Temperature / time -
(click image to enlarge) |
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| Selection of
soldering tips |
The temperature curve shown in the diagram is
an example of a miniature soldering point, e.g. for a component-wire
joint on a PCB. But each soldering point requires a specific
thermal
efficiency. This is the ratio of the supplied heat to the achieved
temperature rise within a certain time. In the iron soldering
process the energy supply from the heat medium to the soldering
tip shows a certain inertia. Therefore the soldering tip must
be capable to store a certain amount of heat. The thermal capacity
of the soldering tip is in proportion to its mass and temperature.
The temperature range specifies the solder to be used. The size
of the soldering tip is a parameter for the temperature course.
If the soldering tip is too small in relation to the heat requirement
of the soldering point, the soldering will freeze in while the
solder is deposited. This results in the cored solder broken
off or upset, mostly with reaction on the feed mechanism and
an insufficient soldering result. If a too large soldering tip
is chosen, the temperature of the soldering point keeps on rising
while the solder is deposited.
This minimizes the efficiency of the flux as it has its best
efficiency between 200 and 300°C. Besides a bulky soldering
tip is often disadvantageous for the welding accessibility. |
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| More information available on request! |
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