The temperature change between the soldering iron and the solder joint
4. 1 Ideal welding conditions
The ideal welding state is that the heat energy of the electric soldering iron is constant and does not change due to changes in the outside world. The welding process can be achieved by controlling the welding time according to the heat capacity of the objects to be welded.
Assuming that 63Sn/37Pb solder wire is selected, its melting point is 183 °C, the ideal welding temperature is 223 °C, and the welding is completed after 2 s to 5 s, the ideal heat energy conversion curve of the solder joint during the welding process.
When the temperature of the soldering iron is constant at 223°C, the time required for the temperature of the object to be soldered to rise from the normal temperature of 25°C to 223°C is related to the heat capacity of the object to be soldered. When the heat capacity of the object to be welded is small, the temperature rises rapidly. When the heat capacity of the object to be welded is large, the temperature rise rate is slow. Therefore, in actual operation, according to the size of the solder joints, different sizes of soldering iron tips should be selected and the temperature of the soldering iron should be adjusted to obtain a good soldering effect.
4. 2 The case of the soldering iron
There are roughly three forms of electric soldering irons today:
(1) Ordinary electric soldering irons rely on the size of the resistance to obtain a relatively constant temperature output, without temperature compensation control, and poor temperature stability;
(2) Constant temperature electric soldering iron, the temperature output is controlled by temperature compensation, the temperature stability is good, the design is fixed temperature output and cannot be adjusted;
(3) The constant temperature and temperature-adjustable electric soldering iron has the characteristics of a constant temperature electric soldering iron, and can adjust the output temperature according to needs. At the same time, it can be checked that the set temperature is consistent with the actual temperature of the soldering iron tip. However, in actual use, none of the existing electric soldering irons can fully reach a constant temperature state. Usually, the soldering quality is ensured by increasing the power or temperature of the electric soldering iron, which is commonly known as increasing the idle temperature of the electric soldering iron for welding. For example: choose 63Sn/37Pb solder wire, its melting point is 183 ℃, the ideal welding temperature is 223 ℃, raise the temperature of the electric soldering iron to be higher than the ideal welding temperature for welding, such as 260 ℃,
280°C and 320°C etc.
