6 selection skills of electric soldering iron
1 Classification of electric soldering iron
Electric soldering irons can be divided into induction type and direct heating type. Since the induction type soldering iron head has an induced charge, it is not suitable for soldering electronic components that are sensitive to the induced charge. There are two kinds of external heating type, the internal heating type is small in size, fast in temperature rise, high in thermal efficiency and easy to use. Broken wire phenomenon, the life of the heating element ranges from a few hours, more than ten hours, to dozens of hours. The heating element needs to be replaced frequently, and it is not easy to adjust the temperature, so it is not suitable for students' practical training; Slow, low thermal efficiency, but the heating element is not easy to damage and easy to adjust the temperature. The external heating type electric soldering iron is divided into ordinary type and constant temperature type. Manual soldering on the assembly line; ordinary external heating electric soldering iron has a simple temperature adjustment method, is economical and durable, and is suitable for students' electronic training.
2 Select the power of the soldering iron according to the welding object
The power of external heating electric soldering iron has various specifications such as 20, 25, 30, 45, 50, 60, 75, ..., 500 W, etc. The greater the power, the larger the diameter of the soldering iron tip, and the greater the heat generated per unit time More, the more stable and higher the temperature of the soldering iron tip.
When soldering, you can choose a soldering iron with the corresponding wattage according to the size of the weldment and the solder joint. The larger the weldment and the solder joint, the greater the power of the soldering iron. The welding objects of the students' electronic training are mainly on the printed board For soldering electronic components, general textbooks recommend using 25 or 30 W electric soldering irons, but during the training, it was found that when the ambient temperature is low in winter, electric soldering irons below 30 W cannot be used for normal soldering due to insufficient heat generation. Considering that most of the electronic training is to practice welding on ordinary printed boards. For connecting small common electronic components with large solder joints, we have used a 45 W or 50 W externally heated soldering iron for many years with good results.
When soldering transistors and integrated circuit devices, when the internal temperature of the soldering iron exceeds 200 °C for a long time[2], its performance may be deteriorated or even damaged. When using a small or excessively high-power soldering iron, The welding time becomes longer, which can easily cause excessive temperature and damage electronic components.
3 Select the shape of the soldering iron tip according to the size and shape of the solder joint
Soldering iron tips with different shapes are suitable for welding solder joints of different shapes and sizes. In practical applications, you can choose a soldering iron tip according to your personal habits and experience, or you can pre-configure several soldering iron tips with different shapes, and choose different soldering iron tips according to the welding object. Shaped soldering iron tip. If necessary, you can also use a file to modify the shape of the soldering iron tip at any time. Generally speaking, round inclined surfaces and compound inclined surfaces are used more.
4 Tin plating of soldering iron tip
The soldering iron tip is generally made of red copper, and its function is to store heat, heat the weldment and melt the solder. It can be divided into two types: ordinary type and long-life type. The liquid solder wraps the working surface of the front end of the soldering iron tip, and the copper atoms will continue to diffuse into the solder, and the higher the temperature is, the faster the diffusion will be. In addition, the flux corrosion and mechanical wear with the weldment will cause pits and pits on the working surface of the soldering iron tip. In addition, during the welding operation, the liquid solder dipped in the front end of the soldering iron tip will accelerate oxidation and fall off from the working surface at high temperature, which will cause the surface of the working surface to oxidize and is not conducive to heat transfer. In severe cases, the soldering iron tip will be " Burned to death", non-stick tin, no heat transfer, no melting of tin. When the soldering iron tip has slight pits or oxidation, it can be cleaned and trimmed with fine sandpaper. , Tinning should be carried out before use. The method is: put an appropriate amount of rosin and solder on the wooden board. When the temperature of the tip rises enough to melt the solder, rub the tip of the soldering iron repeatedly in the molten solder and rosin until the finishing work surface is covered with a layer of solder.
The long-life soldering iron tip is to plate a layer of pure iron that is not easy to diffuse with tin, wear-resistant and corrosion-resistant on the outer surface of the ordinary soldering iron tip, and then plate a layer on the iron layer on the front working surface to have a good wetting effect with tin Nickel. The long-life soldering iron tip is not easy to wear and does not need to be trimmed. Its life is about 20 times that of the ordinary soldering iron tip[3]. The longevity soldering iron tip will also be oxidized or "burned" at high temperature. Once it is "burned to death" , can only use a rubber whetstone to wipe off the oxide layer, and use a high-activity flux to tin-plate the soldering iron tip. You cannot use sandpaper and a file to repair the long-lived soldering iron tip. Once the iron-nickel layer on the front working surface is damaged, it will become an ordinary soldering iron. head off.
Ordinary soldering iron tips are generally used in electronic training teaching. During the continuous maintenance and repair of the soldering iron tips, students are trained to master the basic skills of electronic welding. When engaged in electronic welding work for a long time, choosing long-life soldering iron tips can greatly improve work efficiency.
5 Temperature adjustment of ordinary soldering iron
Under the condition of normal power supply voltage, the temperature of ordinary soldering iron is mainly determined by the following factors: the power of the soldering iron, the relative position of the soldering iron tip and the heating element, and the ambient temperature. The higher the power, the higher the temperature that the soldering iron tip can reach; The longer the package is, the shorter it extends out of the body of the soldering iron, and the higher the temperature; the higher the ambient temperature, the slower the heat dissipation of the soldering iron tip, and the higher its temperature. When soldering, you can adjust the length of the soldering iron tip extending out of the soldering iron body according to the melting point of the solder used. Adjust the temperature of the soldering iron tip. Theoretically, it is believed that the soldering effect is better when the solder joint is heated to 50 ℃ higher than the melting point of the solder [2]. The temperature has dropped. According to the solder joint and the size of the weldment, the temperature of the front end of the soldering iron tip can be adjusted to 30~80 °C higher than the melting point of the solder. Generally, it should not exceed the melting point of the solder by 100 °C. When it is used, it is easy to oxidize or be "burned to death".
Table 1 is a set of temperature adjustment experimental data of a commonly used 50 W external heating electric soldering iron. The heating element is a tubular ceramic body with a length of 45 mm and a cold resistance of 1060 Ω; the length of the soldering iron tip is 85 mm and the diameter is 5 mm; ℃; the experimental single-phase AC power supply voltage is 228 V.
