PCB Fabrication

Flux heating

by:A-TECH      2020-04-27
Chemicals emitted by flux heating are harmful to human body. If the nose is too close to the welding head during operation, harmful gases can be easily inhaled. Generally, the distance between the soldering iron and the nose should be at least 30 cm, usually 40 cm. There are three ways to use electric soldering iron, as shown in Figure 1. The anti-grip method is stable in action, and it is not suitable for fatigue for long-term operation, and is suitable for operation of high-power soldering iron. The positive grip method is suitable for the operation of medium power soldering iron or electric soldering iron with elbow. Generally, when welding PCB and other weldments on the operating table, the pen grip method is often used. Solder wire generally has two methods, as shown in figure 2. As lead accounts for a certain proportion of the welding wire composition, it is well known that lead is a heavy metal harmful to human body, so gloves should be worn or hands should be washed after operation to avoid ingestion. 'With electric iron to configuration iron frame General prevent again on the right front electric iron after certain to safe defense iron frame on and attention wire and of Don't touch iron head. (II) . Five-step training as a training method for beginners to master manual soldering technology, five-step training is effective and worth discussing as a separate section. Many electronics enthusiasts re-operate a welding operation method, that is, first use the soldering iron head to apply some solder, and then put the soldering iron on the solder joint to wait for heating and then solder to wet the weldment. This method is not the correct operation method. Although the weldment can be welded in this way, the quality cannot be guaranteed. It is not difficult to understand this point from the soldering mechanism we know. As shown in Fig. 3, when we put the solder on the welding head of the melting channel, the heavy flux of the solder wire lies on the surface of the solder, because the temperature of the welding head is generally above 250 ℃-350 ℃, before the soldering iron is placed on the solder joint, the rosin flux will continue to volatilize, and when the soldering iron is placed on the solder joint, due to the low temperature of the weldment, heating takes a while, during this period, the flux is likely to volatilize more than half or even completely, thus poor wetting due to lack of flux during wetting. At the same time, due to the large temperature difference between the solder and the weldment, the bonding layer is not easy to form, and it is difficult to avoid virtual welding. Moreover, due to the protective effect of flux, the solder is easy to oxidize after death, and it is inevitable that the quality cannot be guaranteed. The correct method should be a five-step method: 1. Prepare for welding and prepare for soldering tin wire and soldering iron. At this time, the special emphasis on the welding head should be kept clean, that is, it can be stained with solder (Commonly known as eating tin). 2. Heating weldment contact the soldering iron with the solder joint. Pay attention to first keep the soldering iron heating all parts of the weldment, for example, the leads and pads on the printed board are heated, and then pay attention to the flat part of the soldering iron head (Larger part) For weldments with large contact heat capacity, the side or edge part of the welding head contacts the weldment with small heat capacity to keep the weldment evenly heated. 3. Melting solder when the weldment is heated to a temperature that can melt the solder, place the welding wire at the solder joint, and the solder begins to melt and wet the solder joint. 4. Remove the solder. Remove the solder wire after melting a certain amount of solder. 5. Remove the soldering iron when the solder completely moistens the solder joint, remove the soldering iron. Note that the direction of removing the soldering iron should be approximately 45. The above process is about two or three seconds for general solder joints. For solder joints with small heat capacity, such as small pads on printed circuit boards, the operation method is sometimes summarized by three-step method, I . e. the above steps 2 and 3 are combined into one step and 4 and 5 into one step. In fact, the subtle distinction is still five steps, so the five-step method is universal and is the basic method to master manual soldering iron welding. In particular, the time spent between each step is very important to ensure the welding quality, and only through practice can it be gradually mastered.
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