A. Bend the legs of the component Before installing the component, the pins of the component must be bent and arranged in an appropriate shape. This step is often referred to as "bending legs" or "nesting legs". Because the connection part (or root) between the component and the pin is fragile, it can't bear too much mechanical stress. When bending the leg, clamp the part near the root of the pin with tweezers (to protect the root), and use the fingers of the other hand to bend the pin. The distance between the bending point and the root shall not be less than 3mm; Do not bend at right angles, and the bending radius of the pin shall not be less than 2MM. Figure 1-8 shows the correct shaping method.
B. Surface treatment and surface treatment of electronic components. Pay special attention to the operation of pins and printed boards of pipes or integrated circuits when conducting tin dipping and the operation of tin dipping of the board to be brushed.
Pin of pipeline or integrated circuit: Because the outer layer of the pin of pipeline or integrated circuit has only a very thin gold layer or silver layer, it is difficult to tin-plate the replaceable wire inside, and the pin is rusty, so it is not easy to tin-plate. Therefore, the method of processing printed boards must not be used. So when their pins rust, they can only use fine sandpaper to gently hit them twice. Even if the rust is not completely removed, the knife should not be perforated again. At this time, you should dip a soldering iron into a big tin ball to "rub" the pin and let it "bury" in the melted tin ball. If the wire is welded after friction, it can still be used. If the pins are tinned in only a few places, the device can no longer be used.
Printed board: If there is protective wax or paint on the printed board, or the surface is too dirty, knock it off gently with fine sand or steel wool until the exposed copper foil or tin is bright, then wipe it off gently with alcohol cloth, and then tin plating.
When tin is plated on the through hole, it should be ensured that the pin of the component can still pass through the through hole. If the hole is blocked, you can suck the tin in the hole with a tin absorber, or poke the hole with a tin-free iron wire or aluminum wire.
C. welding is divided into spot welding and drag welding.
Spot welding: there are two kinds of welding with tin wire and welding without tin wire.
Wire-assisted welding is to hold the wire in the left hand and the soldering iron in the right hand to spot weld. The welding process is as follows: insert the component pin to be welded into the welding hole of the circuit board, and adjust the height of the component after checking the correct position (for example, the transformer cannot stick the bottom surface to the motherboard). Weld one foot first, and then spot weld the other foot. When welding, let solder wire touch the solder joint, weld the solder wire with a soldering iron, and then electroplate on the solder joint. At this time, the left hand moves forward according to the size of the welding point. After canning, the left hand immediately recovers and stops canning. At this time, the soldering iron of the right hand stays on the solder joint, and the residence time is generally about 0.8 seconds, so that the spot welding can be completed. In addition, the soldering iron should move away from the solder joint quickly and be pulled out horizontally.
There is no solder wire welding, which means that there is enough solder on the solder joint or a certain amount of solder on the welding head, and then the solder joint is spot-welded with an electric soldering iron. For example, the transistor is directly soldered to the copper foil circuit board. First, put enough solder on the solder joint on the copper foil analysis board, and then weld the triode on the solder joint. The process is to melt the solder with a soldering iron first, and when it is in full contact with the solder, the soldering iron quickly leaves the solder joint.
Drag welding is generally a welding method used in welding multi-needle assemblies. When operating, try to fix the components in a good position (which can be fixed by soldering), and then lean the welding wire on the welding feet. When the C-type welding head of large area contact melts solder wire, tin will continue to enter the solder joint; When the solder joint (molten solder) is large enough, the welding wire of the left hand and the soldering iron of the right hand move to the left synchronously, that is, the position of the solder joint moves to the left. When moving, the welding head will not touch the pin of the component. Instead, high-temperature molten solder is filled between the lead and the solder joint of the circuit board, which is the special feature of drag welding. In order to ensure the welding quality of drag welding, the moving speed and tin feeding speed of soldering iron should be specially controlled during operation.
D, using cleaning flux to wipe off the coking rosin on the pins of the printed circuit board and around the through holes. Available fluxes are: ethanol (anhydrous alcohol) and isopropanol.
(8) Stripping of electronic components
When soldering printed circuit board components, special attention should be paid not to damage the circuit board, and the components must be protected.
A. The welding head of the soldering iron used in the desoldering method of components with less than three pins should be filed very sharply, so that welding head will not touch other parts of the printed circuit board when touching the solder joint. When removing the solder joint, touch the solder joint on the back of the printed board with the welding head. At the same time, tweezers should be used to clamp the component pins on the front of the printed board to prevent excessive heat from being conducted into the components. When the solder begins to melt, use tweezers to slowly pull the pin out of the through hole. If the pin pulling process is not smooth, the welding head should be temporarily removed from the solder joint.
B. Welding method of multi-pin components For example, for integrated circuits, tin absorbents are usually needed. If there is no tin absorbing board, the following alternative methods can be adopted: the back of the printed board is tilted downwards, the soldering point on the back is contacted with the soldering head of the electric soldering iron, and the soldering point is contacted with the aluminum wire. The other end of the aluminum wire faces down. After the solder melts, insert the aluminum wire into the through hole. At this time, the molten solder will fall down along the aluminum wire. This method is also very useful.
Pay special attention to the contact time between the welding head and the solder joint, which cannot exceed 10 second. Overheating will separate the copper-clad layer from the printed board or the printed board will be burned. Do it after the solder joint is a little cold.