Welding of printed circuit boards
1.Selection of electric soldering iron
When welding printed circuit board, the best choice of electric iron is 205W, the temperature is kept at 300℃-350℃, if the condition permits, you can choose the temperature-regulating type electric soldering iron. The shape of the iron head should be selected according to the size of the printed circuit board pad, generally using chisel or conical soldering iron head. Small tapered iron heads are often used for compact printed circuit boards with high density.
2. Heating methods
When the printed circuit board is heated, it is necessary to heat the copper box and the lead wire of the components on the printed circuit board at the same time by the soldering iron head. For large pads with a diameter greater than 5mm, the electric iron may be rotated from time to time, so do not stay at a point for a long time and lead to a local Part overheating
3. Welding of polar components
When the capacitor is welded, it is welded in the order of the capacitive electrolytic， capacitance of the expanded glass and the capacitor metal.
Triode is not resistant to high temperature, welding time can not be too long, welding is best to use silver to use the Triode lead to help heat, prevent ironing pipe.
High-power Triode welding-mounting of radiators or mats: insulation is smooth, and the common feet of the transistor must be used the edge wire is connected to the board.
4. Welding of integrated circuits
In manual welding of integrated circuits, due to the small lead spacing of integrated circuits, it is necessary to select the appropriate soldering head and temperature, to prevent the connection of tin between leads, and to select internal thermal electric soldering iron less than 45W as a general rule. The daily ground wire should be in good contact. If the external heat type, it is best to use soldering iron off the residual heat welding, if necessary, also take human grounding measures.
It is best to weld the ground end and the power end of the integrated circuit first, and then to weld the human end. For integrated circuits that are particularly sensitive to temperature, cotton balls dipping with alcohol can be used to protect the roots of the components so that heat is as little as possible transmitted to the components. When welding the gate circuit, the input end should be handled correctly and should not be suspended. The time of each welding of the integrated circuit should be depending on the heat dissipation of the device.
When welding double tree FET and CMOS integrated circuit, it is easy to induce electrostatic high voltage because of its high impedance and small capacitance between electrodes, which leads to device breakdown and damage. The lead wires of integrated circuits cannot withstand high temperature to prevent static electricity, also must be very careful when welding.
It is best to use a stored electric iron for welding CMOS integrated circuits to prevent damage to the integrated circuits due to the weak leakage of the soldering iron.
There are two ways to assemble and weld integrated circuits: one is to weld the integrated circuit chip directly to the printed circuit board; the other is to use a special integrated chip socket / IC socket to weld the IC socket to the printed circuit board. Then the integrated circuit board is plugged into the human IC socket.
The IC shall be installed in accordance with the requirements of the corresponding position of the printed circuit board, and in accordance with the drawing requirements to further check the type of integrated circuit, pin position to meet the requirements, to ensure that the correct welding can be carried out.
7. welding of several vulnerable components
Easily damaged, these components are vulnerable elements in the welding process, such as heating or soldering iron containers, common vulnerable components such as cast plastic components, Reed components and so on.
In welding injection molding components, cast plastic components are widely used in manufacturing, the biggest characteristic of which is that they are not resistant to high temperature.
When welding cast plastic components and Reed components, attention should be paid to the preparation of surface cleaning and tin plating before welding. The prewelding process should not be repeated as successful as possible: the temperature of the soldering iron and iron should be appropriate. It is best to choose a sharper soldering head to prevent contact with adjacent solder joints during welding; the flux should be less used. Prevent the flux from dipping the electrical contact point of the human component, causing damage to the component; do not allow the electric iron to contact the component for a long time during welding, the heating time should be short, the welding time should be short, and do not press the welded components.
8. Others
In addition, in PCB welding, if the wettability of solder needs to be enhanced, the method of surface cleaning and welding should be used, and it must be remembered that the friction pad or butt pad can not be used directly. For components with poor heat resistance, auxiliary T devices should be used to help dissipate heat to prevent damage to components.
If rosin is used as flux, it is necessary to clean up rosin after welding. The solder joints coated with inorganic flux must be scrubbed to avoid corrosion. After welding, use tweezers to gently pull each component pin to see if the welding is secure to prevent virtual welding. It should also be compared with the schematic diagram, carefully check whether there is leakage welding phenomenon.