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1. welding tools
Choose an electric soldering iron with a power of about 25W. The welding head should be in the shape of a sharp mouth, and trim the tip with a chisel to prevent the burr on the tip from dragging the needle during welding.
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2. Welding materials
The welding materials mainly include rosin, solder wire, solder paste, natural water and pure alcohol. Welding wire must choose low melting point.
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3.？ Clean the printed circuit board
Before soldering, level the printed circuit board with an electric soldering iron, clean the parts of the printed circuit board that need to be soldered with natural water with a small brush, and carefully check the printed circuit board for peeling and damage. If there is peeling, it only needs leveling, if there is damage, it needs to be connected with thin copper wire.
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4. Tin on the pin
When the new integrated circuit leaves the factory, its pins have been tinned without any treatment. If it is a used integrated circuit, it is necessary to clean the dirt on the pins and adjust the tin on the pins before use.
Specific operation steps of soldering integrated circuits
First, put the integrated circuit on the printed circuit board, align the pins, and weld the head and tail pins of each column of pins to prevent the integrated circuit from shifting, and then weld by "pull welding". The so-called pull welding is to take a small drop of solder from the welding head and gently pull the welding head from left to right along the whole row of pins of the integrated circuit, so that each pin is welded on the printed circuit board.
After welding, each solder joint shall be inspected. If there is a virtual solder joint, it can be repaired with an electric soldering iron. Wipe the pins with pure alcohol cotton balls to remove rosin and welding slag from the pins.
Matters needing attention in welding
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The circuit soldering iron for welding should be connected to zero or ground.
After the electric soldering iron is heated, the power plug should be unplugged or the shell of the electric soldering iron should be well grounded to avoid the induced charge from penetrating the integrated circuit, especially the welding MOS integrated circuit.
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Welding time should not be too long.
Pay attention to temperature and time when soldering integrated circuits. Generally, the temperature of integrated circuit welding is 260℃, and the time is 10s or 350℃ or 3s, that is to say, all pins of an integrated circuit are immersed in the temperature and time allowed by the distance from the package base 1~ 1.5mm at the same time, so the temperature of spot welding and immersion welding should be controlled at about 250℃ and the welding time is about 7s.
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Pay attention to heat dissipation
Some high-power integrated circuits have good heat dissipation conditions. When replacing the integrated circuit, the heat sink should be fixed again to make it closely contact with the integrated circuit to prevent the integrated circuit from being damaged by heat. Please pay attention to the following points when installing the radiator:
Do not weld the ground wire to the heat sink without determining whether the heat sink of the power integrated circuit should be grounded;
The installation of the heat sink should be smooth, and the fastening torque should be moderate, generally 0.4 ~ 0.6 N.m
Before installation, dust and rust should be removed between the heat sink and the integrated circuit, and silicone grease should be coated between them to reduce the thermal resistance.
After the heat sink is installed, it is generally welded to the grounding end of the printed circuit board with lead wires;
Before installing the radiator, you can't turn on the electricity at will.
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Pay attention to the direction when installing integrated circuits.
When installing the integrated circuit on the printed circuit board, pay attention to the wrong direction, otherwise the integrated circuit is likely to be burned when it is powered on. Generally speaking, the pins of an integrated circuit are upward with a gap or a point. Or take the vertical line as the standard, and the needles are arranged counterclockwise. If the integrated circuit is packaged in a single line, the front side (the side printed with the model trademark) faces itself and the pins face down, and the pin numbering sequence is generally arranged from left to right. In addition to the above conventional pin arrangements, there are some special pin arrangements that need attention. Most of them belong to single-line in-line package structure, and their pin arrangement is just the opposite of the above. +
Stress that pins can bear and insulation between pins.
Don't put too much pressure on the pins of the integrated circuit. Be careful when disassembling the integrated circuit to prevent damage. For high-voltage integrated circuits, there should be enough gap between power supply VCC and ground wire and other input wires. Disassembly and welding of integrated circuits
The following is an example of disassembling a soldered chip integrated circuit with a hot air gun: before disassembling, the soldering iron and the maintenance platform should be grounded, and the positioning of the integrated circuit should be remembered. Then the nozzle of the hot air gun is selected according to different integrated circuits, and then rosin water is filled around the pins of the integrated circuits.
Adjust the temperature and wind speed of hot air. In general, when disassembling the integrated circuit, the temperature switch is set to 3~6, and the wind speed switch is set to 2 or 3.
Use the hot air gun nozzle to slowly rotate along the pins around the integrated circuit and heat evenly. The nozzle should not touch the integrated circuit and surrounding components. After the solder on the pins of the integrated circuit is completely melted, gently lift the integrated circuit with a small screwdriver.
Repair the solder joint with a flat soldering iron, and align the replaced integrated circuit with the soldering position of the circuit board. First, the integrated circuit is fixed at four corners, and then the periphery is blown and welded by hot air blowing pipe.
Pay attention to cooling after welding, and do not move the integrated circuit immediately to avoid its displacement. After being fully cooled, use a magnifying glass to check whether there is any virtual soldering on the pins of the integrated circuit. If yes, repair welding with a pointed electric soldering iron until everything is normal.