Circuit board manual soldering process
1. Check before operation
(1) Insert the plug of the soldering iron into the specified socket 3-5 minutes before going to work every day, and check whether the soldering iron is hot. If it is not hot, first check whether the socket is plugged in. If it is plugged in, if it is not hot, you should immediately report to the management. The staff reported that the soldering iron cannot be disassembled at will, and the tip of the soldering iron cannot be directly touched with their hands.
(2) The soldering iron tip that has been oxidized and uneven or has a hook should be updated: 1. It can ensure a good heat conduction effect; 2. It can ensure the quality of the welded object. If you use a new soldering iron tip, wipe off the maintenance paint after heating, and immediately add tin for maintenance. The cleaning of the soldering iron should be carried out before the soldering operation. If the soldering iron is not used for more than 5 minutes, the power must be turned off. The sponge should be cleaned. Dirty sponges containing metal particles or sulphur-containing sponges will damage the tip of the soldering iron.
(3) Check whether the tin absorbing sponge has water and is clean. If there is no water, please add a proper amount of water (a proper amount means that water seeps out when the sponge is half as thick as normal. The specific operation is: humidity requires that the sponge is completely wet , Hold it in the palm of your hand and fold your fingers together naturally.) The sponge should be cleaned. Dirty sponges containing metal particles or sulphur-containing sponges will damage the tip of the soldering iron.
(4) Whether the human body and the soldering iron are reliably grounded, and whether the human body is wearing an electrostatic ring.
2. Welding steps
The specific operation steps of soldering iron welding can be divided into five steps, which is called the five-step engineering method. To obtain good welding quality, it must be operated strictly according to the steps. Step-by-step welding is one of the keys to obtaining good solder joints. In actual production, the most prone way to violate the operation steps is that the soldering iron tip does not first contact the part to be welded, but first contacts the solder wire, and the molten solder drips on the part to be welded that has not yet been preheated. In this way, it is easy to produce virtual solder joints, so the tip of the soldering iron must be in contact with the welded parts. Preheating the welded parts is an important means to prevent virtual welding.
3. The essentials of welding
(1) The contact method between the soldering iron tip and the two welded parts
Contact position: The soldering iron head should be in contact with the two welded parts (such as solder feet and pads) to be connected to each other at the same time. The soldering iron is generally inclined at 45 degrees. Avoid contact with only one of the welded parts. When the heat capacity of the two welded parts is very different, the tilt angle of the soldering iron should be adjusted appropriately. The smaller the tilt angle between the soldering iron and the soldering surface, the larger the contact area of the welded part with the larger heat capacity and the soldering iron will increase, and the thermal conductivity will be strengthened. For example, the inclination angle of LCD welding is about 30 degrees, and the inclination angle of welding microphones, motors, speakers, etc. can be about 40 degrees. Two welded parts can reach the same temperature in the same time, which is regarded as an ideal heating state.
Contact pressure: A slight pressure should be applied when the soldering iron tip is in contact with the welded part. The strength of heat conduction is proportional to the applied pressure, but the principle of not causing damage to the surface of the welded part.
(2) Supply method of welding wire
The supply of welding wire should master three essentials, namely supply time, location and quantity.
a. Supply time: In principle, when the temperature of the weldment reaches the melting temperature of the solder, the solder wire is immediately delivered.
b. Supply position: It should be between the soldering iron and the welded part and as close to the pad as possible.
c. Supply quantity: It depends on the size of the welded part and the pad. After the pad is covered by the solder, the solder can be higher than 1/3 of the diameter of the pad.
(3) Welding time and temperature setting
a. The temperature is determined by actual use. It is most suitable to solder a tin point for 4 seconds, and the maximum is no more than 8 seconds. Observe the soldering iron tip at ordinary times. When it turns purple, the temperature is set too high.
b. Generally direct plug-in electronic materials, set the actual temperature of the soldering iron tip to (350~370 degrees); for surface mount materials (SMC) materials, set the actual temperature of the soldering iron tip to (330~350 degrees)
c. For special materials, the soldering iron temperature needs to be specially set. FPC, LCD connectors, etc. use silver-containing tin wires, and the temperature is generally between 290 degrees and 310 degrees.
d. For soldering large component feet, the temperature should not exceed 380 degrees, but the power of the soldering iron can be increased.
(4) Precautions for welding
a. Before welding, observe whether each solder joint (copper skin) is smooth and oxidized.
b. When soldering items, be sure to spot the solder joints to avoid short circuits caused by poor wire soldering
4. Check after operation
(1) After using the soldering iron, wipe the remaining tin of the soldering iron tip on the sponge.
(2) After get off work every day, the tin beads, tin dross, dust, etc. must be removed from the soldering iron seat, and then the soldering iron must be placed on the soldering iron stand.
(3) Put the cleaned soldering iron on the upper right corner of the workbench.