PCBA Tech - Avoid false soldering of SMT automatic soldering machine

How to avoid the virtual soldering of automatic soldering machine in SMT chip processing

Virtual soldering means that there is only a small amount of solder at the solder joints, resulting in poor contact, which is always on and off. Welding means that the surface of the weldment is not fully plated with tin, and the weldment is not fixed by tin. It is caused by the surface of the weldment is not cleaned, or the flux is used too little, and the welding time is too short. The so-called "post-failure of solder joints" means that the solder joints on the surface appear to be of acceptable quality, and there are no welding defects such as "lap welding", "half spot welding", "snap welding", "exposed copper" and so on. During production in the workshop, There is no problem with the installed whole machine, but after the user has used it for a period of time, failures caused by poor welding and poor conductivity have occurred from time to time. This is one of the reasons for the high early repair rate. This is "virtual welding". . The quality of the solder joints will seriously affect the overall quality of the potentiometer, and care must be taken not to produce false soldering. Here we are going to discuss how to control the phenomenon of SMT virtual welding during production and processing.

1. Wipe frequently to keep the tip of the soldering iron clean. Because the soldering iron head of the energized automatic soldering machine is in a high temperature state for a long time, its surface is easily oxidized or burned to death, which makes the thermal conductivity of the soldering iron worse and affects the welding quality. Therefore, you can wipe the impurities on the soldering iron tip with a damp cloth or wet sponge.

When the temperature is too high, you can temporarily unplug the plug or dip the rosin to cool down, so that the soldering iron tip can be properly tinned at any time.

2. Precautions for tinning: If the surface of the weldment and solder joint is stained with rust, dirt or oxide, it should be cleaned up before soldering, so that the surface of the weldment or solder joint can be plated with tin.

3. The temperature of PCB soldering should be appropriate, not too high or too low. In order to make the temperature appropriate, an automatic soldering machine with appropriate power should be selected according to the size of the electronic component. When the power of the selected automatic soldering machine is constant, attention should be paid to controlling the length of the heating time. When the solder is automatically scattered from the tip of the soldering iron to the object to be soldered, it indicates that the heating time is sufficient. At this time, quickly remove the tip of the soldering iron, leaving a smooth solder joint at the soldered area. If after removing the automatic soldering machine, there is little or no tin left in the soldered area, it means that the heating time is too short, the temperature is not enough or the object to be soldered is too dirty; if the automatic soldering machine is removed, the solder will flow down. It indicates that the heating time is too long and the temperature is too high. Generally, the temperature control of the soldering iron tip is the best soldering temperature when the flux melts faster and does not emit smoke.

4. The amount of tin should be moderate. The amount of dipping tin of the automatic soldering machine can be determined according to the size of the required solder joints, so that the solder is enough to cover the toughness of the solder to form a suitable size and smooth solder joint. The solder joint is not too much tin, tin is better, on the contrary, this kind of SMT solder joint is more likely to be soldered, and it may be that the solder is accumulated on it instead of soldering on it. If the amount of tin applied at one time is not enough, it can be repaired again, but the automatic soldering machine must be removed after the previous tin is melted together; if the amount of tin applied at one time is too much, the soldering iron tip can be used to take away the appropriate amount.

5. The welding time should be controlled well and not too long. The proper use of welding time is also an important part of welding skills. If it is soldering of printed circuit boards, 2~3S is generally appropriate. If the soldering time is too long, the flux in the solder will be completely volatilized, and the soldering function will be lost, and the surface of the solder joint will be oxidized, causing the solder joint surface to be rough, black, not shiny, burr or flowing. At the same time, the soldering time is too long and the temperature is too high, and it is easy to burn the components or the copper foil of the printed circuit board. If the soldering time is too short and the soldering temperature cannot be reached, the solder will not be fully melted, which will affect the wetting of the flux and easily cause false soldering.

6. During the solidification of PCB solder joints, remember not to touch the solder joints with your hands. Before the welding point is completely solidified, even a small vibration will cause the welding point to deform and cause false welding. Therefore, the soldering parts should be fixed before the soldering iron tip is withdrawn, such as clamping with tweezers, or blowing quickly with the mouth after the soldering iron tip is withdrawn. The purpose of adopting these methods is to shorten the time for the solder joint to solidify.

7. When a soldering point is finished welding, the selection of the withdrawal angle of the soldering iron tip is also particularly important. When the soldering iron tip is evacuated diagonally upward, a small amount of tin bead is taken away from the soldering iron tip, which can form a smooth solder joint; when the soldering iron tip is withdrawn vertically upwards, it can form a solder joint with sharp burrs; when the soldering iron tip is horizontally oriented When evacuating, the soldering iron tip can take away most of the tin beads.

In summary, the most direct and fundamental way to avoid SMT false soldering is to clean up before soldering. It is best not to use solder paste for cleaning, because it contains acidic materials, which may corrode the pins of electronic components in the future. Welding. After removing the oxides, tin the SMT soldering surface first, and then soldering is easy, and it is not easy to produce false soldering. You should also hang tin on the pins of the electronic components, and master the soldering time, so as to ensure the quality of soldering, thereby ensuring the quality of the entire circuit board.