1. The flux is in poor contact with the bottom surface; the floor and the welding angle are improper
2. The specific gravity of the flux is too high or too low, and the original bottom plate and leads are not handled properly.
3. The transmission speed is too fast or too slow; the standard speed is 1.2-1.5M/min. When it is too fast, the solder joint will be sharp and shiny; if it is too slow, the solder joint will be slightly round and stubby;
4. Too much anti-oxidation oil in the tin furnace or deterioration, and the direction and arrangement of the component wiring are not good;
5. The preheating temperature is too low or too high; before entering the tin furnace, the standard bottom surface is 78-98 ℃;
6. The temperature of the tin furnace is too low or too high; the standard temperature is 250-254 ℃; when it is too low, the solder joints are sharp and shiny; when it is too high, the solder joints are slightly round and stubby;
7. The solder in the tin furnace contains impurities, and the wave peak of the tin furnace is unstable;
The influence of impurities on the performance of solder joints
In addition to tin and lead, the flux cored tin wire often contains a small amount of other elements, such as copper, antimony, bismuth, etc. In addition, the impurities on the PCB and component feet will also be brought into the tin furnace during the soldering operation. These elements will affect the performance of the solder. The following table lists the allowable range of impurities in the Chinese electronics industry standard SJ/T10134-94. and its effect on solder joint performance.