1. During the inspection of the finished product, it is found that the PCB? circuit board is cleared of solder paste, rosin, tin beads, and metal oxides when soldering with an electric soldering iron, which will cause unknowable failures of the product.

2. Solder paste and rosin will not cause a short circuit on the PCB board, but because inferior solder paste and rosin are often bought on the market now, they contain a lot of water. After use, the water remains on the surface of the circuit board, which is easy to cause a short circuit.

3. In addition, after the solder paste and rosin are used, some solid or powdery residues will remain on the circuit board. These residues will not cause a short circuit under normal conditions, but when the circuit board is tested for withstand voltage, it is found that the high voltage will When the residue breaks down the vital parts of the circuit board or when it is stored in a low temperature and high humidity environment, these residues will absorb moisture in the air, so that moisture will invade the metallization layer of the chip, and a thin film will be generated on the surface of the circuit board. Moisture layer, the moisture layer is sufficient to reduce the insulation resistance of the circuit board surface, and cause the circuit board to cause corrosion or produce metal dendrites. The greater the humidity, the thicker the moisture layer, and the faster the corrosion or dendrite growth. When the dendrite bridges between the wires or between the welding areas, it will cause a short circuit. (The customer returns the product to verify that the circuit board has not dealt with the three preventions and caused a short circuit event)

4. If there are residues left on the circuit board after soldering, it is recommended to use special board washing water into an ultrasonic cleaning machine to automatically clean it; Of course, there are no-clean fluxes on the market now, so that no residue will be left after use Thing. (There are not many good quality after investigation, no-clean flux is not recommended)

5. Incorrect cleaning operation:

⑴. Use a brush dipped in cleaning agent to scrub the circuit board infrequently. The composition of the flux residue is complex and the cleaning is difficult. It can not be cleaned by just a few brushes.

⑵. Among the flux residues, non-polar contaminants mainly composed of rosin or other synthetic resins coat halogens, organic acids, salts, etc., and act as a "plastic encapsulation", thereby greatly reducing the ion contaminants. Corrosion, to avoid problems such as leakage after moisture absorption. In the cleaning process, the resin is washed off first. If the cleaning operation is stopped at this time, the ion contaminants will be left on the circuit board. The ion contaminants are usually caused by the flux, fingerprints and other factors used in the soldering process. The consequences of other substances such as dust and dirt can be imagined. The problems caused by incomplete cleaning are far more serious than non-cleaning, so once cleaned, it must be washed thoroughly.

6. How to improve the cleaning effect:

⑴, First of all, the cleaning staff has a correct working attitude and strong sense of responsibility;

⑵. It should be cleaned as soon as possible after welding (within 1 hour);

⑶, increase the working temperature of the cleaning agent;

⑷, extend the cleaning time.