source:News release time:2023-06-16 Hits: Popular:PCB Assembly company
The metal content, the oxidation of metal powder, and the size of the metal powder can affect the generation of tin beads.
a. The metal content of tin paste
The mass ratio of the metal content in the tin paste is about 88%to 92%, and the volume ratio is about 50%. When the metal content increases, the viscosity of the tin paste can increase the force generated by vaporization during the preheating process. The increase in metal content makes the metal powder arrange tightly, making it easier to combine when melting without being blown. In addition, the increase in metal content may also reduce the "collapse" after the printing of the tin paste, so it is not easy to produce welded beads.
b. The oxidation of the metal powder of the tin paste
The higher the oxidation of the metal powder in the tin paste, the greater the resistance of the metal powder binding in the metal powder during welding. It is not easy to infiltrate between the tin paste and the pads and components, resulting in a reduction in welding. Experiments have shown that the incidence of tin beads is directly proportional to the oxidation of metal powder. Generally, the weld oxidation in the tin paste is controlled below 0.05%, and the maximum limit is 0.15%
c.
The smaller the granularity of the metal powder in the tin paste, the larger the overall surface area of the tin paste, which will cause higher oxidation of fine powder, so the phenomenon of welded beads intensified. Experiments have proved that tin beads are more likely to produce tin beads when using more fine particles.
d. The amount of welding and the activity of the welded in the tin paste
Too much welding dosage will cause the local collapse of the tin paste, which makes it easy for tin beads to produce. In addition, when the activity of the solder is too weak, the ability to remove oxidation is weak, and it is more likely to produce tin beads.
e. Other precautions
After removing the tin paste from the refrigerator, it was opened and used without warming up. The tin paste absorbed the moisture, and the tin beads were splattered during preheating. Adding excessive diluents, too long machine stirring time, and so on will promote the generation of tin beads.
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