What is the phenomenon of solder beads in the SMT processing?

SMTDuring the processing, the tin bead phenomenon is one of the main defects in production. Because it has many causes and is difficult to control, it often troubles peopleSMTSMT and engineering technicians,The production of tin beads is a complex process and one of the most troublesome problems,The following solder paste manufacturer will discussSolder pasteRelated issues with tin beads:

First of all, the quality of solder paste is the most influential factor, the metal content of lead-free solder paste. The mass ratio of metal content in solder paste is approximately88%～92%The volume ratio is approximately50%. When the metal content increases, the viscosity of the solder paste rises, which can effectively resist the force generated by evaporation when heated. In addition, the increase in metal content makes the metal powder align closely, making it easier to bond and not being blown away during the melting process. Moreover, the increased metal content can also reduce the "collapse" of the solder paste after printing, thus making it less likely for solder beads to appear. The degree of metal oxidation of solder paste. In solder paste, the higher the degree of metal oxidation, the greater the resistance to the adhesion of metal powder during the soldering process, and the less the penetration between the solder paste and the pad and components, resulting in a decrease in solderability. Experiments show that the occurrence rate of tin beads is directly proportional to the oxidation degree of the metal powder. The oxidation degree of the solder in the solder paste should generally not be exceeded0.05％The maximum can be reached0.15％.

The particle size of the metal powder in solder paste. For reflow soldering, the smaller the particle size of the powder in the solder paste, the larger the total surface area of the solder paste, which leads to a higher degree of oxidation of the finer powder, thereby intensifying the solder beads. Experiments show that when choosing a solder paste with a finer particle size, it is easier to produce solder beads.

The printing thickness of solder paste on the printed circuit board. The thickness of lead-free solder paste after printing is an important parameter for template printing, usually in0.12mm-20mmBetween. Excessive thickness of solder paste can cause it to "sink", promoting the formation of solder beads. Excessive use of flux can cause part of the solder paste to collapse, making it easy to form solder beads. In addition, if the activity of the flux is low, its deoxidation ability is also weak, which can also easily lead to the formation of solder beads. The activity of no-clean solder paste is lower than that of rosin and water-soluble solder paste, so it is more likely to produce solder beads.

There are many reasons for the formation of solder beads. The presence of solder beads will inevitably affect the quality and appearance of solder products. The solder mask layer on the circuit board is the most important factor affecting the formation of solder beads. Based on the above reasons, there are the following several coping strategies. There are specifically the following several methods to reduce the production of tin beads:

1Choosing the appropriate solder mask layer can prevent the formation of solder balls.

2Using some specially designed fluxes can also prevent the formation of solder balls.

3Minimize the temperature of solder products to the greatest extent.

4Use sufficient flux to prevent the formation of solder balls.

5Maximize the preheating temperature, but pay attention to the preheating parameters of the flux to prevent the activation period of the flux from being too short.

6Try to increase the speed of the conveyor belt as much as possible.

That's all.SMTThis article introduces the causes and solutions of solder beads during processing, hoping to be helpful to everyone. Meanwhile, if you want to learn more about soldering, please continue to follow the online message of JJY Solder Paste Factory to interact with us.