Sometimes there will be some poor processing phenomenon in the process of SMT machine, tin bead is one of them, to solve the problem, we must first know the cause of the problem. Solder beading is in the solder paste slump or in the process of pressing out of the pad occurs. During reflow oven soldering, the solder paste is isolated from the main deposit and pooled with excess solder paste from other pads, either emerging from the side of the component body to form large beads, or remaining underneath the component. The elimination of tin beads as far as possible by direct removal of the way, in the production process to pay attention to, can be avoided. The following is to analyze which conditions will produce solder beading:
I. Steel Mesh
1. Steel mesh opening directly in accordance with the size of the pad opening will lead to tin bead phenomenon in the process of patch processing.
2. If the thickness of the steel net is too thick, it is also possible to cause the collapse of the solder paste, which will also produce tin beads.
3. If the pressure of pick and place machine is too high, the solder paste will be easily extruded to the solder resistance layer below the component, and the solder paste will melt and run around the component to form solder beads during reflow oven.
II. The solder paste
1. Solder paste without temperature return processing in the preheating stage will splash phenomenon to produce tin beads.
2. The smaller the particle size of the metal powder in the solder paste, the larger the overall surface area of the solder paste, which leads to a higher oxidation degree of the fine powder, so the phenomenon of solder beads is intensified.
3. The higher the oxidation degree of metal powder in the solder paste, the greater the metal powder bonding resistance during welding, the solder paste and pad and SMT components are not easy to infiltrate, resulting in the reduction of solderability.
4. The amount of flux and the amount of active flux is too much, which will lead to local collapse of solder paste and tin beads. When the activity of flux is not enough, the oxidized part can not be completely removed, which will also lead to tin beads in the processing of patch processing factory.
5. Metal content in the actual processing of the tin paste is generally 88% to 92% of the metal content and mass ratio, volume ratio of about 50%, increasing the metal content can make the metal powder arrangement become more closely, so that it is easier to combine when melting.
Post time: Sep-18-2021