In the process of PCBA processing, there are many production processes and many quality problems are prone to occur. At this time, it is necessary to continuously improve the PCBA welding method and improve the process to effectively improve the product quality.
1. Improve welding temperature and time
The intermetallic bond between copper and tin forms crystal grains. The shape and size of the crystal grains depend on the duration and strength of the temperature during welding. Less heat during welding can form a fine crystalline structure, forming an excellent welding point with the best strength. PCBA patch processing reaction time is too long, whether it is due to too long welding time or due to high temperature or both, it will lead to a rough crystalline structure, which is gritty and brittle, and has relatively high shear strength. small.
2. Reduce surface tension
The cohesion of tin-lead solder is even greater than that of water, so that the solder is spheres to minimize its surface area (under the same volume, the sphere has the smallest surface area compared with other geometric shapes to meet the needs of the lowest energy state) . The effect of the flux is similar to the effect of the cleaner on the grease-coated metal plate. In addition, the surface tension is also highly dependent on the cleanliness and temperature of the surface. Only when the adhesion energy is much greater than the surface energy (cohesion) can ideal adhesion occur. tin.
Three, PCBA board dip tin corner
When the eutectic point temperature of solder is about 35°C higher, when a drop of solder is placed on a hot flux-coated surface, a meniscus is formed. To a certain extent, the ability of the metal surface to dip tin It can be evaluated by the shape of the meniscus. If the solder meniscus has an obvious undercut edge, shaped like a drop of water on a greased metal plate, or even tends to be spherical, the metal is not weldable. Only the meniscus stretches to a size less than 30. It has good weldability at a small angle.
