In the process ofPCBA processing, there are many production processes and many quality problemsare prone to occur. At this time, it is necessary to continuously improve thePCBA welding method and improve the process to effectively improve the productquality.

1. Improve weldingtemperature and time

The intermetallicbond between copper and tin forms crystal grains. The shape and size of thecrystal grains depend on the duration and strength of the temperature duringwelding. Less heat during welding can form a fine crystalline structure,forming an excellent welding point with the best strength. PCBA patchprocessing reaction time is too long, whether it is due to too long weldingtime or due to high temperature or both, it will lead to a rough crystallinestructure, which is gritty and brittle, and has relatively high shear strength.small.

2. Reduce surfacetension

The cohesion oftin-lead solder is even greater than that of water, so that the solder isspheres to minimize its surface area (under the same volume, the sphere has thesmallest surface area compared with other geometric shapes to meet the needs ofthe lowest energy state) . The effect of the flux is similar to the effect ofthe cleaner on the grease-coated metal plate. In addition, the surface tensionis 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 boarddip tin corner

When the eutecticpoint temperature of solder is about 35°C higher, when a drop of solder isplaced 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 ofthe meniscus. If the solder meniscus has an obvious undercut edge, shaped likea drop of water on a greased metal plate, or even tends to be spherical, themetal is not weldable. Only the meniscus stretches to a size less than 30. Ithas good weldability at a small angle.