During the PCBA processing process, there are many production processes and many quality problems are easy 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.
First, improve the temperature and time of welding
The intermetallic bonds of copper and tin form grains, and the shape and size of the grains depend on the duration and strength of the temperature at the time of soldering. Less heat during welding can form a fine crystalline structure, resulting in an excellent solder joint with optimum strength. The PCBA chip processing reaction time is too long, whether it is due to long welding time or too high temperature or both, it will lead to a rough crystalline structure, which is gravel and brittle, and the shear strength is higher. small.
Second, reduce surface tension
The cohesion of tin-lead solder is even larger than that of water, making the solder a sphere to minimize its surface area (the same volume, the sphere has the smallest surface area compared to other geometries, to meet the minimum energy requirements) . The role of the flux is similar to the effect of the cleaning agent on the greased metal sheet. In addition, the surface tension is highly dependent on the cleanliness and temperature of the surface. The ideal stain can only occur if the adhesion energy is much greater than the surface energy (cohesion). tin.
Second, PCBA board dip tin angle
When the temperature of the eutectic point of the solder is about 35 ° C higher, when a drop of solder is placed on the hot flux-coated surface, a meniscus is formed, and to some extent, the metal surface is tinned. It can be evaluated by the shape of the meniscus. If the solder meniscus has a distinct undercut, shaped like a water droplet on a greased metal plate, or even tends to be spherical, the metal is not solderable. Only the meniscus is stretched to a less than 30. The small angle has good weldability.