It’s an important issue about how to ensure the quality of solder joints in Pcb manufacturing process. Solder joints are a direct result of soldering, and its quality and reliability determine the quality of electronic products. That is to say, the assembly quality is ultimately expressed as the welding quality in the production process. So how does pcb assembly process reflect the quality of solder joints?
First, the appearance evaluation of solder joints
A good solder joint should be within the usage life of the equipment, and its mechanical and electrical properties will not fail. Its appearance is:
2, A complete and smooth surface;
3, The appropriate amount of solder and solder completely cover the solder joints (or solder joints) of the pads and leads, the component height is moderate.
In principle, these guidelines are suitable for all types of solder joints soldered by all soldering methods in pcb assembly. In addition, the edge of the solder joint should be thin. If the solder surface is large enough, the solder and solder surface should have a wetting angle of 300 or less, and the maximum is 600.
Second, the failure form of the solder joint in the life cycle
Considering the relationship between failure and time, the failure form is divided into three different periods:
1. The early failure stage is mainly caused by a large number of solder joints with poor quality, and some solder joints are damaged due to improper process operation and loading and unloading. Process optimization can be used to reduce early failure rates.
2. Stabilization failure rate stage, the quality of most of the solder joints in this stage is good, the failure rate (loss rate) is very low, and it is relatively stable.
3. At the end step of life, the failure is mainly caused by accumulated destructive factors, including chemical, metallurgical, thermal-mechanical characteristics, such as metallization reaction between solder and metal to be welded, or thermal-mechanical Stress causes solder joint failure. Failure is primarily determined by the nature of the material, the specific structure of the solder joint, and the load being applied.