PCB Fabrication

Judgment of SMT process of solder joint quality aspects

by:A-TECH      2020-05-22
SMT plug-in processing and how to ensure the quality of solder joint is an important issue. As a direct result of the welding joint and quality and reliability of it decide the quality of the electronic products. That is to say, in the process of production, the quality of the final assembly of the quality of welding. So how SMT plug-in processing reflects the quality of solder joint? Zhongshan fu chong electronic co. , LTD. Below small make up for all finishing is introduced. Good solder joints should be in the service life of equipment cycle, the mechanical and electrical performance failure didn't happen. Its appearance is: 1, good wetting; 2, complete and smooth and shining surface; 3, the proper amount of solder and completely covers the solder and lead solder welding parts ( Or welding end) High moderate, components. In principle, these guidelines for SMT plug-in processing all the welding method of welding of all kinds of solder joints. In addition to the edge of the weld shall be thinner, if welding surface is enough big, on the surface of the solder and solder wetting Angle below 300 as well, no more than 600. Considering the relationship between failure and time, the failure modes are divided into three different periods: 1, early failure stage, it is bad quality of solder joint failure occurred amount, there is also a part of the solder joint is caused by improper operation and handling damage. Processes can be optimized to reduce the early failure rate. 2, stability failure rate stage, the stage most of the solder joint quality is good, the incidence of failure ( Failure rate) Low and stable. 3, end of life stage, and failure is mainly caused by cumulative damage factor, including chemical, metallurgy, thermal factors such as the mechanical properties, such as metal compound reaction taking place between solder and the weld metal, heat or a solder joint failure caused by mechanical stress. SMT processing failure is mainly composed of concrete structure and the characteristic of material, welds are determined by the load. Virtual welding judgment: 1, the online test instrument use special equipment to test. 2, visual or AOI inspection. When found too little solder solder solder infiltration, or solder joints have broken seam, or solder surface convex globular, or solder not dating with SMD melting, etc. , will pay attention, even slight phenomenon can lead to hidden trouble, should immediately determine whether batch virtual welding problems. Virtual welding the cause and solution: 1, the welding plate design is flawed. Welding plate hole is one of the main defects, PCB design less than not, don't use, the hole can make the solder erosion caused by insufficient solder; Welding plate spacing, area also need standard match, otherwise should be correct design as early as possible. 2, PCB has oxidation phenomenon, namely welding twist uri is not bright. If there are any oxidation phenomenon, can use the eraser to oxidation layer, make the light again. PCB be affected with damp be affected with damp, such as the suspect can be put inside oven drying. PCB is oily be soiled, perspiration, such as pollution, at this time to wash clean with anhydrous ethanol. 3, print the PCB solder paste, solder paste blown, ceng, reduce the volume of solder paste relevant bonding pad, the insufficient solder. Should be up in a timely manner. Fill method can be used or glue use bamboo stick to pick up a little.
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