With the advancement of technology, some electronic products, such as mobile phones, tablets, etc., are developing towards lightweighting. Electronic components used for SMT processing are also becoming smaller and smaller, and how to ensure the quality of solder joints has become an important issue in high-precision mounting. As a bridge for welding, the quality and reliability of solder joints determine the quality of electronic products. In other words, in the production process, the quality of SMT is ultimately the quality of solder joints

At present, although significant progress has been made in the research of lead-free solder in the electronics industry, it has begun to be promoted and applied worldwide, and environmental protection issues have also received widespread attention. The welding technology using tin lead solder alloys remains the main connection technology for electronic circuits.

During the lifecycle of the equipment, good solder joints should not experience mechanical and electrical efficiency failures. Its appearance is as follows:

(1) The surface is intact, smooth, and glossy;

(2) An appropriate amount of solder and solder should completely cover the solder pads and the soldering parts of the leads, and the component height should be moderate;

(3) Good wettability; The edge of the solder joint should be thin, and the wetting angle between the solder and the surface of the solder pad should be less than 300, with a maximum of 600.

SMT processing appearance inspection content:

(1) Whether the components are missing;

(2) Whether the parts are pasted incorrectly;

(3) Is there a short circuit;

(4) Whether there is virtual welding; The reasons for virtual welding are quite complex.

1. Welding judgment

Use dedicated online testing equipment for testing.

2 . Visual inspection or AOI inspection. When there is too little solder at the solder joint, there may be poor solder penetration, cracks in the middle of the solder joint, protruding solder surfaces, or incompatibility between the solder and SMD. It should be immediately determined whether there is a large amount of virtual welding. The judgment method is to check whether there are many problems with solder joints at the same position on the PCB. If this is only a problem on a single PCB, it may be caused by solder paste scratches, pin deformation, and other reasons, such as being in the same position on multiple PCBs. There are some issues. At this point, it is likely caused by poor components or faulty gaskets.

3、 The causes and solutions of virtual welding

(1) . Shim design defect: The through-hole on the solder pad is the main defect in PCB design during welding. If it is not absolutely necessary, please do not use them. The through-hole may cause solder loss and insufficient solder; The spacing and area of solder pads also need to be matched according to standards, otherwise the design should be corrected as soon as possible

(2) . PCB board oxidation, that is, the solder pads turn black and do not emit light. If there is oxidation, an eraser can be used to remove the oxide layer to reproduce bright light. PCB board is damp, if suspected, it can be placed in a drying oven for drying. The PCB board is contaminated with oil stains, sweat stains, etc., and should be cleaned with anhydrous ethanol at this time.