Procedure requirements of SMT printing solder paste
Printing procedure is one of the key procedures to ensure the quality of surface assembly. According to statistics, 70% of the quality problems in surface assembly happened in the printing process under the premise of correct PCB design, component and PCB quality. Therefore, whether the printing position is correct or not (printing accuracy), the amount of solder paste, whether the amount of solder paste is uniform, whether the solder paste pattern is clear, whether there is adhesion, whether the surface of the printed board is stained by solder paste, etc. directly affects welding quality of the surface assembly.
In order to ensure the quality of SMT assembly, the quality of the printed solder paste must be strictly controlled. (Narrow-pitch components with a lead center distance of 0.65 mm or less must be fully inspected.)
1. Applying solder paste requirements
(1) The amount of solder paste applying is uniform and the consistency is good. The solder paste pattern should be clear, and try not to stick between adjacent graphics. The solder paste pattern should be consistent with the welding pad pattern, so try not to be misplaced.
(2) Innormal circumstances, the amount of solder paste per unit area on the welding pad should be about 0.8 mg/mm2. For narrow-pitch components, it should be about 0.5mg/mm2 (in practice operation, the thickness of the template and the size of the opening are used to control).
(3) The weight of the solder paste printed on the PCB can be allowed to have a certain deviation compared with the weight value required by the design. The area of the solder paste covering eachwelding pad should be more than 75%.
(4) After the solder paste is printed, there should be no serious collapse, the edges are neat, the misalignment is not over2mm, and for the narrow-pitch component welding pads, the misalignment is not more than 0.1mm. PCB is not allowed to be contaminated by solder paste.
2. Inspection method
Visual inspection, for a narrow spacing 2 to 5 times magnifying glass or 3 to 20 times microscopy are used.
3. Inspection standard
In accordance with this company standard or with reference to other standards (such as IPC standards or SJ/T10670-1995 surface assembly craft general technical requirements etc standard) to execute. If you need to check the standard source file, please leave a message to us!
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