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Printing process is to ensure the quality of the surface assembly of one of the key processes, according to statistics, in the PCB design is correct, components and PCB quality assurance premise, the surface assembly of 70% of the quality problems in the printing process. Therefore, the printing position is correct or not (printing accuracy), how much the amount of solder paste, solder paste amount is uniform, whether the solder paste pattern is clear, with or without adhesion, PCB surface is solder paste dirt directly affect the surface assembly Plate welding quality.
In order to ensure the quality of SMT chip assembly, we must strictly control the quality of printed solder paste. (Lead spacing 0.65mm below the narrow pitch device, must be full inspection).
1, apply solder paste requirements
(1) the amount of solder paste applied uniform, good consistency. Solder paste graphics should be clear, as far as possible between adjacent graphics do not stick. Solder paste graphics and pad graphics to be consistent, try not to misplaced.
(2) Under normal circumstances, the amount of solder paste per unit area on the pad should be about 0.8mg / mm2. Narrow pitch components, should be about 0.5mg / mm2 (in practice with the template thickness and opening size to control).
(3) The weight of the solder paste printed on the PCB, compared with the weight value required by the design, may allow a certain deviation. The area of each solder paste that covers the solder paste should be more than 75%.
(4) after the solder paste printing, there should be no serious slump, neat edges, misalignment is not greater than 0.2mm, narrow pitch components pads, misalignment is not greater than 0.lmm. PCB is not allowed to be contaminated by solder paste.
2, test methods
Visual inspection, a narrow pitch with 2-5 times magnifying glass or 3 to 20 times the microscope test.
3, test standards
In accordance with this corporate standard or with reference to other standards (such as the IPC standard or SJ / T10670-1995 surface assembly process, general technical requirements and other standards) implementation.
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