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SMT solder joint quality and appearance inspection process

As technology developed, mobile phones, consumer electrics and other electronic products are become more and more light, small, portable, The development trend in the SMT Assembly process of the electronic components become more smaller, Many previous 0603 ,0402 chips already changed to 0201 01005 size. How to ensure the quality of solder joints between chips and PCB become an important issue precision placement. Welded joints as a solder bridge, its quality determines the quality and reliability of electronic products. That is, in the SMT production process,final performance of the soldering quality is the solder joints.

In the past few years, in the electronics industry,The studies of lead-free solder made great progress, we have mostly use the lead free solder in the world, and environmental issues are also receiving widespread attention, using soldering technique SnAgCu,SnCu and other lead free solder alloy has become the main connection technology in electronic circuits.

Good joints should be within the life cycle of the equipment, The mechanical and electrical properties are not failures occur. The appearance as follows:

(1) complete and smooth shiny surface;
(2) The appropriate amount of solder and solder pads completely cover the welded parts and the PCB;
(3) Good wetting; edge solder should be thin, the wetting angle of the solder and the pad surface 300 or less, the maximum no more than 600.

SMT processing visual inspection content:
(1) whether there is missing element;
(2) Have posted the wrong element;
(3) short-circuit;
(4) what's the solder problem ; if the reason is complex.
First,Solder quality judgment
1. Using line tester equipment for testing.
2, or AOI visual inspection. When they find too little solder joints solder wetting ability is bad, or the middle of a broken seam solder, solder or convex spherical surface, or solder melting time and the SMD place wrong position and so on, will draw attention, even if the phenomenon will cause a slight risk, It should immediately determine whether a problem exists. Judgment method is: to see whether the same position has more joints problems on the PCB, as only one individual PCB, solder paste may be scratched, pin deformation and other reasons, If in the same position on many PCB has a problem, then it might be a bad component or have problems caused by pick and place machine.

Third, sldering problem and solutions
PCB pad design defects.PCB Pad is a major participator in SMT PCB soldering process, if the pin pad distance is too samll, maybe will lead the solder bridge and other problem, so need check PCB design and this kind problem should be corrected as soon as possible.


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