PCB manufacturing solder joint appearance quality inspection
With the advancement of technology, the electronic components are getting smaller in pcb manufacturing . The previous 0402 resistors are mostly replaced by 0201 size . How to ensure the quality of solder joints becomes an important issue for high-precision mounting. Solder joints serve as a bridge for welding, and its quality and reliability determine the quality of electronic products. That is to say, in the production process, the quality of SMT is ultimately expressed as the quality of the solder joint.
At present, in the electronics industry, although the research on lead-free solder has made great progress, it has been promoted and applied worldwide, and environmental protection issues have also received widespread attention. PCB manufacturing processing uses Sn-Pb solder alloy technology is still the main connection technology for pcb manufacturing electronic circuits.
A good solder joint should be within the life of the equipment, and its mechanical and electrical properties will not fail. Its appearance is as below:
(1) a complete, smooth, shiny surface;
(2) Appropriate amount of solder and solder completely cover the solder area of the pads and leads, and the component height is moderate;
(3) Good wettability; the edge of the solder joint should be thin, and the wetting angle of the solder and the pad surface should be 300 or less, and the maximum should not exceed 600.
SMT processing visual inspection content:
(1) Whether the components are missing;
(2) Whether the components are mislabeled;
(3) Whether there is a short circuit;
(4) Whether there is virtual welding; the cause of virtual welding is relatively complicated.
First, the judgment of the virtual welding
Third, the cause and solution of the virtual welding
(1) The oxidized component is not bright. The melting point of the oxide is increased. At this time, more than 300 degrees of electric ferrochrome and rosin-type flux can be used for welding, butit’s difficult to melt solder paste by more than 200 degrees of SMT reflow is used together with the use of less corrosive no-cleaning. Therefore, the oxidized SMD should not be welded by the reflow oven. When buying components, be sure to see if there is oxidation, and use it in time when you buy it back. Similarly, oxidized solder paste cannot be used.
(2) The surface mount components of multiple legs have small legs and are easily deformed under the action of external force. Once deformed, the phenomenon of virtual welding or lack of welding will occur. Therefore, it is necessary to carefully check and repair in time before mounting or after welding.
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