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What exceptions will occur during SMT production? Normally
Time:2021-10-08 Read: 347

1. Ideal solder joints

It has good surface wettability, that is, the molten solder should spread on the surface of the welded metal and form a complete, uniform and continuous solder covering layer, and its contact angle should not be greater than 90


The correct amount of solder, the amount of solder is sufficient but not too much or too little

For a good welding surface, the surface of the solder joint should be complete, continuous and smooth, but it does not require a very bright appearance.

Good solder joint position The position deviation of the solder end or pin of the component on the pad is within the specified range.


2. No wetting

The contact angle formed by the solder on the solder joint and the surface of the welded metal is greater than 90


3. Open welding

The pad is separated from the PCB surface after soldering.


4. Suspension bridge (drawbridging)

One end of the component leaves the pad and faces the bag upright diagonally or upright


5. Bridging

The solder between two or more solder joints that should not be connected is connected, or the solder joints of the solder joints are connected with adjacent wires.


6. Welding

After soldering, electrical isolation sometimes occurs between the solder end or the pin and the pad


7. Draw the tip

There are solder burrs protruding outward in the solder joints, but they are not in contact with other conductors or solder joints


8. Solder ball

A small ball of solder that adheres to the printed board, the solder mask or the conductor during soldering.


9. Holes

Holes with different apertures appear in the weld


10. Position offset (skewing)

When the solder joint deviates from the predetermined position in the horizontal, vertical or rotational direction in the plane.


11. Visual inspection

With the aid of a magnifying glass of 2~5 times of the illumination, inspect the quality of PCBA solder joints with naked eyes


12. Inspection after aoldering

Quality inspection after PCB is soldered.


13. Reworking

Repair process to eliminate local defects of surface mount components.


14. Placement inspection

When surface mount components are mounted or after they are mounted, quality inspection is carried out for any missing, misplaced, mis-mounted, damaged, etc. conditions.


In SMT inspection, two methods, visual inspection and optical equipment inspection, are often used. Some only use the visual inspection method, and there are also two mixed methods. They can all inspect the product, but if the visual inspection method is used, people will always get tired, so there is no guarantee that employees will conduct a careful inspection. Therefore, we need to establish a balanced inspection and monitoring (monitering) strategy that is to establish quality process control points.


In order to ensure the normal operation of SMT equipment, strengthen the quality inspection of the processed workpieces in each process, so as to monitor its operating status, and establish quality control points after some key processes. These control points are usually established in the following locations:


1) PCB inspection

a. Whether the printed board is deformed; b. Whether the pad is oxidized; c. Whether the surface of the printed board is scratched;

Inspection method: visual inspection according to inspection standards.


2) Silk screen inspection

a. Is the printing complete; b. Is there any bridging; c. Is the thickness uniform; d. Is there any sag; e. Is there any deviation in the printing;

Inspection method: visual inspection according to inspection standards or inspection with magnifying glass.


3) Patch inspection

a. The placement position of the component; b. Whether there is a chip; c. whether there is a wrong part;

Inspection method: visual inspection according to inspection standards or inspection with magnifying glass.


4) Reflow soldering inspection

a. The soldering condition of the component, whether there are bad soldering phenomena such as bridging, tombstones, dislocation, solder balls, virtual soldering, etc. b. Soldering joints.

Inspection method: visual inspection according to inspection standards or inspection with magnifying glass.

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