Quality Standard for SMT (1/3)

 1. SMT Quality Terminology

1.  Ideal Solder Joint

Good surface wettability. That is, the molten solder shall be spread on the surface of the metal to be welded and form a complete, uniform and continuous solder coating, and its contact angle shall not be greater than 90.

Enough correct amount of solder. Not too much or too little.

Good welding surface. The surface of welding joint shall be complete, continuous and smooth, but it is not required to have a bright appearance.

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

2. Non wetting

The contact angle between the solder on the solder joint and the surface of the metal to be welded is greater than 90.

3. Open welding

After welding, the pad is separated from the PCB surface.

4. Drawbridge

One end of the component leaves the pad and faces the bag obliquely or vertically.

5. Bridging

The solder between two or more solder joints that should not be connected is connected, or the welding section of the solder joint is connected with the adjacent conductor.

6. False soldering

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

7. Tip

The solder in the solder joint has protruding burrs, but it is not in contact with other conductors or solder joints.

8. Solder Ball

Solder ball adhered to printed board, cathode film or conductor during welding.

9. Holes

Holes with different apertures appear at the welding position.

10. 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 Welding

Quality inspection after PCB welding.

13. Reworking

Repair process for removing local defects of surface assembled components.

14. Placement Inspection

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

2. SMT Inspection Method

Visual inspection and optical equipment inspection are often used in the inspection of SMT, either only visual inspection or two mixed methods. All of them can inspect 100% of the products, but if the visual inspection method is adopted, people will always be tired, so it is impossible to ensure that employees can inspect 100% carefully. Therefore, we should establish a balanced inspection and monitoring strategy, that is, establish quality process control points.

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

1) PCB Inspection

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

Inspection method: Visual inspection according to the inspection standard.

2) Screen Printing Inspection

a. Whether the printing is complete. b. Whether there is bridging. c. Whether the thickness is uniform. d. Whether there is edge collapse. e. Whether there is deviation in printing.

Inspection method: Visual inspection or inspection with the aid of magnifying glass according to the inspection standard.

3) Patch Inspection

a. Mounting position of components. b. Whether there is chip drop. c. Whether there are wrong parts;

Inspection method: Visual inspection or inspection with the aid of magnifying glass according to the inspection standard.

4) Reflow Inspection

a. The welding condition of components, whether there are bad welding phenomena such as bridging, monument, dislocation, solder ball and false welding. b. the condition of solder joints.

Inspection method: Visual inspection or inspection with the aid of magnifying glass according to the inspection standard.