Quality analysis of solder paste printing
The common quality problems caused by poor printing of solder paste are as follows:
① Insufficient solder paste (partial or even overall lack) will lead to insufficient solder content, open circuit, offset and vertical position of components.
② Adhesion of solder paste will lead to short circuit of circuit and deviation of components after welding.
③ Solder paste printing overall offset will lead to poor soldering of the whole board components, such as lack of tin, open circuit, offset, vertical parts, etc.
④ Solder paste tip drawing is easy to cause short circuit after welding.
1. The main factors leading to insufficient solder paste are as follows
① The solder paste was not added in time when the printing machine was working.
② The quality of solder paste is abnormal, which is mixed with foreign matters such as hard block.
③ The solder paste that has not been used up before has expired and is used again.
④ Circuit board quality problems, there are inconspicuous covers on the pad, such as solder resist (green oil) printed on the pad.
⑤ The fixing and clamping of the circuit board in the press is loose.
⑥ Solder paste leakage screen plate thickness is not uniform.
⑦ Solder paste leakage screen board or there are pollutants on the circuit board (such as PCB packaging, screen cleaning paper, floating foreign matters in the ambient air, etc.).
⑧ The solder paste scraper is damaged and the mesh plate is damaged.
⑨ The pressure, angle, speed and demoulding speed of solder paste scraper are not suitable.
⑩ The solder paste was knocked off due to human factors after printing.
2. The main causes of solder paste adhesion are as follows
① The design defect of the circuit board is that the pad spacing is too small.
② There is a problem with the mesh plate, and the position of the hole is not correct.
③ The mesh plate was not cleaned.
④ The problem of screen plate causes the solder paste to fall off badly.
⑤ Solder paste performance is poor, viscosity, collapse unqualified.
⑥ The fixing and clamping of the circuit board in the press is loose.
⑦ The pressure, angle, speed and demoulding speed of solder paste scraper are not suitable.
⑧ After the printing of solder paste is completed, it is pressed and adhered due to human factors.
3. The main factors leading to the overall offset of solder paste printing are as follows
① The positioning reference point on the circuit board is not clear.
② The positioning reference point on the circuit board is not aligned with the reference point of the screen board.
③ The fixed clamping of the circuit board in the printing machine is loose, and the positioning thimble is not in place.
④ The optical positioning system of the press is faulty.
⑤ The opening of solder paste leakage screen board does not conform to the design documents of circuit board.
4. The main causes of solder paste tip are as follows
① The viscosity and other performance parameters of solder paste have problems.
② There is a problem in the setting of demoulding parameters when the circuit board is separated from the screen board,.
③ There are burr on the hole wall of the stencil.