SMT solder paste printing quality analysis
There are several common quality problems caused by poor printing of solder paste:
1.Insufficient solder paste (local lack or even overall lack) will lead to insufficient solder amount of the component solder joints after the soldering, open components, and component misalignment and vertical components
2.The solder paste adhesion will cause the circuit to be short-circuited and the components to be offset after soldering.
3.The overall misalignment of solder paste printing will lead to poor soldering of the entire board components, such as less tin, open circuit, misalignment, vertical parts, etc.
4.The tip of solder paste can easily cause short circuit after soldering.
Main factors leading to insufficient solder paste
1.When the printing press is working, the solder paste is not added in time.
2.The quality of solder paste is abnormal, which contains foreign matter such as hard blocks.
3.The previously unused solder paste has expired and is used twice.
4.The quality of the circuit board has inconspicuous coverings on the pads, such as solder resist (green oil) printed on the pads.
5.The fixed clamping of the circuit board in the printing machine is loose.
6.The solder paste misses the screen and the thickness is uneven.
7.Contaminants (such as PCB packaging, stencil wiping paper, foreign matter floating in the ambient air, etc.) are missing from the solder paste on the screen or circuit board.
8.The solder paste scraper is damaged and the screen is damaged.
9.The equipment parameters such as the pressure, angle, speed and demolding speed of the solder paste scraper are not set properly.
10.After the solder paste printing is completed, it is accidentally touched off due to human factors.
Main factors causing solder paste adhesion
1.Design defect of the circuit board, the pad pitch is too small.
2.Screen problem, the position of the perforation is not correct.
3.The stencil is not wiped clean.
4.The problem of the stencil makes the solder paste fall off badly.
5.The solder paste has poor performance, and the viscosity and collapse are unqualified.
6.The fixed clamping of the circuit board in the printing machine is loose.
7.The equipment parameters such as pressure, angle, speed and demolding speed of solder paste scraper are not set properly
8.After the solder paste is printed, it is squeezed and stuck due to human factors.
Main factors that cause overall misalignment of solder paste printing
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.
3.The fixed clamping of the circuit board in the printing machine is loose. The positioning pin is not in place.
4.The optical positioning system of the printing press is faulty.
5.The opening of the solder paste screen does not match the design documents of the circuit board.
The main factors that cause the sharpening of printed solder paste
1.There are problems with performance parameters such as solder paste viscosity.
2.There is a problem in setting the demolding parameters when the circuit board is separated from the missing screen.
3.There are burrs on the hole wall of the screen hole.