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nozzle to check if it moves smoothly. Let each nozzle head up and down beyond the normal
range.
Vacuum
pressure
Checking all nozzles’ vacuum pressure. If abnormal, please clean nozzles.
Positive
pressure
Checking if the positive pressure normal.
Optical axis
Checking whether it is covered dusk. Please keep it clean and lubricated
Operation
button
Checking each button to make sure they are well-worked
Connector
Checking if well-connected the air hose and air connector.
PCB clamp
block
check their wear pattern
14.3 Related issues during solder paste printing process
14.3.1 Stencil Printing Technology
Screen printing technology refer to using ready-made stencil, directly connect to the printer in a certain way, make the
solder paste evenly flow on the stencil and then leak into the mesh through the holes. When getting the stencil away, solder
paste had been covered to the printed circuit board solder graphics, then finish the solder paste printing on the PCB.
14.3.2 Inspecting of solder paste printing
Printing process is one of the key working procedures to ensure the quality of surface mounting. According to the statistics,
under the premise of guaranteed quality about components and PCB, correctly PCB design, 70% of the surface quality
problem caused during printing process. In order to ensure the quality of SMT assembly, it is necessary to strictly control
the quality of the solder paste printing.
The amount of solder paste printing requirements are as follows:
The using amount of solder paste should be uniform, good consistency. Solder paste graphics should be clear, try to
avoid adhesion between adjacent graphics. Solder paste graphics and solder graphics should be consistent.
In general, keep unit area amount of solder paste about 0.8 mg/mm². For fine pitch components, should be 0.5 mg/mm²
(using stencil thickness and hole size to control in the actual operation).
Printed on the substrate of solder paste compared with required value, a certain deviation is permissible, the covering
area of the solder paste on each solder pad should be more than 75%.
Should be no seriously collapsing problem and edges neatly after solder paste had been printed, the dislocation
shouldn’t be larger than 0.2 mm, for solder pad of fine pitch components, dislocation shouldn’t be larger than 0.1MM,
pollution by solder paste is not permitted to the PCB.
Inspection by 2~5 times magnifier or 3~20 times microscope.
