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3.2.5. Related Issues During Solder Paste Printing Process
3.2.5.1. Stencil Printer Technology
Screen printing technology refer to using ready-made stencil, directly contact 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 corresponding, thus complete the
solder paste printing on the PCB.
3.2.5.2. Inspecting of Solder Paste Printing
Printing process is one of the key working procedure 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.
