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1.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.
2.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).
3.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%.
4.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.
3.The defects of solder paste printing, reasons and solutions
Excellent printing graphics should be uniform in both vertical and horizontal direction,full,clean
all round, solder paste fill solder pad. Using above such printing graphics device, after reflow
soldering,will get good welding effect then.
Solder Paste graphics dislocation
Reasons: Holes on the stencil not good match with solder pad; No enough precision of the Printing
machine
Issues: easily cause bridge connection
Solutions:Adjust the stencil position; Adjust the printing machine.
Solder paste graphics have icicles and dents
Reasons:Scraper’s pressure is too large; Rubber scraper’s hardness is not enough; Holes are too
big in the stencil
Issues: Solder paste’s required volume is not enough, easy to appear faulty soldering;solder joint
strength is not enough.
Solutions:Adjust the printing pressure; Use metal scraper; Improved holes designing in the stencil.
Too much solder paste
Reasons:Holes are too big in the stencil; The gap is too big between stencil and PCB.
Issues: easily cause bridge connection
Solutions:Check the holes size in stencil; Adjust the parameters of printing, especially the gap
between PCB and stencil
Graphic uneven(have breakpoints)
Reasons:Holes’ wall are not smoothness enough; not wipe residual solder paste in using for many
times; Solder paste’s thixotropy is bad.
Issues: Easy cause no enough solder paste, lead to the problem such as faulty soldering.
Solutions:Wipe the stencil
Contamination of the graphics
Reasons:Not wipe residual solder paste in stencil after using for many times;Poor quality of solder
paste; Shake problem when getting the stencil way
Issues: easily cause bridge connection
Solutions:Wipe and clean stencil; replace solder paste;adjust the machine.
