Solder paste Printing process parameters (stencil printing) for Electronic Manufacturing PCBA

Printing process parameters (stencil printing)

Print speed100mm/s recommended, min 70mm/s, max 120mm/s

Note: Under non-conforming situations caused by technical problems, lower than specified speeds are temporarily accepted.

Squeegee pressure for 200mm wide squeegee** in constant force mode (force automatically adjusted, print head floating)minimum pressure that will wipe stencil surface clean +5N as safety margin, normally between 40 50 N
Squeegee adjustment for MPM printers (constant squeegee distance (negative) from PWB surface, force against down stops)Minimal adjustment that will wipe stencil surface clean +0.5mm as safety margin
Snap-off distance-0.5 – 0.0mm on whole panel area (negative snap-off recommended to give margin against machine misadjustments)
Separation speedMax. 20 mm/sec until stencil has released, then maximum speed.
Automatic wipe rateAfter every 10 ± 5 prints Note: Under non-conforming situations caused by temporary technical problems more frequent wipe may be applied.
Wipe cycle recommendation1 dry with vacuum or 1 dam followed by 1 dry for printers without vacuum option
Recommended cleaning fluid for printer automatic wipingMulticore Prozone SC-01 or equivalent high flash point solvent officially accepted by printer manufacturer. Use of isopropanol (IPA) or equivalent solvents is not recommended due to fire safety.
Recommended cleaning fluid for cleaning of misprinted boardsMulticore Prozone SC-02 is preferred (SC-02 will attack slightly acrylics and some rubbers used in protective gloves)

Use of isopropanol (IPA) is allowed but not recommended. Waste must be handled properly.

Note! Components that are not designed for liquid cleaning process, have to be removed and changed after cleaning.

PWB with laser (micro) vias, OSP plating or which are totally or partly Aramid based, ARE NOT ALLOWED TO BE WASHED! Cleaning solvent traps into PWB structures and reduces esp. CSP components joint reliability.

Support table vacuumOFF while printing, unless dedicated workholder is of such construction that no vacuum is created between PWB and stencil OR vacuum is limited to 100-200mbar. Vacuum ON during loading and table movements (activate special 1043 in AP-25 SW 6.1 or later).
Kneading18 kneads after every 20min or longer pause in printing process and recommended after addition of paste. Otherwise not needed.
Solder paste amount on stencil150 160 g + paste attached to squeeze (200mm )
Printing accuracy+/- 0.05 mm

*) Sometimes referred as ”squeegee pressure” and force given in KGs, 1kg=9.81N

**) Depends linearly on squeegee width

1) Automatic procedure to soften paste and dissolve partly dried paste residues at stencil aperture opening edges instead of stencil manual cleaning. The panel used for kneading can be fed to production line as normally printed board. After pauses beyond 120min careful stencil cleaning in dedicated cleaner is recommended.