Print speed and Squeegee pressure are inter-related
Factors effecting speed
Temperature
Cold = slow as pastes are very temperature sensitive
Squeegee Material
Polymer is faster than metal
Poly is simply a better squeegee (windshield wipers)
Poly wears very quickly, not common today
Sharpness
Not all metal squeegees are equal
Plating of Transition Automation is round and dull
Angle
60 degree is faster than 45 degree
Watch out for MPM; long blades = low angles with high pressures
Various Metal Blade Characteristics
Stock DEK | E-Blade | Print-Perfect | DuraGlide | Ultraprint | |
Supplier | DEK | AMTX (PhotoStencil) | Transition Automation | Photo Stencil | Alpha Metals |
Material | Spring Stainless | Nickel | Spring Steel | Spring Steel | Spring Steel |
Forming Method | Machined | Electroplated | Machined | Etched | Machined |
Coating | None | None | “Permalex” Teflon/nickel | Titanium Nitride | Nickel plate |
Body Thickness | 7.5 mils | 10 mils | 9.5 mils | 12 mils | 17 mils |
Tip Thickness (bottom 0.1”) | 7.5 mils | 10 mils | 10 mils | 11.5 mils | 17 mils |
Relative Sharpness** | 6 | 8 | 4 | 7 | 4 |
Stencil Roughness
Rougher better for roll
Rougher requires more pressure for clean wipe
Etched or lasered foil is more rougher than EFAB
Paste factors
Higher viscosity usually equates to slower print speed and higher pressure.
Higher tackiness usually equates to slower print speed and higher pressure.
Squeegee pressure take away message
“Apply minimum pressure to get a clean wipe, (no solder powder) around the apertures”
This is independent of all of the other variables effecting squeegee pressure
Stencil Issues
Not all stencils release equally well
EFAB is best
Laser is OK, with electro polish or nickel plate is better
Chemical etch is worst
Stencil wiping not totally effective
Automated better than manual
Coined solder can remain and cause more needed wiping
Sticking to squeegee
Paste viscosity too high
Solids too high
Paste got hot in storage or shipment
Insufficient paste on the stencil
Start with 15gr/cm of squeegee length
Squeegee lift incorrect
Too high after stroke
0.5” to 0.75” is OK
Too slow
Fast (>10mm/s) helps shear paste and leave on stencil
Pause between prints too long
Paste rheology goes back to rest viscosity
Short stroke
AOI too slow
Gasketing is critical for good paste release
Aperture must be smaller than pad in both length and width
Critical for fine pitch, small components
Legend near fine pitch is NG
Bar code or other labels near fine pitch is NG
Mask should be < pad height except over traces
HASL can be a hassle
Contact: Tommy
Phone: +86 13691605420
E-mail: tommy@flason-smt.com
Add: No.94,Guangtian Road,Songgang Street,Bao an District Shenzhen China