SMT钢网印刷培训汇.ppt

ENVIRONMENT Printing Process The Perfect Print Clean edges Flat on top Height = Stencil Thickness Good Alignment No Flux Bleed ... Basic Stencil Process Basic Stencil Process Factors Affecting the Print MATERIAL CHECKLIST STENCIL SQUEEGEES PROFLOW PASTE TOOLING SOLVENT/PAPER BOARDS... Stencils Chemical Etching Laser Cutting Electroformed Stencil Selection Finishing of Various Method Stencil Design Stencil Design Stencil Design 265, Edge Justified 265, Centre Justified Stencil Cleaning Manual: Use a Lint free Cloth With a solvent soaked cloth in each hand clean both sides simultaneously (Wear Gloves!) Screen Clean Machine Under Screen cleaner: Program to clean as seldom as possible! Use Vacuum to clear blocked apertures Always follow a wet wipe with a dry wipe ... Solvent / Paper SOLVENT: DISOLVES THE PASTE CAN BE WIPED OFF EVAPORATES QUICKLY LEAVES NO RESIDUE DOES NOT HARM THE USC HOSES AND WIPER BLADES PAPER: ABSORBENT LINT FREE... Stencil Maintenance Stencils are Fragile - Store and Handle With Care Keep Stencils Clean Inspect for Damage and Stretch Repair Fiducials when Damaged ... Stencil - Board alignment Cause: Poor Artwork Poor Quality Stencil Manufacture Poor board manufacturing Board Stretch Poor Fiducial Alignment Machine not calibrated Solution: Print Offsets Buy New Stencil Improve Fiducial Score Buy better boards Calibrate machine Solder Paste Solder Powder IPC Powder Specification Particle Size Paste Storage Using the Paste Good Working Practices Stir Paste Gently Before Use Regulate Paste Diameter at 15mm Perform Small Top-Ups Regularly Regulate Temperature and Humidity Do Not Leave Paste drying on Stencil ... Squeegees Squeegees Squeegee Principles Squeegee Principle In general, squeegee speed can be increase as the solder paste viscosity decrease Have the highest speed setting while having enough time for the paste to flow into the aperture. A rule of thumb setting is about 20 to 50 mm/s (5 - 7 kg) Angle o Metal squeegees Metal squeege