SMT钢网印刷培训.ppt

process theory,personal safety,board clamps are sharp brakes are hot wear eye protection and gloves with solvent based products always fit the head prop if in doubt press the e stop do not bypass the cam safes.,objective 1,environment,is the environment in control?,constant temperature? constant relative humidity?,printing process,printing process,the perfect print,clean edges flat on top height = stencil thickness good alignment no flux bleed .,basic stencil process,paste rolling,controlled print speed even squeegee pressure,basic stencil process,basic stencil process,board is lowered under controlled separation speed,hardware,software,environment,squeegees,print speed,temperature,paste,humidity,stencil,pressure,tooling,print gap?,board,factors affecting the print,separation speed,material checklist,stencil squeegees proflow paste tooling solvent/paper boards.,stencils,stencils,chemical etching,minimum apertures 0.1 mm + (50% of metal thickness) ie 0.150mm at 0.10 mm thick 0.175 mm at 0.15 mm thick* 0.200 mm at 0.20 mm thick* minimum qfp pitch 0.4 mm 0.3 mm but with poor stencil yield *but paste may not release from such narrow apertures,laser cutting,minimum apertures equal to metal thickness down to 0.05 mm ie 0.050 mm at 0.05 mm thick* 0.100 mmat 0.10 mm thick* 0.150 mm at 0.15 mm thick* minimum qfp pitch to leave a wall 0.05 mm between apertures *but paste may not release from such narrow apertures,electroformed,minimum apertures equal to metal thickness down to 0.05 mm ie 0.050 mm at 0.05 mm thick* 0.100 mmat 0.10 mm thick* 0.150 mm at 0.15 mm thick* minimum qfp pitch to leave a wall 0.190 mm between apertures! (narrower walls will not plate between resist) *but paste may not release from such narrow apertures,stencil selection,chemical,etching,laser,cut,electro-,formed,hybrid,cost,cost effective,cost effective,expensive,less expensive,accuracy,ok,very,very,mixed,min. aperture,size,0.2mm,(0.4mmpitch),no limit!,no limit!,no limit!,aperture shape,material,stainless steel,brass,stainless steel,nickel alloy,stainless steel,brass,?,fiducials,good,good,weak,good,finishing of various method,process: etching material: crni-steel,process: laser cut material: crni-steel,process: electroformed material: nickel,stencil design,pitch,length,width,design stencil apertures to allow a clearance of at least 50 m between paste and edge of pad,paste,pad,stencil design,release equation 1 release equation 2 w t paste release equation w avg.particle size, 0.66,1.5, 5,l*w 2*(l+w)*t,stencil design,739mm (29”),739mm (29”),622mm,265, edge justified,265, centre justified,739mm (29”),739mm (29”),368.3mm,368.3mm,center point,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,remember ,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 paste,solder powder,type 2 powder,type 3 powder,consistent alloy, particle size and particle shape. oxide free,ipc powder specification,type 3 is the typical size for current smt,the smaller the particle size the better the print definition but the more expensive the paste will be and the greater chance of reflow problems!,rule of thumb: keep a minimum of 5 particles per aperture width,stencil,board,particle size,maybe, for less than 3 months,definitely for 3 - 6 months,hmmmm never!,paste storage,using the paste,cold storage,working pot,printer,fresh paste,after 8 hours,end of run / extended downtime,end of day,disposal,return only if paste quality is good and it makes economic sense,temporary pot,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,squeegees,transfer / driving forces are influenced by:-,squeegee angle print speed paste rheology paste roll volume,driving force,transfer force,squeegee principles,reaction force,squeegee force,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 ,45,60,intrusive reflow high speed printing printing thick stencils printing glue printing mesh screens,standard smt printing,increased force,reduce force,metal squeegees,metal squeegees,overhang,15 mm - widely used, reduced risk of stencil/blade damage due to increased flexibility,6 mm - historically used but no longer recommend due to increased risk of stencil/blade damage.,property,metal,polyurethane,fine pitch,good,excellent,large apertures,excellent,good,pressure effect,does not cause scooping,needs control,damage resistance,poor,good,damage to stencil,poor,good,life,until broken,25,000,paste height, stencil thickness, stencil thickness,metal v polyurethane,length,choose the closest length to the board size,board,squeegees,paste,dry paste,gap,effect of excess pressure,print direction,aperture scooped,pads,board,stencil,scooping,squeegees,metal squeegees polyurethane squeegees right length right hardness ( overhang for metal ) angle not damaged not worn.,objective 8,tooling,tooling,tooling,magnetic pillars dedicated manuflex vacuflex f.p.a formflex tooling problems & solutions.,19 mm and 4 mm pin diameter simple and robust construction inexpensive,table,rail,rail,magnetic tooling,can provide 100% support can contain milled out areas for underside components can be fitted with vacuum cups .,dedicated tooling plate with milled out areas,dedicated tooling plate providing 100% support,dedicated tooling plates,dedicated tooling,board lifted by tooling causing: board damage squeegee pressure problems uneven paste heights dirty stencil .,tooling problems,table,rail,rail,clean table top of solder paste & debris keep tooling pins clean replace worn transport belts be careful not to mix different lettered pins (autoflex only ) ensure underside of board is flat and clear of labels, solder mask etc. remove or move the pin .,solutions,excess,insufficient,insufficient,1 worn,print direction,print direction,support,support,support?,squeegee,other tooling problems,tooling,tooling type: magnetic, autoflex, dedicated tooling, vacuflex, manuflex clean tooling & table correct position of the tooling proflow: stencil support.,objective 10,boards,boards,uneven pad surface can cause loss of gasket seal resulting in bridging etc. if the resist is higher that the pad the gasket seal will be lost resulting in bridging etc. .,the board design can impinge on the effectiveness and quality of the print process. here are some things to look out for ,pad with uneven surface coating,pad,resist,board issues,underside components can restrict the use of tooling pins - use tooling plate or fpa large underside components may impede board transport - increase under clearance .,the board design can impinge on the effectiveness and quality of the print process. here are some things to look out for ,board issues,via holes can cause problems with vacuum tooling labels, bar code stickers etc. increase board thickness leading to tooling, print and pressure problems .,the board design can impinge on the effectiveness and quality of the print process. here are some things to look out for ,tested ok,board issues,boards with tapered or chamfered edges are difficult to clamp and may be liable to movement during print leading to random offsets .,board issues,fibres these can block stencil apertures old solder this can cause solder balls fingerprints these can corrode pads, tracks etc handle board by edges, wear gloves use cm20.,ensure that production boards are free of .,board issues,in-line board cleaner,uneven pad surface solder resist too high underside components restricts tooling via holes with vacuum tooling barcode lables,| | | | | | | |,boards,troubleshooting,troubleshooting,bridging,bridging causes,no aperture reduction solder resist higher than the pads area close to obstruction ( board clamp, label, etc ) board - stencil misaligned uneven hasl finish stencil damaged squeegee pressure / proflow piston pressure too high squeegee worn.,incomplete print,incomplete print,paste viscosity too high dried up paste in proflow head dirty stencil - too much aperture blockage not enough paste on the stencil print speed too high proflow piston pressure too low wet stencil after cleaning wet or dirty boards stencil apertures too small in relation to the stencil thickness no stencil support with proflow separation speed set incorrectly.,scooping,scooping,squeegee pressure on polyurethane squeegee too high apertures too large high temperature or humidity board poorly supported (too high) large aperture (especially east-west opening) squeegees too soft.,excess print height,excess print height,paste viscosity too low ( too warm or humid) squeegee / proflow pressure too low print speed with proflow too low squeegee pressure too low squeegee blunt snap-off gap (possible print gap with whatever reason) squeegee edge not straight squeegee edge damaged board poorly supported stencil damaged solder mask/notation ink/barcode labels nearby,misalignment,misalignment,board