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1、Process Theory,PERSONAL SAFETY,Board Clamps are SHARPBrakes are HOTWear Eye Protection and Gloves with Solvent Based Products Always fit the HEAD PROPIf in doubt press the E STOPDo Not bypass the CAM SAFES.,OBJECTIVE 1,ENVIRONMENT,IS THE ENVIRONMENT IN CONTROL?,CONSTANT TEMPERATURE?CONSTANT RELATIVE
2、 HUMIDITY?,PRINTING PROCESS,Printing Process,The Perfect Print,Clean edgesFlat on topHeight=Stencil ThicknessGood AlignmentNo Flux Bleed.,Basic Stencil Process,PasteRolling,Controlled Print SpeedEven Squeegee Pressure,Basic Stencil Process,Basic Stencil Process,Board is lowered under controlled Sepa
3、ration Speed,Hardware,Software,Environment,Squeegees,Print Speed,Temperature,Paste,Humidity,Stencil,Pressure,Tooling,Print Gap?,Board,Factors Affecting the Print,Separation Speed,MATERIAL CHECKLIST,STENCILSQUEEGEESPROFLOWPASTETOOLINGSOLVENT/PAPERBOARDS.,STENCILS,Stencils,Chemical Etching,Minimum ape
4、rtures0.1 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 aperturesEqual to metal thickness down to 0.05 mm
5、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 pitchto leave a wall 0.05 mm between apertures*but paste may not release from such narrow apertures,Electroformed,Minimum aperturesEqual to metal thickness down to 0.05 mmie 0.050 mm at 0.05 mm thick*0.100 mm
6、at 0.10 mm thick*0.150 mm at 0.15 mm thick*Minimum QFP pitchto 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 effe
7、ctive,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:etchingma
8、terial:CrNi-steel,Process:laser cut material:CrNi-steel,Process:electroformed material:Nickel,Stencil Design,Pitch,Length,Width,Design StencilApertures toallow a clearanceof at least 50 mbetweenPaste and edgeof Pad,Paste,Pad,Stencil Design,Release Equation 1 Release Equation 2 W TPaste Release Equat
9、ion WAvg.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 ClothWith a solvent soaked cloth in each hand clean both sides simultaneously(
10、Wear Gloves!)Screen Clean MachineUnder Screen cleaner:Program to clean as seldom as possible!Use Vacuum to clear blocked aperturesAlways follow a wet wipe with a dry wipe.,Solvent/Paper,SOLVENT:DISOLVES THE PASTECAN BE WIPED OFFEVAPORATES QUICKLYLEAVES NO RESIDUEDOES NOT HARM THE USC HOSES AND WIPER
11、 BLADESPAPER:ABSORBENTLINT FREE.,Stencil Maintenance,Remember.,Stencils are Fragile-Store and Handle With CareKeep Stencils CleanInspect for Damage and StretchRepair Fiducials when Damaged.,Stencil-Board alignment,Cause:Poor ArtworkPoor Quality Stencil ManufacturePoor board manufacturingBoard Stretc
12、hPoor Fiducial AlignmentMachine not calibratedSolution:Print OffsetsBuy New StencilImprove Fiducial ScoreBuy better boardsCalibrate 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
13、 is the typical size for current SMT,The smaller the particle size the better the print definitionbut the more expensive the paste will be and the greaterchance of reflow problems!,Rule of thumb:keep a minimum of 5 particlesper aperture width,Stencil,Board,Particle Size,Maybe,for less than 3 months,
14、Definitely for3-6 months,hmmmm.Never!,Paste Storage,Using the Paste,ColdStorage,Working Pot,Printer,FreshPaste,After 8 Hours,End of Run/Extended Downtime,End of Day,Disposal,Return only if paste qualityis good and it makeseconomic sense,Temporary Pot,Good Working Practices,Stir Paste Gently Before U
15、se Regulate Paste Diameter at 15mmPerform Small Top-Ups RegularlyRegulate Temperature and HumidityDo Not Leave Paste drying on Stencil.,SQUEEGEES,Squeegees,Squeegees,Transfer/Driving forcesare influenced by:-,Squeegee anglePrint speed Paste rheology Paste roll volume,Driving force,Transfer force,Squ
16、eegee Principles,Reaction force,Squeegee force,Squeegee Principle,In general,squeegee speed can be increase as the solder paste viscosity decreaseHave 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),Ang
17、le,45,60,Intrusive reflowHigh speed printingPrinting thick stencilsPrinting GluePrinting mesh screens,Standard SMT Printing,IncreasedForce,Reduce Force,Metal squeegees,Metal squeegees,Overhang,15 mm-widely used,reduced risk of stencil/blade damagedue to increased flexibility,6 mm-historically used b
18、utno longer recommend due toincreased risk of stencil/bladedamage.,Property,Metal,Polyurethane,Fine pitch,Good,Excellent,Large apertures,Excellent,Good,Pressure effect,Does not causescooping,Needs control,Damage resistance,Poor,Good,Damage to stencil,Poor,Good,Life,Until broken,25,000,Paste Height,S
19、tencil 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,ApertureScooped,Pads,Board,stencil,Scooping,Squeegees,METAL SQUEEGEESPOLYURETHANE SQUEEGEESRIGHT LENGTHRIGHT HARDNE
20、SS(OVERHANG for metal)ANGLENOT DAMAGEDNOT WORN.,OBJECTIVE 8,TOOLING,Tooling,Tooling,Magnetic PillarsDedicatedManuflexVacuflexF.P.AFormflexTooling problems&Solutions.,19 mm and 4 mm Pin Diameter Simple and Robust Construction Inexpensive,Table,Rail,Rail,Magnetic Tooling,Can provide 100%support Can co
21、ntain milled out areas for underside components Can be fitted with vacuum cups.,Dedicated Tooling Plate withMilled out areas,Dedicated Tooling Plateproviding 100%support,Dedicated Tooling Plates,Dedicated tooling,Board Lifted By Tooling causing:Board Damage Squeegee Pressure Problems Uneven Paste He
22、ights 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.,
23、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,MANUFLEXCLEAN TOOLING&TABLECORRECT POSITION OF THE TOOLINGPROFLOW:STENCIL SUPPORT.,OBJECTIVE 10
24、,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 qualityof the print process.Here are some things to look out fo
25、r.,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 qualityof the print proc
26、ess.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 qualityof the print process.Here are som
27、e 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 Solderthis can cause solder balls Fingerprints these can corr
28、ode pads,tracks etc handle board by edges,wear glovesUse CM20.,Ensure that production boards are free of.,Board Issues,In-line board cleaner,UNEVEN PAD SURFACESOLDER RESIST TOO HIGHUNDERSIDE COMPONENTS RESTRICTS TOOLINGVIA HOLES WITH VACUUM TOOLINGBARCODE LABLES,|,Boards,TROUBLESHOOTING,Troubleshoot
29、ing,Bridging,Bridging Causes,No aperture reductionSolder resist higher than the padsArea close to obstruction(board clamp,label,etc)Board-stencil misalignedUneven hasl finishStencil damagedSqueegee pressure/Proflow piston pressure too highSqueegee worn.,Incomplete print,Incomplete print,Paste viscos
30、ity too highDried up paste in Proflow headDirty stencil-too much aperture blockageNot enough paste on the stencilPrint speed too highProflow piston pressure too lowWet stencil after cleaningWet or dirty boardsStencil apertures too small in relation to the stencil thicknessNo stencil support with Pro
31、flowSeparation speed set incorrectly.,Scooping,Scooping,Squeegee pressure on polyurethane squeegee too highApertures too largeHigh temperature or humidityBoard poorly supported(too high)Large aperture(especially East-West opening)Squeegees too soft.,Excess print height,Excess print height,Paste visc
32、osity too low(too warm or humid)Squeegee/Proflow pressure too lowPrint speed with Proflow too lowSqueegee pressure too lowSqueegee bluntsnap-off gap(possible print gap with whatever reason)Squeegee edge not straightSqueegee edge damagedBoard poorly supportedStencil damagedSolder mask/notation ink/ba
33、rcode labels nearby,Misalignment,Misalignment,Board-stencil mismatchFiducials set or found incorrectly(video model)board stretchLoose mesh on stencilmachine not calibrated.,Clean edgesFlat on topHeight=Stencil ThicknessGood AlignmentNo Flux Bleed.,The Perfect Print,SMEAR,SQUEEGEE/PROFLOW PRESSURE TO
34、O HIGH?ALIGNMENTPRINT DEPOSITS 1?USC SETUP?PASTE KNEAD SETUP?.,ALIGN,FIDUCIAL SETUPOFFSETSALIGNMENT WEIGHTING.,INSUFFICIENT PASTE,PRINT SPEEDPRINT PRESSURE,PROFLOW PRESSUREPRINT DEPOSITSSEPARATION SPEEDUSC SETUPPASTE KNEAD SETUP.,BRIDGE,PRINT PRESSURE,PROFLOW PRESSUREPRINT DEPOSITS USC SETUPPASTE KN
35、EAD SETUP.,VARIABLES CAN BITE YOU,Variables,THE BATTLE IS CONTINUAL TO MAINTAIN THE QUALITY.ANY CHANGE IN ANY VARIABLE MAY AFFECT THE PRINTED PRODUCT.,EXAMPLES,PASTE SIZE,EXAMPLES,BOARD THICKNESS,BOARDS MAY TYPICALLY VARY BY+/-0.2mmThis will affect the separation parameter,EXAMPLES BEYOND OUR DIRECT CONTROL,TEMPERATURE(OPENING COVERS)HUMIDITY(OPENING COVERS)LIGHT(DAY TO NIGHT)HUMANS(BIGGEST PROBLEM)BOARD QUALITY“HEARTBEAT”IF LINE GOES DOWN,HOORAH,CONGRATULATIONSANDHAVE A SAFEJOURNEY.,Process Theory,
