printprocess(诺基亚smt印刷工艺).pptVIP

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printprocess(诺基亚smt印刷工艺).ppt

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printprocess(诺基亚smt印刷工艺)

nokia Stencil Printing Process Overview of Stencil Printing Stencil Printing Variables Solder Paste Stencil Design Squeegee Printing Parameters Solder Paste Overview Solder Paste A consistent homogeneous mixture of solder powder in a stable viscous flux vehicle which is used to join two metal surfaces upon heating. 90% metal content for stencil application 50/50% metal/flux by volume 10 mil thick deposit leaves 5 mil solder after reflow. Solder Paste Solder Powder Primary function is to form a permanent metallurgical bond between two or more metallic surfaces Paste Flux Provide 2 main functions. First, it suspends the powder to maintenance the homogeneous mixture. And second, it chemically removes oxide from the components, the PCB pad, and the powder to allow a good metallic bond to form. Solder PasteWhat it is made of…. Metal Powder -electrical/mechanical contact Flux: Rosin/Resin -flow properties, tack, activity Solvent -dissolve rosin/resin and activitor Activitor -oxide scrubbing and cleaning thickeners/rheological agents/viscosity modifiers -keep powder from settling,tackifiers, coloring. Solder Paste Metal Powders Typical powder alloys: Eutectic: Sn63/Pb37 Tmelt =183 w/ silver: Sn62/Pb36/Ag2 Tmelt =179 No lead : Sn96.5/Ag3.5 Tmelt =221 High Temp: sn10/Pb88/Ag2 Tmelt =268--302 Paste Powder Sizes Solder Alloy Powder Recommendations for Fine Pitch Technology Lead Pitch Mesh Particle Size 25 mil (0.635mm) Type 3 -325/+400 25 mil (0.635mm) Type 3 -325/+400 to 500 20 mil (0.5mm) Type 3 -325/+500 16 mil (0.4mm) Type 4,3 -400/+500 12 mil (0.3mm) Type 4 -400/+625 Paste Mesh Designations ASTM Mesh Opening Size Designation (um) (in) 200 69 0.0027 250 58 0.0023 325 43 0.0017 400 38 0.0015 500 30 0.0012 625 20 0.00078 Paste - Viscosity Viscosity Characteristics Application Method Viscosity Syringe Dispensing 200-400 kcps Mesh Screen Prin