Step stencil ppt
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The document outlines the technology and applications of step stencils in solder paste printing, discussing the different manufacturing methods including chemical etching, laser welding, and micro-machining. Experimental results indicate that solder paste volume is optimized when applied 10-20 mils away from the step edge, and that the FPN coating improves paste volume consistency. Future work includes further investigations into paste volume distribution and performance comparisons with non-stepped stencils.
Step stencil ppt
- 1. Step Stencil Technology Greg Smith gsmith@fctassembly.com Tony Lentz tlentz@fctassembly.com
- 2. Outline/Agenda Introduction Step Stencils Technologies Step Stencil Design Printing Experiment Experimental Results Future Work Acknowledgements Q & A
- 3. Introduction 1.1.7 Relief Etch Also known as Etch Relief and Under Etch. Adding an under etch of the foil to create a pocket for raised features, labels, or a mulit-print function. 1.1.22 Step Stencil A Stencil with more than one foil thickness level. *IPC 7525B, “Stencil Design Guidelines”, 2011-October.
- 4. Introduction Step Down Stencils: Material thickness is reduced in areas where smaller components are placed on the PWB so that proper Area Ratios are maintained to obtain good paste release. *Image from http://laser-stencil.eu/en/step_stencils/ *Step Down Stencil
- 5. Introduction Step UP Stencils: Material thickness is increased around specific components such as edge connectors, large BGA’s, D-PAK’s and other devices to increase the volume of paste deposited. Step Up Stencil
- 6. Step Stencil Technologies Currently there are three technologies in the U.S. to manufacture step stencils. Welded Technology Etched Technology Micro-Machined Technology
- 7. Step Stencil Technologies Photo-Chemical Etching • Historically, the primary method to manufacture step stencils • Photographic process applies resist to areas that will not be etched. • Etchant is sprayed onto surface and removes material until the desired thickness is achieved. Etched Technology
- 8. Step Stencil Technologies Laser Welded Technology • The area of the step is cut from the stencil. • The required thickness of the step area is cut from another foil the exact same size. • The new foil blank is placed into the cut out area and the foil is welded together. • Apertures are then laser cut. Laser Welded Technology
- 9. Step Stencil Technologies Micro-Machining Technology • Material is attached to cooled vacuum plate. • CNC based milling machine removes very small amounts of material at a time until desired thickness is achieved. • Stepped foil is mounted to frame and apertures are laser cut. Laser Welded Technology
- 10. Step Stencil Design • Base stencil thickness 4 mils (101.6 microns) • Step Pocket Depths (Foil Thickness) • 3.5 mils (88.9 microns) • 3.0 mils (76.2 microns) • 2.5 mils (63.5 microns) • 2.0 mils (50.8 microns) • Each step area was 1 inch square (25.4 mm) and the step design is shown here. The 3.5 Mil Step Pocket (.5 mil step depth) was not used in this paper.
- 11. Printing Experiment Apertures were created for the following components: • 03015 Metric • 01005 • 0.3 mm BGA • 0.4 mm BGA • 0.5 mm pitch QFNs. Apertures were cut at varying distances from the step edges: 10, 20, 30, 40, and 50 mils.
- 12. Printing Experiment Data was collected after printing 10 boards with each stencil. The effects of the FPN coating were compared to the uncoated part of the stencil on printing of solder paste. Fluoro-Polymer Nano (FPN) coating
- 13. Printing Experiment A 10 print study was run on each step stencil using a popular no clean, SAC305 Type 4 solder paste. The circuit boards used were bare copper clad material 0.062” (1.57 mm) thick. Step Stencil Contact Side with FPN Nano-Coating.
- 14. Equipment Parameter Value Squeegee Length 300 mm Squeegee Pressure 0.18 kg/cm (5.4 kg) Squeegee Speed 30 mm/sec Squeegee Angle 60 degrees Separation Speed 1.0 mm/sec Cleaning Cycle W/V/D every print Cleaning Solvent Isopropanol (IPA) Solder Paste NC SAC305 T4
- 15. Stencil Thickness Measurements Step Thickness (mils) Step Depth (mils) Etched – Depth / STDev (mils) Welded - Depth / STDev (mils) Machined - Depth / STDev (mils) 2.0 2.0 2.36 / 0.11 2.08 / 0.19 2.01 / 0.17 2.5 1.5 1.69 / 0.16 1.60 / 0.18 1.25 / 0.15 3.0 1.0 1.15 / 0.19 0.97 / 0.18 1.08 / 0.17 • Chemical etching process created deeper step downs than the nominal value • Welding and Micro-Machining processes created steps that are closer to the target depth. • Overall, the standard deviations are very similar for each technology.
- 16. Printing Results Solder Paste Volumes for the 3.0 mil Etched Step. Etched Step
- 17. Printing Results Solder Paste Volumes for the 2.5 mil Etched Step. Etched Step
- 18. Printing Results Solder Paste Volumes for the 2.0 mil Etched Step. Etched Step
- 19. Printing Results Tukey-Kramer HSD Analysis for the FPN Coated, Etched 3.0 mil Step (1 mil step down) and the 9.8 x 35.4 Aperture. Etched Step
- 20. Printing Results The printed solder paste volume is higher for the 10 and 20 mil distances than the 50 mil distance. Level Mean 10 A 839.52500 20 A 823.35000 40 A B 798.30000 30 A B 796.65000 50 B 776.22500 Tukey-Kramer HSD Analysis for the FPN Coated, Etched 3.0 mil Step(1 mil step down) and the 9.8 x 35.4 Aperture. Etched Step
- 21. Printing Results The printed solder paste volume is higher for the 10 and 20 mil distances than the 50 mil distance for the 9.8 x 35.4 mil apertures but smaller aperture volumes seem to be consistent from 10 – 50 mils from the step edge. Etched Step 8 x 9 mil AperturesPaste w/ blue U.V. dye added
- 22. Printing Results Solder Paste Volumes for the 3.0 mil Welded Step. Welded Step
- 23. Printing Results Solder Paste Volumes for the 2.5 mil Welded Step. Welded Step
- 24. Printing Results Solder Paste Volumes for the 2.0 mil Welded Step. Welded Step
- 25. Printing Results Tukey-Kramer HSD Analysis for the Uncoated, Welded 2.5 mil Step and the 9.8 x 35.4 Aperture. Welded Step
- 26. Printing Results Paste volume at the 10 mil distance is significantly higher than the 40 and 50 mil distances. Paste volume is significantly higher at the 20 mil distance than then 50 mil distance. Welded Step Level Mean 10 A 1015.3250 20 A B 988.8000 30 A B C 954.1750 40 B C 916.4750 50 C 891.8500 Connecting Letters Report Tukey-Kramer HSD Analysis for the Uncoated, Welded 2.5 mil Step and the 9.8 x 35.4 Aperture.
- 27. Printing Results The printed solder paste volume is higher for the 10 and 20 mil distances than the 50 mil distance for the 9.8 x 35.4 mil apertures but smaller aperture volumes seem to be consistent from 10 – 50 mils from the step edge. Welded Step 8 x 9 mil AperturesPaste w/ blue U.V. dye added
- 28. Printing Results Solder Paste Volumes for the 3.0 mil Micro-Machined Step. Micro-Machined Step
- 29. Printing Results Solder Paste Volumes for the 2.5 mil Micro-Machined Step. Micro-Machined Step
- 30. Printing Results Solder Paste Volumes for the 2.0 mil Micro-Machined Step. Micro-Machined Step
- 31. Printing Results Tukey-Kramer HSD Analysis for the Uncoated, Machined 2.0 mil Step (2 mil step down) and the 8 x 9 Aperture. Micro-Machined Step
- 32. Printing Results Printed solder paste volume is significantly higher at the 10 and 20 mil distances than the 30, 40, and 50 mil distances. This is also true for the 9.8 x 35.4 mil aperture with 2.0 mil and 2.5 mil machined step thicknesses. Micro-Machined Step Connecting Letters Report Tukey-Kramer HSD Analysis for the Uncoated, Micro-Machined 2.0 mil Step (2 mil step down) and the 8 x 9 Aperture. Level Mean 10 A 116.82500 20 A 113.92500 40 B 104.20000 30 B 103.72500 50 B 101.42500
- 33. Printing Results The printed solder paste volume is higher for the 10 and 20 mil distances than the 50 mil distance for the 9.8 x 35.4 mil apertures but smaller aperture volumes seem to be consistent from 10 – 50 mils from the step edge. Machined Step 8 x 9 mil Apertures Paste w/ blue U.V. dye added
- 34. What Have We Learned About Step Stencil Technology? Chemical Etching, Laser Welding, and Micro-Machining are each viable methods of producing step stencils. The surface texture and appearance of each step technology is different Solder paste volumes tend to be higher 10-20 mils from the step edge than 30-50 mils away for the QFN lead designs (9.8 x 35.4 mil aperture). In general, standard deviation is tighter and volume greater for apertures coated with the FPN coating. The smaller apertures (8, 8x9, 10 mil) tend to give statistically similar results regardless of distance from the step edge.
- 35. Future Work Step Stencil Investigations are Ongoing Printed paste volumes in the center of the step area will be compared to volumes near the edge. Non-Stepped Stencils will be made of the same thickness as the step down areas and print studies run to compare volumes. Printed paste volumes from horizontal versus vertical apertures with respect to the squeegee will be compared. Squeegee pressure and speed will be varied and the effects on printing down in step stencils studied.
- 36. Acknowledgements Many thanks to Bill Kunkle and MET for their support and providing Welded step stencils for this experiment. We also appreciate the support of Fine Line Stencil for providing the Etched and Machined step stencils and the nano- coating for this experiment.