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Final Report 04.15.2009 Rev.: 22.05.2009 Dr. László Jakab, László Milán Molnár, Olivér Krammer

FEM simulation of stencil deformation. Final Report 04.15.2009 Rev.: 22.05.2009 Dr. László Jakab, László Milán Molnár, Olivér Krammer. WORKPLAN OF THE PROJECT. CONTENTS. 1. Investigating stencil deformation in case of point loading:

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Final Report 04.15.2009 Rev.: 22.05.2009 Dr. László Jakab, László Milán Molnár, Olivér Krammer

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  1. FEM simulation of stencil deformation Final Report 04.15.2009 Rev.: 22.05.2009 Dr. László Jakab, László Milán Molnár, Olivér Krammer

  2. WORKPLAN OF THE PROJECT BOSCH - STENCIL_FEM

  3. CONTENTS 1. Investigating stencil deformation in case of point loading: Stencil is loaded at the center; different sizes of underside supports were used; pilot FEM model of the stencil was created according to deformation results. 2. FEM model of a real squeegee: Finite Element model of a printing squeegee was created on the base of squeegee deformation experiments; squeegee is inserted into the stencil FEM model. 3. Stencil deformation by squeegee loading: Stencil is loaded at different locations by a printing squeegee; different sizes of underside supports were used; final FEM model of the stencil was created (including the squeegee) according to deformation results. 4. Testboard for stencil printing experiment: Testboard was designed according to BOSCH requirements; thick steps (with different distances from pads) were formed by selective electroplating. 5. Stencil printing experiment: Stencil printing experiment was carried out using testboards with different step thicknesses; the deposited paste height was measured and simulated; keepout area rule was set up on the basis of simulation results. BOSCH - STENCIL_FEM

  4. 1. Stencil deformation by point loading BOSCH - STENCIL_FEM

  5. STENCIL DEFORMATION EXPERIMENT frame 58x58 cm stencil 50x50 cm underside support 30x30 cm 16 cm Stencil: - stainless steel - lasercut - thickness: 175 µm - ordered from DEK BOSCH - STENCIL_FEM

  6. STENCIL DEFORMATION EXPERIMENT fixed micrometer clock free to move measuring probe clock loading arm clock stand clock fixing stencil 365 mm 953 mm Clock: range: 0…1 mm accuracy: 10 µm Load: 2.26…7.5 kg / 22…131 N m underside support stencil BOSCH - STENCIL_FEM

  7. STENCIL DEFORMATION RESULTS BOSCH - STENCIL_FEM

  8. FEM MODEL OF THE STENCIL FOIL FEM model has been created for both 16 cm and 30 cm underside support, to match to both experimental results. The material parameters obtained from Comsol library: Steel AISI 4340 – E: 205·109 Pa, ν: 0.28, ρ:7850 kg/m3 stencil thickness: 175 µm BOSCH - STENCIL_FEM

  9. SIMULATION RESULTS measured: 1.95 µm/N, simulated: 2.11 µm/N measured: 2.84 µm/N, simulated: 3.03 µm/N BOSCH - STENCIL_FEM

  10. STENCIL DEFORMATION EXPERIMENT frame 58x58 cm stencil 50x50 cm underside support 30x30 cm 16 cm Stencil deformation experiment has been extended by underside supports of 10x10 cm and 5x5 cm. BOSCH - STENCIL_FEM

  11. STENCIL DEFORMATION RESULTS Stencil thickness: 125 µm BOSCH - STENCIL_FEM

  12. 2. FEM model of a real squeegee BOSCH - STENCIL_FEM

  13. DEFORMATION OF A REAL SQUEEGEE The bending of the squeegee measured with the same loads as the stencil before to create the FEM model of the squeegee. BOSCH - STENCIL_FEM

  14. SQUEEGEE UNDER INVESTIGATION 19 Length: 300 mm Blade: stainless steel Thickness: 200 µm 35 15 BOSCH - STENCIL_FEM

  15. SIMULATING SQUEEGEE DEFORMATION FEM parameters of the squeegee: Length: 300 mm Thickness: 200 µm Height: 15 mm Initial angle: 60 ° E: 195·109 Pa ν: 0.28 ρ:7850 kg/m3 BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  16. SIMULATING SQUEEGEE DEFORMATION BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  17. 3. Stencil deformation by squeegee loading BOSCH - STENCIL_FEM

  18. MEASURING STENCIL DEFORMATION PUSHED WITH SQUEEGEE y x Squeegee length: 300 mm Stencil thickness: 125 µm Loads are the sameas previous:22…131 N Underside support: 31 cm, 20 cm, 10 cm BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  19. FEM MODEL OF THE STENCIL WITH SQUEEGEE Stencil dimensions: real size – 580 mm x 580 mm x 125 µm Mesh: 1:1:100 (x:y:z) ratio for numerical accuracy, finer mesh size at pressure area (see figures) Squeegee is pressed from the top side, by uniform pressure Material properties: steel, E=195 GPa, Poisson’s Ratio: 0,28. Boundary conditions: surfaces inside the supported area can move and bend, other surfaces are fixed Squeegee location: y=0 mm Support size in example: 20 cm Width of support system: 30 mm Support size in example: 20x20 cm BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  20. DEFORMATION IN X DIRECTION, 30 cm SUPPORT BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  21. DEFORMATION IN X DIRECTION, 20 cm SUPPORT BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  22. DEFORMATION IN X DIRECTION, 10 cm SUPPORT BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  23. DEFORMATION IN Y DIRECTION, 30 cm SUPPORT BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  24. DEFORMATION IN Y DIRECTION, 20 cm SUPPORT BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  25. DEFORMATION IN Y DIRECTION, 10 cm SUPPORT BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  26. MEASURING STENCIL DEFORMATION OF THE 150 µm TEST STENCIL Squeegee length: 300 mm Stencil thickness: 150 µm Loads are the sameas previous:22…131 N Point load and squeegee load is applied too Underside support: 20 cm BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  27. DEFORMATION OF 150 µm STENCIL IN CASE OF POINT LOADINGS BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  28. DEFORMATION OF 150 µm STENCIL IN CASE OF SQUEEGEE LODING AT 55 mm FROM CENTRE BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  29. DEFORMATION OF 150 µm STENCIL IN CASE OF SQUEEGEE LODING AT 25 mm FROM CENTRE Conclusion: including apertures in simulation is not necessary BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  30. 4. Testboard for stencil printing experiment BOSCH - STENCIL_FEM

  31. THE TESTPATTERN Stencil aperture for paste deposition (0.5x0.5 mm), the paste transfer efficiency is not affected by Area Ratio, base thickness 35 µm Clear pad for reference thickness of paste measurement Step in different height from board to board: for example +20 µm, +40 µm, +60 µm The height of steps is formed by selective electroplating The clearance between the steps and the pads is varying from 300 µm to 5 mm BOSCH - STENCIL_FEM

  32. THE TESTBOARD The testboard was designed according to Bosch requirements. Base thickness: contour and pads Higher steps by selective electroplating BOSCH - STENCIL_FEM

  33. THE TESTBOARD Nine pieces of testboard were made with immersion Ag finish;3-3 of each step thicknesses: +20 µm, +40 µm, +60 µm. BOSCH - STENCIL_FEM

  34. MEASURING THE STEP THICKNESSES The thickness of the steps was measured with a Tencor Alphastep 500. Horizontal range: 2 mm Vertical range: 10 nm…300 µm Vertical resolution: 0.1 µm or 2.5 nm BOSCH - STENCIL_FEM

  35. MEASUREMENT POINTS narrow steps square wide steps BOSCH - STENCIL_FEM

  36. RESULTS OF ALPHASTEP MEASURING BOSCH - STENCIL_FEM

  37. 5. Stencil printing experiment BOSCH - STENCIL_FEM

  38. STENCIL PRINTING EXPERIMENT Printer model: DEK 248 Accuracy: (achievable) ±25μm Repeatability: ±10 μm Printing speed: 10-70 mm/s Squeegee force: 0-150 N Experimental settings: Printing speed: 30 mm/s, squeegee force: 92 N, blade length: 300 mm, separation speed: 6mm/s,5 testboards were used for process setup. 1. Print 1 testboard -> print 1 fake board -> dry clean of stencil underside (repeated for 3 testboards) 2. Stencil direction / board direction was changed, stencil cleaned by wet wipe and with pressured air 3. Same run steps as No. 1. for another 3 boards BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  39. TEST RUN vertical printing narrow steps square1 wide steps horizontal printing square2 BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  40. MEASURING DEPOSITED PASTE HEIGHT Measuring equipment: ASC-Visionmaster 150 Maximum sample height: 5.1 cm Resolution: 1.78 μm Maximum measurable height: 365 μm Field of view: 2.1x2.8 mm solder pad step solder paste BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  41. ID. 2.: STEPS ARE PARALLEL TO SQUEEGEE *Line is only for guide, not simulation result. Paste is higher than Cu step because if the stencil did not bend down to the pad, it lifted the paste during separation. *Line is only for guide, not simulation result. Paste is higher than Cu step because if the stencil did not bend down to the pad, it lifted the paste during separation. BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  42. ID. 7.: STEPS ARE PARALLEL TO SQUEEGEE *Line is only for guide, not simulation result. Paste is higher than Cu step because if the stencil did not bend down to the pad, it lifted the paste during separation. *Line is only for guide, not simulation result. Paste is higher than Cu step because if the stencil did not bend down to the pad, it lifted the paste during separation. BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  43. ID. 8.: STEPS ARE PARALLEL TO SQUEEGEE *Line is only for guide, not simulation result. Paste is higher than Cu step because if the stencil did not bend down to the pad, it lifted the paste during separation. *Line is only for guide, not simulation result. Paste is higher than Cu step because if the stencil did not bend down to the pad, it lifted the paste during separation. BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  44. ID. 1.: STEPS ARE PERPENDICULAR TO SQUEEGEE *Line is only for guide, not simulation result. Paste is higher than Cu step because if the stencil did not bend down to the pad, it lifted the paste during separation. *Line is only for guide, not simulation result. Paste is higher than Cu step because if the stencil did not bend down to the pad, it lifted the paste during separation. BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  45. ID. 5.: STEPS ARE PERPENDICULAR TO SQUEEGEE *Line is only for guide, not simulation result. Paste is higher than Cu step because if the stencil did not bend down to the pad, it lifted the paste during separation. *Line is only for guide, not simulation result. Paste is higher than Cu step because if the stencil did not bend down to the pad, it lifted the paste during separation. BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  46. ID. 6.: STEPS ARE PERPENDICULAR TO SQUEEGEE *Line is only for guide, not simulation result. Paste is higher than Cu step because if the stencil did not bend down to the pad, it lifted the paste during separation. *Line is only for guide, not simulation result. Paste is higher than Cu step because if the stencil did not bend down to the pad, it lifted the paste during separation. BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  47. STENCIL DEFORMATION OF NARROW STEPS Conclusion: if steps are perpendicular to the squeegee, the deposited paste has higher height with higher deviation, and the stencil can bend less. BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  48. MEASURING THE DEPOSITED PASTE AREA Paste area was measured when the steps were perpendicular to printing direction The results were averaged from the pads outlined by the red rectangle BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  49. MEASURING THE DEPOSITED PASTE AREA Left: ID. 1 - no step Right: ID. 6 – 0.5 mmstep distance BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

  50. 3D SIMULATIONS FOR DIFFERENT DIRECTION OF PRINTING Simulations showed basically different printing process depending on the printing direction. The bending of the stencil can be senn in the figures above. BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM BOSCH - STENCIL_FEM

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