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“Understanding AXI Acquisition Techniques and Image Quality”

“Understanding AXI Acquisition Techniques and Image Quality”. Michael J Smith Michael.J.Smith@Teradyne.com. Teradyne Assembly Test Division Website: www.teradyne.com/cbti. AXI. AOI. X-Ray Inspection. ICT. Major Components. 1. X-ray Tube Produces high resolution x-ray beam cone. PCB.

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“Understanding AXI Acquisition Techniques and Image Quality”

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  1. “Understanding AXI Acquisition Techniques and Image Quality” Michael J Smith Michael.J.Smith@Teradyne.com Teradyne Assembly Test Division Website: www.teradyne.com/cbti

  2. AXI AOI X-Ray Inspection ICT

  3. Major Components • 1.X-ray Tube • Produces high resolution x-ray • beam cone PCB • 2. Image Intensifier / Detector • Converts radiation into visible light • 3. Camera • Sends video signal to computer • 4. Computer • Analyzes Image Imaging Analysis

  4. Penetration Density and Thickness PCB’s & Solder Joint materials block x-rays based on: • Material Density(Lead, Copper, Plastics, Heat Sinks, etc.) • Material Thickness t Lightest - Darkest

  5. 60 128 200 250 Computer prefer a gray scale (0-255) X-ray Image

  6. Smaller FOV Higher Resolution Larger FOV Low Resolution Field of View (FOV) • FOV Influences: • Test Throughput • Resolution / Detection • Clearance 1.0 in 25.4mm .25 in 6.4 mm .5 in 12.7 mm

  7. Resolution • Resolution is measured as Line Pairs • X-ray Tube spot size • Detector resolution • Field of View • Resolution Influences • Clarity of image • Measurement repeatability • Detection capabilities • False calls .5in (12.5mm) FOV 1in (25mm) FOV

  8. Types of X-ray Imaging • Transmission Imaging • Automated X-ray Inspection Systems (AXI) • Cross-Section Imaging • AXI Systems • Digital Tomosynthesis • Off-set Transmission • Laminography

  9. Automatic X-Ray Inspection Technology Evolution Xstation 4000 ‘94 1st Digital Tomosynthesis AXI NIS MV6100 ‘86 1st Commercial AXI IRT CXI-5300 ‘97 NIS CXI-5700 ‘89 1st In-line AXI IRT CXI-3300 ‘98 NIS CXI-3600DG ‘94 IRT CXI-3600 ‘ 94 4pi 5DX ‘98 HP 5DX Series 2 ‘00 Agilent 5DX Series 3 ‘89 1st Laminography AXI 4pi 3DX Teradyne Acquires GenRad IRT Licenses X-ray Laminography to 4pi NIS acquires IRT 4 Pi Formed (spins off from IRT) GenRad acquires NIS HP invests in 4 Pi HP acquires 4 Pi ‘85 ‘87 ‘89 ‘91 ‘93 ‘95 ‘97 ‘99 ‘01 ‘03

  10. Transmission AXI X-ray Image

  11. Types of Cross-Section Imaging • Tomosynthesis • Digital Image Synthesis • Laminography • Mechanical Image Integration Generate Off-axis X-rays Generate Off-axis X-rays Stationary Detector Rotating Detector

  12. Principle of Laminography • * Z-Axis Mapping required

  13. Principle of Laminography • Steer-able x-ray source and rotating detector • “Smear/Average” out objects above/below focal plane • Mechanical integration generates one slice per rotation (or acquisition) • Image acquisition and synthesis occur concurrently Off-axis images

  14. Steer-ableX-Ray Source Inspection Plane Large AreaDetector Principle of Digital Tomosynthesis Multiple Transmission Images

  15. Principle of Digital Tomosynthesis Digital Tomosynthesis is a Computational Technique Z= X / tan Z • Objects at different elevations move by • different horizontal distances X

  16. Digital Tomosynthesis is a Computational Technique Z= X / tan Z • Objects at different elevations move by • different horizontal distances X Principle of Digital Tomosynthesis

  17. Top Side QFP PCB Resistor Bottom Side Principle of Digital Tomosynthesis Cross Section x-ray provides the capability to generate un-obscured views of top and bottom side components Use multiple off-axis x-ray images to separate top/bottom overlapping or obscured solder connections

  18. Tomosynthesis vs. Laminography Tomosynthesis Laminography [Max Value Method] [Average Method] Some Digital Blurring Compared to Transmission AXI

  19. Imaging Performance Examples • Transmission AXI • Resolution • ~ 20 lp/mm at 1.21 Sq-in FOV • Image noise 4.5% • Laminography AXI • resolution • ~ 8lp/mm at 0.64 Sq-in FOV • Image noise 7.5%

  20. LaminographyAXI Transmission AXI Imaging Performance Better image quality and lower noise reduce false fails and increases fault detection.

  21. 1 1 2 3 4 Tomosynthesis vs. Laminography • Tomosynthesis • Multiple Cross-sections per Acquisition: ‘infinite slicing’ • Laminography • Laser Mapping to focus on layer • 1 Cross-section per Acquisition • board warp • board bounce & vibration • laser map repeatability

  22. Flat to a 3D representation GULLWING SOLDER JOINT X-RAY IMAGE Heel Fillet Transmission Solder Joint Histogram

  23. Adoption of Standards - IPC 7-32 • IPC 610 • Human Inspection Solder Joint Acceptability • IPC 7-32 Subcommittee (Automated Inspection Technologies) • Working with the IPC 610 Subcommittee • Translate the IPC 610 solder joint acceptability into language that is directly measurable by automatic inspection • Team will study the reliability of lead free joints through thermo-cycling • www.ipc.org

  24. Void MeasurementA potential problem with Lead Free manufacturing process

  25. Void Measurement Calculations can vary • Void Area = 31 pixels • Radius = 12 pixels • ( 12 * 12 ) *  = 452.4 = 6.85% • Void Area = 60 pixels • Narrow Radius = 12 pixels • Wide Radius = 16 pixels • Circle = ( 12 * 12 ) *  = 452.16 = 13.26% • Oval = ( 12 * 16 ) *  = 603 = 9.85%

  26. Void Issues Related to Ball Shape X-ray source • Similarly sized voids in may appear to vary in size • Side voids appear brighter and thus larger because rays travel thru a shorter distance through the ball • Voids at mid-ball appear darker or smaller as x-rays travel through more solder than at the sides

  27. Issues with Voids Multiple small and misshaped voids looks similar

  28. Measure Void Accuracy • Use real voids from production boards and grind the ball to detail actual void size. • Correlation between actual and void measurements were made.

  29. Transmission AXI Graphed Results

  30. AXI AOI 30 mm QFP BGA 20 mm TAB 15 mm COB CSP FC 10 mm (.4 in.) Technology Summary • AXI Vs other inspection techniques • Hidden joints Vs Visible Joints • 2D Vs Shape and Volume. ICT

  31. Technology Summary • Transmission • Sharpe images • Reduces False Pass/Failure. • Can measure relative shape and volume • Large FOV • High Throughput • Can not easily resolve obscured solder joint • Solder joints on both sides of the board

  32. Technology Summary • Laminography • Resolve most obscured solder joints • Averaging produces “smeared” images • Increases False Pass/Fail • Mechanical tolerances “smearing” effect • Increases False Pass/Fail • Smaller FOV or larger pixel detector can help reduce “smearing” • But Reduces throughput • Requires Z Axis mapping • Reduces throughput

  33. Technology Summary • Digital Tomosynthesis • Resolve most obscured solder joints • Most of the advantages of Transmission AXI • Maximum image values produces sharper images • Minimise false pass/fail • Can have long image acquisition times • Reduce Throughput • Image processing has to take advantage of Moore’s Law. • Throughput issue

  34. “Understanding AXI Acquisition Techniques and Image Quality” Michael J Smith Michael.J.Smith@Teradyne.com Teradyne Assembly Test Division Website: www.teradyne.com/cbti

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