led, bga, and qfn inspection - x-ray inspection for smt quality assurance and control
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X-Ray Inspection for SMT Quality Assurance and Control
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The X-Ray Machine You Didn’t Know Existed!The first inline/offline hybrid x-ray inspection, designed to meet the needs of
the high mix/low volume manufacturers
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TruView 6 & the Power of Crowdsourcing
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Schedule for this presentation
Introduction to x-ray technologyWhere SMT problems come from?Case studies - assembly and inspection of:
LEDBGAPTHQFN
How to use statistical analysis to diagnose your SMT line
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How do we image the X-rays?
When X-rays hit certain materials, they cause them to fluoresce. In this process, the
energy of the X-ray is absorbed and re-emitted as visible light. Usually this light is very
faint and needs to be amplified, else very sensitive detectors need to be used.
Flat Panel Detector.Photo by Teledyne Technologies.
Image intensifier.Photo by Hamamatsu Corporation
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How do we get a magnified image?
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Just like light, X-rays travel in straight lines.Unlike light, we cannot use a lens, so we use geometric magnification.The magnification is increased by moving the sample closer to the X-ray source (and vice versa).
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Field of View
The electron beam generated by the cathode is rapidly accelerated against the anode. Upon colliding with the anode, a cone-shaped beam of x-rays is generatedAs the x-ray beam moves farther from the anode target, the diameter of the beam increases proportionally. The angle of the x-ray cone beam, α, is determined by the angle of the anode targetDiameter of the x-ray beam increases as it moves away from the sourceMagnification is a function of the distances between source, sample, and detector
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Where Are Defects Introduced?
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Defects associated with paste applicationExcess solderSolder bridgesInsufficient solder
Solder Paste Application Defects
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Component Placement Defects
Defects associated with component placementMisalignmentPolarity (tantalum)Missing component
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Reflow Oven Defects
Defects associated with the Reflow ovenVoidingBridgingSolder ballsExcess solderInsufficient solder
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Statistical Process Control
Manufacturing process quality assurance.Solder joint measurement data, collected during x-ray test, can be statistically analyzed to identify manufacturing drifts, trends and other relevant process quality issues.
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Other PCB Issues Under X-Ray: QFN Short
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Other PCB Issues Under X-Ray: Blown Trace
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PCB broken trace
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Broken Wirebonds
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Other PCB Issues Under X-Ray: Misaligned Cap
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Other PCB Issues Under X-Ray: Tombstoning
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Other PCB Issues Under X-Ray: Missing Cap
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Wire Crimp Defect
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Wire Crimp Defect
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Manufacturing Inspection Case studies
LEDBGAPTH
QFN
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Typical LED luminaire fabricated by GMC
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LED Voiding
This relationship shows us the operating temperature of the LED grows exponentially with the void area. For this reason it is critical to keep
the voiding area to a minimum.
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Typical samples prior to quality inspection; prior to adoption of x-ray imaging
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First samples after implementation of quality program and inspection
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Summary of results for luminaire “A”
SinkPAD IITM substratePrior to quality program
Initial samples after implementation of quality program
Voiding Luminaire “A”Mean 40%
Std Deviation 15
Voiding Luminaire “A”Mean 8%
Std Deviation 0.9
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How GMC improved SMT assembly quality?
• Substrate surface cleanness • Substrate and LED metallization • Reflow oven temperature profile
• Paste selection, dispensing, and storage• LED and substrate handling and storage
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Current quality inspection program
Use x-ray inspection to set proper manufacturing parameters for each product. Use voiding area a key metric to determine process variationUse LED information to determine maximum operating temperature to achieve expected lifespanMeasure temperature as a function of voiding area to determine maximum voiding allowedSet plan to continuously measure voiding area with x-ray to verify conformity of manufacturing process
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Medical device assembly
GMC started assembling medical device probes for radiotherapy RMAs have reached $25k per month
Design has never worked well…
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Medical device probe assembly
Complex construction2 reflow cycles: first for FPGA, second for sensorLot’s of connectivity problems with the FPGA, likely due to the second reflow
Sensor
FPGA
PCB
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Sensor side assembly
Bare PCB PCB with sensors removed
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Simplified assembly – 1 sensor, 1 FPGA
Sensor
FPGA
PCB
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X-ray of assembly – 1 sensor, 1 FPGA
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X-ray of assembly – 1 sensor, 1 FPGA
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X-ray of assembly – 1 sensor, 1 FPGA
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X-ray of assembly – 1 sensor, 1 FPGA
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X-ray of assembly – 1 sensor, 1 FPGA
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BGA inspection with dual energy imaging
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BGA Opens
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BGA Head In Pillow Visual Inspection
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BGA Head In Pillow X-Ray Inspection
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BGA inspection – ball size analysis
Gradient in ball sizes indicate planarity issues with the assemblyDifferent ball sizes also cause voiding discrepancies in the assembly
Small
Large
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BGA Co-planarity Inspection
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Planarity issues with FPGA assembly
Sensor
FPGA
PCB
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Fixing the problem
• Epoxy on the corners of the FPGA• Underfill also an option
Sensor
FPGA
PCB
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Plated Thru Hole
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Plated Thru Hole per IPC-A610
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Measuring PTH Fill with X-Rays
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Measuring PTH Fill with X-Rays – Side View
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Measuring PTH Fill with X-Rays – Top View
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Data processing board
• High volume production -thousands of boards per week
• Intermittent issues with QFN parts
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QFN assembly with excess voiding
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Problem QFN assembly – open pin
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Detail of open pin in QFN package
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Excessive Pad Voiding
A
B
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Another QFN problem: improper alignment
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Quality control inspection with x-ray
• Problem of open pins of QFN traced to dirty stencil
• Review of stencil cleaning process was done. Proper procedures were not being followed
• Training of cleaning staff was repeated to assure they follow all steps
• Since proper stencil cleaning procedures were followed, no more issues of this nature were found.
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For more information
Contact us:www.creativeelectron.comChat with us live at our websiteEmail us at [email protected] us at 760.752.1192
Learn more at X-Ray University
http://creativeelectron.com/x-ray-university/
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Thanks for your time!