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


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


TruView 6 & the Power of Crowdsourcing


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


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


How do we get a magnified image?

8

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).


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


Where Are Defects Introduced?


Defects associated with paste applicationExcess solderSolder bridgesInsufficient solder

Solder Paste Application Defects


Component Placement Defects

Defects associated with component placementMisalignmentPolarity (tantalum)Missing component


Reflow Oven Defects

Defects associated with the Reflow ovenVoidingBridgingSolder ballsExcess solderInsufficient solder


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.


Other PCB Issues Under X-Ray: QFN Short


Other PCB Issues Under X-Ray: Blown Trace


PCB broken trace


Broken Wirebonds


Other PCB Issues Under X-Ray: Misaligned Cap


Other PCB Issues Under X-Ray: Tombstoning


Other PCB Issues Under X-Ray: Missing Cap


Wire Crimp Defect


Manufacturing Inspection Case studies

LEDBGAPTH

QFN


Typical LED luminaire fabricated by GMC


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.


Typical samples prior to quality inspection; prior to adoption of x-ray imaging


First samples after implementation of quality program and inspection


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


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


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


Medical device assembly

GMC started assembling medical device probes for radiotherapy RMAs have reached $25k per month

Design has never worked well…


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


Sensor side assembly

Bare PCB PCB with sensors removed


Simplified assembly – 1 sensor, 1 FPGA

Sensor

FPGA

PCB


X-ray of assembly – 1 sensor, 1 FPGA


BGA inspection with dual energy imaging


BGA Opens


BGA Head In Pillow Visual Inspection


BGA Head In Pillow X-Ray Inspection


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


BGA Co-planarity Inspection


Planarity issues with FPGA assembly

Sensor

FPGA

PCB


Fixing the problem

• Epoxy on the corners of the FPGA• Underfill also an option

Sensor

FPGA

PCB


Plated Thru Hole


Plated Thru Hole per IPC-A610


Measuring PTH Fill with X-Rays


Measuring PTH Fill with X-Rays – Side View


Measuring PTH Fill with X-Rays – Top View


Data processing board

• High volume production -thousands of boards per week

• Intermittent issues with QFN parts


QFN assembly with excess voiding


Problem QFN assembly – open pin


Detail of open pin in QFN package


Excessive Pad Voiding

A

B


Another QFN problem: improper alignment


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.


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/


Thanks for your time!

led, bga, and qfn inspection - x-ray inspection for smt quality assurance and control

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