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 technology
Where SMT problems come from?
Case studies - assembly and inspection of:
LED
BGA
PTH
QFN
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 byTeledyne 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
generated
As 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 target
Diameter of the x-ray beam increases as
it moves away from the source
Magnification is a function of the
distances between source, sample, and
detector

Where Are Defects Introduced?

Defects associated with paste application
Excess solder
Solder bridges
Insufficient solder
Solder Paste Application Defects

Component Placement Defects
Defects associated with component placement
Misalignment
Polarity (tantalum)
Missing component

Reflow Oven Defects
Defects associated with the Reflow oven
Voiding
Bridging
Solder balls
Excess solder
Insufficient 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
LED
BGA
PTH
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 substrate
Prior 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
variation
Use LED information to determine maximum
operating temperature to achieve expected lifespan
Measure temperature as a function of voiding area to
determine maximum voiding allowed
Set 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 construction
2 reflow cycles: first for FPGA, second for sensor
Lot’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 assembly
Different 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.com
Chat with us live at our website
Email us at info@creativeelectron.com
Call 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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