Keith Bryant
Technology Editor SMT Today Magazine
Chairman SMART Group
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Keith Bryant
Technology Editor SMT Today Magazine
Chairman SMART Group
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Chen, et al.; ASSEMBLY PROCESS RESEARCH ON 01005 CHIP
COMPONENTS IN LEAD-FREE SYSTEM; SMTAI-06
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Flash Memory (Top)
+ =
Logic (Bottom)
Courtesy of Spansion
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Inspection Options
 Manual Options
 Magnifiers / Comparators
 Digital Imaging Devices
 Video Microscopes
 Eyes
Inspection Options
 Manual Options
 Compact, ergonomic design
 Digital zoom from 4x to 160x
 Image capture and video output
 Large workspace with sliding stage
 for easy inspection and handling of PCB
 Very simple to use lifted lead Misplacement another angle cold solder joint another angle
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Reliability of Visual Inspection
Solder Joint Visual Inspection of the same PC Board
44 %
Inspection Options
 Automatic Options
 FT (Functional Test) of finished product
 ET/FP (Electrical Test/Flying Probe) of partial or finished assemblies
 ICT (In Circuit Test) of circuits/components on PCB
 AXI / XI (Automatic X-ray Inspection) for soldering and presence of components
 A O I (Automatic Optical Inspection) for soldering and components
 SPI (Solder Paste Inspection)
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Where do you place an AOI System?
 In-Line

To check Solder Paste (2.5 or 3D)

To check Part Placement

To check solder post reflow
Solder Paste Placement
Parts &
Solder fillets
Where do you place an A O I System?
 Off-line

Test for all three defect ty pes

O r test at any stage
Printer
X
Mounter
X
Reflow
X
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Insert Picture of brick


Precise Volume (l, w, t) or ( D, t)
◦ Metal
◦ Flux (Can be an issue)
Precise Location (x, y, θ )

2-D Inspection detects bridges, inadequacies, and checks alignment
◦ AOI on-board Printers is a recent innovation
◦ In-Line or Off-Line

3-D Inspection checks above as well as solder paste height, allowing volume calculation but at a slower rate
◦ In-Line or Off-Line
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H-P Study in late 1980 ’ s
Solder Paste Printing Fish Bone
Equipment Methods
Printer
Snap-Off
Squeegee Pressure
Alignment
Stencil
Holder
Squeegee
Humidity
Solder
Paste
Materials
Stencil
Temperature
Environment People
Training
Authority
Awareness
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
Component Presence and Position

Correct Component

Orientation / Polarity

Skew / Mis-alignment

Lost or Extra components

Replaces the DANGEROUS Tweezer
People!



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Reliable Interconnection

Component Location



Solder Volume
Wetting
Residues

Copyright 2007- 2008 ITM
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
Component Presence and Position

Correct Component

Orientation / Polarity

Skew / Mis-alignment

Tombstoning

Opens

Shorts
AOI here is not easy !

Post-Reflow Inspection is difficult -

“ Good ” Solder joint difficult to
“ define ”

Solder joints are shiny and hard for some optical systems to “ see ” .
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A O I



Inspection technologies / principles
Colour vs. B/W analysis
Capturing devices (cameras or scanners)

Optics (Lenses, Moray or LCOS)

Software, algorithms and libraries

Lighting, type, colours and controls

2D, 2.5D, Pseudo 3D and ‘Real’ 3D
A O I Inspection technologies / principles



Solutions available
Black and White Image Recognition
Scanner Types (OCR)


C o l o u r moving cameras
Colour comparator imaging (OCR)
Colour synthetic imaging
Multiple Cameras (2.5D or Pseudo3D imaging)
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A O I Inspection technologies / principles
Inspection technologies
Different calculation principles can be categorized as follows:
1. Correlation (picture comparison) ~ OCR
2. Synthetic modeling
3. Vector modeling
A O I Types

“Average” picture creation

Picture comparison using an average picture, based on the
“average” pixel-value of multiple pictures of the same component.

Most used in scanner type and entry level AOI systems.

Operator display in Colour (Colour Camera) but actual imaging & inspection in grey scale and Black and White

Formula for Average Picture:
Image = (Image 1 + Image 2 + … + Image N) / N
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A O I Types
Correlation principle
Advantages:

"Self learning“
 adding a new picture on every false or real alarm
Fast programming

Flexible

Low Cost
A O I Types
Correlation principle Disadvantages:

Risk of “Slip” when programmer adds “wrong pictures”

Alternative components require renewed debugging
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A O I Types
Picture comparison using a sy nthetic picture, deriv ed from real picture by image processing
U sed in more adv anced camera systems, sometimes in combination w ith v ector based models
Normal: Sy nthetic:
A O I Types



Based on a single image reference
Tolerance setting done by modeling graphical filters
Flexible (low volume, high mix)


Easy use of alternative components
“STAMP”
Ability to add “ Special Features ”
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A O I Types


Experience, Skill + Library required to make modeling easier (operator training)
More powerful computer needed
(higher resolution graphics & imaging)
A O I Types




 numbers (not images)
Many inspection fields for each component component / solder joint
Usually only Grey-scale analysis
Both “Self Learning” (via statistics) or “Fixed
1001
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A O I Types





Measurements based on exact numbers
Sometimes Rotation measurements possible
Simple calculations (only grey-scale and small frames)
Fast in combination with fast hardware
Pseudo 3D possible in case of angled cameras
A O I Types





Need large library
(extensive programming and experience)
New components or design need new modeling
(for library)
Modeling odd components (THT) complicated
Limited flexibility (e.g. low volume-high mix)
Additional technology for text needed
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A O I Types





More powerful detection (e.g. dark green
PCB with black components)
24bit vs. 8bit measurements
Requires more processing power and inspection time
Easier interface for Operators,
Programmers, Repairers
SMT industry uses many colours.
A O I Types ~ B&W vs. Colour
Dark components on dark green PCB
Nor mal lighting Gr ey only
- Poor contrast
- Difficult detection
Nor mal lighting Colour
- Good contrast
- Easy detection
Nor mal lighting Gr ey only
- Poor contrast
- Difficult detection
Nor mal lighting Colour + signal emphasis
- Good contrast
- Easy detection
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A O I Types
Two different Image Capturing devices:

Moving XY Field Camera

Line Camera or “Scanner”
A O I Types



Camera/Light head is moving
Mixed resolutions possible in one program
Lighting can be changed per inspection location



Omni directional lighting (360 degrees)
Larger Field Of View (FoV) increases speed
Orthogonal camera(s): Top view
(more cameras = more speed)

Angled cameras: Side view ~ Pseudo 3D speed slows down + increases programming time


Live picture easy for programming/debugging
Higher Pixel count image slows system, requires bigger PC and reduces depth of field

Stitching of image can also be an issue
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A O I Types






Fast scanning
Scanning time independent of component numbers
Single resolution per board
Single lighting per board (not 360 degrees)
Large file sizes
Inexpensive
A O I Types
Lighting systems
Top Light (around lens)


70-80 degrees normal inspection
White
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A O I Types
Lighting systems
Side light (around lens)



45 degrees
Better v isibility of text
V isibility of solder meniscus
Red
A O I Types
Lighting systems
Coloured lighting at different angles
Lights can be in different colours to help algorithms to “see” more information
White
+
Red
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A O I Types
Lighting Systems
Coaxial light ( through the lens)




Prism Construction
Light beam lands with 90º on PCB surface
High contrast between flat and non-flat items
Excellent visibility of solder defects
Top
White
Gold
A O I Types ~ Lighting
Silv er Tin O SP
C o
A xial
More lighting options offer a measurable difference
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A O I Types ~ Lighting effects
Melf Diode polarities
Nor mal lighting (Grey only)
- Poor contrast
- Difficult detection
Nor mal lighting Colour
- Good contrast
- Easier detection
Nor mal lighting Colour + Synthetic Imaging
- Good contrast
- Easy detection
Coaxial lighting + Colour Emphasis
(before Synthetic Imaging)
- Best contrast
- Easy detection and programming
A O I Types ~ Lighting effects
SOT23 Upside Down detection by joints
Component OK:
Nor mal lighting
- C ontrast O K
- Large meniscus v ariation
Component OK:
Red Side lighting (before Synthetic Imaging)
- Meniscus emphasized
- Easy detection w ith focus on meniscus
Component NOT OK (upside down):
Red Side lighting (before Synthetic Imaging)
- If SO T upside dow n, meniscus is gone
- C lear detection by Red Side light
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A O I Types / Solder ~ Lighting effects
Solder joint inspection: 4 ways

Synthetic modeling
Using different lighting settings

Sidelight Extraction + Synthetic modeling
A O I Types / Solder ~ Lighting effects
Solder joint inspection: 4 ways

Greyscale Thresholds
Set upper and lower limits

Sidelight Extraction & Histogram analysis
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How A O I Works ~ Component Library
1 ~ Automatically scan & map the board
2 ~ Import CAD / Gerber data
How A O I Works ~ Component Library
3 ~ Stamps
• Select component stamp from library.
• Or create stamp by selecting area around component.
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How A O I Works ~ Component Library
4. Place stamp over component.
 Software then seeks all components on
PCB matching this type.
5. Run program / adjust Filters until no false errors occur.
How A O I Works ~ STAMP Library
• Filter Settings
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A O I Types
A O I Type 1 ~ C orrelation
A O I Type 2 ~ Synthetic Imaging
A O I Type 3 ~ V ector Imaging
Moving from 2D to 3D Inspection

Typical Problems of 2D AOI
 Lifted Pins/Leads
 Flipped Components
 Lifted Components
• The 100%“ solution of the problems listed above is to have accurate component height information.
2D 3D
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Moving from 2D to 3D Inspection

Pseudo 3D
(Side/Angled View Camera)
 2D programming
 High Components/Shadows
 Local Information
 Inspection Speed
(Lasers)
 Very Local height information
 Unsuitable for Solder
Joint Inspection
 Inspection Speed
Real 3D with 2D overcomes most AOI issues
Shadow area Translucent surface Dark surface issue
Brightness
Real phase
Digitize
Error phase
2
1
0
4
3
6
5
Unwanted projection
Normal projection
Multiple reflections of projection
Multiple reflections
Normal projection
Unwanted projection
Multiple reflections of image acquisition
Brightness
Bright surface issue
Real phase
Saturation
Saturation level
Error phase
Position of stripe pattern
Position of stripe pattern
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Height Measurement Methods
Phase Measurement Profilometry
180deg phase
0deg phase
Phase round height
Base height
Brightness
One of raw images
Phase overlapped image
Phase difference
Position of stripe pattern
Illustration for imagination
The   High   End   Systems   calculate   zero   reference   correction   automatically   for   each   height   of   the   PCB   and   each   FOV.
The   correction   is   performed   to   calculate   the   average   value   of   the   points   that   have   been   recognized   as   the   PCB   surface   in   each   FOV.
Automatic Zero
Reference Correction
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Defect Examples in 3D View
Tombstone Chip Component - 01005in.
232um Bad
Defect Examples in 3D View
Lifted Leads of IC Component
192um Good
922um
181um
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A O I Types

Factors:
Which defects appear in my factory?


What is the required detection depth?
Large or small Batch sizes?





Is my process stable (False failure sensitivity)?
Is the an operator available for classification?
Is there a programmer available for programming?
What is my expected Pay-back time?
What is my investment/leasing budget
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