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Real-Time X-Ray Imaging Theory for EMS Inspection Systems
- Added: March, 30th 2011
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- Name: lantos
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for EMS Inspection Systems
X-Ray System Terminology
X-Ray Imaging System Components
Basic X-Ray Physics, Principles and Theory
SMT Component Test Access by Package Type
(858) 536-5050 | www.focalspot.com
The Inspection & Rework Specialists
Real-Time X-Ray Imaging (Major Components)
1.
X-Ray Tube (Source): A vacuum tube containing a filament
(Cathode) and a tungsten “target” (Anode). The target is
bombarded with fast-moving electrons which produce x-rays in
relation to the quantity of power applied.
2.
Sample Manipulator (Board Holder): This fixture positions
the inspection sample within the path of the x-rays and provides
off-axis (tilt /rotate) of the sample between the source and
detector.
3.
X-Ray Image Detector (Scintillator or Image Intensifier):
The II converts x-rays into visible light (photons), and then
amplifies these low-level photons to a visible real-time image,
thereby permitting lower x-ray doses to be used during
inspection.
4.
Camera (lens optics and CCD Sensor): The optics focuses and
magnifies the image, while the CCD sensor converts visible light
into electrical signals (RS-170, grayscale video).
5.
Image Processor: (Computer, Frame Grabber & Software):
The Frame Grabber converts the (analog) RS-170 video signal into
digital signals and displays “live” x-ray images in real-time. While
the Image Processing software provides tools to enhance,
analyze, measure and report quality characteristics displayed in
the grayscale images of the sample under inspection.
Power to Spot Size Relationships
• Relative Relationships of Spot Size to Applied Power
Tech Note: Nanofocus spot size grows to microfocus size as the power to penetrate
materials of relative density and/or thickness is increased.
Spot Size (Resolution)
• Spo t Size is the size of the electron spot on the emission side
of a tungsten target (used to generate x-rays). This is a
function of an x-ray tubes ability to focus the electron beam
and is a major component of image resolution.
• Factors of X-Ray Resolution:
– Spot Circularity (roundness)
– Applied Power (watts)
50 micon
– Field-of-View / Magnification
35 micon
– Material Density
(Resistance to X-Ray Penetration)
Components of X-Ray Resolution
•
Spo t Size: X-ray spot size is the size of the electron spot on the emission
side of a tungsten target. This is a function of an x-ray tubes ability to
focus the electron beam.
•
Spot Circularity: In combination with spot size also determines image
resolution. The more symmetrically round a spot shape is the better the
image quality.
•
Applied Power: Spot size will de-focus (bloom) as the power to penetrate
materials of relative density and/or thickness is increased.
•
Unsharpness Effect: X-Ray imaging at <40X magnification will cause a
condition known as the “Unsharpness Effect”. This occurs when x-rays are
distributed across a broader image detection area, as in the case of low-
magnification / large field-of-view, which makes an x-ray image appear
fuzzy or de-focused.
Geometrical Unsharpness (Penumbra Effect)
• The size of an x-ray Focal Spot on the source target will affect
the blurred perimeter of the image (penumbra).
Image Quality Indicators
• A Line Pair Gauge has calibrated angular lines converging to a
single point. Line-to-space ratios determine line pair
resolution. (most common measure for x-ray resolution)
• A Calibrated Zone Plate has a grid of concentric circles and
patterns. Bar-to-space ratios determine resolution in microns.
Sample Handling Systems
• Sample Manipulation refers to the ability of a sample to be
positioned within the image area during real-time x-ray
inspection.
Example: Verifier Series
Example: Concept FX Series
X-Ray Inspection System
X-Ray Inspection System
Component Handling
Fixed Rotation
No Clamp Sample Tray
Manipulator Systems (Rotation Fixtures)
• Sample manipulator systems (such as Rotation Fixtures) can
be Manual, Motorized or Logic Controlled (automated by macro
or test programming software).
• Each type of board manipulation system will influence machine
cost and operator convenience, but makes little difference to
the effectiveness of the inspection.
Manual Rotation Fixture
Motorized Rotation Fixture
Large Board Rotation Fixture
Off-Axis Sample Manipulation
•
Off-Axis Sample manipulation is accomplished to reveal shape, size faults,
etc. of electrical solder connections. This is especially important with
double-sided boards, where top and bottom side components may obscure
clear viewing of object details.
40°
40°
Z2
Y
Z1
Motorized Rotation Fixture
Ro
X
tate
Z3
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