Brochure

181
System set-up
Figure 3-17 shows the concept of a two-dimensional (2D) X-ray microscopy system to inspect
small components consisting of a micro- or nanofocus X-ray tube, an X-Y-Z manipulator and
detector. The manipulator can be joystick- or CNC-controlled. Full automation is possible.
The geometric magnification can be controlled by the Z-axis. Closer to the tube results in a
larger magnification factor.
The set-up of figure 3-17 is used for flat components. For certain applications, dependent on
the geometry of the component, the so called “ovhm” technique (oblique view at highest mag-
nification) is in use.
In such cases an open transmission X-ray tube generates an adjustable oblique (angled) beam,
the detector is angled accordingly as illustrated in figure 4-17. Instead of tilting the sample,
which would result in a certain distance D that would limit the magnification factor, the beam
is tilted as
illustrated reducing D to almost zero.
180
D
Z
Y
X
0 -70°
Tube control
X-ray tube
Manipulator
Component
Detector (image chain)
Joystick / CNC
Image processing
Workstation
Fig. 3-17. System set-up for X-ray microscopy
Fig. 4-17. Oblique (ovhm) technique for maximum magnification.
Effect of focal dimensions
Figure 1-17 illustrates in one way the effect of focal spot size (unsharpness), figure 5-17
shows the same in another way for a micro- and nanofocus tube head.
Figure 6-17 shows the effect of focus size on images of a connection (wire diameter 25
micron) in an electronic package. Image A is taken with a focal spot size of 10 micron, image
B shows the result for a 5 micron focus and image C was taken with a focus of less than 1
micron. Details of approximately 250 nm are visible.
There are rules-of-thumb to determine resolution and potential defect detectability as
a function of focal spot size.
For large magnifications, exceeding 100x, the following applies:
• resolution equals the focal spot size divided by two
• detectability or feature recognition equals focal spot size divided by three
Focal spot : 10 microns 5 microns <1 micron
Fig. 6-17. Effect of spot sizes on image sharpness for different focal spot sizes
X-ray tube
Detector
Adjustable
detector position
Detector
ABC
Object
Source
Fig. 5-17. Effect of focal spot size on sharpness