X-ray or gamma ray systems or devices – Specific application – Tomography
Reexamination Certificate
2000-12-06
2004-06-08
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Tomography
C378S002000, C378S021000
Reexamination Certificate
active
06748046
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to imaging inspection systems and methods. Specifically, the present invention relates to an X-ray inspection system using tomosynthesis imaging techniques.
BACKGROUND OF THE INVENTION
The mounting of Integrated Circuits (“IC”) chips on Printed Circuit Boards (“PCBs”) requires inspection of the interconnections on the PCBs to determine whether the interconnections contain significant defects. Continual increases in the IC chip complexity, performance, and placement density place demands on the density and functionality of package interconnections. The Ball-Grid-Array (“BGA”) is one example of a Surface-Mount-Technology (“SMT”) package with interconnections that demand specialized inspection techniques. The continually increasing complexity and density of the PCB interconnections have resulted in the development of a number of interconnection inspection techniques for detecting defects on or within the interconnections.
One such interconnection inspection technique, tomosynthesis, is capable of detecting defects by creating a digital image representation of a sliced view along a single plane passing through a three-dimensional electrical solder joint connection. A digital tomosynthesis system makes it possible to inspect various PCB solder joint qualities, which cannot be inspected by visual methods or conventional X-ray radiography methods. U.S. Pat. No. 4,688,241 issued on Aug. 18, 1987 to Richard S. Peugeot, incorporated herein by reference, discloses a number of tomosynthesis inspection systems, including a system
10
depicted in
FIG. 1
of the instant application. The system
10
includes a steerable microfocus X-ray source
12
, a large-format image detector
30
capable of imaging X-rays, and an inspection plane
20
positioned between the source and the detector. As used herein, the term “steerable” in reference to the source
12
refers to the capability to direct an electron beam within the source
12
to various locations on a target anode. In contrast, a stationary or non-steerable source, as used herein, refers to a source that lacks such capability, i.e. the electron beam strikes the target anode at a single location.
The regions A, B, and C to be imaged may be placed on an X-Y table (not shown), which lies in the inspection plane
20
. When an object is on the X-Y table, the test object may be translationally moved along the x and y directions so that a region of interest, such as a solder joint, can be imaged. The source
12
produces an X-ray beam
50
having sufficient energy to penetrate the test object and reach the detector
30
, while also having a low enough energy so that a resulting image has contrast within the region of interest.
The X-ray source
12
and the detector
30
may be mounted on independent vertical drive mechanisms allowing a continuously variable field-of-view, ranging from approximately 2.5 mm×2.5 mm to approximately 25 mm×25 mm, to be obtained. In particular, the X-ray source
12
is mounted on a programmable Z-axis, which changes the distance between the X-ray source
12
and the inspection plane
20
. The distance between the X-ray source
12
and the plane
20
is referred to herein as Z
1
. The detector is also mounted on a programmable Z-axis, which changes the distance between the inspection plane
20
and the detector
30
. The distance between the inspection plane
20
and the detector
30
is referred to herein as Z
2
. Variation of the field of view may be accomplished by varying either or both distances Z
1
and Z
2
.
The operation of the system of
FIG. 1
now will be explained. A circuit board having regions of interest A, B, and C is positioned on the X-Y table, in the inspection plane
20
. The board is then moved translationally along the x and y directions so that a region of interest A, B, or C, such as a solder joint, or a component can be imaged. Once the board is properly positioned, a beam of radiation, such as X-ray beam
50
, is projected towards an object on the circuit board. A portion of the X-ray beam
50
transmits through and is modulated by the object.
The portion of the beam
50
that passes through the object then strikes the image detector
30
. The detector
30
is capable of producing an X-ray shadowgraph containing the modulation information from the test object. The X-rays striking the input screen of the detector
30
produce a visible light or shadowgraph image of the volume of the object that falls within the X-ray beam
50
. If the detector
30
includes an image intensifier, the image at the output of the image intensifier is amplified in brightness.
The image that appears on the output face of the detector
30
is viewed, through a mirror, by a video camera (not shown). The images from various regions of the detector
30
, such as the regions numbered
1
,
3
,
5
and
7
in
FIG. 1
, may be sequentially directed to the camera by adjusting the position of the mirror.
The resulting images are then input into a video digitizer. The video digitizer provides as an output digitized image sets. Each image in the set is supplied to a memory and stored. The images may then be separately fed into a tomosynthesis computer, which is programmed with a known tomosynthesis algorithm that effects a combination of the images and provides a resultant image to a monitor. In order to improve the resolution of the digitized image sets, it is desirable to limit the field of view of the camera to a region of the detector
30
, such as the regions
1
,
3
,
5
or
7
, rather than to acquire images for tomosynthesis viewing the entire detector
30
.
For system
10
, the center of the region of interest must coincide with a line extending from the center of the path of the x-ray source to the center of the detector
30
. As can be seen in
FIG. 1
, the center of object B coincides with the centerline of X-ray beam
50
and the center of the field of view of detector
30
.
To acquire tomosynthetic images for object B, for example, the X-ray source
12
is positioned at multiple points
1
-
8
along a circular path that is perpendicular to the Z axis. Each point on the circle falls in a plane that is perpendicular to the Z axis and maintains the same angle with, or is equidistant from, the Z axis. At each point, the X-ray source
12
emits an X-ray beam
50
towards, and at least partially through, the object B, thereby generating an image of object B at the detector
30
. For example, to acquire image
1
for object B, the X-ray source
12
is steered to position
1
and the detector field of view is moved to position
1
. This process is repeated for images
2
through
8
of object B. The 8 images are acquired sequentially since the electron beam inside the X-ray source housing and the detector field of view must be moved after each acquisition. As a result, 8 scanned images of object B at a known pre-determined angle are captured.
After the required images of object B are taken, then the X-Y table is moved so that the center of object A coincides with the centerline of the X-ray beam
50
and the center of the detector field of view. To acquire image
1
for object A, the X-ray source
12
is steered to position
1
and the detector field of view is moved to position
1
. This process is repeated for images
2
through
8
of object A. Thus, 8 scanned images of object A are captured. This process is continued for each of the objects, or regions of interest, to be imaged.
In order for tomosynthesis to be effective, the angle phi should be at least a 25-30 degree angle from perpendicular to generate a useful tomosynthetic slice of the object. However, the practical limitations of the diameter of the X-ray source, the diameter of the detector, the distance between the source and the object, Z
1
, and the distance between the object and the detector, Z
2
, result in compromises to be made with respect to the angle that can be achieved, the field-of-view, the resolution, and the speed of the system. In order to achieve the desired angle and
Bruce David V.
Kiknadze Irakli
McDonnell & Boehnen Hulbert & Berghoff
Sampson Matthew J.
Teradyne, Inc.
LandOfFree
Off-center tomosynthesis does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Off-center tomosynthesis, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Off-center tomosynthesis will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3339410