X-ray or gamma ray systems or devices – Specific application – Tomography
Reexamination Certificate
2000-03-24
2004-11-23
Glick, Edward J. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Tomography
C378S021000
Reexamination Certificate
active
06823040
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of X-ray inspection and an apparatus used for the method and, more particularly, to a method of X-ray inspection for inspecting the mounting condition (connection) of electronic devices such as BGAs (Ball Grid Arrays) and CSPs (Chip Scale Packages) which are small in size and have high densities on boards and the like using X-rays and an apparatus used for the method.
2. Description of the Relevant Art
In recent years, the performance of cellular phones, personal computers, video and audio equipment and the like has been getting remarkably higher. What makes it possible is IC packaging technology, which is at the core of the high performance. The density of packages for mounting IC chips and the speed of signal processing have been getting higher.
In particular, array packages such as BGAs and CSPs, which have recently appeared as a means of enabling an innovative packaging technology, and which are effective in having more terminals, have attracted attention.
However, though array packages such as BGAs are excellent at having more terminals, it is difficult to judge whether the mounting condition of an array package on a printed circuit board is good or bad by an optical or a laser visual inspection, since, on account of the construction thereof, the connecting portion of the package and the printed circuit board is hidden from sight by the package itself when it is mounted on the printed circuit board. In the case of fine-pitch packages, it is difficult to accurately pinpoint the location of defects even by an electrical test.
FIG. 1
is a perspective view diagrammatically showing the state of an example of a BGA
1
seen from the side of terminals.
FIG. 2
is a perspective view diagrammatically showing a printed circuit board
2
in a situation where the BGA
1
shown in
FIG. 1
is mounted thereon. As is obvious from
FIG. 2
, it is extremely difficult to judge by their appearance whether the connection condition of solder balls
1
a,
except for those at the outermost periphery of the BGA
1
and the printed circuit board
2
, is good or bad when the BGA
1
is mounted on the printed circuit board
2
.
Present exemplary techniques of inspecting the connection condition of an array package such as a BGA and a printed circuit board, include a system wherein various and precise two- or three-dimensional perspective images of the connecting portion, seen from a given direction, are obtained (radiography), and a system wherein sectional images of the connecting portion taken as if it had been sliced on a plane parallel to the main surface of the printed circuit board (so-called transverse sectional images) are obtained (sectional radiography).
Radiography uses an X-ray three-dimensional inspection apparatus, for example.
FIG. 3
shows examples of X-ray photographs of the connecting portion taken using the X-ray three-dimensional inspection apparatus for radiography.
As is obvious from
FIG. 3
, by utilizing the X-ray three-dimensional inspection apparatus, the inner shape, which cannot be observed from the outside, can be observed as perspective images. Therefore, even if the inner shape is complicated, whether the inner condition is good or bad can be judged with fair precision.
However, it is difficult to precisely detect the open state of terminals (solder balls) which users like to inspect most in the mounting of array packages such as BGAs and CSPs, forming the heart of the latest high-density packaging.
FIG. 4
diagrammatically shows an example of the open state of solder balls.
By obtaining transverse sectional (horizontal slice) images of the connecting portion at two or more vertical positions thereof using sectional radiography, and measuring and comparing the degrees of shadow, the inner shape thereof can be inspected to some extent.
However, it is essentially difficult to precisely detect open terminals (solder balls) in the situation where an array package such as a BGA or a CSP is mounted on a printed circuit board through slice-shaped sectional images of transverse sectional images, because it means trying to detect an open state, which appear in a direction vertical to the main surface of a printed circuit board from the horizontal direction.
SUMMARY OF THE INVENTION
The present invention was achieved in order to solve the above problems. It is an object of the present invention to provide a method of and apparatus for X-ray inspection whereby the condition of electronic equipment, like the mounting condition of electronic devices such as BGAs and CSPs, which are steadily getting smaller and reaching higher densities on boards, and particularly open terminals, can be precisely judged.
As described above, hitherto the connecting portion of an array package, such as a BGA and a printed circuit board, hidden from sight by the package itself, has been inspected using perspective images from horizontal or oblique directions (see
FIG. 3
) or transverse sectional images. But it is essentially impossible to precisely detect opens terminals (solder balls) by these inspection systems.
The present inventor noticed that open solder balls (see
FIG. 4
) are problems essentially appearing in a direction vertical to a BGA or the main surface of a printed circuit board, rather than in a direction parallel thereto, and appreciated that the detection of open solder balls can be certainly carried out by obtaining sectional images which are vertical to the main surface of a printed circuit board (so-called vertical sectional images), and not by obtaining sectional images which look as if the printed circuit board had been sliced in a direction parallel to the main surface thereof (transverse sectional images) as before. By finding a method whereby vertical sectional images can be photographed, and developing an apparatus with which the method can be realized, the present invention was completed.
FIGS.
5
(
a
) and
5
(
b
) are diagrams showing vertical sectional images of a connecting portion. FIG.
5
(
a
) shows a case wherein no defective connection exists, and FIG.
5
(
b
) shows a case wherein open solder balls
1
a
exist.
A method of X-ray inspection according to the present invention, wherein a section of a sample is photographed using X-rays to be inspected, includes arranging an X-ray source to apply X-rays and an X-ray detecting means to detect X-rays facing each other with the sample in between. An X-ray incidence plane in the X-ray detecting means is made parallel to the section. The X-ray detecting means is swung about a straight line on the same plane with the section as the central axis, with the parallel relationship between the X-ray incidence plane and the section maintained, while applying X-rays to the sample from the X-ray source as the X-ray source is rotated about the straight line on the same plane with the section as the axis of rotation in synchronization with the X-ray detecting means. X-rays passing through the sample in the X-ray detecting means are then detected.
In the method of X-ray inspection, by mutually moving the X-ray source and the X-ray detecting means while a uniform geometric relationship between them is maintained on the basis of a section of the sample as the subject, a section which is a base of the movements is in a state where it can be regarded as being fixed. On the other hand, the more distant other portions are from the base of the movements, the larger the deformation of the images thereof becomes. As a result, the images thereof become obscure, so that they cannot be the subject of visual recognition. Accordingly, a vertical sectional image is successfully obtained.
This principle is described below using diagrams in
FIGS. 6-8
, provided for describing the method of X-ray inspection.
FIGS. 6
,
7
and
8
show a plan view, a front view, and a side view, respectively.
FIG. 9
is a perspective view diagrammatically showing a sample.
In the figures, reference numeral
13
represents a sample, and the sample
13
is placed on a st
Glick Edward J.
Song Hoon
Techno Enami Corporation
Wenderoth , Lind & Ponack, L.L.P.
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