JPH04310813A - X-ray inspection apparatus - Google Patents

Abstract

PURPOSE:To make it possible to enlarge the magnification of an X-ray transmission image by making an X-ray focus of an X-ray generating source approach a substance to be inspected and, besides, to enable application of an X-ray in an arbitrary direction, regarding an X-ray inspection apparatus being employed for automatic inspection of a printed circuit board after packaging, in particular. CONSTITUTION:An X-ray generating source comprising an electron emitting means 2, an acceleration electrode 3 accelerating an electron emitted from the electron emitting means 2 and a target 4 subjected to application of the electron accelerated by the acceleration electrode 3 and generating an X-ray, a stage 6 moving with a substance 5 to be inspected which is set thereon, and an X-ray detector 7 detecting the X-ray generated by the X-ray generating source and transmitted through the substance 5, are provided in a vacuum case body 1 having an exhaust port 8. A vacuum pump is provided so that it communicates with the exhaust port 8 of the vacuum case body 1.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to an X-ray inspection apparatus, in particular,
The present invention relates to an X-ray inspection device used for automatic inspection of printed circuit boards after mounting.

0002

[Background Art] In recent years, with the miniaturization of electronic devices, the mounting density of printed circuit boards has increased, and in circuit systems of large computers, the length of wiring connecting LSIs is shortened to propagate signals. To improve speed, LS
It is desired to provide the input terminal of I within the size range of the LSI chip, and the flip-chip bonding method is attracting attention as a means to meet this demand.

What is the flip chip bonding method?LS
This is a method in which lead/tin based solder is formed into a ball shape on the electrode pad part of the I through a thin film electrode metal, and by reflowing it, it is bonded all at once to the electrodes formed on the printed circuit board. Excellent in terms of high reliability and high productivity.

The details of the flip chip bonding process will be explained below with reference to FIG.

Referring to FIG. 2, as shown in FIG. 2(a), a thin film electrode 32 made of gold or the like is formed on the electrode of a semiconductor chip 31.

As shown in FIG. 2B, solder balls are placed on thin film electrodes 32 or solder is supplied using a vapor deposition method, and solder bumps 33 are formed by heating and melting the solder.

On the other hand, as shown in FIG. 3C, electrodes 35 made of gold or the like are formed on the printed circuit board 34 at positions corresponding to the bumps 33 of the flip chip.

As shown in FIG. 1D, a glass dam 36 is formed in a region surrounding the solder bump forming region, and solder bumps 37 are formed using the same method as in the case of the semiconductor chip 31 described above.

As shown in FIG. 3(e), the printed circuit board 3
The bumps 33 of the semiconductor chip 31 are superimposed on the solder bumps 37 formed on the semiconductor chip 31.

As shown in FIG. 3(f), solder bumps 33
and 37 are heated and melted to form an integrated bump 38, and the semiconductor chip 31 and printed circuit board 34 are connected. At this time, the positions of the bumps on the semiconductor chip and the bumps on the printed circuit board are automatically aligned due to the surface tension of the molten solder. Figure (g) is a perspective view after connection.

By the way, typical examples of the shapes of solder bumps after being connected in this manner are shown in FIGS. 3 and 4.

Refer to FIGS. 3 and 4 The bump shape shown in FIG. 3 is determined to be normal;
The bump shape shown in FIG. 4 has the following defects. In other words, in Figure (a), the fusion between the bumps is insufficient;
Figures (b), (c, and d) are locally constricted, Figure (e) has a void inside, Figure (f) has a positional shift, and Figure (g) shows that the upper end is It's getting thinner.

[0013] Therefore, it is necessary to inspect the bonding state of each bump after flip chip bonding, but when using an optical method, it is not possible to inspect the bumps formed on the outer periphery of the flip chip. However, it is impossible to inspect the bumps formed inside. Further, when inspecting using X-rays, there is a problem in that if the X-rays are irradiated from directly above, it is not possible to accurately determine the outline of the bump as shown in FIGS. 3 and 4. To solve this problem, it is necessary to irradiate the bumps with X-rays from right sideways.

By the way, the X-ray generation source used in the conventional X-ray inspection apparatus will be explained below.

Refer to FIGS. 5(a) and 5(b) FIG. 5(a) is a configuration diagram of a reflection type X-ray generation source. In the figure, 24 is connected to a vacuum pump 25, and the inside is maintained in a vacuum. 21 is a filament that generates electrons, 22 is a bias cup, and 26 is a target. X-rays generated when the electron beam generated by the filament 21 collides with the target 26 are extracted to the outside through the beryllium window 27.

FIG. 5(b) is a block diagram of a transmission type X-ray generation source, and the same components as those shown in FIG. 5(a) are indicated by the same symbols. X-rays are generated from the back surface of the target 26.

[0017]

[Problem to be Solved by the Invention] Refer to FIG. 6 Assuming that the X-ray focal point size of the X-ray source is close to a point, as shown in FIG.
The distance from the X-ray focal point 51 to the object 52 (52a, 52b) is a (a1 ・a2), and the object 52 (52a, 52b) is
2a, 52b) to the detector 53 is b(b1
・b2), the magnification rate M of the X-ray transmission image is M=(a+b)/a. Therefore, the shorter the distance a between the X-ray focal point 51 and the object to be inspected 52, and the longer the distance b between the object to be inspected 52 and the detector 53, the larger the projected image becomes. increases, and inspection accuracy improves.

However, when increasing the distance between the object to be inspected and the detector, the air that exists between them causes the X-rays to
It is absorbed and scattered, resulting in poor S/N ratio. Therefore, in order to increase the magnification, it is necessary to shorten the distance a between the X-ray focal point 51 and the object to be inspected 52.

However, when using the conventional reflection type X-ray source shown in FIG. 5(a), the distance between the X-ray focal point and the object to be inspected is
It cannot be shorter than the distance from 7.

Furthermore, when using the transmission type X-ray source shown in FIG. 5(b), when irradiating X-rays perpendicularly to the object to be inspected, it is necessary to limit the object to the X-ray focal point. It is possible to get close without any problems. However, when the object to be inspected is irradiated with X-rays obliquely, the casing 24 of the X-ray source comes into contact with the object 5, as shown in FIG. The object to be inspected 5 cannot be brought close. especially,
In the case of a two-dimensional plate-shaped object with a large width, such as a printed circuit board, this restriction becomes more severe.

In FIG. 7, using an X-ray source whose housing 24 has a cylindrical shape with a radius r, the object 5 to be inspected is
When irradiating X-rays with an irradiation angle θ, the part to be inspected is
The minimum distance d that can approach the line focal point is d=r/tan θ.

Therefore, as the irradiation angle θ becomes smaller, the distance d between the X-ray focal point and the object to be inspected becomes longer, and the image magnification ratio decreases. That is, if an attempt is made to irradiate a flip-chip bonding bump with X-rays from right side, there is a drawback that a sufficient image magnification cannot be obtained.

An object of the present invention is to eliminate this drawback, and it is possible to increase the magnification of an X-ray image by bringing the X-ray focal point of the X-ray source close to the object to be inspected, and furthermore, An object of the present invention is to provide an X-ray inspection device that can irradiate X-rays in any direction.

[0024]

[Means for Solving the Problems] The above object is to provide an electron emitting means (2), an accelerating electrode (3) for accelerating the electrons emitted from the electron emitting means (2), and an accelerating electrode (3) that accelerates the electrons emitted from the electron emitting means (2). an X-ray generation source consisting of a target (4) that is irradiated with electrons and generates X-rays; a stage (6) on which an object to be inspected (5) is placed and moves; An X-ray detector (7) for detecting X-rays generated by the transmitted X-ray source is provided in a vacuum housing (1) having an exhaust port (8). 1) Exhaust port (8)
This is achieved by an X-ray inspection device which is provided with a vacuum pump (9) in communication with the .

Note that the X-ray detector (7) is provided outside the vacuum casing (1), and the X-ray detector (7) of the vacuum casing (1) is
) may be formed with an X-ray transmitting window (10) in the area facing the area.

[0026] Furthermore, it is preferable that at least one low vacuum chamber (41) is provided in connection with the vacuum casing (1).

Furthermore, the target (4), the electron emitting means (2), and the X-ray detector (7) are each movable, and the X-ray source is a micro focus type. It is preferable that

[0028]

[Operation] Fig. 1 shows a diagram explaining the principle.

Referring to FIG. 1, reference numeral 1 denotes a vacuum casing, which is maintained in a vacuum by a vacuum pump 9. As shown in FIG. Inside the housing 1 is an electron emitting means 2 consisting of a filament 21 that generates electrons, a bias cup 22 that controls the amount of electrons, and an electron lens 23 that deflects and focuses the electrons, and an electron emitting means 2 that accelerates the electrons emitted from the electron emitting means 2. It is equipped with an accelerating electrode 3, a target 4 that is irradiated with accelerated electrons to generate X-rays, and a stage 6 on which an object to be inspected 5 is placed and moves. is detected through the beryllium window 10 by an X-ray detector 7 such as an X-ray image intensifier. 11 is a power source that accelerates electrons. In addition, X with respect to the inspected object 5
Depending on the radiation direction, the X-ray detector 7 may be provided inside the housing 1.

In this way, by providing the object to be inspected 5 and the target 4 in the same vacuum housing, the target 4
The X-ray focus can be brought closer to the inspected object 5, and the S/N
It is possible to increase the magnification without deteriorating the ratio. Further, since the target 4 can be inserted between the chips of the mounted printed circuit board, it is possible to easily irradiate the mounted components with X-rays from right side.

Note that the resolution of the X-ray image is improved by using a microfocus type X-ray generation source.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An X-ray inspection apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

Refer to FIG. 8 FIG. 8 shows a configuration diagram of the X-ray inspection apparatus. In the figure, the same parts as those shown in FIG. 1 are indicated by the same symbols. Note that the vacuum casing is omitted to avoid complicating the drawing.

An example of inspecting the results of flip-chip bonding of a mounted printed circuit board will be described below.

The stage controller 12 drives the stage drive motor 12a to move the stage 6 so that the target 4 is located between the chips 31 mounted on the printed circuit board 34.

The target controller 13 drives the target drive motor 13a to insert the target 4 between the chips 31.

The electron emitting means controller 14 drives the electron emitting means drive motor 14a to move the electron emitting means so that the target 4 is irradiated with the electron beam.

The X-rays generated from the target 4 irradiate the bump 38 , which is the object to be inspected, from almost directly sideways, and the X-ray image transmitted through the bump 38 is detected by the X-ray detector 7 . Note that it is preferable that the X-rays be irradiated in a direction that reduces the overlap between the bumps.

The image detected by the X-ray detector 7 is A
The signal is converted into a digital signal by the /D converter 15, and is input to the memory 17 via the image input circuit 16 as a gray scale image, after which edges are extracted by the CPU 18 and the outline of the bump is output. The outline of this bump is evaluated to determine whether the bonding is good or bad. Note that which bump was inspected is determined by the moving direction and moving distance of the stage 6, which are input via the I/O board 19, and the X-ray image magnification.

When the inspection of one chip is completed, the printed circuit board 34 is moved using the stage 6, and the above-mentioned inspection process is repeated for the next chip.

Refer to FIG. 9 There is a problem that the degree of vacuum inside the casing 1 decreases when the object to be inspected is carried into and out of the casing 1. ), low vacuum chambers 41 and 42 are provided in connection with the high vacuum casing 1. The low vacuum chambers 41 and 42 are maintained at a low vacuum by a rotary pump 43, and the casing 1 is maintained at a high vacuum by a turbo pump 44.

To carry in the object to be inspected, first close the cock 45 of the rotary pump 43 in the low vacuum chamber 41, open the shutter 46, and move the object 5 to be inspected.
1 into the low vacuum chamber 41, the shutter 46 is closed and the cock 45 is opened to evacuate the low vacuum chamber 41.

As shown in FIG. 9(c), the cock 45 is closed, the shutter 47 is opened, and the object 51 to be inspected is carried into the housing 1 of the X-ray inspection apparatus. At this time, the low vacuum chamber 42 is evacuated using a rotary pump.

After the X-ray inspection is completed, as shown in FIG. 9(d), the cock 48 of the low vacuum chamber 42 is closed, the shutter 49 is opened, the object to be inspected 51 is moved to the low vacuum chamber 42, and the shutter 49 is closed. .

Finally, as shown in FIG. 9(e), the shutter 50 is opened and the object to be inspected 51 is carried out.

[0046] Note that only one low vacuum chamber may be provided, and the same low vacuum chamber may be used for carrying in and carrying out the object to be inspected.

[0047] In this way, it is possible to reduce the vacuum drop in the housing 1 equipped with the X-ray inspection apparatus and increase the inspection throughput.

[0048]

[Effects of the Invention] As explained above, in the X-ray inspection apparatus according to the present invention, the X-ray generation source and the stage on which the object to be inspected is placed and moved are provided in the same vacuum housing. Since the target for generating X-rays can be brought close to the object to be inspected, it is possible to increase the magnification of the X-ray transmission image and improve inspection accuracy without degrading the S/N ratio. Furthermore, by moving the target, it is possible to irradiate the object to be inspected with X-rays in any direction, which is extremely effective for inspecting flip-chip bonding of mounted printed circuit boards.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining the principle of the present invention.

FIG. 2 is a process diagram of flip chip bonding.

FIG. 3 is a shape diagram of a normal bump.

FIG. 4 is a shape diagram of a defective bump.

FIG. 5 is a configuration diagram of an X-ray generation source.

FIG. 6 is a diagram illustrating the magnification ratio of an X-ray transmission image.

FIG. 7 is a diagram illustrating problems in the prior art.

FIG. 8 is a configuration diagram of an X-ray inspection apparatus according to the present invention.

FIG. 9 is an explanatory diagram of a method for carrying in and out an object to be inspected when a low vacuum chamber is provided.

[Explanation of symbols]

1 Vacuum housing 2　Electron emission means 3 Accelerating electrode 4 Target 5 Object to be inspected 6 Stage 7 X-ray detector 8 Exhaust port 9 Vacuum pump 10 X-ray transmission window 11 Acceleration power supply

Claims (5)

[Claims] 1. An electron emitting means (2), an accelerating electrode (3) for accelerating the electrons emitted from the electron emitting means (2), and an X-ray beam irradiated with the electrons accelerated by the accelerating electrode (3). an X-ray generation source consisting of a target (4) that generates
and an X-ray detector (7) that detects the X-rays generated by the X-ray source that have passed through the object to be inspected (5).
), and a vacuum pump (9) is provided in communication with the exhaust port (8) of the vacuum housing (1). Line inspection equipment. 2. The X-ray inspection apparatus according to claim 1, wherein the X-ray detector (7) is provided outside the vacuum housing (1), and the X-ray detector (7) of the vacuum housing (1) 7) An X-ray inspection apparatus characterized in that an X-ray transmission window (10) is formed in a region facing the. 3. The X-ray inspection apparatus according to claim 1, further comprising at least one low vacuum chamber (41) connected to the vacuum housing (1). 4. The target (4), the electron emitting means (2), and the X-ray detector (7) are each movable. The X-ray inspection device described. 5. The X-ray inspection apparatus according to claim 1, wherein the X-ray generation source is of a micro focus type.