JP3969337B2 - Bump inspection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for inspecting bumps formed on a substrate, for example, an apparatus for nondestructively inspecting solder bumps formed on a substrate for mounting and mounting a semiconductor chip.
[0002]
[Prior art]
As a substrate to be inspected in the present invention, for example, as shown in FIG. 2, a plurality of solder bumps 4 are arranged on the surface of the substrate 2, and a plurality of pads 6 are formed on the back surface of the substrate 2. Individually formed. In this substrate, bumps 4 and pads on the back surface are connected by wiring formed in the substrate. The substrate 2 is mounted with the IC chip 8 on which the semiconductor device is formed placed on the solder bump formation region of the substrate 2 with its pad formation surface facing downward, and the chip 8 is connected to the substrate 2 by the solder bump 4. It is what is done. Thereafter, a terminal is attached to the pad 6 on the back surface of the substrate 2, a case is put on the chip 8, and a heat radiating fin is attached to form a packaged semiconductor device such as a CPU chip. The substrate to be inspected by the present invention is in a state before the chip 8 is mounted.
[0003]
As a method for inspecting a solder bump, a defect of the bump is detected by irradiating the X-ray, detecting the X-ray transmitted through the bump, and performing image processing (for example, Patent Document 1). reference.).
[0004]
In such an inspection apparatus using X-rays, generally, a substrate to be inspected is arranged with bumps facing upward, an X-ray generator is provided on the lower side, and X-rays transmitted through the substrate are placed above the substrate. It arrange | positions so that it may detect with the provided X-ray detector. This is partly to allow visual inspection of the bumps to be inspected.
[0005]
In an apparatus in which an X-ray generator is disposed under an object, the inspection object is often placed on a support plate such as a carbon plate in order to support the inspection object. An image tube is generally used as a detector.
[0006]
As for the X-ray detector, a flat panel is used in medical X-ray CT. The flat panel has features such as low distortion and good resolution, but the flat panel is not generally used in a substrate inspection apparatus or the like. This is because the flat panel has a drawback of low sensitivity.
[0007]
[Patent Document 1]
JP-A-2001-358161
[Problems to be solved by the invention]
The configuration of the conventional inspection apparatus in which the inspection object is arranged with the bumps facing upward and the X-ray generator is provided on the lower side has the following problems.
When the inspection object is supported so that the bumps face upward, at least the thickness of the substrate of the inspection object exists between the X-ray generator and the bumps. Further, when the inspection object is placed on and supported by a support member such as a carbon plate, the thickness of the support member is also added. Therefore, there is a problem that the distance between the X-ray generator and the bumps cannot be kept below a certain level. Further, since the substrate thickness of the inspection object varies depending on the object, there is a problem that the distance between the X-ray generator and the bump is not constant.
[0009]
For solder bumps, not only inspection of the outer diameter shape but also inspection of whether or not voids (voids) exist inside is important, but in this type of conventional inspection apparatus, the bump and X-ray generator Since there is a limit to approaching the distance, not only is the S / N ratio (signal-to-noise) of the obtained image low, but the distance between the X-ray generator and the bump is not constant, so the size of the void, etc. It leads to the problem that it is difficult to measure stably.
Accordingly, an object of the present invention is to improve the S / N ratio of an X-ray image so that a bump can be inspected stably.
[0010]
[Means for Solving the Problems]
The present invention provides a bump inspection apparatus that inspects a plurality of bumps formed on a substrate by transmission of X-rays, and supports a substrate that is an object to be inspected so that the bump forming surface faces downward. A substrate support mechanism that can be moved by the X-ray generator, an X-ray generator that is disposed below the substrate supported by the substrate support mechanism and emits X-rays upward, and an X-ray above the substrate supported by the substrate support mechanism And a flat panel as an X-ray detector arranged at a position for detecting X-rays emitted from the generator.
[0011]
In the present invention, since the bump forming surface of the substrate that is the inspection object faces the direction of the X-ray generator, the observation site that is the inspection object, that is, the distance between the bump and the X-ray generator can be reduced. it can. Therefore, it is possible to increase the detection accuracy of the voids of the bumps.
[0012]
Furthermore, the flat panel which is a detector can also be brought close to the tube. By adopting such an arrangement, the brightness of the detector increases even with the same imaging magnification and the same X-ray output. When an image tube is used as a detector as in a conventional apparatus, the detector is saturated with this arrangement. Further, when the image tube is brought closer to the X-ray generator by a certain distance or more, shading becomes tight based on the curvature of the image tube, the luminance distribution of the obtained image becomes non-constant, and image processing after binarization becomes difficult.
[0013]
On the other hand, since a flat panel is used as a detector according to the present invention, there are no problems such as shading, and the disadvantage of the flat panel that the brightness is low is an advantage only in the present invention, Since the output is difficult to saturate, the output can be increased within a margin of the X-ray generator, and as a result, the S / N ratio of the image can be improved.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Next, based on an Example, this invention is demonstrated in detail.
FIG. 1 schematically shows an embodiment. A substrate support mechanism 10 supports the substrate 2 to be inspected so that the bump forming surface faces downward. The substrate support mechanism 10 includes a tray-like substrate holder 12 for supporting the substrate 2 with its bump formation surface facing downward and the bumps 4 exposed. The substrate support mechanism 10 includes a drive mechanism such as an XY stage so that the substrate 2 is supported in a horizontal plane and can be positioned in the inspection position by moving in the X and Y directions in the horizontal plane. The movement is controlled by the unit 14.
[0015]
An X-ray generator 16 is disposed and fixed below the substrate 2 supported by the substrate support mechanism 10. The X-ray generator 16 includes an X-ray tube, and X-rays 18 generated from the X-ray tube pass through the substrate 2.
[0016]
A flat panel 20 as an X-ray detector is disposed above the substrate 2 supported by the substrate support mechanism 10 so as to face the X-ray generator 16. An image processing apparatus 22 captures an X-ray image detected by the flat panel 20 and determines the shape of the bump 4 and the presence or absence of voids therein.
[0017]
In this embodiment, the substrate 2 supported by the substrate support mechanism 10 is positioned at the inspection position by the movement control unit 14, and the X-rays 18 irradiated from the X-ray generator 16 pass through the bumps 4 on the substrate and are flat paneled. 20, the X-ray image is taken into the image processing device 22 to determine whether the bump is good or bad.
[0018]
FIG. 3 schematically shows a target portion of the X-ray generator. X-ray tube 16a for the X-ray generator 16, the comprises a target 16b in the vacuum region of the (lower side in the drawing) inside, X from the target 16 b by the electron beam 27 is irradiated on the target 16b Line 18 is generated.
[0019]
FIG. 4 shows an example of a preferred arrangement of the substrate support mechanism 10 and the X-ray generator 16. The X-ray tube 16a of the X-ray generator 16 has a plate 24 such as a fluororesin attached to the peripheral portion of the upper surface thereof. The X-ray tube 16a is arranged so that the plate 24 contacts the lower surface of the tray 12 of the substrate support mechanism. As a result, the distance between the X-ray tube 16a and the substrate 2 is always constant, and accordingly, the point 26 where X-rays are generated at the target 16b of the X-ray tube 16a, that is, the distance between the focal point of the X-ray tube 16a and the bump 4 Approaches and reaches a certain distance.
[0020]
FIG. 5A shows a preferable example of the frame 12 of the substrate support mechanism. Openings 30 for supporting the substrates 2 one by one are opened in the frame 12, and the substrate 2 is inserted and supported in the openings 30 so that the bumps face downward. Two adjacent sides among four sides of each aperture 3 0 of the frame 12, a spring member 32 for fixing the position by pressing the substrate 2 that is inserted into the opening 3 0 in the horizontal direction is provided. As shown in FIG. 5B, the spring material 32 has a bent shape, and a spring force is applied in the direction of pressing the substrate 2 against the edge of the opposite frame interposed in the gap between the frame 12 and the substrate 2. Make it work. As indicated by the arrows in FIG. 5A, the two spring members 32 press the substrate 2, whereby the substrate 2 is pressed against the frame 12 and the position is fixed.
[0021]
FIG. 6 shows a preferred embodiment for accurately positioning bumps to be inspected on the substrate 2 to be inspected. Among the bump forming surfaces of the substrate 2 fixed to the frame 12 of the support mechanism, at two or more locations in the periphery of the region where the bumps 4 are arranged as shown in FIG. Measure the image of the area as shown. The position of the substrate 2 is corrected based on the image.
[0022]
In order to capture the images in the areas a and b, X-rays for inspection may be used, or an image reading device such as a CCD camera may be separately provided at another position.
[0023]
【The invention's effect】
In the present invention, the substrate to be inspected is supported so that the bump forming surface faces downward so that the substrate can be moved in a horizontal plane, the X-ray generator is below the supported substrate, and the X-ray is above the substrate. Since the detector is arranged, the distance between the bump and the X-ray generator can be reduced, and the detection accuracy of the void of the bump can be increased.
In addition, since a flat panel is used as the X-ray detector, there is no problem of shading or the like even if it is close to the X-ray tube, and the output is difficult to saturate. And the S / N ratio of the image can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an embodiment.
FIG. 2 is a perspective view showing a substrate to be inspected by the inspection apparatus of the present invention together with a chip mounted thereon.
FIG. 3 is a schematic cross-sectional view of a main part of one embodiment.
FIG. 4 is a schematic cross-sectional view of a main part of another embodiment.
5A is a plan view showing a frame of the substrate support mechanism and the supported substrate, and FIG. 5B is a perspective view showing a spring material provided in the substrate support mechanism.
FIG. 6 is a plan view of the substrate for explaining the positioning of the inspection site of the substrate.
[Explanation of symbols]
2 Substrate 4 to be inspected 4 Bump 10 Substrate support mechanism 12 Substrate holder 14 Movement controller 16 X-ray generator 16a X-ray tube 16b Target 18 X-ray 20 Flat panel 32 Spring material

Claims (3)

In a bump inspection apparatus for inspecting a plurality of bumps formed on a substrate by transmission of X-rays,
A substrate support mechanism that supports the substrate to be inspected so that the bump forming surface faces downward, and can be moved in a horizontal plane;
An X-ray generator disposed below the substrate supported by the substrate support mechanism and emitting X-rays upward;
A flat panel as an X-ray detector disposed above the substrate supported by the substrate support mechanism at a position for detecting X-rays emitted from the X-ray generator ;
The substrate support mechanism includes a tray-like substrate holder that supports a substrate peripheral portion so as to expose a bump forming surface of the substrate,
In the X-ray generator, the peripheral portion of the upper surface of the X-ray tube contacts the lower surface of the substrate holder, and the distance between the focal point of the X-ray tube and the bump forming surface is kept constant.
The bump inspection apparatus is characterized in that the position where the flat panel is disposed is a position close to the X-ray tube so that the output is saturated when an image tube is used as an X-ray detector . The bump inspection apparatus according to claim 1 , wherein the substrate holder includes an urging member that fixes a position by pressing a supported substrate in a horizontal direction. Means for measuring at least two images of the periphery of the area where the bumps are arranged on the bump forming surface for each substrate supported by the substrate holder, and correcting the inspection position for each substrate based on the measured images. The bump inspection apparatus of Claim 1 or 2 provided.

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