JPH05259249A - Method and apparatus for inspecting flip chip - Google Patents

Abstract

PURPOSE:To be preferable in using for inspection of a junction state of a bump joined by a flip chip method, eliminate need of calculating complicated image information and allow an inspection to be done in a short time. CONSTITUTION:An X-ray applying means 12 wherein an emitting position of X-rays rotates is provided above a table 11 for mounting a substrate 5. An image intensifier 18 and a line sensor 19 are provided oppositely to the X-ray applying means 12 with a table 11 interposed. Image information having a semi-shadow part due to the X-rays is processed by a computer 25 to determine whether or not a bump is good.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flip chip inspection method and device, and more particularly to a flip chip inspection method and device suitable for inspecting a bonding state of bumps bonded by a flip chip method.

In recent years, with the miniaturization of electronic devices, the mounting of semiconductor chips on a printed circuit board used has become increasingly denser. Also, in the circuit of a large computer, L
In order to shorten the wiring length between SIs (Large Scale Integrated Circuits) to improve the signal propagation speed and the packaging density, LS
It is necessary to fit the I input terminal within the chip size. As a chip mounting method satisfying such requirements, a flip chip is attracting attention. The flip chip is a method of connecting the LSI to the substrate by forming a ball-shaped bump (usually using Pb, Sn based solder) on the electrode pad portion of the LSI, mounting it on the substrate, and then reflowing the bump. Is. This method has the advantages of high-density mounting, high productivity, and excellent reliability.

However, as the distance between the bumps of the flip chip becomes narrower, the number of defects due to contact between the bumps increases, and it becomes necessary to inspect the defects. However, since the bump portion of the flip chip is located in a very narrow space between the substrate and the semiconductor chip, the visual inspection is difficult, and the X-ray inspection and the electrical inspection are time-consuming. ..

Therefore, a method of shortening the inspection time of the bump portion of the flip chip is desired.

[0005]

2. Description of the Related Art For convenience of description, first, a flip chip bonding process and bump defects that occur during bonding will be described.

FIG. 8 is a diagram for explaining a flip chip bonding process. FIG. 8A shows a state before bonding, and FIG. 8B shows a state after bonding.

A thin film electrode 3 is formed on the electrode 2 on the semiconductor chip 1 and solder bumps 4 are formed on the thin film electrode 3 by supplying solder by a solder ball or a vapor deposition method.

A glass dam 7 is formed on a portion of the electrode 6 formed on the substrate 5 facing the solder bump 4, and a solder bump 8 is similarly formed.

As shown in FIG. 8A, the semiconductor chip 1
The solder bumps 4 of 4 and the solder bumps 8 of the substrate 5 are butted against each other and the whole is heated. Then, the solder bump 4 and the solder bump 8 are melted by heat and integrated to form the bump 9. When the solder is solidified, the electrodes of the semiconductor chip 1 and the substrate 3 are connected and the semiconductor chip 1 is mechanically fixed to the substrate 3 as shown in FIG. 8B.

FIG. 9 is a diagram for explaining defects that occur during flip chip bonding. In the figure, (A) shows a state in which adjacent bumps 9 are in contact with each other or the gap between the bumps is narrow, (B) shows a state in which solder dust remains between the bumps 9, and (C) shows the width of the bumps 9. Shows a state where is smaller than a predetermined size.

As shown in FIG. 9A, when the bumps 9 are in contact with each other or the distance between the bumps 9 is smaller than a predetermined dimension (indicated by a in the figure), the circuit is short-circuited. Further, as shown in FIG. 2B, there is a problem that the circuit may be short-circuited also when there is a solder scrap 10 having a predetermined size or more (shown by b in the drawing) between the bumps 9. is there. If the width of the bump 9 (indicated by c in the figure) is narrower than a predetermined dimension as shown in FIG. 6C, it may cause a poor electrical continuity.

Next, the conventional inspection method input / output device 24 will be described.

For the inspection of defects in the above-mentioned flip chip bonding, a method of observing the appearance with a stereoscopic microscope, a method of an electrical continuity test, a method of X-ray, etc. have been used. However, with the method using a stereoscopic microscope, only the outer bumps can be observed, and it has been extremely difficult to observe the bumps located in the back to inspect for defects. Further, since the electrical continuity test is also inspected by a combination of logics, the time required for the inspection is long, and the inspection time becomes longer as the number of bumps increases.

On the other hand, a method of obtaining an image of the horizontal sectional shape of the bump by using X-ray is suitable for inspecting the bump located at the back. FIG. 10 is a diagram for explaining a fluoroscopic image by conventional X-ray irradiation. The electron beam 13 focused by the focusing coil 14 is applied to the target 16, and the target 16 and the surroundings thereof are irradiated with X-rays. Then, an object to be inspected with little X-ray transmission becomes a shadow, and an X-ray fluoroscopic image is obtained. In order to make the outline of the shadow of the inspection object clear, the electron beam 13 is focused so that the X-ray emission source is as close to the point as possible.

FIG. 11 is a flow chart showing the procedure of a conventional X-ray inspection method. In the inspection by X-ray, first, the table is moved to move the bump 9 to be inspected to the inspection position in the X-ray irradiation range (step S1). next,
The X-ray is irradiated to obtain image information of the X-ray fluoroscopic image of the horizontal cross-sectional shape of the bump 9 (step S2). Then, the obtained image information is input to the computer to obtain the two-dimensional image data of each bump (step S3). Next, the contour of a region (hereinafter referred to as a measurement region) having a width of 1/2 a outside the contour of the horizontal section is calculated (step S4). Then, this measurement area is imaged again and displayed (step S
5). Next, the image is visually observed to check whether the measurement areas of the respective bumps are overlapped with each other, and a case where adjacent bumps are overlapped is determined to be a defect.

[0016]

However, in the inspection method using X-rays, in order to convert the two-dimensional image information into data and further obtain the data of the measurement region by calculation and display it again as an image, one bump It takes some time to process. Therefore, there is a problem that a flip chip having several thousand bumps per chip requires a considerable processing time and the inspection speed is slow.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a flip chip inspection method and apparatus capable of performing inspection in a short time without calculating complicated image information.

[0018]

In order to solve the above-mentioned problems, the invention according to claim 1 determines whether or not there is a defect in the bump based on the image information obtained by irradiating the bump of the mounted semiconductor chip with X-rays. A flip chip inspection method for inspecting,
The table is moved to move the bump to be inspected into the X-ray irradiation range, X-ray is irradiated from above the bump, and image information having a penumbra part of a predetermined width is provided outside the contour of the horizontal sectional image of the bump. Then, when the penumbra parts of the adjacent bumps overlap each other, it is determined that the bumps have a defect.

According to the second aspect of the present invention, it is determined that the bump has a defect when the perimeter of the outer contour of the penumbra is out of a predetermined range.

According to a third aspect of the present invention, a substrate on which a semiconductor chip is mounted is placed and movable, and a horizontal sectional image of the bump and a contour of the horizontal sectional image of the bump by irradiating an X-ray from vertically above the table. X-ray irradiating means for forming a penumbra on the outside, and X penetrating the semiconductor chip, the substrate and the bumps.
The detection means converts a line into image information, and the image information obtained by the detection means is converted into data for calculation to determine the quality of the bump of the semiconductor chip.

According to a fourth aspect of the present invention, the X-ray irradiation means is
An annular target is used as the X-ray source, and image information having a dense penumbra is obtained.

According to a fifth aspect of the invention, the X-ray irradiating means is
It has a control means for irradiating a target with an electron beam having a small focus size so as to draw a circle, the emission point of the X-ray draws a circle, and a dense penumbra is formed outside the horizontal sectional image of the bump. It is configured to be formed.

[0023]

According to the first aspect of the present invention, the method for determining the presence or absence of a defect by forming a penumbra of a bump by X-ray irradiating means and overlapping of penumbra portions reduces the calculation by a computer and shortens the time required for this. To do.

According to the second aspect of the present invention, the method of determining the length of the contour of the penumbra portion and determining that this value is outside the predetermined dimension range is a defect enables a computer to determine the presence or absence of the defect. ..

According to the third aspect of the present invention, the structure having the X-ray source having a large focal point size produces a penumbra portion having a predetermined width outside the contour of the bump to be inspected.

According to the fourth aspect of the invention, the X-ray is emitted from the annular target, and the X-ray dose near the central portion of the target is weaker than that of the circular target.
Therefore, the range of light and darkness of the image is narrowed, and the contrast of the entire image can be increased.

In the fifth aspect of the present invention, in the configuration in which the electron beam having a small focal point size is applied to the target so as to draw a circle, the emission position of the X-ray draws a circle and the contour of the image of the bump to be inspected is drawn. A penumbra with a predetermined width is formed on the outside. Therefore, the range of light and darkness of the image is narrowed, and the contrast of the entire image can be increased.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of an embodiment of the present invention. Substrate 5 with semiconductor chip mounted by flip chip method
Above the table 11 on which the X is placed, the X-ray irradiation means 1
2 are arranged. The X-ray irradiation means 12 is an electron beam 1.
It has a focusing coil 14 for focusing 3 and a control means 15 for biasing the focused electron beam 13. Then, the electron beam 13 controlled by the control means 15 is applied to the target 16 and the target 16 emits X-rays 17.

An image intensifier 18 and a line sensor 19 which receive the X-rays 17 and convert them so that they can be read by a CCD sensor are located on the opposite side of the X-ray irradiation means 12 with the table 11 interposed therebetween. There is. The image information converted into an electric signal by the line sensor 19 is A /
The image data is sent to the D converter 20, the image input device 21, and the bus 22.
Sent to. A memory 2 for storing image information on the bus 22
3, an input / output device 24, and a computer 25 for controlling the processing of image information are connected. And table 1
The motor 16 for moving 1 is connected to the input / output device 24. Here, for convenience of description, a measurement area of a bump image and a bump defect determination method using the measurement area will be described with reference to FIG.

FIG. 2A shows an image in which a measurement area 30 having a predetermined width is set around the horizontal sectional image 9a of the bump 9. The width of the measurement region 30 is 1/2 of the minimum required separation distance between adjacent bumps 9 as a. That is, unless the measurement areas of the adjacent bumps 9 overlap with each other, those bumps 9 have a minimum required separation distance a.
Can be determined to have. Therefore, the bump 9 shown in FIG. 2A can be determined to be a normal bump.

On the other hand, in FIG. 2B, a part of the measurement region 30 of the left bump 9 and a part of the measurement region 30 of the right bump 9 overlap each other. It is clear from the figure that the outer peripheral portions of the bumps 9 in the vicinity of the portion where the measurement regions 30 overlap each other do not have the minimum required separation distance a, and these bumps 9 may have either or both of them. Can be determined to be defective.

FIG. 2C shows the case where the width of the measurement region 30 is set to the minimum required separation distance a, and the measurement region 3
When 0 overlaps the horizontal cross-sectional image 9a of the adjacent bump 9, it can be determined to be defective.

The setting and imaging of the above-mentioned measurement region 30 is performed by
This can be calculated by using a computer based on the image information of the horizontal cross-sectional image 9a of the bump photographed by X-ray, but if there are thousands of bumps per chip,
The amount of calculation becomes enormous, and the time spent for inspection becomes long.

Therefore, in the present invention, the X-ray irradiating method is different from the conventional one, and the X-ray irradiation method is not the calculation of the image information but the X-ray irradiation method.
The measurement area is displayed on the line image itself.

FIG. 3 is a diagram for explaining an example thereof. Figure 3
3A shows a conventional X-ray irradiation method, and FIG. 3B shows an X-ray irradiation method for forming a measurement region.

As shown in FIG. 3A, in the conventional X-ray irradiation, the X-ray focus is set close to a point in order to make the contour of the inspection object clear. A profile A drawn below the X-ray fluoroscopic image shows the intensity of light and darkness of the fluoroscopic image taken by X-ray irradiation, and the enlargement ratio of the fluoroscopic image to the actual size of the inspection object is M = (b + c) / Represented by b. Here, b represents the distance from the X-ray focus to the inspection object, and c represents the distance from the inspection object to the surface on which the X-ray fluoroscopic image is captured.

FIG. 3B shows a case in which the focal spot size F of X-rays is intentionally increased. As the focal spots of X-rays become larger, the contour of the object to be inspected in the X-ray fluoroscopic image becomes wider. To form a penumbra 31 having a width H. Penumbra 31
Is represented by H = F · c / b, and the contour of the penumbra 31 is H from the perspective image when the original X-ray source is close to a point.
It is widened outward by a dimension of / 2. Similar to FIG. 3A, the profile B drawn under the X-ray fluoroscopic image has a gentle slope at the portion B'corresponding to the penumbra 31.

FIG. 4 shows a case where the target for emitting X-rays has a ring shape. Since no X-rays are emitted from the central portion of the annular target 27, the dark portion of the shadow having a high density inside the penumbra 31 in the X-ray fluoroscopic image has a low density, and the density difference from the penumbra 31 is small. Less. Therefore, if the contrast of the entire image is increased, the contour of the penumbra 31 becomes clear.

FIG. 5 shows a method of forming the penumbra 31 by slightly shifting the emission position of X-rays by rotating the electron beam 13 applied to the target 16 which emits X-rays.

By changing the X-ray irradiation method as described above, the penumbra 31 can be easily formed, and the contour of the penumbra 31 is set to be the same as the outer circumference of the measurement region 30. Then, the measurement region 30 can be easily imaged without the need for calculation based on the image information. Therefore, calculation of the measurement region is omitted, and the inspection time can be shortened.

Next, a method of automatically recognizing the overlap of the measurement areas 30 by a computer instead of visually will be described with reference to FIG. This method obtains the length of the contour of the measurement region 30 obtained by the above-mentioned method to obtain the measurement region 3
It is to find zero overlap. The method for obtaining the length of the contour of an image has already been established as computer software and can be easily obtained.

FIG. 6A shows the case where the distance between the bumps 9 is smaller than the minimum required separation distance a. A horizontal cross-sectional image 9a of the bump 9 is shown on the left side of the arrow, and an image in which a penumbra 31 is formed at a width of half the separation distance a, that is, a / 2 is shown on the right side. Since the separation distance of the bumps 9 is smaller than a, the penumbra 31 partially overlaps. When the length L of the contour of the penumbra 31 is obtained in this state, the arrow A in the figure
As shown by, it is obtained over the two penumbra parts 31. When the distance between the bumps 9 is larger than a, such a state does not occur. Therefore, assuming that the maximum allowable diameter of the normal bump 9 is d ₁ , the length L of the contour of the penumbra 31 of the bump 9 is obtained, and when the value is larger than π (d ₁ + a), the bumps 9 are separated from each other. The distance is insufficient, and it can be determined that there is a defect.

As shown in FIG. 6B, the bump 9
If the minimum permissible diameter of is equal to d ₂ and the length L of the contour of the penumbra 31 of the bump 9 is smaller than π (d ₂ + a), then the diameter of the bump 9 to be inspected is outside the permissible range, which is a defect. Can be determined.

Thus, π (d ₂ + a) ≦ L ≦ π (d
₁ + a), the bump 9 to be inspected has no defect,
When L has a value other than that, it can be determined whether there is a defect or not.

According to this method, as shown in FIG. 6C, the length of the contour of the penumbra 31 of the solder scrap 10 is inspected even when the solder scrap 10 is present between the bumps 9, and L < π
(D ₂ + a) or L> π (d ₁ + a), and it is determined that there is a defect. In addition, as shown in FIG.
The so-called bridge in which the bumps 9 are integrated when melted is also determined to be defective as L> π (d ₁ + a). Then, as shown in FIG. 6 (E), even if a minute void having no influence on the performance exists inside the bump 9, the judgment is made based on the length of the contour, so that there is no defect.

As described above, all of the methods of obtaining the length of the contour of the penumbra 31 and comparing it with a predetermined size can be processed by a computer, so that visual observation is not necessary and the inspection time is shortened.

Next, returning to the embodiment of FIG. 1, the inspection procedure will be described.

First, the substrate 5 to which the semiconductor chip 1 is bonded by the flip chip method to be inspected is placed on the table 11, and the bump 9 to be inspected (see FIG. 8B) is irradiated with X-rays. Move to (step S
11). Next, the bumps 9 are irradiated with X-rays from the X-ray irradiation means 12. The irradiated X-rays pass through the semiconductor chip 1, the bumps 9 and the substrate 5 and the image intensifier 1
8 and is guided to the line sensor 19 (step S
12).

The line sensor 19 converts the signal from the image intensifier 18 into an electric signal. Since this electric signal is an analog signal, it is converted by the A / D converter 20 into a digital signal that can be processed by a computer. Then, the digital signal from the A / D converter 20 enters the bus 22 via the image input device 21 and is input to the memory 23. On the other hand, since the table 11 is moved in a fixed direction by the motor 26, two-dimensional X-ray transmission image information can be obtained (step S13). And this two-dimensional X
The line-transparent image information is processed by the computer 25 according to the method for determining the presence / absence of a defect described in FIG. 6 (step S14).

Since the position information of the table 11 is input to the input / output device 24 by the table controller (not shown), the computer 25 recognizes the position of the bump determined as the defect. The position of the defective bump is displayed on the display device (not shown) (step S15).

Then, returning to step S11, steps S11 to S15 are repeated to inspect other bumps.

As described above, according to the bump inspection of the flip chip according to this embodiment, the calculation of the measurement area shown in FIG. 11 (see step S4) is not required, and the X-ray transmission image is visually observed. Since it is not necessary to perform (see steps S5 and S6), the inspection time can be shortened significantly.

[0053]

As described above, according to the invention of claim 1,
Since the measurement area is formed as an image as a penumbra of X-ray and does not require the calculation of the measurement area by the computer, the time spent for this calculation is shortened and the inspection time is shortened.

According to the second aspect of the present invention, since the presence or absence of a bump defect is determined by the length of the contour of the penumbra portion, all can be processed by a computer, the inspection time is shortened, and the inspection accuracy is improved. To do.

According to the third aspect of the present invention, the measurement region is formed as an image as a penumbra part of the X-ray, and the calculation of the measurement region by the computer is not required. Therefore, the time spent for this calculation can be shortened. Then, since the presence or absence of a bump defect is determined based on the length of the contour of the penumbra portion, all can be processed by a computer, the inspection time is shortened, and the inspection accuracy is improved.

According to the invention of claim 4, an image having a high density of the penumbra can be obtained by the X-ray irradiating means using the annular target, so that the image resolution is improved,
Inspection accuracy is improved.

According to the fifth aspect of the present invention, since the X-ray irradiation range moves so as to draw a circle, a penumbra part can be formed in the image of the bump, and the measurement region is defined as the X-ray penumbra part. Since it is formed as an image and does not require computer calculation of the measurement area, the time spent for this calculation is shortened.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an exemplary embodiment of the present invention.

FIG. 2 is a diagram illustrating a measurement area and a determination method.

FIG. 3 is a diagram illustrating a penumbra portion of an X-ray fluoroscopic image.

FIG. 4 is a diagram illustrating irradiation of X-rays by an annular target.

FIG. 5 is a diagram illustrating irradiation of X-rays by rotating an electron beam.

FIG. 6 is a diagram illustrating a method of determining the presence / absence of a defect based on the contour length of a measurement region.

FIG. 7 is a flowchart showing a procedure of inspection by the apparatus of FIG.

FIG. 8 is a diagram illustrating a flip chip bonding process.

FIG. 9 is a diagram illustrating a defect of a bump.

FIG. 10 is a diagram illustrating a fluoroscopic image by conventional X-ray irradiation.

FIG. 11 is a flowchart showing a conventional inspection procedure using X-rays.

[Description of Reference Signs] 1 semiconductor chip 4,8 solder bump 5 substrate 9 bump 9a horizontal cross-sectional image 10 solder scrap 11 table 12 X-ray irradiation means 13 electron beam 14 focusing coil 15 control means 16 target 17 X-ray 18 image intensifier 19 line sensor 20 A / D converter 21 image input device 22 bus 23 memory 24 input / output device 25 computer 26 motor 27 annular target 30 measurement region 31 penumbra

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yoji Nishiyama 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (5)

[Claims] 1. A flip-chip inspection method for inspecting a bump (9) of a mounted semiconductor chip (1) for defects of the bump (9) by image information obtained by irradiating the bump (9) with X-rays (17). Then, the table (11) is moved to move the bump (9) to be inspected to within the X-ray irradiation range, and the X-ray (17) is irradiated from above the bump (9). Image information having a penumbra part (31) of a predetermined width outside the contour of the horizontal cross-sectional image (9a) of (1) is obtained, and the penumbra parts (31) of the adjacent bumps (9) overlap each other. A flip chip inspection method, characterized in that the bump (9) is determined to have a defect. 2. The flip according to claim 1, wherein the bump (9) is determined to be defective when the perimeter of the outer contour of the penumbra (31) is outside a predetermined range. Chip inspection method. 3. A substrate (5) on which a substrate (5) on which a semiconductor chip (1) is mounted is placed, and a movable table (11), and an X-ray (17) is irradiated from vertically above the table (11) to obtain a bump. (9) horizontal cross-sectional image (9a) and X-ray irradiation means (12) for forming a penumbra (31) outside the outline of the horizontal cross-sectional image (9a), the semiconductor chip (1), the substrate ( 5) and bumps (9)
Detecting means (18,
19) and a means (25) for judging the quality of the bump (9) of the semiconductor chip (1) by converting the image information obtained by the detecting means (18, 19) into data and calculating the data. A flip-chip inspection device having the following configuration. 4. The X-ray irradiating means (12) is configured to use an annular target (27) as an X-ray source so as to obtain image information having a penumbra part having a high density. The flip chip inspection device according to claim 3. 5. The X-ray irradiating means (12) has a control means (15) for irradiating a target with an electron beam having a small focus size so as to draw a circle, and the emission point of the X-ray is a circle. The flip-chip inspection apparatus according to claim 3, wherein the pen-shade portion (31) is formed outside the horizontal sectional image (9a) of the bump (9) drawn.