JP4192679B2 - Inspection method and apparatus for double-sided mounting board - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus and method for inspecting a bump defect based on an X-ray transmission image of a double-sided mounting board, and more particularly to an inspection apparatus and method for extracting only a bump image from the X-ray transmission image. .
[0002]
[Prior art]
Some semiconductor device packaging includes bumps for connection on one surface of a package, such as BGA (ball grid array) and CSP (chip size package). When such a semiconductor device is mounted on the mounting substrate by bumps, the bumps can no longer be visually observed. Therefore, the quality of bump connection of a mounting board on which such a semiconductor device is mounted is determined by irradiating X-rays from one side of the mounting board and detecting transmitted X-rays on the other side. Inspection is performed based on an X-ray image.
[0003]
When a double-sided mounting board on which components are mounted on both sides in an inspection based on such a transmission X-ray image is to be inspected, the transmission X-ray image includes a bump image to be inspected and an image of components such as a resistor and a capacitor on the back surface. May overlap and may not be accurately inspected. Therefore, it is necessary to extract only the bump image on the surface.
[0004]
As a conventional method for inspecting a double-sided mounting substrate, there is a subtraction method in which only a bump image on the surface is extracted. In the subtraction method, apart from the double-sided mounting board to be inspected, a board with components mounted only on the back side is prepared, and an image of only the front surface is obtained by taking the difference between the respective transmission X-ray images. It is.
[0005]
[Problems to be solved by the invention]
In the conventional subtraction method, the back side images of different mounting boards are compared, so the error in the back side image due to the displacement of the mounting parts and the individual differences in shape remains strongly in the surface image after the difference, which hinders inspection. Come on.
In view of the above, the present invention has an object of avoiding the displacement of the components mounted on the back surface and individual differences in shape from remaining on the front surface image extracted from the X-ray transmission image of the double-sided mounting board.
[0006]
[Means for Solving the Problems]
The inspection method of the present invention that achieves this object is directed to a double-sided mounting board that includes components mounted on both sides, and that includes components that are connected to only the front-side components via bumps. A step of irradiating X-rays from one surface side of the substrate and detecting transmitted X-rays on the other surface side to obtain an inspection object image; and a binarized image representing a planar shape of the bump from the inspection object image A bump model image creating step for creating a bump model image in which only a bump shape is extracted by applying a filter expressing a cross-sectional image of the bump to the binarized image, and the inspection object image and the bump model A back side image creating step for creating a back side image of the double-sided mounting substrate from a difference from the image, and a smoothing step for performing a smoothing process on the back side image created in the back side image creating step And a bump image creation step of creating a bump image from the difference between the rear surface image smoothing process has been performed by the smoothing step and the inspection object image.
In this specification, the surface of the double-sided mounting board on which components are connected and mounted by bumps is referred to as the front surface, and the opposite surface is referred to as the back surface.
[0007]
In the present invention, instead of using the back image of another individual, a back image is created from the image of the double-sided mounting substrate to be inspected, and a bump image that is a front image is created by taking the difference between the back image and the image to be inspected To do. As a result, the influence of the positional deviation and the individual shape difference of the mounted parts is reduced.
[0008]
The image of the bump to be inspected has a cross-sectional shape with a flat central portion from the shape of the bonded state. The back image is constructed so that the image after the difference satisfies this property and the density distribution of the back image is continuous and smooth.
[0009]
For this purpose, an image of a bump physically predicted from the shape of the bonded state is assumed. When the difference between this and the inspection target image is taken, a back image including an error between the original bump image and the assumed bump image is obtained. This error makes the density distribution of the back image discontinuous and lacks smoothness. If the difference between the image subjected to the smoothing process and the image to be inspected is taken, an image closer to the original bump can be obtained while maintaining the properties of the flat cross-sectional image.
[0010]
The inspection apparatus of the present invention that realizes this inspection method targets a double-sided mounting board that includes components mounted on both sides, and includes components that are connected to the surface side components only via bumps. An X-ray generator that emits X-rays from one side of the mounting board, an X-ray detection apparatus that detects transmitted X-rays on the other side of the double-sided mounting board, and detection of the X-ray detection apparatus An image processing device that performs image processing based on an image to be inspected that is signal data and extracts and outputs the shape of the bump, and the image processing device is a binary that represents a planar shape of the bump from the image to be inspected. A binarized image creating unit for extracting a binarized image, a filter holding unit holding a filter representing a cross-sectional image of a bump, and the filter holding unit in the binarized image created by the binarized image creating unit Filters held in A bump model image creating unit that creates a bump model image by acting; a back image creating unit that creates a back image of the double-sided mounting substrate from a difference between the inspection object image and the bump model image; and the back image creating A smoothing unit that performs a smoothing process on the back surface image created by the unit, and a bump image creation unit that creates a bump image from a difference between the inspection target image and the back image subjected to the smoothing process by the smoothing unit. ing.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Next, based on an Example, this invention is demonstrated in detail.
FIG. 1 schematically shows an inspection apparatus according to the present invention. Reference numeral 2 denotes a double-sided mounting board to be inspected, and components are mounted on both sides. On the surface side, for example, the semiconductor device 4 is mounted connected by bumps 6. Another component 8 is mounted on the back side of the substrate 2. The component 8 includes various electronic components such as a resistor, a capacitor, and a semiconductor device, but the connection of the component 8 to the substrate 2 is performed by other methods such as soldering instead of bumps.
[0012]
The substrate 2 is held by an appropriate support mechanism and can be moved in the XY direction, which is an in-plane direction, so that a predetermined portion can be inspected.
The X-ray generator 10 is arranged on one side of the substrate 2, in this example, on the lower side. The X-ray generator 10 includes an X tube, and X-rays 11 generated from the X tube pass through the substrate 2.
[0013]
With respect to the substrate 2, an X-ray detector 12 is disposed on the opposite side of the X-ray generator 10 so as to detect X-rays transmitted through the substrate 2. As the X-ray detector 12, various detectors used for X-ray detection, such as a flat panel, can be used in addition to an image tube.
[0014]
Reference numeral 14 denotes an image processing apparatus for processing a transmission X-ray image detected by the X-ray detector 12, extracting an image of the bump 6 mounted by connecting the semiconductor device to the substrate 2, and determining the quality. is there.
[0015]
The image processing operation performed by the image processing apparatus 14 is performed according to a program, and its function is shown in FIG.
Reference numeral 16 denotes a binarized image creating unit that extracts a binarized image representing the planar shape of the bump 6 from the inspection target image of the double-sided mounting substrate 2 detected by the X-ray detector 12. Reference numeral 18 denotes a filter holding unit that holds a filter that represents a cross-sectional image of a bump. Reference numeral 20 denotes a binarized image created by the binarized image creating unit 16 that applies the filter held in the filter holding unit 18. This is a bump model image creation unit that creates a bump model image. 22 is a back surface image creating unit that creates a back surface image of the double-sided mounting substrate 2 from the difference between the inspection target image and the bump model image, and 24 is a smoothing unit that performs a smoothing process on the back surface image created by the back surface image creating unit 22. Is a bump image creation unit that creates a bump image from the difference between the inspection target image and the back image subjected to the smoothing process by the smoothing unit 24.
[0016]
The operation of this embodiment will be described with reference to FIGS. Of these, FIG. 3 corresponds to an embodiment of an inspection method performed by this inspection apparatus.
Prior to processing of the substrate to be inspected, a filter expressing a normal bump-shaped cross-sectional image is created as shown in FIGS. For the production of a filter, a substrate on which a semiconductor device is mounted with normal bumps is inspected by this inspection apparatus, and a bump image shown in FIG. 4B is obtained. Sampling is performed on edge portions (intersections between the periphery of the bump image and the chain line) in the four directions of the image, and an average filter is created. The filter is a function F created under the conditions shown in FIG. 4C so that the X-ray intensity corresponding to the cross-sectional shape as shown in FIG. Here, n represents each position, and a represents the X-ray intensity at each position. In addition, it is assumed that the edge portion of the bump is symmetrical on the left and right.
The filter function obtained in this way is held in the filter holding unit 18.
[0017]
As shown in FIG. 3, the operation of this inspection apparatus is to measure a double-sided mounting board to be inspected, capture its X-ray transmission image (step S1), detect the edge of the bump area, and detect only the bump area. A binary image is created (step S2). The binary image is the one indicated by (2) in FIG.
[0018]
A filter held in the filter holding unit 18 is applied to the binary image to create a model image of an expected bump (step S3). The created model image has a cross-sectional shape indicated by (3) a in FIG. 5B, and a planar image thereof is indicated by (3) b.
[0019]
Next, the difference between the inspection object image and the bump model image created in step S3 is taken. This difference becomes the measured back surface image of the substrate 2 as indicated by (4) in FIG. 5B (step S4). This back image includes an error between the original bump image and the bump model image (3) b, and the fine structure of the original bump is included in this back image. For this reason, the density distribution of the back image may be discontinuous or lack smoothness.
[0020]
Therefore, in order to remove such discontinuity, the back image is subjected to a smoothing process (step S5), and only the bump image is removed as indicated by (5) in FIG. 5B. An X-ray transmission image of the substrate to be inspected can be obtained. The smoothing process can be performed, for example, by applying a low-pass filter.
[0021]
Next, a difference process is performed in which the back image smoothed in step S5 is subtracted from the inspection target image, and as shown by (6) in FIG. 5B, a front surface image (bump image) representing only the bump image. Is created. The bump image error removed from the back image is added to the bump image model, and the bump image becomes closer to the original bump image of the substrate to be inspected.
[0022]
This surface image is displayed and used to determine whether the bump connection is good or bad. Whether the bump connection is good or bad may be determined by a person by looking at the displayed image, or may be automatically determined based on the image.
[0023]
【The invention's effect】
According to the present invention, instead of using a back surface image of another individual, a back surface image is created from an image of a double-sided mounting board to be inspected, and a difference between the back image and the inspection target image is taken to obtain a bump image that is a front surface image Compared with the conventional subtraction method that prepares another board to obtain the back image, the effect of error due to the positional deviation of the mounted part of the back image with respect to the image after the difference and individual differences is small. Improvement of inspection accuracy can be expected.
[Brief description of the drawings]
FIG. 1 is a block diagram schematically showing an inspection apparatus of the present invention.
FIG. 2 is a block diagram showing an embodiment of the inspection apparatus of the present invention.
FIG. 3 is a flowchart showing one embodiment of the inspection method of the present invention.
FIG. 4 is a diagram for explaining a filter used in the embodiment.
FIG. 5 is a diagram schematically showing an image at each step in the embodiment.
[Explanation of symbols]
2 Double-sided mounting substrate 4 Semiconductor device 6 Bump 8 Component 10 X-ray generator 11 X-ray 12 X-ray detector 14 Image processing device 16 Binary image creation unit 18 Filter holding unit 20 Bump model image creation unit 22 Back surface image creation unit 24 Smoothing section 26 Bump image creation section

Claims (2)

A double-sided mounting board that includes parts mounted on both sides and that is connected to the front-side parts only via bumps is targeted for inspection, and X-rays are irradiated from one side of the double-sided mounting board. And detecting a transmission X-ray on the other surface side to obtain an inspection object image;
A binary image representing the planar shape of the bump is created from the inspection object image, and a bump model image in which only the bump shape is extracted is created by applying a filter representing the cross-sectional image of the bump to the binary image. Bump model image creation step,
A back side image creating step for creating a back side image of the double-sided mounting substrate from the difference between the inspection target image and the bump model image;
A smoothing step for performing a smoothing process on the back side image created in the back side image creation step;
An inspection method comprising: a bump image creating step for creating a bump image from a difference between the inspection object image and a back image subjected to the smoothing process by the smoothing step. A double-sided mounting board that includes parts mounted on both sides and that is connected to the front-side parts only via bumps is targeted for inspection, and X-rays are irradiated from one side of the double-sided mounting board. An X-ray generator to
An X-ray detector for detecting transmitted X-rays on the other surface side of the double-sided mounting substrate;
An image processing device that performs image processing based on an inspection target image that is detection signal data of the X-ray detection device and extracts and outputs the shape of the bump;
The image processing apparatus includes:
A binarized image creating unit for extracting a binarized image representing a planar shape of a bump from the inspection target image;
A filter holding unit holding a filter representing a cross-sectional image of the bump;
A bump model image creating unit that creates a bump model image by applying a filter held in the filter holding unit to the binarized image created by the binarized image creating unit;
A back surface image creation unit for creating a back surface image of the double-sided mounting substrate from the difference between the inspection object image and the bump model image;
A smoothing unit that performs a smoothing process on the back image created by the back image creation unit;
An inspection apparatus comprising: a bump image creation unit that creates a bump image from a difference between the inspection target image and the back image subjected to smoothing processing by the smoothing unit.

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