WO2009038242A1

WO2009038242A1 - Optical test method

Info

Publication number: WO2009038242A1
Application number: PCT/KR2007/004483
Authority: WO
Inventors: Ssang-Geun Im; Sang-Yun Lee; Mingu Kang; Seok-Joon Jang
Original assignee: Intekplus Co., Ltd.
Priority date: 2007-09-18
Filing date: 2007-09-18
Publication date: 2009-03-26

Abstract

An optical test method captures an external appearance image of a target object, analyzes the captured image, and determines the presence or absence of a defect in the target object according to the analyzed result. The optical test method mounts different BPFs to several white lights, illuminates an illumination light signal on the test surface to acquire a wavelength band on which a lattice image is clearly shown, divides the acquired color image into several wavelengths, calculates individual phases of the divided images at the wavelengths, adds the calculated phases, calculates the added result as a single phase, analyzes the calculated single phase, and determines the presence or absence of a defect.

Description

OPTICAL TEST METHOD

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an optical test method, and more particularly to an optical test method for acquiring an image where a lattice image is clearly shown on a test surface on which illumination saturation occurs by a regular reflection, thereby increasing test reliability.

Description of the Related Art

Typically, semiconductor devices have been widely used as important components for computers or household appliances, so that they must pass complicated tests before coming into the market. The semiconductor devices require high precision superior to those of other components. If any defect occurs in internal elements or outer appearance of the semiconductor package, the defect has a negative influence upon the performance or throughput of the semiconductor package .

The external appearance defect of the semiconductor device, specifically, the lead- or ball- defect, may occur during the assembling process between the semiconductor device and a PCB circuit, so that the process for testing the lead- or ball- status of the semiconductor device such as a QPF or BGA has been considered to be one of the principal processes . In recent times, there has been widely used an optical method for measuring a three-dimensional shape, which configures a reference pattern for an optical signal, generated from the light source, applies the optical signal to a target object to be measured, compares the optical signal modified by the shape of the target object with the reference pattern, and measures the shape of the target object to be measured, so that the three-dimensional shape of the target object is measured.

The above-mentioned optical method for measuring the three-dimensional shape requires a high speed, a high precision, and non-contact measurement. Recently, a representative example of the above-mentioned optical method for measuring the three-dimensional shape is an optical method for measuring a three-dimensional shape using a moire pattern.

The moire pattern is indicative of an interference pattern formed when at least two periodic patterns overlap with each other. The moire scheme is classified into a shadow moire scheme and a projection moire scheme according to methods for forming the moire pattern. The projection moire scheme applies an optical signal or light beam to a target object to be measured, so that it applies a lattice pattern on the target object. The projection moire scheme allows a lattice image modified by the shape of the target object to overlap with a reference lattice having the same pitch as that of the lattice providing the lattice image, so that it can acquire the moire pattern.

However, the above-mentioned optical method for measuring the three-dimensional shape has a disadvantage in that it has difficulty in accurately acquiring the image of a regular reflection surface by the regular reflection of a three-dimensional surface.

In order to solve the above-mentioned problems, there has been proposed a method for acquiring a desired image by adjusting the filter or the light quantity. However, this method has difficulty in measuring a peripheral area of the regular reflection surface, resulting in deterioration of the test accuracy. In addition, in order to solve the problem of generating the difficulty in measuring the peripheral image of the regular reflection surface, a plurality of illumination devices are used, and the target object to be tested may be tested by different illumination devices installed at coaxial and lateral surfaces. However, the above-mentioned illumination devices unavoidably make the construction complicated.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in view of the above problems, and it is an object of the invention to provide an optical test method for arranging several white lights and filters having different wavelengths in the individual white lights, adjusting a wavelength of a light signal illuminated on the target object by adjusting a brightness of each white light, acquiring a color image, calculating phases for every color wavelength on the basis of the acquired image, adding the individual phases, and calculating the added result as a single phase, so that it can acquire an accurate image of the target object to be tested.

It is another object of the invention to provide an optical test method for illuminating a white light on a target object, reducing an illumination saturation area by adjusting a gain of a specific wavelength of a color camera, acquiring a color image, calculating phases of individual color wavelengths on the basis of the acquired image, adding the individual phases, and calculating the added result as a single phase, so that it can acquire an accurate image of the target object.

In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of an optical test method which captures an external appearance image of a target object to be tested, analyzes the captured image, and determines the presence or absence of a defect in the target object according to the analyzed result, the method comprising: mounting different band pass filters (BPFs) to several white lights, respectively, reducing a saturation area of a test surface of the target object by adjusting a brightness of each white light, and illuminating an illumination light signal on the test surface to acquire a wavelength band on which a lattice image is clearly shown; capturing the test surface, and acquiring a color image; dividing the acquired color image into several wavelengths, and calculating individual phases of the divided images at the wavelengths; and adding the calculated phases, calculating the added result as a single phase, analyzing the calculated single phase, and determining the presence or absence of a defect.

In accordance with another aspect of the present invention, there is provided an optical test method which captures an external appearance image of a target object to be tested, analyzes the captured image, and determines the presence or absence of a defect in the target object according to the analyzed result, the method comprising: illuminating a white light on a test surface of the target object; reducing a saturation area of the test surface by adjusting gains of several wavelengths of a color camera, capturing the test surface, and acquiring a color image; dividing the acquired color image into several wavelengths, and calculating individual phases of the divided images at the wavelengths; and adding the calculated phases, calculating the added result as a single phase, analyzing the calculated single phase, and determining the presence or absence of a defect.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: FIG. 1 is a flow chart illustrating an optical test method according to an embodiment of the present invention;

FIG. 2 is a schematic diagram illustrating an optical test apparatus for use in the optical test method according to an embodiment of the present invention; FIG. 3 is a flow chart illustrating an optical test method according to another embodiment of the present invention; and

FIG. 4 is a schematic diagram illustrating an optical test apparatus for use in the optical test method according to another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, preferred embodiments of the present invention will be described in detail with reference to the annexed drawings. In the drawings, the same or similar elements are denoted by the same reference numerals even though they are depicted in different drawings. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

FIG. 1 is a flow chart illustrating an optical test method according to an embodiment of the present invention. Referring to FIG. 1, the optical test method according to the present invention captures an external appearance image of the target object, analyzes the captured image, and determines the presence or absence of a defect in the target object according to the analyzed result. The above-mentioned optical test method mounts different band pass filters (BPFs) to several white lights, respectively, reduces a saturation area of the target object by adjusting a brightness of each white light, and illuminates an illumination light signal on a test surface to acquire a wavelength band on which the lattice image is clearly shown at step SlO. The optical test method captures the test surface and acquires a color image at step S20. The optical test method divides the acquired color image into several wavelengths, and calculates individual phases of the divided images at the wavelengths at step S30. The optical test method adds the calculated phases, calculates the added result as a single phase, analyzes the calculated single phase, and determines the presence or absence of a defect at step S40.

The different BPFs may be implemented with color filters or polarizing filters. If the BPFs are implemented with the color filters, a red filter, a green filter, and a blue filter may be used as the different BPFs. As described above, according to the above-mentioned embodiment of the present invention, different BPFs are mounted to at least two white lights, respectively, the saturation area of the target object to be tested is reduced by adjustment of the brightness (i.e., an illumination value) of each white light, so that a color image of a corresponding test surface is acquired. The color image is divided into several wavelengths, and the divided images are mixed with each other, so that the presence or absence of a defect in the target object is determined according to the mixed result.

E^-1IG. 2 is a schematic diagram illustrating an optical test apparatus for use in the optical test method according to an embodiment of the present invention.

The optical test method according to the embodiment of the present invention will hereinafter be described with reference to FIGS. 1 and 2.

Referring to FIG. 2, the optical test apparatus according to the present invention includes an illumination unit 1, a target object 2 to be tested, an image-capturing unit 3, and an analyzing unit 4.

The illumination unit 1 acts as a unit for illuminating an optical signal on a test surface of the target object 2. The illumination unit 1 includes a plurality of white lights 11a, lib and lie, a plurality of BPFs 111, 112, and 113 contained in the individual white lights 11a, lib, and lie, a lattice unit 12, a projection optical system 13, and a reflection mirror 14, etc.

In this case, the BPFs 111, 112, and 113 may be implemented with color filters or polarizing filters. If the BPFs are implemented with the color filters, R-, G-, and B- filters may be used as the above-mentioned BPFs.

The target object 2 may be a semiconductor package equipped with balls. Although the semiconductor package is not shown in the drawings, it is delivered and arranged on a test table.

The image-capturing unit 3 is used as an image pickup element for capturing an image reflected from the surface of the target object 2. The image-capturing unit 3 includes a CCD camera 32 and an image optical system 31 for focusing the light on the CCD camera, and transmits the image captured by the CCD camera 32 to the analyzing unit 4.

If an analog signal of the image captured by the image-capturing unit 3 is converted into a digital signal via a frame grabber and the digital signal is applied to the analyzing unit 4, the analyzing unit 4 analyzes the received signal, compares the analyzed image with a reference image, and determines the presence or absence of a defect in a corresponding target object according to the comparison result. Generally, the analyzing unit 4 may be implemented with a computer.

According to the optical test method based on the above-mentioned components, a light or optical signal is illuminated on the test surface using the white lights 11a, lib, and lie. When the light or optical signal is illuminated on the test surface, a saturation area of the test surface is reduced, and a wavelength band is adjusted to clearly show the lattice pattern.

In other words, if the strengths of the individual white lights 11a, lib, and lie passing through the individual filters 111, 112, and 113 are adjusted, the wavelength band can also be adjusted.

For example, if the semiconductor package including balls is tested, a blue wavelength band is appropriate for the central rounding surface of each ball so that regular reflection points are removed from the central rounding surface of the ball. The green wavelength is the most suitable for clearly showing the lattice pattern on the bottom. Therefore, the light quantity of the blue-filter white light must increase at the ball's central rounding surface during the illumination process, and the light quantity of the green-filter white light must increase at the bottom surface. However, it should be noted that the above-mentioned operations have been disclosed for only illustrative purposes, are not limited to the above- mentioned examples, and can also be applied to other examples as necessary.

In the meantime, if the strength of the white light is adjusted, the illuminated light signal passes through the lattice unit 12. The light signal generated from the lattice unit 12 is focused as a lattice pattern on the test surface .

Subsequently, the image of the test surface of the target object to be tested is captured by the CCD color camera 32, and analog signals of the captured image are converted into digital signals via a frame grabber, so that the color image is acquired.

Then, the analyzing unit 4 divides the color image acquired via the frame grabber into red, green, and blue wavelength bands, and calculates the phases of images for every wavelength band.

The analyzing unit 4 adds the calculated phases, calculates the added result as a single phase, compares the calculated phase with a reference phase, and determines the presence or absence of a defect in the target object according to the comparison result.

In this case, it should be noted that the method for determining the presence or absence of a defect by comparing the captured image of the target object with a reference image is well known to those skilled in the art, so that a detailed description of the above-mentioned determining method will herein be omitted for the convenience of description.

The above-mentioned optical test method properly adjusts the wavelength bands of the individual white lights to reduce the number of regular reflection points on the regular reflection surface, and increases the accuracy of the captured image, resulting in increased test reliability. In this case, the reducing of the regular reflection points on the regular reflection surface may be equal to the reducing of the illumination saturation area of the test surface.

FIG. 3 is a flow chart illustrating an optical test method according to another embodiment of the present invention. Referring to FIG. 3, the optical test method according to another embodiment of the present invention captures an external appearance image of the target object, analyzes the captured image, and determines the presence or absence of a defect in the target object according to the analyzed result.

The above-mentioned optical test method illuminates the white light on the test surface at step SlOO. The optical test method reduces a saturation area of the target surface by adjusting gains of several wavelength bands of the color camera, captures the test surface, and acquires a color image at step S200. The optical test method divides the acquired color image into several wavelengths, and calculates individual phases of the divided images at the wavelengths at step S300. The optical test method adds the calculated phases, calculates the added result as a single phase, analyzes the calculated single phase, and determines the presence or absence of a defect at step S400.

The different BPFs may be implemented with color filters or polarizing filters. If the BPFs are implemented with the color filters, a red filter, a green filter, and a blue filter may be used as the different BPFs.

FIG. 4 is a schematic diagram illustrating an optical test apparatus for use in the optical test method according to another embodiment of the present invention. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

Referring to FIG. 4, the optical test apparatus according to another embodiment of the present invention includes an illumination unit 1, a target object 2 to be tested, an image-capturing unit 3, and an analyzing unit 4.

The illumination unit 1 acts as a unit for illuminating an optical signal on the target object 2 such as a semiconductor package equipped with balls. The illumination unit 1 includes a white light 11, a lattice unit 12, a projection optical system 13, and a reflection mirror 14, etc.

Although the target object is not shown in FIG. 4, it is delivered and arranged on a test table.

The image-capturing unit 3 is used as an image pickup element for capturing an image reflected from the surface of the target object 2. The image-capturing unit 3 includes a CCD camera 32 and an image optical system 31 for focusing the light on the CCD camera, and transmits the image captured by the CCD camera 32 to the analyzing unit 4. If an analog signal of the image captured by the image-capturing unit 3 is converted into a digital signal via a frame grabber and the digital signal is applied to the analyzing unit 4, the analyzing unit 4 analyzes the received signal, compares the analyzed image with a reference image, and determines the presence or absence of a defect in a corresponding target object according to the comparison result. Generally, the analyzing unit 4 may be implemented with a computer.

The optical test method according to another embodiment of the present invention will hereinafter be described with reference to FIGS. 3 and 4.

During the illumination process, the optical test method adjusts the light quantity of the white light 11 on the test surface (i.e., the surface of the target object. The illuminated optical signal passes through the lattice unit 12, and the light signal generated from the lattice unit 12 is focused as a lattice pattern on the test surface .

Subsequently, the image of the test surface of the target object to be tested is captured by the CCD color camera 32, and analog signals of the captured image are converted into digital signals via the frame grabber, so that the color image is acquired.

In this case, the most important duty of the above- mentioned operations is to acquire the image by adjusting a gain of each wavelength band of the CCD color camera while the image is captured by the CCD color camera. In this case, it is preferable that the gain of a specific wavelength band is adjusted to reduce an illumination saturation area of the test surface of the target object, so that a color image capable of clearly showing the lattice pattern on all areas should be acquired.

As described above, in the case of capturing the image of the test surface of the target object, the above- mentioned optical test method according to another embodiment of the present invention adjusts a gain of a specific wavelength band of a color camera to reduce saturation areas of all the areas of the test surface, and acquires a color image, so that it increases the accuracy of the captured image, resulting in increased test reliability.

As apparent from the above description, the optical test method according to the present invention arranges several white lights and BPFs having different wavelengths in the individual white lights, adjusts a brightness of each white light, provides an illumination light signal having a wavelength band adjusted to reduce an illumination saturation area of a 3D surface, acquires a color image using the illumination light signal, calculates phases for every color wavelength on the basis of the acquired color image, adds the individual phases, and calculates the added result as a single phase. As a result, the optical test method reduces the number of regular reflection points on the 3D surface, and acquires the accurate image, resulting in increased test reliability. Also, the optical test method illuminates the white light on the target object, reduces an illumination saturation area by adjusting a gain of a specific wavelength of the color camera, acquires a color image, calculates phases of individual color wavelengths on the basis of the acquired image, adds the individual phases, and calculates the added result as a single phase, so that it can clearly show the lattice pattern on all the areas of the target object, resulting in increased test reliability. And, the optical test method uses a single illumination device, so that it does not make the configuration complicated, resulting in reduction of production costs and installation space of the apparatus associated with the test method.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

WHAT IS CLAIMED IS:

1. An optical test method which captures an external appearance image of a target object to be tested, analyzes the captured image, and determines the presence or absence of a defect in the target object according to the analyzed result, the method comprising: mounting different band pass filters (BPFs) to several white lights, respectively, reducing a saturation area of a test surface of the target object by adjusting a brightness of each white light, and illuminating an illumination light signal on the test surface to acquire a wavelength band on which a lattice image is clearly shown; capturing the test surface, and acquiring a color image; dividing the acquired color image into several wavelengths, and calculating individual phases of the divided images at the wavelengths; and adding the calculated phases, calculating the added result as a single phase, analyzing the calculated single phase, and determining the presence or absence of a defect.

2. The method according to claim 1, wherein the band pass filters (BPFs) are color filters or polarizing filters.

3. The method according to claim 2, wherein the color filters are a red filter, a green filter, and a blue filter.

4. An optical test method which captures an external appearance image of a target object to be tested, analyzes the captured image, and determines the presence or absence of a defect in the target object according to the analyzed result, the method comprising: illuminating a white light on a test surface of the target object; reducing a saturation area of the test surface by adjusting gains of several wavelengths of a color camera, capturing the test surface, and acquiring a color image; dividing the acquired color image into several wavelengths, and calculating individual phases of the divided images at the wavelengths; and adding the calculated phases, calculating the added result as a single phase, analyzing the calculated single phase, and determining the presence or absence of a defect.