WO2009044944A1

WO2009044944A1 - Optical test method

Info

Publication number: WO2009044944A1
Application number: PCT/KR2007/004807
Authority: WO
Inventors: Ssang-Geun Im; Sang-Yun Lee; Mingu Kang; Seok-Joon Jang
Original assignee: Intekplus Co., Ltd.
Priority date: 2007-10-02
Filing date: 2007-10-02
Publication date: 2009-04-09
Also published as: CN101815925A; EP2195607A1; JP2010540955A; CN101815925B

Abstract

An optical test method acquires not only an image having a low regular reflection rate on a regular reflection surface, but also a peripheral image on which a peripheral lattice plane in the vicinity of a regular reflection surface is clearly seen, employs the acquired images, and improves the accuracy of a target image to be measured. The optical test method projects a lattice pattern on a target object on which a 3D image is formed, compares an optical signal modified by the shape of the target object with a reference pattern, and determines the presence or absence of a defect in the target object according to the comparison result.

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 not only an image having a low regular reflection rate on a regular reflection surface, but also a peripheral image on which a peripheral lattice plane in the vicinity of a regular reflection surface is clearly seen, employing the acquired images, and improving the accuracy of a target image to be measured, so that it can solve the problem of deteriorating the image accuracy on the regular reflection surface including several steps.

Description of the Related Art

Typically, in order to check manufactured states of a variety of electronic components (e.g., a semiconductor memory module) , a variety of items of the electronic components should be measured, for example, the size, shape, surface-roughness precision.

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 ib has difficulty in accurately acquiring the image of a regular reflection surface by the regular reflection of a three-dimensional surface.

For example, in the case of testing the BGA package, the BGA package generates serious reflection on the central rounding surface of the ball, so that the above-mentioned optical measuring method has difficulty in accurately acquiring the image on the central rounding surface.

In order to solve the above-mentioned problem, there is proposed another method for reducing a regular reflection rate of a regular reflection surface by adjusting a filter or a light quantity so as to acquire an image. In this case, the lattice pattern on the 3D surface having a high regular reflection rate becomes prominent, however, the other lattice pattern on a peripheral area becomes invisible, so that the measurement accuracy is decreased.

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 acquiring a first image in which an illumination saturation area on a 3D surface having a high regular reflection rate is decreased, acquiring a second image in which a lattice image becomes prominent on a peripheral area of the 3D surface, mixing the first image and the second image, and comparing the mixed resultant image with a reference image to determine the presence or absence of a defect in a target object on which the 3D shape is formed, thereby acquiring an accurate image. In accordance with the present invention, the above and other objects can be accomplished by the provision of an optical test method which projects a lattice pattern on a target object on which a 3D image is formed, compares an optical signal modified by a shape of the target object with a reference pattern, and determines the presence or absence of a defect in the target object according to the comparison result, the method comprising: acquiring a first image by adjusting an illumination value to reduce a regular reflection rate of a 3D surface of the target object so that a saturation area is reduced by the reduced regular reflection rate; acquiring a second image by adjusting an illumination value to clearly form a lattice pattern on a peripheral area of the 3D surface of the target object; mixing the first image and the second image; and determining the presence or absence of a defect in the target object by analyzing the mixed image of the first and second images.

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 the present invention;

FIG. 2 is a schematic diagram illustrating an optical test apparatus for use in the optical test method according to the present invention; FIG. 3 shows exemplary photo-images, each of which has a low saturation degree on a 3D surface according to the optical test method;

FIG. 4 shows exemplary photo-images, each of which has a low saturation degree on a peripheral area of a 3D surface according to the optical test method; and

FIG. 5 shows a mixed image of an image acquired by the optical test method according to 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 the present invention.

Referring to FIG. 1, the optical test method according to the present invention projects a lattice pattern on a target object on which a 3D image is formed, compares an optical signal modified by the shape of the target object with a reference pattern, and determines the presence or absence of a defect in the target object according to the comparison result. The above-mentioned optical test method acquires a first image by adjusting an illumination value to reduce a regular reflection rate of a 3D surface of the target object at step SlOO, acquires a second image by adjusting an illumination value to clearly form the lattice pattern on a peripheral area of the 3D surface of the target object at step S200, mixes the first image and the second image at step S300, and determines the presence or absence of a defect in the target object by analyzing the mixed image of the first and second images at step S400.

In this case, the adjustment of the illumination values for acquiring the first and second images may be implemented by adjusting the light quantity using a single lamp or illumination, or may be implemented by reducing the size of a saturation area using a specific BPF (Band Pass Filter) . The adjustment of the illumination value using the above-mentioned specific BPF may be implemented by a color filter or a polarizing filter.

If the illumination value is adjusted by the adjustment of the light quantity when each of the above- mentioned images is acquired, it is preferable that the first image may be acquired with a light quantity less than that of the second image.

FIG. 2 is a schematic diagram illustrating an optical test apparatus for use in the optical test method according to the present invention.

Referring to FIG. 2, the optical test system 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 to be tested. The illumination unit 1 includes a light source 11, a band pass filter (BPF) 12, a lattice unit 13, a projection optical system 14 for focusing the light generated from the light source 11, and a reflection mirror 15, etc.

The BPF may be a color filter or a polarizing filter.

For example, 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. The test method for use in the above-mentioned optical test apparatus will hereinafter be described in detail. For the convenience of description, a semiconductor package equipped with balls is exemplarily used as the target object to be tested.

FIGS. 3A~3C show exemplary photo-images, each of which has a low saturation degree on the 3D surface according to the optical test method. Referring to FIG. 3A, the test method adjusts an illumination value to remove a regular reflection point from the 3D surface (i.e., the part on which many regular reflections occur) of the target object 2 delivered to the test table. The test method acquires the image captured by the CCD camera 32 as shown in FIGS. 3B~3C, so that a phase map and a visibility map are depicted.

In this case, the illumination value may be adjusted by adjusting either the light quantity generated from the light source 11 or the filter 12.

FIGS. 4A~4C show exemplary photo-images, each of which has a low saturation degree on a peripheral area of the 3D surface according to the optical test method.

Referring to FIG. 4A, the test method adjusts the illumination value to clearly show the lattice image on a peripheral area of the 3D surface. The test method acquires the image captured by the CCD camera 32, and acquires the phase map and the visibility map as shown in FIGS. 4B~4C.

Then, the test method searches for a 3D image having good visibility using the analyzing unit 4, and selects a first image. The test method searches for an image of a peripheral area of the 3D image having good visibility, selects a second image, and calculates a phase map of each image. The test method mixes the phase maps of the individual images as shown in FIG. 5, analyzes the mixed image, and determines the presence or absence of a defect in a corresponding target object to be tested. FIG. 5 shows a mixed image of an image acquired by the optical test method according to the present invention.

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. As apparent from the above description, the optical test method according to the present invention adjusts the illumination value using a light quantity or a filter to remove a regular reflection point caused by a glittering part of the 3D surface, so that it acquires the 3D-surface image having a smaller illumination saturation area. And, the optical test method adjusts the illumination value using the light quantity or the filter to clearly show the lattice image on a peripheral area of the 3D surface, acquires the image of the peripheral area, selects a specific image having good visibility from among several images, mixes the 3D-surface image and the selected image, and compares the reference image with the mixed image to determine the presence or absence of a defect in the target object. As a result, the above-mentioned optical test method prevents the test accuracy from being deteriorated by the regular reflection on the 3D surface, so that the test reliability increases.

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 projects a lattice pattern on a target object on which a 3D image is formed, compares an optical signal modified by a shape of the target object with a reference pattern, and determines the presence or absence of a defect in the target object according to the comparison result, the method comprising: acquiring a first image by adjusting an illumination value to reduce a regular reflection rate of a 3D surface of the target object so that a saturation area is reduced by the reduced regular reflection rate; acquiring a second image by adjusting an illumination value to clearly form a lattice pattern on a peripheral area of the 3D surface of the target object; mixing the first image and the second image; and determining the presence or absence of a defect in the target object by analyzing the mixed image of the first and second images.

2. The method according to claim 1, wherein: the adjusting of the illumination values for acquiring the first and second images is implemented by adjusting a light quantity.

3. The method according to claim 2, wherein: the first image is acquired with a light quantity less than that of the second image.

4. The method according to claim 1, wherein: the adjustment of the illumination values for acquiring the first and second images is implemented by reducing a saturation area using a band pass filter (BPF¹) .

5. The method according to claim 4, wherein the band pass filter (BPF) is used as a color filter or a polarizing filter.