KR100472966B1 - Flatness level inspection apparatus and method of the ball grid array package - Google Patents

Abstract

The present invention provides an inspection apparatus capable of measuring the flatness of the solder ball of the BGA package that can inspect the defect in order to reduce the defect of the solder ball affecting the reliability of the package during semiconductor manufacturing. The present invention is a flatness inspection apparatus and method of a ball grid array package using one line CCD camera and slit light projection, and capable of detecting height and positional error of solder balls through a geometric algorithm of an image. The line CCD element used in this inspection device is 4096 cells, and the two ends are distorted due to the spherical aberration of the camera lens, and the image is acquired by 2048 cells in the center. Less than 1 second per BGA package, detectable to less than 0.12mm (± 0.06mm) height tolerance for 0.8mm diameter solder balls, allowable deviation of solder ball position (XY plane) Although the error is 0.1mm, the resolution can be realized (40mm / 2048) at 20μm.

Description

Flatness inspection device and method of ball grid array package {FLATNESS LEVEL INSPECTION APPARATUS AND METHOD OF THE BALL GRID ARRAY PACKAGE}

The present invention relates to a flatness inspection device and method for a ball grid array package, and in particular, can be applied to BGA package-related inspection equipment, other IC inspection equipment, various machinery, and the electronic component industry, and one line CCD camera and slit light The present invention relates to a flatness inspection apparatus and method for a ball grid array package capable of detecting height and positional error of solder balls through a geometric algorithm of an image using projection.

Recently, image processing technology has been applied to the inspection of appearance of various products such as the application to non-manufacturing lines, including the practical use of inspection and assembly of manufacturing lines. As the algorithm for measuring the height of the solder ball, a stereo vision method using two area cameras and a slit-type light source and a moire method are known as this algorithm for visual inspection. In the case of visual inspection using these methods, the following three conditions are required to introduce an image processing technology for practical use.

The first is high speed, and the conditions for the speed of the parameter extraction of the feature which is the object of image processing are compatible with the processing speed of the outgoing product and whether the required feature extraction is possible and the speed thereof.

The second is stability, which can be judged as defective or good quality, in terms of human personality. In terms of hardware, stability can be influenced by changes in interior lighting and the effects of natural light from the outside. It is about whether the light source can be controlled stably.

Finally, the third is the price of the device, and the cost of the equipment is reduced when the automation of appearance inspection is built, and it is surprisingly simple to accomplish by understanding not only the knowledge but also the application cases when constructing the device. have. The automation of visual inspection is based on the acquisition of technology of image processing technique, but it is also necessary to integrate with the surrounding automation devices.

Accordingly, an object of the present invention is to compensate for the disadvantages of using the above-described stereo vision method and moire method, and to reflect reflected light by irradiating an object with one slit type light source for measuring the height of the solder ball more precisely and quickly. After imaging through a large line-type camera, the error of the three-dimensional depth information is detected and the flatness height measurement algorithm is provided.

Flatness inspection method of the ball grid array package (BGA) according to the present invention

Setting the start position of the image input and the end position of the input by the motor controller (step 52),

After finding the origin in the motor control unit, correcting the binarization, labeling, and image level by a basic processing algorithm (step 54),

The camera measurement variable is determined using a standard object with all dimensions known to determine the camera's coordinate system (step 56),

 Determining whether the camera measurement variable is allowed (step 58),

Next, if it is determined that the position coordinates are calculated and allowed, the image recognition algorithm calculates the geometric structure of the incoming BGA package (step 60).

Comparing the calculated measured values with standard data (step 62),

Confirming the measurement result of step 62 to be compared (step 64),

Checking the measurement result to determine whether the measurement value is within a set range (step 66),

If the judging step (step 66) is a measured value, file processing and outputting as data (step 68), and

And displaying it on the computer monitor (step 68).

In addition, the flatness inspection device of the ball grid array package according to the present invention

 A motor for adjusting the irradiation angle, the horizontal state and the angle of the light source in a process for checking the flatness of the solder ball of the BGA package,

A CCD camera having an x-axis photosensitive element having a CCD sensor for determining an image resolution in the horizontal direction, the CCD camera having a speed and a y-z-axis CCD photosensitive element for a horizontal moving motor for determining the resolution of the vertical and the height;

A digitizer for processing the photographed line image of the CCD camera;

Adjusting the motor to move the BGA package of the moving object horizontally, while inputting the total reflection component of the light from the CCD camera in order to obtain an image, and inputs a given number of lines includes a display that outputs a two-dimensional image.

First, the slit light projection method is used to inspect the flatness of the ball grid array package (BGA) according to the present invention. This slit light projection method is effective for the input of a distance image for object recognition or the position and posture of a three-dimensional object. This method is also suitable for measuring the depth and shape of three-dimensional objects.

In the device of the present invention, since the reflected light on the metal surface, that is, the surface reflection characteristic is sensitive to the microstructure of the surface, the basic principle considering the measurement or inspection of such microstructure is applied, and the solder ball of the BGA package is applied. The error of flatness is detected.

1 shows a representative structure of a BGA package, in which FIG. 1A shows the BGA package from above and FIG. 1B shows the view from the side.

In the structure of the ball grid array (BGA) package of FIG. 1, the BGA package has a matrix structure of the balls according to the arrangement of the solder balls and the pitch pitch of the balls, but the diameter of the solder balls is generally 1 mm or less. Is characteristic.

In Fig. 1A, the symbol e is the distance between the ball centers, and the symbol s is the distance between the ball centers and the centers between the balls. In Fig. 1B the tolerance of the height is the difference between the maximum and minimum points among the balls, the average being the exact height of the ball. Therefore, the normal height of the reference becomes max + min / 2, and if it is out of the error range of ± based on this, it is detected as a defect.

Measuring the height of the balls in FIG. 1 is not possible with a 2-D image. In the current BGA package, if the height of a given ball is out of tolerance, a serious problem arises. Therefore, such a defective product must be sorted at the manufacturing stage. Therefore, it is necessary to effectively detect this and reduce the defective rate.

2A shows light reflection characteristics of the solder balls, FIG. 2B shows total reflection characteristics of the ball vertices, and FIG. 2C shows total reflection patterns of the solder balls. 2A and 2B, it can be assumed that the solder balls are spherical and the top portion of the balls is planar. This is because the point where the value becomes zero when differentiating the circumference can be regarded as a plane with zero slope. Therefore, by using the linearity and total reflection characteristics of the light, it is possible to receive the total reflection portion on the surface of the line CCD as shown in Fig. 2a. The precondition is satisfied when the incident angle of the light source and the incidence angle viewed by the line CCD are exactly the same. In FIG. 2A, the rounded one is a solder ball, the upper left is a slit light source, and the upper right is a line CCD camera.

   In the case of FIG. 2B, the light source and the CCD camera are fixed, and when the solder ball, that is, the BGA package moves horizontally, the total reflection light of the surface appears bright and the other diffuse reflection part appears dark. Using this process, the reflected light at the top of the ball is not only one point, and the surface of the CCD sensor is received not only in one line but also in several lines, resulting in an elliptical shape as shown in FIG. 2C. Will appear. In FIG. 2B, the shadow of the ball due to the angle of the incident light and the light receiving element is shown at the bottom.

 This total reflection component also occurs on the substrate surface. This pattern is shown in each ball as shown in Figure 2c, and in order to effectively process this, a slit-type light source is required to obtain uniform optical properties throughout the package. If the light source is a point light source or an area camera, it may be difficult to obtain a uniform reflection characteristic of light. In addition, it is impossible to obtain uniform total reflection characteristics in an area camera.

Figure 3 shows the geometrical structure of the height of the solder ball for measuring the height of the solder ball. In order to measure the height of each solder ball of the BGA package according to the structure of FIG. 3, each actual height of the solder balls is determined using the geometric analysis and processing of the image using the slit total reflection characteristic described above from the geometry of the device mechanism. I can measure it. First, for ease of understanding, FIG. 3 shows a geometric structure based on one ball.

3 is a view of the ball viewed from the side, the angle of slit light source SLP irradiation with the horizontal plane is θ, the angle of the line CCD camera line of sight (LCC) direction with the horizontal plane is also θ, above the center line of the ball The two straight lines that meet at the vertex become the center point (O) of the total reflection. Here, the MaxY point and the MinY point are respectively shown as upper and lower edge points of the ball image. As a result, a straight line (SLP) made by the light source and a line made by the camera's line of sight (LCC) form a two-sided triangle around the ball. Assuming that the ball in the BGA package is placed on the substrate, the length between the top and bottom edges is MaxY-MinY, and the distance △ Y between the point where the straight line and the bottom face meet through the center of the MaxY point and the total reflection area is Since the length between the point where the center line and the bottom face of this total reflection area meet and the MinY point are the same, the inner triangle in FIG. 3 also becomes an isosceles triangle.

Therefore, the height of the solder ball (diameter including the bone depth P) bh is, in principle, the diameter of the ball. However, the length of MaxY minine = Y can be known by calculating the number of lines of the line image acquired by the CCD while the motor is moving in the direction of the horizontal arrow. Thus, ΔY is also calculated in the same way. In FIG. 3, the length AB of the bottom side of the inner triangle ΔAOB is (MaxY−MinY) −2ΔY, and the height bh of the ball may be obtained as shown in Equation 1 below.

                 bh = AB / 2tanθ

At this time, the reference of the floor surface is an average of three reference points for the entire floor surface. In actual BGA packages, the solder ball is attached to a groove having a predetermined reference depth (about 0.2 mm) on the substrate, so the length minus that depth becomes the actual height.

4 is a schematic diagram of an apparatus for checking BGA package flatness. As shown in FIG. 4, an apparatus for realizing a height measuring algorithm of the solder ball is implemented by applying the height measuring method of the solder ball shown in FIG. 3.

On the other hand, Figure 5 is a functional block diagram of the device manufactured to check the flatness of the BGA package. The accuracy of the measurement result is an important parameter in the line image of uniform image quality and the digitizer 40, the angle of the illuminator 36 of the light source, the horizontal state and the angle adjustment of the CCD camera 38. Here, the image resolution of the horizontal (x-axis) depends on the number of cells of the CCD element, and the resolution of the vertical (y-axis) and height (z-axis) is determined by the speed of the horizontal motor 40 and the number of lines of the CCD sensor. do.

The CCD camera 38 includes an x-axis photosensitive element having a CCD sensor for determining image resolution in the horizontal direction, and has a speed and a y-z-axis CCD photosensitive element of a horizontal motor for determining resolution of height and height. The photosensitive line image of the CCD camera 38 is processed by the digitizer 40.

The horizontal movement motor 40 adjusts the irradiation angle, the horizontal state, and the angle of the light source in a process for checking the flatness of the solder ball of the BGA package. Image acquisition method is to adjust the motor 40 to move the BGA package 44 on the mobile workbench 42 horizontally while inputting the total reflection component of the light from the line CCD camera 38 in order to input the given number of lines, the image is A two-dimensional image such as an area type is output to the display 48.

In order to measure the BGA package from the measuring apparatus described with reference to FIGS. 3 and 4, the first requirement is that the slit light, the CCD cell, and the measurement surface be horizontally parallel, and the error range of the angle between the incident light and the reflected light is 1 It is necessary to adjust to be within degrees. In addition, it is necessary to accurately measure the standard BGA package, which is a regular product for measurement, and to have a low spherical aberration caused by the lens of the camera.

5 is a flowchart of a measurement process for determining measurement parameters of an apparatus.

In order to measure the flatness of the BGA package solder ball is made in the order shown in FIG. In FIG. 5, when the standard data is input, the initial value is set in advance to the height of the ball, the distance between the balls, the number of balls in the horizontal direction, the number of balls excluded from the horizontal and vertical directions in the package, and the like. The motor control unit finds the origin for setting the measurement range. The start position of the image input and the end position of the input can be set, and the acceleration / deceleration and the distance, the movement speed, and the like can be arbitrarily changed (step 52). After finding the origin in the motor controller, the basic processing algorithm processes the binarization, labeling, and image level correction to effectively extract the total reflection area of the solder ball and shadow in the image (step 54). Using a standard object of known dimensions, the value of the variable for determining the camera's coordinate system is checked (step 56), and the camera's measurement variable is judged to be acceptable (step 58). It is calculated and stored in memory. This step 58 is an initial setting step for measuring the BGA package, and the measurement process to be measured is executed later.

The image recognition algorithm calculates the geometric coordinates of the BGA package, such as the position coordinates, the distance between the balls, the tolerance, and the ball diameter of the solder balls of the input BGA package (step 60), wherein the measured values are calculated as standard data. (Step 62), and the measurement result is confirmed (step 64). The measurement result is checked to determine whether the measured value is within the set range (step 66). If the determined measured value is within the set range, the file is processed and output as data (step 68). Thereafter, it is displayed on the computer monitor (step 68).

According to the measurement processing procedure described above, the results of the present invention, which test the performance of the device manufactured in the present invention, centered on a BGA package having a diameter of 0.8 mm, are as follows.

First, the inspection speed of the implemented device can be implemented in less than 1 second per one BGA package, and can be detected to less than 0.12mm (± 0.06mm), which is a tolerance of height for 0.8mm diameter solder balls.

Second, the position (XY plane) deviation range tolerance of the solder balls is 0.1mm, but the resolution is 20μm (40mm / 2048), the resolution in the vertical direction (Y direction) is further improved by reducing the speed of the motor You can.

6 is an example of acquiring the entire image of the BGA package to be measured, and it can be seen that total reflection reflected from the vertex appears at the bottom of the ball. The diameter of the ball here is 0.8 mm. In this image, the number of CCD devices is 4096. The camera lens used is a Nikon 35mm standard lens, but the lens aperture is small compared to the length of the CCD, so the error due to the spherical aberration of the lens is left and right. In the center of the image, a relatively clear image can be obtained, but a slightly blurry image appears on both left and right sides, resulting in a measurement error of about 40-50 μm. To correct this, the use of a large aperture lens is required. Since the slit light is irradiated with an inclination on the upper part of the ball, the shadow of the ball appears, but since it becomes a uniform pattern for the entire ball, the height of the ball can be measured by the geometric analysis of the solder ball described above.

7 is a partial image of the inspection result of the BGA package, showing the result of measuring the height of the solder ball and corresponds to a part of the entire image. In FIG. 7, a ball indicated by a rectangle on the outside is out of the allowable range of the height, and it is determined that the ball is defective. The measurement result value for the actual height (flatness) of the ball is displayed on each ball. The dot marked with a + in the middle of the ball indicates the positional coordinates for inspecting the horizontal and vertical positional deviation of the solder ball. Therefore, the inspection of the BGA package by this algorithm can find not only the flatness of the ball but also the defects due to the X-Y coordinate, that is, the positional deviation.

In FIG. 7, rectangular portions 71, 72, 73, 74, and 75 show an example in which the solder balls are defective. The balls of this type are detected as defective.

8 is an enlarged partial image of a ball determined to be normal. 8 is a partial image of the BGA package determined to be normal.

As described above, the present invention is the result of measuring the size of the image to 2048 × 2048 pixels in the height measurement of the solder ball, but the resolution of the X-axis is fixed to improve the accuracy, but if the speed of the motor is reduced, Y ( Since the resolution in the vertical) direction is variable, more accurate height measurement is possible by increasing the number of lines of the acquired image.

1 illustrates a representative structure of a ball grid array (BGA) package, in which FIG. 1A is a plan view of a BGA package, FIG. 1B is a side view,

2A is an explanatory diagram showing light reflection characteristics of a solder ball;

2B is an explanatory diagram showing total reflection characteristics of a ball vertex;

2C is an explanatory diagram showing a total reflection pattern of a solder ball;

3 is a view showing a geometrical structure of the height of the solder ball for measuring the height of the solder ball,

4 is a schematic diagram of a BGA package flatness inspection apparatus for realizing the height measurement algorithm of the solder ball described in FIG.

5 is a functional block diagram of an apparatus fabricated to check BGA package flatness,

6 is an exemplary view acquiring an entire image of a BGA package to be measured;

7 is a view showing the inspection results of the BGA package measuring the height of the solder ball,

8 is a partial image diagram of a BGA package showing a magnified partial image of a ball determined to be normal.

Claims (4)

In the flatness inspection method of the ball grid array package (BGA), Setting the start position of the image input and the end position of the input by the motor controller (step 52), Processing the binarization, labeling, and correction of the image level to effectively extract the total reflection areas of the solder balls and shadows in the image by finding the origin in the motor control unit (step 54); The camera measurement variable is determined using a standard object with all dimensions known to determine the camera's coordinate system (step 56), Determining whether the camera measurement variable is allowed (step 58), If it is determined that the position coordinates by the camera measurement variable is allowed to be calculated and calculated by measuring the solder ball position coordinates, the distance between the ball, the tolerance, the diameter of the ball of the BGA package input by the image recognition algorithm (step 60), Comparing the calculated measured values with standard data (step 62), Confirming the measurement result of step 62 to be compared (step 64), Checking the measurement result to determine whether the measured value is within a set range (step 66), If the determining step (step 66) is a measured value, file processing and outputting as data (step 68), and And displaying it on a computer monitor (step 68). delete delete In the flatness inspection device of the ball grid array package, A motor for adjusting the irradiation angle, the horizontal state, and the angle of the light source in a process for checking flatness on the solder balls of the ball grid array package; A CCD camera having an x-axis photosensitive element having a CCD sensor for determining image resolution in the horizontal direction, the CCD camera having a speed and a y-z-axis CCD photosensitive element of a horizontally movable motor for determining the resolution of the vertical and the height; A digitizer for processing the photographed line image of the CCD camera; Adjusting the motor to move the ball grid array package of the moving object horizontally, while inputting the total reflection component of the light from the CCD camera in order to obtain an image, characterized in that it comprises an indicator that outputs a two-dimensional image by inputting a given number of lines Flatness inspection device of the ball grid array package.