JP2001118880A - First bonding point inspection method in wire bonding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a first bonding point inspection method in a wire bonding, in which the position of a ball and the size of the ball can be detected stably. SOLUTION: In a first bonding point inspecting method, which detects the size of a ball bonded to a bonding point on a pad on a chip and the position of the ball, an image of a double circle, which consists of an outer circle to show the outline of the external shape of the ball, and an inner circle to show the inside of an impression due to a capillary tool, is acquired, first the inner circle to show the inside of the impression due to the capillary tool is detected, the outer circle to show the outline of the external shape of the ball is detected by searching the outside of this impression, then the position coordinates of the ball and the size of the ball are detected from the detected outer circle, to show the outside of the external shape of the ball. Hereby, even in the case where the ball is crushed and even in the case, where the position of the ball is shifted and the ball is protruded from the pad, the position coordinates of the ball and the size of the ball can be stably detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bonding point inspection method in wire bonding for connecting a chip and a substrate.

2. Description of the Related Art Wire bonding for connecting a chip to a substrate, such as a lead frame or a printed circuit board, on which the chip is mounted by wires is performed as follows. First,
An electrical spark is generated between the lower end of the wire drawn down from the lower end of the capillary tool and the torch, and a ball is formed at the lower end of the wire. Bonding is performed on the upper surface of the mounted chip (hereinafter, referred to as “first bonding”). Next, after once moving the capillary tool upward, the lower end of the capillary tool is lowered toward the pad of the substrate while drawing a predetermined trajectory to bond the wire to the substrate (hereinafter, referred to as “second bonding”). After the wire bonding, resin sealing is performed to protect the chips and wires. Prior to this resin sealing, an inspection for confirming the state of the wire bonding is performed, and whether or not the normal wire bonding is performed is inspected. In this inspection, the size and position of the bonded ball are to be detected at the first bonding point.
By detecting these, it can be checked whether or not the bonding has been performed normally, and it can be estimated whether or not there is any abnormality in the setting of the bonding conditions of the bonding apparatus such as the bonding pressure and the bonding position. By the way, as a method of detecting the position and size of an indentation of a ball or a capillary tool, a method based on image recognition is known. In this method, a bonding point is imaged by a camera, and the shape of the ball is determined based on the contrast difference between the ball and the pad on the obtained image, thereby detecting the size and position of the ball.

However, the above-described conventional inspection method at the first bonding point includes:
There were the following problems. In the first bonding, a ball formed at the lower end of a wire is pressed against a pad by a capillary tool. At this time, depending on the pressing force, the ball may be crushed and may not have a normal circular shape. In such a case, the portion crushed by the capillary tool becomes a glossy portion on the image, and there is no contrast difference with the pad, so that it is not possible to obtain an accurate approximate circle of the ball. When the edge of the crushed ball protrudes from the pad, a process of obtaining an approximate circle from an incomplete partial arc is performed, but the result of this approximation may be significantly different from the actual arc shape. As described above, according to the conventional bonding point inspection method, when the ball is greatly crushed or protruded, the ball shape cannot be accurately detected, and therefore, the ball position and size cannot be correctly detected, and it is difficult to perform a normal inspection. There was a problem. Therefore, an object of the present invention is to provide a method of inspecting a first bonding point in wire bonding, which can stably detect the position and size of a ball.

According to a first aspect of the present invention, there is provided a method for inspecting a bonding point in wire bonding, wherein a bonding point of a chip pad is imaged by a camera, and the imaged result is image-processed to bond to the bonding point. A method for inspecting a first bonding point in wire bonding for detecting a size and a ball position of a ball, wherein an indentation detecting step of detecting an indentation by a capillary tool generated in the ball, and searching outside the indentation by searching for an indentation The method includes a contour detecting step of detecting a contour of the ball, and a position / size detecting step of detecting a position coordinate and a size of the ball from the detected contour of the ball. A method for inspecting a bonding point in wire bonding according to claim 2 is the method for inspecting a bonding point in wire bonding according to claim 1, wherein a temporary center coordinate of the ball is determined based on an indentation detection result in the indentation detecting step. A provisional size is obtained, and if no contour is detected in the contour detection step, the provisional center coordinates and the provisional size are output as the center coordinates and size of the ball. According to the present invention, after the indentation detecting step of detecting the indentation of the ball by the capillary tool, the outside of the indentation is searched to detect the contour of the ball, so that the ball is crushed and the double circle is formed on the image. The position coordinates and size of the ball can be stably detected even when the ball is in an arc shape or when the ball position is shifted and protrudes from the image.

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a bonding point inspection apparatus in wire bonding according to an embodiment of the present invention, FIG. 2 is a plan view of a substrate on which the wire bonding is performed, and FIG. 3 is an enlarged side view of the first bonding point. FIG. 4, FIG. 4 is an image diagram of the first bonding point, FIG. 5 is a flowchart of the ball detection processing of the first bonding point, FIG. 6, FIG. 7, FIG.
0 and FIG. 11 are explanatory diagrams of the ball detection processing at the first bonding point. First, a configuration of a bonding point inspection apparatus in wire bonding will be described with reference to FIG. In FIG. 1, a substrate 2 is placed on a stage 1. A chip 4 is mounted on the substrate 2.
The pads 3 on the substrate 2 and the pads 5 on the chip 4 are connected by wires 6. A movable table 11 including an X table 9 and a Y table 10 is disposed above the stage 1. The camera 8 is mounted on the movable table 11. The camera 8 is moved by the movable table 11 in the X direction and the Y direction.
It moves horizontally in the direction to image the wire 6 connecting the chip 4 and the substrate 2. A lighting unit 7 is mounted below the camera 8. The illumination unit 7 illuminates the substrate 2 and the chip 4 from above during imaging. An AD converter 12 is connected to the camera 8. The AD converter 12 converts the image data captured by the camera 8 into image data. The image storage unit 13 is A
The D-converted image data is stored. The inspection processing unit 14 performs processes such as searching for an edge of an indentation of a ball or a capillary tool, and calculating an approximate circle of the obtained edge point based on the image data of the bonding point. The storage unit 15 stores bonding coordinate data, data used during wire bonding such as wire size, detected data, determination values, and the like. The display unit 16 is a monitor that displays an inspection screen. Next, the wire bonding point will be described with reference to FIG. In FIG. 2, a chip 4 is mounted on a substrate 2. A large number of pads 5 are formed on the upper surface of the chip 4 along the edge. The pads 3 are formed on the substrate 2 at positions corresponding to the respective pads 5 of the chip 4. Wires 6 are radially bonded so as to connect the pads 5 of the chip 4 and the pads 3 of the substrate 2. The bonding point of the pad 5 of the chip 4 is a first bonding point 20, and the bonding point of the pad 3 of the substrate 2 is a second bonding point 30. Here, the state of the ball at the first bonding point will be described. At the first bonding point, bonding is performed by pressing the ball formed by the spark onto the pad 5 of the chip 4 using a capillary tool. When the bonding is performed normally, the ball B is bonded to a substantially central portion of the pad 5 while maintaining a substantially spherical outer shape, as shown in FIG. However, when the conditions such as the pressure load and the bonding position change, the condition shown in FIG.
In some cases, the ball B does not have a normal ball shape, and the ball B is crushed by the capillary tool to have an abnormal ball shape. In this case, as shown in FIG. 3B, the ball B is crushed halfway, and the indented portion formed by the capillary tool becomes a flat flat portion Ba, and the entire shape of the ball B has an irregular shape having a step. Further, when the bonding position is shifted, the ball B is pressure-bonded to one end of the pad 5 as shown in FIG. Next, the inspection of the first bonding point by the bonding point inspection apparatus will be described with reference to the drawings. First, as shown in FIG. 1, the substrate 2 on which the chip 4 is mounted is placed on the stage 1. Next, the movable table 1
The camera 1 is driven to move the camera 8 above the bonding points 20 and 30 to be inspected, the illumination unit is turned on, and the camera 8 images the bonding points 20 and 30. The captured data passes through an AD conversion unit 12 and is stored in an image storage unit 13.
And stored as image data. The image data is sent to the inspection processing unit 14, and the inspection processing of the image data of each bonding point described below is performed. Here, an image of a first bonding point obtained by imaging will be described with reference to FIGS. FIG.
(A) and (b) indicate the direction of incidence of illumination light, and the upward arrow b indicates the direction of reflection of reflected light. The light incident on the surface of the pad 5 and the indented portion Ba is reflected upward, and the light incident on the side surfaces of the wire 6 and the ball B is reflected in an oblique direction. Therefore, on the image data captured from above by the camera 8, With the pad 5 and the indentation part Ba,
The brightness differs between the side surfaces of the wire 6 and the ball 6a.
Therefore, by binarizing the image data,
As shown in FIG. 4A, an image in which the surface of the pad 3 is a bright image and the ball B and the wire 6 are dark images is obtained. When the bonding point is in the state shown in FIG.
As shown in FIG. 7, a substantially double circular image is obtained in which the surface of the pad 3 and the indented portion Ba are bright images and the side portions Bb of the wire 6 and the ball B are dark images. When the bonding position is shifted as shown in FIG. 3C, an image in which the relative position between the ball B and the pad 5 is deviated as shown in FIG. A method for obtaining the position and size of the ball B from the image data thus obtained will be described with reference to the drawings. Here, in the case where bonding is performed in a normal state as shown in FIG. 4A, there is no particular difficulty in the conventional detection method using contour detection.
In the case where the ball B is partially crushed or the position is largely displaced as in (b) and (c), it is difficult to detect an appropriate ball position and size by the conventional method using contour detection. . Hereinafter, a method of detecting the position and size of the ball for such a case will be described with reference to the drawings along the flow of FIG. First, an indentation detection step of detecting an indentation (tool indentation) generated by a capillary tool will be described. In FIG. 5, first, primary detection of a tool impression is performed using a square pattern (ST1). In this primary detection, a reference pattern corresponding to the size of the dark image portion B1 inside the tool impression is set in the field of view as shown in FIG. That is, a square reference pattern R having a size inscribed in a circle (inner circle) indicating the inner boundary of the tool indentation is set. When an indentation is detected by pattern matching using the reference pattern R, the position where the reference pattern R is inscribed in the inner circle is detected by moving the control area in the field of view and searching. The position of the impression area is defined as the position of the control area. In setting the reference area, a reference window W is set at a predetermined position on the opposite side to the wire extending direction in order to remove noise due to the extension of the wire 6. That is, in pattern matching, indentation detection is performed on the condition that the inside of the reference window W is a bright image portion. As a primary detection method of the tool indentation, a method of detecting using the black-and-white pixel ratio in the reference area in addition to the pattern matching may be used. Next, secondary detection of tool impressions is performed by contour detection (ST2). As shown in FIG. 7, the contour of the inner circle is detected by searching the inward direction from the inside of the indentation detected in (ST1) and detecting the contour point Pa. Next, the temporary center coordinates of the ball B and the temporary size of the ball B are calculated based on the detected outline (ST3). Here ball B
The temporary center coordinates and the temporary size mean the coordinates and the diameter d of the center point Bc of the inner circle of the double circle appearing in the image when the ball B is crushed. Next, a contour detecting step of detecting the contour of the ball will be described. Here, a process for detecting the true shape of the ball B, that is,
Processing for detecting a circle (outer circle) outside the tool impression is performed. First, a start point Ps for detecting the contour of the ball B is detected (ST4). Here, a search is performed outward from the already detected center point Bc of the inner circle, and the contour point of the outer circle is obtained as the contour tracking start point Ps. In this case, as shown in FIG. 8, the search direction is set to four directions at an angle of 45 degrees so that the probability of picking up noise due to the outer periphery of the pad 5 is reduced as much as possible. here,
It is determined whether or not the start point Ps has been detected (ST
5). As described above, when bonding is performed normally, no double circle appears in the image, and therefore, the outline of the ball provided that it is located outside the inner circle detected by the primary detection is not detected. . In this case, the process proceeds to the step described later. When the start point Ps is detected, the contour of the ball B is detected from the detected start point Ps by contour tracing (ST6). In this contour tracking, a case where the contour points Pb are continuously detected at a predetermined pitch from the first start point, that is, a case where the contour can be detected with one stroke as shown in FIG.
As shown in (c), there is a case where the contour point cannot be detected continuously due to a shift in the bonding position. In the former case, an operation for obtaining an approximate circle is performed based on the obtained contour point Pb. In the latter case, a plurality of start points Ps detected in (ST4) are determined as shown in FIG. A process of obtaining an approximate circle by connecting pieces of a contour line formed by the contour points Pb detected as the starting points is performed. In any case, an approximate circle indicating the outline of the ball B is obtained by this outline detection. Next, the position / size detection step will be described. Here, the center coordinates and the diameter of the ball are calculated from the detected outline of the ball (ST7). FIG.
As shown in FIG. 1, the coordinates of the center point C of the approximate circle CR determined from the contour point Pb and the diameter D of the approximate circle CR are determined. If the start point Ps is not detected in (ST5), that is, if the indentation of the crushed ball B is not detected, it is determined that the normal bonding as shown in FIG. 3B is performed. Then, the center coordinates and the temporary size of the temporary ball obtained in (ST3) are replaced with the center coordinates of the ball B and the diameter of the ball (ST3).
8). Then, the center coordinates of the ball and the diameter of the ball are output (ST9), and the detection processing of the ball position / size is completed. Then, the first bonding point is inspected by comparing the output ball position and ball size with the reference data. The inspection results obtained in this way are used for pass / fail judgment of each inspection object, and by analyzing the data tendency of a large number of continuously obtained inspection results, it is possible to determine whether there is an abnormality in the bonding apparatus. Is used as data for

According to the present invention, the contour of the ball is detected by searching outside the indentation after the indentation detecting step of detecting the indentation of the ball by the capillary tool, so that the ball is crushed. Thus, even when the image is formed into a double circle on the image, or when the ball position is shifted and protrudes from the image, the position coordinates and the size of the ball can be detected stably.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a bonding point inspection apparatus in wire bonding according to an embodiment of the present invention.

FIG. 2 is a plan view of a substrate on which wire bonding is performed according to an embodiment of the present invention.

FIG. 3 is an enlarged side view of a first bonding point according to the embodiment of the present invention;

FIG. 4 is an image diagram of a first bonding point according to the embodiment of the present invention;

FIG. 5 is a flowchart of a first bonding point ball detection process according to one embodiment of the present invention;

FIG. 6 is an explanatory diagram of a first bonding point ball detection process according to one embodiment of the present invention;

FIG. 7 is an explanatory diagram of ball detection processing at a first bonding point according to the embodiment of the present invention;

FIG. 8 is an explanatory diagram of a first bonding point ball detection process according to one embodiment of the present invention;

FIG. 9 is an explanatory diagram of a first bonding point ball detection process according to one embodiment of the present invention;

FIG. 10 is an explanatory diagram of ball detection processing of a first bonding point according to one embodiment of the present invention;

FIG. 11 is an explanatory diagram of a first bonding point ball detection process according to one embodiment of the present invention;

[Explanation of symbols]

 2 substrate 4 chip 5 pad 6 wire 8 camera 20 first bonding point B ball Ba flat part Bc center point Pa, Pb contour point

Claims (2)

[Claims] 1. A method of inspecting a first bonding point in wire bonding in which a bonding point of a pad of a chip is imaged by a camera, and the imaged result is processed to detect a size and a position of a ball bonded to the bonding point. An indentation detecting step of detecting an indentation by a capillary tool generated in the ball, an outline detecting step of detecting an outline of the ball by searching outside the indentation, and a step of detecting an outline of the ball. A method for detecting a bonding point in wire bonding, comprising: a position / size detection step of detecting a center coordinate and a size of a ball. 2. The provisional center coordinates and provisional size of the ball are obtained in the indentation detection step based on the indentation detection result. If no contour is detected in the contour detection step, the provisional center coordinates and the provisional size are determined. 2. The method for inspecting a bonding point in wire bonding according to claim 1, wherein is output as the center coordinates and the size of the ball.