JPH06224267A - Inspection device for wire bonding - Google Patents

Abstract

PURPOSE:To provide an inspection device which can accurately measure the thickness of a ball pressed in the upper surface of a semiconductor chip by measuring an amount of movement of a focus lens moved until the plane image of the ball is into agreement with the pattern image of the cone part of the preset ball. CONSTITUTION:This inspection device is provided with an optical camera 11 having a focus lens 15 for taking in the plane image of a ball 3 pressed on a semiconductor chip 1 and a setting means for setting predetermined clearance bet the upper surface of the semiconductor chip 1 and the focus lens 15, and also provided with a driving means 12 for moving the focus lens 15 in the direction of being at a right angle to the upper surface of the semiconductor chip 1 and a measuring means for measuring an amount of movement of the focus lens 15 moved by the driving means 12. Further, it is provided with a decision means for deciding as to whether the plane image of a ball 3 taken in through the focus lens 15 is in agreement with the pattern image of the cone part 5 of a preset ball 3 or not.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire bonding inspection apparatus suitable for inspecting the thickness of a ball pressed onto a semiconductor chip.

[0002]

2. Description of the Related Art Generally, in a wire bonding process of a semiconductor device, various shape inspections are performed after bonding in order to ensure the reliability of products. Most of this type of inspection can be performed by so-called two-dimensional inspection such as the ball diameter and position on the first bond side and the crescent diameter and position on the second bond side, as well as the bending of the wire and the distance between the wires. It was

[0003]

By the way, in order to grasp the crimp strength of the wire more accurately, in addition to the above-mentioned inspection items, it is necessary to inspect the thickness of the ball after bonding. This is because the crushing condition of the ball crimped on the semiconductor chip greatly affects the crimp strength of the wire. However, in the conventional inspection apparatus, when the measurement range is as wide as 100 to 300 μm like the height dimension of the wire, the measurement can be performed relatively easily by the well-known autofocus technique. In the case where the measurement range is as narrow as 10 to 30 μm as described above, it was not possible to accurately measure it even by making full use of the well-known autofocus technology.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a wire bonding inspection device capable of accurately measuring the thickness of a ball pressed onto the upper surface of a semiconductor chip. And

[0005]

The present invention has been made in order to achieve the above-mentioned object, and an electrode pad formed on the upper surface of a semiconductor chip and an inner lead arranged around the semiconductor chip are connected to a wire. In a wire bonding for connecting with each other, an inspection device for inspecting a thickness of a ball crimped on an upper surface of a semiconductor chip, comprising an optical camera having a focus lens for capturing a plane image of the ball crimped on the semiconductor chip. A setting means for setting a predetermined distance between the upper surface of the semiconductor chip and the focus lens of the optical camera, and a driving means for moving the focus lens of the optical camera in a direction perpendicular to the upper surface of the semiconductor chip, Measuring means for measuring the amount of movement of the focus lens by the driving means, and the bow taken through the focus lens Plane image is obtained by including a determination means for determining whether matching cone pattern image of a ball which is set in advance.

[0006]

In the wire bonding inspection apparatus of the present invention, the movement amount of the focus lens moved until the planar image of the ball taken in through the focus lens and the preset cone pattern image of the ball coincide with each other. Based on this, the thickness of the ball pressed onto the upper surface of the semiconductor chip is detected.

[0007]

First, before describing the wire bonding inspection apparatus in this embodiment, the ball pressure bonding mode in wire bonding will be described. Generally, wire bonding is performed using a bonding tool such as a wedge tool or a capillary, and in particular, in the case of ball bonding, the capillary is used.

In this type of wire bonding, first, a wire is paid out from the tip of the capillary, and then a spherical ball is formed at the tip of the drawn wire by heat fusion. Next, as shown in FIG. 2A, the semiconductor chip 1
The ball 3 is pressed against the electrode pad (not shown) formed on the upper surface of the device by the pressing force of the capillary 2, and ultrasonic waves or heat is further applied to press the ball 3 onto the electrode pad. After that, as shown in FIG. 2B, the capillary 2 is raised, and the capillary 2 is moved toward the second bond side, that is, the inner lead (not shown) as it is.

The ball 3 thus crimped to the electrode pad on the semiconductor chip 1 is in a crushed state as shown in FIG. At this time, on the upper side of the ball 3, a cone portion called a cone portion 5 is always formed by the inside chamfer portion 4 (see FIG. 2) formed at the tip of the capillary 2, and the periphery of the cone portion 5 is flat. The part 6 is formed. Therefore, for example, when a light source is installed above the semiconductor chip and light is emitted from this light source toward the balls on the semiconductor chip, as shown in FIG.
The light radiated to the outside is reflected outward, and the light radiated to the flat portion 6 around the cone portion 5 is reflected toward the original light source. From this, the ball on the semiconductor chip is irradiated with light,
When this is displayed on the monitor with an optical camera,
As shown in the upper part of the drawing, the area from the center to the contour of the cone 5 is projected dark (blackish),
The peripheral flat portion 6 is bright (whitish) due to the reflection of light.
Projected.

Based on the above contents, the wire bonding inspection apparatus of the embodiment will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram for explaining a wire bonding inspection apparatus according to the present invention.
First, in the figure, 1 is a semiconductor chip, and an electrode pad (not shown) is formed on the upper surface of the semiconductor chip 1. In addition, inner leads 7 are provided around the semiconductor chip 1.
Are arranged, and the electrode pads (not shown) on the semiconductor chip 1 and the inner leads 7 are connected via the wires 8. The ball 3 formed at one end of the wire 8 is pressure-bonded onto the semiconductor chip 1 by a capillary (not shown).

Here, the wire bonding inspection apparatus of this embodiment is for inspecting the thickness t of the ball 3 pressed onto the semiconductor chip 1, and roughly includes an optical camera 11 and setting means. Drive means 12 and measuring means 13
And a determination means 14.

First, the optical camera 11 is mounted on an XY table (not shown) and is designed to move horizontally according to a pre-programmed instruction by driving the XY table. Further, the optical camera 11 has a built-in focus lens 15 for taking in a planar image of the ball 3 pressed onto the semiconductor chip 1. Furthermore,
The optical camera 11 has a built-in diaphragm mechanism, and this diaphragm mechanism is opened during inspection so that the subject depth of the focus lens 15 can be set as shallow as possible.

The setting means sets a predetermined distance between the upper surface of the semiconductor chip 1 and the focus lens 15 of the optical camera 11. In the present embodiment, for example, the laser light emitted from the laser emitting section 16 is reflected by the half mirror 17 incorporated in the optical camera 11 as shown by the broken line arrow in the figure, and this is irradiated onto the upper surface of the semiconductor chip 1. Thus, the separation distance from any three points on the upper surface of the semiconductor chip 1 to the focus lens 15 is obtained, and the plane equation of the upper surface of the semiconductor chip 1 is calculated. Then, the optical camera 11 is moved based on the calculated equation of the plane, and the semiconductor chip 1 at the pressure-bonded portion of the ball 3 to be measured is moved.
A predetermined separation distance (described later) can be set between the upper surface of the lens and the focus lens 15 of the optical camera 11.

The driving means 12 drives the focus lens 1 of the optical camera 11 in a direction perpendicular to the upper surface of the semiconductor chip 1.
It is for moving 5. In the present embodiment, the focus lens 15 of the optical camera 11 is set to move by 1 pitch in 1/60 seconds, and the lens movement amount per pitch can be set arbitrarily in consideration of inspection accuracy and the like. .

The measuring means 13 measures the amount of movement of the focus lens 15 by the driving means 12,
In this embodiment, the plane image of the ball 3 is passed through the focus lens 15 to 1 / 60th by the operation control of the optical camera 11.
It was set to capture every second. As a result, the timing of capturing the screen and the moving speed of the focus lens 15 are synchronized with each other, so that the amount of movement of the focus lens 15 can be accurately measured from the number of captured planar images.

The determination means 14 determines whether or not the plane image of the ball 3 taken in through the focus lens 15 matches a preset cone portion pattern image (described later) of the ball, and in the present embodiment. By comparing the plane image of the ball 3 actually taken in with the preset cone portion pattern image by image processing,
It was determined whether or not both images match.

Next, the operation procedure for inspecting the ball thickness using the wire bonding inspection apparatus of this embodiment will be described. First, in the first step, the optical camera 11 is arranged above the ball 3 to be measured, and a predetermined distance is provided between the upper surface of the semiconductor chip 1 and the focus lens 15 of the optical camera 11 at the pressure-bonded portion of the ball 3. Set the separation distance of. In this embodiment, the optical camera 11 is positioned so that the focus position of the focus lens 15 is on the upper surface of the semiconductor chip 1, and the above-mentioned distance is set.

In consideration of the processing capability of the inspection device, it is better to position the optical camera 11 so that the initial focus position of the focus lens 15 is slightly above the standard range of the thickness t of the ball 3. It is efficient. As an example, the standard range of the thickness t of the ball 3 is 10 to 20 μm.
If it is set to, the focus position of the focus lens 15 is set to be above the upper surface of the semiconductor chip 1 by about 8 μm.

Next, in the second stage, the semiconductor chip 1
While moving the focus lens 15 in a direction perpendicular to the upper surface of the device, in this case, at a constant pitch, the plane images of the balls 3 pressed onto the semiconductor chip 1 are sequentially taken in through the focus lens 15.

Here, a plane image of each ball 3 when the focus position of the focus lens 15 exists in F1 to F5 as shown in FIG. 5 will be briefly described. First, when the focus position is at F1, the pattern of the ball 3 is projected in a faint form as shown in FIG. 6 (a).
Next, when the focus position is at F2, FIG.
As shown in, the outline of the ball 3 is slightly blurred and slightly projected. Then, when the focus position is at F3, the contour portion of the cone portion 5 of the ball 3 is clearly projected as shown in FIG. 6 (c). Further, when the focus position is at F4, the root portion of the wire 8 and the ball 3 is thinly projected in an overall blurred form as shown in FIG. 6 (d). When the focus position is located at F5, the streak of the wire 8 is lightly projected as shown in FIG. 6 (e).

In the plane image, the plane image of the ball 3 shown in FIG. 6 (c) corresponds to the cone portion pattern image of the ball stored and set in the inspection apparatus in advance.
That is, the image previously set in the device as the cone image pattern of the ball means the ball 3 to be measured.
It is an image in which the contour portion of the cone portion 5 is clearly captured. The position at which the contour of the cone portion 5 is clearly projected is only when the focus position of the focus lens 15 is at F3. This is because when the ball 3 is irradiated with light, The light is reflected outwardly and is projected darkly, and in the flat portion 6 around the cone portion 5, the light is reflected toward the optical camera 11 side and is projected brightly, so that the boundary portion is the contour portion of the cone portion 5. Because it was clearly projected.

Therefore, in the present embodiment, the plane image of the ball 3 actually taken in through the focus lens 15 and the preset cone portion pattern image are compared one after another by image processing, and the two images match each time. Whether or not it is determined. Then, when the both images described above match, the thickness t of the ball 3 (FIG. 1) is determined based on the amount of movement of the focus lens 15 that has been moved until then.
Is detected. That is, displacing the focus position from F1 to F3 means, in other words, moving the focus lens 15 upward by that much, that is, from f1 to f3 (FIG. 1). The thickness t of the ball 3 is accurately determined by measuring the amount of movement by the measuring means.

In the above embodiment, one ball 3 is described as the object to be measured. However, if a plurality of balls are projected on one screen, the number of balls can be measured by one operation. It is also possible to inspect the thickness at the same time.

[0024]

As described above, according to the wire bonding inspection apparatus of the present invention, the plane image of the ball taken in through the focus lens and the preset cone image of the ball are matched. By detecting the ball thickness based on the amount of movement of the focus lens, it becomes possible to measure the thickness of the pressure-bonded ball on the semiconductor chip with high accuracy. As a result, it is possible to more accurately grasp the crimping strength of the wire, and it can be expected that the reliability of the product in the wire bonding process is improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram for explaining a wire bonding inspection device according to the present invention.

FIG. 2 is a schematic diagram illustrating an operation of wire bonding.

FIG. 3 is a perspective view showing a pressure bonding shape of a ball after bonding.

FIG. 4 is a diagram illustrating a traveling direction of light emitted from an optical camera.

FIG. 5 is a diagram illustrating a focus position of a focus lens.

FIG. 6 is a diagram illustrating a plane image of a ball at each focus position.

[Explanation of symbols]

 1 Semiconductor Chip 3 Ball 5 Cone Part 7 Inner Lead 8 Wire 11 Optical Camera 12 Driving Means 13 Measuring Means 14 Judging Means 15 Focus Lens

Claims (1)

[Claims] 1. In wire bonding for connecting an electrode pad formed on an upper surface of a semiconductor chip and an inner lead arranged around the semiconductor chip with a wire, the thickness of a ball pressed onto the upper surface of the semiconductor chip. And an optical camera having a focus lens for capturing a planar image of a ball crimped on the semiconductor chip, between an upper surface of the semiconductor chip and a focus lens of the optical camera. Setting means for setting a predetermined separation distance, driving means for moving the focus lens of the optical camera in a direction perpendicular to the upper surface of the semiconductor chip, and measuring the amount of movement of the focus lens by the driving means. A plane image of the ball captured through the measuring means and the focus lens is preset. A wire bonding inspection device, comprising: a determining means for determining whether or not the image matches a cone portion pattern image of the formed ball.