JP2880355B2 - Wire bonding inspection equipment - Google Patents

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, and more particularly to an apparatus for measuring a wire height.

[0002]

2. Description of the Related Art Conventionally, a wire bonding inspection apparatus has
It is configured as shown in FIG. Inspection items of the wire bonding inspection apparatus are roughly classified into measurement of wire height, measurement of wire position, measurement of ball shape, and measurement of crescent shape.

[0003] The measurement of the wire height is performed in the following procedure.
According to the first method, the epi-illumination device including the light source 1, the first condenser lens 2, the second condenser lens 3, and the like is used to connect the chip surface 17, the wire portion 18, and the inner lead 19 via the objective lens 4. Perform epi-illumination. The reflected light from the chip surface 17, the wire portion 18, and the inner lead 19 by this illumination passes through the objective lens 4 again, further passes through the half mirror 5 and the half mirror 6, and is connected to the TV camera 9 by the relay lens 7. Image. Then, the TV camera 9 uses the chip surface 17 and the wire portion 1.
8. Observe the inner lead 19. Further, the chip 1 is moved by the autofocus unit 8 through the objective lens 4.
7. Focus on the wire portion 18 and the inner lead 19.

When the optical head 10 composed of the light source 1 to the TV camera 9 is mounted on the stage 12, the optical axis of the optical head 10 is perpendicular to the upper surface of the rail 14.
Adjust with high accuracy. Adjustment is performed by the optical head 10 and the support 1
This is performed by the tilt of 1 or the tilt of the document stand 13.

Next, as the first stage of actual measurement, the stage 12 is moved so as to observe the center of the chip, and the autofocus unit 8 detects the focus state.
The objective lens 4 is moved up and down by the objective lens drive unit 20,
Focus on chip surface 17 (center), and stores the height h _p of the chip at this time in a memory or the like. Next, the objective lens drive unit 20 raises the objective lens 4 to a position near the approximate height of the wire top (the approximate value is known in advance). Then, the objective lens is moved at a fine pitch near the approximate height, and for each height, as shown in FIG. 7, a wire top portion that looks bright on an image 72 of the wire portion in the entire surface 71 of the TV camera light receiving surface. The video signal 74 of the image 73 is detected by the image processing device. At each height obtained here, the objective lens height at which the peak value 75 of the video signal 74 as shown in FIG. In the screen (x _i, y _i) if there is a wire peaks, the wire height obtained in each h _w (x _i, y _i) and. Usually, the height of the wire is defined as the height from the chip surface to the wire top. Therefore, the desired wire height h _w0 (x _i , y
_i) may pull the tip height h _p of the previously obtained, obtained as equation (1).

[0006]

(Equation 1) The second method is a method using a ring illumination device instead of the epi-illumination in the first method. Except for the illumination method, it is almost similar to the first method. In addition, since the field curvature actually occurs in the optical system, the field curvature is measured in advance, and the field curvature amount h _fc (x _i , y) at each point (x _i , y _i ).
_i ) is stored in a memory, and the field curvature amount is further subtracted from equation (1), and the wire height is calculated as equation (2). However, the field curvature amount at the center of the screen is set as a reference (0).

[0007]

(Equation 2)

[0008]

However, the conventional example has the following disadvantages. First, the optical head 1
Since the orthogonality between the optical axis of the optical head 10 and the surface of the rail 14 falls over a long period of time due to 0 or movement of the sample table 13, the rotation (tilt) of the image plane with respect to the center of the screen
As a result, the height measurement error increases as the position approaches the periphery of the visual field.

Secondly, since the field curvature changes over time similarly, an error occurs in height detection.

Third, in the case of a sample in which the inner lead surface 19 and the chip surface 17 are inclined, the inclination causes an error in height measurement to approach the periphery of the visual field.

Fourth, when the two rail surfaces 14 are twisted, the chip surface 17 and the wire portion 18 are distorted because the inner lead surface 19 is fixed so as to be in close contact with the rails 14. Since the height measurement is performed in that state, a measurement error occurs.

An object of the present invention is to improve the accuracy of measuring the wire height in a wire bonding inspection apparatus in view of the above-mentioned problems of the prior art.

[0013]

According to the present invention, there is provided an optical observation means for observing a wire-bonded lead frame, a holding means for holding the lead frame, and an optical observation means. In a wire bonding inspection apparatus provided with a moving means for changing a relative positional relationship between the holding means and the holding means, a wire is observed by the optical observation means at a fixed position with respect to the holding means, and is observed over substantially the entire observation area by the optical observation means. One or both of a calibration sample on which an obtained pattern is formed and an autofocus unit provided in the optical observation unit are provided.

The calibration sample measures the curvature of field and the tilt of the optical axis of the optical observation means based on the image of the calibration sample observed by the optical observation means. To determine the correction amount when measuring the wire height, or to adjust the relative inclination between the optical observation means and the holding means to correct the field curvature change amount and the optical axis tilt amount of the optical observation means. Used for

When the optical observation means has an auto-focus means, the following operation is performed when observing the wires of the lead frame.

When the inclination of the chip surface in the lead frame or the inclination of the two rails of the holding means is measured by the autofocus means, and the wire height of the lead frame is measured based on the measurement result. Or the amount of inclination of the chip surface in the lead frame is measured by the autofocus means, and the relative inclination between the optical observation means and the holding means is adjusted based on the measurement result to perform optical observation. The amount of change in curvature of field of the means and the amount of tilt of the optical axis are corrected.

[0017]

In this structure, the height of the wire of the lead frame can be obtained based on the positional relationship between the optical system and the holding means when the wire is properly observed by the optical system. The pattern of the sample for calibration
Observe by the optical system in a fixed positional relationship with the holding means, and determine the positional relationship between the holding means and the optical system so that the image is properly observed for each of a plurality of parts on the pattern, and consider this This eliminates the effects of curvature of field and tilt of the optical axis of the optical system.

That is, for example, a calibration sample adjusted in parallel with the rail surface of the holding means is provided, a change in the degree of perpendicularity between the optical axis and the rail surface is measured, and the result is used to calculate the highest point of the wire. The measurement error due to a long-term change in the optical axis can be reduced by feeding back the calculation formula or the optical axis tilt adjusting means. Similarly, the field curvature is measured and fed back to the height calculation formula.

When an auto-focus means is provided, the focus position is measured at least at three points within the chip surface of the lead frame, the amount of inclination between the inner lead and the chip surface is obtained, and a height calculation formula or optical axis inclination adjustment is performed. Feedback to the means further reduces height measurement errors.

Further, the focus position is measured at least at four points on the rail surface, the torsion of the two rails is obtained, the amount of distortion of the wire portion is obtained based on this, and this is fed back to the height calculation formula. Height detection errors are reduced.

[0021]

FIG. 1 is a schematic diagram showing the configuration of a wire-boarding inspection apparatus according to one embodiment of the present invention. As shown in the figure, this apparatus is different from the conventional example of FIG. 6 in that a calibration sample table 15 is further provided on a sample table 13 and a calibration sample 16 as shown in FIG. 3 is provided thereon. . The upper surface of the calibration sample 16 and the rail 4 are previously adjusted so as to be parallel to each other.

In FIG. 1, 1 is a halogen lamp, LE
A light source 2 such as D; a first condenser lens 2 for collecting the light flux of the light source 1 at an aperture or a field stop; 4 is an objective lens, 5 is an illumination system half mirror, 6 is an AF system half mirror for guiding an AF light beam to the objective lens 4, and 7 is an objective lens 4.
A relay lens for forming an image of light rays from the camera, 8 an autofocus unit, 9 a TV camera, and 10 a light source 1
An optical head composed of a TV camera 9 and an objective lens driving unit 20, a support 11 for supporting the optical head 10,
12 is a stage, 13 is a sample stage, 14 is a rail for holding a lead frame, 15 is a calibration sample stage, 16
Is a calibration sample, 17 to 19 are a chip surface, a wire portion, an inner lead portion, and 20 of a lead frame, respectively.
Denotes an objective lens driving unit for vertically driving the objective lens.

The optical head 10 illuminates the light from the light source 1 onto the chip surface 17, the wire portion 18, and the inner lead portion 19 in the same manner as in the prior art, and these portions are respectively illuminated by two half mirrors 5, 6 and a relay. This is a so-called microscope that is observed by the TV camera 9 via the lens 7.

In order to perform inspection in this configuration, first,
The optical head 10 is moved by the stage 12 to the calibration sample 16.
Move over The calibration sample 16 has a grid-like chart 32 as shown in FIG. 3 printed at the center, and is observed by the optical head 10. An image of the grid chart 32 as shown in FIG. 4 is formed on the screen 41 of the TV camera 9. Here, the video signals at points A and B near the cross point 43 (x _i , y _i ) of the lattice are as shown by signals 51 and 52 in FIGS. 5A and 5B. In the same manner as in the conventional example, the objective lens 4 is moved at a fine pitch by the objective lens driving unit 20 to detect video signals as shown in FIGS. The height h _fc ′ (x _i , y _i ) of the objective lens 4 when the maximum value is obtained. Here, h _fc ′ is an average value of the heights at which the signal peaks of the points A and B are maximum. For each cross point of the line in FIG. 4, h _fc ′ (x _i , y
_{If i} ) is obtained, the best image plane at each of those points in the screen can be obtained. Here, by driving the stage, etc., even if the change or the like has occurred in the slope and curvature of field of the optical axis of the optical head 10, the _{h fc '(x i, y} i) By using, according to these changes Height measurement errors can be corrected. That is, the field curvature amount h _fc (x
_i , y _i ) is stored in the memory of equation (3).

[0025]

(Equation 3) Next, the optical head 10 is moved by the stage 12 to the chip surface 1.
7, and the auto-focus unit 8 detects the focus position within the chip surface 17. Here, the detection of the focus position is performed at least at three or more points in the plane of the chip surface 17 by moving the stage 12.
The inclination of the chip surface 17 is calculated from the focus position of each point, and the height _hp (x) of the chip surface at an arbitrary point (x _i , y _i ) of the chip surface 17, the wire portion 18, and the inner lead 19 is calculated from the inclination. _i , _yi ) are interpolated and extrapolated and stored in memory. Then, the height h _w (x _i , y _i ) of the objective lens at which the video signal at the wire top is maximized is detected in the same procedure as in the conventional example, and the wire height h is calculated by equation (4).
Calculate _w0 (x _i , y _i ).

[0026]

(Equation 4) Further, by adding the following procedure, even when the two rails 14 are twisted in the height direction, the height can be accurately measured. That is,
Before placing the sample 16 on the rails 14, the focus positions on the two rails 14 are detected. At this time, at least two or more points are detected for one rail. From the focus data, the inclination of the two rails and the relative inclination difference Δθ are obtained, and the amount of change in height of the wire top Δh due to the distortion of the wire when the inclination difference is Δθ is calculated by Expression 5.
_{Find w} (x _i , y _i ). Where f (Δθ) is Δθ
This is a function of experimental data.

[0027]

(Equation 5) Therefore, the equation (5) is added to the equation (4) to obtain the equation (6). By using Equation 6, it is possible to measure the wire height with higher accuracy.

[0028]

(Equation 6) FIG. 2 is a schematic diagram showing a configuration of a wire bonding inspection apparatus according to another embodiment of the present invention. The difference from the apparatus of FIG. 1 is that the tilt mechanism of the TV camera 9 tilts the TV camera 9 as indicated by an arrow 21 and the tilt mechanism of the optical head 10 tilts the optical head 10 as indicated by an arrow 22 or the sample indicated by an arrow 23 The point is that at least one of the tilt mechanisms of the sample stage 13 for tilting the stage 13 is provided.

In this configuration, the amount of change in the degree of orthogonality between the optical axis of the optical head 10 and the surface of the rail 14 and the amount of change in field curvature are measured using the calibration sample 16 in the same manner as in the above-described embodiment. The amount of inclination of the surface 17 is measured by multi-point autofocus in the chip surface 17. However, in the above-described embodiment, the accuracy is improved by adding a correction term using a calculation formula. However, here, at least one of the tilt mechanism of the TV camera 9, the tilt mechanism of the optical head 10, or the tilt mechanism of the sample stage 13 is used. Accuracy is improved by correcting at least one of them in a hardware manner.

[0030]

As described above, according to the present invention, the calibration sample is provided. By observing the sample by the optical observation means, the inclination between the optical observation means and the holding means and the optical observation can be obtained. Measuring the field curvature change of the means,
By feeding these back to the formula for calculating the height of the wire and the angle between the optical observation means and the holding means, the measurement accuracy of the wire height can be improved.

Also, since the auto focus means is provided, the focus on the chip surface on the lead frame is reduced.
Focus on the point or more, determine the height of the chip surface by calculating the height, feedback this to the angle between the wire height calculation formula and the optical observation means and the holding means,
Measurement accuracy of the wire height can be improved. In addition, the same effect can be obtained by obtaining the amount of inclination of the two rails of the holding means in the same manner and feeding it back.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of a wire boding inspection apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a configuration of a wire bonding inspection apparatus according to another embodiment of the present invention.

FIG. 3 is a schematic diagram showing a calibration sample of the apparatus of FIG.

FIG. 4 is a schematic diagram showing a lattice chart image of a calibration sample formed on a screen of a TV camera of the apparatus of FIG. 1;

FIG. 5 is a schematic diagram showing a video signal of a grid chart image detected by the TV camera of the apparatus of FIG. 1;

FIG. 6 is a schematic diagram showing a configuration of a wire-boarding inspection device according to a conventional example.

7 is a schematic diagram showing an image of a wire top portion formed on a screen of a TV camera of the apparatus of FIG. 6 and a video signal thereof.

[Explanation of symbols]

1: light source, 2: first condenser lens, 3: second condenser lens, 4: objective lens, 5: illumination system half mirror, 6: AF system half mirror, 7: relay lens, 8:
Auto focus unit, 9: TV camera, 10: optical head, 11: support, 12: stage, 13: sample stage, 14: rail, 15: calibration sample stage, 16: calibration sample, 17: chip surface, 18: wire Section, 19: inner lead section, 20: objective lens driving section, 32: grid chart, 41: screen of TV camera, 43: cross point of grid, 51, 52: video signal.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-148828 (JP, A) JP-A-64-44805 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01B 11/00-11/30 102 H01L 21/60 321 H01L 21/64-21/66

Claims (8)

(57) [Claims] 1. An optical observation means for observing a wire-bonded lead frame via an optical system, a holding means for holding the lead frame, and a relative positional relationship between the optical observation means and the holding means. In a wire bonding inspection apparatus provided with a moving means for changing the
A calibration sample which is observed by the optical observation means at a predetermined position with respect to the holding means and has a pattern formed with a pattern which can be observed in substantially the entire area of the observation area by the optical observation means, and which is observed by the optical observation means Measuring the curvature of field and tilt of the optical axis of the optical observation means based on the image of the optical observation means, and obtaining a correction amount when measuring the wire height of the lead frame based on the measurement result. Wire bonding inspection equipment. 2. An optical observation unit for observing a wire-bonded lead frame via an optical system, a holding unit for holding the lead frame, and a relative positional relationship between the optical observation unit and the holding unit. In a wire bonding inspection apparatus provided with a moving means for changing the
A calibration sample which is observed by the optical observation means at a predetermined position with respect to the holding means and has a pattern formed with a pattern which can be observed in substantially the entire area of the observation area by the optical observation means, and which is observed by the optical observation means The curvature of the field of view and the tilt of the optical axis of the optical observation means are measured based on the image of the optical observation means, and the relative inclination between the optical observation means and the holding means is adjusted based on the measurement result to adjust the image plane of the optical observation means. A wire bonding inspection apparatus, comprising: means for correcting a curvature change amount and an optical axis tilt amount. 3. An optical observation means for observing a wire-bonded lead frame having an autofocus means via an optical system, a holding means for holding the lead frame, and an optical observation means and holding means. In a wire bonding inspection apparatus provided with a moving means for changing the relative positional relationship with the holding means, a pattern that can be observed by the optical observation means at a fixed position with respect to the holding means and that can be observed over substantially the entire observation area by the optical observation means It is provided with the formed calibration sample, the amount of inclination of the chip surface in the lead frame is measured by the autofocus means, and the correction amount when measuring the wire height of the lead frame is obtained based on the measurement result. A wire bonding inspection apparatus comprising: 4. An optical observation means for observing a wire-bonded lead frame having an autofocus means via an optical system, a holding means for holding the lead frame, and an optical observation means and holding means. In a wire bonding inspection apparatus provided with a moving means for changing the relative positional relationship with the holding means, a pattern that can be observed by the optical observation means at a fixed position with respect to the holding means and that can be observed over substantially the entire observation area by the optical observation means It is provided with the formed calibration sample, the inclination amount of the chip surface in the lead frame is measured by the auto focus means, and the relative inclination between the optical observation means and the holding means is adjusted based on the measurement result. Characterized in that the optical observation means has means for correcting the amount of change in curvature of field and the amount of tilt of the optical axis. Wire bonding inspection equipment. 5. Optical observation means having an autofocus means for observing a wire-bonded lead frame via an optical system, holding means having two rails for holding the lead frame, and In a wire bonding inspection apparatus provided with a moving unit that changes a relative positional relationship between the optical observation unit and the holding unit, the wire observation device is observed by the optical observation unit at a fixed position with respect to the holding unit and substantially within an observation area by the optical observation unit. When a calibration sample having a pattern that can be observed in the entire area is provided, the inclination amount of the two rails is measured by an auto-focus means, and the wire height of the lead frame is measured based on the measurement result. A wire bonding inspection apparatus comprising means for calculating a correction amount of the wire bonding. 6. An optical observation means for observing a wire-bonded lead frame having an auto-focus means, a holding means for holding the lead frame,
And in a wire bonding inspection apparatus provided with a moving means for changing the relative positional relationship between the optical observation means and the holding means, the inclination amount of the chip surface in the lead frame is measured by the auto focus means, and the measurement result is A wire bonding inspection apparatus, comprising: means for obtaining a correction amount when measuring a wire height of the lead frame based on the wire bonding. 7. An optical observation means for observing a wire-bonded lead frame having an autofocus means, a holding means for holding the lead frame,
And in a wire bonding inspection apparatus provided with a moving means for changing the relative positional relationship between the optical observation means and the holding means, the inclination amount of the chip surface in the lead frame is measured by the auto focus means, and the measurement result is A wire bonding inspection apparatus comprising means for adjusting the relative inclination between the optical observation means and the holding means based on the information and correcting the amount of change in curvature of field of the optical observation means and the amount of tilt of the optical axis. 8. An optical observation means having an auto focus means for observing a wire-bonded lead frame, a holding means having two rails for holding the lead frame, and an optical observation means. In a wire bonding inspection apparatus provided with a moving unit for changing a relative positional relationship with a holding unit, an inclination amount of the two rails is measured by an autofocus unit, and a wire height of the lead frame is determined based on the measurement result. A wire bonding inspection apparatus, characterized in that it has means for obtaining a correction amount when measuring the wire bonding.