JPH05251540A - Bonding wire inspecting apparatus - Google Patents

Abstract

PURPOSE:To accurately detect an absolute height of a bonding wire by storing distribution information of a focus evaluated value and a focus position of the wire to be previously obtained, and imaging a few times at the focus position. CONSTITUTION:An inspecting apparatus comprises a camera 11 of imaging means, focus evaluated value calculating circuit 12, a picture processing memory 13 of distributed information storage means, a calculating circuit 14 of height calculating means, etc. Regarding a focus evaluated value distribution to be used for an inspection of an object S to be inspected, relationship between the height of a bonding wire 1 and the focus evaluated value is previously obtained by finely varying a focus position at an arbitrary position. The object S to be inspected is fed directly under the camera 11, and the wire 1 of the object S to be inspected is imaged at several positions of the focus position by the camera 11. Thus, an absolute height of the wire 1 is accurately obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bonding wire inspection apparatus, and more specifically, for example, IC (Integrated C
ircuit) and LSI (Large Scale Integrated circuit)
The present invention relates to a bonding wire inspecting apparatus suitable for inspecting the loop shape of a bonding wire, which is suitable for use in the field of assembling process.

In recent years, as the scale and density of LSIs have increased, the number of pins of leads, which are the outlets for signal lines, and the pitch thereof have become smaller. Therefore, semiconductor chips such as ICs and LSIs have been developed. In the wire bonding process for establishing electrical continuity with the package leads, the number of bonding wires is increasing and the pitch between the wires is decreasing.

FIG. 7 shows an IC package after wire bonding. In the figure, 1 is a bonding wire, 2 is a chip, 3 is a pad, and 4 is an internal lead in a package. The wire bonding step is a step of connecting the pad 3 which is the electrode of the chip 2 and the internal lead 4 with the bonding wire 1 made of a gold wire or an aluminum wire having a diameter of 20 to 30 μm, and the bonding wire 1 after the wire bonding. Is too loose (see FIG. 8A), drooping (see FIG. 8B), as shown in FIG.
It must not have any defects such as overtension (see Figure (c)). It should be noted that FIG. 3D shows a normal bonding wire loop shape.

The size of the IC chip 2 is about 1 mm square for small ones and 10 m for large ones.
There are up to m-square, and the number of wires in one IC is from a few wires to 400, like the one called VLSI.
Some are up to 500. Further, the height of the wire loop is generally about 200 to 400 μm from the chip surface.

Therefore, a wire made of gold or aluminum having a diameter of 20 to 30 μm and a length of about 2 mm is bonded to the surrounding inner leads 4 from several hundred chips at intervals of about 100 μm. In this case, since the operator inspects the loop shape of the bonding wire under a microscope, for example, the fatigue caused by the operator's simple work, and the risk of overlooking defects due to fine repetitive wires, etc. are increasing. And
Visual inspection of bonding wires is required instead of visual inspection.

[0006]

2. Description of the Related Art As a conventional method for inspecting a wire loop shape in this type of bonding wire inspection apparatus, there is a method as shown in FIG. This is to inspect the loop shape from the focal plane position where the wire image is in focus, by controlling the depth of field of the imaging device that images the bonding wire with the bonding wire inspection device.

More specifically, as shown in FIG. 7, two arbitrary arbitrary points P, P are set with respect to preset focus positions F ₁ -F ₃ .
Focus evaluation value E _P , E of the bonding wire 1 at Q
The loop shape of the bonding wire 1 is inspected based on how much _Q is. That is, the above-mentioned excessive slack defect is detected because the focus evaluation value E _P at the point _P exceeds the focus evaluation value E _P1, as shown in FIG. The focus evaluation value E _Q at the point _Q is detected because it is lower than the focus evaluation value E _Q2 .
It is detected because the focus evaluation value E _{P at the} point P is lower than the focus evaluation value E _P2 .

Incidentally, a normal bonding wire rule
In the case of a loop shape, the focus evaluation value E at the point P_PIs E_P1<
E_P<E_P2, Focus evaluation value E at point Q_QIs E_Q1<E_Q
<E _Q2When the condition of is satisfied.

[0009]

However, in such a conventional bonding wire inspecting apparatus, bonding at arbitrary two points P and Q with respect to preset focus positions F _{1 to} F ₃ is performed. Since the loop shape of the bonding wire 1 is inspected based on how much the focus evaluation values E _P and E _Q of the wire 1 are, it is possible to globally inspect defects in the loop shape of the bonding wire. Is suitable, but there is a problem in that it is not possible to accurately know the height of a specific portion or the entire bonding wire.

That is, in the conventional method, the focus evaluation value E _P (E _Q ) of the bonding wire 1 at the point P (point _Q ) is the focus evaluation values E _P1 (E _Q1 ), E _P2 (E _Q2 ), E _P3 ( E _Q3 )
On the other hand, the height amount could only be known to the extent to which it belongs. Therefore, in order to accurately know the height at an arbitrary point R, the height to be compared is increased from the conventional three points as shown in FIG. 10 (in this case,
It is conceivable that n pieces are set on the point R).
In order to know the total height of the bonding wire 1 with high accuracy, many images must be taken (measurement point x
(Comparative height number) Since the time required for one imaging is fixed, the inspection time increases as the number of imaging increases.
Not practical.

[Purpose] Therefore, an object of the present invention is to provide a bonding wire inspection apparatus which detects the height amount with high accuracy by a small number of times of imaging.

[0012]

In order to achieve the above object, a bonding wire inspection apparatus according to the present invention has an image pickup means for picking up an image of a bonding wire at a predetermined focal plane position, and the focal plane based on the picked-up image of the bonding wire. Focus evaluation value calculation means for calculating a focus degree at a position as a focus evaluation value, and distribution information storage for storing the relationship between the focus evaluation value calculated by the focus evaluation value calculation means and the actual focus position as distribution information. And a focus evaluation value obtained by imaging the bonding wire to be inspected at a plurality of focal plane positions based on the distribution information stored in the distribution information storage means and the height of the wire loop of the bonding wire. It is configured to include a height calculating means for calculating.

The height calculation means stores the distribution information stored in the distribution information storage means on the basis of each focus evaluation value obtained by picking up images at a plurality of focal plane positions of the bonding wire to be inspected. By sliding the distribution curve at the focal position, and the focus evaluation value calculated at a plurality of focal plane positions, and the focal position in the distribution information at which the sum of the differences between the distribution information at each focal plane position is the minimum. It is effective to obtain the height of the wire from the specific point, and in this case, the focus evaluation value of the outermost focus position in each focus evaluation value of the bonding wire to be inspected at the multiple focal plane positions. It is preferable that the direction in which the distribution curve is slid is determined based on the magnitude of the difference between the distribution information and the distribution information corresponding to the focus position.

[0014]

According to the present invention, the absolute height of the bonding wire can be accurately obtained at a small number of focal positions from the distribution information of the focal point evaluation value and the focal position of the bonding wire obtained in advance. That is, the height of the wire loop is accurately detected with a small number of times of imaging, and the loop shape of the bonding wire is accurately inspected.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a bonding wire inspection apparatus according to the present invention, and is a diagram showing a schematic configuration of the present embodiment. First, the configuration will be described.

The bonding wire inspection apparatus of this embodiment is roughly classified into a camera 11 as an image pickup means, a focus evaluation value calculation circuit 12 as a focus evaluation value calculation means, an image processing memory 13 as a distribution information storage means, and a height. The arithmetic circuit 14 is an arithmetic means, and the illuminating means 15 is provided.
The light source 16, the light irradiation unit 17, and the light condensing unit 18 are included.

In the figure, S is an inspection object. As for the focus evaluation value distribution used for the inspection, the relationship between the height of the bonding wire 1 and the focus evaluation value is obtained in advance by finely changing the focus position at an arbitrary point, as shown in FIG. Figure 2 shows the focus evaluation value of the bonding wire,
It is a figure which shows the relationship with the focus position with respect to each height.

It should be noted here that the relationship between the focus evaluation value and the focus position does not have a normal distribution as shown in FIG. In the case of the normal distribution, it is easy to calculate the center of the distribution, that is, the in-focus position by using a mathematical expression, but the actual distribution of focus evaluation values is as shown in FIG. Since there is a range where the image lens is in focus, that is, there is a depth of field,
In addition, since the distribution just before and after the focus position does not show symmetry, if the distribution of focus evaluation values is assumed to be a normal distribution and the center is calculated, a large error occurs.

Therefore, in the present embodiment, the focus evaluation value distribution shown in FIG. 2 is applied to the actual focus evaluation value to cope with the problem. Next, the operation will be described. First, the inspection object S is sent to a position right below the camera 11 by a transport device (not shown), and the camera 11 causes the focus positions F ₁ to
The bonding wire 1 on the inspection object S is imaged at three locations F ₃ .

Next, as shown in FIG. 4, the focus evaluation values E _{1 to} E ₃ for the respective focus positions F _{1 to} F ₃ at predetermined positions where the height is to be detected are calculated by the focus evaluation value calculation circuit 12. The focus evaluation value distribution is scanned so that the focus evaluation values E _{1 to} E ₃ are applied, and the center position of the distribution is set as the wire height H. Incidentally, in FIG. 4, it can be seen that the wire height H is at a position separated from the focal position F ₂ by the distance D.

FIGS. 5 and 6 show how to fit the focus evaluation value distribution.
It is a figure for explaining. Figure 5 is the actual focus evaluation value
The focus evaluation value distribution is shifted to the left.
Yes, in this state, how to scan the focus evaluation value distribution
Direction is the focus position F ₁~ F₃Bonding wire 1
Each focus evaluation value E₁~ E₃Outermost focus position in
F₁, F₃Focus evaluation value E₁, E₃And the outermost focus position
F₁, F₃Focus evaluation value E in the focus evaluation value distribution corresponding to
₁ ^', E₃ ^'Difference with dE₁, DE₃The scanning direction is determined by the size of
Is determined.

That is, in this case, since -dE ₁ <dE ₃ , the distribution curve of the focus evaluation value distribution is scanned rightward in the figure. Also, the focus evaluation value distribution and the focus position F ₁
Deviation degree D of the focus evaluation value E ₁ to E ₃ at three positions to F ₃
The IFF can be represented by DIFF = dE ₁ + dE ₂ + dE ₃ , and it is assumed that the fitting of the focus evaluation value distribution is completed when the deviation degree DIFF becomes the smallest value.

FIG. 6 shows the focus evaluation value rather than the actual focus evaluation value.
This shows that the distribution is shifted to the right.
, The focus evaluation value E of the bonding wire 1₁~ E₃To
Outermost focus position F in₁, F₃Focus evaluation value E₁, E
₃And the outermost focus position F₁, F ₃Focus evaluation value corresponding to
Focus evaluation value E in distribution₁ ^', E₃ ^'Difference with dE₁, DE₃of
From large to small, dE₁> -DE₃Therefore, focus evaluation value
The cloth distribution curve is scanned to the left in the figure.

Then, similarly to the case shown in FIG. 5, it is assumed that the fitting of the focus evaluation value distribution is completed when the deviation degree DIFF becomes the smallest value. When the fitting of the focus evaluation value distribution is completed, the wire height H is calculated by the calculation circuit 14, and the calculated wire height H
The wire loop shape is inspected by a system processor (not shown).

As described above, in this embodiment, the wire height H of the bonding wire can be accurately obtained at a small number of focus positions based on the focus evaluation value distribution obtained in advance. Therefore, the height of the wire loop can be accurately detected with a small number of times of imaging, and the loop shape of the bonding wire can be inspected with high accuracy. In the above embodiment, the measurement points are set to 3
Although the case has been described as an example, the number is not limited to this, and the number of measurement points is arbitrary.

Further, as means for changing the focal position in this embodiment to take an image, a method of inserting an optically dense substance between the inspection object S and the camera 11 and changing the thickness of this substance, A method of moving the camera 11 away from or closer to the inspection object S, a method of moving the inspection object S away from or closer to the camera 11, and the like can be considered.

[0027]

According to the present invention, the absolute height of the bonding wire can be accurately obtained at a small number of focus positions based on the distribution information of the focus evaluation value and the focus position of the bonding wire obtained in advance. Therefore, the height of the wire loop can be accurately detected with a small number of times of imaging, and the loop shape of the bonding wire can be inspected with high accuracy.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a present embodiment.

FIG. 2 is a diagram showing a relationship between a focus evaluation value of a bonding wire and a focus position for each height.

FIG. 3 is a diagram showing a normal distribution.

FIG. 4 is a diagram for explaining an operation example of the present embodiment.

FIG. 5 is a diagram for explaining a method of fitting a focus evaluation value distribution.

FIG. 6 is a diagram for explaining a method of fitting a focus evaluation value distribution.

FIG. 7 is a perspective view of the IC package after wire bonding.

FIG. 8 is a diagram showing an example of a loop shape of a bonding wire.

FIG. 9 is a diagram for explaining a conventional bonding wire inspection method.

FIG. 10 is a diagram for explaining one method for accurately measuring the wire height of the bonding wire.

[Explanation of symbols]

 1 bonding wire 2 chip 3 pad 4 internal lead 11 camera (imaging means) 12 focus evaluation value calculation circuit (focus evaluation value calculation means) 13 image processing memory (distribution information storage means) 14 arithmetic circuit (height arithmetic means) 15 lighting Means 16 Light source 17 Light irradiation unit 18 Condensing unit S Inspection target

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Gotoshi Ando 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (3)

[Claims] 1. An image pickup means for picking up an image of a bonding wire at a predetermined focal plane position, and a focus evaluation value calculation means for calculating a degree of in-focus at the focal plane position as a focus evaluation value based on an imaged image of the bonding wire. Based on the distribution information stored in the distribution information storage means, the distribution information storage means storing the relationship between the focus evaluation value calculated by the focus evaluation value calculation means and the actual focus position as distribution information,
Bonding wire inspection, comprising: height calculating means for calculating the height of a wire loop of the bonding wire from focus evaluation values obtained by imaging the bonding wire to be inspected at a plurality of focal plane positions. apparatus. 2. The height calculation means stores the distribution stored in the distribution information storage means based on each focus evaluation value obtained by imaging at a plurality of focal plane positions of the bonding wire to be inspected. The focus position in the distribution information where the sum of the differences between the focus evaluation values calculated at multiple focus plane positions and the distribution information at each focus plane position is minimized by sliding the distribution curve in the information with respect to the focus position. 2. The bonding wire inspection apparatus according to claim 1, wherein the height of the wire is obtained from the specific point. 3. The difference between the focus evaluation value of the outermost focus position and the distribution information corresponding to the focus position in each focus evaluation value of the bonding wire to be inspected at the plurality of focal plane positions is determined according to the magnitude of the difference. The bonding wire inspection apparatus according to claim 2, wherein a direction in which the distribution curve is slid is determined.