JPH05175311A - Wire bonding inspection method - Google Patents

Abstract

(57) [Summary] [Objective] To provide a wire bonding inspection method capable of inspecting a bonded wire at high speed and automatically. [Structure] A wire ball of a wire bonded to a semiconductor chip, the wire itself, and a wire crescent are measured under different illuminations.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for automatically inspecting the quality of wire bonding for connecting a semiconductor chip and a lead frame.

[0002]

2. Description of the Related Art A conventional method for automatically inspecting the state of wire bonding generally determines only the quality of the wire loop shape.

However, in the above-mentioned conventional example, it is extremely difficult to accurately and promptly measure and inspect the joints at both ends of the wire, that is, the shapes, dimensions and joint positions of the wire balls and crescents, which are particularly important for quality control of wire bonding. Met. For this reason, these inspection methods are not practical as in-process inspections, and in reality, a method in which a person directly observes a stereoscopic microscope image to discriminate is adopted, which is a great obstacle to automation of the IC assembly process.

The present invention has been made to solve the above problems, and an object thereof is to provide a wire bonding inspection method capable of inspecting a bonded wire at high speed and automatically.

[0005]

A wire bonding inspection method according to the present invention for solving the above-mentioned problems includes a wire ball of a wire bonded to a semiconductor chip, a wire itself,
It is characterized in that each of the wire crescents is measured under different illumination.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing the construction of an apparatus according to an embodiment of the present invention, and FIG. 2 is a flow chart of an inspection sequence.
Embodiments of the present invention will be specifically described with reference to these drawings.

First, numerical data of each shape, size, and position that serves as a reference for wire bonding of an IC to be inspected is made into a file and recorded. Prior to the inspection, this numerical data file is read into the image processing unit 1 and set as an inspection reference value.

Next, one of the plurality of wire-bonded IC lead frames housed in the magazine 2 is pulled out from the magazine 2 and conveyed to a predetermined position of the carrier 5 on the inspection stage 4.

Here, the function of the autofocus unit 6 of the image pickup optical system 7 is activated to perform focusing with a predetermined position (reference position mark or specific pattern) on the IC chip as a reference point.

Then, the inclination of the IC chip and the amount of deviation from the normal position in the horizontal plane are measured by optical means in a non-contact manner,
Position correction processing is performed. Here, the position correction processing is a method of operating the position adjusting mechanism of the carrier that conveys the IC lead frame to make the chip surface horizontal and correcting the deviation from the reference position, or storing the tilt and the deviation amount in advance. In this method, when the wire bonding state is measured in the next step, a bias value is added to the measured value and the bias value is corrected.

After that, the measurement sequence is started. First, the position where the existence of the wire ball is predicted based on the inspection reference value data read in advance is caught by the image pickup optical system 7 and the function of the autofocus unit 6 is operated to obtain a focused image of the wire ball.

Next, the illumination is set in the epi-illumination system 8 and the shape, length and position of the wire ball are measured. FIG. 3 is a diagram showing this state, in which 23 is a wire and 26 is a wire ball. In the measurement of the wire ball, it is necessary to clearly observe the outer peripheral contour of the ball and the horizontal spread of the ball seen from above, and it is necessary to capture the image data by the TV camera 9. Since the reflected light of the wire ball that is to be inspected with respect to the regular reflection light of the base surface is diffused from its shape, the shape of the wire ball can be seen as a shadow and the contrast can be increased. ..

Next, the illumination is switched to the slit light illumination system 10 and the height of the wire is measured. Here, a method of measuring the wire height by slit light illumination will be specifically described with reference to FIG.

When a plurality of slit light beams 21 (slit-shaped light beams) arranged at a constant interval are irradiated at a constant angle (θ) with respect to the upper surface of the IC chip 22, the wire 23 is irradiated.
From the mutual relationship between the position A of the bright spot observed above and the crossing position B of the virtual plane obtained by extending the surface of the IC chip 22 and the slit light forming the bright spot, the height h of the point A is It is represented by.

H = Δl × tan θ The maximum value of h is obtained by a method such as spline interpolation or quadratic curve approximation based on the values of h obtained by the above equation for each of a plurality of slit lights, and the value Is the height of the wire.

Next, the measurement of the wire crescent will be described. When the height of the upper surface of the lead frame 24 on which the wire crescent 24 is formed is designed to be different from the height of the upper surface of the IC chip 22, the focus position of the imaging optical system 7 is a design value from the surface of the IC chip 22. Move it by a minute. When the upper surface of the lead frame 25 is tilted, the restriction of the measuring range of the measuring means is changed from the above state,
The reference plane to be corrected is replaced with the upper surface of the lead frame, and the same position correction process as described above is performed in advance.

The illumination is switched to the oblique diffusion illumination system 11 to measure the shape, size and position of the wire crescent. FIG. 5 is a diagram showing this state, and 24 is a wire crescent. The reason why the oblique diffuse illumination is used here is as follows. That is, since the surface of the wire crescent 24 is normally inclined at a certain angle from the surface of the lead frame 25, when observing the surface of the wire crescent 24, as shown in FIG.
It is necessary to illuminate from the diagonal direction. Also, in order to illuminate with a constant amount of light even if the inclination of the surface of the wire crescent 24 varies, a light source that illuminates the illumination light from multiple directions, that is, a diffused light source is required.

The above-mentioned three types of measurements are performed on the lead frame.
When the unit section corresponding to each chip is completed, the lead frame is moved by one section or the imaging optical system 7 is moved by one section, and the next new measurement sequence is started. At the same time, the measured data obtained in the previous sequence is compared with the inspection reference value to perform the quality determination process for the bonding state, and the result is transferred to the host computer 13 via the communication line 12.

In this way, when the inspection is completed for the sections corresponding to all the chips on one IC lead frame, they are carried out from the carrier 5 and collected in the magazine 2.
Then, the IC lead frame is newly taken out from the magazine 2 and the measurement is repeated.

The shape, size, and position can be measured by an image processing unit that processes a binarized image.
By applying multi-valued image processing, it is possible to measure with higher accuracy and reproducibility.

The system controller 14 shown in FIG. 1 is a functional unit that controls each constituent unit shown in the drawing in a fixed procedure according to a measurement sequence, and a control computer can be usually used.

Although the wire ball, the wire and the crescent are individually measured in the above embodiment, if the slit light illumination and the oblique diffusion illumination are simultaneously performed, the wire height can be measured at one time. The measurement time can be shortened.

Further, although slit light illumination is used to measure the wire height in the above embodiment, the function of the autofocus unit 6 of the image pickup optical system 7 is activated to sequentially move the focus position so that the maximum wire height is reached. A method of measuring the wire height by searching for a point may be used.

Further, in the above embodiment, three types of measurement are sequentially performed within the same field of view of the image pickup optical system 7. However, when the resolution of the image pickup optical system or the image processing system is insufficient, the field of view is divided into a plurality of regions. It is sufficient to divide and repeat three types of measurement for each divided area. This is particularly effective when the inspection device is incorporated in the wire bonder device to monitor the bonding state in real time.

The following method is also conceivable as an alternative method of performing three types of measurement in each divided area. That is, the wire ball is first measured in each divided area, the wire ball is similarly measured after moving to the next area, and the measurement of the wire ball is completed for all divided areas. The field of view of the wire portion is then divided and the wire height is measured for all areas. Finally, the wire crescent is similarly measured for all the regions.

[0026]

As described above, according to the present invention, the state of wire bonding is not determined only by the wire shape, but
By simultaneously inspecting the ball and the crescent, which are the bonding portions of the bonding, it becomes possible to perform more strict quality control of the wire bonding.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of an embodiment.

FIG. 2 is a flowchart of a processing procedure of the embodiment.

FIG. 3 is a diagram showing how a wire ball is measured.

FIG. 4 is a diagram showing how the wire height is measured.

FIG. 5 is a diagram showing how the wire crescent is measured.

[Explanation of symbols]

 1 Image Processing Unit 2 Magazine 3 IC Lead Frame 4 Inspection Stage 5 Carrier 6 Auto Focus Unit 7 Imaging Optical System 8 Epi-illumination System 9 TV Camera 10 Slit Light Illumination System 11 Oblique Diffuse Illumination System 12 Communication Line 13 Host Computer 14 System Controller 21 Slit Light 22 IC Chip 23 Wire 24 Wire Crescent 25 Lead Frame 26 Wire Ball

Claims (5)

[Claims] 1. A method for inspecting wire bonding, which comprises measuring a wire ball of a wire bonded to a semiconductor chip, a wire itself, and a wire crescent under different illuminations. 2. The inspection method according to claim 1, wherein the measurement of the wire ball is performed by epi-illumination, the measurement of the wire itself is performed by slit illumination, and the measurement of the wire crescent is performed by diffuse illumination. 3. The inspection method according to claim 1, wherein the positional relationship between the semiconductor chip and the measurement optical system is corrected before the measurement of the wire ball. 4. The inspection method according to claim 3, wherein the positional relationship between the lead frame of the semiconductor chip and the measurement optical system is corrected before the measurement of the wire crescent. 5. The inspection method according to claim 3, wherein the above procedure is repeated every time one semiconductor chip is inspected.