JP2004226338A - Circuit board inspection apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit board inspection apparatus which detects a short circuit or a break of wire in a circuit board by detecting voltage distribution of a circuit pattern by specifying an input position and detecting it as an image when a plurality of pads are connected to one or more pads to be detected in the circuit pattern. <P>SOLUTION: The circuit board inspection apparatus places an electrooptic device having an electrooptic crystal on a fixed position of the circuit board, irradiates the electrooptic device with a plurality of lighting light sources having different wavelength bands, and detects for every voltage wave form of a plurality of different voltage waveforms applied to the circuit board as an image by a two-dimensional photodetector. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a voltage distribution measuring device for inspecting an electrically defective portion of a circuit pattern on a circuit board, and more specifically, a voltage distribution applied from a plurality of input portions of a circuit pattern, by using optical means, Alternatively, the present invention relates to a circuit board inspection apparatus that detects non-contact, identifies an input point of a voltage distribution, and inspects a circuit pattern for a defect such as disconnection or short circuit.
[0002]
[Prior art]
Conventionally, as a method of inspecting a circuit board for disconnection, short circuit, and the like, a method has been employed in which a dedicated jig is formed with a long probe and the pads are collectively contacted to perform electrical inspection. However, in recent years, a large number of expensive spring probes are required due to an increase in the number of pads, and the cost of a dedicated jig is rising. In addition, it is difficult to physically secure the contact property due to the increase in the density of the pad, and damage to the pad due to contact with a sharp spring probe is also a problem.
[0003]
In some circuit boards, a circuit pattern branches off from one pad or a plurality of pads and is connected to a plurality of pads. In such a case, there is a problem that the inspection time for disconnection / short circuit becomes enormous. In view of such a background, a technique for detecting a voltage distribution of a circuit pattern in a non-contact manner is desired.
[0004]
Conventionally, as a method of measuring a voltage distribution of a circuit pattern by using an electro-optic effect, there is Japanese Patent Application Laid-Open No. H11-157, in which electric field intensity at a specific position is detected using an EO sensor in a non-contact manner, and solder connection of a circuit board is performed. Check the condition. However, in this method, only the electric field at the tip of the EO sensor can be detected, so that the EO sensor needs to be scanned to obtain the voltage distribution of the circuit pattern.
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 9-72947 discloses a method for non-contactly measuring a voltage distribution and electrically inspecting a defect of a liquid crystal display. Patent Document 2 discloses a method of applying a voltage to a circuit pattern of a liquid crystal display and an ITO film of an electro-optical element. Then, there is a method of irradiating a light beam to an electro-optical element arranged near a liquid crystal display, and two-dimensionally detecting a voltage distribution of a circuit pattern from the reflected light. However, according to this method, when the circuit pattern is connected to one or a plurality of pads to be detected from a plurality of pads, it is not possible to identify from which pad the voltage is applied even if the voltage distribution is detected. Therefore, it is necessary to sequentially switch and detect the input voltage, and the inspection time increases.
[0006]
[Patent Document 2]
JP-A-5-256794
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and a voltage distribution of a circuit pattern is detected as an image by identifying an input location and a short-circuit / disconnection of the circuit board is inspected. It is an object to provide an inspection device.
[0008]
[Means for Solving the Problems]
To achieve the above object, according to the first aspect of the present invention, an electro-optical element having an electro-optical crystal layer is disposed on a fixed position of a circuit board, and the electro-optical element is irradiated with a plurality of lighting light sources in different wavelength bands. In addition, the present invention provides a circuit board inspection apparatus that detects an image for each of a plurality of different voltage waveforms applied to the circuit board by a two-dimensional photodetector.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0010]
First, a circuit board inspection apparatus according to the present invention will be described with reference to FIGS.
[0011]
As the electro-optical element 1, the electro-optical element 1 is provided with a dielectric reflection film 1-1 on an electro-optical crystal 1-2. As this electro-optic crystal, for example, there is a Pockels crystal.
[0012]
When an electric field is detected by light using a Pockels crystal, there are a lateral electric field detection that is sensitive to an electric field in a direction perpendicular to the light and a vertical electric field detection that is sensitive to an electric field in a direction parallel to the light.
[0013]
Here, in order to correctly detect the electric field distribution according to the shape of the voltage distribution generated on the circuit board, the vertical electric field detection is performed.
[0014]
Pockels crystals capable of performing vertical electric field detection include KDP (KH ₂ PO ₄ , potassium hydrogen phosphate), KTP (KTiOPO ₄ , potassium titanyl phosphate), ZnSe, BSO (Bi ₁₂ SiO ₂₀ , bismuth silicon oxide), and GaAs. (Gallium arsenide), LiNbO ₃ -55 ° cut, or the like is used.
[0015]
Here, KDP and KTP have deliquescence, and ZnSe and GaAs have low electro-optic coefficients.
[0016]
Therefore, a BSO crystal having a high refractive index but no deliquescence, having a cubic system and isotropic properties, and having a relatively large electro-optic coefficient is desirable.
[0017]
For example, a BSO crystal of about 1 to 30 mm is polished to a thickness of desirably 100 to 500 μm, and a dielectric reflection layer is deposited on the bottom surface, and an ITO film is deposited on the light incident surface side, thereby forming an electro-optical element.
[0018]
If the BSO crystal is less than 100 μm, the potential difference becomes smaller, and the electric field detection sensitivity becomes smaller.
[0019]
On the other hand, if it exceeds 500 μm, the electric field spreads in the plane direction, making it difficult to detect the voltage distribution.
[0020]
Further, as another example of the electro-optical element, a Pockels crystal whose refractive index changes depending on the magnitude of an applied electric field can be used.
[0021]
The optical crystal used for the electro-optical element 1 used in the present invention is not limited to the above-described one as long as the refractive index changes. The electro-optical element 1 may be any one. The crystal 1-2 is provided with a dielectric reflection film 1-1. An ITO film 1-3 is provided on a transparent substrate 1-5, and bonded to an electro-optic crystal 1-2 with an adhesive layer 1-4. The ITO film 1-3 is grounded to the ground, and when an AC voltage is applied from the signal source 3, an electric field is generated between the ITO film 1-3 and the circuit pattern 2-1 of the circuit board 2.
[0022]
The refractive index of the electro-optic crystal 1-2 forming the electro-optic element changes due to the generated electric field.
[0023]
The control device 11 controls the timing of the application of the AC voltage by the signal source 3 and the detection timing of the photodetector.
[0024]
The position where the circuit board is to be fixed and the electro-optical element are arranged so that the electro-optic element 1 can be arranged near the circuit board 2 to be inspected. At this time, the electro-optical element 1 may be capable of contacting the circuit board 2 or may be non-contact at a distance of about 20 μm. Hereinafter, a description will be given assuming that the circuit board 2 is fixed at a position to be fixed on the circuit board.
[0025]
The incident light from the light source device 4 is polarized by the polarizer 5, slightly compensated for the phase by the 波長 wavelength plate 6, and is incident on the electro-optical element 1. The phase compensation angle varies depending on the dynamic range of the CCD and the applied voltage, but for an applied voltage of about 100 V or less, about 0.5 to 5 degrees is appropriate.
[0026]
The polarization angle at this time is determined by the electro-optic tensor of the electro-optic crystal and the direction of the electric field vector to be detected.
[0027]
The ITO film 1-3 is grounded. When a voltage is applied from the signal source 3, an electric field is generated between the circuit pattern 2-1 and the ITO film 1-3. Light incident on the electro-optical element 1 is reflected by the dielectric reflection film 1-1, and the reflected light changes its polarization state according to the electric field distribution generated in the electro-optical crystal 1-2. The change in the polarization state due to the electric field in the analyzer 8 is defined as a change in light intensity. The characteristics of the intensity of the reflected light with respect to the applied voltage from the signal source 3 are as shown in FIG. Due to the phase compensation by the quarter-wave plate 6, the change in light intensity with respect to the polarity of the voltage is asymmetric. The light transmitted through the analyzer 8 is detected by the photodetector 9, and the analysis device 10 obtains a modulation component due to voltage application from a difference between detection results when voltage is applied and when voltage is not applied, thereby obtaining a voltage distribution of a circuit pattern.
[0028]
As shown in FIG. 3, when a voltage is applied from the signal source 3 to the pads 2-2 and 2-3 of the circuit pattern 2-1 at the same time, there is a disconnection on the way from one of the pads to the branch point of the circuit pattern. Also, the voltage applied from the other pad is detected as an image by the electro-optical element 1, and no disconnection is detected. The signal source 3 sequentially applies a voltage to the pads 2-2 and 2-3 to detect a voltage distribution, so that a disconnection inspection with the pad 2-4 to be detected can be performed. Since the detection is performed by the photodetector, the detection time increases.
[0029]
According to the present invention, the distribution of the voltage applied from a plurality of pads to the detection target pad is detected by one detection of the two-dimensional photodetector, and the voltage from which pad is detected is specified.
[0030]
The two-dimensional photodetector 9 is capable of capturing a color image. In the light source device 4, a plurality of lighting light sources having different wavelengths are used. LED light sources having different wavelengths may be used, or the wavelength of light from a white light source may be selected by a band-pass filter.
[0031]
The waveform of the signal during a period in which the two-dimensional photodetector 9 performs one detection is 4c. At this time, a pulse voltage is applied to the pad 2-2 with a waveform like 4a in a cycle much shorter than the detection period of the two-dimensional photodetector 9. Similarly, a pulse voltage waveform 4b having a phase different from that of the pulse voltage of the waveform 4a is applied to the pad 2-3 at a period much shorter than the detection period of the two-dimensional photodetector 9.
[0032]
From the lighting light sources 4-1 (wavelengths 350 to 1000 nm) and 4-2 (wavelengths 350 to 1000 nm) of different wavelengths of the light source device 4, the pulsed lights 12 and 13 are synchronized with the pulse voltages of the waveforms 4a and 4b, respectively. Irradiate. At this time, the reflected light has a waveform like 4e, and the reflected light includes the modulated light intensities 14 and 15 by the applied voltage waveforms 4a and 4b. The two-dimensional photodetector integrates the reflected light intensity waveform 4e during the detection period to detect a color image.
[0033]
By irradiating pulse light having a waveform 4d, color images corresponding to the voltage waveform 4a at the time of application and the voltage waveform 4b at the time of non-application are respectively detected.
[0034]
In this case, since a normal CCD is constituted by sensors of three colors of RGB or YMC, only three pads can be separated. However, if a sensor capable of separating other multicolor wavelengths is used, only the type of sensor can be separated. .
[0035]
In the analyzer 10, a difference image of each color image is obtained. This difference image is obtained as an image of the voltage distribution of the modulated light intensities 14 and 15 due to the electric field. The modulated light intensities 14 and 15 are not modulated by the applied voltages that are not synchronized, and have different wavelengths. Therefore, in the modulation components of the color image, the modulated light intensities are equal to the wavelengths of the lighting light sources 4-1 and 4-2. The modulated light intensities 14 and 15 can be image-detected by separating the colors in the color image accordingly.
[0036]
In this way, a voltage distribution image corresponding to the applied voltage waveform can be obtained by one-time detection of the two-dimensional photodetector, so that the voltage distribution when the voltage of the pad corresponding to this voltage waveform is applied is obtained. Can be obtained for each pad to be applied, and it is possible to detect a short circuit or disconnection of the circuit board based on the voltage distribution.
[0037]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the apparatus of this invention, the voltage distribution of a circuit pattern can be detected with sufficient spatial resolution by the method which applied the electro-optic effect. By analyzing this voltage distribution, it is possible to realize an electrical test for disconnection / short circuit of a highly integrated circuit board.
[0038]
As a conventional method for inspecting a circuit board using the electro-optic effect, there is a method of detecting a voltage at one point of the circuit board as an electric field intensity. In this method, in order to detect an electric field in many parts of the circuit board, it is necessary to scan the electro-optical sensor, so that the inspection speed is reduced. In addition, there is a problem that a positioning mechanism for scanning is required and the structure of the apparatus is complicated. According to the method of the present invention, since the voltage distribution is detected as an image in two dimensions using the electro-optical element, the inspection can be performed in a short time with simple positioning.
[0039]
As a conventional inspection for a liquid crystal display to which the electro-optic effect is applied, there is a method of switching an applied voltage to be inputted and detecting a voltage distribution each time. In this method, when a circuit pattern is connected from a pad to which a plurality of voltages are applied to one or a plurality of pads to be detected, it is necessary to sequentially apply a voltage from the plurality of pads and to detect a voltage distribution each time. According to the method of the present invention, it is possible to specify which pad is applied from the detected voltage distribution image, so that the inspection time can be greatly reduced.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing one embodiment of the present invention.
FIG. 2 is a graph showing a relationship between an applied voltage and a reflected light intensity in the description of the present invention.
FIG. 3 is a configuration diagram showing the same embodiment as FIG. 1 of the present invention.
FIG. 4 is a waveform diagram showing the same embodiment as FIG. 1 of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Electro-optical element 1-1 ... Dielectric reflection film 1-2 ... Electro-optic crystal 1-3 ... ITO film 1-4 ... Transparent substrate 2 ... Circuit substrate 2-1 ... Circuit pattern 2-2 ... Pad 2-3 .. Pad 2-4 Pad 3 Signal source 4 Light source device 4-1 Lighting light source 4-2 Lighting light source 5 Polarizer 6 Quarter-wave plate 7 Beam splitter 8 Analyzer 9 Light detection Device 10 Analysis device 11 Control device 12 Pulse light 13 Pulse light 14 Modulated light intensity 15 Modulated light intensity

Claims (1)

An electro-optic element having an electro-optic crystal layer is arranged on a fixed position of a circuit board, and the electro-optic element is irradiated with a plurality of lighting light sources of different wavelength bands, and a plurality of different light sources applied to the circuit board by a two-dimensional photodetector. Circuit board inspection device that detects an image for each voltage waveform.

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