JP2006126026A - Apparatus for inspecting disconnection of wire of circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric field distribution detecting device of a circuit pattern for detecting and inspecting a wire disconnection defect of the circuit pattern having a resistance that does not result in complete disconnection. <P>SOLUTION: The electric field distribution detecting device 100 of the circuit pattern comprises an electric optical element 10 that is disposed near a circuit board 70 having the circuit pattern 71 and has a polarization surface varying according to the variation of double refractive index by the electrical field, a signal source 20 for applying alternating voltage to the circuit pattern 71 through a coil 21, a light source 30 for radiating light to the electric optical element 10, a two-dimensional photo detector 40 for detecting intensity distribution of the reflected light of the electric optical element 10, an image processing device 50, and a controller 60. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an apparatus for inspecting an electrical defect portion of a circuit board. Specifically, the probe is brought into contact with a specific pad of a circuit pattern, and the voltage of the pad to be inspected is detected by applying an electro-optic effect. The present invention relates to a disconnection inspection apparatus for a printed circuit board for inspecting disconnection defects.

As a method for inspecting a circuit board for disconnection, short circuit, etc., conventionally, a method has been employed in which a dedicated jig is formed with a spring probe and the pads are collectively contacted to perform electrical inspection. However, an increase in the number of pads necessitates a large number of expensive spring probes, and the cost of dedicated jigs is rising.
In addition, due to the high density of the pad spacing, it is difficult to physically ensure contact, and pad damage due to contact with a sharp spring probe is also a problem.
Therefore, an inspection method corresponding to a high-density pad interval has become necessary, and there is a method of performing a disconnection inspection or a short-circuit inspection by detecting an image of a voltage distribution by applying an electro-optic effect.

  In the electrical inspection method using the electro-optic effect, a voltage is applied to a circuit pattern, an electric field generated from the voltage of the circuit pattern is detected, and a voltage is generated at a place to be conducted or insulated. Check for disconnection and short circuit depending on whether or not they are present.

Conventionally, as a method of inspecting a voltage distribution of a circuit pattern using an electro-optic effect, a method of inspecting a solder connection state of a circuit board by detecting an electric field intensity at a specific position in a non-contact manner using an electro-optic sensor. Has been proposed (see, for example, Patent Document 1).
However, in this method, only the electric field at the tip portion of the electro-optic sensor can be detected, and the electro-optic sensor needs to be moved to obtain the voltage distribution of the circuit pattern. Therefore, there is a problem that it takes time to measure voltages at a plurality of locations to be inspected.

There has been proposed a method in which a voltage distribution is measured in a non-contact manner and a defect of a transparent conductive film of a liquid crystal display is electrically inspected (for example, see Patent Document 2).
This irradiates an electro-optical element arranged in the vicinity of a circuit board with a parallel light beam, and detects the voltage distribution of the circuit pattern in two dimensions from the reflected light.
Here, since the impedance of the capacitive coupling of the electro-optic element is high, when a resistance value that causes a disconnection defect is added in series to the preceding stage, if the resistance value of the disconnection defect is not high, the voltage value applied to the capacitive coupling changes. It is scarce and it is difficult to judge disconnection defects. Therefore, in Patent Document 2, a transient voltage when a step voltage is applied to an RC integrating circuit formed by the resistance value R of the disconnection defect and the capacitive coupling C generated in the electro-optic element portion is detected after the application. It is detected by adjusting the timing.

However, when the step voltage is applied, it is necessary to adjust the timing according to the time constant of the formed RC integration circuit. Further, when the detection timing after application of the step voltage is delayed, in the inventor's experiment, charges are diffused in the surface direction of the dielectric reflecting film of the electro-optic element, and the voltage distribution is significantly deteriorated. .
Therefore, the inventor has proposed that an AC voltage be applied to solve the problem and obtain a voltage distribution resolution of the order of μm (see, for example, Patent Document 3).

When liquid crystal is used as the electro-optic material of the electro-optic element, the response speed of the electro-optic effect with respect to the frequency of the applied AC voltage is slow in the order of msec. When an electro-optic crystal is used as the electro-optic material, the response speed of the electro-optic crystal is fast because the dielectric is polarized, but the sensitivity of the electro-optic effect is low. The inventor increases the sensitivity by applying optical phase compensation when an electro-optic crystal is used. At this time, since electro-optic modulation becomes asymmetrical modulation, the pulsed light is used when the reflected light intensity increases or decreases with the positive and negative polarity and cancels out during the detection time when the AC voltage has a period shorter than the detection time of the two-dimensional photodetector. Is detected in synchronization with each polarity, thereby increasing the sensitivity (see, for example, Patent Document 3).

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 strength. In this method, in order to detect an electric field in many places on a circuit board, it is necessary to scan the electro-optical element, the inspection speed becomes slow, and a positioning mechanism for scanning is required, so that the device structure Has problems such as becoming complicated.
Japanese Patent Laid-Open No. 9-72947 JP-A-5-256794 JP 2002-286812 A

  The present invention has been made to solve the above-described problems, and detects the voltage distribution of a highly integrated circuit pattern by a method applying the electro-optic effect, and detects it with an electro-optic element having a high input impedance. An object of the present invention is to provide a circuit pattern electric field distribution detection device for detecting and inspecting a defect in a circuit pattern having a resistance value that does not lead to complete disconnection.

  In order to achieve the above object in the present invention, first, in claim 1, an electric circuit is provided in the vicinity of a circuit board on which a circuit pattern is formed, and the plane of polarization changes according to a change in birefringence due to an electric field. An optical element, a voltage applying device that applies an AC voltage to the circuit pattern through a coil, a light source that irradiates light to the electro-optical element, and a two-dimensional photodetector that detects an intensity distribution of reflected light of the electro-optical element And a circuit pattern electric field distribution detecting device comprising an image processing device and a control device.

  According to a second aspect of the present invention, the frequency of the AC voltage is a resonance of an RLC series circuit including the circuit pattern, the capacitive coupling C generated in the electro-optic element, the resistance R of the electro-optic element, and the inductance L of the coil. The circuit pattern electric field distribution detection device according to claim 1, wherein the frequency distribution is a frequency.

  The circuit pattern electric field distribution detecting apparatus according to claim 1 or 2, wherein the RLC series circuit has a Q value higher than 1 / √2.

According to the apparatus of the present invention, the voltage distribution of the circuit pattern is improved in spatial resolution, the sensitivity of the electro-optic effect is increased, and the sensitivity to disconnection resistance is increased in an electro-optic element having a high input impedance. Can be detected.
By analyzing this voltage distribution, it is possible to realize an electrical inspection of the disconnection of the circuit pattern of the highly integrated circuit board.
According to the present invention, an electro-optic element is arranged on a circuit pattern, and a two-dimensional photodetector such as a CCD camera is used to convert an electric field intensity distribution generated from the voltage distribution of the circuit pattern into a two-dimensional light intensity distribution. Can be detected as Therefore, by comparing and determining the detected electric field intensity distribution and the non-defective electric field intensity distribution, it is possible to perform an electric inspection of the circuit pattern with a simple positioning system at a high inspection speed. .

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration schematic diagram showing an embodiment of a circuit pattern electric field distribution detection apparatus according to the present invention.

  The circuit pattern electric field distribution detection device 100 is provided in the vicinity of the circuit board 70 on which the circuit pattern 71 is formed, and the circuit pattern 71 includes the electro-optic element 10 whose polarization plane changes according to the change in the birefringence due to the electric field. A signal source 20 for applying an alternating voltage through the coil 21, a light source 30 for irradiating light to the electro-optic element 10, a two-dimensional photodetector 40 for detecting the intensity distribution of the reflected light of the electro-optic element 10, and image processing The apparatus 50 and the control apparatus 60 are comprised.

A method for inspecting a circuit board for disconnection of a circuit pattern using the circuit pattern electric field distribution detection apparatus of the present invention will be described.
First, the electro-optical element 10 is disposed in the vicinity of the circuit pattern 71 to be detected on the circuit board 70. The electro-optical element 10 may be brought into contact with the circuit board 70 or may be non-contact at a distance of about 20 μm.

The electro-optic element 10 is obtained by forming a transparent conductive film 12 on one surface of an electro-optic material 11 and a dielectric reflecting film 13 on the other surface. As the electro-optic material 11, Bi ₁₂ SiO ₂₀ or the like that shows sensitivity to a longitudinal electric field is used. The thickness of the electro-optic material 11 is desirably about 10 to 500 μm. By providing the transparent conductive film 12 on the incident surface of the electro-optic element 10, the range of the electric field generated from the circuit pattern 71 of the circuit board 70 can be controlled within the thickness of the electro-optic material 11. By providing the dielectric reflection film 13 on the circuit substrate 70 side of the electro-optic element 10, the reflectance of light incident from the light source 30 can be increased.

A circuit pattern 71 is formed on one surface of the circuit board 70 (contact surface with the electro-optical element), and a pad electrode 72 is formed on the other surface. The circuit pattern 71 and the pad electrode 72 are electrically connected. .
Next, the probe 23 is brought into contact with the pad electrode 72 of the circuit board 70, and an AC voltage is applied from the signal source 20 to the circuit pattern 71 through the coil 21. In the scanner device 22, power supply to the probe 23 can be turned on / off.

  On the other hand, the light emitted from the light source 30 is polarized by the polarizer 31 and is irradiated to the electro-optic element 10 by changing the optical path by the beam splitter 32. Incident light that has entered the electro-optic element 10 is reflected by the dielectric reflecting film 13 and enters the two-dimensional photodetector 40. The transparent conductive film 12 is grounded. As the light source 30, a halogen light source or an LED light source is used.

  When a voltage is applied from the signal source 20, an electric field distribution generated from the voltage distribution of the circuit pattern 71 is generated between the circuit pattern 71 of the circuit board 70 and the transparent conductive film 12, and the electro-optic material 11 is refracted by the electric field distribution. The rate changes. By applying an AC voltage, it is possible to suppress the diffusion of charges generated in the surface direction of the electro-optic element 10. The reflected light from the electro-optical element 10 changes its polarization state according to the voltage distribution of the circuit pattern 71.

By making the analyzer 34 orthogonal to the polarizer 31, the reflected light whose polarization state has been changed by the electric field is made an intensity distribution of light corresponding to the voltage distribution. At this time, phase compensation may be performed by the quarter wavelength plate 33 to achieve linearization.
An area CCD or the like is used for the two-dimensional photodetector 40. A two-dimensional voltage distribution is obtained by detecting reflected light when a periodic zero sum voltage is applied from the signal source 20 with the two-dimensional photodetector 40 and taking a difference between the images detected by the image processing device 50. Can be requested.
The operation and control of the entire circuit pattern electric field distribution detection device are performed by the control device 60.

  As described above, in the circuit pattern electric field distribution detection apparatus 100 of the present invention, the spatial resolution of the voltage distribution generated from the circuit pattern 71 is increased by applying an alternating voltage to the circuit pattern 71 of the circuit board 70 through the coil 21. And can be detected by the electro-optic element 10. By applying an AC voltage and further increasing the frequency, the spatial resolution of the electric field strength distribution generated from the circuit pattern 71 can be increased, and the two-dimensional photodetector 40 can detect images as multiple points simultaneously.

In the invention according to claim 2, the frequency of the AC voltage applied through the coil 21 to the circuit pattern 71 of the circuit board 70 is the capacitive coupling C generated between the circuit pattern 71 and the electro-optical element 10 and the resistance of the electro-optical element 10. The resonance frequency of the RLC series circuit including R and the inductance L of the coil 21 is obtained.
This is constituted by the capacitive coupling C generated from the circuit pattern 71 to the electro-optical element 10, the R generated in the transparent conductive film 12 of the electro-optical element 10, and the inductance L of the coil 21. By using the resonance frequency of the RLC series circuit, the voltage generated in the capacitive coupling C can be increased. As a result, the disconnection defect detection accuracy of the circuit board 70 can be improved.

An inspection method when a disconnection defect occurs in the circuit board 70 will be described.
As shown in FIG. 2A, it is assumed that a disconnection defect 73 that does not lead to disconnection occurs in the circuit board 70. At this time, the signal source 20, an inductance L ₂₁ of the coil 21, the resistance R ₇₃ of the disconnection defect 73, the resistance R ₁₂ of the transparent conductive film, capacitive coupling C ₁₀ generated in the electro-optical element 10 are connected in series to the ground, FIG. 2 An equivalent circuit as shown in FIG. Equivalent circuit becomes a resonant circuit of the RLC series, this time will detect a voltage generated in the capacitive coupling C ₁₀ as the electric field intensity distribution.

In the equivalent circuit, when the capacitive coupling C ₁₀ is measured, the characteristic with respect to the frequency of the applied voltage is a low-pass filter, and the amplitude characteristic is as shown in the graph of FIG. 2C. When the resonance frequency is f ₀ , the AC voltage The amplitude intensity with respect to becomes the largest. In the RLC resonance circuit, the Q value affects the amplitude strength in inverse proportion to the R component, and the influence of the resistance R ₇₃ of the disconnection defect appears greatly in the electric field strength as compared with the case where the coil 21 is not inserted.

In the invention according to claim 3, in the RLC resonance circuit including the inductance L _{21 of the} coil 21, the resistance R ₇₃ of the disconnection defect 73, the resistance R ₁₂ of the transparent conductive film, and the capacitive coupling C ₁₀ generated in the electro-optic element 10, Increase the value from 1 / √2. This time will become higher than 0dB in the amplitude characteristic (see FIG. 3), the resonance frequency f ₀ of the capacitive coupling C _10, it is possible to increase the sensitivity to the applied voltage increases the voltage generated in the capacitive coupling C _10. Further, since the Q value is increased, the change in amplitude due to the resistance of the disconnection defect 73 can be increased.

It is a schematic block diagram which shows one Example of the electric field distribution detection apparatus of the circuit pattern of this invention. (A) is explanatory drawing which shows the state which the disconnection generate | occur | produced in the circuit board. (B), the inductance L ₂₁ of the coil 21 is an equivalent circuit showing a relation between the resistor R _73, capacitive coupling C ₁₀ generated in the resistor R ₁₂ electro-optical element 10 of the transparent conductive film of the disconnection defect 73. (C) is an explanatory view showing an amplitude characteristic of the capacitive coupling C ₁₀ in the equivalent circuit. It is an explanatory view showing an amplitude characteristic of the capacitive coupling C ₁₀ in the equivalent circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Electro-optic element 11 ... Electro-optic material 12 ... Transparent conductive film 13 ... Dielectric reflective film 20 ... Signal source 21 ... Coil 22 ... Scanner device 23 ... Probe 30 ... Light source 31 ... Polarizer 32 ... Beam splitter 33 ... 1/4 wavelength plate 34 ... Analyzer 40 ... Two-dimensional photodetector 50 ... Image processing device 60 ... Control device 70 ... Circuit board 71 ... Circuit pattern 72 …… Pad electrode 100 …… Electric field distribution detector for circuit pattern

Claims (3)

  An electro-optic element that is provided near a circuit board on which a circuit pattern is formed and whose polarization plane changes in accordance with a change in birefringence due to an electric field; a signal source that applies an AC voltage to the circuit pattern through a coil; A circuit pattern electrolysis comprising: a light source that irradiates light to an electro-optic element; a two-dimensional photodetector that detects an intensity distribution of reflected light of the electro-optic element; an image processing device; and a control device. Distribution detector.   The frequency of the AC voltage is a resonance frequency of an RLC series circuit including a capacitive coupling C generated in the circuit pattern and the electro-optic element, a resistance R of the electro-optic element, and an inductance L of the coil. The circuit pattern electrolytic distribution detection device according to claim 1.   The circuit pattern electrolytic distribution detection device according to claim 1, wherein a Q value of the RLC series circuit is higher than 1 / √2.

Images