JPH065238B2 - Continuity inspection device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuity inspection of a circuit pattern of a wiring board such as a printed circuit board, and more particularly to a continuity inspection apparatus suitable for a wiring board having a fine circuit pattern.

[Background of the Invention]

The conventional continuity inspection apparatus has adopted a method in which an electrode needle is brought into direct contact with a circuit pattern on a wiring board, the electric resistance between the circuit pattern electrodes is measured, and disconnection or short circuit of the circuit pattern is detected.

However, according to this method, the contact of the electrode needle damages the circuit pattern, and particularly when the circuit pattern is fine, a fine electrode needle is required, which makes stable contact of the electrode needle difficult. Had problems such as.

On the other hand, as a means for measuring the circuit operating state in a non-contact manner, for example, the Japan Society for the Promotion of Science, Industrial Application of Charged Particle Beam, 132nd Committee, 89th Research Committee There is an electron beam tester as shown in the paper "Improvement of performance of EB tester by potential detector (TLD type energy filter)" (Tosho et al.).

According to this, the voltage of the circuit pattern can be measured in a non-contact manner, so it can be applied to a continuity inspection machine for wiring boards. However, in this electron beam tester, it can be applied from outside (contactly).
Since it is premised that a voltage is applied to the circuit, it is necessary to use a contact-type electrode needle as the voltage applying means, and the above-mentioned problems in the contact-type continuity inspection machine cannot be fundamentally solved.

[Object of the Invention]

The object of the present invention is to solve the above-mentioned problems of the prior art efficiently with respect to a wiring board having a fine wiring pattern, and moreover accurately detect the emission of secondary electrons due to the disconnection and short circuit of the wiring pattern based on the conduction state. Wiring pattern disconnection,
An object of the present invention is to provide a continuity inspection device capable of detecting a short circuit with high accuracy.

[Outline of Invention]

In order to achieve the above object, the present invention provides an electron gun that generates an electron beam in a continuity inspection device that detects a disconnection or a short circuit defect of the wiring pattern on a wiring board on which a wiring pattern is formed. An electron beam irradiating means constituted by an electron lens for converging the electron beam and an electrostatic deflection electrode for scanning the electron beam converged by the electron lens, and a connector connected to the external electrode of the wiring board are grounded and predetermined. Switching application means for switching and applying a voltage, and an electron beam converged by the electron beam irradiating means on a predetermined wiring pattern on the wiring substrate, which is switched and applied to ground and a predetermined voltage by the switching application means. And an electric charge is applied to the wiring pattern to which the electric charge is applied by the electric charge applying means for applying the electric charge to the wiring pattern. Only the extraction electrode that draws secondary electrons obtained from the wiring pattern by irradiating the electron beam converged by the beam irradiation means and only the electrons that exceed a specific energy of the secondary electrons extracted by the extraction electrode An energy filter means composed of a decelerating electrode to be passed, a secondary electron detector for detecting secondary electrons obtained through the energy filter means, and fluctuations and normalization of secondary electrons detected by the secondary electron detector. 2. A continuity inspection apparatus comprising: a determination unit that determines a disconnection or a short circuit defect of the wiring pattern by comparing with a variation state of secondary electrons expected from the connection relationship of the wiring pattern. Further, the present invention, in the continuity detecting device, the electron beam irradiation means, when applying a charge by the charge applying means and when detecting secondary electrons by the energy filter means and a secondary electron detector, An accelerating voltage control means for switching and controlling the accelerating voltage of the electron beam is provided.

First, a method of applying a voltage to a circuit pattern according to the present invention will be described. FIG. 2 shows a cross-sectional structure of a general multilayer wiring board. Signal lines 1a and 1b are made of conductors. This disconnection or short circuit is the detection target of the device of the present invention. The signal line normally faces the power supply or the ground layer 3 (collectively referred to as a power supply layer hereinafter) via the insulator 2 at regular intervals and forms a so-called microstrip line. In addition, the signal line, through the through hole 4a,
It is connected to two or more electrodes (pads) 5 on the surface of the wiring board. In such a situation, as taught by the electromagnetic theory, an electric capacity (hereinafter simply referred to as a capacity) is generated between the signal line and the power supply or the ground layer. An equivalent circuit focusing only on the capacitance in FIG. 2 is shown in FIG.

Now, when the electrode 5a is irradiated with an electron beam, electric charges are generated in the signal line 1a, so that a voltage V ₁ (unit: volt [V]) shown below is generated between the needle wire and the power supply layer.

Here, Q ₁ is a given charge amount (unit: Coulomb [C]), C ₁ is a capacitance between the signal line 1 a and the power supply layer 3 (unit:
Farad [F]). When the electron beam current has a constant value I (unit: ampere [A]) and irradiation time t (unit: second [S]), the charge amount Q ₁ is −Q ₁ = (1−δ) It ( 2) Here, δ is the secondary electron emission rate (ratio between the irradiation electron beam current and the emitted secondary electron current), which is determined by the material to be irradiated with the electron beam and the acceleration voltage of the electron beam. An example of the relationship between δ and the acceleration voltage is shown in FIG. In order to efficiently apply the electric charge to the signal line, it is desirable that δ be small as shown in the equation (2). In the present invention, a sufficiently high accelerating voltage is used within the range of C in FIG.

Next, a method of measuring the voltage of the circuit pattern according to the present invention will be described. It is emitted when the voltage of the irradiation target is changed while the acceleration voltage of the irradiation electron beam is constant.
The energy distribution of secondary electrons changes. This change is detected by the energy filter. An example of how to construct an energy filter is shown in the aforementioned paper. In the present invention, in order to prevent the voltage from changing during voltage measurement, the vicinity of point E in FIG. 4 is selected as the electron beam acceleration voltage.

Example of Invention

An embodiment of the present invention will be described below with reference to FIG. The device consists of a field emission electron gun 11 whose accelerating voltage can be switched by an accelerating voltage switching circuit 10 and an electron lens for converging an electron beam.
12, two-dimensional deflection of electron beam by electrostatic field 2
An electron beam irradiation system composed of a pair of electrostatic deflection plates 13, an extraction electrode 14 to which a positive voltage V _E is applied in order to extract secondary electrons generated from a circuit pattern, and only electrons exceeding a specific energy are selectively selected. Through an energy filter system consisting of a deceleration electrode 15 for passing through the deceleration electrode, a plurality of secondary electron detectors 16 for detecting secondary electrons passing through the deceleration electrode 15, an external electrode 17 of the wiring board and a connector 18. To establish electrical continuity and selectively apply the voltage of the power supply to the external connection electrode or to selectively extract the signal, and the signal current-voltage conversion 20c selectively extracted from the external connection electrode. , A / D conversion 21c, then microcomputer
A circuit for inputting to 22 and a circuit for current-voltage converting 20a, b the signals detected by a plurality of secondary electron detectors, and then taking the sum 23 and A / D converting 21a to input to the microcomputer 22. The deflection control circuit 24 for controlling the beam irradiation position according to the instruction of the microcomputer 22, the vacuum chamber 25 for keeping the electron beam irradiation system, the energy filter system, and the table system in a vacuum state, and the object to be inspected according to the instruction of the microcomputer 22. It is composed of a table control circuit 31 for positioning 30 and a microcomputer 22 for controlling the entire apparatus described above and detecting disconnection and short circuit.

FIG. 5 shows an example of a current-voltage conversion circuit using an operational amplifier. The secondary electron detector 16 is a combination of a scintillator and a photomultiplier tube.

Next, the operation will be described.

First, the table 32 is moved to the wiring board mounting position. When the wiring board of the inspection object 30 is attached to the connector 18 and the microcomputer 22 is instructed to start the work, the microcomputer 22 executes the following automatic inspection operation according to the built-in software.

First, the air in the vacuum chamber 25 is exhausted to a high vacuum state. Next, the table 32 is driven to position the wiring board 30 at a predetermined position. In the memory device 33, the microcomputer 22 includes the positions of electrodes (hereinafter referred to as pads) on the wiring pattern on the substrate surface, the correct electrical connection between them, the electrical connection between external electrodes, and the external electrodes and pads. It has information on the conduction relationship between the electrodes and information on the electrodes connected on the power supply layer and the ground layer among the external electrodes.

The automatic inspection operation is performed as follows.

(1) Switching circuit 1 using information on the conduction relationship between external electrodes
Control 9 to detect disconnection and short circuit between external electrodes. At this time, the voltage is applied to the external electrodes for each circuit pattern that is originally in a connection relationship, and each voltage is applied by applying an electron beam to all pads on the surface of the wiring board, and is obtained through the energy filter system. Secondary electron detector 16
To detect the change in voltage. The acceleration voltage at this time is set to point E shown in FIG. 4, that is, about 1 KV. A disconnection or short circuit between the external electrode and the pad is detected based on the measurement result and the information indicating the conduction relationship between the external electrode and the pad.
That is, when a positive voltage is applied to the external electrode and the electrode on the surface of the substrate is conductive, the voltage increases and the emitted secondary electrons decrease. On the other hand, when there is no conduction, the emitted secondary electron current does not change. A disconnection or a short circuit can be detected from this information and the information indicating the conduction relationship between the external electrode pads described above.

(2) Next, by controlling the switching circuit 19, among the external electrodes, the electrode connected to the power supply layer is grounded and the other electrodes are opened. Of the circuit patterns originally having a connection relationship, one that is not connected to an external electrode is selected, and one of the pads on the surface of the substrate on the circuit pattern is irradiated with an electron beam. According to the principle
Apply voltage to the pattern. The acceleration voltage in this case is the fourth
The range of C shown in the figure, for example, 20 KV. Next, an electron beam is applied to all pads on the surface of the wiring board one by one, and secondary electrons obtained through the energy filter system are detected by the secondary electron detector 16 to measure the voltage change. The acceleration voltage at this time is the E point shown in FIG. 4, for example, about 1 KV.
And If there is no short circuit with the power supply layer, a negative voltage is applied to the circuit pattern by irradiation with an electron beam with an acceleration voltage of 20 KV. When an electron beam is applied to a pad having a conductive relationship, the emitted secondary electron current increases, and when there is no conductivity, there is no change. This information is compared with the above-mentioned information indicating the conductive relationship between the pads to detect disconnection or short circuit.

Here, the voltage application time by the electron beam is trial calculated. For example, the electron beam current is 10nA, δ = 0.5, the applied voltage is 1V, and the characteristic impedance is 50 when the epoxy board is an insulator.
When targeting a 100 mm long signal line of Ω,
From equations (1) and (2), C = 0.12 × 100 = 12 [pF] (3) Q = CV = 12 × 10 ⁻² × (-1) = ^-12 × 10 ^-12 [C] (4) That is, 2.4 ms per circuit pattern.

According to the present embodiment, since the voltage application from the external electrode and the voltage application by the electron beam are used together, the continuity inspection of all circuit patterns can be efficiently performed.

Although the field emission type electron gun is used in the present embodiment, a thermionic emission type electron gun may be used. In addition, when the deflection angle of the electron beam can be reduced by using table movement together,
Electromagnetic deflection may be used instead of electrostatic deflection. further,
Although the sum of the analog signals was taken as a means for synthesizing the signals of the plurality of secondary electron detectors, this may be performed digitally after A / D conversion. Further, in FIG. 1, the external electrode terminals of the substrate to be inspected are described as being projected from the back surface of the substrate, but it goes without saying that they may be projected from the side surface or the top surface of the substrate. Further, the secondary electron detector shown in FIG. 1 is not limited to the combination of the scintillator and the photomultiplier tube,
It may be a multi-channel plate, a semiconductor sensor, or the like.

〔The invention's effect〕

According to the present invention, the application of the voltage from the external electrode of the wiring board and the application of the electric charge to the wiring pattern by the convergent electron beam are used together, and the secondary electron from the wiring pattern is accurately captured by the energy filter means. Since it can be detected by the secondary electron detector, it is efficient for a wiring board having a fine wiring pattern, and it is possible to detect disconnection and short circuit of the wiring pattern based on the conduction state with high precision, and An effect that a high-density wiring pattern continuity test can be realized is achieved.

[Brief description of drawings]

FIG. 1 is an embodiment of the present invention, FIG. 2 is a diagram showing an example of a cross section of a wiring board to which the present invention is applied, FIG. 3 is an electrical equivalent circuit of FIG. 2, and FIG. FIG. 5 is a diagram showing a change in secondary electron emission rate by a beam, and FIG. 5 is a diagram showing an example of a current-voltage conversion circuit. DESCRIPTION OF SYMBOLS 1 ... Signal line, 2 ... Insulator, 3 ... Power supply layer, 4 ... Through hole, 5 ... Electrode, 10 ... Accelerating voltage switching circuit, 11 ... Electron gun, 12
... Electron lens, 13 ... Deflection plate, 14 ... Extraction electrode, 15 ... Deceleration electrode, 16 ... Secondary electron detector, 17 ... External electrode, 18 ... Socket, 19 ... Switching circuit, 20 ... Current-voltage conversion circuit, 21 … A
/ D converter, 22 ... Microcomputer, 23 ... Addition circuit, 24 ... Deflection control circuit, 25 ... Vacuum chamber, 30 ... Inspected substrate,
31 ... Table control circuit, 32 ... Table, 33 ... Storage device.

Front page continuation (72) Hitoshi Kubota, Hitoshi Kubota, 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Pref., Institute of Industrial Science, Hitachi, Ltd. (72) Inventor, Fumiyuki Kobayashi, 1 Horiyamashita, Hadano, Kanagawa, Japan (56) References JP-A-57-196539 (JP, A) JP-A-59-79167 (JP, A)

Claims (2)

[Claims] 1. An electron gun for generating an electron beam, and an electron lens for converging the electron beam generated by the electron gun, in a continuity inspection device for detecting a disconnection or a short circuit defect of the wiring pattern on a wiring substrate on which a wiring pattern is formed. And an electron beam irradiating means constituted by an electrostatic deflection electrode for scanning the electron beam converged by the electron lens and a connector connected to the external electrode of the wiring board by switching between ground and a predetermined voltage. The switching application unit and the predetermined wiring pattern on the wiring substrate, which is switched between the ground and a predetermined voltage by the switching application unit, are irradiated with the electron beam converged by the electron beam irradiation unit to impart an electric charge. Charge applying means and a wiring pattern to which the charge is applied by the charge applying means is collected by the electron beam irradiating means. An extraction electrode for irradiating the secondary electron obtained from the wiring pattern by irradiating the generated electron beam, and a deceleration electrode for selectively passing only electrons exceeding a specific energy among the secondary electrons extracted by the extraction electrode. Connection of configured energy filter means, secondary electron detector for detecting secondary electrons obtained through the energy filter means, fluctuation of secondary electrons detected by the secondary electron detector, and regular wiring pattern A continuity inspection apparatus comprising: a determination unit that determines a disconnection or a short circuit defect of the wiring pattern by comparing with a fluctuation state of secondary electrons expected from a relationship. 2. The electron beam irradiating means determines an accelerating voltage of an electron beam at the time of applying charges by the charge applying means and at the time of detecting secondary electrons by the energy filter means and a secondary electron detector. The continuity inspection apparatus according to claim 1, further comprising an accelerating voltage control means for switching and controlling.