JPS6287875A - Apparatus for inspecting continuity - Google Patents

Abstract

PURPOSE:To realize automatic inspection with high reliability by bringing the generation of inferiority during inspection due to the damage of a pattern, by performing continuity inspection by utilizing electron beam without bringing the direct contact with the surface of a fine circuit pattern. CONSTITUTION:An electron beam irradiating system consists of an electric field radiation type electron gun 11 capable of changing acceleration voltage by an acceleration voltage changeover circuit 10, an electronic lens and an electrostatic deflection plate 13. An energy filter system consists of a lead-out electrode 14, a speed-reducing electrode 15 and secondary electron detectors 16a, 16b. The signal selectively taken out from an external connection electrode 17 through a signal changeover circuit 19 is converted by a current/voltage converter 20c and further converted by an A/D converter 21c to be inputted to MC(microcomputer)22. The signals detected by a plurality of secondary electron detectors are converted by current/voltage converters 20a, 20b and added by an adder 23 while the added signal is converted by an A/D converter 21a to be inputted to MC22. MC22 compares voltage variation obtained from these measuring means with a variation state expected from normal connection relation to judge disconnection and a short circuit failure.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to continuity testing of circuit patterns on wiring boards such as printed circuit boards, and particularly to a continuity testing device suitable for wiring boards having fine circuit patterns.

[Background of the invention]

Conventional continuity testing devices employ a method in which a polarization needle is brought into direct contact with a circuit pattern on a wiring board, and the electrical resistance between electrodes of the circuit pattern is measured to detect breaks or short circuits in the circuit pattern.

However, according to this method, if the circuit pattern is damaged by contact with the turtle needle, or if the circuit pattern is particularly fine, there is no possibility of damaging the circuit pattern due to contact with the turtle needle. Since the electrode needle needs to be thin, there are problems such as making stable contact with the electrode needle difficult.

On the other hand, as a means to measure the circuit operating state without contact, for example, there is a method for measuring the operating state of a circuit using the "integrated There is an electron beam tester such as the one described in the paper "Improving the performance of EB tester using a potential detector (TLD type energy filter)" (by Todokoro et al.).

According to this, the voltage of the circuit pattern can be measured without contact, so it can be applied to a continuity tester for wiring boards, but with this electron beam tester, it is not possible to apply pressure to the circuit K from the outside (contact). Because of this assumption, it becomes necessary to use a contact-type electrode needle as a voltage application means, and the problems of the above-mentioned contact-type continuity tester cannot be fundamentally solved.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a non-contact continuity tester suitable for testing continuity of a wiring board having a fine circuit pattern.

[Summary of the invention]

In order to perform an electrical continuity test, a means for applying a voltage or current to a circuit pattern, and a means for measuring the voltage or current in order to detect the connection state of the circuit pattern are required. In the present invention, each of these steps is performed in a non-contact manner using an electron beam.

First, a method of applying voltage to a circuit pattern according to the present invention will be explained. FIG. 2 shows a cross-sectional structure of a general multilayer wiring board.

1α and 1b are signal clothing made of conductors. These disconnections and short circuits are the objects of detection by the device of the present invention. The signal lines usually face the power supply or ground (N5C and below, collectively referred to as the power supply layer) at regular intervals via an insulator 2, and the so-called
It forms a microstrip line. In addition, the signal line is connected to the 2nd side of the wiring board surface via the through hole 4a etc.
It is connected to electrodes (pads) 5 at the same location.

In such a situation, as taught by electromagnetic theory, an electrical capacitance (hereinafter simply referred to as capacitance) occurs between the signal line and the power supply or ground layer. In FIG. 2, an equivalent circuit focusing only on capacitance is shown in FIG.

Now, when the electrode 5GVC electron beam is irradiated, a IIc charge is generated on the signal line 1α, so the following voltage X (unit:
pol) [V)) is generated between the signal layer and the power layer.

's ” (11C1 Here, Ql is the given charge (unit: coulomb [C
]), q is the signal line 1α and the power layer 5F! 'l capacity (unit: two farads [F]). When the electron beam current is constant (unit: 2 amperes [A]) and the irradiation time t (unit: 2 seconds [S]), the charge tQl is expressed as -Q, = (1 - δ) It (21). Here, δ is the secondary electron emission rate (the ratio of the irradiated electron beam current to the emitted secondary electron current), which is determined by the material to be irradiated with the electron beam and the accelerating voltage of the electron beam. .

An example of the relationship between δ and acceleration voltage is shown in FIG. Efficient (to give charge to the signal line, as shown in equation (21), δ
It is desirable that the value is small. In the present invention, C in FIG.
Use a sufficiently high accelerating voltage within the range of .

Next, a method for measuring the voltage of a circuit pattern according to the present invention will be explained. When the acceleration voltage of the irradiated electron beam is constant and the voltage of the irradiated object is changed, 2 is emitted.
The energy distribution of secondary electrons changes. This change is detected by an energy filter. An example of how to purchase an energy filter is given in the aforementioned article. 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.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. The device includes a field emission type electron gun 11 capable of switching accelerated electrons by an accelerating voltage switching circuit 1o, an electron lens 12 for converging the electron beam, and two pairs of static titers that deflect the electron beam two-dimensionally by an electrostatic field. An electron beam irradiation system consisting of a facing plate 15, an extraction electrode 14 to which a positive voltage VE is applied in order to extract secondary electrons generated from the circuit pattern, and an extraction electrode 14 to selectively pass only electrons exceeding a specific energy. Electrical conduction is achieved through an energy filter system consisting of a deceleration electrode 15 and a plurality of secondary electron detectors 16 that detect secondary electrons that have passed through the deceleration electrode, an external electrode 17 of the wiring board, and a connector 18. , a signal switching circuit 19 that selectively applies a power supply voltage to externally connected electrodes or selectively extracts signals;
After voltage conversion 20C and A/Di conversion 21C, the circuit input to the microcomputer 22 and the signals detected by the plurality of secondary electron detectors are subjected to current-pressure conversion 20α, b, and then the sum 25 is taken, A circuit for A/D conversion 21α and input to the micro combinator 22; a deflection control circuit 24 for controlling the beam irradiation position according to instructions from the micro combinator 22; an electron beam irradiation system; and an energy filter system.

A vacuum chamber 25 that keeps the table system in a solid state, a table control circuit 51 that positions the object 50 to be tested according to instructions from the microcomputer 22, and a j6 microcomputer 22 that controls the entire device and detects disconnections and short circuits. Consists of.

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

Next, the operation will be explained.

First, the table 52 is moved to the wiring board mounting position.

When the wiring board of the object to be inspected 50 is attached to the connector 18 and the micro combinator 22 is instructed to start work, the micro combinator 22 executes the following automatic inspection operation according to the built-in software.

First, the air in the vacuum chamber 25 is evacuated to create a high vacuum state.

Next, the table 52 is driven to position the wiring board 50 at a predetermined position. The microcomputer 22 stores in the storage device 55 the positions of electrodes (hereinafter referred to as pads) on the wiring pattern on the substrate surface and the correct conductive relationship between them, the conductive relationship between the external electrodes, and the external electrodes and the pads. It has information on the conduction relationship between the external electrodes and the electrodes connected to the power layer and ground layer among the external electrodes.

The automatic inspection operation is performed as follows.

(1) The switching circuit 19 is controlled using the information regarding the conduction relationship between the external electrodes, and a disconnection or short circuit between the external electrodes is detected. At this time, voltage is applied to the external electrodes for each circuit pattern that is originally in a connection relationship, and for each voltage applied, an electron beam is applied to all pads on the surface of the wiring board one by one to measure changes in voltage. Measure. The acceleration voltage at this time is set to point E shown in FIG. 4, that is, about 1 KV. Based on this measurement result and information representing the conduction relationship between the external electrode and the pad, v@ between the external electrode and the pad and a short circuit are detected. That is, when a positive voltage is applied to the external electrode and there is conduction with the electrode on the surface of the substrate, the voltage increases and the secondary electron current decreases. On the other hand, when there is no conduction, the 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, the switching circuit 19 is controlled to ground the external electrodes that are connected to the power supply layer, and to open the other electrodes. Among the circuit patterns that are originally in a connection relationship, one of the circuit patterns that has no connection with the external electrode is selected, and among the pads on the surface of the substrate on the circuit pattern, one pad is irradiated with an α electron beam, and the method of the present invention is performed. Ryo @ shown in the overview
Apply voltage to the pattern according to the following. The accelerating voltage in this case is set in the range C shown in FIG. 4, for example, 20 KV. Next, an electron beam is applied to all pads on the surface of the wiring board one by one, and changes in voltage are measured. The X-speed zero pressure at this time is set to point E shown in FIG. 4, for example, about 1 Kv. If there is no short circuit with the power supply layer, a negative voltage is applied to the circuit pattern by irradiation with the steron beam at an accelerating voltage of 20 KV. When a conductive pad is irradiated with a beam, the double current increases; when there is no conduction, there is no change. This information is compared with the information indicating the continuity between the pads described above to detect disconnections and short circuits.

Here, the voltage application time using the Seiko beam is estimated. For example, the electron beam DC is 10 A, δ=0.5. The applied voltage is 1V, and the epoxy board is,! When considering a signal line with a characteristic impedance of 50Ω and a length of 100 mm, the formula (I) is expressed as follows.

From (2), C=0°12 x 100 = 12 (pF)
(3) Q: eV: 12 x 10-
'X(-1)>12X10') (4)-Q 1
2X10-”t Knee: :0,0024 (S)
+51(1-J)I a, 5x1ox1o-', that is, 2,477 per circuit pattern! JF yells.

According to this embodiment, since the application of voltage from the external electrode and the application of voltage by the electron beam are used together, continuity testing of all circuit patterns can be carried out efficiently.

In this embodiment, a field emission type electron gun is used, but a thermionic emission type electron gun may also be used. In addition, if the deflection angle of the electron beam can be reduced by using table movement, etc.,
Electromagnetic deflection may be used instead of electrostatic deflection. Further, although analog signals are summed as means for synthesizing signals from a plurality of secondary electron detectors, this may be done digitally after A/D conversion. Further, in FIG. 1, the external electrode terminals of the substrate to be inspected are described as coming out from the back surface of the substrate, but it goes without saying that they may come out 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 a mintilator and a photomultiplier tube, but may be a multi-channel plate, a semiconductor-based sensor, or the like.

[Effects of the Invention] According to the present invention, continuity testing can be performed without directly touching the surface of the circuit pattern, so the occurrence of defects during testing due to damage to the pattern can be reduced to zero, and highly reliable automatic testing can be realized. .

Furthermore, since an electron beam is used for voltage application and detection, it is possible to inspect 24 fine and high-density patterns.

[Brief explanation 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. 5 is an electrical equivalent circuit of Fig. 2, and Fig. 4 is an electronic FIG. 5 is a diagram showing changes in the secondary electron emission rate due to the beam, and is a diagram showing an example of a current-voltage conversion circuit. 1... Signal line, 2...; I8 edge body, 5... Power supply 1
Grind, 4... Through hole, 5... Electrode, 10...
Accelerating voltage switching circuit, 11... Electronic mirror, 12... Electronic lens, 15... Deflection plate, 14... Drawer '1 pole, 15... Deceleration electrode, 16... Secondary electron detection vessel, 1
7... External electrode, 18... Socket, 19... Switching circuit, 20... Current-voltage conversion circuit, 21...
A, f) Converter, 22...Microcomputer, 2
5... Addition circuit, 24... Deflection control wholesale circuit, 25.
. . . Vacuum display, 60 . . . Board to be inspected, 51 . . . Table system circuit, 32 .

Claims (1)

[Claims] 1. A continuity testing device for detecting disconnections and short-circuit defects in a circuit wiring pattern, comprising means for applying an electric charge to the circuit wiring pattern using an electron beam, and detecting voltage fluctuations in the circuit wiring pattern by irradiating the electron beam. A means for measuring by detecting fluctuations in secondary electrons generated; and a means for comparing the voltage fluctuation obtained by the measuring means with a fluctuation state expected from a normal connection relationship to determine a disconnection or short circuit defect. A continuity testing device comprising: