JPH10142271A - Measuring method for pattern electrostatic capacity of circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the measurement of the electrostatic capacity of a surface pattern even in the case where a pattern provided on the surface of a detected circuit board and a mat pattern provided on its back are mutually conducted. SOLUTION: An electrode 10 being common to all surface patterns is arranged on the side of the back of a detected circuit board 24 provided with a plurality of patterns 28 on the surface, and an insulating layer 30 is insertedly set between the circuit board 24 and a common electrode 10, and a probe 16 is brought into contact with the surface pattern 28 being a measurement object, and low or high voltage is applied to them, and low or high voltage is applied to the common electrode, and a current flowing in the surface pattern 28 is measured to compute an electrostatic capacity between the surface pattern and the common electrode 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a pattern capacitance of a circuit board using a circuit board inspection apparatus such as an XY type in-circuit tester, a bare board tester, or the like.

[0002]

2. Description of the Related Art Conventionally, a mounting substrate, that is, a printed circuit board on which a large number of electronic components are soldered, uses an in-circuit tester to appropriately contact the tip of a probe to a required measurement point on the substrate, and to connect each of those components. The quality of the board is determined by electrically detecting the presence or absence of the component or by electrically measuring the characteristic value of each component. In particular, in an XY-system in-circuit tester, an XY unit is installed on a measuring table on which a circuit board to be inspected is mounted and fixed, and a Z-axis movable in the Y-axis direction on an arm movable in the X-axis direction. A unit is provided, and the probe is movably supported in the Z-axis direction by the Z-axis unit. At the time of inspection, the XY unit is controlled, the probe is appropriately moved in the X-axis, Y-axis, and Z-axis directions from above the substrate, and sequentially comes in contact with preset measurement points. Therefore, the XY type in-circuit tester is suitable for inspection of a circuit board of a large variety of small production.

When the capacitance of a wiring pattern provided on a printed circuit board is measured using such an XY type in-circuit tester, disconnection or short-circuit of the pattern can be inspected. At this time, a plate as shown in FIG. 9 is used as the common electrode 10 and a plurality of patterns 12 (1
The printed circuit board 14 to be inspected is placed with the surface provided with 2a,... 12f) facing up. Then, the probe 16 is brought into contact with the pattern 12 a to be measured, and a high or low voltage is applied to the probe 16 from the AC voltage source 20 provided in the measuring unit 18, and a low or high voltage is applied to the common electrode 10. Then, the current flowing through the pattern 12a is measured by the AC ammeter 22, and the capacitance between the pattern 12a and the common electrode 10 can be calculated from the voltage value and the current value. Here, assuming that the effective value of the voltage is E, the effective value of the current is I, and the frequency is f, the capacitance C is C = I / 2πf
It can be calculated from E.

After the capacitance of the pattern 12a is calculated in this way, it is compared with a reference value previously obtained from a good substrate. judge. Since the common electrode 10 is an electrode common to all the patterns 12, the same determination can be made for the other patterns 12b,..., 12f.

[0005]

However, even when such a common electrode 10 is used, the solid pattern 26 is provided on the back surface of the printed circuit board 24 as shown in FIG. When the pattern 26 is conductive, if the resist is not applied to the solid pattern 26, the pattern 28a and the common electrode 10 are also conductive, so that the capacitance of the pattern 28a cannot be measured. Therefore, it is not possible to inspect the pattern 28a for disconnection, short circuit and the like. Even if a resist is applied to the solid pattern 26, if there is a through hole, that part is not insulated, so that there is still a problem.

The present invention has been made in view of such conventional problems. First, the present invention relates to a case where a pattern provided on the front surface of a circuit board to be inspected and a solid pattern provided on the back surface are conductive. It is another object of the present invention to provide a method of measuring the capacitance of a circuit board, which can measure the capacitance of the surface pattern.

Second, even when the pattern provided on the front surface of the circuit board to be inspected and the solid pattern provided on the back surface are conducting, not only can the capacitance of the surface pattern be measured, It is an object of the present invention to provide a method for measuring the capacitance of a circuit board pattern that can increase the inspection speed.

[0008]

In order to achieve the above object, in the method for measuring the capacitance of a circuit board according to the first object of the present invention, the back side of a circuit board to be inspected having a plurality of patterns provided on the front side. In addition, an electrode common to all of these surface patterns is arranged, a probe is brought into contact with the surface pattern to be measured, and a high or low voltage is applied, and a low or high voltage is applied to the common electrode. , The current flowing through the surface pattern is measured, and the capacitance between the surface pattern and the common electrode is calculated. Further, an insulating layer is interposed between the circuit board and the common electrode.

In the method for measuring the pattern capacitance of a circuit board corresponding to the second object, an electrode common to all the surface patterns is arranged on the back side of a circuit board to be inspected having a plurality of patterns provided on the front side. Then, a plurality of probes are simultaneously brought into contact with the corresponding surface patterns selected from all the surface patterns respectively, and a high or low voltage is applied to the common electrode, and a low or high voltage is applied to the surface pattern to be measured. Apply a voltage and measure the current flowing through the surface pattern,
The procedure is to calculate the capacitance between the surface pattern and the common electrode. An insulating layer is interposed between the circuit board and the common electrode, and the same potential voltage as that of the common electrode is applied to each of the unmeasured surface patterns contacted by the probe.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram 1 showing the application of the invention.
FIG. 4 is a circuit diagram when a pattern capacitance of a circuit board to be inspected is measured by a probe moving type XY in-circuit tester. In the method for measuring the pattern capacitance of a circuit board according to the present invention, an insulating sheet 30 made of plastic or the like is attached to the entire upper surface of the common electrode 10 for use. Therefore, unlike the conventional device shown in FIG. 10, even if the circuit board 24 to be inspected is placed on the common electrode 10, the insulating sheet 30 becomes an insulating layer, and the circuit board 24 and the common electrode 10 Intervene in between. Then, even if the pattern 28a on the front surface of the circuit board 24 to be inspected and the pattern 26 on the rear surface are conductive, the solid pattern 26 and the common electrode 10 are not conductive.

Therefore, as in the prior art, one probe 16 is brought into contact with one pattern 28 on the surface to be measured, and a high voltage is applied to the pattern 28 from the AC voltage source 20 provided in the measuring unit 18. In addition, when a low voltage is applied to the common electrode 10, the current flowing through the pattern 28 is measured by the AC ammeter 22, and the capacitance C between the pattern 28 and the common electrode 10 is measured based on the voltage value and the current value. Can be calculated. At this time, since the pattern 28a and the solid pattern 26 are conducting, the capacitance Ca of the pattern 28a
As shown, the capacitance becomes equal to the capacitance C2 between the solid pattern 26 and the common electrode 10.

Each of the other patterns 28 (28b,..., 2)
8f) of the capacitance C (Cb,... Cf)
8 (28b,..., 28f) and the solid pattern 26 are represented by C1 (C1b,... C1f), and the capacitance between the solid pattern 26 and the common electrode 10 is represented by C2. Since the capacitances C1 and C2 are connected in series as shown in FIG. 3 for the pattern 28, the capacitance C of each pattern 28 is C = C1.C2 / (C1 + C2). Moreover, if the pattern on the back side is the solid pattern 26, C
Since 1≪C2, C ≒ C1. Therefore, the capacitances Cb,..., Cf of the respective patterns 28b,..., 28f are Cb ≒ C1b,. As a result,
Even when the pattern 28a and the solid pattern 26 are electrically connected, the capacitance C can be calculated for each of the patterns 28, and it is possible to determine whether each pattern 28 is disconnected or short-circuited. Note that a low voltage may be applied to each pattern 28 and a high voltage may be applied to the common electrode 10.

However, in such a measuring method, each time the capacitance C of each pattern 28 is measured, the probe 1
6 must be moved up and down in the Z-axis direction or the like. Therefore, if the number of patterns is large, the measurement time is considerably required, and the inspection cannot be speeded up. Therefore, it is conceivable to move a plurality of probes by simultaneously raising and lowering them. For example, as shown in FIG.
The probe 16 (16a, 16b, 16c) is simultaneously lowered and the corresponding pattern 28 (28a, 28b, 28
c) respectively. At this time, it is preferable to use a multi-pin probe unit disclosed in Japanese Patent Application No. 6-172136 previously presented by the present applicant. A scanner 32 selects a pattern 28 to be measured.

However, in order to measure the capacitance Cb of the pattern 28b, for example, as shown in FIG.
When a high voltage H is applied to 0 and a low voltage L is applied to the pattern 28b, when the patterns are adjacent to each other at a close distance like a bus line or when a solid pattern is included in the inner layer, etc. , A floating capacitance C01 exists between the probes 16b and 16c, and a floating capacitance C02 exists between the probes 16b and c. Therefore, the capacitance Cb is erroneously determined as C01 + C1b + C02.C1c.
/ (C02 + C1c) is measured and C1b cannot be measured. In addition, as shown in FIG.
If the potential voltage of c is set to guard (earth), a current flows through the pattern 28a that is in conduction with the solid pattern 26 due to the guard effect, and no current flows through the pattern 28b, so that C1b cannot be measured.

To measure the capacitance Ca of the pattern 28a, a high voltage H is applied to the common electrode 10 and a low voltage L is applied to the pattern 28a as shown in FIG.
Further, the same high voltage H as that of the common electrode 10 is applied to each of the patterns 28b and c that are not measured. Then, no current flows through each of the patterns 28b and c and the floating capacitance C02, so that the influence of the capacitances C1b, C1c and C02 disappears, and the measured value C becomes C = C01 + C2. Therefore, when the floating capacitance C01 is measured without the circuit board 24 to be inspected and is subtracted from the measured value C, C-C01 = C2.
Thus, the capacitance Ca of the pattern 28a can be measured.

When measuring the capacitance Cb of the pattern 28b, a high voltage H is applied to the common electrode 10 and a low voltage L is applied to the pattern 28b as shown in FIG. , C, the same high voltage H as that of the common electrode 10 is applied. Then, the pattern 28
Since no current flows through c, the influence of the capacitance C1c disappears, and the measured value C becomes C = C01 + C02 + C1b. However,
C≪C2. Therefore, when C01 and C02 are measured without the circuit board 24 to be inspected and subtracted from C, C-C01-
C02 = C1b, and the capacitance Cb of the pattern 28b can be measured. Similarly, the capacitance Cc of the pattern 28c can be measured as Cc = C1c.
The remaining probes 28d, e, and f can also be moved by raising and lowering the three probes 16 at the same time, and the capacitances Cd, Ce, and Cf can be measured in the same manner. A high voltage is applied to the pattern 28 to be measured, and each of the unmeasured patterns 2
A lower voltage may be applied to the common electrode 8 and the common electrode 10.

[0017]

According to the present invention described above, claim 1
In the described invention, even when the pattern provided on the front surface of the circuit board to be inspected and the solid pattern provided on the back surface are in a conductive state, an insulating layer is interposed between the circuit board and the common electrode. The capacitance of the surface pattern can be measured.

In the invention according to claim 2, an insulating layer is interposed between the circuit board to be inspected and the common electrode, and a plurality of probes are simultaneously brought into contact with corresponding surface patterns selected from all the surface patterns, respectively. The same high or low voltage as the common electrode is applied to each non-measurement surface pattern contacted by the probe, eliminating the influence of each non-measurement pattern contacted by the probe. Also, the capacitance of the surface pattern can be measured. And the inspection speed can be increased.

[Brief description of the drawings]

FIG. 1 is a circuit diagram when a pattern capacitance of a circuit board to be inspected is measured by an XY type in-circuit tester of a one-probe moving type to which the present invention is applied.

FIG. 2 is a diagram showing an equivalent circuit for measuring a capacitance of a front surface pattern that is conductive to a solid back surface pattern by the XY type in-circuit tester of the same probe moving type.

FIG. 3 is a diagram showing a capacitance measurement equivalent circuit of a front surface pattern that does not conduct with a solid back surface pattern by the XY type in-circuit tester of the same probe moving type.

FIG. 4 shows a three-probe simultaneous movement type X- to which the present invention is applied.
FIG. 4 is a circuit diagram when a pattern capacitance of a circuit board to be inspected is measured by a Y-system in-circuit tester.

FIG. 5 shows the measurement of the capacitance of a surface pattern that does not conduct with the solid pattern on the back surface showing the stray capacitance coupling of each surface pattern that is not measured by the probe and that is not measured by the XY type in-circuit tester of the three-probe simultaneous movement type. It is an equivalent circuit diagram.

FIG. 6 is an equivalent circuit diagram of capacitance measurement of a surface pattern that does not conduct with a solid pattern on the back surface showing a guard effect of each surface pattern that is not measured by a probe and that is in contact with the XY type in-circuit tester of the three-probe simultaneous movement type. It is.

FIG. 7 is a diagram showing an equivalent circuit for measuring capacitance of a surface pattern which is conducted to a solid pattern on the back surface of the XY type in-circuit tester of the three-probe simultaneous movement type, which eliminates the influence of each surface pattern which is not measured and which is in contact with the probe. FIG.

FIG. 8 shows an equivalent circuit for capacitance measurement of a surface pattern that does not conduct with a solid pattern on the back side by eliminating the influence of each surface pattern that is not measured by the probe and the XY type in-circuit tester of the three-probe simultaneous movement type. FIG.

FIG. 9 is a circuit diagram when a pattern capacitance of a circuit board to be inspected is measured by a conventional one probe moving type XY in-circuit tester.

FIG. 10 is a circuit diagram showing a state in which the capacitance of a front surface pattern that is electrically connected to a solid back surface pattern cannot be measured by the XY type in-circuit tester of the same probe moving type.

[Explanation of symbols]

10 Common electrode 16 Probe 18 Measurement unit 20
... AC voltage source 22 ... AC ammeter 24 ... circuit board to be inspected 26 ... solid pattern 28 ... surface pattern 30 ... insulating sheet

Claims (2)

[Claims] An electrode common to all the surface patterns is arranged on the back side of a circuit board to be inspected having a plurality of patterns on the surface, and a probe is brought into contact with the surface pattern to be measured. A high or low voltage is applied to the common electrode, a low or high voltage is applied to the common electrode, a current flowing through the surface pattern is measured, and a capacitance between the surface pattern and the common electrode is calculated. In the capacitance measuring method, an insulating layer is interposed between the circuit board and the common electrode, wherein the pattern capacitance of the circuit board is measured. 2. An electrode common to all the surface patterns is arranged on the back surface side of a circuit board to be inspected having a plurality of patterns on the surface, and a plurality of probes are simultaneously selected from all the surface patterns. Contact each corresponding surface pattern, apply a high or low voltage to the common electrode, apply a low or high voltage to the surface pattern to be measured, measure the current flowing in the surface pattern, In the method for measuring the capacitance of a circuit board, which calculates the capacitance between the surface pattern and the common electrode, an insulating layer is interposed between the circuit board and the common electrode, and is common to each unmeasured surface pattern contacted by a probe. A method for measuring the capacitance of a pattern on a circuit board, comprising applying the same potential voltage as an electrode.