JP2001153902A - Method of measuring resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely measure the resistance of a substance to be measured, without being influenced by oxide films existing at probe points. SOLUTION: This concerns a resistance measuring method by a two-terminal method which causes specified measuring current to flow by bringing a pair of probes P1, P2 connected to a constant current source 10 into contact with a substance to be measured X, measures voltage generated then in the substance X by a voltage measuring means 20 through the pair of probes P1, P2, and finds the resistance value of the substance X from this measured voltage and the measuring current. After the pair of probes P1, P2 is brought into contact with the substance X and a specified high-voltage current is caused to flow from the current source 10, and an oxide film existing in the touching region of each probe P1, P2 is removed, the current of the current source 10 is switched over to the specified measuring current, and the resistance value of the substance X is found.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance measuring method for measuring a resistance value of an object to be measured, and more particularly, to a resistance measuring method capable of performing accurate measurement without being affected by an oxide film existing at a probing point. It is about.

[0002]

2. Description of the Related Art In an in-circuit tester or a bare board tester, a continuity test or a dielectric strength test is performed by measuring a resistance value of an object to be measured and comparing the measured value with a reference value. I have.

The resistance measurement method includes a two-terminal method and a four-terminal method. The four-terminal method can measure only the potential difference generated at both ends of the object to be measured, and can eliminate an error due to the resistance of the probe. Therefore, the four-terminal method is generally employed in a measurement circuit such as an in-circuit tester.

However, in the case of the four-terminal method, it is necessary to bring two probes, a current supply probe and a voltage detection probe, into contact with one measurement point (pad or via of a circuit board), and in recent years, it has been increasingly used in recent years. For a circuit pattern having an increasingly fine pitch, it may be difficult to measure four terminals. Therefore, the two-terminal method must be used for the fine pitch measurement points.

[0005]

The problem is that there is an oxide film on the surface of the measuring point. According to the four-terminal method, it is possible to cancel the resistance of the oxide film if a certain degree of continuity is achieved, but the measurement by the two-terminal method cannot cancel the resistance of the oxide film.

Therefore, when the resistance of the circuit pattern is measured by the two-terminal method, the resistance of the oxide film is added as an error. There is a case where an open judgment is made for an item that should be.

[0007] On the other hand, when a dielectric strength test is performed, for example, although there is an inherent dielectric strength failure between circuit patterns, an oxide film exists between them, which may result in erroneous determination as a good product. In addition, if the probing is performed so as to penetrate the oxide film, the resistance of the oxide film can be reduced to some extent, but this method is not a preferable solution because a dent remains.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to remove an oxide film without forming a dent and to reduce the resistance of the oxide film. It is an object of the present invention to provide a resistance measurement method capable of accurately performing a continuity test, a dielectric strength test, and the like without being affected by the resistance.

In order to achieve the above object, according to the present invention, a predetermined measurement current is applied by bringing a pair of probes connected to a constant current source into contact with an object to be measured. The voltage is measured by voltage measuring means via the pair of probes, and the resistance value of the device under test is determined from the measured voltage and the measured current. After contacting with a measurement object and applying a predetermined high-voltage current from the constant current source to remove an oxide film present at a contact portion of each probe, the current of the constant current source is switched to the predetermined measurement current. Thus, the resistance value of the object to be measured is obtained.

According to the present invention, when an oxide film is present, Joule heat is generated by application of a high-voltage current, whereby the oxide film is removed, and without being affected by the oxide film.
The resistance value of the device under test can be measured. The high-voltage current is a current having an open-terminal voltage higher than the open-terminal voltage at a predetermined measurement current of the constant current source.

At this time, since the probing point is locally heated by power loss, a thermoelectromotive force may be generated. The voltage due to the thermoelectromotive force may cause an error particularly in the case of measuring a small resistance.

For this reason, when obtaining the resistance value of the DUT, voltage measurement is performed at least twice by switching the direction of current flow to the DUT, and the DUT is determined from the average value and the measured current. Is preferably obtained. Note that AC measurement may be performed instead.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to an embodiment shown in FIG.

In carrying out this resistance measuring method, a DC constant current source 10 and a voltmeter 20 are used. The DC constant current source 10 has a pair of current supply probes P1 and P
2 are connected, and in this embodiment, a switch 30 is connected between them.

The switch 30 includes first and second two switches 31 and 32 that operate in conjunction with each other. First
The switch 31 has a switching contact 31a to which one current supply probe P1 is connected, a switching contact 31b to which the other current supply probe P2 is connected, and a movable contact 31c to be switched to any one of them. The movable contact 31c is connected to the positive electrode 10a side of the DC constant current source 10.

The second switch 32 also has two switching contacts 32
a and 32b, and a movable contact 32c that can be switched to either one of them.
Contrary to 1, the switching contact 32a is connected to the other current supply probe P2, and the switching contact 32b is connected to one current supply probe P1. The movable contact 32c is connected to the negative electrode 10b of the DC constant current source 10.

Since this resistance measuring method is a two-terminal method,
The voltmeter 20 is connected between the current supply probes P1 and P2. Although not shown, in this embodiment,
The voltmeter 20 is connected via an A / D converter to a CPU (or microcomputer) as arithmetic and control means.

In order to measure the resistance value of the device under test X, the current supply probes P1 and P2 are brought into contact with the leads L1 and L2 of the device under test X, respectively. It is assumed that an oxide film is formed on the surface of L2, and its resistance is indicated by Re in FIG.

In the present invention, the resistance measurement is not immediately started. First, each movable contact 31 of each switch 31, 32
After switching c and 32c to, for example, the switching contacts 31a and 32a, the DC constant current source 10 applies a voltage between the open terminals of the DC constant current source 10 to the device under test X of 50 to 50, for example.
A high-voltage current of about 100 V is applied to generate Joule heat at the probing point to fly away the oxide film and remove it. At this time, the voltmeter 20 may be turned off.

Thus, the current supply probe P
After activating the respective contact surfaces of P1 and P2 to improve the electrical continuity, the output range of the DC constant current source 10 is switched to supply a predetermined measurement current I to the device under test X, and the voltmeter 20 Is turned on, and a voltage V1 generated at the object X at that time is measured.

Since the measurement voltage V1 does not include the resistance component Re due to the oxide film, the resistance of the object X not affected by the oxide film is determined from the measurement voltage V1 and the measurement current I according to Ohm's law. A value is required.

By the way, when the voltages Ve1 and Ve2 due to the thermoelectromotive force are generated at the probing points of the current supply probes P1 and P2 due to the application of the high-voltage current, if the resistance value of the object X is R, The measured voltage V1 measured by the voltmeter 20 is V1 = IR + (Ve1 + V
e2), which is affected by the thermoelectromotive force.

Therefore, in this embodiment, the above-described voltage measurement is set as the first time, and the second voltage measurement is performed. That is, this time each movable contact 31 of each switch 31, 32
c, 32c are switched to the switching contacts 31b, 32b, and a measurement current I is passed from the lead portion L2 toward the lead portion L1 toward the DUT X. Is measured.

The measured voltage V2 has a flow direction of the measured current I opposite to that of the first measurement, and therefore, V2 = IR- (V
e1 + Ve2). Therefore, by obtaining the average value Va of the first measurement voltage V1 and the second measurement voltage V2, the voltages Ve1 and Ve2 due to the thermoelectromotive force are offset, and the measurement voltage V without the influence of the thermoelectromotive force is obtained. And
Thus, the true resistance value of the device under test X is obtained.

In the dielectric strength test between circuit patterns, the influence on the oxide film can be eliminated by measuring the resistance value of the object X in the same manner as in the above embodiment. It is needless to say that the present invention can be applied not only to being incorporated in an in-circuit tester or a bare board tester, but also to a single-function resistance measuring device.

[0026]

As described above, according to the present invention,
Prior to measuring the resistance of the device under test, a high-voltage current was applied to the probe point to remove the oxide film, so that no dents were formed at the probe point, and the probe point was accurately measured. The resistance value can be measured.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram for explaining an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 10 constant current source 20 voltmeter 30 switch P1, P2 probe L1, L2 lead part X DUT

Claims (2)

[Claims] 1. A predetermined measurement current is applied by bringing a pair of probes connected to a constant current source into contact with an object to be measured, and at this time, a voltage generated in the object to be measured is applied through the pair of probes. In a resistance measurement method by a two-terminal method of measuring a resistance value of the object to be measured from the measured voltage and the measured current, the pair of probes are brought into contact with the object to be measured, and the constant current is measured. After applying a predetermined high-voltage current from the source to remove the oxide film present at the contact portion of each probe, the current of the constant current source is switched to the predetermined measurement current to change the resistance value of the DUT. A resistance measuring method characterized by being determined. 2. When obtaining the resistance value of the device under test, voltage measurement is performed at least twice by switching the direction of current flow with respect to the device under test, and the average value and the measurement current are used to measure the voltage of the device under test. The resistance measuring method according to claim 1, wherein a resistance value is obtained.