JP2001281281A - Probe for impedance measurement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a probe for impedance measurement which can easily be brought into contact with a measured circuit and a ground circuit in a short time and stabilize the contact state. SOLUTION: An internal conductor 2 having a contact pin 6 to be brought into contact with the measured circuit 4 on a circuit board 3 and an external conductor 1 are arranged in a coaxial line shape. The tip of the contact pin 6 is projected from an end surface of the external conductor 1 and a ground circuit contact part 8 to be brought into contact with the ground circuit 7 on the circuit board 3 is provided on the end surface of the external conductor 1. When the contact pin 6 is brought into contact with the measured circuit 4, the ground circuit contact part 8 always comes into contact with the ground circuit 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a probe for measuring impedance used for measuring the impedance of a circuit board such as a multilayer printed wiring board.

[0002]

2. Description of the Related Art In a circuit board used for electronic equipment, etc.,
The impedance matching between a circuit provided on a circuit board and a signal transmitted through the circuit is performed. Particularly, in the case of a circuit for transmitting a high-frequency signal (high-speed signal), this impedance matching is important. is there. Therefore, the circuit of the circuit board is designed so that impedance matching with a signal to be transmitted can be obtained, and the circuit board is checked whether the impedance (value) of the circuit is within an allowable range from the design value. Products that have been commercialized and whose circuit impedance falls outside a certain allowable range are discarded as defective products.

Conventionally, when measuring the impedance of a circuit on a circuit board, mainly TDR (Time Domain Ref) is used.
rectrometry) method is used. In this method, a pulse or step signal is transmitted to a transmission circuit including a signal circuit (circuit under test) whose impedance is to be measured and a reference ground circuit, and a reflection signal in the transmission circuit is detected and a reflection signal is detected. The impedance value of the transmission circuit (circuit under test) is obtained by using the reflection coefficient obtained from the above.

When transmitting a signal to a transmission circuit, a probe is used as an intermediary for electrically connecting a cable derived from a signal source to the transmission circuit. Such an impedance measuring probe mainly includes a contact pin for a circuit to be measured for contacting a circuit to be measured and a contact pin for a ground circuit for contacting a ground circuit. A macrostrip structure formed by sandwiching a plate-shaped dielectric layer between circuit contact pins, an inner conductor and an outer conductor are arranged in a coaxial line shape, and the contact pin for a circuit under test is drawn from the inner conductor. In addition, a coaxial line structure formed by extracting a ground circuit contact pin from an external conductor is roughly classified into two types. In any of the impedance measurement probes described above, the tip of the contact pin for the circuit to be measured and the tip of the contact pin for the ground circuit are simultaneously brought into contact with the signal circuit and the ground circuit, respectively, to measure the impedance. Do it.

[0005]

As described above, in the TDR measurement, it is necessary to input a signal by simultaneously bringing the contact pin for the circuit under test and the contact pin for the ground circuit into contact with the signal circuit and the ground circuit, respectively. Therefore, in a conventional probe having two contact pins, the tip of the contact pin for the circuit to be measured contacts the signal circuit, and the tip of the contact pin for the ground circuit contacts the ground circuit. It is necessary to perform position control by rotating the probe or the like, and there is a problem that it takes time to make contact or the contact state becomes unstable.

In particular, when the area of the portion where the contact pin for the circuit to be measured or the contact pin for the ground circuit is small is small, for example, the signal circuit or the ground circuit is exposed on the end face of the circuit board and the portion for the circuit to be measured When contacting the contact pin or the contact pin for the ground circuit, it is necessary to control the probe position very finely.
The above problem became remarkable.

The present invention has been made in view of the above points, and can easily make contact with a circuit to be measured or a ground circuit, does not require much time to make contact, and stabilizes the state of contact. It is an object of the present invention to provide a probe for impedance measurement that can perform the measurement.

[0008]

According to a first aspect of the present invention, there is provided an impedance measuring probe having an inner conductor and an outer conductor provided with contact pins for contacting a circuit to be measured on a circuit board. Are arranged in a coaxial line shape, and a ground circuit contact portion 8 for projecting the tip of the contact pin 6 from the end surface of the external conductor 1 and making contact with the ground circuit 7 of the circuit board 3 is provided on the end surface of the external conductor 1. It is characterized by comprising.

A probe A for impedance measurement according to a second aspect of the present invention, in addition to the configuration of the first aspect, has a ground circuit contact portion 8 formed so as to protrude from an end surface of the external conductor 1 and a ground circuit contact portion 8. Are formed in a frame shape continuous in the circumferential direction of the external conductor 1.

According to a third aspect of the present invention, in addition to the configuration of the first or second aspect, the impedance measuring probe A is characterized in that the ground circuit contact portion 8 is formed of pressurized conductive rubber. It is.

The probe A for impedance measurement according to a fourth aspect of the present invention is characterized in that, in addition to the configuration of the first or second aspect, the ground circuit contact portion 8 is formed of conductive rubber. is there.

A probe A for impedance measurement according to a fifth aspect of the present invention, in addition to any one of the first to fourth aspects, has a contact pin 6 formed so as to be able to be inserted into and removed from the external conductor 1. It is characterized by the following.

A probe A for impedance measurement according to a sixth aspect of the present invention is characterized in that the contact pin 6 has a cushioning property in addition to any one of the first to fifth aspects. is there.

A probe A for impedance measurement according to a seventh aspect of the present invention is characterized in that, in addition to any one of the first to sixth aspects, the contact pin 6 is formed to be expandable and contractable by a spring 23. Is what you do.

An impedance measuring probe A according to an eighth aspect of the present invention, in addition to the configuration according to any one of the first to seventh aspects, has a tip of the ground circuit contact portion 8 formed in a substantially triangular cross section. It is characterized by the following.

According to a ninth aspect of the present invention, in addition to the configuration of any one of the first to seventh aspects, the impedance measuring probe A has a tip of the ground circuit contact portion 8 formed in a substantially semicircular cross section. It is characterized by the following.

According to a tenth aspect of the present invention, in the impedance measuring probe A, in addition to any one of the first to ninth aspects, a dielectric layer 9 is provided between the inner conductor 2 and the outer conductor 1. The body layer 9 is formed of a material having a low dielectric constant and a low dielectric loss tangent.

[0018]

Embodiments of the present invention will be described below.

Probe A for Impedance Measurement of the Present Invention
Is formed by arranging an outer conductor 1 and an inner conductor 2 in a coaxial line shape, as shown in FIG. The impedance measuring probe A is designed so as to have the same impedance as a coaxial cable described later, and is impedance-matched.

The outer conductor 1 is made of any conductive metal material such as copper or stainless steel, which is generally used for electric parts, or any conductive material having the same conductivity and the same shape stability as the metal material. It can be formed of a material. Further, the outer conductor 1 is formed in a substantially cylindrical shape having a through hole 11, and the opening of the through hole 11 at the front end face of the outer conductor 1 is formed as a pin projecting port 15 and at the rear side of the outer conductor 1. The opening of the through hole 11 on the end face of the cable is formed as a cable insertion port 16.

A ground circuit contact portion 8 is provided on the front surface of the outer conductor 1 so as to project therefrom. The ground circuit contact portion 8 is integrally formed of the same material as the external conductor 1, and is formed in a substantially circular frame shape continuous in the circumferential direction of the external conductor 1.
In addition, the ground circuit contact portion 8 is formed so as to surround the pin protrusion 15. As shown in FIG.
The ground circuit contact portion 8 can be formed to have a substantially triangular cross section.
Of the ground circuit contact portion 8, the ground circuit contact portion 8 can be reliably contacted with the ground circuit 7, even if the ground circuit contact portion 8 is small. The ground circuit contact portion 8 and the ground circuit 7 can be brought into contact with a relatively strong force. Further, as shown in FIG. 3B, the ground circuit contact portion 8 can be formed to have a substantially semicircular cross section, so that even if the tip of the ground circuit contact portion 8 contacts the ground circuit 7, Damage such as damage to the circuit 7 can be relatively reduced.

It should be noted that the ground circuit contact portion 8 may not be protruded as described above, and the peripheral portion of the pin protrusion 15 on the front surface of the external conductor 1 may be formed as the ground circuit contact portion 8. In this case, the risk of damaging (damaging) the ground circuit 7 is reduced as compared with the case where the ground circuit contact portion 8 is formed so as to protrude. However, in order to easily and stably contact the ground circuit contact portion 8 with the ground circuit 7 to improve the contact property, the ground circuit contact portion 8 is connected to the external conductor 1 as shown in FIGS. Is preferably formed so as to protrude from the front surface.

A mounting piece 18 is formed on the outer peripheral surface in the middle of the outer conductor 1 so as to protrude over the entire circumference. By fixing the mounting piece 18 to another member, the impedance measurement of the present invention can be performed. Probe A can be attached to another member. Further, a thread 17 is formed on the outer peripheral surface of the rear portion of the outer conductor 1, and a connector provided at an end of a coaxial cable described later can be screwed into the thread 17. And the impedance measuring probe A of the present invention can be easily connected.

The internal conductor 2 is composed of the contact pins 6 and the connection conductor 30. The contact pin 6 is formed of a conductive metal such as copper or nickel. As shown in FIG. 4, the contact pin 6 has a needle-shaped pin body 21 having a sharp tip and a cylindrical shape having an open front surface and a closed rear surface. , And a spring 23 such as a coil spring. The tip of the pin body 21 is the socket 2
2 is inserted into the socket 22 so as to protrude from the front opening of the socket 22.
Is formed in a state of covering. The spring 23 is provided between the rear end of the pin body 21 and the bottom of the socket 22. Further, the pin body 21 is formed so as to be slidable in the front-rear direction with respect to the socket 22. Also,
The pin body 21 is formed so as to be able to be inserted into and removed from the socket 22. In addition, when the outer peripheral surface of the pin main body 21 and the inner peripheral surface of the socket 22 come into contact with each other, the pin main body 21 and the socket 22 are electrically connected.

The above-mentioned contact pin 6 is
Are formed so as to be slidable in the front-rear direction with respect to the socket 22, so that the pin body 21 protrudes greatly from the socket 22 and the pin body 21 is inserted deeply into the socket 22 against the elastic force of the spring 23. It is formed so as to be able to expand and contract with the state in which it is moved. Further, the contact pin 6 is configured such that a spring 23 is provided between the rear end of the pin body 21 and the socket 2.
Since the pin main body 21 is provided between the bottom surfaces of the circuit board 2 and has a cushioning property, the pin main body 21 can elastically contact the circuit 4 to be measured of the circuit board 3. The cushioning property in the present invention means that when measuring the impedance of the circuit 4 to be measured on the circuit board 3, it is determined whether the tip of the pin body 21, the tip of the ground circuit contact portion 8, or the contact portion of the contact pin 6 of the circuit 4 to be measured. In order to prevent weighting, it refers to the property of absorbing a weight above a certain threshold. In the contact pin 6, the cushioning property is exerted by the contraction of the spring 23, thereby reducing the damage to the pin body 21 and the circuit 4 to be measured and reducing the damage of the pin body 21 to the circuit 4 to be measured. The contact property can be improved.

The connection conductor 30 is for electrically connecting the contact pin 6 and the core wire of the coaxial cable inserted into the through hole 11 from the cable insertion port 16 and is of the same kind as the contact pin 6 and the external conductor 1. It can be formed of the following materials. The connection conductor 30 is provided with a pin connection hole 31, and the pin connection hole 31 is formed so as to open on the front surface of the connection conductor 30. The connection conductor 30 is provided with a core wire connection hole 32, and the core wire connection hole 32 is
0 is formed on the rear surface. By inserting the rear part of the contact pin 6 into the pin connection hole 30, the connection conductor 30 is attached to the rear side of the contact pin 6, and the contact pin 6 and the connection conductor 30 are electrically connected.

The inner conductor 2 formed as described above has a shape in which the tip of the pin body 21 of the contact pin 6 is projected from the pin projecting hole 15 to the outside (front side) of the outer conductor 1. Are accommodated in the through-hole 11. The inner conductor 2 is an outer conductor 1 passing through the through hole 11.
Are arranged along the center line. In addition, the tip of the pin body 21 of the contact pin 6 is about 1 m longer than the tip of the ground circuit contact portion 8 normally protruding from the front surface of the external conductor 1.
The contact pins 6 are projected forward by about m, but the dimensions of the contact pins 6 projecting from the pin body 21 can be set arbitrarily. Since the contact pin 6 is formed so as to be extendable and contractible as described above, the pin body 21 of the contact pin 6 can be moved in the front-rear direction with respect to the external conductor 1, but the pin body 21 is weighted from the front side. When the contact pin 6 is received, the contact pin 6 is designed to be contracted until at least the tip of the pin main body 21 and the tip of the ground circuit contact portion 8 are located in the same plane. Further, the ground circuit contact portion 8 is formed so as to surround the tip of the pin body 21 of the contact pin 6, but the pitch (interval) between the tip of the pin body 21 of the contact pin 6 and the tip of the ground circuit contact portion 8 is covered. It is formed so as to match the pitch between the measurement circuit 4 and the ground circuit 7.
Further, the core wire connection hole 32 of the connection conductor 30 faces the cable insertion port 16 of the through hole 11 and is in communication with the cable insertion port 16.

The outer peripheral surface of the inner conductor 2 and the inner peripheral surface of the outer conductor 1 (through hole 1)
A dielectric layer 9 is formed between the two (1 wall surfaces). The dielectric layer 9 includes the outer conductor 1 and the inner conductor 2 adjacent to each other with the dielectric layer 9 interposed therebetween.
And to hold the internal conductor 2 in the through hole 11. The dielectric layer 9 is preferably formed of a material having a low dielectric constant and a low dielectric loss tangent in order to improve the characteristics at high frequencies. For example, PTFE (fluororesin such as polytetrafluoroethylene, PPO (polyphenylene ether), PPE (polyphenylene oxide)
Such a resin can be used, but any material having a low dielectric constant and a low dielectric loss tangent similar to that of the fluororesin, and having the same shape stability as the fluororesin can be used. When the contact pins 6 are held by the dielectric layer 9 as described above, the socket 22 is fixed, but since the pin body 21 is formed so as to be able to be inserted into and removed from the socket 22, the pin body 21 is connected to the external conductor 1. Can be inserted and removed from Therefore, the pin body 21 whose life has expired due to wear due to contact with the circuit 4 to be measured is extracted from the socket 22 and a new pin body 21 is replaced with the socket 22.
, The pin body 21 alone can be replaced. That is, at the time of impedance measurement, the tip of the contact pin 6 repeatedly contacts the circuit 4 to be measured on the circuit board 3, so that the contact pin 6 is inevitably deteriorated. However, in the present invention, since only the pin body 21 can be replaced, the running cost can be reduced.

It should be noted that a stable cavity in which the pin body 21 can be directly accommodated by the dielectric layer 9 alone is formed, and the rear portion of the pin body 21 is securely brought into contact with the connection conductor 30 so that the socket 22 is formed.
Can be avoided. A spring 2 is provided between the contact pin 6 and the connection conductor 30 or the external conductor 1.
3 may be provided.

The impedance measuring probe A of the present invention formed as described above is electrically connected via a coaxial cable to an oscilloscope or an impedance measuring instrument having an input signal generator for generating a signal for measurement. Things. When connecting the coaxial cable to the impedance measuring probe A, one end of the coaxial cable is inserted into the through hole 11 from the cable insertion port 16, and the core wire (center conductor) at one end of the inserted coaxial cable is connected to the inner conductor 2.
And the coated conductor (outer conductor) at one end of the coaxial cable inserted into the through-hole 11 is brought into contact with the wall surface of the through-hole 11,
A connector provided at the end of the coaxial cable is screwed into the thread 17 of the outer conductor 1. Then, the end of the coaxial cable is connected to the impedance measuring probe A as described above.
, The core wire of the coaxial cable can be electrically connected to the pin main body 21 of the contact pin 6 and the coated conductor of the coaxial cable can be electrically connected to the outer conductor 1. The other end of the coaxial cable is connected to an impedance measuring device.

Probe A for Impedance Measurement of the Present Invention
Can be used for characteristic impedance measurement by the TDR method or the like. In this case, the end of the circuit 4 to be measured on the circuit board 3 and the end of the ground circuit 7 are brought into contact with the end of the contact pin 6 and the end of the ground circuit contact portion 8 so that the end of the circuit board 3 can be brought into contact with the end. It is formed so as to be exposed from the end face of the circuit board 3. The circuit under test 4 may be a signal circuit to which a signal is actually transmitted, or may be a test pattern for measuring impedance.

FIG. 5A shows an example of a method for measuring the impedance of the circuit 4 to be measured on the circuit board 3 using the impedance measuring probe A of the present invention. This method uses the circuit board 3
The end of the circuit under test 4 and the end of the ground circuit 7 are exposed on the surface of the device. A ground circuit 7 is formed on the surface of the circuit board 3 and a circuit 4 to be measured is formed inside the circuit board 3, and a measurement opening 33 extending from the surface of the circuit board 3 to the circuit 4 to be measured. Are formed on the circuit board 3. Then, the contact pins 6 are inserted into the measurement openings 33 from the surface side of the circuit board 3 and the tips of the contact pins 6 are brought into contact with the surface of the end of the circuit 4 to be measured.
The tip of the ground circuit contact portion 8 is brought into contact with the end of the ground circuit 7 at the periphery of the measurement opening 33. In this way, the impedance of the circuit under test 4 can be measured. In this example, even if the impedance measuring probe A of the present invention is manually operated, it can be easily brought into contact with the circuit under test 4 and the ground circuit 7.

FIG. 5B shows another example of a method for measuring the impedance of the circuit 4 to be measured on the circuit board 3 using the impedance measuring probe A of the present invention. This method uses the circuit board 3
The end of the circuit under test 4 and the end of the ground circuit 7 are exposed on the end face of the circuit. A ground circuit 7 is formed on the surface and inside of the circuit board 3, and a circuit 4 to be measured is formed inside the circuit board 3. Then, the probe A for impedance measurement is brought close to the circuit board 3 from the side,
The tip of the contact pin 6 is brought into contact with the surface of the end of the circuit under test 4, and the tip of the ground circuit contact portion 8 is brought into contact with the end of the ground circuit 7. In this way, the impedance of the circuit under test 4 can be measured. In this example, since the impedance measuring probe A is brought into contact with very small end surfaces of the circuit under test 4 and the ground circuit 7, the position of the impedance measuring probe A is adjusted while observing the contact portion in an enlarged manner using a camera or the like. It is preferred to do so. In the TDR measurement, it is preferable to treat all conductive parts of the circuit board 3 other than the circuit under test 4 as grounds (circuits) in order to perform impedance measurement with high accuracy and stability.
Since the ground circuit contact portion 8 is formed so as to surround the entire circumference of the contact pin 6, the tip of the ground circuit contact portion 8 can be simultaneously contacted with a plurality of conductive portions near the end of the circuit 4 to be measured. This makes it possible to measure impedance with high accuracy and stability.

In the probe A for impedance measurement of the present invention, the inner conductor 2 having the contact pins 6 for making contact with the circuit under test 4 and the outer conductor 1 are arranged in a coaxial line shape. A ground circuit contact portion 8 for projecting the front end from the front surface of the external conductor 1 and making contact with the ground circuit 7 of the circuit board 3 is provided on the front surface of the external conductor 1, and the ground circuit contact portion 8 is connected to the front end of the contact pin 6. Is formed so as to surround the entire circumference of the circuit under test 4 without controlling the position in the rotational direction with the contact pin 6 as the axial direction.
It is only necessary to perform only horizontal or vertical position control to make contact with the circuit, and it can be easily brought into contact with the circuit under test 4 and the ground circuit 7 without requiring time to make contact. The state can be stabilized.

FIGS. 6A and 6B show another embodiment. In the impedance measuring probe A, the ground circuit contact portion 8 is formed of pressurized conductive rubber, and the ground circuit contact portion 8 extends over the entire front surface of the external conductor 1 so as to surround the tip of the contact pin 6. It is provided integrally. Other configurations are the same as those of the above embodiment. Pressurized conductive rubber usually has the same conductive properties as general rubber, but when compressed, the resistance value decreases, leading to the same conductivity as conductive metals. is there. Specifically, “PCR” manufactured by Nippon Synthetic Rubber Co., Ltd. can be used.

The probe A for impedance measurement according to this embodiment can be used for impedance measurement in the same manner as the method shown in FIGS. 5A and 5B. It is necessary to press the ground circuit contact portion 8 against the ground circuit 7 with a sufficient pressure (contact pressure) so that the resistance value of the contact portion 8 decreases to a sufficiently small value.

Further, the ground circuit contact portion 8 is formed by using conductive rubber instead of the pressurized conductive rubber, and FIG.
(A) The probe A for impedance measurement shown in (b) can be formed. The conductive rubber has a lower resistance value than normal rubber even when there is no distortion due to pressure or the like, and the change in resistance value due to compression is small. Specifically, “EC-A” manufactured by Shin-Etsu Chemical Co., Ltd. or the like can be used.

As described above, by forming the ground circuit contact portion 8 from a pressurized conductive rubber or a rubber of a conductive rubber, the ground circuit contact portion 8 has a cushioning property. Even if the ground circuit 7 has roughness such as unevenness, the ground circuit contact portion 8 can be deformed and brought into close contact with the roughness to prevent the occurrence of a contact failure. Damage can also be reduced. Furthermore, the outer conductor 1 with the contact pins 6 protruding
Since the ground circuit contact portion 8 is formed over the entire front surface of the device, it is possible to respond to a change in pitch between the end of the circuit under test 4 and the end of the ground circuit 7 with a certain width. It is.

As described above, when the ground circuit contact portion 8 is formed of pressurized conductive rubber or rubber of conductive rubber, the resistance value of the ground circuit contact portion 8 is an important parameter for increasing the measurement accuracy. When the ground circuit contact portion 8 is formed of pressurized conductive rubber, the resistance value can be reduced by applying a sufficient contact pressure, but when the conductive rubber is used, the rate of change of the resistance value is small. For this reason, it is preferable to use a conductive rubber having a ground circuit contact portion 8 originally having a resistance value as small as possible. In order to measure impedance with sufficiently high precision, at least the ground circuit contact portion 8 is required.
Is preferably 1 Ω or less, but since the resistance of the ground circuit contact portion 8 also depends on its thickness, it is preferable to make the resistance as thin as possible in consideration of the balance with the reduction in cushioning property.

As described above, the ground circuit contact portion 8 made of the same material as the external conductor 1 protrudes from the end surface of the external conductor 1 and is provided integrally, or the ground circuit contact portion 8 made of conductive rubber protrudes from the end surface of the external conductor 1. If they are provided integrally, the characteristic impedance may deviate from the design value at the location of the ground circuit contact portion 8, causing impedance mismatching, leading to a decrease in the measurement accuracy of the TDR measurement.
Therefore, it is preferable that the ground circuit contact portion 8 is formed as thin as possible (with a small protrusion size).

A ground circuit contact portion 8 made of the same material as the external conductor 1 protrudes from the end surface of the external conductor 1 and is provided integrally with the external conductor 1, or the ground circuit contact portion 8 made of conductive rubber or pressurized conductive rubber is provided on the end surface of the external conductor 1. When the TDR measurement is performed, a waveform disturbance due to impedance mismatch occurs in a time axis region corresponding to a region extending from a tip of the contact pin 6 of the probe to a shallow portion of the circuit under test 4 in a waveform obtained by the TDR measurement. May occur. The disturbance of the waveform is attenuated as the reference time axis coordinate becomes deeper in the measuring circuit 4. Therefore, when reading the characteristic impedance of the circuit under test 4, the value is read at a stable portion of the waveform in the time axis coordinate corresponding to a slightly deeper portion in the circuit under test 4, and the impedance value of the circuit 4 to be measured is read. It is preferred that

[0042]

As described above, according to the first aspect of the present invention, the inner conductor and the outer conductor having the contact pins for contacting the circuit to be measured on the circuit board are arranged in a coaxial line shape, Since the tip of the pin protrudes from the end surface of the external conductor and a ground circuit contact portion for contacting the ground circuit of the circuit board is provided on the end surface of the external conductor, the contact pin is provided on the circuit under test of the circuit board in the TDR measurement. If the contact pins are brought into contact with the circuit to be measured when the ground circuit contacts are brought into contact with the ground circuit, the ground circuit contacts can inevitably come into contact with the ground circuit.
Only position control in the horizontal or vertical direction for bringing the contact pins into contact with the circuit to be measured is required without controlling the position in the rotational direction, and the circuit can be easily brought into contact with the circuit to be measured and the ground circuit. No time is required for the contact, and the contact state can be stabilized. Further, when the contact is made from the end face of the circuit board, it is possible to make contact with a plurality of conductors of the circuit board, which are grounds, so that more accurate impedance measurement can be performed.

According to the invention of claim 2 of the present invention, the ground circuit contact portion is formed so as to protrude from the end surface of the external conductor, and the ground circuit contact portion is formed in a frame shape continuous in the circumferential direction of the external conductor. The contact area of the ground circuit contact portion to the ground circuit can be increased, and the contact between the ground circuit and the ground circuit contact portion can be performed more stably in TDR measurement.

According to the invention of claim 3 or 4 of the present invention, since the ground circuit contact portion is formed of pressurized conductive rubber or conductive rubber, even if the ground circuit of the circuit board has roughness such as irregularities, it can cope with it. In this way, the contact portion of the ground circuit can be deformed and brought into close contact with each other, so that contact failure does not occur. In addition, the pitch between the end of the circuit to be measured and the end of the ground circuit can be reduced. It is possible to respond to the change with a certain width.

According to the invention of claim 5 of the present invention, since the contact pins are formed so as to be able to be inserted into and removed from the external conductor, only the contact pins having a relatively short life can be replaced, and the replacement of the entire probe is reduced. As a result, the running cost can be reduced.

Further, according to the invention of claim 6 of the present invention, since the contact pin has a cushioning property, the pressure at the time of contact with the circuit to be measured can be absorbed by the cushioning property of the contact pin, and the contact pin has a cushioning property. It is possible to reduce damage and damage to a contact portion of a circuit to be measured.

According to the invention of claim 7 of the present invention, the contact pin is formed to be expandable and contractible by a spring, so that the contact pin can be easily provided with cushioning properties.

According to the invention of claim 8 of the present invention, since the tip of the ground circuit contact is formed in a substantially triangular cross section, the area of the tip of the ground circuit contact can be reduced, and a relatively strong contact can be formed. What you can get.

According to the ninth aspect of the present invention, since the tip of the ground circuit contact portion is formed to have a substantially semicircular cross section, damage to the ground circuit can be reduced.

According to a tenth aspect of the present invention, since a dielectric layer is provided between the inner conductor and the outer conductor and the dielectric layer is formed of a material having a low dielectric constant and a low dielectric loss tangent, loss in a high frequency region is reduced. Can be reduced, and the characteristics of the probe can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of an embodiment of the present invention.

FIG. 2 (a) is a front view of the same, and FIG. 2 (b) is a side view.

FIGS. 3A and 3B are cross-sectional views showing a ground circuit contact portion.

FIG. 4 is a sectional view showing the contact pin according to the first embodiment;

FIG. 5 (a) is a cross-sectional view showing an example of the measurement method of the above,
(B) is sectional drawing which shows the other example of a measuring method same as the above.

FIG. 6 (a) is a front view showing another embodiment of the above,
(B) is a side view.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Outer conductor 2 Inner conductor 3 Circuit board 4 Circuit to be measured 6 Contact pin 7 Ground circuit 8 Ground circuit contact part 9 Dielectric layer 23 Spring

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mitsuhide Nagasou 1048, Kazuma Kadoma, Osaka Prefecture Matsushita Electric Works Co., Ltd. In-house F-term (reference) 2G011 AA02 AA09 AA22 AB01 AB08 AB09 AC12 AC14 AC32 AD01 AE01 AF01 2G028 AA01 AA04 CG08 HM05 HN01 HN09 4M106 AA20 BA01 CA10 DD03 DD15

Claims (10)

[Claims] An internal conductor having contact pins for making contact with a circuit to be measured on a circuit board and an external conductor are arranged in a coaxial line shape, and the tips of the contact pins protrude from the end surface of the external conductor. A ground circuit contact portion for making contact with the ground circuit is provided on an end face of the external conductor. 2. The method according to claim 1, wherein the ground circuit contact portion is formed so as to protrude from an end face of the external conductor, and the ground circuit contact portion is formed in a frame shape continuous in a circumferential direction of the external conductor. The probe for impedance measurement according to the above. 3. The impedance measuring probe according to claim 1, wherein the ground circuit contact portion is formed of pressurized conductive rubber. 4. The impedance measuring probe according to claim 1, wherein the ground circuit contact portion is formed of conductive rubber. 5. The impedance measuring probe according to claim 1, wherein the contact pin is formed so as to be able to be inserted into and removed from an external conductor. 6. The impedance measuring probe according to claim 1, wherein the contact pin has a cushioning property. 7. The impedance measuring probe according to claim 1, wherein the contact pin is formed to be expandable and contractable by a spring. 8. The impedance measuring probe according to claim 1, wherein a tip of the ground circuit contact portion is formed to have a substantially triangular cross section. 9. The impedance measuring probe according to claim 1, wherein a tip of the ground circuit contact portion is formed in a substantially semicircular cross section. 10. The method according to claim 1, wherein a dielectric layer is provided between the inner conductor and the outer conductor, and the dielectric layer is formed of a material having a low dielectric constant and a low dielectric loss tangent. The probe for measuring impedance described in 1.