JP7586645B2 - Probe, measuring device, and measuring method - Google Patents

Description

The present invention relates to a probe, a measuring device, and a measuring method.

The manufacturing process for strain gauges includes a measurement process in which the input resistance, output resistance, and output voltage of the strain gauge are measured. This measurement process is performed to check whether the strain gauge has the designed electrical characteristics. A similar measurement process is also performed when mounting a circuit board on a product.

In the above measurement process, for example, a probe is brought into contact with a strain gauge or a terminal of a circuit board to pass a test current. Patent Document 1 shows an example of a probe.

JP 2009-210443 A

When a probe is brought into contact with the terminals of an object to be measured (such as a strain gauge or circuit board) to measure the electrical characteristics of the object, variations in the measured values may occur. In other words, the results of multiple measurements performed under the same conditions on the same object may not be identical. Such variations in the measured values are undesirable because they affect the reliability of the measurement results.

The present invention aims to provide a probe that can suppress variation in measurement values, a measurement device equipped with the probe, and a measurement method that uses the probe.

According to a first aspect of the present invention,
A probe for measuring an electrical characteristic of a device under test, comprising:
a contact surface to be brought into contact with the object to be measured;
The probe has a maximum height Rz of the contact surface of 3 μm or more and 8 μm or less.

In the probe of the first aspect, an oxide film may be formed on the portion of the object to be measured that comes into contact with the contact surface.

In the first aspect of the probe, the object to be measured may be a strain gauge.

According to a second aspect of the present invention,
A measuring apparatus for measuring electrical characteristics of a device under test, comprising:
A probe according to the first aspect;
A jig for holding the probe;
There is provided a measuring apparatus including a device for moving the device to hold the device and bring the device into contact with the contact surface of the probe.

In the measuring device of the second aspect, the object to be measured moving mechanism may bring the object to contact the contact surface of the probe so that the contact pressure between the contact surface of the probe and the object to be measured is 850 to 1150 gf/ ^mm2 .

The measuring device of the second aspect may be provided with a roughening member moving mechanism that holds a roughening member for roughening the contact surface of the probe and brings the roughening member into contact with the contact surface.

In the measuring device of the second aspect, the jig may be configured to hold a plurality of the probes in a matrix, and the measurement object moving mechanism may be configured to simultaneously bring the plurality of probes held in a matrix into contact with the measurement object.

According to a third aspect of the present invention,
A method for measuring an electrical characteristic of a device under test, comprising:
bringing the contact surface of the probe of the first aspect into contact with the object to be measured and measuring an electrical characteristic of the object to be measured;
A method of measurement is provided that includes roughening the contact surface.

In the measurement method of the third aspect,
The surface roughening treatment may be performed every time a predetermined number of measurements of the object are made, or every time a predetermined time period elapses.

The probe of the present invention, the measuring device equipped with the probe, and the measuring method using the probe can reduce the variability in the measured values.

Fig. 1(a) is a top view of a strain gauge strip, Fig. 1(b) is a top view of a strain gauge included in the strain gauge strip, and Fig. 1(c) is a circuit diagram of a Wheatstone bridge configured within the strain gauge. FIG. 2 is a side view of the measuring device according to the embodiment of the present invention. FIG. 3 is a perspective view of a table provided in the measuring device. FIG. 4 is a top view, with a portion thereof omitted, of the measuring device according to the embodiment of the present invention. FIG. 5 is a side view of a probe according to an embodiment of the present invention. FIG. 6 is a flowchart of a measurement method according to an embodiment of the present invention. Figures 7(a) to 7(d) are diagrams for explaining the operation of the measuring device. Figure 7(a) shows the state where the table is in the workpiece exchange position. Figure 7(b) shows the state where the table is in the standby position. Figure 7(c) shows the state where the table is in the workpiece measurement position. Figure 7(d) shows the state where the table is in the marking position. FIG. 8 is a table showing the results of determining the maximum height Rz and the variation for the probes of Examples 1 to 11 and the probes of Comparative Examples 1 to 3. 9A, 9B, and 9C are diagrams for explaining the influence of a change in the contact state between the contact surface of the probe and the terminal on the contact resistance. 10A, 10B, and 10C are diagrams for explaining the influence of a change in the contact state between the contact surface of the probe and the terminal on the contact resistance.

<Embodiment>
The probe 50 and measuring device (in-circuit tester) 100 according to an embodiment of the present invention will be described using an example in which the electrical characteristics (input resistance, output resistance, output voltage, etc.) of multiple strain gauges included in a strain gauge strip 900 (FIG. 1(a)) are measured.

[Strain Gauge Strip 900]
A strain gauge strip 900 to be measured includes a gauge base 910 having a substantially rectangular shape in a plan view, and a wiring layer 920 formed on the gauge base 910, as shown in FIG.

The gauge base 910 may be a film-like sheet made of insulating resin, such as PI (polyimide) resin, epoxy resin, PET (polyethylene terephthalate) resin, etc. The thickness of the gauge base 910 may be, for example, about 20 μm to 30 μm. An alignment hole 910h is formed at each of the four corners of the gauge base 910, penetrating the gauge base 910 in the thickness direction.

The wiring layer 920 is formed of, for example, a copper-nickel alloy. The wiring layer 920 includes a plurality of gauge patterns _GP11 to _GP54 arranged in a matrix of 5 rows and 4 columns. The thickness of the wiring layer 920 may be, for example, about 3 μm to 5 μm.

1(b) and 1(c), each of the gauge patterns _GP11 to _GP54 includes four resistors _R1 , _R2 , _R3 , and _R4 , four terminals T1, _T2 , _T3 , and _T4 , and wiring _W that connects them. The four resistors _R1 to _R4 , the four terminals _T1 to _T4 , and the wiring W form a Wheatstone bridge circuit.

Strain gauges _SG11 to _SG54 are respectively formed by a portion of the gauge base 910 and the gauge patterns _GP11 to _GP54 formed on that portion. Hereinafter, the gauge patterns _GP11 to _GP54 are collectively referred to as gauge pattern _GPmn , and the strain gauges _SG11 to _SG54 are collectively referred to as strain gauge _SGmn .

[Measuring device 100]
2, the measuring device 100 includes a base 10, a driving mechanism 20 built into the base 10, a table 30 movably supported by the driving mechanism 20, and a probe holding mechanism 40 disposed on an upper surface of the base 10. The probe holding mechanism 40 holds a plurality of probes 50.

The measuring device 100 further includes a measurement execution unit 60 connected to each of the multiple probes 50 by wiring (not shown), a marking mechanism 70 adjacent to the probe holding mechanism 40, and a control unit CONT that controls the overall operation of the measuring device 100.

In the following, the left-right direction in Fig. 2 is referred to as the sliding direction of the measuring device 100, and the depth direction in Fig. 2 (the direction perpendicular to the paper surface) is referred to as the width direction of the measuring device 100. The sliding direction is the direction in which the driving mechanism 20 slides the table 30 along the horizontal plane, and the width direction is the direction perpendicular to the sliding direction within the horizontal plane. The up-down direction in Fig. 2, i.e., the direction perpendicular to the sliding direction and the width direction, is referred to as the up-down direction. In the sliding direction, the side on which the table 30 is located in Fig. 2 is referred to as the work installation side, and the side on which the probe holding mechanism 40 is located is referred to as the work measurement side.

The base 10 is a hollow box-like structure with a top plate 10t that extends along a horizontal plane. The top plate 10t has a longitudinal opening 10A (Figs. 2 and 4) that extends in the sliding direction.

The drive mechanism 20 is a mechanism for moving the table 30 in the sliding direction and the up-down direction. The drive mechanism 20 has a main body part 21 and a support part 22 that is moved by the main body part 21.

The main body 21 is housed inside the base 10 and is located near the top plate 10t. The main body 21 may be any mechanism capable of moving the support 22 in the sliding direction and the up-down direction. As an example, the main body 21 is composed of a power generation mechanism including a motor and a piezoelectric actuator, and a power transmission mechanism including gears, belts, chains, pulleys, etc.

The support part 22 is a columnar structure that extends in the vertical direction. The support part 22 extends from the upper surface of the main body part 21 through the opening 10A of the top plate 10t to above the top plate 10t.

As shown in FIG. 3, the table 30 is a flat plate that is roughly square in plan view.

At each of the four corners of the top surface 30u of the table 30, a cylindrical alignment pin 30p is provided upright from the top surface 30u. A plurality of intake holes 30h are provided along each side on the periphery of the top surface 30u of the table 30. Each of the plurality of intake holes 30h is connected to an intake device (not shown) via an air flow path (not shown) inside the table 30 and a flexible intake hose (not shown) connected to the table 30 and communicating with the air flow path.

The underside of the table 30 is fixed to the upper end of the support part 22 of the drive mechanism 20. This allows the table 30 to be supported by the drive mechanism 20 in a state in which it can move in the sliding direction and the up-down direction.

The probe holding mechanism 40 has a rectangular jig 41 that holds multiple probes 50, and four support columns 42 that support the jig 41.

As shown in FIG. 4, the jig 41 has a matrix of multiple retaining holes 41h that penetrate the jig 41 in the vertical direction. In this embodiment, 80 retaining holes 41h (5 rows in the width direction × 16 columns in the sliding direction) are formed.

The four support columns 42 extend upward from the top surface of the top plate 10t and are connected to the four corners of the bottom surface of the jig 41. Two support columns 42 aligned in the width direction sandwich the opening 10A in the width direction.

Each of the multiple probes 50 (FIG. 5) is formed of a metal such as tungsten, copper, platinum, gold, etc. Each of the multiple probes 50 has a cylindrical shape, for example. One end of the probe 50 is a contact surface 50c that comes into contact with the terminals T _A to T _D of the strain gauges SG _mn during measurement.

As an example, the contact surface 50c is circular. As an example, the diameter of the contact surface 50c may be approximately 0.1 mm to 1.2 mm. The surface roughness (maximum height Rz) of the contact surface 50c is preferably 3 μm≦Rz≦8 μm. This reduces the variation in the measured values and prevents damage to the strain gauge during measurement. The reason for this will be described later. In this specification and the present invention, "maximum height Rz" means the maximum height Rz defined and measured in accordance with JIS B 0601-2001.

The multiple probes 50 are arranged in a matrix by being inserted into multiple holding holes 41h of the jig 41. As shown in FIG. 2, each of the multiple probes 50 is housed inside the holding hole 41h with the contact surface 50c facing downward and penetrating the jig 41 from top to bottom.

As shown in Fig. 4, the jig 41 holds 80 probes 50 and arranges them in a matrix of 5 rows x 16 columns. If the four probes 50 arranged in the width direction are regarded as a probe set 50S (Fig. 4), the jig 41 holds 20 probe sets 50S and arranges them in a matrix of 5 rows x 4 columns. The four probes 50 of each probe set 50S contact the four terminals T _A to T _D of each strain gauge SG _mn during measurement (described in detail later).

The measurement execution unit 60 is a part that measures the input resistance, output resistance, and output voltage of the strain gauge SG _mn using the probes 50. The measurement execution unit 60 is disposed inside the base 10, and is connected to each of the multiple probes 50 by wiring (not shown).

The measurement execution unit 60 includes a power supply 61, a digital multimeter (DMM) 62, and a relay circuit (measurement circuit) 63. The power supply 61 supplies an input voltage for measurement. The DMM 62 measures the input resistance, output resistance, output voltage, etc. of the strain gauge SG _mn . The relay circuit 63 is a circuit that connects the power supply 61, the DMM 62, and each of the multiple probes 50. The configuration of the relay circuit 63 is switchable (changeable) depending on the measurement content.

The marking mechanism 70 is a mechanism for applying a mark to a predetermined strain gauge SG _mn based on the result of the measurement performed by the measurement execution unit 60. The marking mechanism 70 is disposed on the workpiece installation side of the jig 41 in the sliding direction.

The marking mechanism 70 has a pen 71 having a pen tip 71t, and a pen holding mechanism 72 that holds the pen 71 so that it can move in the width direction and the up and down direction. Note that the marking mechanism 70 is not limited to one that uses a pen, and may be one that uses a needle or a cutter for marking.

The pen 71 is held by the pen holding mechanism 72 with the pen tip 71t facing downward. The pen holding mechanism 72 may be any mechanism capable of moving the pen 71 in the width direction and the up-down direction. One example of the pen holding mechanism 72 is an air slider.

The control unit CONT is housed inside the base 10. The control unit CONT is connected to the drive mechanism 20, the measurement execution unit 60, and the marking mechanism 70, and can communicate with them.

[Measurement method]
Measurement of the electrical characteristics (input resistance, output resistance, output voltage, etc.) of the strain gauge SG _mn using the probe 50 and the measuring device 100 includes a workpiece setting step S1, a measuring step S2, and a marking step S3, as shown in the flowchart of FIG.

In the workpiece installation step S1, the strain gauge strip 900, which is the object to be measured, is installed on the table 30 of the measuring device 100. Specifically, the workpiece installation step S1 is performed, for example, as follows.

First, the table 30 is moved to the position farthest from the jig 41 (FIG. 7(a) hereinafter referred to as the "workpiece installation position"), and the strain gauge strip 900 is installed on the table 30. At this time, the alignment pins 41p at the four corners of the table 30 are placed inside the alignment holes 910h at the four corners of the gauge base 910, respectively, so that the strain gauge strip 900 can be easily aligned with the table 30.

Next, air is sucked in through the air intake holes 30h of the table 30 to suck in the strain gauge strip 900, and the strain gauge strip 900 is fixed to the table 30. In addition to or instead of suction through the air intake holes 30h, a weight can be used. Specifically, for example, a weight with resin attached to the bottom surface of a picture frame-shaped metal frame can be placed on the peripheral portion of the strain gauge strip 900 to press down on the peripheral portion of the strain gauge strip 900 from above.

By closely contacting the strain gauge strip 900 with the upper surface 30u of the table 30, in other words by holding the strain gauge strip 900 flat, the multiple probes 50 can be brought into contact with the terminals T _A to T _D of the multiple strain gauges SG _mn in a uniform state. This can further improve the accuracy of the measurement in the measurement step S2.

In the measurement step S2, the electrical characteristics of each of the strain gauges SG _mn included in the strain gauge strip 900 are measured mainly using the multiple probes 50 and the measurement execution unit 60. Specifically, the measurement step S2 is performed, for example, as follows.

First, the table 30 is slid to a position directly below the jig 41 (FIG. 7(b) hereinafter referred to as the "standby position"). After that, the table 30 is raised to a position where the contact surfaces 50c of the multiple probes 50 contact the strain gauge strip 900 (FIG. 7(c) hereinafter referred to as the "measurement position") and stopped there.

When the table 30 is stopped at the measurement position, each of the multiple probes 50 contacts each of the multiple strain gauges SG _mn of the strain gauge strip 900. Specifically, the four probes 50 included in each probe set 50S contact the terminals T _A to T _D of each of the strain gauges SG _mn . The contact pressure (probe pressing pressure) may be, for example, about 60 to about 80 gf (about 850 to about 1150 gf/mm ² ) per probe 50.

Next, the measurement execution unit 60 measures the input resistance, the output resistance, and the output voltage for each of the strain gauges SG _mn . An example of a specific measurement method is as follows.

The measurement execution unit 60 first performs measurement of the strain gauge _SG11 through the following steps.

(1) Using a relay circuit 63, a closed circuit is formed connecting the power supply 61, the probe 50 in contact with terminal T _A , terminal T _A , terminal T _C , the probe 50 in contact with terminal T _C , and the DMM 62, and the input resistance of the strain gauge SG ₁₁ is measured.
(2) Using a relay circuit 63, a closed circuit is formed connecting the power supply 61, the probe 50 contacting terminal _TB , terminal _TB , terminal _TD , the probe 50 contacting terminal _TD , and the DMM 62, and the output resistance of the strain gauge _SG11 is measured.
(3) Using the relay circuit 63 and the probe 50, the power supply unit 61 is connected to the terminals T _A and T _C , and the DMM 62 is connected to the terminals T _B and T _D. With the power supply unit 61 applying an input voltage _V in to the strain gauge _SG11 , the DMM 62 measures the output voltage V _out of the strain gauge _SG11 (zero balance measurement).

The measurement execution section 60 sends the measured input resistance, output resistance, and output voltage of the strain gauge _SG11 to the control section CONT.

After completing the measurement of strain gauge _SG11 , the measurement execution unit 60 switches the relay circuit 63 to perform a similar measurement on strain gauge _SG12 . The measurement execution unit 60 performs a similar measurement on all 20 strain gauges _SGmn in turn. The measured input resistance, output resistance, and output voltage of each strain gauge _SGmn are sent to the control unit CONT.

In the marking step S3, the marking mechanism 70 applies marking to a predetermined one of the strain gauges SG _mn in accordance with the measurement result in the measuring step S2. Specifically, the marking step is performed, for example, as follows.

First, the table 30 is lowered from the measurement position to the standby position, and then slid to a position directly below the marking mechanism 70 (Figure 7(d) (hereinafter referred to as the "marking position").

On the other hand, the control unit CONT compares each measurement value (input resistance, output resistance, output voltage) of the strain gauge SG _mn received from the measurement execution unit 60 in the measurement process S2 with a predetermined reference value, and determines whether each measurement value is within the allowable tolerance.

When the measured value of any of the plurality of strain gauges SG _mn is outside the allowable tolerance, the control unit CONT disposes that strain gauge directly below the pen 71. Alignment in the sliding direction is performed by moving the table 30, and alignment in the width direction is performed by moving the pen holding mechanism 72.

The control unit CONT then uses the pen holding mechanism 72 to lower the pen 71 and mark the strain gauges whose measured values are determined not to be within the allowable tolerance.

The control unit CONT marks all strain gauges whose measured values are determined to be outside the allowable tolerance, and then returns the table 30 to the workpiece installation position.

Then, the measured strain gauge strip 900 is removed from the table 30, and the workpiece installation process S1, the measurement process S2, and the marking process S3 are repeated.

[Dressing method]
Here, a dressing method (surface roughening method) for dressing (roughening) the contact surface 50c of the probe 50 to give the contact surface 50c a desired surface roughness will be described.

It has been observed that when measurements of the strain gauge strip 900 are continuously performed using the measuring device 100, the surface roughness of the contact surface 50c of the probe 50 of the measuring device 100 decreases (the maximum height Rz becomes smaller). This is because the contact surface 50c is pressed by the terminals T _A -T _D that come into contact with the contact surface 50c every time a measurement is performed, causing the contact surface 50c to become smooth.

Therefore, it is preferable to dress the contact surface 50c after each measurement of a predetermined number of strain gauge strips 900 or after each predetermined time (periodically) to return the maximum height Rz of the contact surface 50c to the range of 3 μm≦Rz≦8 μm.

Specifically, dressing is performed as follows, for example:

First, the table 30 is moved to the work placement position, and sandpaper (roughened member) that is rectangular in plan view is placed on the table 30. Alignment holes may be provided at the four corners of the sandpaper so that alignment can be performed using the alignment pins 30p. The sandpaper may have the same dimensions and thickness as the strain gauge strip 900.

Next, the table 30 on which the sandpaper is placed is moved to the standby position and raised. This causes the sandpaper to be pressed against the contact surface 50c with a predetermined pressure (which may be, for example, approximately 60 gf to approximately 80 gf per probe), transferring the roughness of the sandpaper to the contact surface 50c and dressing the contact surface 50c. The table 30 may be raised and lowered multiple times to press the sandpaper against the contact surface 50c multiple times.

Then, return the table 30 to the workpiece installation position, replace the sandpaper with a cleaning cloth (wiping cloth), and press it against the contact surface 50c once or multiple times in the same way as the sandpaper. The cleaning cloth may be soaked in ethanol or the like.

After the wiping is completed, the table 30 is returned to the workpiece installation position, the cleaning cloth is replaced with the next object to be measured (strain gauge strip 900), and measurement of the electrical characteristics of the strain gauge SG _mn is resumed.

[Significance of surface roughness (maximum height Rz) being 3 μm≦Rz≦8 μm]
Next, the reason why it is preferable to set the maximum height Rz of the contact surface 50c to 3 μm or more and 8 μm or less in the probe 50 of this embodiment will be described.

First, the reason why it is preferable to set the maximum height Rz of the contact surface 50c to 3 μm or more is as follows.

The inventors of the present invention have intensively studied methods for suppressing the variation in measurement values that occurs when measuring the electrical characteristics of a strain gauge using a probe, and have focused on the surface roughness (maximum height Rz) of the contact surface of the probe. According to the knowledge of the inventors of the present invention, the variation in measurement values is caused by the contact state between the contact surface of the probe and the terminal of the strain gauge being slightly different each time a measurement is performed, which changes the contact resistance that occurs between the contact surface and the terminal. Furthermore, the inventors of the present invention have found that by making the maximum height Rz of the contact surface of the probe 3 μm or more, the contact state between the contact surface of the probe and the terminal of the strain gauge can be stabilized, and the change in contact resistance can be sufficiently suppressed.

Based on the above findings, the inventors of the present invention conducted the following tests.

First, the contact surfaces of the same type of probes were processed with files of different grits to prepare four probes each of Examples 1 to 11, in which the maximum height Rz of the contact surface is approximately 3 μm or more, and Comparative Examples 1 to 3, in which the maximum height Rz of the contact surface is less than approximately 3 μm. In addition, one sample strain gauge was prepared.

The probes in Examples 1 to 11 and Comparative Examples 1 to 3 are all made of tungsten and have a circular contact surface with a diameter of 0.3 mm.

The maximum height Rz of the contact surface of each of the probes of Examples 1 to 11 and Comparative Examples 1 to 3 is as shown in Figure 8.

The maximum height Rz of the probes in Examples 1 to 11 and Comparative Examples 1 to 3 was measured in accordance with JIS B 0601-2001.

The sample strain gauge had the structure shown in Figure 1(b). The wiring layer of the sample strain gauge was made of copper-nickel alloy and had a thickness of approximately 5 μm. The gauge base of the sample strain gauge was made of PI (polyimide) and had a thickness of approximately 25 μm.

Next, the probes of Example 1 were held by the jig 41 of the measuring device 100 to form one probe set 50S, and the input resistance and output resistance of the sample strain gauge were measured three times each using the measuring device 100. The probe pressing pressure was kept constant (70 gf per probe) during the three measurements. After that, the variance (difference between the maximum and minimum values) of the three measured values obtained by the three measurements for each of the input resistance and output resistance was calculated.

For each probe of Examples 2 to 11 and Comparative Examples 1 to 3, the input resistance and output resistance of the sample strain gauge were each measured three times in the same manner as in Example 1, and the variation in the three measured values for each of the input resistance and output resistance was determined. The same sample strain gauge was used in the measurements of each Example and Comparative Example.

The measurement results are shown in Figure 8. In Figure 8, input and output resistances with a variation between the three measured values of less than ±1 Ω are indicated with a circle. On the other hand, input and output resistances with a variation between the three measured values of more than ±1 Ω are indicated with an x. As shown in Figure 8, in Examples 1 to 11, where the maximum height Rz is 3 μm or more, the variation in the measured values is less than ±1 Ω, while in Comparative Examples 1 to 3, where the maximum height Rz is less than 3 μm, the variation in the measured values is more than ±1 Ω.

According to the knowledge of the inventors of the present invention, one of the reasons why the variation in the measurement values increases when the maximum height Rz of the probe contact surface is small is as follows.

Fig. 9(a) shows a simplified cross-sectional view of the contact surface CS1 of the probe, and Fig. 10(a) shows a simplified cross-sectional view of the contact surface CS2 of the probe. The maximum height Rz of the contact surface CS1 is smaller than the maximum height Rz of the contact surface CS2. In Fig. 9(a) and Fig. 10(a), dotted lines _L11 and _L21 indicate the positions of the surfaces of the terminals of the strain gauge. In the portions of the contact surfaces CS1 and CS2 located below the dotted lines _L11 and _L21 , the contact surfaces CS1 and CS2 press down on the surfaces of the terminals and are embedded inside the terminals. In other words, the contact surfaces CS1 and CS2 bite into the surfaces of the terminals.

As shown in Figures 9(b) and 10(b), when the probe is tilted at a small angle _θ0 with respect to the terminal and the surface of the terminal moves to the position indicated by the dotted lines _L12 and _L22 , the area of the contact surface between the contact surfaces CS1 and CS2 and the surface of the terminal changes approximately by an amount corresponding to the length of the thick lines shown in Figures 9(b) and 10(b). As can be seen from Figures 9(b) and 10(b), when the angle of the probe with respect to the terminal changes, the change in the contact area is large at contact surface CS1, which has a small maximum height Rz, and the change in contact resistance also tends to be large.

In addition, in the case of contact surface CS1 having a small maximum height Rz, when the probe is inclined with respect to the terminal by more than the small angle _θ13 , a part of contact surface CS1 moves away from the surface of the terminal at the position indicated by dotted line _L13 , resulting in a small contact area. In the case of contact surface CS2 having a large maximum height Rz, when the probe is inclined with respect to the terminal by more than the small angle _θ23 , a part of contact surface CS2 moves away completely from the surface of the terminal at the position indicated by dotted line _L23 , but the angle _θ23 is greater than the angle _θ13 .

In this way, when the angle of the probe relative to the terminal changes, the contact area and contact resistance tend to change more significantly on contact surface CS1, which has a relatively small maximum height Rz, than on contact surface CS2, which has a relatively large maximum height Rz.

9(c) and 10(c), when the probe moves away from the terminal by an infinitesimal distance _d0 and the surface of the terminal moves to the position indicated by the dotted lines _L14 and _L24 , the contact areas between the contact surfaces CS1 and CS2 and the surface of the terminal change by an amount that generally corresponds to the length of the thick lines shown in Fig. 9(c) and 10(c). As can be seen from Fig. 9(c) and 10(c), even when the distance between the probe and the terminal changes, there tends to be a large change in the contact area and a large change in contact resistance at contact surface CS1, which has a small maximum height Rz.

Thus, when the maximum height Rz of the probe's contact surface is small, the contact area and therefore the amount of change in contact resistance in response to changes in the contact state with the terminal tend to increase, leading to greater variance in the measured values.

The terminals of strain gauges made of copper-nickel alloys usually have an oxide film of about 3 μm or thinner. According to the findings of the inventors of the present invention, when the maximum height of the contact surface is greater than 3 μm, the convex parts of the contact surface (the parts that form micro-mountains in the cross-sectional view of the contact surface) break through the oxide film, and a larger area of the contact surface comes into direct contact with the terminals of the strain gauge. In this way, by bringing a larger area of the contact surface into direct contact with the terminals without an oxide film, the contact state is stabilized, and the amount of change in contact resistance in response to changes in the contact state is suppressed.

For these reasons, it is preferable that the maximum height Rz of the contact surface 50c is 3 μm or more. This makes it possible to effectively suppress the variation in the measurement values.

Next, the reasons why it is preferable to set the maximum height Rz of the contact surface 50c to 8 μm or less are as follows.

Strain gauges generally have a structure in which a conductive wiring layer including a resistor is formed on a gauge base made of a flexible dielectric material, and when in use, the gauge base is attached to the strain element, which is a conductor such as metal. In other words, the gauge base serves the function of insulating the wiring from the strain element.

Here, in order to properly measure strain using a strain gauge, it is necessary for the resistor in the wiring layer to expand and contract appropriately in response to the expansion and contraction of the strain-generating body. For this reason, it is not realistic to make the gauge base thicker by considering only insulation properties.

Taking the above into consideration, strain gauges generally have a wiring layer thickness of about 3 to 5 μm and a gauge base thickness of about 25 μm.

According to the findings of the inventors of the present invention, when the maximum height of the contact surface of the probe is 8 μm or less, the convex portion of the contact surface of the probe does not excessively damage the gauge base when the contact surface of the probe is brought into contact with the terminal of the strain gauge. This prevents damage to the gauge base from degrading the insulation performance of the gauge base and causing performance degradation of the strain gauge.

For these reasons, it is preferable that the maximum height Rz of the contact surface 50c be 8 μm or less.

The effects of the probe 50, measuring device 100, and measuring method of this embodiment are summarized below.

In the probe 50 of this embodiment, the surface roughness (maximum height Rz) of the contact surface that comes into contact with the terminals T _A to T _D of the strain gauge SG _mn, which is the object to be measured, is 3 μm or more. Therefore, the change in contact resistance in response to the change in the contact state with the terminals T _A to T _D is small, and the variation in the measured values can be suppressed when measurements are performed multiple times.

Furthermore, since an oxide film that is generally about 3 μm or thinner is formed on the terminals T _A to T _D of the strain gauge SG _mn , by making the maximum height of the contact surface 3 μm or more, the oxide film can be broken through and good contact can be made between the contact surface 50c and the terminals T _A to T _D. This makes it possible to suppress the amount of change in contact resistance according to changes in the contact state, and suppress variations in the measurement values.

In the probe 50 of this embodiment, the surface roughness (maximum height Rz) of the contact surface 50c is 8 μm or less. Therefore, damage to the gauge base 910 due to contact between the contact surface 50c and the terminals T _A to T _D is prevented. In addition, contact marks remaining on the terminals T _A to T _D are also suppressed.

That is, in the probe 50 of this embodiment, by making the surface roughness (maximum height Rz) of the contact surface 50c 3 μm or more, the contact state of the contact surface 50c with the terminals T _A to T _D can be stabilized and variation in the measurement values can be suppressed, and by making the surface roughness (maximum height Rz) of the contact surface 50c 8 μm or less, damage to the strain gauges SG _mn that may occur during measurement can be prevented.

The measuring device 100 of this embodiment includes a probe 50 with reduced variation in measured values (i.e., highly reliable measured values), and therefore can obtain highly reliable measured values by performing only one measurement for each strain gauge SG _mn . Therefore, the measurement time can be significantly reduced compared to conventional measuring devices that require multiple measurements for each strain gauge to be performed and the average value to increase the reliability of the measured values.

The measurement method of this embodiment uses the measurement device 100, and therefore produces the same effects as the measurement device 100. In addition, the contact surface 50c of the probe 50 is dressed (roughened) at a predetermined timing, and the maximum height Rz of the contact surface 50c is maintained at 3 μm or more and 8 μm or less, so that highly reliable measurements can be performed continuously for a long period of time.

<Modification>
In the probe 50, the measuring device 100, and the measuring method of the above embodiment, the following modified aspects may also be used.

The probe 50 of the above embodiment may be used independently of the measuring device 100. Specifically, for example, an operator may operate the probe 50 to bring the probe into contact with the terminals T _A to T _D of the strain gauge SG _mn , thereby measuring the electrical characteristics of the strain gauge SG _mn .

In the above embodiment, the probe 50 has a cylindrical shape and the contact surface 50c is circular, but this is not limited to this. The shape of the probe 50 and the contact surface 50c is arbitrary. For example, the shape of the contact surface 50c may be a square or polygon.

Moreover, the object to be measured is not limited to the strain gauge SG _mn . Specifically, for example, the probe 50 can be used in measuring the electrical characteristics (such as circuit resistance) of a PCBA (printed circuit board assembly). The terminals of the PCBA are also generally made of a copper-nickel alloy, and an oxide film of about 3 μm or thinner is formed on them.

The object to be measured may be any other electrical or electronic component whose electrical characteristics need to be measured.

In the measuring device 100 of the above embodiment, 80 holding holes 41h (5 rows in the width direction × 16 columns in the sliding direction) are formed in the jig 41, but this is not limited to this. The number and arrangement of the holding holes 41h in the jig 41, i.e., the number and arrangement of the probes 50 held by the jig 41, can be set arbitrarily according to the design of the measuring device 100.

The measuring device 100 of the above embodiment can be modified as needed to make a measuring device for measuring any electrical component, electronic component, etc. whose electrical characteristics need to be measured. Specifically, for example, the configuration of the table 30 and the configuration of the jig 41 can be modified.

As long as the characteristics of the present invention are maintained, the present invention is not limited to the above-described embodiment, and other forms that are conceivable within the scope of the technical concept of the present invention are also included within the scope of the present invention.

10 Base, 20 Driving mechanism, 30 Table, 40 Probe holding mechanism, 50 Probe, 60 Measurement execution unit, 70 Marking mechanism, 100 Measuring device, 900 Strain gauge strip, SG _mn strain gauge

Claims (2)

A method for measuring electrical characteristics of a strain gauge, comprising the steps of:
a probe having a contact surface, the maximum height Rz of which is 3 μm or more and 8 μm or less, is brought into contact with a surface of a terminal of the strain gauge, the terminal having an oxide film formed on its surface, to measure electrical characteristics of the strain gauge;
A measuring method comprising subjecting the contact surface to a roughening treatment. The measurement method according to claim 1 , wherein the surface roughening treatment is performed every time a predetermined number of measurements are made with the strain gauge, or every time a predetermined time has elapsed.

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