JP2025112476A - probe card - Google Patents

Abstract

A highly convenient probe card is provided that can achieve some or all of improved reliability and durability and mass production.
[Solution] The probe card 1 includes a coaxial cable 70 to which a high-frequency test signal is input from the outside, and a flexible coaxial probe 10 whose base end is connected to the coaxial cable 70 and whose tip end contacts an electrode of an object to be measured (wafer 90). The tip of the coaxial probe 10 has an inner conductor that contacts a signal electrode of the wafer 90, and an outer conductor that contacts a ground electrode of the wafer 90. The coaxial probe 10 has a coaxial structure that extends to just before the protective film so that even if the inner conductor bends when it contacts the signal electrode of the wafer 90, which is provided with a protective film, the tip portions of the inner insulator and outer insulator do not come into contact with the protective film.
[Selected Figure] Figure 4

Description

The present invention relates to a probe card used for testing the electrical characteristics of high-frequency devices.

In recent years, with the commercial launch of 5G (fifth generation mobile communications systems) in 2020 in the field of high-speed communications such as smartphones, development of 5G high-frequency devices has been progressing. In line with this, development is also progressing on probe cards required for testing the electrical characteristics of high-frequency devices (high-frequency device chips) used at 5G frequencies.

5G high-frequency devices will support a variety of fields, including smart industry, logistics, construction, agriculture, health and medicine, education, and remote offices, and there is a demand for mass production of probe cards. At the same time, probe cards are also required to be reliable, such as minimizing signal attenuation and impedance variations during wafer testing, as well as durable.

Prior art related to probe cards is disclosed in Patent Documents 1 to 4.
Patent Document 1 describes a probe card capable of improving the measurement accuracy of electrical characteristics. Specifically, the probe card 100 includes a probe pin 10 made of a metal conductor, which is elastically deformable and has a tip end 11 protruding from an end surface 72A, and a cable 30 having a core 31 made of an electric conductor and electrically connected to the probe pin 10 and an inspection device, and an insulating coating 32 made of an insulator that covers the core 31 (see FIG. 1). In the probe card 100, the base end 11 of the probe pin 10 and the tip end of the core 31 are in direct contact with each other.

Patent Document 2 also describes a probe card equipped with a vertical probe needle that prevents a decrease in contact stability with the test object and can be used repeatedly for long periods of time. Specifically, this vertical probe needle consists of a thin metal wire 1 with a diameter of 0.02 to 0.04 mm and a length of 3.0 to 6.0 mm, whose body 1b is coated with an insulating coating 2 made of SiO2 and whose tip 1a is formed with a metal coating 3 having granular protrusions 3a. The edge 2a of the insulating coating 2 is located 20 to 60 μm from the apex 5, and the apex 5 is formed in an arc shape with a radius of curvature of 26 to 45 μm in vertical cross section (see Figure 1).

Patent Document 3 describes a probe card using a probe designed to maintain electrical isolation of the probe and ensure impedance matching of the needles, thereby improving the accuracy of high-frequency electrical characteristic testing. Specifically, the document describes a probe 1 that includes a coaxial cable 2 having an inner conductor 21, an insulator 22 covering the inner conductor 21, and an outer conductor 23 covering the insulator 22; a first probe 3 electrically connected to the inner conductor 21 of the coaxial cable 2; and an auxiliary conductor 4 electrically connected to the outer conductor 23 and arranged to cover the front side of the first probe 3 (see Figure 1). Furthermore, the probe 1 includes a connecting conductor 6 that connects the auxiliary conductor 4 to the second probe 5.

Furthermore, Patent Document 4 describes a coaxial probe designed to suppress impedance fluctuations even when the distance between the signal pad and ground pad of the measurement target differs from the distance between the signal terminal and ground terminal. Specifically, the coaxial probe 1 includes a coaxial line portion 12 having an inner conductor 121 and an outer conductor 122, a signal terminal 124 formed by extending the inner conductor 121, a ground terminal 125 formed by extending the outer conductor 122 and arranged alongside the signal terminal 124, and an attachment signal conductor 13 having a cylindrical structure with a hole 131 through which the signal terminal 124 can be inserted, and which is attached to and electrically connected to the signal terminal 124 (see Figure 4).

Japanese Patent Application Laid-Open No. 2023-022720 JP 2012-181045 A Japanese Patent Application Laid-Open No. 2016-194412 Japanese Patent Application Laid-Open No. 2016-180746

However, the probe card described in Patent Document 1 has direct contact between the base end of the probe pin and the tip end of the cable core. This means that degradation of the electrical signal obtained through the probe pin can be suppressed compared to when the probe pin and cable core are connected via an intervening member with poor transmission loss at high frequencies, such as a connector, soldered joint, or coaxial pin. While this can improve the accuracy of measuring the electrical characteristics of the object being tested, such as a chip on a semiconductor wafer, it cannot further improve the accuracy of measuring the electrical characteristics.

This is because the probe structure disclosed in Patent Document 1 consists only of a conductive probe pin and insulating coating, and does not have a shielding structure to prevent signal loss in the high-frequency range (a structure in which the signal line is surrounded by a dielectric and outer conductor, like a coaxial cable). Therefore, the structure in Patent Document 1 does not provide a shielding effect to prevent signal loss in the high-frequency range (the effect of protecting internal signals from interference from external signals and the effect of preventing internal signals from leaking to the outside), thereby improving the accuracy of measuring electrical characteristics.

The probe card (vertical probe needle) described in Patent Document 2 also prevents a decrease in contact stability with the test object by forming a metal coating with granular protrusions 3a on the tip 1a of the probe needle, allowing for repeated use over long periods of time. However, since the probe needle structure is the same as Patent Document 1, consisting of a thin metal wire surrounded by an insulating coating (it is not a shielded structure), it is ineffective in preventing signal loss in the high-frequency range.

On the other hand, the probe card described in Patent Document 3 is equipped with an auxiliary conductor that is electrically connected to the external conductor of the probe card's probe and is positioned to cover the front side of the first signal line probe, in order to maintain the electrical isolation of the probe and ensure impedance matching of the needle, thereby improving the accuracy of high-frequency electrical characteristic testing. Furthermore, as an effect of this, it is described that an increase in impedance can be suppressed, as shown in Figure 14, and that noise can be reduced by 10 to 20 dB, as shown in Figure 14.

However, while there is a shielding effect only in the area where the auxiliary conductor is located, centered around the internal conductor, there is no auxiliary dielectric in other directions, and so no shielding effect is obtained. This is clearly evident from the 3 ohm difference from the coaxial section, as shown in Figure 14.

Furthermore, Figure 14 of Patent Document 3 shows that when auxiliary conductors are provided, noise is reduced by 10 to 20 dB compared to when they are not provided, but the measurement frequencies are 10 MHz to 6 GHz, which is lower than the frequency of 5 GHz. It is well known that noise increases as frequency increases, so while this may be sufficient in this frequency band, it cannot be said that this structure can sufficiently reduce noise in high-frequency bands above 5 GHz.

Furthermore, the coaxial probe described in Patent Document 4 suppresses impedance fluctuations and achieves sufficient resolution even when the distance between the signal pad and ground pad of the object to be measured differs from the distance between the signal terminal and ground terminal. It includes a coaxial line section 12 having an inner conductor 121 and an outer conductor 122, a signal terminal 124 formed by extending the inner conductor 121, a ground terminal 125 formed by extending the outer conductor 122 and arranged alongside the signal terminal 124, and a cylindrical structure having a hole 131 through which the signal terminal 124 can be inserted, and an attachment signal conductor 13 attached to and electrically connected to the signal terminal 124.

As such, the ground terminal 125 of the coaxial probe described in Patent Document 4 is simply linear and does not have a coaxial structure surrounding the signal terminal 124 to prevent high-frequency signal leakage, and therefore cannot prevent signal loss in high-frequency bands above 5 GHz.

Specifically, as shown in FIG. 5(a), the transmission characteristic after the improvement (corresponding to the insertion loss described later) is −4 dB at 20 GHz, which is merely comparable to the performance of the prior art.
Furthermore, as shown in FIG. 5(b), the impedance after improvement is also about 55 Ω.

As mentioned above, it is not possible to further improve the measurement accuracy of electrical characteristics. For example, with the probe card described in Patent Document 1, the insertion loss exceeds the standard (within -2.0 dB) in the 5 GHz high-frequency band (approximately 28 GHz). Furthermore, even if the probe card described in Patent Document 1 were to use a signal loss prevention structure such as those described in Patent Documents 3 and 4 to suppress reflections, this would have been sufficient for conventional high-frequency bands up to 4 GHz, but would not meet the insertion loss and impedance variation standards (within 50.0 Ω ±5%) in high-frequency bands of 5 GHz and above.

Therefore, there is a demand for a probe card that can improve on at least one of these standards.
In light of the above-mentioned background, there is a demand for probe cards to be more convenient, including being able to improve reliability and durability and being able to be mass-produced.

Therefore, the present invention aims to provide a highly convenient probe card that can achieve some or all of the following: improved reliability and durability, and mass production.

The probe card according to the present invention is a probe card for measuring electrical characteristics of a measurement object,
a coaxial cable to which a test signal is input from outside;
a flexible coaxial probe having a base end connected to the coaxial cable and a tip end contacting an electrode of the object to be measured;
The tip of the coaxial probe has an inner conductor that contacts the signal electrode of the object being measured, and an outer conductor that contacts the ground electrode of the object being measured.
When the internal conductor of a coaxial probe contacts the signal electrode of a measurement object that has a protective film, even if the internal conductor bends, the tip portions of the internal insulator and external insulator do not come into contact with the protective film, and the coaxial structure extends up to just before the protective film.

The probe card of the present invention has such a configuration that the coaxial probe does not damage the protective film of the object being measured. This allows for the insertion loss to be reduced to the utmost.

The probe card is an intermediate layer provided between the coaxial cable and the coaxial probe, and includes an inner conductor and an outer conductor;
It is desirable that the inner and outer conductors of the intermediate layer are configured to connect to the inner and outer conductors of the coaxial probe and the inner and outer conductors of the coaxial cable, respectively.

In this way, by providing an intermediate layer containing an inner conductor and an outer conductor between the coaxial cable and the coaxial probe, changes in the characteristic impedance at the connection between the coaxial cable and the coaxial probe can be suppressed.

In particular, in this intermediate layer, the outer diameter of the inner conductor of the intermediate layer on the coaxial cable side is equal to or smaller than the outer diameter of the inner conductor of the coaxial cable, and/or the inner diameter of the outer conductor of the intermediate layer on the coaxial cable side is equal to or smaller than the inner diameter of the outer conductor of the coaxial cable,
the outer diameter of the inner conductor of the intermediate layer on the coaxial probe side is equal to or larger than the outer diameter of the inner conductor of the coaxial probe, and/or the inner diameter of the outer conductor of the intermediate layer on the coaxial probe side is equal to or larger than the inner diameter of the outer conductor of the coaxial probe,
Furthermore, it is desirable that the intermediate layer be configured so that the outer diameter of the inner conductor and the inner diameter of the outer conductor are continuously reduced toward the coaxial probe side, thereby allowing the joint to be performed without changing the ratio between the outer diameter of the inner conductor of the coaxial cable and the inner diameter of the outer conductor of the coaxial probe.

In this way, the ratio of the outer diameter of the inner conductor to the inner diameter of the outer conductor in the intermediate layer at the connection between the coaxial cable and the coaxial probe is designed to remain constant, so the characteristic impedance of the intermediate layer remains unchanged or changes can be minimized.

The probe card is a tip-side attachment that is attached to the outer conductor of the coaxial probe.
It is desirable to have a configuration including a tip attachment having a probe portion whose shape can be changed so that electrical continuity can be established between the ground electrode of the test object and the external conductor of the coaxial probe depending on the position of the ground electrode.

By including a tip-side attachment, even if the spacing between the electrodes of the object to be measured differs (changes), the probe (connection part) of the tip-side attachment can be bent or curved according to the spacing to ensure an appropriate connection.

With the above-mentioned configuration, the probe card of the present invention can achieve some or all of the following: improved reliability and durability, and mass production.

1A to 1C are diagrams for explaining a manufacturing process of a high-frequency device. FIG. 1 is a schematic diagram illustrating an example of an apparatus used in a wafer test. FIG. 1 is a schematic diagram illustrating an example of a conventional probe card. 1 is a schematic diagram illustrating an example of a probe card according to the present invention. (A) is a schematic vertical cross-sectional view of the coaxial probe, and (B) is a schematic VV cross-sectional view of (A). (A) is an image diagram showing the state before the base end attachment and the tip end attachment are attached to the coaxial probe, and (B) is an image diagram showing the state after the base end attachment and the tip end attachment are attached to the coaxial probe. FIG. 10 is an image diagram showing the deflection of the tip of a coaxial probe (inner conductor). 10 is a schematic diagram for explaining a connection configuration between a coaxial probe having an end-side attachment and a tip-side attachment attached thereto, a semi-rigid cable, and an object to be measured. FIG. (A) is an image diagram showing the state in which the tip of the coaxial probe is in contact with the object to be measured, and (B) is an image diagram showing the state in which the base end of the coaxial probe is joined to a semi-rigid cable by the base end side attachment. 10A and 10B are diagrams for explaining the configuration of a base end side plate. 10A and 10B are diagrams for explaining the relationship between frequency and signal attenuation in a conventional probe card. 1A and 1B are diagrams for explaining the joint configuration between a semi-rigid cable and the base end of a coaxial probe, in which (A) is a schematic diagram of the joint configuration, and (B) is a diagram showing the results of an electromagnetic field simulation for the joint configuration shown in (A). 10 is a schematic diagram for explaining a joint configuration between a semi-rigid cable and a base end portion of a coaxial probe. FIG. 10A and 10B are diagrams showing simulation results of the electrical characteristics (reflection loss characteristics) between the semi-rigid cable and the base end of the coaxial probe in each joint configuration.

The following describes in detail an embodiment of the present invention. However, the following description of the components is one example (representative example) of an embodiment of the present invention, and the present invention is not limited to the following content unless the gist of the present invention is changed. In this description, parts having the same configuration or function are designated by the same reference numerals in the drawings, and detailed description thereof will be omitted.

[High frequency device manufacturing process]
The manufacturing process for high-frequency devices includes processes such as front-end processing, wafer testing, back-end processing, and product testing (see Figure 1).

To give an overview of each process, first, in the pre-processing stage, hundreds to tens of thousands of high-frequency device chips are formed on wafers (material for manufacturing high-frequency device elements formed on a disc-shaped plate). Then, each of these formed high-frequency device chips (hereinafter sometimes simply referred to as "chips" or "test objects") undergoes a wafer test (electrical characteristics test) to separate them into good and bad products. After that, in the post-processing stage, only those deemed good in the wafer test undergo wiring and resin encapsulation. Finally, each high-frequency device that has been wired and resin encapsulated undergoes a product test, and only those that pass are shipped.

Therefore, if the quality (accuracy) of the wafer test is poor, problems such as cost and time waste and failure to achieve production plans will occur in the manufacture of high frequency devices.
For example, if a good product is judged to be defective in a wafer test, materials and work (pre-processing) will be wasted. Conversely, if a defective product is judged to be good in a wafer test, there is a risk that the defective product will be shipped as is, and the defective product will also be subjected to post-processing (wiring, resin encapsulation, etc.).

Thus, wafer testing is an important step in the manufacturing process of high frequency devices.
2 is a schematic diagram showing an example of an apparatus used in wafer testing, in which a probe card 1 placed on a wafer 90 is used to test the electrical characteristics of each chip formed on the wafer 90. More specifically, the test apparatus used in wafer testing is composed of a tester that generates and transmits test signals and judges the pass/fail of electrical characteristics based on returned operation signals, a test head, and a prober.

The prober transmits and receives signals to and from the chips on the wafer 90 via the probe card 1. The probe card 1 also ensures that test signals and operation signals are transmitted and received between the tester and the chips.
In other words, the probe card's role is to accurately transmit test signals generated by the tester to the chip, and also to receive the chip's operating signals and accurately transmit them to the tester. For this reason, it is no exaggeration to say that the quality of wafer testing depends on the probe card, and there is a global demand for highly convenient probe cards that offer improved reliability and durability, and that can be used in mass production.

[Conventional probe card]
3 is a schematic diagram showing an example of a conventional probe card. More specifically, it is a perspective view of the probe card described in Patent Document 1. The conventional probe card has a connector 81 provided on the top of a printed circuit board 80, to which signal lines extending from a tester are connected (see FIG. 2).

Further, a cable 82 connected to a connector 81 is provided on the lower side of the printed circuit board 80 (on the side facing the wafer 90).
The cable 82 is composed of a core and an insulating coating that covers the core, and the base ends of the probe pins 83 are in direct contact with the tip (distal end) of the core (see FIG. 2 of Patent Document 1). Note that a conventional probe card has one signal line probe pin 83 and two ground line probe pins 83, which contact the signal electrode portion E1 and the ground electrode portion E2 (E21, E22) of the test object (chip), respectively.

The test signal sent from the tester travels from the signal line through the connector 81, through the cable 82, and into the chip from the tip of the probe pin 83 that contacts the electrode part of the chip. On the other hand, the operating signal received from the chip follows the reverse route.

However, with conventional probe cards, the signal line probe pins and ground line probe pins are separate, so impedance matching cannot be said to be achieved all the way to the electrodes on the chip. Therefore, as mentioned above, it is difficult to use conventional probe cards for electrical testing and measurement of high-frequency devices used in high-frequency bands of 5 GHz or higher.

[Probe card of the present invention]
4 is a schematic diagram showing an example of a probe card of the present invention, shown in a partially omitted cross section. The probe card 1 of the present invention includes a printed circuit board 80 having a connector 81 provided on the top thereof, a coaxial cable (semi-rigid cable 70) connected to the connector 81, and a coaxial probe 10 connected to the semi-rigid cable 70. In this description, the coaxial cable used in the probe card 1 will be described as the semi-rigid cable 70.

The semi-rigid cable 70 is fixed to the electrode plate 40, and the tip of the semi-rigid cable 70 is connected to the base end of the coaxial probe 10. The base end of the coaxial probe 10 is fixed by the base end side plate 41. Meanwhile, the tip of the coaxial probe 10 is fixed by the tip end side plate 50. The tip of the coaxial probe 10 is provided with a portion (coaxial probe needle) that comes into contact with the chip on the wafer 90.

The semi-rigid cable 70 used in the probe card 1 of the present invention also has a coaxial structure consisting of an inner conductor 71, an inner insulator 72, an outer conductor 73, and an outer insulator 74, with the outer conductor 73 electrically shielding the inner conductor 71 (see Figures 8 and 9(B)).

In this embodiment, the printed circuit board 80 and electrode plate 40 are fixed by support pillars P1. The base end plate 41 and tip end plate 50 are fixed to the electrode plate 40 by support pillars P2. Note that this configuration is merely an example, and the design can be modified as appropriate.

[Coaxial probe]
The coaxial probe 10 is a generally linear, elongated rod-like body (cylindrical body) and is a vertical type that is disposed substantially perpendicular to the object under test. The coaxial probe 10 has a coaxial structure except for a portion of the base end 10p and a portion of the tip end 10t (see FIG. 5).

Specifically, as shown in Figure 5, the coaxial probe 10 is composed of, from its center, an inner conductor 11, an inner insulator 12, and an outer conductor 13. The outer conductor 13 is covered with an outer insulating material 14. The inner conductor 11 and outer conductor 13 are made of materials such as rhenium-tungsten, palladium alloy, beryllium steel, and various other metals and alloys. On the other hand, the outer insulating material 14 is made of insulating resin such as polyurethane, polyester, polyesterimide, polyamideimide, polyimide, or fluororesin.

The inner conductor 11 is cylindrical, with a diameter of 50 μm to 250 μm and a total length of 10 mm to 30 mm, and the tip 11N of the protruding portion (see Figure 6(B)) is rounded to have a shape such as a hemisphere, semi-ellipse, cone, or truncated cone. The width L2 of the coaxial probe 10 (see Figure 5(A)) is designed based on the distance between the signal electrode and ground electrode of the object to be measured, but is generally around 0.5 mm.

The coaxial probe 10 is configured by multiple outer conductors 13 surrounding an inner insulator 12. The outer conductors 13 are elastically deformable wires made of the above-mentioned material, and the inner conductors 11, inner insulators 12, and outer insulators 14 are also elastically deformable.
Therefore, the coaxial probe 10 as a whole is elastically deformable, and by deforming, it is possible to absorb the impact that occurs when it comes into contact with the electrode portion of the measurement object during wafer testing.

Furthermore, since the coaxial probe 10 is rod-shaped (cylindrical), its cross section is circular. In this embodiment, the external conductor 13 surrounds the internal insulator 12 (see Figure 5 (B)). Here, it is desirable that the multiple external conductors 13 be arranged without any gaps to ensure measurement accuracy. Of course, since the diameter of the internal insulator 12 changes if the core diameter (diameter of the internal conductor 11) changes, the number of external conductors 13 to be provided is designed appropriately depending on the core diameter.

Thus, while the coaxial probe tip portion (corresponding to the outer conductor 13 of the present invention) of the conventional probes disclosed in Patent Documents 3 and 4 is a simple single conducting wire that does not have a shielding structure for the inner conductor 11, the outer conductor 13 of the present invention is arranged to surround the inner conductor 11 via the inner insulator 12 (providing a shielding structure). This makes it possible to confine the high-frequency signal flowing through the inner conductor 11 with the outer conductor 13, preventing the high-frequency signal from leaking to the outside and preventing signal loss. Furthermore, because the outer conductor 13 prevents the intrusion of noise signals such as external electromagnetic waves and noise, the high-frequency signal can be transmitted to the electrode of the object to be measured with high quality.

In addition, by configuring the coaxial probe 10 in such a way that the internal insulator 12 is surrounded by multiple external conductors 13, as in this embodiment, the pressure exerted inside the coaxial probe 10 can be reduced, and the elasticity of the entire coaxial probe 10 can be improved. This improves the durability of the coaxial probe 10 (increasing the number of times it can be used repeatedly).

However, if measurement accuracy is more important than durability, the outer conductor 13 may be coated around the inner insulator 12.

[Proximal end attachment, distal end attachment]
In the probe card 1, a base end side attachment 20 is attached to the base end 10p of the coaxial probe 10 (see FIG. 6 ). In addition, in the probe card 1, a tip end side attachment 30 is attached to the tip end 11t of the coaxial probe 10 (see FIG. 6 ).

In this embodiment, the base end attachment 20 is composed of a main body 20A and multiple connection portions 20B. The main body 20A is formed in a shape that allows it to be fitted into the base end 10p of the coaxial probe 10 so as to establish electrical continuity with the outer conductor 13 of the coaxial probe 10, and in this embodiment is ring-shaped. For example, the base end attachment 20 is fitted into the exposed portion of the outer conductor 13 of the coaxial probe 10 that is not covered by the outer insulating material 14.

Furthermore, connection portion 20B functions to connect to semi-rigid cable 70. More specifically, connection portion 20B functions to connect outer conductor 13 of coaxial probe 10 to outer conductor 73 of semi-rigid cable 70. In this embodiment, four connection portions 20B are provided (connection portions 20B1 to 20B4) (see Figures 6 and 8), but the shape and number are not limited to these.

As will be described later with reference to Figure 13, it is desirable for the base end attachment 20 to have a structure in which an intermediate layer is provided between the semi-rigid cable 70 and the base end of the coaxial probe 10, but it is sufficient if electrical continuity can be established between the outer conductor 73 of the semi-rigid cable 70 and the outer conductor 13 of the coaxial probe 10. For example, as shown in Figure 9 (B), a structure in which a space S is provided around the internal insulator 12 of the coaxial probe 10 may also be used.

On the other hand, the tip end attachment 30 is composed of a main body 30A and multiple connection portions 30B. The main body 30A is shaped to fit onto the tip end 10t of the coaxial probe 10 so as to establish electrical continuity with the outer conductor 13 of the coaxial probe 10, and in this embodiment is ring-shaped. While two connection portions 30B are provided (connection portions 30B1 and 30B2), the shape and number are not limited to this example, and connection portions 30B1 and 30B2 are configured to function as probes that are respectively connected to the ground electrode portion E2 (ground electrodes E21 and E22) of the object to be measured (see Figure 8). The connection portions 30B can be bent or curved.

Here, the length L1 of the portion 11N of the coaxial probe 10 with the tip-side attachment 30 attached that protrudes from the coaxial structure (the portion that contacts the signal electrode portion of the test object) is designed based on the thickness of the protective film F (see Figure 7) provided on the test object (wafer 90). In other words, length L1 is the thickness of the protective film F plus a margin for deflection of the inner conductor 11 and/or the outer conductor 13 due to the elasticity of the coaxial probe 10, and is approximately 30 μm to 1 mm.

Depending on the type of object being inspected, the protective film F may not be present on the electrodes, but its thickness is generally approximately 0.5 μm to 5 μm. Furthermore, the inner conductor 11 and outer conductor 13 of the coaxial probe 10, and the connection portion 30B of the tip attachment 30, will bend when they come into contact with the signal electrode portion E1 and ground electrode portions E21 and E22 of the wafer 90 (see Figure 8) (see Figure 7 for an example). To prevent this bending from causing the tip portions of the inner conductor 12 and outer insulator 14 of the coaxial probe 10 to come into contact with the protective film F and to obtain a shielding effect in terms of electrical characteristics, it is desirable for the length L1 to be approximately 30 μm to 1 mm.

In this embodiment, the measurement object formed on the wafer 90 has one signal electrode portion E1 and two ground electrodes E21 and E22 (see Figure 8). The signal electrode portion E1 is in contact with the inner conductor 11 (protruding portion 11N) of the coaxial probe 10.

Meanwhile, the connection portions 30B1 and 30B2 of the tip attachment 30 contact the ground electrode portions E21 and E22, respectively. In other words, the outer conductor 13 of the coaxial probe 10 (any of the multiple outer conductors 13) contacts the ground electrode portions E21 and E22 of the object to be measured via the connection portions 30B1 and 30B2 of the tip attachment 30.

In this embodiment, the distance between the signal electrode E1 and the ground electrodes E21 and E22 of the object to be measured is 0.25 mm, but the sizes of the main body 30B and connection portion 30B of the tip attachment 30 are also designed appropriately to match this distance. Furthermore, the number of connection portions 30B can be as many as necessary depending on the number of ground electrodes of the object to be measured.

There are multiple types of measurement objects, and the spacing between the electrodes varies depending on the type. However, by attaching the tip attachment 30 to the tip 10t of the coaxial probe 10, even if the type of measurement object changes, the connection part 30B can be bent or curved according to the spacing between the electrodes, allowing for an appropriate connection.

Of course, as shown in Figure 9(A), if the distance between the signal electrode portion E1 and the ground electrode portions E21 and E22 of the measurement object is approximately the same as the distance between the inner conductor 11 and the outer conductor 13 (outer conductors 131 and 132) at the tip portion 10t of the coaxial probe 10, it is possible to configure the coaxial probe 10 without attaching the tip attachment 30.

[Base end plate]
The base end 10p of the coaxial probe 10 of the probe card 1 is fixed by a base end side plate 41. The base end side plate 41 is made of ceramic or engineering plastic resin and is composed of multiple plates. For example, in this embodiment, the base end side plate 41 is composed of three stacked base end side plates 411, 412, and 413 (see FIG. 10 ).

The base end side plates 411, 412, and 413 are provided with a through hole through which the base end 10p of the coaxial probe 10 can be inserted. The cross-sectional diameter of this through hole is approximately 1.1 to 1.2 times the diameter of the coaxial probe 10 including the insulating material 14. The cross-sectional shape of this through hole may be circular, elliptical, polygonal, or other shapes.

The base end side plates 411, 412, and 413 are stacked so that their respective through holes are connected while being slightly offset horizontally (left and right in Figure 10). The stacked base end side plates 411, 412, and 413 are fixed in place with fasteners 42 such as bolts and screws.

As a result, when the base end 10p of the coaxial probe 10 is inserted through each of the through-holes of the base end side plates 411, 412, and 413, which are connected while being slightly offset from each other, the base end 10p of the coaxial probe 10 elastically deforms and bends. The insulating material 14 covering the coaxial probe 10 then comes into contact with the corners of each through-hole, elastically or plastically deforming so that the corners bite into them. This deformation prevents the coaxial probe 10 from slipping off and allows it to be supported by the base end side plate 41.

In short, the probe card 1 uses the elastic force of the coaxial probe 10 itself to fix the base end 10p of the coaxial probe 10 to the base end side plate 41.

(Example)
Next, the configuration of the probe card 1 will be described in more detail, including problems with conventional probe cards and examples.

As mentioned at the beginning, one of the issues with conventional probe cards is that they cannot be used in high-frequency bands above 5 GHz due to their large signal attenuation. For example, it is desirable for a probe card to have low signal attenuation, with the general standard value being set at -2.0 dB or less. In other words, if the signal attenuation exceeds -2.0 dB, the card cannot be used for wafer testing.

Figure 11 is a graph showing the measured signal attenuation of a conventional probe card obtained from an experiment conducted at Toho Electronics Co., Ltd.

The length of the portion of the coaxial probe of the conventional probe card measured here that comes into contact with the chip on the wafer 90 (the non-coaxial portion of the coaxial probe, the unshielded portion of the coaxial probe) is 2.0 mm. As can be seen from this graph, signal attenuation is within the standard value (-2.0 dB or less) up to a frequency of about 10 GHz, but at frequencies higher than 10 GHz, signal attenuation exceeds this standard value. This is because if the length of this portion is long (for example, 2.0 mm as mentioned above), reflections occur in the exposed portion (unshielded portion), resulting in poor insertion loss and return loss.

As a result, conventional probe cards cannot be used for wafer testing because the signal attenuation in the 5G high-frequency band (approximately 28 GHz) significantly exceeds the standard value.

In response to this issue, the inventors of the present invention discovered that signal attenuation can be reduced by shortening the length of the unshielded portion of the coaxial probe (length L1 of portion 11N protruding from the coaxial structure of coaxial probe 10 shown in Figure 6(B)), and were successful in shortening length L1.

Length L1 is designed based on the thickness of the protective film on the electrode of the object being measured. This length includes the thickness of the protective film as well as a margin for bending of the inner and outer conductors due to the elasticity of the coaxial probe, and is preferably between 30 μm and 1 mm.

In this way, the probe card 1 of this embodiment has a shielded structure (coaxial path with impedance matching) right up to the tip 10t of the coaxial probe 10, so signal attenuation (loss) can be minimized to the utmost. Therefore, the probe card 1 can be used for wafer testing of high-frequency device chips used in high-frequency bands of 5 GHz or higher.

Furthermore, one of the issues with conventional probe cards is that the electrical characteristics (impedance) between the semi-rigid cable and the base end of the coaxial probe do not meet the standard values. Because the diameter of the semi-rigid cable and the diameter of the coaxial probe are different (the diameter of the semi-rigid cable is larger), it is necessary to join the two to ensure that test signals from the tester (see Figure 1) are transmitted correctly.

For example, the impedance variation at the joint between the base end of a coaxial probe and a semi-rigid cable is specified as "within 50.0 Ω ± 5%," but there are probe cards that do not meet this condition (e.g., Patent Documents 3 and 4).

One of the reasons for this is that the base end of the coaxial probe and the semi-rigid cable are joined with solder, and variations in the volume of the solder cause variations in impedance.

The inventors of this invention have therefore researched and developed a solder-free joining structure, and have succeeded in realizing it.

(Joining configuration 1)
Fig. 12(A) is a schematic diagram showing a configuration in which the base end of the coaxial probe 10 is directly joined to the semi-rigid cable 70. While it is possible to join the semi-rigid cable 70 and the coaxial probe 10 in this manner without using solder, in this case, the electric field will concentrate at the corners of the inner conductor 71 of the semi-rigid cable 70 (see the dotted line frame in Fig. 12(A)). This is clear from the results of the electromagnetic field simulation shown in Fig. 12(B), which causes reflections and increases impedance variations.

(Joining configuration 2)
13A (hereinafter referred to as "junction configuration 2"), an intermediate layer is provided between the semi-rigid cable 70 and the proximal end of the coaxial probe 10. This intermediate layer is a layer including an inner conductor, an insulator, and an outer conductor, and in this embodiment, the proximal end side attachment 20 is configured to include an inner conductor 21, an inner insulator 22, and an outer conductor 23.

In addition, in joint configuration 2, the outer diameter R21 of the inner conductor 21 of the base end attachment 20 on the semi-rigid cable 70 side (the side that joins with the semi-rigid cable 70) is equal to or smaller than the outer diameter R11 of the inner conductor 71 of the semi-rigid cable 70. In addition, the inner diameter R22 of the outer conductor 23 of the base end attachment 20 on the semi-rigid cable 70 side is equal to or smaller than the inner diameter R12 of the outer conductor 73 of the semi-rigid cable 70.

In connection configuration 2, the outer diameter R21 of the inner conductor 21 of the base end attachment 20 on the coaxial probe 10 side (the side that connects to the coaxial probe 10) is equal to or greater than the outer diameter R31 of the inner conductor 11 of the coaxial probe 10. Furthermore, the inner diameter R22 of the outer conductor 23 of the base end attachment 20 on the coaxial probe 10 side is equal to or greater than the inner diameter R32 of the coaxial probe 10.

Furthermore, in joint configuration 2, the outer diameter of the inner conductor 21 and the inner diameter of the outer conductor 23 of the base end attachment 20 are not changed between the semi-rigid cable 70 side and the coaxial probe 10 side, and the relationships "R11 ≧ R21 ≧ R31" and "R12 ≧ R22 ≧ R32" are satisfied.

(Joining configuration 3)
13B (hereinafter referred to as "joint configuration 3"), the inner diameters of the outer conductor 23 of the proximal end attachment 20 and the inner diameters of the inner conductor 21 of the proximal end attachment 20 are different. Specifically, the inner diameter R221 of the outer conductor 23 of the proximal end attachment 20 on the semi-rigid cable 70 side is larger than the inner diameter R222 of the coaxial probe 10 side (R221>R222). Moreover, the outer diameter R211 of the inner conductor 21 of the proximal end attachment 20 on the semi-rigid cable 70 side is larger than the inner diameter R212 of the coaxial probe 10 side (R211>R212).

In short, in joint configuration 3, the inner diameter of the outer conductor 23 of the base end attachment 20 gradually (continuously) decreases (inclines) from the semi-rigid cable 70 side to the coaxial probe 10 side, and the outer diameter of the inner conductor 21 of the base end attachment 20 also gradually (continuously) decreases (inclines) from the semi-rigid cable 70 side to the coaxial probe 10 side.

In this case, the ratio of the outer diameter R211 of the inner conductor 21 of the base end attachment 20 to the inner diameter R221 of the outer conductor 23 and the ratio of the outer diameter R212 of the inner conductor 21 to the inner diameter R222 of the outer conductor 23 are configured to remain unchanged. In other words, "R211:R221" = "R212:R222", and the same applies to the ratio of the outer diameter of the inner conductor 21 to the inner diameter of the outer conductor 23 in between.

In other words, joint configuration 3 joins the semi-rigid cable 70 so that the ratio between the outer diameter R11 of the inner conductor 71 and the inner diameter R12 of the outer conductor 73 and the ratio between the outer diameter R31 of the inner conductor 11 and the inner diameter R32 of the inner conductor 13 of the coaxial probe 10 remain unchanged along the way.

For these connection configurations 1 to 3, a simulation was performed on the electrical characteristics (reflection loss characteristics) between the semi-rigid cable 70 and the base end of the coaxial probe 10, and the results were summarized in a graph (see Figure 14).

As can be seen from these results, the amount of reflection loss is reduced when an intermediate layer is provided (joint configuration 2, joint configuration 3) compared to when the fibers are directly joined (joint configuration 1). Furthermore, the amount of reflection loss is further reduced when the outer diameter of the inner conductor 21 or the inner diameter of the outer conductor 23 of the base end attachment 20 is changed (joint configuration 3).

Here, we will explain why the amount of return loss is suppressed in joint configuration 3. If the outer diameter of the inner conductor 21 of the base end side attachment 20 is a (mm), the outer diameter of the outer conductor 23 is b (mm), and the relative dielectric constant of the inner insulator 22 is ε _s , the characteristic impedance Z ₀ (Ω) of the coaxial line can be calculated using Equation 1.

Z ₀ =138・(ε _s )1/2・log(b/a)...Formula (1)

If there is a step in the impedance of the electrical path, reflection loss occurs at that step, resulting in signal loss.

However, because joint configuration 3 is designed so that the ratio between the outer diameter of the inner conductor 21 of the base-end attachment 20 and the inner diameter of the outer conductor 23 remains unchanged, no difference in impedance occurs (or any change is minimized) between the semi-rigid cable 70 and the intermediate layer (base-end attachment 20), and between the intermediate layer (base-end attachment 20) and the coaxial probe 10. This minimizes impedance variation at the joint between the semi-rigid cable 70 and the base end of the coaxial probe 10, and as a result, minimizes reflection loss.

The probe card 1 described above is an example of a probe card according to the present invention, and the configuration of the present invention is not limited to this example as long as it does not deviate from the spirit of the present invention.

For example, the configuration of the base end attachment 20 and the tip end attachment 30 is not limited to the configuration of the main body 20A, 30A and the connection portion 20B, 30B shown as examples, and can be designed as appropriate. Furthermore, the intermediate layer provided between the semi-rigid cable 70 and the base end of the coaxial probe 10 may be a separate part (a separate body) from the base end attachment 20.

The probe card of the present invention can be used in the manufacturing process (wafer testing) of 5G high-frequency devices, and of course can also be used in the manufacturing process of 4G high-frequency devices and next-generation high-frequency devices (6G and above), making it industrially useful.

1 Probe card 10 Coaxial probe 10p Base end of coaxial probe 10t Tip of coaxial probe 11 Internal conductor 11N Portion protruding from coaxial structure 12 Internal insulator 13 External conductor 14 External insulating material 20 Base end side attachment 20A Main body of base end side attachment 20B, 20B1, 20B2, 20B3, 20B4 Connection part of base end side attachment 21 Internal conductor of base end side attachment 22 Internal insulator of base end side attachment 23 External conductor of base end side attachment 30 Tip end side attachment 30A Main body of tip end side attachment 30B, 30B1, 30B2 Connection part of tip end side attachment (probe)
40 Electrode plate 41 Base end side plate 411 Base end side plate (first layer)
412 Base end side plate (second layer)
413 Base end side plate (3rd layer)
42 Fixture 50 Tip end plate 70 Semi-rigid cable 71 Inner conductor of semi-rigid cable 72 Inner insulator of semi-rigid cable 73 Outer conductor of semi-rigid cable 74 Outer insulating material of semi-rigid cable 80 Printed circuit board 81 Connector 82 Cable 83 Probe pin 90 Wafer E1 Signal electrode part of object to be inspected E2, E21, E22 Ground electrode part of object to be inspected F Protective film P1, P2 Support part L1 Length of part not having shield structure L2 Width of coaxial probe R11 Outer diameter of inner conductor of semi-rigid cable R12 Inner diameter of outer conductor of semi-rigid cable R21 Outer diameter of inner conductor of base end side attachment R211 Outer diameter of inner conductor of base end side attachment on the semi-rigid cable side R212 Outer diameter of inner conductor of base end side attachment on the coaxial probe side R22 Inner diameter of the outer conductor of the base end attachment R221 Inner diameter of the semi-rigid cable side of the outer conductor of the base end attachment R222 Inner diameter of the coaxial probe side of the outer conductor of the base end attachment R31 Outer diameter of the inner conductor of the coaxial probe R32 Inner diameter of the outer conductor of the coaxial probe S Space

Furthermore, Patent Document 2 describes a probe card equipped with a vertical probe needle that can prevent a decrease in contact stability with a measurement object and can be used repeatedly for a long period of time. Specifically, this vertical probe needle is made of a thin metal wire 1 having a diameter of 0.02 to 0.04 mm and a length of 3.0 to 6.0 mm, with a body 1b covered with an insulating coating 2 of SiO2 and a tip 1a on which a metal coating 3 having granular protrusions 3a is formed. The edge 2a of the insulating coating 2 is located 20 to 60 μm from the apex 5, and the apex 5 is formed in an arc shape with a radius of curvature of 26 to 45 μm in vertical cross section (see FIG. 1).

However, in the probe card described in Patent Document 1, the base end of the probe pin and the tip end of the cable core are in direct contact with each other. This makes it possible to suppress deterioration of the electrical signal obtained through the probe pin compared to when the probe pin and the cable core are connected via an intervening member such as a connector, soldered portion, or coaxial pin, which has poor transmission loss at high frequencies. This makes it possible to improve the measurement accuracy of the electrical characteristics of the object to be measured , such as a chip on a semiconductor wafer, but it is not possible to further improve the measurement accuracy of the electrical characteristics.

The probe card (vertical probe needle) described in Patent Document 2 also prevents a decrease in contact stability with the object to be measured by forming a metal coating having granular protrusions 3a on the tip 1a of the probe needle, thereby enabling repeated use over a long period of time. However, since the probe needle has the same structure as Patent Document 1, which is a thin metal wire surrounded by an insulating coating (it is not a shielded structure), it is ineffective in preventing signal loss in the high frequency range.

The probe card is a tip-side attachment that is attached to the outer conductor of the coaxial probe.
It is desirable that the configuration include a tip attachment having a probe portion whose shape can be changed so that electrical continuity can be established between the ground electrode of the object to be measured and the external conductor of the coaxial probe depending on the position of the ground electrode.

To give an overview of each process, first, in the pre-processing, hundreds to tens of thousands of high-frequency device chips are formed on wafers (material for manufacturing high-frequency device elements formed on a disc-shaped plate). Then, each of these formed high-frequency device chips (hereinafter sometimes simply referred to as "chips" or " measurement objects") undergoes a wafer test (a test of electrical characteristics) and is separated into good and bad products. After that, in the post-processing, only those judged to be good in the wafer test undergo wiring and resin encapsulation. Finally, each high-frequency device that has been wired and resin encapsulated undergoes a product test, and only those that pass are shipped.

Further, a cable 82 connected to a connector 81 is provided on the lower side of the printed circuit board 80 (on the side facing the wafer 90).
The cable 82 is composed of a core and an insulating coating that covers the core, and the base ends of the probe pins 83 are in direct contact with the tip (distal end) of the core (see FIG. 2 of Patent Document 1). Note that a conventional probe card has one signal line probe pin 83 and two ground line probe pins 83, which contact the signal electrode portion E1 and the ground electrode portion E2 (E21, E22) of the measurement object (chip), respectively.

[Coaxial probe]
The coaxial probe 10 is a vertical type that is a linear, elongated rod (cylinder) that is positioned substantially perpendicular to the object to be measured . The coaxial probe 10 has a coaxial structure except for a portion of the base end 10p and a portion of the tip end 10t (see FIG. 5).

Here, the length L1 of the portion 11N of the coaxial probe 10 to which the tip-side attachment 30 is attached, which protrudes from the coaxial structure (the portion that comes into contact with the signal electrode portion of the object to be measured ), is designed based on the thickness of the protective film F (see FIG. 7) provided on the object to be measured (wafer 90). In other words, length L1 is the length that includes the thickness of the protective film F as well as a margin for flexure of the inner conductor 11 and/or the outer conductor 13 due to the elasticity of the coaxial probe 10, and is approximately 30 μm to 1 mm.

Depending on the type of object to be measured , the protective film F may not be present on the electrodes, but its thickness is generally about 0.5 μm to 5 μm. Furthermore, the inner conductor 11 and outer conductor 13 of the coaxial probe 10 and the connection portion 30B of the tip attachment 30 bend when they come into contact with the signal electrode portion E1 and ground electrode portions E21 and E22 (see FIG. 8 ) of the wafer 90 (see FIG. 7 for an example). To prevent such bending from bringing the tip portions of the inner conductor 12 and outer insulator 14 of the coaxial probe 10 into contact with the protective film F and to obtain a shielding effect in terms of electrical characteristics, it is desirable that the length L1 be about 30 μm to 1 mm.

1 Probe card 10 Coaxial probe 10p Base end of coaxial probe 10t Tip of coaxial probe 11 Internal conductor 11N Portion protruding from coaxial structure 12 Internal insulator 13 External conductor 14 External insulating material 20 Base end side attachment 20A Main body of base end side attachment 20B, 20B1, 20B2, 20B3, 20B4 Connection part of base end side attachment 21 Internal conductor of base end side attachment 22 Internal insulator of base end side attachment 23 External conductor of base end side attachment 30 Tip end side attachment 30A Main body of tip end side attachment 30B, 30B1, 30B2 Connection part of tip end side attachment (probe)
40 Electrode plate 41 Base end side plate 411 Base end side plate (first layer)
412 Base end side plate (second layer)
413 Base end side plate (3rd layer)
42 Fixture 50 Tip end plate 70 Semi-rigid cable 71 Inner conductor of semi-rigid cable 72 Inner insulator of semi-rigid cable 73 Outer conductor of semi-rigid cable 74 Outer insulating material of semi-rigid cable 80 Printed circuit board 81 Connector 82 Cable 83 Probe pin 90 Wafer E1 Signal electrode part of object to be measured E2, E21, E22 Ground electrode part of object to be measured F Protective film P1, P2 Support part L1 Length of part not having shield structure L2 Width of coaxial probe R11 Outer diameter of inner conductor of semi-rigid cable R12 Inner diameter of outer conductor of semi-rigid cable R21 Outer diameter of inner conductor of base end side attachment R211 Outer diameter of inner conductor of base end side attachment on the semi-rigid cable side R212 Outer diameter of inner conductor of base end side attachment on the coaxial probe side R22 Inner diameter of the outer conductor of the base end attachment R221 Inner diameter of the semi-rigid cable side of the outer conductor of the base end attachment R222 Inner diameter of the coaxial probe side of the outer conductor of the base end attachment R31 Outer diameter of the inner conductor of the coaxial probe R32 Inner diameter of the outer conductor of the coaxial probe S Space

Claims (4)

A probe card for measuring electrical characteristics of a measurement object,
a coaxial cable to which a test signal is input from outside;
a flexible coaxial probe having a base end connected to the coaxial cable and a tip end in contact with an electrode of the measurement object,
The tip of the coaxial probe has an inner conductor that contacts a signal electrode of the object to be measured and an outer conductor that contacts a ground electrode of the object to be measured,
The coaxial probe is a probe card characterized in that when the internal conductor contacts the signal electrode of the object to be measured, which has a protective film provided thereon, even if the internal conductor bends, the tip portions of the internal insulator and external insulator do not come into contact with the protective film, and the coaxial structure extends up to just before the protective film. an intermediate layer provided between the coaxial cable and the coaxial probe, the intermediate layer including an inner conductor and an outer conductor;
2. The probe card according to claim 1, wherein the inner conductor and the outer conductor of the intermediate layer are connected to the inner conductor and the outer conductor of the coaxial probe and the inner conductor and the outer conductor of the coaxial cable, respectively. an outer diameter of the inner conductor of the intermediate layer on the coaxial cable side is equal to or smaller than the outer diameter of the inner conductor of the coaxial cable, and/or an inner diameter of the outer conductor of the intermediate layer on the coaxial cable side is equal to or smaller than the inner diameter of the outer conductor of the coaxial cable,
an outer diameter of the inner conductor of the intermediate layer on the coaxial probe side is equal to or larger than an outer diameter of the inner conductor of the coaxial probe, and/or an inner diameter of the outer conductor of the intermediate layer on the coaxial probe side is equal to or larger than an inner diameter of the outer conductor of the coaxial probe,
The probe card of claim 2, characterized in that the outer diameter of the inner conductor and the inner diameter of the outer conductor of the intermediate layer are continuously reduced toward the coaxial probe, thereby allowing the coaxial cable to be joined without changing the ratio between the outer diameter of the inner conductor of the coaxial cable and the inner diameter of the outer conductor of the coaxial probe. a tip-end side attachment attached to the outer conductor of the coaxial probe,
The probe card according to any one of claims 1 to 3, characterized in that it is provided with a tip-side attachment having a probe portion whose shape is changeable so that electrical conduction can be achieved between the ground electrode of the test object and the outer conductor of the coaxial probe depending on the position of the ground electrode.