Probe card

Abstract

Provided is a highly convenient probe card with which it is possible to obtain some or all of such effects as enhanced reliability or durability and scaling up of production.　A probe card 1 is provided with: a coaxial cable 70 to which a high-frequency test signal is input from the outside; and a coaxial probe 10 that has flexibility, has a base end part connected to the coaxial cable 70, and has a tip part in contact with an electrode of a measurement object (wafer 90). An inner conductor of the tip part of the coaxial probe 10 is brought into contact with a signal electrode of the wafer 90, and an outer conductor is brought into contact with a ground electrode of the wafer 90. The coaxial probe 10 is configured such that even if the inner conductor is bent when the inner conductor is brought into contact with the signal electrode of the wafer 90 provided with a protective film, tip portions of an inner insulator and an outer insulator do not come into contact with the protective film, and the coaxial probe 10 has a coaxial structure up to just before the protective film.

Description

probe card

[0001] The present invention relates to a probe card used for testing the electrical characteristics of high frequency devices.

[0002] In recent years, the development of 5G high-frequency devices has been progressing in the field of high-speed communications such as smartphones, with the commercial launch of 5G (fifth-generation mobile communications system) in 2020. In line with this, the development of probe cards required for testing the electrical characteristics of high-frequency device chips used at 5G frequencies is also progressing.

[0003] 5G high-frequency devices will support a variety of fields, including smart industry, logistics, construction, agriculture, health and medicine, education, and remote offices, and require mass production of probe cards. At the same time, probe cards are also required to be reliable, such as reducing signal attenuation and impedance variations during wafer testing, as well as durable.

[0004] 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, Patent Document 1 describes a probe card 100 including a probe pin 10 made of a metal conductor and elastically deformable, with a tip end 11 protruding from an end face 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.

[0005] Furthermore, Patent Document 2 describes a probe card equipped with a vertical probe needle that can prevent a decrease in contact stability with an object to be tested (object to be measured) 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).

[0006] Patent Document 3 describes a probe card using a probe that aims 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 FIG. 1). The probe 1 further includes a connecting conductor 6 that connects the auxiliary conductor 4 to a second probe 5.

[0007] Furthermore, Patent Document 4 describes a coaxial probe that aims to suppress impedance fluctuations even when the distance between the signal pad and the ground pad of the device under test is different from the distance between the signal terminal and the 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 side by side with the signal terminal 124, and an attachment signal conductor 13 having a cylindrical structure having a hole 131 into which the signal terminal 124 can be inserted and attached to and electrically connected to the signal terminal 124 (see FIG. 4).

[0008] JP 2023-022720 A JP 2012-181045 A JP 2016-194412 A JP 2016-180746 A

[0009] 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. Therefore, compared to conventional cases in which 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, the probe card can suppress deterioration of the electrical signal obtained through the probe pin and improve the measurement accuracy of the electrical characteristics of the object to be measured, such as a chip on a semiconductor wafer, but it cannot further improve the measurement accuracy of the electrical characteristics.

[0010] This is because the probe structure disclosed in Patent Document 1 consists only of a conductive probe pin and an insulating coating, and does not have a shielding structure to prevent loss of high-frequency signals (a structure in which a signal line is surrounded by a dielectric and an outer conductor, as in a coaxial cable).Therefore, the structure of 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 making it impossible to improve the accuracy of measuring electrical characteristics.

[0011] 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, the probe needle has the same structure as Patent Document 1, which is a thin metal wire surrounded by an insulating coating, and therefore is not a shielded structure, and is therefore ineffective in preventing signal loss in the high frequency range, which is the objective of the present invention.

[0012] On the other hand, the probe card described in Patent Document 3 is provided with an auxiliary conductor that is electrically connected to an external conductor on the probe of the probe card and is arranged 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, and to improve the accuracy of high-frequency electrical characteristic testing.As a result, 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.

[0013] However, while there is a shielding effect only in the area where the auxiliary conductor is located around the inner conductor, there is no auxiliary dielectric in other directions, and so no shielding effect can be obtained. This is clearly evident from the results shown in Figure 14, which show a difference of 3 Ω from the coaxial section.

[0014] 14 of Patent Document 3 shows that when an auxiliary conductor is provided, noise is reduced by 10 to 20 dB compared to when no auxiliary conductor is provided, but the measurement frequency is 10 MHz to 6 GHz, which is lower than the frequency of 5 G. It is a well-known fact that noise increases as the frequency increases, so while this frequency band may be sufficient, it cannot be said that this structure can sufficiently reduce noise in high-frequency frequency bands of 5 G and above.

[0015] Furthermore, the probe card described in Patent Document 4 is equipped with 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 an attachment signal conductor 13 which has a cylindrical structure having a hole 131 into which the signal terminal 124 can be inserted and which is attached to and electrically connected to the signal terminal 124, in order to suppress impedance fluctuations and obtain sufficient resolution even when the distance between the signal pad and the ground pad of the object to be measured is different from the distance between the signal terminal and the ground terminal.

[0016] As described above, the ground terminal 125 of the probe card described in Patent Document 4 is simply linear and does not have a coaxial structure surrounding the signal terminal 124 to prevent leakage of high-frequency signals, and therefore cannot prevent signal loss in high-frequency bands of 5 GHz or higher.

[0017] Specifically, as shown in Figure 5(a), the improved transmission characteristics (corresponding to the insertion loss described below) are -4 dB at 20 GHz, which is no more than the results of the prior art. Also, as shown in Figure 5(b), the improved impedance is also about 55 Ω.

[0018] As described above, the probe card described in Patent Document 1, for example, has an insertion loss exceeding the standard (within -2.0 dB) in the high frequency band (about 28 GHz) of the 5 GHz range. Furthermore, even if the probe card described in Patent Document 1 uses a structure for preventing signal loss as described in Patent Documents 3 and 4 to suppress reflection, this would have been sufficient for the conventional high frequency band up to 4 GHz, but would not satisfy the insertion loss and impedance variation standards (within 50.0 Ω±5%) in the high frequency band of 5 GHz or higher.

[0019] Therefore, there is a demand for a probe card that can improve at least one of the above-mentioned standards. In light of the above-mentioned background, there is a demand for probe cards that are more convenient, including being able to improve reliability and durability and being able to be mass-produced.

[0020] Therefore, an object of the present invention is to provide a highly convenient probe card that can achieve some or all of the improvements in reliability and durability and mass production.

[0021] The probe card of the present invention is a probe card for measuring high-frequency electrical characteristics of an object to be measured, and comprises: a coaxial cable to which a high-frequency test signal is input from the outside; and a flexible coaxial probe whose base end is connected to the coaxial cable and whose tip end is in contact with an electrode of the object to be measured; the tip end 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; and when the inner conductor contacts a signal electrode of the object to be measured which has a protective film provided thereon, even if the inner conductor bends, the tip portions of the inner insulator and outer insulator do not come into contact with the protective film, and the coaxial structure extends up to just before the protective film.

[0022] The probe card according to the present invention has such a configuration that the coaxial probe does not damage the protective film of the object to be measured, thereby reducing insertion loss to the greatest extent possible.

[0023] Furthermore, it is desirable that the probe card has an intermediate layer provided between the coaxial cable and the coaxial probe, the intermediate layer including an inner conductor and an outer conductor, and that the inner conductor and outer conductor of the intermediate layer are connected to the inner conductor and outer conductor of the coaxial probe and the inner conductor and outer conductor of the coaxial cable, respectively.

[0024] In this way, by providing an intermediate layer including an inner conductor and an outer conductor between the coaxial cable and the coaxial probe, it is possible to suppress changes in the characteristic impedance of the connection between the coaxial cable and the coaxial probe.

[0025] In particular, in this intermediate layer, it is desirable that 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, and the outer diameter of the inner conductor of the intermediate layer is continuously smaller toward the coaxial probe side, thereby allowing joining 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.

[0026] In this way, the intermediate layer at the connection point between the coaxial cable and the coaxial probe is configured so that the ratio of the outer diameter of the inner conductor to the inner diameter of the outer conductor does not change, so the characteristic impedance of the intermediate layer does not change or changes can be minimized.

[0027] The probe card is a tip-side attachment that is attached to the outer conductor of the coaxial probe, and is preferably configured to include a tip-side attachment having a probe portion whose shape is changeable so that electrical continuity can be established between the ground electrode of the object to be measured and the outer conductor of the coaxial probe depending on the position of the ground electrode.

[0028] By configuring the device with a tip-side attachment, even if the spacing between the electrode parts 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.

[0029] With the above-described configuration, the probe card according to the present invention can achieve some or all of improved reliability and durability, and mass production.

[0030] 1 is a diagram for explaining a manufacturing process of a high-frequency device. It is a schematic diagram showing an example of an apparatus used in a wafer test. It is a schematic diagram showing an example of a conventional probe card. It is a schematic diagram showing an example of a probe card of the present invention. (A) is a schematic vertical cross-sectional view of a coaxial probe, and (B) is a schematic VV cross-sectional view of (A). (A) is an image diagram showing a state before a base end side attachment and a tip end side attachment are attached to the coaxial probe, and (B) is an image diagram showing a state after the base end side attachment and the tip end side attachment are attached to the coaxial probe. It is an image diagram showing the deflection of the tip of the coaxial probe (inner conductor). It is a schematic diagram for explaining the connection configuration between a coaxial probe having a tip end side attachment and a tip end side attachment attached, a semi-rigid cable, and a measurement object. (A) is an image diagram showing a state in which the tip of the coaxial probe is in contact with the measurement object, and (B) is an image diagram showing a state in which the base end of the coaxial probe is joined to the semi-rigid cable by the base end side attachment. It is a diagram for explaining the configuration of a base end side plate. Fig. 1 is a diagram for explaining the relationship between frequency and signal attenuation in a conventional probe card. Fig. 2 is a diagram for explaining a joint configuration between a semi-rigid cable and a base end of a coaxial probe, (A) is a schematic diagram of the joint configuration, and (B) is a diagram showing the results of an electromagnetic field simulation in the joint configuration shown in (A). Fig. 3 is a schematic diagram for explaining a joint configuration between a semi-rigid cable and a base end of a coaxial probe. Fig. 4 is a diagram showing the results of a simulation of the electrical characteristics (reflection loss characteristics) between a semi-rigid cable and a base end of a coaxial probe in each joint configuration.

[0031] The following is a detailed description of an embodiment of the present invention, but the following description of the components is one example (typical 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 given the same reference numerals in the drawings, and detailed description thereof will be omitted.

[0032] [Manufacturing Process of High Frequency Devices] The manufacturing process of high frequency devices includes processes such as front-end processing, wafer testing, back-end processing, and product testing (see FIG. 1).

[0033] 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.

[0034] Therefore, poor quality (accuracy) of wafer testing can result in cost and time waste and failure to achieve production plans in the manufacture of high-frequency devices. For example, if a good product is judged to be defective in wafer testing, materials and work (pre-processing) will be wasted. Conversely, if a defective product is judged to be good in wafer testing, 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.).

[0035] Thus, wafer testing is an important step in the manufacturing process of high-frequency devices. Fig. 2 is a schematic diagram showing an example of an apparatus used in wafer testing. 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 testing apparatus used in wafer testing is composed of a tester that generates and transmits test signals and determines whether the electrical characteristics are good or bad based on the returned operation signals, a test head, and a prober.

[0036] 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 reliable transmission and reception of test signals and operation signals between the tester and the chips. In other words, the probe card accurately transmits test signals generated by the tester to the chips, and also receives operation signals from the chips and accurately transmits 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 worldwide demand for highly convenient probe cards that offer improved reliability and durability, and that can be mass-produced.

[0037] [Conventional Probe Card] Fig. 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).

[0038] Furthermore, a cable 82 connected to the connector 81 is provided below the printed circuit board 80 (toward the wafer 90). The cable 82 is composed of a core and an insulating coating covering the core, and the base ends of the probe pins 83 are in direct contact with the tip (tip) 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 respectively contact a signal electrode portion E1 and a ground electrode portion E2 (E21, E22) of the measurement object (chip).

[0039] A test signal sent from the tester travels from the signal line through connector 81, through cable 82, and into the chip from the tip of probe pin 83 that contacts the electrode of the chip. Meanwhile, the operation signal received from the chip follows the reverse route.

[0040] However, in conventional probe cards, the signal line probe pins and the ground line probe pins are separated, so impedance matching cannot be achieved up to the vicinity of the chip electrodes. Therefore, as mentioned above, it is difficult to use conventional probe cards for electrical inspection and measurement of high-frequency device chips used at 5G frequencies.

[0041] [Probe Card of the Present Invention] Fig. 4 is a schematic diagram showing an example of the probe card of the present invention, and is shown in a partially omitted cross-sectional view similar to Fig. 3. 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.

[0042] 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 a base end side plate 41. On the other hand, the tip of the coaxial probe 10 is fixed by a 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 a chip on the wafer 90.

[0043] In addition, 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, and the outer conductor 73 electrically shields the inner conductor 71 (see Figures 8 and 9(B)).

[0044] In this embodiment, the printed circuit board 80 and the electrode plate 40 are fixed by a support P1. The base end side plate 41 and the tip end side plate 50 are fixed to the electrode plate 40 by a support P2. Note that this configuration is merely an example, and the design can be modified as appropriate.

[0045] [Coaxial Probe] The coaxial probe 10 is a vertical type that is an elongated, linear 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.

[0046] 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 the outer conductor 13 are made of materials such as rhenium-tungsten, palladium alloy, beryllium steel, and various other metals and alloys. The outer insulating material 14 is made of insulating resin such as polyurethane, polyester, polyesterimide, polyamideimide, polyimide, or fluororesin.

[0047] 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 FIG. 6B) is rounded to have a semi-spherical, semi-elliptical, conical, truncated conical, or other shape. The width L2 of the coaxial probe 10 is designed based on the distance between the signal electrode and the ground electrode of the object to be measured, but is generally about 0.5 mm (see FIG. 5A).

[0048] The coaxial probe 10 is configured by multiple outer conductors 13 surrounding an internal insulator 12. The external conductors 13 are elastically deformable wires made of the aforementioned material, and the internal conductors 11, internal insulators 12, and external insulator 14 are also elastically deformable. Therefore, the coaxial probe 10 as a whole is elastically deformable, and by deforming, it can absorb the impact that occurs when it comes into contact with the electrode portion of the measurement object during wafer testing.

[0049] Furthermore, since the coaxial probe 10 is a rod-shaped body (cylindrical body), its cross section is circular. In this embodiment, the outer conductor 13 is provided so as to surround the internal insulator 12 (see FIG. 5B ). Here, it is desirable that the multiple external conductors 13 are provided without any gaps to ensure measurement accuracy. Of course, since the diameter of the internal insulator 12 changes depending on the core diameter (diameter of the internal conductor 11), the number of external conductors 13 to be provided is appropriately designed depending on the core diameter.

[0050] Therefore, in the conventional coaxial probes of Patent Documents 3 and 4, the portion of the tip corresponding to the outer conductor 13 of the present invention is a simple single conductor and does not have a shielding structure for the inner conductor 11. In contrast, the outer conductor 13 of the present invention is provided so as to surround the periphery of the inner conductor 11 via the inner insulator 12 (shielding structure), so that the outer conductor 13 can contain the high-frequency signal flowing through the inner conductor 11, 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 delivered to the electrode of the object to be measured with good quality.

[0051] By configuring the coaxial probe 10 in such a manner that the inner insulator 12 is surrounded by a plurality of outer conductors 13 as in this embodiment, it is possible to reduce the pressure applied to the inside of the coaxial probe 10 and improve the elasticity of the entire coaxial probe 10. This improves the durability of the coaxial probe 10 (the number of times it can be used repeatedly can be increased).

[0052] However, if measurement accuracy is more important than durability, the periphery of the inner insulator 12 may be coated with the outer conductor 13 .

[0053] [Base End Side Attachment, Tip End Side 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 ).

[0054] In this embodiment, the proximal end attachment 20 is composed of a main body 20A and a plurality of connection portions 20B. The main body 20A is formed in a shape that allows it to be fitted into the proximal end 10p of the coaxial probe 10 so as to establish electrical continuity with the outer conductor 13 of the coaxial probe 10, and is ring-shaped in this embodiment. For example, the proximal 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.

[0055] Furthermore, the connection portion 20B has a function of connecting to the semi-rigid cable 70. More specifically, the connection portion 20B has a function of connecting the outer conductor 13 of the coaxial probe 10 to the outer conductor 73 of the semi-rigid cable 70, and in this embodiment, four connection portions 20B are provided (connection portions 20B1 to 20B4) (see FIGS. 6 and 8), but the shape and number are not limited to these.

[0056] 13, the proximal end side attachment 20 is preferably configured to have an intermediate layer provided between the semi-rigid cable 70 and the proximal end of the coaxial probe 10, but it is sufficient if it can provide electrical continuity 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 FIG. 9B, a structure in which a space is provided around the internal insulator 12 of the coaxial probe 10 may also be used.

[0057] Meanwhile, the tip end attachment 30 is composed of a main body 30A and multiple connection portions 30B. The main body 30A is shaped so that it can be fitted into 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. Although two connection portions 30B (connection portions 30B1 and 30B2) are provided, the shape and number of connection portions 30B are not limited to this example, and the connection portions 30B1 and 30B2 function as probes that are respectively connected to the ground electrode portion E2 (ground electrodes E21 and E22) of the measurement object (see FIG. 8 ). The connection portions 30B can be bent or curved.

[0058] 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 provided on the object to be measured (wafer 90). In other words, the length L1 is the length including 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.

[0059] Although the protective film F may not be present on the electrodes depending on the type of object to be measured, its thickness is generally about 0.5 μm to 5 μm. Furthermore, when the inner conductor 11 and the outer conductor 13 of the coaxial probe 10 come into contact with the signal electrode portion E1 and the ground electrode portions E21 and E22 (see FIG. 8) of the wafer 90, they bend as shown in FIG. 7. However, in order to prevent the tip portions of the inner conductor 12 and the outer insulator 14 of the coaxial probe 10 from coming into contact with the protective film F due to such bending 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.

[0060] The chip, which is the measurement object formed on the wafer 90, has one signal electrode E1 and two ground electrodes E21 and E22 (see FIG. 8). The signal electrode E1 is in contact with the inner conductor 11 (protruding portion 11N) of the coaxial probe 10.

[0061] Meanwhile, the ground electrodes E21 and E22 are in contact with the connecting portions 30B1 and 30B2 of the tip end attachment 30. In other words, the outer conductor 13 of the coaxial probe 10 (any of the multiple outer conductors 13) is in contact with the ground electrodes E21 and E22 of the object to be measured via the connecting portions 30B1 and 30B2 of the tip end attachment 30.

[0062] 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 the connection portion 30B of the tip end attachment 30 are also designed appropriately to match this distance. In addition, 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.

[0063] There are multiple types of measurement objects, and the spacing between the electrodes also varies. However, by attaching the tip end attachment 30 to the tip end 10t of the coaxial probe 10, even if the type of measurement object changes, the connection portion 30B can be bent or curved according to the spacing between the electrodes, allowing for appropriate connection.

[0064] Of course, as shown in Figure 9 (A), if the distance between the signal electrode portion E1 of the object to be measured and the ground electrode portions E21 and E22 are 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 also possible to configure the coaxial probe 10 without attaching the tip side attachment 30.

[0065] [Base End Side Plate] The base ends 10p of the coaxial probes 10 of the probe card 1 are 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 ).

[0066] The base end side plates 411, 412, and 413 are provided with through holes through which the base end 10p of the coaxial probe 10 can be inserted. The cross-sectional diameter of the through holes 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 the through holes may be circular, elliptical, polygonal, or the like.

[0067] The base end side plates 411, 412, and 413 are stacked so that the through holes formed in each are connected while being slightly offset in the horizontal direction (the left-right direction in FIG. 10 ). The stacked base end side plates 411, 412, and 413 are fixed with fasteners 42 such as bolts and screws.

[0068] 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 is elastically deformed and bent. Then, the insulating material 14 covering the coaxial probe 10 comes into contact with the corners of each through-hole, and elastically or plastically deforms so that the corners bite into them. Due to this deformation, the coaxial probe 10 is supported by the base end side plate 41 without slipping off.

[0069] In short, the probe card 1 fixes the base end 10 p of the coaxial probe 10 to the base end side plate 41 by utilizing the elastic force of the coaxial probe 10 itself.

[0070] (Examples) Next, the configuration of the probe card 1 will be described in more detail, including problems with conventional probe cards and examples.

[0071] As mentioned at the beginning, one of the issues with conventional probe cards is that they cannot be used in high-frequency bands above the 5G band due to their large signal attenuation. For example, it is desirable for a probe card to have low signal attenuation, and the general standard value is set at within -2.0 dB. In other words, if the signal attenuation exceeds -2.0 dB, the card cannot be used for wafer testing.

[0072] FIG. 11 is a graph showing the measured values ​​of the signal attenuation of a conventional probe card obtained from an experiment conducted within Toho Electronics Co., Ltd.

[0073] Here, the length of the portion of the coaxial probe of the conventional probe card that contacts the chip on the wafer 90 (the non-coaxial portion of the coaxial probe / the unshielded portion of the coaxial probe) measured is 2.0 mm. As can be seen from this graph, the signal attenuation is within the standard value (within -2.0 dB) up to a frequency of about 10 GHz, but at frequencies higher than 10 GHz, the signal attenuation exceeds the standard value. This is because if the length of this portion is long (for example, 2.0 mm as mentioned above), reflection occurs in the exposed portion (the unshielded portion), resulting in poor insertion loss and return loss.

[0074] Therefore, with conventional probe cards, the amount of signal attenuation in the high frequency band (approximately 28 GHz) in the 5G region significantly exceeds the standard value, making them unusable for wafer testing.

[0075] To address this issue, the inventors of the present invention discovered that the amount of signal attenuation can be reduced by shortening the length of the unshielded portion of the coaxial probe (the length L1 of the portion 11N protruding from the coaxial structure of the coaxial probe 10 shown in FIG. 6(B)), and succeeded in shortening the length L1 of that portion.

[0076] The length L1 of this portion is designed based on the thickness of the protective film on the electrode of the object to be measured, and this length is determined by 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 approximately 30 μm to 1 mm.

[0077] In this way, the probe card 1 of this embodiment has a shield structure (coaxial path with impedance matching) right up to the tip 10t of the coaxial probe 10, so that the amount of signal attenuation (loss) can be minimized. Therefore, the probe card 1 can be used for wafer testing of high-frequency device chips used at 5G frequencies.

[0078] 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), they must be joined to ensure that test signals from the tester are transmitted correctly.

[0079] For example, the impedance variation at the joint between the base end of a coaxial probe and a semi-rigid cable is regulated to be "within 50.0 Ω±5%," but there are some probe cards that do not meet this condition (Patent Documents 3 and 4).

[0080] One of the reasons for this is that the base end of the coaxial probe and the semi-rigid cable are joined by solder, and the impedance varies due to variations in the volume of the solder.

[0081] The inventors of the present invention have therefore carried out research and development into a joining structure that does not use solder, and have succeeded in realizing it.

[0082] (Joint 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. It is possible to join the semi-rigid cable 70 and the coaxial probe 10 in this manner without using solder, but 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.

[0083] 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 insulator 22, and an outer conductor 23.

[0084] In the joint configuration 2, the outer diameter R21 of the inner conductor 21 of the base end side 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 side 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.

[0085] On the other hand, in the joint configuration 2, the outer diameter R21 of the inner conductor 21 of the base end side attachment 20 on the coaxial probe 10 side (the side connected to the coaxial probe 10) is equal to or larger than the outer diameter R31 of the inner conductor 11 of the coaxial probe 10. Also, the inner diameter R22 of the outer conductor 23 of the base end side attachment 20 on the coaxial probe 10 side is equal to or larger than the inner diameter R32 of the coaxial probe 10.

[0086] 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 side attachment 20 are not changed between the semi-rigid cable 70 side and the coaxial probe 10 side, and the relationships are "R11 ≧ R21 ≧ R31" and "R12 ≧ R22 ≧ R32."

[0087] 13B (hereinafter referred to as "joint configuration 3"), the inner diameter of the outer conductor 23 of the proximal end attachment 20 and the inner diameter 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).

[0088] In short, in joint configuration 3, the inner diameter of the outer conductor 23 of the base end side 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 side attachment 20 also gradually (continuously) decreases (inclines) from the semi-rigid cable 70 side to the coaxial probe 10 side.

[0089] In this case, the ratio between the outer diameter R211 of the inner conductor 21 of the base end side attachment 20 and the inner diameter R221 of the outer conductor 23 and the ratio between the outer diameter R212 of the inner conductor 21 and the inner diameter R222 of the outer conductor 23 are formed so as to remain unchanged. In other words, "R211:R221" = "R212:R222", and the same applies to the ratio between the outer diameter of the inner conductor 21 and the inner diameter of the outer conductor 23 in between.

[0090] 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 do not change along the way.

[0091] 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 FIG. 14).

[0092] As can be seen from these results, the amount of return loss is reduced when an intermediate layer is provided (joint configurations 2 and 3) compared to when the connection is direct (joint configuration 1). Furthermore, the amount of return loss is further reduced when the outer diameter of the inner conductor 21 of the base end side attachment 20 or the inner diameter of the outer conductor 23 is changed (joint configuration 3).

[0093] The reason why the amount of reflection loss is suppressed in the joint configuration 3 will be explained. 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 Then, the characteristic impedance Z0 (Ω) of the coaxial line is calculated by Equation 1.

[0094] Z0 = 138 (ε s )1 / 2・log(b / a)...Formula (1)

[0095] If there is a step in the impedance of the electrical path, a reflection loss occurs at the step, resulting in a loss of signal.

[0096] Therefore, in joint configuration 3, the ratio between the outer diameter of the inner conductor 21 of the proximal end attachment 20 and the inner diameter of the outer conductor 23 remains unchanged, and therefore no difference in impedance occurs (or the change is minimized) between the semi-rigid cable 70 and the intermediate layer (proximal end attachment 20), and between the intermediate layer (proximal end attachment 20) and the coaxial probe 10. Therefore, the variation in impedance at the joint between the semi-rigid cable 70 and the proximal end of the coaxial probe 10 is minimized, and as a result, the reflection loss is also minimized.

[0097] The probe card 1 described above is an example of the probe card according to the present invention, and the configuration of the present invention is not limited to the example provided that it does not deviate from the spirit of the present invention.

[0098] For example, the configurations of the proximal end attachment 20 and the distal end attachment 30 are not limited to the configurations of the main body portions 20A, 30A and the connecting portions 20B, 30B as exemplified, and can be designed as appropriate. In addition, the intermediate layer provided between the semi-rigid cable 70 and the proximal end of the coaxial probe 10 may be a separate part (a separate body) from the proximal end attachment 20.

[0099] The probe card according to 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 (6G or higher) high-frequency devices, making it industrially useful.

[0100] 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 Body of base end side attachment 20B, 20B1, 20B2, 20B3, 20B4 Connection portion 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 Body of tip end side attachment 30B, 30B1, 30B2 Connection portion 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 (third layer) 42 Fixture 50 Tip end side 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 insulation 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 semi-rigid cable side of inner conductor of base end side attachment R212 Outer diameter of the inner conductor of the base end attachment on the coaxial probe side R22 Inner diameter of the outer conductor of the base end attachment R221 Inner diameter of the outer conductor of the base end attachment on the semi-rigid cable side R222 Inner diameter of the outer conductor of the base end attachment on the coaxial probe side 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

1. A probe card for measuring the high-frequency electrical characteristics of a measurement object, comprising: a coaxial cable to which a high-frequency test signal is input from the outside; and a coaxial probe having flexibility, a proximal end portion of which is connected to the coaxial cable and a distal end portion of which contacts an electrode of the measurement object. The distal end portion of the coaxial probe has an inner conductor contacting a signal electrode of the measurement object and an outer conductor contacting a ground electrode of the measurement object. The coaxial probe is configured such that when the inner conductor contacts the signal electrode of the measurement object provided with a protective film, even if the inner conductor is bent, the tip portions of the inner insulator and the outer insulator do not contact the protective film, and the coaxial structure extends up to immediately before the protective film.

2. An intermediate layer provided between the coaxial cable and the coaxial probe, the intermediate layer having an inner conductor and an outer conductor, 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.

3. The outer diameter of the inner conductor of the intermediate layer on the coaxial cable side is less than or equal to 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 less than or equal to 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 greater than or equal to 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 greater than or equal to the inner diameter of the outer conductor of the coaxial probe. Further, the intermediate layer is configured such that the outer diameter of the inner conductor and the inner diameter of the outer conductor continuously decrease toward the coaxial probe side, so that the ratio of the outer diameter of the inner conductor to the inner diameter of the outer conductor of the coaxial cable and the ratio of the outer diameter of the inner conductor to the inner diameter of the inner conductor of the coaxial probe are joined without change.

4. A tip-side attachment attached to the outer conductor of the coaxial probe, the tip-side attachment having a probe portion with a shape that can be changed so that electrical conduction can be established between the ground electrode and the outer conductor of the coaxial probe according to the position of the ground electrode of the measurement object.

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