Inspection tool and adjustment method of characteristic impedance of inspection tool

Abstract

Provided is an inspection jig and a method for adjusting the characteristic impedance of an inspection jig, which can accurately inspect a printed wiring board that transmits high-frequency signals. An inspection jig (1) for inspecting a printed wiring board (200) includes an inspection substrate (10) having a signal line (11) for transmitting an inspection signal output from a measuring device (50) and a ground layer (12) insulated from the signal line (11); a signal pin (21) electrically connected to the signal line (11); a ground pin (22) electrically connected to the ground layer (12); a holding portion (30) that holds the signal pin (21) and the ground pin (22); and a connector portion (40) mounted on the inspection substrate (10) for connecting the inspection substrate (10) and the measuring device (50). The characteristic impedance of the inspection jig is converged within a prescribed range throughout a transmission region from the connector portion to the signal pin, through which the inspection signal is transmitted. The prescribed range is narrower than an allowable range of the characteristic impedance of the printed wiring board. Furthermore, a reference impedance is located at the center of the prescribed range.

Description

Technical Field

[0001] This invention relates to an inspection fixture and a method for adjusting the characteristic impedance of the inspection fixture. Background Technology

[0002] In recent years, with the miniaturization and high-speed development of electronic devices such as smartphones, laptops, digital cameras, and game consoles, the amount of information processed has increased dramatically. Therefore, there is a trend towards increasingly faster signal speeds. Furthermore, portable communication terminals such as smartphones began transitioning to the next-generation communication standard, 5G, in 2019. In 5G, the frequency of signals transmitted and received by communication terminals changes from several GHz to 20-30 GHz. Moreover, it is predicted that the signal frequency will reach as high as 50 GHz around 2023.

[0003] To accommodate the increasing speed of signals, the signal lines (high-speed transmission lines) on printed circuit boards (PCBs) need to meet various specifications regarding transmission characteristics. For example, to suppress signal reflection, specifications define the characteristic impedance and the voltage standing wave ratio (VSWR), which specifies the degree and frequency of reflection. Furthermore, since transmission loss tends to increase with signal frequency, specifications sometimes limit the transmission loss of the lines. Moreover, when multiple signal lines are located on the same PCB, specifications also limit the interference (crosstalk / isolation) between adjacent signal lines.

[0004] To confirm that the specifications for transmission characteristics are met, the manufactured printed circuit boards (PCBs) are inspected. The inspection uses an inspection fixture for connecting measuring instruments such as vector network analyzers to the PCB being inspected. The inspection fixture includes: an inspection board with signal lines for transmitting inspection signals; a coaxial connector (SMA connector, etc.) mounted on the inspection board for interface connection with the measuring instrument; and a probe section with contact probes (signal pins and ground pins). The inspection board has interlayer connection portions (through holes, etc.) for electrically connecting the signal lines and signal pins.

[0005] During inspection, the contact probes of the inspection fixture are brought into contact with the signal and ground terminals of the printed circuit board (PCB) being inspected. The number and location of these signal and ground terminals vary depending on the type of PCB being inspected (e.g., FPC products). Therefore, the inspection fixture is specifically designed for each type of PCB being inspected.

[0006] In addition, Patent Document 1 describes an invention related to a contact probe for an inspection fixture. Existing technical documents

[0007] Patent Document 1: Japanese Patent Publication No. 2020-085695

[0008] However, when ensuring the inspection accuracy of printed circuit boards (PCBs) for high-frequency signals of tens of GHz, the characteristic impedance of the inspection fixture must be within a specified range. Of course, the characteristic impedance of the inspection fixture must be within a narrower range than the permissible range of the PCB's characteristic impedance. Therefore, the "specified range" within which the characteristic impedance of the inspection fixture should be narrower than the permissible range of the PCB's characteristic impedance. Furthermore, the reference impedance is located at the center of this permissible range.

[0009] Here, "permissible range" refers to the allowable range of characteristic impedance of a printed circuit board (PCB) while meeting transmission characteristic specifications. For example, with a reference impedance of 50Ω, based on the formulas for signal reflectivity and VSWR calculation, as long as the characteristic impedance of the PCB is within the range of 50±4Ω, the VSWR will meet the specification of 1.1 or less. That is, 50±4Ω is the permissible range. Therefore, the specified range in this case is narrower than 50Ω±4Ω, for example, 50±2Ω. Furthermore, the permissible range expands when specifications are relaxed (VSWR below 1.3, etc.).

[0010] Existing inspection fixtures are extensions of fixtures used for inspecting open / short circuits. Therefore, the characteristic impedance of the inspection fixture is not considered. Consequently, the characteristic impedance of the signal lines, interlayer connections, and signal pins on the substrate deviates from the specified range. In particular, the characteristic impedance of interlayer connections and signal pins has never been considered.

[0011] Figure 19 This represents the results of determining the characteristic impedance of an existing examination fixture using the TDR (Time Domain Reflectometry) method. For example... Figure 19 As shown, the characteristic impedance in vias and signal pins deviates significantly from the specified range (50±2Ω). This means that existing inspection fixtures fail to adequately guarantee transmission characteristics, resulting in low inspection accuracy. Therefore, it is necessary to maintain a margin in inspection specifications (good / bad criteria), and the benchmark for judging the good / bad of printed circuit boards becomes correspondingly more stringent based on this margin. Consequently, a decrease in the yield of products such as FPCs is inevitable. Alternatively, it may be necessary to manufacture high-cost products that exceed specifications. Summary of the Invention

[0012] The present invention addresses the aforementioned technical problems. Specifically, the object of the present invention is to provide an inspection fixture capable of high-precision inspection of printed circuit boards transmitting high-frequency signals, and a method for adjusting the characteristic impedance of the inspection fixture.

[0013] The inspection fixture of the present invention is an inspection fixture for inspecting printed circuit boards, comprising: an inspection substrate having a signal line for transmitting an inspection signal output from a measuring instrument and a ground layer insulated from the signal line; a signal pin electrically connected to the signal line; a ground pin electrically connected to the ground layer; a holding portion for holding the signal pin and the ground pin; and a connector portion mounted on the inspection substrate for connecting the inspection substrate and the measuring instrument. The entire transmission area from the connector portion to the signal pin for transmitting the inspection signal is distributed throughout the inspection fixture. The characteristic impedance of the inspection fixture is within a specified range, which is narrower than the permissible range of the characteristic impedance of the printed circuit board, and a reference impedance is located at the center of the specified range.

[0014] Furthermore, in the inspection fixture, the allowable range is a range used to ensure that the voltage standing wave ratio (VSWR) of the printed wiring board is below 1.1.

[0015] Furthermore, in the inspection fixture, the reference impedance is 50Ω, and the allowable range is 50±4Ω.

[0016] Furthermore, in the inspection fixture, the eight ground pins are arranged on a grid in a manner that surrounds the signal pins.

[0017] Furthermore, the inspection fixture is equipped with only two ground pins that are separated from the signal pins.

[0018] Furthermore, in the inspection fixture, the signal line is disposed on the first main surface of the inspection substrate, the ground layer is disposed on the second main surface opposite to the first main surface, the signal pin is disposed on the second main surface side, and the inspection substrate also has an interlayer connection portion that electrically connects the signal line and the signal pin, wherein the characteristic impedance of the interlayer connection portion is within a specified range.

[0019] Furthermore, in the inspection fixture, the interlayer connection portion is a through hole with a solid structure, and the end of the interlayer connection portion is protected by a plating layer, with the signal pin abutting against the plating layer.

[0020] The method for adjusting the characteristic impedance of an inspection fixture according to an embodiment of the present invention is a method for bringing the characteristic impedance of an inspection fixture for inspecting printed circuit boards within a specified range. The inspection fixture includes: an inspection substrate having a signal line for transmitting an inspection signal output from a measuring instrument and a ground layer insulated from the signal line; a signal pin electrically connected to the signal line; a ground pin electrically connected to the ground layer; a holding portion for holding the signal pin and the ground pin; and a connector portion mounted on the inspection substrate for connecting the inspection substrate and the measuring instrument. The specified range is set to be greater than the capacitance of the characteristic impedance of the printed circuit board. The range is further narrowed, with the reference impedance set at the center of the specified range, and includes at least one of the following: reducing the spacing between the signal pin and the ground pin when the characteristic impedance of the inspection fixture is higher than the upper limit of the specified range; increasing the spacing between the signal pin and the ground pin when the characteristic impedance of the inspection fixture is lower than the lower limit of the specified range; increasing the number of ground pins when the characteristic impedance of the inspection fixture is higher than the upper limit of the specified range; and decreasing the number of ground pins when the characteristic impedance of the inspection fixture is lower than the lower limit of the specified range.

[0021] Another embodiment of the present invention provides a method for adjusting the characteristic impedance of an inspection fixture, which is used to bring the characteristic impedance of an inspection fixture for inspecting printed circuit boards within a specified range. The inspection fixture includes: an inspection substrate having a signal line for transmitting an inspection signal output from a measuring instrument and a ground layer insulated from the signal line; a signal pin electrically connected to the signal line; a ground pin electrically connected to the ground layer; a holding portion holding the signal pin and the ground pin; and a connector portion mounted on the inspection substrate for connecting the inspection substrate and the measuring instrument. The holding portion is an insulator and has a through-hole through which the signal pin and the ground pin are inserted. The specified range is set to be narrower than the permissible range of the characteristic impedance of the printed circuit board, and a reference impedance is set within the specified range. The center of the test fixture includes at least one of the following: increasing the pin diameter of the signal pin and the ground pin when the characteristic impedance of the test fixture is higher than the upper limit of the specified range; decreasing the pin diameter of the signal pin and the ground pin when the characteristic impedance of the test fixture is lower than the lower limit of the specified range; decreasing the diameter of the through hole of the holding portion when the characteristic impedance of the test fixture is higher than the upper limit of the specified range; increasing the diameter of the through hole when the characteristic impedance of the test fixture is lower than the lower limit of the specified range; increasing the capacitance of the insulator when the characteristic impedance of the test fixture is higher than the upper limit of the specified range; and decreasing the capacitance when the characteristic impedance of the test fixture is lower than the lower limit of the specified range.

[0022] According to this embodiment, an inspection fixture capable of high-precision inspection of printed wiring boards transmitting high-frequency signals and a method for adjusting the characteristic impedance of the inspection fixture can be provided. Attached Figure Description

[0023] Figure 1 This is a diagram showing a simplified structure of an inspection system with an inspection fixture having an implementation method. Figure 2 This is a top view of the inspection substrate of the inspection fixture in the embodiment. Figure 3 This is a bottom view of the inspection substrate of the inspection fixture in the embodiment. Figure 4 It is along Figure 2 and Figure 3 A cross-sectional view of the I-I line. Figure 5A This is a process cross-sectional view used to illustrate the manufacturing method of the inspection substrate for implementing the embodiments. Figure 5B yes Figure 5A The following is a process cross-sectional view illustrating the manufacturing method of the inspection substrate for the implementation method. Figure 5C yes Figure 5B The following is a process cross-sectional view illustrating the manufacturing method of the inspection substrate for the implementation method. Figure 6 It is a graph showing the relationship between the linewidth of the signal line on the test substrate and the characteristic impedance of the signal line. Figure 7 This is a top view used to illustrate the gap between the connecting pad and the ground layer of the through-hole in the substrate. Figure 8 It is a graph showing the relationship between the gap between the connector and the ground plane of the through-hole and the characteristic impedance of the through-hole. Figure 9 It is a diagram used to illustrate the configuration of signal pins and ground pins, as well as the number of ground pins. Figure 10 It is a graph showing the relationship between the number of ground pins and the characteristic impedance of signal pins. Figure 11 It is a graph showing the measurement results of the characteristic impedance of the inspection fixture of the embodiment. Figure 12 This is a partial cross-sectional view showing the signal pins and two ground pins held by the holding part and the held part of the inspection fixture. Figure 13 It means Figure 12 A graph showing the measurement results of the characteristic impedance of the inspection fixture under the pin configuration shown. Figure 14 This is a diagram illustrating the parameters used to adjust the characteristic impedance of a signal pin. Figure 15 These are diagrams used to illustrate two embodiments. Figure 16 This is a graph showing the measurement results of the characteristic impedance of the inspection fixture in two embodiments. Figure 17 This is a diagram showing a simplified structure of the inspection system of Modified Example 1 of the implementation method. Figure 18 This is a diagram showing a simplified structure of the inspection system of Modified Example 2 of the implementation method. Figure 19 It is a graph representing the measurement results of the characteristic impedance of existing inspection fixtures. Detailed Implementation

[0024] Hereinafter, this embodiment will be described with reference to the accompanying drawings. Furthermore, in each drawing, structural elements with equivalent functions are labeled with the same reference numerals. Additionally, the scaling ratio of each structural element has been appropriately changed to a size recognizable in the drawings.

[0025] <Inspection System 100> Reference Figure 1 This describes the inspection system 100 of this embodiment.

[0026] Inspection system 100 is an inspection system for inspecting printed wiring boards 200 such as flexible printed wiring boards (FPCs).

[0027] The inspection system 100 includes an inspection fixture 1 and a measuring instrument 50.

[0028] The inspection fixture 1 includes an inspection board 10, signal pins 21, ground pins 22, a holding part 30, and a connector part 40. The inspection fixture 1 will be described in detail later.

[0029] The measuring instrument 50 is a device for measuring the transmission characteristics (characteristic impedance, VSWR, crosstalk, transmission loss, etc.) of the printed wiring board 200, such as a vector network analyzer (VNA), a TDR oscilloscope, or a DC resistance meter.

[0030] The inspection fixture 1 and the measuring instrument 50 are connected by a cable 60. Specifically, the measuring instrument 50 is connected to the connector portion 40 of the inspection fixture 1 via the cable 60. In this embodiment, the connector portion 40 is a coaxial connector, and the cable 60 is a coaxial cable.

[0031] like Figure 1 As shown, during inspection, the pins of the inspection fixture 1 (signal pin 21 and ground pin 22, described later) contact the terminals (signal terminals and ground terminals) of the connector 210 mounted on the printed wiring board 200 of the object being inspected. Alternatively, if the connector 210 is not provided on the printed wiring board 200, the pins can directly contact the terminals of the printed wiring board 200.

[0032] Here, an example of a method for inspecting a printed wiring board 200 using an inspection system 100 is described.

[0033] First, the signal pin 21 of the inspection fixture 1 is brought into contact with the signal line (not shown) of the printed circuit board 200 to be inspected, and the ground pin 22 of the inspection fixture 1 is brought into contact with the ground layer (not shown) of the printed circuit board 200. Then, an inspection signal (pulse signal, etc.) is output from the measuring device 50 to the inspection fixture 1, and the measuring device 50 receives the reflected wave of the inspection signal. Furthermore, the measuring device 50 determines the condition of the printed circuit board 200 based on the received reflected wave.

[0034] Furthermore, the good / bad determination can be performed by the measuring instrument 50 or by an information processing device such as a computer connected to the measuring instrument 50. Additionally, a VSWR based on TDR conversion can be obtained, and the good / bad determination of the printed wiring board 200 can be performed based on the VSWR.

[0035] <Inspection Fixture 1> Next, refer to Figures 1-3 The structure of inspection fixture 1 will be explained in detail. Figure 1 The inspection substrate 10 shown is along Figure 2 and Figure 3 A cross-sectional view of the I-I line. Figure 2 and Figure 3 The top and bottom views of the inspected substrate 10 are shown respectively. Additionally, Figure 2 and Figure 3 The protective film 16 of the substrate 10 is not shown in the diagram.

[0036] The inspection fixture 1 includes an inspection board 10, signal pins 21, ground pins 22, a holding part 30, and a connector part 40.

[0037] The inspection substrate 10 is a rigid printed wiring board, which includes an insulating substrate 15 made of prepreg or the like, and is surface protected by a protective film 16 made of solder resist or the like.

[0038] The substrate 10 has signal lines 11, ground layers 12 and 13, and interlayer connection portions 14.

[0039] Signal line 11 is a transmission line used to transmit the inspection signal output from the measuring instrument 50. In this embodiment, as... Figure 1 As shown, the signal line 11 is configured as a microstrip line disposed on the upper surface of the inspection substrate 10.

[0040] Ground layers 12 and 13 are conductive layers insulated from signal line 11. In this embodiment, as... Figure 1 As shown, ground layer 12 is disposed on the lower surface of inspection substrate 10. Ground layer 13 is disposed on the upper surface of inspection substrate 10.

[0041] like Figure 2 and Figure 3 As shown, ground layers 12 and 13 cover most of the main surface of the inspection substrate 10. To suppress planar resonance, the inspection substrate 10 is provided with multiple through holes 17. Each through hole 17 electrically connects the ground layer 12 and the ground layer 13.

[0042] The through hole Hc is used to fix the connector part 40 to the mounting area A of the inspection substrate 10 with bolts or the like.

[0043] Ground layer 13 is formed to surround signal line 11. Ground layer 12 is formed to surround the connection pad (external connection pad 14a1 described later) of interlayer connection portion 14. As described later, the gap G between ground layer 12 and external connection pad 14a1 is adjusted to bring the characteristic impedance of interlayer connection portion 14 within a specified range.

[0044] Interlayer connection portion 14 electrically connects signal line 11 and signal pin 21. Interlayer connection portion 14 has an external connection pad 14a1. The external connection pad 14a1 is covered by plating layer 14b (described later). In this embodiment, interlayer connection portion 14 is a through-hole. However, interlayer connection portion 14 could also be a filled via or other interlayer connection means.

[0045] Signal pin 21 is a pin that contacts the signal terminal (not shown) of connector 210 mounted on the printed wiring board 200 under inspection. Alternatively, if the printed wiring board 200 does not have connector 210, signal pin 21 contacts a terminal on the printed wiring board 200.

[0046] Signal pin 21 is electrically connected to signal line 11 of the inspection substrate 10. In this embodiment, as... Figure 1 As shown, signal pin 21 is disposed on the lower surface of the inspection substrate 10 and contacts the external connection pad 14a1 of the interlayer connection portion 14. In this way, signal pin 21 is electrically connected to signal line 11 via interlayer connection portion 14.

[0047] The grounding pin 22 is in contact with the ground layer 12 of the inspection substrate 10. In this embodiment, the grounding pin 22 is also electrically connected to the ground layer 13 via a through-hole 17. In this embodiment, a plurality of grounding pins 22 are provided.

[0048] Signal pin 21 and ground pin 22 can be, for example, commercially available spring probes (so-called POGO pins). Spring probes are used in the electrical inspection of semiconductor components or printed circuit boards. Typically, commercially available spring probes have sufficient durability.

[0049] The holding part 30 holds the signal pin 21 and the ground pin 22. The signal pin 21, the ground pin 22, and the holding part 30 constitute a probe.

[0050] In this embodiment, the retaining part 30 is made of an insulating material such as resin and is fixed to the lower surface of the inspection substrate 10. The material of the retaining part 30 is, for example, polyphenylene sulfide (PPS).

[0051] The connector section 40 is mounted on the inspection substrate 10 and serves as a connector for connecting the inspection substrate 10 and the measuring instrument 50. The signal line (not shown) of the connector section 40 is electrically connected to the signal line 11 of the inspection substrate 10. The connector section 40 is, for example, a coaxial connector that connects to a coaxial cable.

[0052] Furthermore, the inspection fixture 1 described above has one signal line 11 and one corresponding signal pin 21. However, the inspection fixture 1 is not limited to this. That is, the inspection fixture 1 may have multiple signal lines 11 and multiple corresponding signal pins 21.

[0053] Here, refer to Figure 4 This describes an example of the inspection substrate 10. The inspection substrate 10 has a four-layer structure. The thickness of the inspection substrate 10 is, for example, about 1 mm. The inspection substrate 10, by having sufficient thickness, ensures the strength of the support holding portion 30 and the connector portion 40. Furthermore, the length of the signal line 11 of the inspection substrate 10 is about several centimeters (for example, 3 to 4 cm).

[0054] exist Figure 4 In the inspection substrate 10, ground layers 18 and 19 are provided inside the insulating substrate 15. Ground layers 18 and 19, like ground layer 12, are arranged to surround the interlayer connection portion 14. Ground layer 18 serves as the ground for the microstrip line, i.e., the signal line 11. Furthermore, by providing ground layers 18 and 19, the rigidity of the inspection substrate 10 can be improved.

[0055] The insulating substrate 15 is composed of three insulating substrates 15a, 15b, and 15c. A grounding layer 13 is provided on the upper surface of insulating substrate 15a. A grounding layer 18 is provided between insulating substrates 15a and 15b. Furthermore, a grounding layer 19 is provided between insulating substrates 15b and 15c. Additionally, a grounding layer 12 is provided on the lower surface of insulating substrate 15c.

[0056] A portion of the grounding layer 12 is not covered by the protective film 16 in a manner that allows it to contact the grounding pin 22. Additionally, this portion may undergo surface treatment such as gold plating.

[0057] Interlayer connection portion 14 has internal connection pads 14a2, 14a2 on the same surface (layer) as ground layers 18, 19. Interlayer connection portion 14 has internal connection pads 14a2 disposed inside the inspection substrate 10. Internal connection pads 14a2, 14a2 are disposed on the same surface as ground layers 18, 19. By adjusting the gap between internal connection pads 14a2 and ground layers 18 (19), the characteristic impedance of interlayer connection portion 14 is contained within a specified range.

[0058] Furthermore, in this embodiment, the gaps between the internal connecting plate 14a2 and the ground layer 18, the gaps between the internal connecting plate 14a2 and the ground layer 19, and the gap G between the ground layer 12 and the external connecting plate 14a1 are equal. This allows for more precise adjustment of the characteristic impedance of the interlayer connection portion 14, i.e., it is converging within a specified range. Additionally, the characteristic impedance of the interlayer connection portion 14 can be adjusted using only the gap between the internal connecting plate 14a2 and the ground layer 18. Furthermore, the gaps of each connecting plate (external connecting plate 14a1, internal connecting plate 14a2) can be changed independently and arbitrarily.

[0059] To ensure contact with the signal pin 21, the outer connecting pad 14a1 of the interlayer connection portion 14 is covered by a plating layer 14b. The signal pin 21 is configured to abut against the plating layer 14b. Furthermore, the plating layer 14b can be surface-treated by methods such as gold plating.

[0060] The interlayer connection portion 14 (through hole) is filled with resin 14c as a reinforcing material. Instead of resin, the interlayer connection portion 14 can be filled with conductive paste. Alternatively, the through hole can be filled by a coating process.

[0061] Thus, in this embodiment, the through-hole serving as the interlayer connection portion 14 has a solid structure. Furthermore, its end is protected by a plating layer 14b. This allows the signal pin 21 to contact the interlayer connection portion 14. Consequently, the transmission path of the inspection signal can be shortened.

[0062] in addition, Figure 4 In the example, the inspection substrate 10 has a four-layer structure. However, the structure of the inspection substrate 10 is not limited to this. That is, the inspection substrate 10 may have... Figure 1 The structure shown is a two-layer structure. Alternatively, the substrate 10 may also have a structure with three or five or more layers.

[0063] Furthermore, the location of the signal line 11 is not limited to the upper surface of the inspection substrate 10. For example, the signal line 11 can be provided on the lower surface of the inspection substrate 10. In this case, for example, the interlayer connection portion 14 is provided directly below the connector portion 40. Moreover, the signal line 11 extends from the lower end of the interlayer connection portion 14 toward the holding portion 30.

[0064] Furthermore, the interlayer connection portion 14 may have a structure that includes multiple through holes for connection.

[0065] In addition, Figure 4 In the inspection substrate 10, the ground layer 19 is not necessary. That is, the ground layer 19 can be omitted depending on the required characteristics.

[0066] Here, as an example of the manufacturing method of inspecting substrate 10, refer to Figures 5A to 5C illustrate Figure 4 The manufacturing method of the inspection substrate 10 shown.

[0067] like Figure 5A As shown in (1), a double-sided metal foil laminate is prepared, with metal foil 112 and metal foil 113 respectively provided on the upper and lower surfaces of the insulating substrate 111. The insulating substrate 111 is, for example, a prepreg (300 μm thick). The metal foils 112 and 113 are, for example, copper foils (18 μm thick).

[0068] Next, as Figure 5AAs shown in (2), metal foils 112 and 113 are patterned using a known photolithography method. This forms connection pads 112a and 113a and ground layers 112b and 113b. Connection pads 112a and 113a become internal connection pads of through-holes 118a formed through a process described later. The diameter of connection pads 112a and 113a is, for example, 350 μm.

[0069] Next, as Figure 5A As shown in (3), a first single-sided metal foil laminate with a metal foil 115 on one side of the insulating substrate 114 and a second single-sided metal foil laminate with a metal foil 117 on one side of the insulating substrate 116 are prepared. Subsequently, the first single-sided metal foil laminate and the second single-sided metal foil laminate are laminated onto the upper and lower surfaces of the wiring substrate obtained through the aforementioned process, respectively, to fabricate... Figure 5A The laminate shown in (3). Additionally, the insulating substrates 114 and 116 are, for example, prepreg (300 μm thick). The metal foils 115 and 117 are, for example, copper foil (18 μm thick).

[0070] Next, as Figure 5B As shown in (1), a through hole H1 is formed in the thickness direction through the laminate obtained in the previous process by drilling. The through hole H1 is formed by penetrating the connecting discs 112a and 113a. The diameter of the through hole H1 is, for example, 200 μm.

[0071] Next, as Figure 5B As shown in (2), an electroplating process is performed on the laminate having a through hole H1. This forms a plating layer 118 on the upper and lower surfaces of the laminate, as well as on the inner wall of the through hole H1. This creates a through hole 118a that electrically connects the metal foil 115 on the upper surface of the laminate and the metal foil 117 on the lower surface of the laminate. The thickness of the plating layer 118 is, for example, 25 μm.

[0072] Next, as Figure 5C As shown in (1), resin 121 is filled into the through hole 118a, and then plating layers 122 and 123 are formed by electroplating.

[0073] Next, as Figure 5C As shown in (2), the conductive layer of the outer layer of the laminate is patterned using a known photolithography method. In this way, signal lines 124, ground layers 125 and 126 and plating layer 127 are formed. Subsequently, a protective film of the outer layer is formed using solder resist or the like, and the inspection substrate 10 is obtained by performing surface treatment (gold plating or the like) on the terminal portions.

[0074] The inspection fixture 1 of this embodiment has been described above. The adjustment of each characteristic impedance will be described later. In the inspection fixture 1 described above, the characteristic impedance of the signal line 11 is within a specified range. Furthermore, the characteristic impedance of the signal pin 21 is also within the specified range. As described above, the reference impedance is located at the center of the specified range. Moreover, it is a narrower range than the permissible range of the characteristic impedance of the printed circuit board being inspected, for example, 50 ± 2 Ω.

[0075] According to this embodiment, the characteristic impedance of the interlayer connection portion 14 is also contained within the specified range. Thus, by containing the characteristic impedances of the signal line 11, the interlayer connection portion 14, and the signal pin 21 within the specified range, the characteristic impedance of the transmission area (region R1 described later) from the connector portion 40 to the signal pin 21, which transmits the inspection signal, is contained within the specified range—that is, the characteristic impedance throughout the entire inspection fixture 1. This improves the inspection accuracy of printed circuit boards transmitting high-frequency signals.

[0076] <Methods for converging characteristic impedance within a specified range> Reference Figures 6 to 11 This describes a method for converging the characteristic impedance of inspection fixture 1 within a specified range.

[0077] Furthermore, in the simulations and actual tests described below, the inspection substrate 10 used was... Figure 4 The inspection substrate described herein has a four-layer structure. The material of the holding part 30 is polyphenylene sulfide (permittivity Dk = 3.6). The pin spacing between the signal pin 21 and the ground pin 22 is set to 0.35 mm.

[0078] First, the method for converging the characteristic impedance of signal line 11 within a specified range will be explained.

[0079] By adjusting the line width of signal line 11, the characteristic impedance of signal line 11 can be narrowed down to a specified range. Specifically, the characteristic impedance of signal line 11 decreases as the line width increases.

[0080] Figure 6 This is a graph showing the relationship between the linewidth of signal line 11 and its characteristic impedance. In the graph, the values ​​in the hollow circles are characteristic impedance values ​​obtained from simulations based on electromagnetic field analysis. The black circles are characteristic impedance values ​​measured using the TDR method. Figure 8 , Figure 10 (The same applies). Additionally, in Figure 6 It is described Figure 11 The value is 900 psec.

[0081] from Figure 6It can be seen that when the line width of signal line 11 is 0.55mm, the characteristic impedance of signal line 11 becomes approximately 50Ω. In order to make the characteristic impedance of signal line 11 converge within the range of 50±2Ω, the line width only needs to be 0.55±0.04mm.

[0082] Next, a method for converging the characteristic impedance of the interlayer connection 14 within a specified range will be described.

[0083] By adjusting the gap G between the external connection plate 14a1 and the ground plane, the characteristic impedance of the interlayer connection portion 14 can be contained within a specified range. Specifically, as follows... Figure 7 As shown, the interlayer connection 14 has a higher characteristic impedance on the side with a larger gap G. Figure 8 This is a graph showing the relationship between the gap G and the characteristic impedance of the interlayer connection 14. Here, the gap between the ground layers 18, 19 and the inner connection plate 14a2 is also adjusted. That is, this gap is adjusted in the same way as the gap between the ground layer 12 and the outer connection plate 14a1. Furthermore, in Figure 8 It is described Figure 11 The value is 1115 psec.

[0084] from Figure 8 It can be seen that when the gap G is 0.25 mm, the characteristic impedance of the interlayer connection 14 is approximately 50 Ω. In order to make the characteristic impedance of the interlayer connection 14 converge within the specified range of 50 ± 2 Ω, the gap G only needs to be 0.25 ± 0.075 mm.

[0085] Next, we will explain how to bring the characteristic impedance of signal pin 21 within a specified range.

[0086] By adjusting the number of ground pins 22 configured around signal pin 21, the characteristic impedance of signal pin 21 can be converged within a specified range. Here, for example... Figure 9 As shown, the cases where the number of ground pins 22 is 2, 4, and 8 were evaluated. The holding part 30 is a block-shaped insulator with multiple through holes Hb, through which signal pins 21 and ground pins 22 are inserted.

[0087] In the case of two ground pins 22, the two ground pins 22 are arranged with a gap between them and the signal pins 21. In the case of four ground pins 22, the four ground pins 22 are arranged with a gap between them and the signal pins 21 in both the longitudinal and transverse directions. In the case of eight ground pins 22, the eight ground pins 22 are arranged with a gap between them and the signal pins 21 in the longitudinal, transverse, and diagonal directions. That is, the eight ground pins 22 are arranged on the grid in a manner that surrounds the signal pins 21. In all cases, the pin spacing (pitch) is fixed.

[0088] Furthermore, the larger the spacing between signal pin 21 and ground pin 22, and the larger the spacing between ground pins 22 (pin spacing), the higher the characteristic impedance of signal pin 21. In other words, the higher the pin configuration density, the lower the characteristic impedance of signal pin 21.

[0089] Figure 10 This is a graph showing the relationship between the number of ground pins 22 and the characteristic impedance of signal pins 21. Additionally, Figure 10 It is described Figure 11 The value is 1170 psec.

[0090] from Figure 10 It can be seen that the more ground pins 22 there are, the lower the characteristic impedance of the signal pin 21. When there are 8 ground pins 22, the characteristic impedance of the signal pin 21 becomes approximately 50Ω. Furthermore, when there are 4 ground pins 22, the characteristic impedance is approximately at the upper limit of the range of 50±2Ω. Moreover, when there are 2 ground pins 22, the characteristic impedance deviates significantly from the range of 50±2Ω. Therefore, to bring the characteristic impedance of the signal pin 21 within the range of 50±2Ω, it is sufficient to arrange 8 ground pins 22 around the signal pin 21.

[0091] As described above, by using the line width of signal line 11, the gap G, and the number of ground pins 22 as parameters (control factors), the characteristic impedances of signal line 11, interlayer connection 14, and signal pin 21 can be narrowed to within a specified range.

[0092] Figure 11 The figure shows the results of measuring the characteristic impedance of inspection fixture 1 using the TDR method. In the figure, region R1 represents the transmission area of ​​inspection fixture 1. Region R2 represents the transmission area of ​​the printed wiring board 200 being inspected. In inspection fixture 1 for measuring characteristic impedance, the line width of signal line 11 is adjusted to 0.55 mm. The gap G of interlayer connection 14 is adjusted to 0.25 mm. The number of grounding pins 22 is adjusted to 8 (spaced 0.35 mm).

[0093] from Figure 11 It can be seen that in region R1, which represents the entire transmission area of ​​inspection fixture 1, the characteristic impedance converges within the specified range of 50±2Ω. That is, the characteristic impedance converges within the specified range throughout the entire region from connector section 40 to signal pin 21 that transmits the inspection signal.

[0094] In addition, Figure 11In this process, the printed circuit board 200 under inspection is considered normal when its characteristic impedance is within the range of 46±4Ω. This range refers to the range where the VSWR of the printed circuit board 200 meets the specification of 1.1 or less. That is, 46±4Ω is the permissible range at this time. The specified range (50±2Ω) is narrower than the permissible range.

[0095] like Figure 10 As shown, when four or more ground pins 22 are configured, the characteristic impedance of the signal pin 21 can be narrowed to within the range of 50 ± 2 Ω. However, depending on the specifications of the terminals of the printed circuit board 200 under inspection, sometimes only two ground pins 22 can be configured, and it is also difficult to change (reduce) the pin spacing. Figure 12 This indicates the signal pin 21 and two ground pins 22 held by the holding unit 30.

[0096] Figure 13 This indicates that the TDR method was used to determine the presence of Figure 12 The characteristic impedance of the pin configuration check fixture 1 was determined. The line width of signal line 11 was adjusted to 0.55 mm. The gap G of the interlayer connection 14 was adjusted to 0.25 mm. From Figure 13 It can be seen that when there are two ground pins 22, the characteristic impedance of the signal pin 21 is about 56Ω, which greatly exceeds the upper limit (52Ω). In addition, when there are four ground pins 22, the characteristic impedance also reaches approximately the upper limit.

[0097] The following describes a method for adjusting the characteristic impedance of the signal pin 21 to a specified range even when the number of ground pins 22 is small, as described above.

[0098] Specifically, the characteristic impedance of the signal pin 21 is adjusted by adjusting the diameter of the signal pin 21 and the ground pin 22 (hereinafter also referred to as "pin diameter" or "pin diameter"), adjusting the diameter of the through hole Hb of the holding part 30 (hereinafter also referred to as "hole diameter"), or adjusting the capacitance of the insulating material constituting the holding part 30.

[0099] Figure 14 This describes the relationship between these parameters and the characteristic impedance of signal pin 21. Regarding the pin diameter, a larger diameter (thicker pin) results in a lower characteristic impedance for signal pin 21. Regarding the diameter of the via Hb in the holding portion 30, a smaller diameter results in a lower characteristic impedance for signal pin 21. Regarding the permittivity of the insulating material constituting the holding portion 30, a higher permittivity results in a lower characteristic impedance for signal pin 21.

[0100] Therefore, to reduce the characteristic impedance of signal pin 21, effective methods include increasing the pin diameter, decreasing the diameter of via Hb, or increasing the capacitance of the holding portion 30. That is, by adjusting at least one of these parameters, the characteristic impedance of signal pin 21 can be brought within a specified range. Next, two embodiments of controlling characteristic impedance through such adjustments will be described.

[0101] like Figure 15 As shown, in Embodiment 1, the capacitance of the holding part 30 is adjusted to 5.1. The pin diameter is adjusted to 0.20 mm. The aperture is adjusted to 0.24 mm. In Embodiment 2, the capacitance of the holding part 30 is adjusted to 3.6. The pin diameter is adjusted to 0.26 mm. The aperture is adjusted to 0.32 mm. Furthermore, in both embodiments, the number of ground pins 22 is always 2. The pin spacing is 0.35 mm. Both the signal pin 21 and the ground pin 22 use commercially available spring probes. The pin diameter mentioned above represents the diameter of the barrel portion of the spring probe.

[0102] In Embodiment 2, the capacitance of the holding part 30 is smaller than that in Embodiment 1. Therefore, a thicker pin was used. The aperture of the holding part 30 was adjusted to an appropriate value to match the pin diameter. The characteristic impedance of the signal pin 21 was measured using the TDR method. As a result, a value of 49 to 50 Ω was obtained in any embodiment. Figure 16 The results show the measurement results of the characteristic impedance of the signal pin 21 of the inspection fixture 1 in Examples 1 and 2.

[0103] In this way, even if the number of ground pins 22 cannot be increased and the pin spacing cannot be reduced, the characteristic impedance of the signal pin 21 can be brought within a specified range by adjusting the capacitance of the insulating material constituting the holding part 30, adjusting the pin diameter of the signal pin 21 and the ground pin 22, or adjusting the aperture of the through hole Hb of the holding part 30.

[0104] Next, two variations of the inspection system will be explained.

[0105] <Example 1 of the inspection system> Figure 17 This illustrates a simplified structure of the inspection system 100A in Modification 1. This modification relates to an inspection system for checking the transmission characteristics of printed circuit boards used to inspect objects such as transmission loss or crosstalk.

[0106] In the inspection system 100A of this modified example, the inspection fixture includes inspection fixture 1A connected to the input terminals of the printed wiring board 200 to be inspected and inspection fixture 1B connected to the output terminals of the printed wiring board 200. The structures of inspection fixtures 1A and 1B are the same as those of the aforementioned inspection fixture 1.

[0107] The measuring device 50 has a measuring interface 51 and a measuring interface 52. The measuring interface 51 is connected to the connector portion 40 of the inspection fixture 1A via a cable 60. The measuring interface 52 is connected to the connector portion 40 of the inspection fixture 1B via a cable 60.

[0108] In addition, by using a printed wiring board 200 with multiple signal lines for inspection, the transmission characteristics between signal lines, such as crosstalk, can also be checked. In this case, one set of inspection fixtures 1A and 1B is used for each signal line. Alternatively, inspection fixtures 1A and 1B with multiple signal lines 11 and multiple signal pins 21 can be used.

[0109] Here is an example of an inspection method for the printed wiring board 200 of the inspection system 100A.

[0110] First, the signal pin 21 of the inspection fixture 1A is contacted with one end (input terminal) of the signal line (not shown) of the printed wiring board 200 to be inspected. The ground pin 22 of the inspection fixture 1A is contacted with the ground layer (not shown) of the printed wiring board 200. The signal pin 21 of the inspection fixture 1B is contacted with the other end (output terminal) of the signal line of the printed wiring board 200. The ground pin 22 of the inspection fixture 1B is contacted with the ground layer of the printed wiring board 200. Then, an inspection signal is output to the inspection fixture 1A from the measurement interface 51 of the measuring instrument 50 (vector network analyzer). Furthermore, the measuring instrument 50 receives the inspection signal from the inspection fixture 1B via the measurement interface 52. Moreover, the measuring instrument 50 determines the condition of the printed wiring board 200 based on the inspection signal sent to the inspection fixture 1A and the inspection signal received from the inspection fixture 1B.

[0111] For example, the measuring device 50 obtains S-parameters based on the transmitted and received inspection signals. At this time, an inspection signal is output from the measuring interface 52 of the measuring device 50 to the inspection fixture 1B. Furthermore, the measuring device 50 receives inspection signals from the inspection fixture 1A via the measuring interface 51. Moreover, if the crosstalk calculated based on the S-parameters is within the normal range, the printed circuit board 200 is determined to be normal. Otherwise, the printed circuit board 200 is determined to be abnormal.

[0112] In addition, the measuring device 50 can determine whether it is good or bad. Alternatively, an information processing device such as a computer connected to the measuring device 50 can also determine whether it is good or bad.

[0113] Furthermore, in the above inspection method, by using a DC resistance meter as the measuring instrument 50, the transmission loss of the signal lines of the printed wiring board 200 can be checked.

[0114] <Modification 2 of the inspection system> Figure 18The simplified structure of the inspection system 100B of Modified Example 2 is shown. This modified example relates to an inspection system having an inspection fixture 1C, which includes an inspection substrate 10A without interlayer connection portion 14.

[0115] In the inspection substrate 10A of this modified example, one main surface of the insulating substrate 15 ( Figure 13 A signal line 11 and a ground layer (not shown) surrounding the signal line 11 are provided on the lower surface. The holding part 30 is fixed to the inspection substrate 10A with the signal pin 21 in contact with the signal line 11 and the ground pin 22 in contact with the ground layer. Thus, in this modified example, the signal line 11 and the signal pin 21 are directly connected.

[0116] According to this modified example, an inspection system can be constructed using an inspection substrate 10A that does not have an interlayer connection portion 14.

[0117] Alternatively, multiple inspection fixtures 1C can be used to construct a modified inspection system like the one described in Example 1, which is used to inspect transmission characteristics such as transmission loss and crosstalk.

[0118] As described above, those skilled in the art will be able to conceive of additional effects and various modifications of the present invention. However, this embodiment is not limited to the embodiments described above. Various additions, modifications, and partial deletions can be implemented within the scope of the claims and within the same essential meaning as those in the invention without departing from the spirit of the invention. Explanation of reference numerals in the attached figures

[0119] 1. 1A, 1B, 1C Inspection Fixtures 10. Inspect the substrate 11 signal lines 12, 13 grounding layers 14-layer inter-layer connection section 14a1 External Connection Disk 14a2 internal connection disk 14b coating 14c resin 15, 15a, 15b, 15c Insulating Substrate 16 Protective Film 17 Through Hole 18, 19 (inner layer) grounding layer 21 signal pins 22 Grounding pin 30. Maintaining section 40 Connector Section 50 measuring instruments 60 cable 100, 100A, 100B Inspection Systems 111, 114, 116 Insulating Substrate 112, 113, 115, 117 metal foil 112a and 113a connecting disks 112b and 113b grounding layers 118, 122, 123 plating layers 118a Through Hole 121 Resin 124 signal line 125, 126 grounding layers 127 Coating 200 Printed Wiring Board 210 connector Installation Area A G gap H1, Hb, Hc through holes R1 and R2 areas

Claims

1. An inspection fixture for inspecting printed wiring boards, the inspection fixture being characterized in that it comprises: The inspection substrate has signal lines for transmitting inspection signals output from a measuring instrument and a ground layer insulated from the signal lines; The signal pins are electrically connected to the signal lines; The grounding pin is electrically connected to the grounding layer; The holding portion of the signal pin and the ground pin is maintained; as well as A connector section, mounted on the inspection substrate, is used to connect the inspection substrate and the measuring instrument. The inspection fixture covers the entire transmission area from the connector to the signal pin, through which inspection signals are transmitted. By adjusting at least one of the following—the spacing between the signal pin and the ground pin, the number of ground pins, the pin diameters of the signal pin and the ground pin, the diameter of the through-hole in the holding part, and the capacitance of the holding part—within a specified range, the characteristic impedance of the inspection fixture is made to be within a specified range. The specified range of the characteristic impedance of the inspection fixture is narrower than the permissible range of the characteristic impedance of the printed wiring board. The reference impedance is located at the center of the specified range of the characteristic impedance of the inspection fixture. The allowable range is the range used to ensure that the voltage standing wave ratio (VSWR) of the printed wiring board is below 1.

1.

2. The inspection fixture according to claim 1, characterized in that, The reference impedance is 50Ω, and the allowable range is 50±4Ω.

3. The inspection fixture according to claim 1, characterized in that, The eight ground pins are arranged on a grid in a manner that surrounds the signal pins.

4. The inspection fixture according to claim 1, characterized in that, Only two ground pins are configured, separated from the signal pins.

5. The inspection fixture according to claim 1, characterized in that, The signal line is disposed on the first main surface of the inspection substrate. The grounding layer is disposed on the second main surface opposite to the first main surface. The signal pins are configured on the second main surface side. The inspection substrate also includes an interlayer connection portion that electrically connects the signal lines and the signal pins. The characteristic impedance convergence of the interlayer connection is within a specified range.

6. The inspection fixture according to claim 5, characterized in that, The interlayer connection is a through hole with a solid structure. The ends of the interlayer connection are protected by a plating layer. The signal pin abuts against the plating layer.

7. A method for adjusting the characteristic impedance of an inspection fixture, used to bring the characteristic impedance of the inspection fixture for inspecting printed circuit boards within a specified range, characterized in that... The inspection fixture includes: The inspection substrate has signal lines for transmitting inspection signals output from a measuring instrument and a ground layer insulated from the signal lines; The signal pins are electrically connected to the signal lines; A grounding pin electrically connected to the ground plane; a holding portion for holding the signal pin and the grounding pin; and a connector portion, mounted on the inspection substrate for connecting the inspection substrate and the measuring instrument. The specified range is set to be narrower than the permissible range of the characteristic impedance of the printed wiring board. Set the reference impedance at the center of the specified range. And includes at least one of the following: If the characteristic impedance of the inspection fixture is higher than the upper limit of the specified range, reduce the spacing between the signal pin and the ground pin; If the characteristic impedance of the inspection fixture is lower than the lower limit of the specified range, increase the spacing between the signal pin and the ground pin; If the characteristic impedance of the inspection fixture is higher than the upper limit of the specified range, increase the number of grounding pins; as well as If the characteristic impedance of the inspection fixture is lower than the lower limit of the specified range, reduce the number of grounding pins. The allowable range is the range used to ensure that the voltage standing wave ratio (VSWR) of the printed wiring board is below 1.

1.

8. The method for adjusting the characteristic impedance of the inspection fixture according to claim 7, characterized in that, The signal line is disposed on the first main surface of the inspection substrate. The grounding layer is disposed on the second main surface opposite to the first main surface. The signal pins are configured on the second main surface side. The inspection substrate also includes an interlayer connection portion that electrically connects the signal lines and the signal pins. And includes at least one of the following: When the characteristic impedance of the inspection fixture is higher than the upper limit of the specified range, the gap between the external connection plate of the interlayer connection and the ground layer is reduced, and If the characteristic impedance of the inspection fixture is lower than the lower limit of the specified range, the gap between the external connecting plate of the interlayer connection and the grounding layer is increased.

9. The method for adjusting the characteristic impedance of the inspection fixture according to claim 8, characterized in that, The interlayer connection portion has an internal connection disk disposed inside the inspection substrate. And includes at least one of the following: When the characteristic impedance of the inspection fixture is higher than the upper limit of the specified range, the gap between the internal connection plate and the grounding layer disposed on the same surface as the internal connection plate is reduced, and If the characteristic impedance of the inspection fixture is lower than the lower limit of the specified range, the gap between the internal connection plate and the grounding layer disposed on the same surface as the internal connection plate is increased.

10. A method for adjusting the characteristic impedance of an inspection fixture, used to bring the characteristic impedance of the inspection fixture for inspecting printed circuit boards within a specified range, characterized in that... The inspection fixture includes: The inspection substrate has signal lines for transmitting inspection signals output from a measuring instrument and a ground layer insulated from the signal lines; The signal pins are electrically connected to the signal lines; A grounding pin electrically connected to the ground plane; a holding portion for holding the signal pin and the grounding pin; a connector portion, mounted on the inspection substrate, for connecting the inspection substrate and the measuring instrument. The holding part is an insulator, and the holding part has a through hole through which the signal pin and the ground pin are inserted. The specified range is set to be narrower than the permissible range of the characteristic impedance of the printed wiring board. Set the reference impedance at the center of the specified range. And includes at least one of the following: If the characteristic impedance of the inspection fixture is higher than the upper limit of the specified range, increase the pin diameter of the signal pin and the ground pin. If the characteristic impedance of the inspection fixture is lower than the lower limit of the specified range, reduce the pin diameter of the signal pin and the ground pin; If the characteristic impedance of the inspection fixture is higher than the upper limit of the specified range, the diameter of the through hole in the holding part is reduced; If the characteristic impedance of the inspection fixture is lower than the lower limit of the specified range, the diameter of the through hole shall be increased. If the characteristic impedance of the inspection fixture is higher than the upper limit of the specified range, the permittivity of the insulator is increased; as well as If the characteristic impedance of the inspection fixture is lower than the lower limit of the specified range, the capacitance is reduced. The allowable range is the range used to ensure that the voltage standing wave ratio (VSWR) of the printed wiring board is below 1.

1.

11. The method for adjusting the characteristic impedance of the inspection fixture according to claim 10, characterized in that, The signal line is disposed on the first main surface of the inspection substrate. The grounding layer is disposed on the second main surface opposite to the first main surface. The signal pins are configured on the second main surface side. The inspection substrate also includes an interlayer connection portion that electrically connects the signal lines and the signal pins. And includes at least one of the following: When the characteristic impedance of the inspection fixture is higher than the upper limit of the specified range, the gap between the external connection plate of the interlayer connection and the ground layer is reduced, and If the characteristic impedance of the inspection fixture is lower than the lower limit of the specified range, the gap between the external connecting plate of the interlayer connection and the grounding layer is increased.

12. The method for adjusting the characteristic impedance of the inspection fixture according to claim 11, characterized in that, The interlayer connection portion has an internal connection disk disposed inside the inspection substrate. And includes at least one of the following: When the characteristic impedance of the inspection fixture is higher than the upper limit of the specified range, the gap between the internal connection plate and the grounding layer disposed on the same surface as the internal connection plate is reduced, and If the characteristic impedance of the inspection fixture is lower than the lower limit of the specified range, the gap between the internal connection plate and the grounding layer disposed on the same surface as the internal connection plate is increased.

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