TW202407348A - Inspection jig, and method for adjusting characteristic impedance of inspection jig - Google Patents

Abstract

The present invention makes it possible to highly accurately inspect a printed wiring board for transmitting high-frequency signals. An inspection jig 1 for inspecting a printed wiring board 200 comprises: an inspection board 10 having a signal line 11 for propagating an inspection signal output from a measuring instrument 50, and a ground layer 12 insulated from the signal line 11; a signal pin 21 electrically connected to the signal line 11; ground pins 22 electrically connected to the ground layer 12; a holding part 30 that holds the signal pin 21 and the ground pins 22; and a connector part 40 that is mounted on the inspection board 10 and is for connecting the inspection board 10 and the measuring instrument 50. The characteristic impedance of the inspection jig falls within a prescribed range over the entire propagation region where the inspection signal is propagated in the inspection jig, from the connector part to the signal pin. The prescribed range is narrower than the allowable range of the characteristic impedance of the printed wiring board. A reference impedance is positioned in the center of the prescribed range.

Description

Inspection fixtures and methods for adjusting characteristic impedance of inspection fixtures

The present invention relates to an inspection jig and a method for adjusting the characteristic impedance of the inspection jig.

In recent years, with the development of miniaturization and high-speed in electronic devices such as smartphones, notebook computers, digital cameras, and game consoles, the amount of information processing has increased dramatically. Therefore, there is a tendency for the signal speed to gradually increase. In addition, portable communication terminals such as smartphones will begin to shift to the next-generation communication standard 5G in 2019. In 5G, the frequency of signals sent and received by communication terminals changes from several GHz to 20 to 30 GHz. And it is predicted that the signal frequency will reach as high as 50GHz around 2023.

In response to this increase in signal speed, printed circuit board signal lines (high-speed transmission lines) need to meet various specifications regarding transmission characteristics. For example, in order to suppress the reflection of signals, specifications define the characteristic impedance and the Voltage Standing Wave Ratio (VSWR) that stipulates both the degree of reflection and the frequency. In addition, since the transmission loss tends to increase as the signal frequency becomes higher, the transmission loss of the line is sometimes limited by specifications. Furthermore, when multiple signal lines are provided on the same printed circuit board, the interference (crosstalk/isolation) between adjacent signal lines is also limited by specifications.

In order to confirm that the transmission characteristics specifications are met, the manufactured printed circuit boards are inspected. Inspection jigs are used to connect measuring instruments such as vector network analyzers and printed circuit boards of the inspection object. The inspection fixture includes: an inspection substrate equipped with signal lines that transmit inspection signals; a coaxial connector (SMA connector, etc.) installed on the inspection substrate for interface connection with the measuring instrument; and a contact probe (signal lead). pin and ground pin) of the probe section. Check that the substrate is provided with interlayer connections (through holes, etc.) that electrically connect signal lines and signal pins.

During inspection, the contact probe of the inspection jig is brought into contact with the signal terminals and grounding terminals of the printed circuit board to be inspected. The number and location of these signal terminals and ground terminals vary according to each type of printed circuit board (such as FPC and other products) of the inspection object. Therefore, the inspection jig is designed specifically for each type of printed circuit board to be inspected.

Patent Document 1 describes an invention related to a contact probe of an inspection jig.

existing technical documents

Patent document 1: Japanese Patent Publication No. 2020-085695

However, when ensuring the inspection accuracy of printed circuit boards for high-frequency signals of tens of GHz, the characteristic impedance of the inspection fixture is required to be within a specified range. Of course, the characteristic impedance of the inspection jig must be in a narrower range than the characteristic impedance of the printed circuit board allows. Therefore, the “prescribed range” within which the characteristic impedance of the inspection jig should be limited is a range narrower than the allowable range of the characteristic impedance of the printed circuit board to be inspected. Furthermore, the reference impedance is located in the center of the allowable range.

Here, the “allowable range” is the allowable range of the characteristic impedance of the printed circuit board under the condition that the specifications of the transmission characteristics are satisfied. For example, when the reference impedance is 50Ω, from the signal reflectivity and the calculation formula of VSWR, it can be known that as long as the characteristic impedance of the printed circuit board is within the range of 50±4Ω, the VSWR will meet the specification of less than 1.1. That is, 50±4Ω is the allowable range. Therefore, the specified range at this time is a narrower range than 50Ω±4Ω, such as 50±2Ω. In addition, after relaxing the specifications (VSWR is 1.3 or less, etc.), the allowable range is expanded.

Existing inspection fixtures constitute an extension of the fixture for checking open/short circuits. Therefore, the characteristic impedance of the inspection fixture is not considered. Therefore, check whether the characteristic impedance of the signal lines, interlayer connections, and signal pins on the substrate deviates from the specified range. In particular, no attention has been paid to the characteristic impedance of interlayer connections and signal pins.

Figure 19 shows the results of measuring the characteristic impedance of a conventional inspection jig using the TDR method (Time Domain Reflectometry). As shown in Figure 19, the characteristic impedance in the through hole and signal pin greatly deviates from the specified range (50±2Ω). That is, the existing inspection fixture cannot fully guarantee the transmission characteristics and the inspection accuracy is low. Therefore, it is necessary to maintain a margin in the inspection specifications (quality judgment), and the standards for quality judgment of printed circuit boards become more stringent in accordance with this margin. As a result, the yield of FPC and other products will inevitably decrease. Or, you have to manufacture over-standard and expensive products.

The present invention is used to solve the above technical problems. That is, an object of the present invention is to provide an inspection jig capable of high-precision inspection of a printed circuit board that transmits high-frequency signals, and a method for adjusting the characteristic impedance of the inspection jig.

An inspection jig according to an embodiment of the present invention is an inspection jig for inspecting a printed circuit board, and includes an inspection substrate, a signal line for transmitting an inspection signal output from a measuring device, 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 installed on the The inspection substrate is used to connect the inspection substrate and the measuring device, and the entire transmission area from the connector part to the signal pin for transmitting inspection signals in the inspection jig is provided. The characteristic impedance of the fixture is within a predetermined range that is narrower than an allowable range of the characteristic impedance of the printed circuit board, and the reference impedance is located at the center of the predetermined range.

In addition, in the inspection jig, the allowable range is a range that satisfies a voltage standing wave ratio (VSWR) of the printed circuit board of 1.1 or less.

In addition, in the inspection jig, the reference impedance is 50Ω, and the allowable range is 50±4Ω.

In addition, in the inspection fixture, the eight ground pins are arranged on the grid points to surround the signal pins.

In addition, in the inspection jig, only two ground pins are provided with the signal pins interposed therebetween.

Furthermore, in the inspection jig, the signal line is provided on the first main surface of the inspection substrate, and the ground layer is provided on the second main surface opposite to the first main surface, so The signal pin is disposed on the second main surface side, the inspection substrate further includes an interlayer connection portion electrically connecting the signal line and the signal pin, and the characteristic impedance of the interlayer connection portion is limited to a predetermined value. within the range.

In addition, in the inspection fixture, the interlayer connection part is a through hole with a solid structure, and the end of the interlayer connection part is protected by a plating layer, and the signal pin is in contact with the plating layer.

A method for adjusting the characteristic impedance of an inspection jig according to an embodiment of the present invention is a method for bringing the characteristic impedance of an inspection jig that inspects a printed circuit board, including an inspection substrate, into a predetermined range. , having a signal line for transmitting the inspection signal output from the 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 that holds 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, and setting the prescribed range to Narrower than the allowable range of the characteristic impedance of the printed circuit board, the reference impedance is set at the center of the specified range, and includes at least one of the following: when the characteristic impedance of the inspection fixture is higher than the specified range If the upper limit of the range is reached, reduce the distance 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 distance between the signal pin and the ground pin. The distance 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, increase the number of the ground pins; and When the characteristic impedance of the inspection fixture is lower than the lower limit of the prescribed range, the number of ground pins is reduced.

A method for adjusting the characteristic impedance of an inspection jig according to another embodiment of the present invention is a method for bringing the characteristic impedance of an inspection jig for inspecting a printed circuit board within a predetermined range. The inspection jig includes: The inspection substrate has a signal line for transmitting an inspection signal output from the measuring instrument and a ground layer insulated from the signal line; a signal pin electrically connected to the signal line; and a ground lead electrically connected to the ground layer. feet; a holding portion that holds the signal pin and the ground pin; a connector portion mounted on the inspection substrate for connecting the inspection substrate and the measuring instrument; and an insulator provided with the The through hole through which the signal pin and the ground pin are inserted sets the predetermined range to be narrower than the allowable range of the characteristic impedance of the printed circuit board, and sets the reference impedance at the center of the predetermined range. , and include at least one of the following: when the characteristic impedance of the inspection fixture is higher than the upper limit of the specified range, thicken the pin diameters of the signal pin and the ground pin; When the characteristic impedance of the inspection fixture is lower than the lower limit of the prescribed range, reduce the pin diameter of the signal pin and the ground pin; when the characteristic impedance of the inspection fixture is higher than When the upper limit of the prescribed range is reached, the diameter of the through hole of the holding part is reduced; when the characteristic impedance of the inspection jig is lower than the lower limit of the prescribed range, the diameter of the through hole is increased. the diameter of the through hole; when the characteristic impedance of the inspection jig is higher than the upper limit of the specified range, increase the permittivity of the insulator; and when the characteristic impedance of the inspection jig is lower than the specified range If the lower limit of the specified range is reached, the permittivity is lowered.

According to this embodiment, it is possible to provide an inspection jig capable of high-precision inspection of a printed circuit board that transmits high-frequency signals, and a method for adjusting the characteristic impedance of the inspection jig.

Hereinafter, this embodiment will be described with reference to the drawings. In addition, in each drawing, the same reference numeral is attached|subjected to the structural element which has an equivalent function. In addition, the scaling ratio of each structural element is appropriately changed to a size that can be recognized on the drawing.

＜Check System 100＞

Referring to FIG. 1 , the inspection system 100 according to this embodiment will be described.

The inspection system 100 is an inspection system for inspecting a printed circuit board 200 such as a flexible printed circuit board (FPC).

The inspection system 100 includes the inspection jig 1 and the measuring device 50 .

The inspection jig 1 includes an inspection substrate 10 , signal pins 21 , ground pins 22 , a holding part 30 and a connector part 40 . The inspection jig 1 will be described in detail later.

The measuring device 50 is a device that measures the transmission characteristics (characteristic impedance, VSWR, crosstalk, transmission loss, etc.) of the printed circuit board 200, and is, for example, a vector network analyzer (VNA), a TDR oscilloscope, or a DC resistance meter.

The inspection jig 1 and the measuring device 50 are connected via a cable 60 . Specifically, the measuring instrument 50 is connected to the connector part 40 of the inspection jig 1 via the cable 60 . In this embodiment, the connector part 40 is a coaxial connector, and the cable 60 is a coaxial cable.

As shown in FIG. 1 , during the inspection, the pins of the inspection jig 1 (signal pins 21 and ground pins 22 to be described later) and the terminals of the connector 210 (signal terminals) mounted on the printed circuit board 200 of the inspection object are and ground terminal). In addition, when the connector 210 is not provided on the printed circuit board 200, the pins may directly contact the terminals of the printed circuit board 200.

Here, an example of an inspection method of the printed circuit board 200 through the inspection system 100 will be described.

First, the signal pin 21 of the inspection jig 1 is brought into contact with the signal line (not shown) of the printed circuit board 200 of the inspection object, and the ground pin 22 of the inspection jig 1 is brought into contact with the ground layer (not shown) of the printed circuit board 200 icon) contact. Subsequently, an inspection signal (pulse signal, etc.) is output from the measuring device 50 to the inspection jig 1, and the measuring device 50 receives the reflected wave of the inspection signal. Furthermore, the measuring device 50 determines the quality of the printed circuit board 200 based on the received reflected waves.

In addition, the quality judgment can be performed by the measuring device 50 or by an information processing device such as a computer connected to the measuring device 50 . In addition, the VSWR based on TDR conversion can be obtained, and the quality of the printed circuit board 200 can be determined based on the VSWR.

＜Inspection jig 1＞

Next, the structure of the inspection jig 1 will be described in detail with reference to FIGS. 1 to 3 . The inspection substrate 10 shown in FIG. 1 is a cross-sectional view taken along line II in FIGS. 2 and 3 . 2 and 3 respectively show a top view and a bottom view of the inspection substrate 10 . In addition, the protective film 16 of the inspection substrate 10 is not shown in FIGS. 2 and 3 .

The inspection jig 1 includes an inspection substrate 10 , signal pins 21 , ground pins 22 , a holding part 30 and a connector part 40 .

The inspection substrate 10 is a rigid printed circuit board and includes an insulating base material 15 made of prepreg or the like, and has a surface protected by a protective film 16 made of a solder resist or the like.

The inspection substrate 10 has a signal line 11 , ground layers 12 and 13 , and an interlayer connection portion 14 .

The signal line 11 is a transmission line for transmitting the inspection signal output from the measuring device 50 . In this embodiment, as shown in FIG. 1 , the signal line 11 is configured as a microstrip line provided on the upper surface of the inspection substrate 10 .

The ground layers 12 and 13 are conductive layers insulated from the signal lines 11 . In this embodiment, as shown in FIG. 1 , the ground layer 12 is provided on the lower surface of the inspection substrate 10 . The ground layer 13 is provided on the upper surface of the inspection substrate.

As shown in FIGS. 2 and 3 , the ground layers 12 and 13 cover most of the main surface of the inspection substrate 10 . In order to suppress plane resonance, the inspection substrate 10 is provided with a plurality of through holes 17 . Each through hole 17 electrically connects the ground layer 12 and the ground layer 13 .

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.

The ground layer 13 is formed to surround the signal line 11 . The ground layer 12 is formed to surround a land (an external land 14a1 to be described later) of the interlayer connection portion 14. As will be described later, the gap G between the ground layer 12 and the external connection pad 14a1 is adjusted so that the characteristic impedance of the interlayer connection portion 14 falls within a predetermined range.

The interlayer connection part 14 electrically connects the signal line 11 and the signal pin 21 . The interlayer connection part 14 has an external connection land 14a1. The external connection pad 14a1 is covered with a plating layer 14b (described later). In addition, in this embodiment, the interlayer connection portion 14 is a through hole. However, the interlayer connection portion 14 may also be filled via holes or other interlayer connection means.

The signal pin 21 is a pin in contact with a signal terminal (not shown) of the connector 210 mounted on the printed circuit board 200 of the inspection object. In addition, when the printed circuit board 200 does not have the connector 210 , the signal pins 21 are in contact with the terminals on the printed circuit board 200 .

The signal pin 21 is electrically connected to the signal line 11 of the inspection substrate 10 . In this embodiment, as shown in FIG. 1 , the signal pin 21 is disposed on the lower surface side of the inspection substrate 10 and is in contact with the external connection pad 14a1 of the interlayer connection part 14. In this way, the signal pin 21 is electrically connected to the signal line 11 through the interlayer connection portion 14 .

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

The signal pin 21 and the ground pin 22 may be, for example, commercially available spring probes (so-called POGO pins). Spring probes are probes used for electrical inspection of semiconductor components or printed circuit boards. Typically, commercially available spring probes are sufficiently durable.

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.

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

The connector part 40 is mounted on the inspection substrate 10 and is a connector for connecting the inspection substrate 10 and the measuring device 50 . The signal line (not shown) of the connector part 40 is electrically connected to the signal line 11 of the inspection substrate 10 . The connector part 40 is a coaxial connector connected to a coaxial cable, for example.

In addition, the above-mentioned inspection jig 1 has one signal line 11 and one corresponding signal pin 21 . However, the inspection jig 1 is not limited to this. That is, the inspection jig 1 may have multiple signal lines 11 and multiple signal pins 21 corresponding thereto.

Here, an example of the inspection substrate 10 will be described with reference to FIG. 4 . The inspection substrate 10 has a four-layer structure. The thickness of the inspection substrate 10 is about 1 mm, for example. Check that the substrate 10 has sufficient thickness to ensure the strength of the support holding portion 30 and the connector portion 40 . In addition, the length of the signal line 11 of the inspection substrate 10 is about several centimeters (for example, 3 to 4 cm).

In the inspection substrate 10 of FIG. 4 , ground layers 18 and 19 are provided inside the insulating base material 15 . Like the ground layer 12 , the ground layers 18 and 19 are provided to surround the interlayer connection portion 14 . The ground layer 18 functions as a ground for the microstrip line, that is, the signal line 11 . In addition, by providing the ground layers 18 and 19, the rigidity of the inspection substrate 10 can be improved.

The insulating base material 15 is composed of three insulating base materials 15a, 15b, and 15c. A ground layer 13 is provided on the upper surface of the insulating base material 15a. A ground layer 18 is provided between the insulating base material 15a and the insulating base material 15b. Furthermore, a ground layer 19 is provided between the insulating base material 15b and the insulating base material 15c. Furthermore, the ground layer 12 is provided on the lower surface of the insulating base material 15c.

A part of the ground layer 12 is not covered by the protective film 16 so as to be in contact with the ground pin 22 . In addition, the above-mentioned portion may be surface-treated through gold plating or the like.

The interlayer connection portion 14 has internal lands 14a2 and 14a2 on the same plane (level) as the ground layers 18 and 19 . The interlayer connection part 14 has an internal connection land 14a2 provided inside the inspection substrate 10. The internal connection lands 14a2 and 14a2 are provided on the same surface as the ground layers 18 and 19. By adjusting the gap between the internal connection pad 14a2 and the ground layer 18 (19), the characteristic impedance of the interlayer connection portion 14 is constrained within a predetermined range.

In addition, in this embodiment, the gap between the internal connection pad 14a2 and the ground layer 18 and the gap between the internal connection pad 14a2 and the ground layer 19 are equal to the gap G between the ground layer 12 and the external connection pad 14a1. In this way, the characteristic impedance of the interlayer connection portion 14 can be adjusted more accurately, that is, it can be kept within a predetermined range. In addition, the characteristic impedance of the interlayer connection portion 14 may be adjusted using only the gap between the internal connection pad 14a2 and the ground layer 18. In addition, the clearance between each land (external land 14a1, internal land 14a2) can be changed independently and arbitrarily.

In order to ensure the contact with the signal pin 21, the external connection pad 14a1 of the interlayer connection part 14 is covered with the plating layer 14b. The signal pin 21 is arranged in contact with the plating layer 14b. In addition, the plating layer 14b may be surface-treated through gold plating or the like.

The interlayer connection portion 14 (through hole) is filled with resin 14c as a reinforcing material. Instead of resin, the interlayer connection portion 14 may be filled with conductive paste. Alternatively, fill the via via a coating process.

In this way, in this embodiment, the through hole serving as the interlayer connection portion 14 has a solid structure. Furthermore, the end portion is protected by the plating layer 14b. In this way, the signal pin 21 can be in contact with the interlayer connection portion 14 . In this way, the transmission path of the inspection signal can be shortened.

In addition, in the example of FIG. 4 , 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 a two-layer structure as shown in FIG. 1 . Alternatively, the inspection substrate 10 may have a structure of three or more layers.

In addition, the position where the signal line 11 is provided is not limited to the upper surface of the inspection substrate 10 . For example, the signal line 11 may be provided on the lower surface of the inspection substrate 10 . At this time, for example, the interlayer connection portion 14 is provided directly below the connector portion 40 . Furthermore, the signal line 11 extends from the lower end of the interlayer connection part 14 to the holding part 30 .

In addition, the interlayer connection portion 14 may have a structure including a plurality of connected via holes.

In addition, in the inspection substrate 10 of FIG. 4 , the ground layer 19 is not necessary. That is, depending on required characteristics, the inspection substrate 10 may be omitted.

Here, as an example of the method of manufacturing the inspection substrate 10 , the method of manufacturing the inspection substrate 10 shown in FIG. 4 will be described with reference to FIGS. 5A to 5C .

As shown in (1) of FIG. 5A , a double-sided metal foil-clad laminate in which metal foil 112 and metal foil 113 are respectively provided on the upper surface and the lower surface of insulating base material 111 is prepared. The insulating base material 111 is, for example, prepreg (300 μm thick). The metal foils 112 and 113 are, for example, copper foils (18 μm thick).

Next, as shown in (2) of FIG. 5A , the metal foils 112 and 113 are patterned using a known photolithography method. In this way, the connection lands 112a and 113a and the ground layers 112b and 113b are formed. The lands 112a and 113a serve as internal lands through the through-hole 118a formed in a process described below. The diameter of the connection lands 112a and 113a is, for example, 350 μm.

Next, as shown in (3) of FIG. 5A , a first single-sided metal foil laminate is prepared in which the metal foil 115 is provided on one side of the insulating base material 114 , and the metal foil is provided on one side of the insulating base material 116 . The second single side of foil 117 is clad with a metal foil laminate. Subsequently, a first single-sided metal foil laminate and a second single-sided metal foil laminate are respectively laminated on the upper surface and the lower surface of the wiring base material obtained through the above-mentioned process to produce a structure shown in (3) of FIG. 5A Laminates. In addition, the insulating base materials 114 and 116 are, for example, prepregs (300 μm thick). The metal foils 115 and 117 are, for example, copper foils (18 μm thick).

Next, as shown in (1) of FIG. 5B , a through hole H1 is formed by drilling processing to penetrate the laminate obtained in the previous step in the thickness direction. The through hole H1 is formed to penetrate the connection lands 112a and 113a. The diameter of the through hole H1 is, for example, 200 μm.

Next, as shown in (2) of FIG. 5B , a plating process is performed on the laminated body provided with the through hole H1 . In this way, the plating layer 118 is formed on the upper and lower surfaces of the laminate and the inner wall of the through hole H1. In this way, the through hole 118a electrically connecting the metal foil 115 on the upper surface of the laminate and the metal foil 117 on the lower surface of the laminate is formed. In addition, the thickness of the plating layer 118 is, for example, 25 μm.

Next, as shown in (1) of FIG. 5C , the through hole 118 a is filled with the resin 121 , and then, plating is performed to form the plating layers 122 and 123 .

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

The inspection jig 1 of this embodiment has been described above. Adjustment of each characteristic impedance will be described later. In the inspection jig 1 described above, the characteristic impedance of the signal line 11 is within a predetermined range. In addition, the characteristic impedance of the signal pin 21 is also within the specified range. As mentioned above, the reference impedance is located at the center of the specified range. Moreover, it is a narrower range than the allowable range of the characteristic impedance of the printed circuit board of the inspection object, for example, 50±2Ω.

According to this embodiment, the characteristic impedance of the interlayer connection portion 14 also falls within the predetermined range. In this way, by constraining the characteristic impedances of the signal line 11, the interlayer connection portion 14, and the signal pin 21 within a predetermined range, the transmission area from the connector portion 40 to the signal pin 21 (to be described later) in which the inspection signal is transmitted is The characteristic impedance of the region R1), that is, the characteristic impedance throughout the entire inspection jig 1 is restrained within a predetermined range. In this way, the inspection accuracy of printed circuit boards that transmit high-frequency signals can be improved.

＜Method to keep the characteristic impedance within the specified range＞

A method for limiting the characteristic impedance of the inspection jig 1 within a predetermined range will be described with reference to FIGS. 6 to 11 .

In addition, in the simulation and actual measurement described below, the inspection substrate having a four-layer structure described in FIG. 4 was used as the inspection substrate 10 . The material of the holding part 30 is polyphenylene sulfide (dictivity Dk=3.6). The pin spacing between the signal pin 21 and the ground pin 22 is set to 0.35mm.

First, a method of controlling the characteristic impedance of the signal line 11 within a predetermined range will be described.

By adjusting the line width of the signal line 11, the characteristic impedance of the signal line 11 can be constrained within a prescribed range. The characteristic impedance of a specific signal line 11 decreases as the line width increases.

FIG. 6 is a graph showing the relationship between the line width of the signal line 11 and the characteristic impedance of the signal line 11 . In the figure, the values in the open circles are the characteristic impedance values obtained based on the analogy based on electromagnetic field analysis. The black circle is the characteristic impedance value measured using the TDR method (the same applies to Figures 8 and 10). In addition, the value of 900 psec of FIG. 11 is plotted in FIG. 6 .

As can be seen from FIG. 6 , when the line width of the signal line 11 is 0.55 mm, the characteristic impedance of the signal line 11 is approximately 50Ω. In order to keep the characteristic impedance of the signal line 11 within the range of 50±2Ω, the line width only needs to be 0.55±0.04mm.

Next, a method of constraining the characteristic impedance of the interlayer connection portion 14 within a predetermined range will be described.

By adjusting the gap G between the external connection pad 14a1 and the ground layer, the characteristic impedance of the interlayer connection portion 14 can be constrained within a predetermined range. Specifically, as shown in FIG. 7 , the larger the gap G, the higher the characteristic impedance of the interlayer connection portion 14 . FIG. 8 is a graph showing the relationship between the gap G and the characteristic impedance of the interlayer connection portion 14 . Here, the gap between the ground layers 18, 19 and the internal land 14a2 is also adjusted. That is, the gap is adjusted so that it becomes the same as the gap between the ground layer 12 and the external land 14a1. In addition, the value of 1115 psec in FIG. 11 is plotted in FIG. 8 .

As can be seen from FIG. 8 , when the gap G is 0.25 mm, the characteristic impedance of the interlayer connection portion 14 is approximately 50Ω. In order to make the characteristic impedance of the interlayer connection portion 14 fall within the predetermined range of 50±2Ω, the gap G only needs to be 0.25±0.075 mm.

Next, a method of controlling the characteristic impedance of the signal pin 21 within a predetermined range will be described.

By adjusting the number of ground pins 22 arranged around the signal pin 21, the characteristic impedance of the signal pin 21 can be constrained within a prescribed range. Here, as shown in FIG. 9 , the cases where the number of ground pins 22 were 2, 4, and 8 were evaluated. The holding portion 30 is a block-shaped insulator provided with a plurality of through holes Hb into which the signal pins 21 and the ground pins 22 are inserted.

In the case of two, the two ground pins 22 are arranged across the signal pins 21 . In the case of four, the four ground pins 22 are arranged across the signal pins 21 in both vertical and horizontal directions. In the case of eight ground pins 22, the eight ground pins 22 are arranged across the signal pins 21 in longitudinal, transverse and diagonal directions. That is, the eight ground pins 22 are arranged on the grid points to surround the signal pins 21 . In either case, the pin spacing (pitch) is fixed.

In addition, the larger the distance between the signal pin 21 and the ground pin 22 and the distance between the ground pins 22 (pin distance), the higher the characteristic impedance of the signal pin 21 will be. In other words, the higher the pin configuration density, the lower the characteristic impedance of the signal pin 21 .

FIG. 10 is a graph showing the relationship between the number of ground pins 22 and the characteristic impedance of the signal pins 21 . In addition, the value of 1170 psec in FIG. 11 is plotted in FIG. 10 .

It can be seen from FIG. 10 that the more the number of ground pins 22 is, the lower the characteristic impedance of the signal pin 21 is. When the number of ground pins 22 is eight, the characteristic impedance of the signal pin 21 becomes approximately 50Ω. In addition, when the number of ground pins 22 is four, the characteristic impedance is approximately the upper limit of the range of 50±2Ω. Furthermore, when the number of ground pins 22 is two, the characteristic impedance greatly deviates from the range of 50±2Ω. Therefore, in order to keep the characteristic impedance of the signal pin 21 within the range of 50±2Ω, it is only necessary to arrange eight ground pins 22 around the signal pin 21 .

As mentioned above, using the line width of the signal line 11, the gap G and the number of ground pins 22 as parameters (control factors), the characteristic impedances of the signal line 11, the interlayer connection part 14 and the signal pin 21 can be narrowed respectively. Within the prescribed range.

FIG. 11 shows the results of measuring the characteristic impedance of the inspection jig 1 using the TDR method. In the figure, area R1 represents the transfer area of the inspection jig 1 . The area R2 represents the transfer area of the printed circuit board 200 of the inspection object. In the inspection jig 1 for measuring characteristic impedance, the line width of the signal line 11 is adjusted to 0.55 mm. The gap G of the interlayer connection portion 14 is adjusted to 0.25 mm. The number of ground pins 22 is adjusted to 8 (spacing 0.35mm).

As can be seen from FIG. 11 , in the region R1 representing the entire transmission region of the inspection jig 1 , the characteristic impedance falls within the predetermined range of 50±2Ω. That is, the characteristic impedance is within a predetermined range throughout the entire area from the connector portion 40 to the signal pin 21 where the inspection signal is transmitted.

In addition, in FIG. 11 , the printed circuit board 200 of the inspection object is judged to be normal when its characteristic impedance is within the range of 46±4Ω. The range is a range in which the VSWR of the printed circuit board 200 satisfies the specification of 1.1 or less. That is, at this time, 46±4Ω is the allowable range. The specified range (50±2Ω) is narrower than the allowable range.

As shown in FIG. 10 , when more than four ground pins 22 are configured, the characteristic impedance of the signal pin 21 can be narrowed within the range of 50±2Ω. However, depending on the terminal specifications of the printed circuit board 200 of the inspection object, only two ground pins 22 may be arranged, and it is also difficult to change (reduce) the pin spacing. FIG. 12 shows the signal pin 21 and the two ground pins 22 held by the holding part 30.

FIG. 13 shows the results of measuring the characteristic impedance of the inspection jig 1 having the pin configuration of FIG. 12 using the TDR method. The line width of signal line 11 is adjusted to 0.55mm. The gap G of the interlayer connection portion 14 is adjusted to 0.25 mm. It can be seen from Figure 13 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 the number of ground pins 22 is four, the characteristic impedance also reaches the approximate upper limit.

Hereinafter, a method of adjusting the characteristic impedance of the signal pins 21 within a predetermined range even when the number of ground pins 22 is small as described above will be described.

Specifically, by adjusting the diameter of the signal pin 21 and the ground pin 22 (hereinafter, also referred to as the "pin diameter" or "pin diameter"), the diameter of the through hole Hb of the holding part 30 (hereinafter, also referred to as the "hole diameter") ”), or the adjustment of the permittivity of the insulating material constituting the holding portion 30, to adjust the characteristic impedance of the signal pin 21.

Figure 14 shows the relationship between these parameters and the characteristic impedance of the signal pin 21. Regarding the diameter of the pin, the larger the diameter (bold pin), the lower the characteristic impedance of the signal pin 21. Regarding the diameter of the through hole Hb of the holding portion 30 , the smaller the diameter, the lower the characteristic impedance of the signal pin 21 . Regarding the permittivity of the insulating material constituting the holding portion 30 , the higher the permittivity, the lower the characteristic impedance of the signal pin 21 .

Therefore, in order to reduce the characteristic impedance of the signal pin 21 , effective methods are to increase the diameter of the pin, reduce the diameter of the through hole Hb, or increase the permittivity of the holding portion 30 . That is, by adjusting at least any one of these parameters, the characteristic impedance of the signal pin 21 can be constrained within a prescribed range. Next, two embodiments of controlling characteristic impedance through such adjustment will be described.

As shown in FIG. 15 , in Example 1, the permittivity of the holding portion 30 is adjusted to 5.1. The pin diameter is adjusted to 0.20mm. The aperture is adjusted to 0.24mm. In Example 2, the permittivity of the holding portion 30 is adjusted to 3.6. The pin diameter is adjusted to 0.26mm. The aperture is adjusted to 0.32mm. In addition, in any embodiment, the number of ground pins 22 is two. The pin spacing is 0.35mm. Commercially available spring probes are used for signal pin 21 and ground pin 22. The above pin diameter represents the diameter of the barrel of the spring probe.

In Example 2, the permittivity of the holding portion 30 is smaller than that in Example 1. Therefore, thicker pins are used. The hole diameter of the holding part 30 is adjusted to an appropriate value according to the diameter of the pin. The characteristic impedance of the signal pin 21 was measured by the TDR method. As a result, a value of 49 to 50Ω was obtained in all examples. FIG. 16 shows the measurement results of the characteristic impedance of the signal pin 21 of the inspection jig 1 of Examples 1 and 2.

In this way, even if the number of ground pins 22 cannot be increased and the pin spacing cannot be reduced, the signal pins 21 and the ground pins 22 can be adjusted by adjusting the permittivity of the insulating material constituting the holding portion 30 By adjusting the diameter of the pin or adjusting the diameter of the through hole Hb of the holding part 30, the characteristic impedance of the signal pin 21 is brought within a predetermined range.

Next, two modifications of the inspection system will be described.

<Modification 1 of the inspection system>

FIG. 17 shows the schematic structure of the inspection system 100A according to the first modification. This modification relates to an inspection system for inspecting the transmission characteristics of a printed circuit board of an inspection object such as transmission loss or crosstalk.

In the inspection system 100A of this modified example, the inspection jig includes an inspection jig 1A connected to the input terminal of the printed circuit board 200 of the inspection object, and an inspection jig 1B connected to the output terminal of the printed circuit board 200 . The structures of the inspection jigs 1A and 1B are the same as the inspection jig 1 described above.

The measuring device 50 has a measurement interface 51 and a measurement interface 52 . The measurement interface 51 is connected to the connector part 40 of the inspection jig 1A via a cable 60 . The measurement interface 52 is connected to the connector part 40 of the inspection jig 1B via a cable 60 .

In addition, by using the printed circuit board 200 as an inspection object having multiple signal lines, transmission characteristics between signal lines such as crosstalk can also be inspected. At this time, each signal line uses a set of inspection jigs 1A and 1B. Alternatively, inspection jigs 1A and 1B having multiple signal lines 11 and multiple signal pins 21 may be used.

Here, an example of an inspection method of the printed circuit board 200 in the transmission inspection system 100A will be described.

First, the signal pin 21 of the inspection jig 1A comes into contact with one end (input end) of the signal line (not shown) of the printed circuit board 200 of the inspection object. Check that the ground pin 22 of the fixture 1A is in contact with the ground layer (not shown) of the printed circuit board 200 . Check that the signal pin 21 of the fixture 1B is in contact with the other end (output end) of the signal line of the printed circuit board 200 . Check that the ground pin 22 of the jig 1B is in contact with the ground layer of the printed circuit board 200 . Then, an inspection signal is output from the measurement interface 51 of the measuring device 50 (vector network analyzer) to the inspection jig 1A. Furthermore, the measuring device 50 receives the inspection signal from the inspection jig 1B through the measurement interface 52 . Furthermore, the measuring device 50 determines the quality of the printed circuit board 200 based on the inspection signal sent to the inspection jig 1A and the inspection signal received from the inspection jig 1B.

For example, the measuring device 50 obtains the S parameter based on the sent inspection signal and the received inspection signal. At this time, the inspection signal is output from the measurement interface 52 of the measuring device 50 to the inspection jig 1B. Furthermore, the measuring device 50 receives the inspection signal from the inspection jig 1A through the measurement interface 51 . Furthermore, as long as the crosstalk calculated based on the S parameters is within the normal range, the printed circuit board 200 is determined to be normal. Otherwise, it is determined that the printed circuit board 200 is abnormal.

In addition, the measuring device 50 can perform quality judgment. Alternatively, an information processing device such as a computer connected to the measuring device 50 performs quality judgment.

In addition, in the above inspection method, by using a DC resistance meter as the measuring device 50 , the transmission loss of the signal line of the printed circuit board 200 can be inspected.

<Modification 2 of the inspection system>

FIG. 18 shows the schematic structure of the inspection system 100B according to Modification 2. This modification relates to an inspection system including an inspection jig 1C including an inspection substrate 10A that does not have the interlayer connection portion 14 .

In the inspection substrate 10A of this modification, a signal line 11 and a ground layer (not shown) surrounding the signal line 11 are provided on one main surface (lower surface in FIG. 13 ) of the insulating base material 15 . The holding part 30 is fixed on the inspection substrate 10A in such a manner that the signal pin 21 is in contact with the signal line 11 and the ground pin 22 is in contact with the ground layer. In this way, in this modification, the signal line 11 and the signal pin 21 are directly connected.

According to this modification, the inspection system can be configured using the inspection substrate 10A without the interlayer connection portion 14 .

In addition, a plurality of inspection jigs 1C can be used to constitute an inspection system for inspecting transmission characteristics such as transmission loss and crosstalk as in Modification 1.

As described above, those skilled in the art will be able to imagine additional effects and various modifications of the present invention. However, this embodiment is not limited to the above-described embodiment. Various additions, changes, and partial deletions may be made within the scope of the patent application and within the scope that is substantially the same and does not deviate from the spirit of the present invention.

1, 1A, 1B, 1C: Inspection fixture 10: Check the substrate 11:Signal line 12, 13: Ground layer 14: Interlayer connection part 14a1:External connection pad 14a2: Internal connecting disk 14b:Plating 14c: Resin 15, 15a, 15b, 15c: Insulating base material 16:Protective film 17:Through hole 18, 19: (inner layer) ground layer 21: Signal pin 22: Ground pin 30:Maintenance Department 40:Connector Department 50:Measuring instrument 60: Cable 100, 100A, 100B: Check system 111, 114, 116: Insulating base material 112, 113, 115, 117: Metal foil 112a, 113a: connection plate 112b, 113b: ground layer 118, 122, 123: coating 118a:Through hole 121:Resin 124:Signal line 125, 126: Ground layer 127:Plating 200:Printed circuit board 210: Connector A:Installation area G: Gap H1, Hb, Hc: through hole R1, R2: area

FIG. 1 is a diagram showing the schematic structure of an inspection system including an inspection jig according to an embodiment. FIG. 2 is a plan view of an inspection substrate included in the inspection jig according to the embodiment. 3 is a bottom view of the inspection substrate included in the inspection jig according to the embodiment. FIG. 4 is a cross-sectional view taken along line II in FIGS. 2 and 3 . 5A is a process cross-sectional view for explaining the manufacturing method of the inspection substrate according to the embodiment. FIG. 5B is a process cross-sectional view following FIG. 5A for explaining the manufacturing method of the inspection substrate according to the embodiment. FIG. 5C is a process cross-sectional view following FIG. 5B for explaining the manufacturing method of the inspection substrate according to the embodiment. FIG. 6 is a graph showing the relationship between the line width of the signal line of the inspection substrate and the characteristic impedance of the signal line. 7 is a plan view for explaining the inspection of the gap between the land and the ground layer of the through hole of the substrate. 8 is a graph showing the relationship between the gap between the land of the via hole and the ground layer and the characteristic impedance of the via hole. FIG. 9 is a diagram illustrating the arrangement of signal pins and ground pins and the number of ground pins. FIG. 10 is a graph showing the relationship between the number of ground pins and the characteristic impedance of the signal pins. FIG. 11 is a graph showing measurement results of characteristic impedance of the inspection jig according to the embodiment. 12 is a partial cross-sectional view showing the holding part of the inspection jig and the signal pins and two ground pins held by the holding part. FIG. 13 is a graph showing measurement results of characteristic impedance of the inspection jig in the case of the pin arrangement shown in FIG. 12 . FIG. 14 is a diagram illustrating parameters for adjusting the characteristic impedance of the signal pin. FIG. 15 is a diagram for explaining two embodiments. FIG. 16 is a graph showing measurement results of characteristic impedance of inspection jigs of two examples. FIG. 17 is a diagram showing the schematic structure of the inspection system according to Modification 1 of the embodiment. FIG. 18 is a diagram showing a schematic configuration of an inspection system according to Modification 2 of the embodiment. FIG. 19 is a graph showing measurement results of characteristic impedance of a conventional inspection jig.

1: Check the fixture

10: Check the substrate

11:Signal line

12, 13: Ground layer

14: Interlayer connection part

14a1:External connection pad

15: Insulation base material

16:Protective film

21: Signal pin

22: Ground pin

30:Maintenance Department

40:Connector Department

50:Measuring instrument

60: Cable

200:Printed circuit board

210: Connector

Claims (11)

An inspection jig for inspecting a printed circuit board, the inspection jig is characterized by 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 holding the signal pin and the ground pin; and a connector portion installed on the The inspection substrate is used to connect the inspection substrate and the measuring device, and the entire transmission area from the connector part to the signal pin for transmitting inspection signals in the inspection jig is provided. The characteristic impedance of the fixture is within a predetermined range that is narrower than an allowable range of the characteristic impedance of the printed circuit board, and the reference impedance is located at the center of the predetermined range. The inspection jig according to claim 1, wherein the allowable range is a range that satisfies the voltage standing wave ratio of the printed circuit board to be 1.1 or less. The inspection fixture according to claim 2, wherein the reference impedance is 50Ω and the allowable range is 50±4Ω. The inspection jig according to claim 1, characterized in that the eight ground pins are arranged on the grid points to surround the signal pins. The inspection jig according to claim 1, characterized in that only two ground pins are provided with the signal pins interposed therebetween. The inspection fixture according to claim 1, wherein the signal line is provided on the first main surface of the inspection substrate, and the ground layer is provided on the second side opposite to the first main surface. On the main surface, the signal pins are arranged on the second main surface side, and the inspection substrate further has an interlayer connection part that electrically connects the signal line and the signal pin. The characteristics of the interlayer connection part The impedance is within the specified range. The inspection fixture according to claim 6, wherein the interlayer connection part is a through hole with a solid structure, the end of the interlayer connection part is protected by a plating layer, and the signal pin is in contact with the plating. A method for adjusting the characteristic impedance of an inspection jig, which is used to make the characteristic impedance of an inspection jig for inspecting printed circuit boards converge within a prescribed range. The method for adjusting the characteristic impedance of the inspection jig is characterized in that: The inspection fixture includes: an inspection substrate having a signal line for transmitting an inspection signal output from the measuring instrument and a ground layer insulated from the signal line; a signal pin electrically connected to the signal line; and the ground layer a ground pin for electrical connection; a holding portion for holding the signal pin and the ground pin; and a connector portion installed on the inspection substrate for connecting the inspection substrate and the measuring instrument, The prescribed range is set to be narrower than the allowable range of the characteristic impedance of the printed circuit board, the reference impedance is set at the center of the prescribed range, and includes at least one of the following: on the inspection jig When the characteristic impedance is higher than the upper limit of the prescribed range, reduce the distance between the signal pin and the ground pin; when the characteristic impedance of the inspection fixture is lower than the prescribed range If the lower limit is reached, increase the distance 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 ground pin. The number of ground pins; and when the characteristic impedance of the inspection fixture is lower than the lower limit of the specified range, reduce the number of ground pins. A method for adjusting the characteristic impedance of an inspection jig, which is used to make the characteristic impedance of an inspection jig for inspecting printed circuit boards converge within a prescribed range. The method for adjusting the characteristic impedance of the inspection jig is characterized in that: The inspection jig includes: an inspection substrate having a signal line for transmitting an inspection signal output from the measuring instrument and a ground layer insulated from the signal line; a signal pin electrically connected to the signal line; and the ground layer an electrically connected ground pin; a holding portion that holds the signal pin and the ground pin; a connector portion mounted on the inspection substrate for connecting the inspection substrate and the measuring instrument; and an insulator , a through hole is provided through which the signal pin and the ground pin are inserted, the prescribed range is set to be narrower than the allowable range of the characteristic impedance of the printed circuit board, and the reference impedance is set to the The center of the specified range, 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, bold the connection between the signal pin and the ground pin Pin diameter; when 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; when the inspection fixture When the characteristic impedance is higher than the upper limit of the prescribed range, reduce the diameter of the through hole of the holding part; when the characteristic impedance of the inspection jig is lower than the lower limit of the prescribed range , increase the diameter of the through hole; when the characteristic impedance of the inspection fixture is higher than the upper limit of the specified range, increase the permittivity of the insulator; and when the inspection fixture When the characteristic impedance is lower than the lower limit of the predetermined range, the permittivity is reduced. The method for adjusting the characteristic impedance of an inspection fixture according to claim 8 or 9, wherein the signal line is provided on the first main surface of the inspection substrate, and the ground layer is provided on the first main surface of the inspection substrate. On the second main surface opposite to the main surface, the signal pins are arranged on the second main surface side, and the inspection substrate further includes an interlayer connection portion that electrically connects the signal lines and the signal pins. , and at least one of the following: when the characteristic impedance of the inspection fixture is higher than the upper limit of the specified range, reducing the resistance between the external connection pad of the interlayer connection part and the ground layer gap, and when the characteristic impedance of the inspection jig is lower than the lower limit of the prescribed range, increase the gap between the external connection pad of the interlayer connection part and the ground layer. The method for adjusting the characteristic impedance of an inspection fixture according to claim 10, wherein the interlayer connection portion has an internal connection pad disposed inside the inspection substrate, and includes at least one of the following: When the characteristic impedance of the inspection jig is higher than the upper limit of the prescribed range, reduce the gap between the internal connection pad and the ground layer provided on the same surface as the internal connection pad, and When the characteristic impedance of the inspection jig is lower than the lower limit of the predetermined range, the gap between the internal connection pad and the ground layer provided on the same surface as the internal connection pad is increased.