TWI858621B - Inspection jig and method for adjusting characteristic impedance of inspection jig - Google Patents

Abstract

The present invention provides an inspection jig and a method for adjusting the characteristic impedance of the inspection jig, which can inspect a printed circuit board that transmits a high-frequency signal with high precision. The inspection jig (1) for inspecting a printed circuit board (200) comprises: an inspection substrate (10) having a signal line (11) for transmitting an inspection signal output from a measuring device (50) and a grounding layer (12) insulated from the signal line (11); a signal pin (21) electrically connected to the signal line (11); a grounding pin (22) electrically connected to the grounding layer (12); a holding portion (30) for holding the signal pin (21) and the grounding 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 within a predetermined range over the entire transmission area from the connector portion to the signal pin where the inspection signal is transmitted in the inspection jig. The predetermined range is narrower than the allowable range of the characteristic impedance of the printed circuit board. Moreover, the reference impedance is located at the center of the predetermined range.

Description

Inspection jig and method for adjusting characteristic impedance of inspection jig

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

In recent years, the amount of information processing has increased dramatically in electronic devices such as smartphones, laptops, digital cameras, and game consoles as they have become smaller and faster. As a result, there is a tendency for signal speeds to gradually increase. In addition, portable communication terminals such as smartphones will begin to migrate to the next-generation communication standard 5G in 2019. In 5G, the frequency of signals sent and received by communication terminals will change from several GHz to 20 to 30 GHz. It is also predicted that the signal frequency will reach as high as 50 GHz around 2023.

In response to the increase in signal speed, the signal lines (high-speed transmission lines) of printed circuit boards need to meet various specifications regarding transmission characteristics. For example, in order to suppress signal reflection, the characteristic impedance and the voltage standing wave ratio (VSWR) that specifies the degree of reflection and frequency are defined by specifications. In addition, since the transmission loss tends to increase as the signal frequency increases, the transmission loss of the line is sometimes defined by specifications. Moreover, when multiple signal lines are provided on the same printed circuit board, the interference (crosstalk/isolation) between adjacent signal lines is also defined by specifications.

In order to confirm that the transmission characteristics meet the specifications, the manufactured printed circuit board is inspected. During the inspection, an inspection jig is used to connect the measuring instrument such as a vector network analyzer and the printed circuit board of the inspection object. The inspection jig includes: an inspection substrate with signal lines for transmitting inspection signals, a coaxial connector (SMA connector, etc.) mounted on the inspection substrate for interface connection with the measuring instrument, and a probe section with contact probes (signal pins and ground pins). The inspection substrate is provided with interlayer connection sections (through holes, etc.) that electrically connect the signal lines and signal pins.

During inspection, the contact probe of the inspection jig contacts the signal terminals and ground terminals of the printed circuit board to be inspected. The number and position of these signal terminals and ground terminals vary depending on the type of printed circuit board to be inspected (such as FPC and other products). Therefore, the inspection jig is designed specifically for each type of printed circuit board to be inspected.

In addition, Patent Document 1 describes the invention of a contact probe for an inspection jig.

Prior art literature

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

However, in order to ensure the inspection accuracy of printed circuit boards for high-frequency signals of tens of GHz, the characteristic impedance of the inspection jig must be within a specified range. Of course, the characteristic impedance of the inspection jig must be within a range narrower than the allowable range of the characteristic impedance of the printed circuit board. Therefore, the "specified range" to which the characteristic impedance of the inspection jig should be confined is a range narrower than the allowable range of the characteristic impedance of the printed circuit board to be inspected. In addition, the reference impedance is located at the center of the allowable range.

Here, the "allowable range" is the range of the characteristic impedance of the printed circuit board that is allowed under the condition that the transmission characteristics specification is met. For example, when the reference impedance is 50Ω, from the calculation formula of the signal reflectivity and VSWR, it can be seen 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. In other words, 50±4Ω is the allowable range. Therefore, the range specified at this time is a narrower range than 50Ω±4Ω, such as 50±2Ω. In addition, after relaxing the specification (VSWR is less than 1.3, etc.), the allowable range is expanded.

The existing inspection jig is an extension of the jig used to inspect open/short circuits. Therefore, the characteristic impedance of the inspection jig is not considered. As a result, the characteristic impedance of the signal line, interlayer connection, and signal pin of the inspection substrate deviates from the specified range. In particular, the characteristic impedance of the interlayer connection and signal pin has never been taken into consideration.

Figure 19 shows the results of measuring the characteristic impedance of existing inspection jigs using the TDR method (Time Domain Reflectometry). As shown in Figure 19, the characteristic impedance in the through-hole and signal pins deviates significantly from the specified range (50±2Ω). In other words, the existing inspection jig fails to fully guarantee the transmission characteristics and the inspection accuracy is low. Therefore, it is necessary to maintain a margin in the inspection specifications (good or bad judgment), and the standard for judging the quality of printed circuit boards becomes more stringent according to the margin. As a result, it is inevitable that the yield of products such as FPC will be reduced. Or, high-cost products that exceed the specifications have to be manufactured.

The present invention is used to solve the above-mentioned technical problems. That is, the purpose of the present invention is to provide a testing jig capable of accurately testing a printed circuit board that transmits a high-frequency signal and a method for adjusting the characteristic impedance of the testing jig.

The inspection jig of the embodiment of the present invention is an inspection jig for inspecting a printed circuit board, comprising: an inspection substrate having 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 for holding the signal pin and the ground pin; and a connector portion for mounting On the inspection substrate, a transmission area from the connector portion to the signal pin for connecting the inspection substrate and the measuring instrument is distributed throughout the inspection jig for transmitting the inspection signal, and the characteristic impedance of the inspection jig is within a specified range, the specified range is narrower than the allowable range of the characteristic impedance of the printed circuit board, and the reference impedance is located at the center of the specified range.

Furthermore, in the inspection jig, the allowable range is a range for satisfying a voltage-to-wave ratio (VSWR) of the printed circuit board of 1.1 or less.

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

Furthermore, in the inspection jig, the eight ground pins are arranged on a grid in a manner surrounding the signal pins.

In addition, in the inspection jig, only the two ground pins provided across the signal pin are provided.

In addition, in the inspection jig, the signal line is arranged on the first main surface of the inspection substrate, the ground layer is arranged on the second main surface on the opposite side of the first main surface, the signal pin is configured 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, and the characteristic impedance of the interlayer connection portion is confined within a specified range.

Furthermore, in the inspection jig, the interlayer connection portion is a through hole having a solid structure, an end portion of the interlayer connection portion is protected by a plating layer, and the signal pin abuts against the plating layer.

The method for adjusting the characteristic impedance of the inspection jig of the embodiment of the present invention is a method for making the characteristic impedance of the inspection jig for inspecting a printed circuit board converge within a specified range, wherein the inspection jig 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 and used to connect the inspection substrate and the measuring instrument, and setting the specified range to a capacitance greater than the characteristic impedance of the printed circuit board. The range of the inspection jig is narrower, the reference impedance is set at the center of the specified range, and at least one of the following is included: when the characteristic impedance of the inspection jig is higher than the upper limit of the specified range, the interval between the signal pin and the ground pin is reduced; when the characteristic impedance of the inspection jig is lower than the lower limit of the specified range, the interval between the signal pin and the ground pin is increased; when the characteristic impedance of the inspection jig is higher than the upper limit of the specified range, the number of the ground pins is increased; and when the characteristic impedance of the inspection jig is lower than the lower limit of the specified range, the number of the ground pins is reduced.

Another embodiment of the present invention is a method for adjusting the characteristic impedance of an inspection jig, which is used to make the characteristic impedance of the inspection jig for inspecting a printed circuit board converge within a specified range. The inspection jig includes: an inspection substrate having 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 layer electrically connected to the ground layer; The test substrate includes a first detection element and a second detection element, wherein the detection element is provided with a first detection element and a second detection element. The detection element includes a first detection element and a second detection element. The detection element includes a first detection element and a second detection element. The detection element includes a first detection element and a second detection element. The detection element includes a first detection element and a second detection element. The detection element includes a first detection element and a second detection element. At least one of the following is included: when the characteristic impedance of the inspection jig is higher than the upper limit of the specified range, the pin diameters of the signal pin and the ground pin are thickened; when the characteristic impedance of the inspection jig is lower than the lower limit of the specified range, the pin diameters of the signal pin and the ground pin are reduced; when the characteristic impedance of the inspection jig is higher than the upper limit of the specified range, , reducing the diameter of the through hole of the holding portion; when the characteristic impedance of the inspection jig is lower than the lower limit of the specified range, increasing the diameter of the through hole; when the characteristic impedance of the inspection jig is higher than the upper limit of the specified range, increasing the capacitance of the insulator; and when the characteristic impedance of the inspection jig is lower than the lower limit of the specified range, reducing the capacitance.

According to this embodiment, a test jig capable of testing a printed circuit board transmitting a high-frequency signal with high accuracy and a method for adjusting the characteristic impedance of the test jig can be provided.

Hereinafter, the present embodiment will be described with reference to the accompanying drawings. In addition, in each figure, the same figure mark is used for the structural elements having the same function. In addition, the scaling ratio of each structural element is appropriately changed to a size that can be recognized in the accompanying drawings.

＜Inspection System 100＞

Referring to FIG1 , an inspection system 100 according to the present embodiment is 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 an inspection jig 1 and a measuring device 50.

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

The measuring device 50 is a device for measuring 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 device 50 is connected to the connector portion 40 of the inspection jig 1 via the cable 60. In the present embodiment, the connector portion 40 is a coaxial connector, and the cable 60 is a coaxial cable.

As shown in FIG1 , during the inspection, the pins of the inspection jig 1 (the signal pin 21 and the ground pin 22 described later) contact the terminals (the signal terminal and the ground terminal) of the connector 210 mounted on the printed circuit board 200 of the inspection object. 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 a method for inspecting a printed circuit board 200 using 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. Then, the 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. And, the measuring device 50 makes a quality judgment of the printed circuit board 200 based on the received reflected wave.

The quality determination may be performed by the measuring device 50 or by an information processing device such as a computer connected to the measuring device 50. Alternatively, the quality determination of the printed circuit board 200 may be performed based on the VSWR obtained by TDR conversion.

＜Inspection jig 1＞

Next, the structure of the inspection jig 1 is specifically described with reference to Figs. 1 to 3. The inspection substrate 10 shown in Fig. 1 is a cross-sectional view along the line I-I of Figs. 2 and 3. Figs. 2 and 3 respectively show a top view and a bottom view of the inspection substrate 10. In addition, Figs. 2 and 3 do not show the protective film 16 of the inspection substrate 10.

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

The inspection substrate 10 is a rigid printed circuit board, including an insulating base material 15 made of prepreg or the like, and the surface of the substrate is 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 , 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 the present 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 line 11. In the present 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 Fig. 2 and Fig. 3, the ground layers 12 and 13 cover most of the main surface of the inspection substrate 10. In order to suppress the plane resonance, a plurality of through holes 17 are provided in the inspection substrate 10. 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 portion 40 to the mounting area A of the inspection substrate 10 by bolts or the like.

The ground layer 13 is formed to surround the signal line 11. The ground layer 12 is formed to surround the connection pad (external connection pad 14a1 described later) of the interlayer connection portion 14. As 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 portion 14 electrically connects the signal line 11 and the signal pin 21. The interlayer connection portion 14 has an external connection pad 14a1. The external connection pad 14a1 is covered by a plating layer 14b (described later). In addition, in the present embodiment, the interlayer connection portion 14 is a through hole. However, the interlayer connection portion 14 may also be other interlayer connection means such as a filled via.

The signal pin 21 is a pin that contacts a signal terminal (not shown) of a 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 pin 21 contacts a terminal 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 contacts the external connection pad 14a1 of the interlayer connection portion 14. In this way, the signal pin 21 is electrically connected to the signal line 11 via the interlayer connection portion 14.

The ground pin 22 is in contact with the ground layer 12 of the inspection substrate 10. In the present embodiment, the ground pin 22 is also electrically connected to the ground layer 13 via the through hole 17. In the present 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). The spring probes are probes used in electrical inspections of semiconductor components or printed circuit boards. Generally, commercially available spring probes have sufficient durability.

The holding portion 30 holds the signal pin 21 and the ground pin 22. The signal pin 21, the ground pin 22, and the holding portion 30 constitute a probe.

In the present embodiment, the holding 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 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, for example, a coaxial connector connected to a coaxial cable.

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

Here, referring to FIG. 4 , an example of the inspection substrate 10 is described. The inspection substrate 10 has a 4-layer structure. The thickness of the inspection substrate 10 is, for example, about 1 mm. The inspection substrate 10 has sufficient thickness to ensure the strength of the support and 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 FIG4 , ground layers 18 and 19 are provided inside the insulating base material 15. The ground layers 18 and 19 are provided in a manner surrounding the interlayer connection portion 14, similarly to the ground layer 12. The ground layer 18 has a function of grounding 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 substrate 15 is composed of three insulating substrates 15a, 15b, and 15c. A ground layer 13 is provided on the upper surface of the insulating substrate 15a. A ground layer 18 is provided between the insulating substrates 15a and 15b. Furthermore, a ground layer 19 is provided between the insulating substrates 15b and 15c. Furthermore, a ground layer 12 is provided on the lower surface of the insulating substrate 15c.

A portion 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 portion may be subjected to surface treatment such as gold plating.

The interlayer connection portion 14 has internal connection pads 14a2, 14a2 on the same plane (layer) as the ground layers 18, 19. The interlayer connection portion 14 has an internal connection pad 14a2 provided inside the inspection substrate 10. The internal connection pads 14a2, 14a2 are provided on the same plane as the ground layers 18, 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 limited within a predetermined range.

In addition, in the present embodiment, the gap between the internal connection land 14a2 and the ground layer 18 and the gap between the internal connection land 14a2 and the ground layer 19 are equal to the gap G between the ground layer 12 and the external connection land 14a1. In this way, the characteristic impedance of the interlayer connection portion 14 can be adjusted with higher accuracy, that is, it can be converged within a prescribed range. In addition, the characteristic impedance of the interlayer connection portion 14 can also be adjusted only by the gap between the internal connection land 14a2 and the ground layer 18. In addition, the gap between each connection land (external connection land 14a1, internal connection land 14a2) can be changed arbitrarily independently.

In order to ensure contact with the signal pin 21, the external connection pad 14a1 of the interlayer connection portion 14 is covered with a plating layer 14b. The signal pin 21 is arranged so as to abut against the plating layer 14b. In addition, the plating layer 14b can be surface-treated by gold plating or the like.

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

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

In the example of FIG4 , the inspection substrate 10 has a four-layer structure. However, the structure of the inspection substrate 10 is not limited thereto. That is, the inspection substrate 10 may have a two-layer structure as shown in FIG1 . Alternatively, the inspection substrate 10 may have a three-layer or five-layer structure or more.

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. In this case, 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 portion 14 toward the holding portion 30.

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

4, the ground layer 19 is not essential. That is, it can be omitted in the inspection substrate 10 according to the required characteristics.

Here, as an example of a method for manufacturing the inspection substrate 10, a method for 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 is prepared in which metal foil 112 and metal foil 113 are provided on the upper and lower surfaces of an insulating substrate 111, respectively. 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).

Next, as shown in (2) of FIG. 5A, the metal foils 112 and 113 are patterned by a known photolithography method. In this way, connection pads 112a and 113a and grounding layers 112b and 113b are formed. The connection pads 112a and 113a become internal connection pads of the through holes 118a formed by the process described later. The diameter of the connection pads 112a and 113a is, for example, 350 μm.

Next, as shown in (3) of FIG. 5A , a first single-sided metal foil laminate having a metal foil 115 on one side of an insulating substrate 114 and a second single-sided metal foil laminate having a metal foil 117 on one side of an insulating substrate 116 are prepared. Subsequently, the first single-sided metal foil laminate and the second single-sided metal foil laminate are laminated on the upper and lower surfaces of the wiring substrate obtained through the above-mentioned process, respectively, to produce the laminate shown in (3) of FIG. 5A . In addition, the insulating substrates 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 FIG5B, a through hole H1 is formed by drilling to penetrate the laminate obtained in the previous step in the thickness direction. The through hole H1 is formed to penetrate the connection pads 112a and 113a. The diameter of the through hole H1 is, for example, 200 μm.

Next, as shown in (2) of FIG. 5B , the laminate having the through hole H1 is subjected to electroplating. Thus, the upper and lower surfaces of the laminate and the inner wall of the through hole H1 are formed with a plating layer 118. Thus, a through hole 118a is formed 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.

Next, as shown in (1) of FIG. 5C , the through hole 118 a is filled with a resin 121 and then, plating layers 122 and 123 are formed by performing an electroplating process.

Next, as shown in (2) of FIG. 5C , the conductive layer of 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, a protective film of the outer layer is formed using a solder resist, and the surface treatment (gold plating, etc.) of the terminal portion is performed to obtain the inspection substrate 10.

The above describes the inspection jig 1 of the present embodiment. The adjustment of each characteristic impedance will be described later. In the above-mentioned inspection jig 1, the characteristic impedance of the signal line 11 is within a specified range. In addition, 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. And it is a range narrower 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 is also within the prescribed range. In this way, by confining the characteristic impedances of the signal line 11, the interlayer connection portion 14, and the signal pin 21 within the prescribed range, the characteristic impedance of the transmission area (region R1 described later) from the connector portion 40 to the signal pin 21 for transmitting the inspection signal, that is, the characteristic impedance of the entire inspection jig 1 is confined within the prescribed range. In this way, the inspection accuracy of the printed circuit board that transmits high-frequency signals can be improved.

<Methods for keeping characteristic impedance within a specified range>

6 to 11 , a method for limiting the characteristic impedance of the inspection jig 1 to a predetermined range will be described.

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

First, a method for keeping 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 brought within a specified range. Specifically, the characteristic impedance of the signal line 11 decreases as the line width increases.

FIG6 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 of the hollow circles are the characteristic impedance values obtained by analogy based on electromagnetic field analysis. The black circles are the characteristic impedance values measured by the TDR method (the same applies to FIG8 and FIG10). In addition, FIG6 depicts the value of 900psec of FIG11.

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 make the characteristic impedance of the signal line 11 within the range of 50±2Ω, the line width only needs to be 0.55±0.04 mm.

Next, a method for keeping the characteristic impedance of the interlayer connecting 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 brought within a predetermined range. Specifically, as shown in FIG7 , the larger the gap G is, the higher the characteristic impedance of the interlayer connection portion 14 is. FIG8 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 connection pad 14a2 is also adjusted. That is, the gap is adjusted in the same manner as the gap between the ground layer 12 and the external connection pad 14a1. In addition, the value of 1115 psec of FIG11 is depicted in FIG8 .

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 prescribed range of 50±2Ω, the gap G only needs to be 0.25±0.075 mm.

Next, a method for making the characteristic impedance of the signal pin 21 fall 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 brought within a predetermined range. Here, as shown in FIG9 , evaluation was performed for the cases where the number of ground pins 22 was 2, 4, and 8. The holding portion 30 is a block-shaped insulating body having a plurality of through holes Hb through which the signal pins 21 and the ground pins 22 are inserted.

In the case of two pins, two ground pins 22 are arranged across the signal pin 21. In the case of four pins, four ground pins 22 are arranged across the signal pin 21 in both the longitudinal and transverse directions. In the case of eight pins, eight ground pins 22 are arranged across the signal pin 21 in each of the longitudinal, transverse and oblique directions. That is, the eight ground pins 22 are arranged on the grid in a manner surrounding the signal pin 21. In either case, the pin interval (pitch) is fixed.

In addition, the larger the interval between the signal pin 21 and the ground pin 22, and the interval between the ground pins 22 (pin interval), the higher the characteristic impedance of the signal pin 21. In other words, the higher the pin arrangement 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. Fig. 10 also plots the value of 1170 psec in Fig. 11 .

As can be seen from FIG. 10 , the more the number of ground pins 22 is, the lower the characteristic impedance of the signal pin 21 is. When there are 8 ground pins 22, the characteristic impedance of the signal pin 21 is approximately 50Ω. In addition, when there are 4 ground pins 22, the characteristic impedance is approximately the upper limit of the range of 50±2Ω. Moreover, when there are 2 ground pins 22, the characteristic impedance deviates greatly from the range of 50±2Ω. Therefore, in order to make 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.

As described above, by 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 portion 14, and the signal pin 21 can be respectively within a specified range.

FIG11 shows the result of measuring the characteristic impedance of the inspection jig 1 using the TDR method. In the figure, region R1 represents the transmission area of the inspection jig 1. Region R2 represents the transmission area of the printed circuit board 200 of the inspection object. In the inspection jig 1 for measuring the characteristic impedance, the line width of the signal line 11 is adjusted to 0.55 mm. The gap G of the interlayer connection part 14 is adjusted to 0.25 mm. The number of ground pins 22 is adjusted to 8 (spacing 0.35 mm).

As can be seen from Fig. 11, the characteristic impedance is within the prescribed range of 50±2Ω in the region R1 representing the entire transmission area of the inspection jig 1. That is, the characteristic impedance is within the prescribed range throughout the entire region from the connector 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 the range in which the VSWR of the printed circuit board 200 meets 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 FIG10, when four or more ground pins 22 are arranged, 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 difficult to change (reduce) the pin interval. FIG12 shows the signal pin 21 and two ground pins 22 held by the holding portion 30.

FIG13 shows the result of measuring the characteristic impedance of the inspection jig 1 having the pin configuration of FIG12 by the TDR method. 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. As can be seen from FIG13, 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.

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

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

FIG14 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 (thicker the 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 capacitance of the insulating material constituting the holding portion 30, the higher the capacitance, the lower the characteristic impedance of the signal pin 21.

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

As shown in FIG15 , in Embodiment 1, the capacitance of the retaining portion 30 is adjusted to 5.1. The pin diameter is adjusted to 0.20 mm. The hole diameter is adjusted to 0.24 mm. In Embodiment 2, the capacitance of the retaining portion 30 is adjusted to 3.6. The pin diameter is adjusted to 0.26 mm. The hole diameter is adjusted to 0.32 mm. In addition, regardless of the embodiment, the number of ground pins 22 is 2. The pin spacing is 0.35 mm. Commercially available spring probes are used for both the signal pin 21 and the ground pin 22. The above-mentioned pin diameter represents the diameter of the barrel of the spring probe.

In Example 2, the capacitance of the retaining portion 30 is smaller than that of Example 1. Therefore, a thicker pin is used. The hole diameter of the retaining portion 30 is adjusted to an appropriate value in accordance with the pin diameter. 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 any of the examples. FIG. 16 shows the measurement results of the characteristic impedance of the signal pin 21 of the inspection fixture 1 of Examples 1 and 2.

In this way, even when 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 capacitive capacity of the insulating material constituting the retaining portion 30, adjusting the pin diameters of the signal pin 21 and the ground pin 22, or adjusting the aperture of the through hole Hb of the retaining portion 30.

Next, two variations of the inspection system are described.

＜Inspection system variation 1＞

Fig. 17 shows a schematic structure of an inspection system 100A according to Modification 1. This modification relates to an inspection system for inspecting transmission characteristics of a printed circuit board as an inspection object, such as transmission loss or crosstalk.

In the inspection system 100A of this modification, 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 those of the inspection jig 1 described above.

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

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

Here, an example of a method for inspecting the printed circuit board 200 using the inspection system 100A will be described.

First, the signal pin 21 of the inspection jig 1A contacts one end (input end) of the signal line (not shown) of the printed circuit board 200 of the inspection object. The ground pin 22 of the inspection jig 1A contacts the ground layer (not shown) of the printed circuit board 200. The signal pin 21 of the inspection jig 1B contacts the other end (output end) of the signal line of the printed circuit board 200. The ground pin 22 of the inspection jig 1B contacts the ground layer of the printed circuit board 200. Then, the inspection signal is output from the measurement interface 51 of the measuring device 50 (vector network analyzer) to the inspection jig 1A. In addition, the measuring device 50 receives the inspection signal from the inspection jig 1B through the measurement interface 52. Then, the measuring device 50 determines whether the printed circuit board 200 is good or bad 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. In addition, the measuring device 50 receives the inspection signal from the inspection jig 1A through the measurement interface 51. In addition, as long as the crosstalk calculated based on the S parameter is within the normal range, the printed circuit board 200 is judged to be normal. Otherwise, the printed circuit board 200 is judged to be abnormal.

In addition, the measuring device 50 can make a good or bad judgment. Alternatively, an information processing device such as a computer connected to the measuring device 50 can make a good or bad judgment.

Furthermore, 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.

＜Inspection system variation 2＞

18 shows a schematic structure of an inspection system 100B according to Modification 2. This modification relates to an inspection system including an inspection jig 1C including an inspection substrate 10A having no 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 portion 30 is fixed to the inspection substrate 10A in such a manner that the signal pin 21 contacts the signal line 11 and the ground pin 22 contacts the ground layer. Thus, in this modification, the signal line 11 and the signal pin 21 are directly connected.

According to this modification, an inspection system can be configured using the inspection substrate 10A that does not have the interlayer connecting portion 14.

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

As mentioned above, those skilled in the art can think of additional effects and various modifications of the present invention. However, the present implementation is not limited to the above implementation. Various additions, changes and partial deletions can be implemented within the scope of the patent application and the scope of the present invention.

1, 1A, 1B, 1C: Inspection jig 10: Inspection substrate 11: Signal line 12, 13: Ground layer 14: Interlayer connection 14a1: External connection plate 14a2: Internal connection plate 14b: Plating 14c: Resin 15, 15a, 15b, 15c: Insulation substrate 16: Protective film 17: Through hole 18, 19: (Inner layer) ground layer 21: Signal pin 22: Ground pin 30: Retaining part 40: Connector part 50: Measuring device 60: Cable 100, 100A, 100B: Inspection system 111, 114, 116: Insulating substrate 112, 113, 115, 117: Metal foil 112a, 113a: Connector pad 112b, 113b: Grounding layer 118, 122, 123: Plating 118a: Through hole 121: Resin 124: Signal line 125, 126: Grounding layer 127: Plating 200: Printed circuit board 210: Connector A: Mounting area G: Gap H1, Hb, Hc: Through hole R1, R2: Area

FIG. 1 is a diagram showing a simplified structure of an inspection system having an inspection jig according to an embodiment. FIG. 2 is a top view of an inspection substrate provided by the inspection jig according to an embodiment. FIG. 3 is a bottom view of an inspection substrate provided by the inspection jig according to an embodiment. FIG. 4 is a cross-sectional view along the line I-I of FIG. 2 and FIG. 3. FIG. 5A is a cross-sectional view for explaining a process of manufacturing a method for manufacturing an inspection substrate according to an embodiment. FIG. 5B is a cross-sectional view for explaining a process of manufacturing a method for manufacturing an inspection substrate according to an embodiment following FIG. 5A. FIG. 5C is a cross-sectional view for explaining a process of manufacturing a method for manufacturing an inspection substrate according to an embodiment following FIG. 5B. FIG. 6 is a graph showing the relationship between the line width of a signal line of an inspection substrate and the characteristic impedance of the signal line. FIG. 7 is a top view for explaining the gap between the connection pad and the ground layer of the through hole of the inspection substrate. FIG. 8 is a graph showing the relationship between the gap between the connection pad and the ground layer of the through hole and the characteristic impedance of the through hole. FIG. 9 is a graph for explaining the arrangement of the signal pin and the ground pin and the number of the ground pins. FIG. 10 is a graph showing the relationship between the number of the ground pins and the characteristic impedance of the signal pin. FIG. 11 is a graph showing the measurement results of the characteristic impedance of the inspection jig of the embodiment. FIG. 12 is a partial cross-sectional view showing the holding portion of the inspection jig and the signal pin and two ground pins held by the held portion. FIG. 13 is a graph showing the measurement results of the characteristic impedance of the inspection jig in the case of the pin configuration shown in FIG. 12. FIG. 14 is a graph illustrating the parameters used to adjust the characteristic impedance of the signal pin. FIG. 15 is a graph for illustrating two embodiments. FIG. 16 is a graph showing the measurement results of the characteristic impedance of the inspection jig of the two embodiments. FIG. 17 is a diagram showing the simplified structure of the inspection system of the variant 1 of the embodiment. FIG. 18 is a diagram showing the simplified structure of the inspection system of the variant 2 of the embodiment. FIG. 19 is a graph showing the measurement results of the characteristic impedance of the existing inspection jig.

1: Check the fixture

10: Check the substrate

11:Signal cable

12, 13: Ground layer

14: Interlayer connection part

14a1: External connection plate

15: Insulation substrate

16: Protective film

21: Signal pin

22: Ground pin

30:Maintenance Department

40: Connector part

50:Measurer

60: Cable

200: Printed circuit board

210: Connector

Claims (12)

A testing jig for testing a printed circuit board, the testing jig comprising: a testing substrate having a signal line for transmitting a testing signal output from a measuring instrument and a grounding layer insulated from the signal line; a signal pin electrically connected to the signal line; a grounding pin electrically connected to the grounding layer; a holding portion for holding the signal pin and the grounding pin; and a connector portion mounted on the testing substrate for connecting the testing substrate and the measuring instrument, the holding portion being provided with a connector for the signal pin and the grounding pin. The insulator of the through hole through which the ground pin is inserted can adjust at least one of the pin diameters of the signal pin and the ground pin, the diameter of the through hole, and the capacitance of the insulator in such a manner that the characteristic impedance of the inspection jig is within a specified range over the entire transmission area from the connector portion to the signal pin in the inspection jig, wherein the specified range is narrower than the allowable range of the characteristic impedance of the printed circuit board, and the reference impedance is located at the center of the specified range. The inspection jig as claimed in claim 1 is characterized in that it is possible to adjust at least one of the interval between the signal pin and the ground pin and the number of the ground pins in such a manner that the characteristic impedance of the inspection jig is within a prescribed range over the entire transmission area from the connector portion to the signal pin where the inspection signal is transmitted in the inspection jig. The inspection jig as described in claim 1 or 2 is characterized in that the allowable range is used to satisfy the voltage ripple ratio of the printed circuit board to be less than 1.1. The inspection jig as described in claim 3 is characterized in that the reference impedance is 50Ω and the allowable range is 50±4Ω. The inspection jig as described in claim 1 or 2 is characterized in that the eight ground pins are arranged on a grid in a manner surrounding the signal pins. The inspection jig as described in claim 1 or 2 is characterized in that only two ground pins are provided across the signal pins. The inspection jig as claimed in claim 1 or 2 is characterized in that the signal line is arranged on the first main surface of the inspection substrate, the ground layer is arranged on the second main surface opposite to the first main surface, the signal pin is arranged on the second main surface side, and the inspection substrate further has an interlayer connection portion for electrically connecting the signal line and the signal pin, and the characteristic impedance of the interlayer connection portion is within a specified range. The inspection jig as described in claim 7 is characterized in that the interlayer connection portion is a through hole with a solid structure, the end of the interlayer connection portion is protected by a plating layer, and the signal pin abuts against the plating layer. A method for adjusting the characteristic impedance of an inspection jig is used to make the characteristic impedance of the inspection jig for inspecting a printed circuit board converge within a specified range. The characteristic impedance adjustment method 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 a measuring instrument and a ground layer insulated from the signal line; a signal pin electrically connected to the signal line; and a ground layer insulated from the ground layer. A ground pin electrically connected to the printed circuit board; a holding portion as an insulator having a through hole for inserting the signal pin and the ground pin and holding the signal pin and the ground pin; and a connector portion mounted on the inspection substrate and used to connect the inspection substrate and the measuring instrument, setting the specified range to be narrower than the allowable range of the characteristic impedance of the printed circuit board, and setting the reference impedance within the specified range. , and at least one of the following is included: when the characteristic impedance of the inspection jig is higher than the upper limit of the specified range, the pin diameters of the signal pin and the ground pin are thickened; when the characteristic impedance of the inspection jig is lower than the lower limit of the specified range, the pin diameters of the signal pin and the ground pin are reduced; when the characteristic impedance of the inspection jig is higher than the upper limit of the specified range, the pin diameters of the signal pin and the ground pin are reduced. In the case of a lower limit of the specified range, the diameter of the through hole of the holding portion is reduced; in the case of a lower limit of the specified range of the characteristic impedance of the inspection jig, the diameter of the through hole is increased; in the case of a higher limit of the specified range of the characteristic impedance of the inspection jig, the capacitance of the insulator is increased; and in the case of a lower limit of the specified range of the characteristic impedance of the inspection jig, the capacitance is reduced. The method for adjusting the characteristic impedance of the inspection jig as described in claim 9 is characterized in that it includes at least one of the following: when the characteristic impedance of the inspection jig is higher than the upper limit of the specified range, the interval between the signal pin and the ground pin is reduced; when the characteristic impedance of the inspection jig is lower than the lower limit of the specified range, the interval between the signal pin and the ground pin is increased; when the characteristic impedance of the inspection jig is higher than the upper limit of the specified range, the number of the ground pins is increased; and when the characteristic impedance of the inspection jig is lower than the lower limit of the specified range, the number of the ground pins is reduced. The method for adjusting the characteristic impedance of the inspection jig as described in claim 9 or 10 is characterized in that the signal line is arranged on the first main surface of the inspection substrate, the ground layer is arranged on the second main surface on the opposite side of the first main surface, the signal pin is arranged on the second main surface side, and the inspection substrate also has an interlayer connection portion for electrically connecting the signal line and the signal pin, and includes at least one of the following: when the characteristic impedance of the inspection jig is higher than the upper limit of the specified range, the gap between the external connection pad of the interlayer connection portion and the ground layer is reduced, and when the characteristic impedance of the inspection jig is lower than the lower limit of the specified range, the gap between the external connection pad of the interlayer connection portion and the ground layer is increased. The method for adjusting the characteristic impedance of the inspection jig as described in claim 11 is characterized in that the interlayer connection portion has an internal connection pad arranged 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 specified range, reducing the gap between the internal connection pad and the ground layer arranged 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 specified range, increasing the gap between the internal connection pad and the ground layer arranged on the same surface as the internal connection pad.