JP7443598B2 - How to adjust the characteristic impedance of the inspection jig - Google Patents

Description

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 processed in electronic devices such as smartphones, notebook computers, digital cameras, and game consoles has rapidly increased as they have become smaller and faster. For this reason, there is a tendency for signal speeds to become faster and faster. In addition, mobile communication terminals such as smartphones are
The transition to the next generation communication standard, 5G, has begun in 2019. In 5G, the frequency of signals transmitted and received by communication terminals will range from several GHz to 20 to 30 GHz. Furthermore, the signal frequency is expected to increase to around 50 GHz around 2023.

In response to such increased signal speeds, signal lines (high-speed transmission lines) of printed wiring boards are required to satisfy various specifications regarding transmission characteristics. For example, in order to suppress signal reflection, the characteristic impedance and the voltage standing wave ratio (which specifies the degree of reflection together with the frequency)
VSWR (Voltage Standing Wave Ratio) is defined in the specifications. Furthermore, since transmission loss tends to increase as the signal frequency increases, the transmission loss of the line is sometimes specified in specifications. Furthermore, when multiple signal lines are provided on the same printed wiring board, interference (crosstalk/isolation) between adjacent signal lines may occur.
may be stipulated in the specifications.

Manufactured printed wiring boards are inspected to confirm that they satisfy specifications regarding transmission characteristics. For inspection, an inspection jig is used that connects a measuring instrument such as a vector network analyzer to a printed wiring board to be inspected. The test jig consists of a test board equipped with signal lines for the test signal to propagate, a coaxial connector (such as an SMA connector) mounted on the test board and connected to the port of the measuring instrument, and a contact probe (signal pin). and a ground pin). The test board is provided with an interlayer connection part (through hole, etc.) that electrically connects the signal line and the signal pin.

During inspection, the contact probe of the inspection jig is brought into contact with the signal terminal and ground terminal of the printed wiring board to be inspected. The number and position of these signal terminals and ground terminals differ depending on the type of printed wiring board (for example, a product such as an FPC) to be inspected. For this reason, the inspection jig is specially designed for each type of printed wiring board to be inspected.

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

JP2020-085695A

By the way, in order to ensure the inspection accuracy of printed wiring boards for signals with a high frequency of several tens of GHz, the characteristic impedance of the inspection jig is required to fall within a predetermined range. Naturally, the characteristic impedance of the inspection jig must be within a narrower range than the allowable range for the characteristic impedance of the printed wiring board. Therefore, the "predetermined range" in which the characteristic impedance of the test jig should fall is centered around the reference impedance and is narrower than the permissible range of the characteristic impedance of the printed wiring board to be tested.

Here, the "tolerable range" refers to an allowable range for the characteristic impedance of a printed wiring board under conditions that satisfy specifications regarding transmission characteristics. For example, if the reference impedance is 5
In the case of 0Ω, if the characteristic impedance of the printed wiring board is within the range of 50±4Ω, VSW
It can be seen from the signal reflectance and the formula for calculating VSWR that the specification that R is 1.1 or less is satisfied. That is, 50±4Ω is an acceptable range. Therefore, the predetermined range in this case is
The range is narrower than 50Ω±4Ω, for example, 50±2Ω. Note that when the specifications are relaxed (such as when the VSWR is 1.3 or less), the allowable range widens.

Since conventional test jigs are configured as an extension of those for testing open/short, the characteristic impedance of the test jig has not been taken into consideration. For this reason, the characteristic impedance of the signal line and interlayer connection portion of the test board, as well as the signal pin, may deviate from a predetermined range. In particular, no attention has been paid to the characteristic impedance of interlayer connections and signal pins.

Figure 19 shows the characteristic impedance of a conventional inspection jig using TDR (Time Domain Reflectometer).
y: Shows the results measured by the time-domain reflection) method. As shown in FIG. 19, the characteristic impedances of the through holes and signal pins are significantly outside the predetermined range (50±2Ω). That is, in the conventional inspection jig, transmission characteristics are not sufficiently ensured, and inspection accuracy is low. Therefore, it becomes necessary to provide a margin in the inspection specifications (pass/fail judgment), and the standards for the pass/fail judgment of printed wiring boards become stricter by this margin. As a result, the yield of products such as FPCs decreases, and products with over-specs and high costs are forced to be manufactured.

The present invention has been made based on the above technical recognition, and provides an inspection jig that can highly accurately inspect printed wiring boards that transmit high-frequency signals, and a method for adjusting the characteristic impedance of the inspection jig. The purpose is to

The inspection jig according to the present invention includes:
An inspection jig for inspecting printed wiring boards,
a test board having a signal line for propagating a test 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 part that holds the signal pin and the ground pin;
a connector section mounted on the test board for connecting the test board and the measuring device;
Equipped with
In the test jig, the characteristic impedance is contained within a predetermined range over the entire propagation region from the connector section to the signal pin in which the test signal is propagated, and the predetermined range is centered around the reference impedance, and the characteristic impedance is within a predetermined range. This range is narrower than the permissible range of the characteristic impedance of the printed wiring board.

Further, in the inspection jig,
The permissible range may be a range in which a voltage standing wave ratio (VSWR) of the printed wiring board satisfies 1.1 or less.

Further, in the inspection jig,
The reference impedance may be 50Ω, and the tolerance range may be 50±4Ω.

Further, in the inspection jig,
Eight of the ground pins may be arranged on a grid point so as to surround the signal pin.

Further, in the inspection jig,
There may be only two ground pins provided to sandwich the signal pin.

Further, in the inspection jig,
The signal line is provided on the first main surface of the test board,
The ground layer is provided on a second main surface opposite to the first main surface,
The signal pin is arranged on the second main surface side,
The test board further includes an interlayer connection part that electrically connects the signal line and the signal pin,
The characteristic impedance of the interlayer connection portion may be within the predetermined range.

Further, in the inspection jig,
The interlayer connection portion may be a through hole having a solid structure, an end portion of which is protected by cover plating, and the signal pin may be in contact with the cover plating.

A method for adjusting the characteristic impedance of an inspection jig according to the first aspect of the present invention includes:
A method for keeping the characteristic impedance of an inspection jig for inspecting a printed wiring board within a predetermined range,
The inspection jig is
a test board having a signal line for propagating a test 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 part that holds the signal pin and the ground pin;
a connector section mounted on the test board for connecting the test board and the measuring device;
Equipped with
The predetermined range is centered around a reference impedance and is narrower than an allowable range of characteristic impedance of the printed wiring board,
The characteristic impedance of the signal pin is
When the characteristic impedance is higher than the upper limit of the predetermined range, narrowing the distance between the signal pin and the ground pin, and when the characteristic impedance is lower than the lower limit of the predetermined range, widening the distance. and/or increasing the number of ground pins if the characteristic impedance is higher than the upper limit of the predetermined range, and decreasing the number of ground pins if the characteristic impedance is lower than the lower limit of the predetermined range. By this,
within the predetermined range.

A method for adjusting the characteristic impedance of an inspection jig according to the second aspect of the present invention includes:
A method for keeping the characteristic impedance of an inspection jig for inspecting a printed wiring board within a predetermined range,
The inspection jig is
a test board having a signal line for propagating a test 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 part that holds the signal pin and the ground pin;
a connector section mounted on the test board for connecting the test board and the measuring device;
Equipped with
The predetermined range is centered around a reference impedance and is narrower than an allowable range of characteristic impedance of the printed wiring board,
an insulator provided with a through hole through which the signal pin and the ground pin are inserted;
The characteristic impedance of the signal pin is
When the characteristic impedance is higher than the upper limit of the predetermined range, the pin diameters of the signal pin and the ground pin are increased, and when the characteristic impedance is lower than the lower limit of the predetermined range, the pin diameters of the signal pin and the ground pin are increased. By reducing the pin diameter,
When the characteristic impedance is higher than the upper limit of the predetermined range, the diameter of the through hole of the holding part is narrowed, and when the characteristic impedance is lower than the lower limit of the predetermined range, the diameter of the through hole is widened. and/or if the characteristic impedance is higher than the upper limit of the predetermined range, the dielectric constant of the insulator is increased, and if the characteristic impedance is lower than the lower limit of the predetermined range, the dielectric constant is increased. By lowering
within the predetermined range.

According to the present invention, it is possible to provide an inspection jig that can highly accurately inspect a printed wiring board that transmits a high-frequency signal, and a method for adjusting the characteristic impedance of the inspection jig.

1 is a diagram showing a schematic configuration of an inspection system having an inspection jig according to an embodiment. It is a top view of the test board which the test jig concerning an embodiment has. It is a bottom view of the inspection board which the inspection jig concerning an embodiment has. FIG. 4 is a sectional view taken along line II in FIGS. 2 and 3. FIG. FIG. 3 is a process cross-sectional view for explaining a method for manufacturing a test substrate according to an embodiment. FIG. 5A is a process cross-sectional view for explaining the method for manufacturing a test substrate according to the embodiment, following FIG. 5A. FIG. 5B is a process cross-sectional view for explaining the method for manufacturing a test substrate according to the embodiment, following FIG. 5B. 7 is a graph showing the relationship between the line width of the signal line of the test board and the characteristic impedance of the signal line. FIG. 3 is a plan view illustrating a land of a through hole of a test board and a gap between a ground layer. 7 is a graph showing the relationship between the gap between the land and ground layer of a through hole and the characteristic impedance of the through hole. FIG. 3 is a diagram for explaining the arrangement of signal pins and ground pins, and the number of ground pins. 7 is a graph showing the relationship between the number of ground pins and the characteristic impedance of a signal pin. It is a graph showing measurement results of characteristic impedance of the inspection jig according to the embodiment. FIG. 3 is a partial cross-sectional view showing a holding part of the inspection jig, and a signal pin and two ground pins held by the holding part. 13 is a graph showing measurement results of the characteristic impedance of the inspection jig in the case of the pin arrangement shown in FIG. 12. FIG. FIG. 3 is a diagram for explaining parameters for adjusting the characteristic impedance of a signal pin. It is a figure for explaining two examples. It is a graph which shows the measurement result of the characteristic impedance of the test|inspection jig based on two Examples. It is a figure showing the rough structure of the inspection system concerning modification 1 of an embodiment. It is a figure showing a rough structure of an inspection system concerning modification 2 of an embodiment. It is a graph which shows the measurement result of the characteristic impedance of the conventional inspection jig.

Embodiments according to the present invention will be described below with reference to the drawings. Note that in each figure, the same reference numerals are given to components having the same function. In addition, the scale ratio of each component is changed as appropriate in order to make the size recognizable on the drawing.

<Inspection system 100>
Referring to FIG. 1, an inspection system 100 according to an embodiment will be described.

The inspection system 100 includes a printed wiring board 2 such as a flexible printed wiring board (FPC).
This is an inspection system for inspecting 00.

The inspection system 100 includes an inspection jig 1 and a measuring instrument 50.

The inspection jig 1 includes a test board 10, a signal pin 21, a ground pin 22, a holding section 30, and a connector section 40. Details of the inspection jig 1 will be described later.

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

The inspection jig 1 and the measuring instrument 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 a cable 60. In this embodiment, the connector section 40 is a coaxial connector, and the cable 60 is a coaxial cable.

As shown in FIG. 1, during inspection, the pins (signal pins 21 and ground pins 22 described later) of the inspection jig 1 are connected to the terminals (signal terminals and ground pins) of the connector 210 mounted on the printed wiring board 200 to be inspected. terminal). Note that if the printed wiring board 200 is not provided with the connector 210, the pins may directly contact the terminals of the printed wiring board 200.

Here, an example of a method for inspecting printed wiring board 200 using 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 wiring board 200 to be inspected, and the ground pin 22 of the inspection jig 1 is connected to the ground layer (not shown) of the printed wiring board 200 to be inspected.
(not shown). Thereafter, a test signal (such as a pulse signal) is output from the measuring device 50 to the test jig 1, and the measuring device 50 receives a reflected wave of the test signal. Then, the measuring instrument 50 is
The quality of the printed wiring board 200 is determined based on the received reflected waves.

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

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

The inspection jig 1 includes a test board 10, a signal pin 21, a ground pin 22, a holding section 30, and a connector section 40.

The test board 10 is a rigid printed wiring board that includes an insulating base material 15 made of prepreg or the like, and whose surface is protected with a protective film 16 made of solder resist or the like.

The test board 10 has a signal line 11, ground layers 12 and 13, and an interlayer connection part 14.

The signal line 11 is a transmission line through which a test signal output from the measuring instrument 50 propagates.
In this embodiment, as shown in FIG. 1, the signal line 11 is provided on the upper surface of the test board 10 and is configured as a microstrip line.

The ground layers 12 and 13 are conductive layers insulated from the signal line 11. In this embodiment,
As shown in FIG. 1, the ground layer 12 is provided on the bottom surface of the test substrate 10, and the ground layer 13 is provided on the top surface of the test substrate.

The ground layers 12 and 13 are formed to cover most of the main surface of the test substrate 10, as shown in FIGS. 2 and 3. A plurality of through holes 17 are provided to suppress plane resonance.
is provided on the test board 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 part 40 to the mounting area A of the test board 10 with a bolt or the like.

The ground layer 13 is formed to surround the signal line 11. The ground layer 12 is formed so as to surround a land (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 land 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 land 14a1. The external land 14a1 is covered with lid plating 14b (described later). In this embodiment, the interlayer connection portion 14 is a through hole, but it may be another 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 wiring board 200 to be inspected. Note that the printed wiring board 200 is the connector 210.
If the signal pin 21 does not have a terminal, the signal pin 21 contacts a terminal on the printed wiring board 200.

The signal pin 21 is electrically connected to the signal line 11 of the test board 10. In this embodiment, as shown in FIG. 1, the signal pin 21 is arranged on the lower surface side of the test board 10 and is in contact with the external land 14a1 of the interlayer connection part 14. As a result, the signal pin 21 is connected to the interlayer connection portion 1
It is electrically connected to the signal line 11 via 4.

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

For example, a commercially available spring probe (so-called pogo pin) may be used as the signal pin 21 and the ground pin 22. Spring probes are used for electrical inspection of semiconductor components and printed wiring boards, and have sufficient durability.

The holding section 30 is configured to hold 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 test board 10. The material of the holding part 30 is, for example, polyphenylene sulfide (PPS).
).

The connector section 40 is mounted on the test board 10 and is a connector for connecting the test board 10 and the measuring instrument 50. A signal line (not shown) of the connector section 40 is electrically connected to the signal line 11 of the test board 10. The connector section 40 is, for example, a coaxial connector that connects to a coaxial cable.

Note that the above inspection jig 1 has one signal line 11 and one signal pin 21 corresponding to it.
However, it is not limited to this. That is, the inspection jig 1 may be configured to have a plurality of signal lines 11 and a plurality of signal pins 21 corresponding thereto.

Here, an example of the test substrate 10 will be described with reference to FIG. 4. This test substrate 10 has a four-layer structure and has a thickness of, for example, about 1 mm. By giving the test board 10 a sufficient thickness, the strength to support the holding section 30 and the connector section 40 is ensured. Further, the length of the signal line 11 of the test board 10 is about several cm (for example, 3 to 4 cm).

In the test board 10 of FIG. 4, ground layers 18 and 19 are provided inside the insulating base material 15. Similar to the ground layer 12, the ground layers 18 and 19 are provided so as to surround the interlayer connection portion 14. The ground layer 18 functions as a ground for the signal line 11, which is a microstrip line. Further, by providing the ground layers 18 and 19, the rigidity of the test board 10 can be increased.

The insulating base material 15 consists 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, and a ground layer 19 is provided between the insulating base material 15b and the insulating base material 15c. A ground layer 12 is provided on the lower surface of the insulating base material 15c.

A portion of the ground layer 12 is not covered with the protective film 16 so that it can come into contact with the ground pin 22. Note that this portion may be surface-treated with gold plating or the like.

The interlayer connection section 14 has internal lands 14a2 and 14a2 on the same surface (level) as the ground layers 18 and 19.
It has 14a2. The interlayer connection portion 14 is an internal land 14 provided inside the test board 10.
It has a2. Internal lands 14a2 and 14a2 are provided on the same surface as ground layers 18 and 19. The characteristic impedance of the interlayer connection portion 14 is kept within a predetermined range by adjusting the gap between the internal land 14a2 and the ground layer 18 (19).

In this embodiment, the gap between the internal land 14a2 and the ground layer 18 and the gap between the internal land 14a2 and the ground layer 19 are the same as the gap between the internal land 14a2 and the ground layer 19.
It is equal to the gap G between 1 and 1. Thereby, the characteristic impedance of the interlayer connection portion 14 can be adjusted with higher accuracy. Further, the characteristic impedance of the interlayer connection portion 14 may be adjusted only by the gap between the internal land 14a2 and the ground layer 18. Further, the gap between each land (outer land 14a1, inner land 14a2) may be independently and arbitrarily changed.

In order to ensure contact with the signal pin 21, the external land 14a1 of the interlayer connection portion 14 is
It is covered with lid plating 14b. The signal pin 21 is arranged so as to come into contact with the lid plating 14b. Note that the lid plating 14b may be surface-treated with gold plating or the like.

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

In this way, in this embodiment, the through hole as the interlayer connection part 14 has a solid structure,
By protecting the end portion with cover plating 14b, it is possible for signal pin 21 to contact interlayer connection portion 14. Thereby, the propagation path of the test signal can be shortened.

In the example of FIG. 4, the test substrate 10 has a four-layer structure, but the structure is not limited to this. That is, the test substrate 10 may have a two-layer structure as shown in FIG. 1, or may have a three-layer, five or more layer structure.

Further, the signal line 11 is not limited to being provided on the top surface of the test board 10, but may be provided on the bottom surface of the test board 10. In this case, for example, the interlayer connection portion 14 is located directly below the connector portion 40.
is provided, and the signal line 11 is provided so as to extend from the lower end of the interlayer connection portion 14 toward the holding portion 30.

Further, the interlayer connection portion 14 may be configured as a plurality of vias connected to each other.

Furthermore, in the test substrate 10 of FIG. 4, the ground layer 19 is not essential and can be omitted depending on required characteristics.

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

As shown in FIG. 5A(1), 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 base material 111, respectively. The insulating base material 111 is, for example, prepreg (300 μm thick), and the metal foils 112, 113 are, for example, copper foil (1
8 μm thick).

Next, as shown in FIG. 5A(2), the metal foils 112 and 113 are patterned using a known photofabrication method. This forms lands 112a, 113a and ground layers 112b, 113b. Lands 112a and 113a become internal lands of a through hole 118a formed in a process described later. The diameters of lands 112a and 113a are
For example, it is 350 μm.

Next, as shown in FIG. 5A(3), a first single-sided metal foil clad laminate is prepared, in which a metal foil 115 is provided on one side of an insulating base material 114, and a metal foil 117 is provided on one side of an insulating base material 116. A second single-sided metal foil-clad laminate is prepared. After that, a first single-sided metal foil-clad laminate and a second single-sided metal foil-clad laminate are respectively laminated on the upper and lower surfaces of the wiring base obtained in the previous step,
A laminate shown in FIG. 5A(3) is produced. Note that the insulating base materials 114 and 116 are, for example, prepreg (300 μm thick), and the metal foils 115 and 117 are, for example, copper foil (18 μm thick).
It is.

Next, as shown in FIG. 5B(1), 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 through the lands 112a and 113a. The diameter of the through hole H1 is, for example, 200 μm.

Next, as shown in FIG. 5B (2), plating is performed on the laminate provided with the through hole H1 to form a plating layer 118 on the upper and lower surfaces of the laminate and on the inner wall of the through hole H1. . This forms a through hole 118a that electrically connects the metal foil 115 on the top surface of the laminate and the metal foil 117 on the bottom surface of the laminate. Note that the thickness of the plating layer 118 is, for example, 25 mm.
It is μm.

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

Next, as shown in FIG. 5C (2), the outer conductive layer of the laminate is patterned by a known photofabrication method. As a result, the signal line 124, the ground layer 125,
126 and lid plating 127 are formed. Thereafter, a protective film as an outer layer is formed using a solder resist or the like, and the terminal portion is subjected to surface treatment (gold plating, etc.), thereby obtaining the test substrate 10.

The inspection jig 1 according to the present embodiment has been described above. The adjustment of each characteristic impedance will be described later, but in the inspection jig 1 described above, the characteristic impedance of the signal line 11 is within a predetermined range, and the characteristic impedance of the signal pin 21 is within the predetermined range. It is contained. As described above, the predetermined range is centered around the reference impedance and is narrower than the allowable range of the characteristic impedance of the printed wiring board to be inspected, and is, for example, 50±2Ω.

In this embodiment, the characteristic impedance of the interlayer connection portion 14 is also within the predetermined range. In this way, by keeping the characteristic impedances of the signal line 11, the interlayer connection part 14, and the signal pin 21 within a predetermined range, the connector part 40 through which the test signal propagates
The characteristic impedance of the propagation region (region R1 to be described later) from to the signal pin 21, that is,
The characteristic impedance throughout the inspection jig 1 is within a predetermined range. This makes it possible to improve the inspection accuracy of printed wiring boards that transmit high-frequency signals.

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

Note that, as conditions for the simulation and actual measurement described below, the test substrate 10 had a four-layer structure as described in FIG. 4. The material of the holding part 30 is polyphenylene sulfide (
Dielectric constant Dk=3.6), pin spacing between signal pin 21 and ground pin 22 is 0.35 mm
And so.

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

The characteristic impedance of the signal line 11 can be kept within a predetermined range by adjusting the line width of the signal line 11. Specifically, the characteristic impedance of the 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 graph, the value of the white circle is the characteristic impedance value obtained from simulation by electromagnetic field analysis, and the black circle is the characteristic impedance value actually measured by the TDR method (the same applies to FIGS. 8 and 10). In addition, in FIG. 6, the value of 900 psec in FIG. 11 is plotted.

From FIG. 6, it can be seen that 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 may be set to 0.55±0.04 mm.

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

The characteristic impedance of the interlayer connection portion 14 can be kept within a predetermined range by adjusting the gap G between the external land 14a1 and the ground layer. Specifically, as shown in FIG. 7, the larger the gap G is, the higher the characteristic impedance of the interlayer connection portion 14 is. 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 was also adjusted so that the gap was the same as the gap between the ground layer 12 and the external land 14a1. Note that in FIG. 8, the value of 1115 psec in FIG. 11 is plotted.

It can be seen from FIG. 8 that when the gap G is 0.25 mm, the characteristic impedance of the interlayer connection portion 14 is approximately 50Ω. In order to keep the characteristic impedance of the interlayer connection portion 14 within the predetermined range of 50±2Ω, the gap G may be set to 0.25±0.075 mm.

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

The characteristic impedance of the signal pin 21 can be kept within a predetermined range by adjusting the number of ground pins 22 arranged around the signal pin 21. Here, as shown in FIG. 9, evaluations were made for cases in which the number of ground pins 22 was two, four, and eight. The holding portion 30 is a block-shaped insulator provided with a plurality of through holes Hb through which the signal pin 21 and the ground pin 22 are inserted.

In the case of two, the two ground pins 22 are arranged to sandwich the signal pin 21.
In the case of four ground pins, the four ground pins 22 are arranged so as to sandwich the signal pin 21 in both the vertical and horizontal directions. In the case of eight ground pins 22, the eight ground pins 22 are arranged so as to sandwich the signal pin 21 in each of the vertical, horizontal and diagonal directions. That is, the eight ground pins 22 are arranged on lattice points so as to surround the signal pin 21.
In either case, the pin spacing (pitch) is constant.

Note that 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 becomes. In other words, the more densely the pins are arranged, the lower the characteristic impedance of the signal pin 21 becomes.

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

From FIG. 10, the characteristic impedance of the signal pin 21 decreases as the number of ground pins 22 increases, and when there are eight ground pins 22, the characteristic impedance of the signal pin 21 is approximately 5.
It can be seen that the value is 0Ω. Note that the characteristic impedance is approximately the upper limit of the range of 50±2Ω when there are four ground pins 22, and 50±2Ω when the number of ground pins 22 is two.
far outside the Ω range. Therefore, the characteristic impedance of signal pin 21 is set to 50±2Ω.
In order to keep it within the range of , it is sufficient to arrange eight ground pins 22 around the signal pin 21.

As described above, the characteristic impedance of the signal line 11, interlayer connection part 14, and signal pin 21 is controlled within a predetermined range by using the line width of the signal line 11, the gap G, and the number of ground pins 22 as parameters (control factors). You can make it fit.

FIG. 11 shows the results of measuring the characteristic impedance of the inspection jig 1 using the TDR method. In the figure, region R1 indicates the propagation region of the inspection jig 1, and region R2 indicates the propagation region of the printed wiring board 200 to be inspected. In the inspection jig 1 in which the characteristic impedance was measured, the line width of the signal line 11 was 0.55 mm, the gap G of the interlayer connection part 14 was 0.25 mm, and the number of ground pins 22 was 8 (pitch 0.35 mm). .

As can be seen from FIG. 11, in the region R1 indicating the entire propagation region of the inspection jig 1, the characteristic impedance is within a predetermined range of 50±2Ω. That is, the characteristic impedance falls within a predetermined range over the entire region from the connector section 40 to the signal pin 21 through which the test signal propagates.

Note that in FIG. 11, the printed wiring board 200 to be inspected is determined to be normal if its characteristic impedance is within the range of 46±4Ω. This range is a range that satisfies the specification that the VSWR of the printed wiring board 200 is 1.1 or less. That is, in this case, 46±4Ω is the allowable range. The predetermined range (50±2Ω) is narrower than the allowable range.

As shown in FIG. 10, when four or more ground pins 22 are arranged, the characteristic impedance of the signal pin 21 can be kept within the range of 50±2Ω. However, depending on the specifications of the terminals of the printed wiring board 200 to be inspected, only up to two ground pins 22 can be arranged, and it may be difficult to change (narrow) the pin spacing. FIG. 12 shows the signal pin 21 and 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 arrangement shown in FIG. 12 using the TDR method. The line width of the signal line 11 was 0.55 mm, and the gap G between the interlayer connections 14 was 0.25 mm. As can be seen from FIG. 13, when there are two ground pins 22, the characteristic impedance of the signal pin 21 is approximately 56Ω, which greatly exceeds the upper limit (52Ω). Also, when there are four ground pins 22, the characteristic impedance almost reaches its upper limit.

In the following, even when the number of ground pins 22 is small as described above, the signal pin 2
A method for adjusting the characteristic impedance of No. 1 within a predetermined range will be described.

Specifically, the diameters of the signal pin 21 and the ground pin 22 (hereinafter also simply referred to as "pin diameter" or "pin diameter"), the diameter of the through hole Hb of the holding part 30 (hereinafter simply referred to as "hole diameter") ), the characteristic impedance of the signal pin 21 is adjusted by the dielectric constant of the insulating material forming the holding part 30.

FIG. 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 (the 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 narrower the diameter, the lower the characteristic impedance of the signal pin 21. Regarding the dielectric constant of the insulating material that constitutes the holding portion 30, the higher the dielectric constant, the lower the characteristic impedance of the signal pin 21 is.

Therefore, in order to reduce the characteristic impedance of the signal pin 21, the diameter of the pin may be increased, the diameter of the through hole Hb may be reduced, and the dielectric constant of the holding portion 30 may be increased. Of course, the characteristic impedance of the signal pin 21 may be kept within a predetermined range by adjusting at least one of these parameters. Next, two embodiments in which the characteristic impedance is controlled by such adjustment will be described.

As shown in FIG. 15, in Example 1, the dielectric constant of the holding part 30 is 5.1, and the pin diameter is 0.20.
mm, and the hole diameter was 0.24 mm. In Example 2, the dielectric constant of the holding portion 30 was 3.6, the pin diameter was 0.26 mm, and the hole diameter was 0.32 mm. In each of the examples, the number of ground pins 22 was two, and the pin interval was 0.35 mm. Commercially available spring probes were used for both the signal pin 21 and the ground pin 22. The above pin diameter is the diameter of the barrel portion of the spring probe.

In Example 2, since the dielectric constant of the holding part 30 is smaller than that in Example 1, a thicker pin is used, and the hole diameter of the holding part 30 is set to an appropriate value according to the pin diameter. When the characteristic impedance of the signal pin 21 was measured by the TDR method, a value of 49 to 50 Ω 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 according to Examples 1 and 2.

In this way, even if it is not possible to increase the number of ground pins 22 or narrow the pin spacing, the dielectric constant of the insulating material constituting the holding part 30, the signal pin 21 and the ground pin 22
By adjusting the pin diameter and the hole diameter of the through hole Hb of the holding portion 30, the characteristic impedance of the signal pin 21 can be kept within a predetermined range.

Next, two modified examples of the inspection system will be described.

<Modification example 1 of inspection system>
FIG. 17 shows a schematic configuration of an inspection system 100A according to modification 1. This modification relates to an inspection system for inspecting transmission characteristics such as transmission loss and crosstalk of a printed wiring board to be inspected.

The inspection system 100A of this modification uses a printed wiring board 20 to be inspected as an inspection jig.
The inspection jig 1A is connected to the input terminal of the printed wiring board 200, and the inspection jig 1B is connected to the output terminal of the printed wiring board 200. The configurations of the inspection jigs 1A and 1B are the same as the inspection jig 1 described above.

The measuring instrument 50 has a measurement port 51 and a measurement port 52. The measurement port 51 is connected to the connector section 40 of the inspection jig 1A via a cable 60. The measurement port 52 is connected to the connector portion 40 of the inspection jig 1B via a cable 60.

Note that when the printed wiring board 200 to be inspected has a plurality of signal lines and the transmission characteristics between the signal lines, such as crosstalk, are to be inspected, one set of inspection jigs 1A and 1B is used for each signal line. It will be done. Alternatively, a plurality of signal lines 11 and a plurality of signal pins 2 may be used as the inspection jigs 1A and 1B.
1 may be used.

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

First, the signal pin 21 of the inspection jig 1A is brought into contact with one end (input end) of the signal line (not shown) of the printed wiring board 200 to be inspected, and the ground pin 22 of the inspection jig 1A is brought into contact with the signal line (not shown) of the printed wiring board 200 to be inspected. Contact with a ground layer (not shown). The signal pin 21 of the inspection jig 1B is brought into contact with the other end (output end) of the signal line of the printed wiring board 200, and the ground pin 22 of the inspection jig 1B is brought into contact with the ground layer of the printed wiring board 200. After that, an inspection signal is output from the measurement port 51 of the measuring instrument 50 (vector network analyzer) to the inspection jig 1A, and the measuring instrument 50
receives the test signal from the test jig 1B at the measurement port 52. Then, the measuring device 50 detects the printed wiring board 200 based on the transmitted inspection signal and the inspection signal received from the inspection jig 1B.
Make a pass/fail judgment.

For example, the measuring instrument 50 acquires S parameters based on the transmitted test signal and the received signal. In this case, the test signal is output from the measurement port 52 of the measuring instrument 50 to the test jig 1B, and the measuring instrument 50 also receives the test signal from the test jig 1A at the measurement port 51.
Then, if the crosstalk calculated from the S parameter is within the normal range, the printed wiring board 200 is determined to be normal; otherwise, it is determined to be abnormal.

Note that the quality determination may be performed by the measuring device 50 or by an information processing device such as a personal computer connected to the measuring device 50.

Furthermore, in the above testing method, a DC resistance measuring device may be used as the measuring device 50 to test the transmission loss of the signal line of the printed wiring board 200.

<Variation example 2 of inspection system>
FIG. 18 shows a schematic configuration of an inspection system 100B according to modification 2. This modification relates to an inspection system that includes an inspection jig 1C that includes an inspection substrate 10A that does not have an interlayer connection portion 14.

In the test board 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. signal pin 21
The holding part 30 is fixed to the test board 10A so that the ground pin 22 contacts the signal line 11 and the ground pin 22 contacts the ground layer. Thus, in this modification, the signal line 11 is directly connected to the signal pin 21.

According to this modification, an inspection system can be configured using the inspection board 10A that does not have the interlayer connection part 14.

Note that a plurality of inspection jigs 1C may be used to configure an inspection system for inspecting transmission characteristics such as transmission loss and crosstalk as in Modification 1.

Based on the above description, those skilled in the art may be able to envision additional effects and various modifications of the present invention, but aspects of the present invention are not limited to the embodiments described above. Various additions, changes, and partial deletions are possible without departing from the conceptual idea and gist of the present invention derived from the content defined in the claims and equivalents thereof.

1, 1A, 1B, 1C Inspection jig 10 Inspection board 11 Signal lines 12, 13 Ground layer 14 Interlayer connection part 14a1 External land 14a2 Internal land 14b Lid plating 14c Resin 15, 15a, 15b, 15c Insulating base material 16 Protective film 17 Through holes 18, 19 (inner layer) ground layer 21 Signal pin 22 Ground pin 30 Holding section 40 Connector section 50 Measuring instrument 60 Cable 100, 100A, 100B Inspection system 111, 114, 116 Insulating base material 112, 113, 115, 117 Metal foil 112a, 113a Land 112b, 113b Ground layer 118, 122, 123 Plating layer 118a Through hole 121 Resin 124 Signal line 125, 126 Ground layer 127 Lid plating 200 Printed wiring board 210 Connector A Mounting area G Gap H1, Hb, Hc Through hole R1, R2 area

Claims (4)

A method for adjusting characteristic impedance of an inspection jig for inspecting printed wiring boards, the method comprising:
The inspection jig is
a test board having a signal line for propagating a test 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 part that holds the signal pin and the ground pin;
a connector section mounted on the test board for connecting the test board and the measuring instrument;
In the adjustment method, the characteristic impedance of the test jig measured using the TDR method is centered at 50Ω over the entire propagation region from the connector portion through which the test signal propagates to the signal pin, and This is a method for keeping the voltage within a range narrower than the width based on the voltage standing wave ratio required for the wiring board,
The characteristic impedance of the signal pin is
If the characteristic impedance is higher than the upper limit of the range , narrow the spacing between the signal pin and the ground pin, and if the characteristic impedance is lower than the lower limit of the range , widen the spacing. and/or if the characteristic impedance is higher than the upper limit of the range , increasing the number of ground pins, and if the characteristic impedance is lower than the lower limit of the range , decreasing the number of ground pins. By this,
A method of staying within the above range . A method for adjusting characteristic impedance of an inspection jig for inspecting printed wiring boards, the method comprising:
The inspection jig is
a test board having a signal line for propagating a test 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 part that holds the signal pin and the ground pin;
a connector section mounted on the test board for connecting the test board and the measuring device;
an insulator provided with a through hole through which the signal pin and the ground pin are inserted ;
In the adjustment method, the characteristic impedance of the test jig measured using the TDR method is centered at 50Ω over the entire propagation region from the connector portion through which the test signal propagates to the signal pin, and This is a method for keeping the voltage within a range narrower than the width based on the voltage standing wave ratio required for the wiring board,
The characteristic impedance of the signal pin is
When the characteristic impedance is higher than the upper limit of the range , the pin diameters of the signal pin and the ground pin are increased, and when the characteristic impedance is lower than the lower limit of the range , the pin diameters of the signal pin and the ground pin are increased. By reducing the pin diameter,
When the characteristic impedance is higher than the upper limit of the range , the diameter of the through hole of the holding part is narrowed, and when the characteristic impedance is lower than the lower limit of the range , the diameter of the through hole is widened. and/or if the characteristic impedance is higher than the upper limit of the range , increasing the dielectric constant of the insulator, and if the characteristic impedance is lower than the lower limit of the range , increasing the dielectric constant By lowering
A method of staying within the above range . The signal line is provided on the first main surface of the test board,
The ground layer is provided on a second main surface opposite to the first main surface,
The signal pin is arranged on the second main surface side,
The test board further includes an interlayer connection part that electrically connects the signal line and the signal pin,
The characteristic impedance of the interlayer connection part is
When the characteristic impedance is higher than the upper limit of the range , narrowing the gap between the external land of the interlayer connection and the ground layer, and when the characteristic impedance is lower than the lower limit of the range , By widening the gap,
The method according to claim 1 or 2, falling within the range . The interlayer connection part has an internal land provided inside the test board,
The characteristic impedance of the interlayer connection part is
When the characteristic impedance is higher than the upper limit of the range , the gap between the internal land and a ground layer provided on the same surface as the internal land is narrowed so that the characteristic impedance is higher than the upper limit of the range. If it is lower than the lower limit, by widening the gap,
4. The method of claim 3, falling within said range .