TWI889906B - Inspection methods and inspection systems - Google Patents

Abstract

The present invention provides an inspection method and an inspection system. The inspection method is used to inspect a printed wiring board having a first wiring as a transmission characteristic inspection target and a second wiring adjacent to the first wiring but not the transmission characteristic inspection target. The inspection method includes: measuring the transmission characteristics of the first wiring using a vector network analyzer; measuring the DC resistance of the second wiring using a DC resistance meter; inspecting the transmission characteristics of the first wiring based on the transmission characteristics of the first wiring, and inspecting the first wiring for open circuit and short circuit conditions; and inspecting the second wiring for open circuit conditions based on the DC resistance of the second wiring.

Description

Inspection methods and inspection systems

The present invention relates to an inspection method and an inspection system. More specifically, one embodiment of the present invention relates to an inspection method and an inspection system for inspecting a printed wiring board including wiring such as a high-speed transmission line as an object of transmission characteristic inspection.

In recent years, the amount of information processed by electronic devices such as smartphones, laptops, digital cameras, and game consoles has increased dramatically with the advancement of miniaturization and higher speeds. Consequently, signal speeds are trending ever higher. Furthermore, starting in 2019, portable communication terminals such as smartphones will begin transitioning to the next-generation communication standard, 5G. In 5G, the frequency of signals transmitted and received by communication terminals will shift from several GHz to 20-30 GHz. Furthermore, around 2022, signal frequencies are expected to increase to around 50 GHz.

Due to this increase in signal speed, signal lines (high-speed transmission lines) on printed wiring boards are required to meet specifications related to transmission characteristics. For example, to suppress signal reflection, characteristic impedance and voltage standing wave ratio (VSWR) are sometimes specified by standards. Furthermore, because transmission loss tends to increase with increasing signal frequency, line transmission loss is sometimes specified by standards. Furthermore, when multiple signal lines are installed on the same printed wiring board, interference (crosstalk/isolation) between adjacent signal lines is sometimes specified by standards. To confirm that specifications related to transmission characteristics are met, printed wiring boards with high-speed transmission lines are inspected by measuring transmission characteristics to determine if they are satisfactory.

Japanese Patent Publication No. 2019-106508 describes a printed wiring board for high-speed signal transmission in electronic devices. This printed wiring board has signal and ground wiring embedded within an insulating substrate made of, for example, a liquid crystal polymer. The signal lines form a high-speed transmission line in the form of a stripline.

As described above, transmission characteristics tests are performed on printed wiring boards with high-speed transmission lines. These tests are performed using a vector network analyzer.

In addition to monitoring transmission characteristics, we also perform open/short circuit checks to check for disconnections in high-speed transmission lines and short circuits between adjacent wiring. This open/short circuit check is performed using a DC resistance meter.

Conventionally, transmission characteristics inspection and open/short circuit inspection were performed separately for high-speed transmission lines on printed wiring boards. This increased inspection time and costs.

Therefore, an object of the present invention is to provide an inspection method and an inspection system capable of improving the inspection efficiency of a printed wiring board having high-speed transmission lines.

The present invention provides an inspection method.

A method for inspecting a printed wiring board having a first wiring line as a transmission characteristic inspection target and a second wiring line adjacent to the first wiring line and not the transmission characteristic inspection target, the method comprising:

measuring the transmission characteristics of the first wiring using a vector network analyzer;

measuring the DC resistance of the second wiring using a DC resistance meter;

Based on the transmission characteristics of the first wiring, checking the transmission characteristics of the first wiring, and checking the open circuit state and the short circuit state of the first wiring; and

An open circuit state of the second wiring is checked based on the DC resistance of the second wiring.

Furthermore, in the inspection method,

Measuring the transmission characteristics of the first wiring may include measuring the reflection characteristics of the first wiring as the transmission characteristics using the vector network analyzer.

Checking the open circuit state and the short circuit state of the first wiring includes: determining that the first wiring is in a short circuit state when a characteristic impedance obtained by performing TDR transformation on the reflection characteristics of the first wiring is lower than a specified short circuit determination threshold; and determining that the first wiring is in an open circuit state when the characteristic impedance exceeds the specified open circuit determination threshold.

Furthermore, in the inspection method,

Measuring the transmission characteristic of the first wiring may include measuring the transmission loss of the first wiring as the transmission characteristic using the vector network analyzer.

Checking the open circuit state and the short circuit state of the first wiring includes: determining that the first wiring is in a short circuit state when the transmission loss of the first wiring is lower than a specified short circuit determination threshold at at least one frequency; and determining that the first wiring is in an open circuit state when the transmission loss exceeds a specified open circuit determination threshold.

Furthermore, the inspection method may include not inspecting the short-circuit state of the second wiring using the DC resistance meter.

Furthermore, in the inspection method,

The first wiring may be a high-speed transmission line, and the second wiring may be a power supply line, a ground wiring, or a low-speed transmission line.

Furthermore, in the inspection method,

The printed wiring board may further include a third wiring adjacent to the first wiring and serving as a transmission characteristic inspection target.

The inspection method further comprises:

measuring the transmission characteristics of the third wiring using the vector network analyzer; and

Based on the transmission characteristics of the third wiring, the transmission characteristics of the third wiring are checked, and the open circuit state and the short circuit state of the third wiring are checked.

Furthermore, in the inspection method,

The printed wiring board may further include a fourth wiring adjacent to the second wiring and serving as a transmission characteristic inspection target.

The inspection method further comprises:

measuring the transmission characteristics of the fourth wiring using the vector network analyzer; and

Based on the transmission characteristics of the fourth wiring, the transmission characteristics of the fourth wiring are checked, and the open circuit state and the short circuit state of the fourth wiring are checked.

Furthermore, in the inspection method,

The printed wiring board may further include a fifth wiring adjacent to the second wiring and not being an object of the transmission characteristic inspection.

The inspection method further comprises:

measuring the DC resistance of the fifth wiring using the DC resistance meter; and

An open circuit state of the fifth wiring is detected based on the DC resistance of the fifth wiring.

Furthermore, in the inspection method,

The printed wiring board may be a flexible printed wiring board mounted with a first connector and a second connector, wherein the first connector is electrically connected to the input terminal of the first wiring and the input terminal of the second wiring, and the second connector is electrically connected to the output terminal of the first wiring and the output terminal of the second wiring.

Furthermore, in the inspection method,

The printed wiring board may be a flexible printed wiring board without a connector and included in a product sheet together with other printed wiring boards.

The present invention also provides an inspection system,

A system for inspecting a printed wiring board having a first wiring line as a transmission characteristic inspection target and a second wiring line adjacent to the first wiring line and not a transmission characteristic inspection target, the inspection system comprising:

a vector network analyzer having a first measurement port electrically connected to one end of the first wiring and a second measurement port electrically connected to the other end of the first wiring, for measuring the transmission characteristics of the first wiring;

a DC resistance meter having a first measurement port electrically connected to one end of the second wiring and a second measurement port electrically connected to the other end of the second wiring, for measuring the DC resistance of the second wiring; and

The information processing device is connected to the vector network analyzer and the DC resistance meter so as to be able to communicate.

The signal processing device checks the transmission characteristics of the first wiring based on the transmission characteristics of the first wiring measured by the vector network analyzer, and checks the open circuit state and the short circuit state of the first wiring,

The signal processing device checks the open circuit state of the second wiring based on the DC resistance of the second wiring measured by the DC resistance meter.

Furthermore, the inspection system may include:

a first inspection tool having a first inspection probe electrically connected to the first measurement port of the vector network analyzer and a second inspection probe electrically connected to the first measurement port of the DC resistance meter; and

a second inspection tool having a first inspection probe electrically connected to the second measurement port of the vector network analyzer and a second inspection probe electrically connected to the second measurement port of the DC resistance meter;

The first inspection probe of the first inspection tool is configured to be electrically connected to the one end of the first wiring, and the second inspection probe of the first inspection tool is configured to be electrically connected to the one end of the second wiring.

The first inspection probe of the second inspection tool is configured to be electrically connected to the other end of the first wiring, and the second inspection probe of the second inspection tool is configured to be electrically connected to the other end of the second wiring.

Furthermore, in the inspection system,

The first and second inspection probes of the first inspection tool may be configured to be mounted on connector terminals of a first connector mounted on the printed wiring board.

The first and second inspection probes of the second inspection tool are configured to be mounted on connector terminals of a second connector mounted on the printed wiring board.

Furthermore, in the inspection system,

The inspection system may inspect not only the printed wiring board but also a printed wiring board different from the printed wiring board.

The different printed wiring board has a third wiring as a transmission characteristic inspection object,

The vector network analyzer further includes a third measurement port electrically connected to one end of the third wiring of the different printed wiring board and a fourth measurement port electrically connected to the other end of the third wiring, for measuring the transmission characteristics of the third wiring.

The present invention also provides a testing method.

A method for inspecting a printed wiring board having wiring as a transmission characteristic inspection target includes:

measuring the transmission characteristics of the wiring using a vector network analyzer; and

Based on the transmission characteristics of the wiring, the transmission characteristics of the wiring are checked, and the wiring is checked for an open circuit state and a short circuit state.

According to the present invention, it is possible to provide an inspection method and an inspection system capable of improving the inspection efficiency of a printed wiring board having high-speed transmission lines.

Before describing the embodiments of the present invention, a comparative example is described.

＜Comparative example＞

Before explaining the embodiment, a comparative example of a method for manufacturing a printed wiring board including a printed wiring board inspection step will be explained according to the flowchart of FIG. 7 .

First, a product sheet (S) comprising multiple flexible printed circuit boards (FPCs) is manufactured (step S101). Figure 8 is a top view of a product sheet (S) comprising multiple printed circuit boards (FPCs) 110. The dashed lines in Figure 8 represent the product outline. In this example, twelve printed circuit boards 110 are formed in the product sheet (S).

As shown in Figure 9A, each printed wiring board 110 of the product sheet S has multiple wirings: wiring 111 (first wiring), wiring 112 (second wiring), and wiring 113 (third wiring). Wiring 111 and wiring 113 are wirings subject to transmission characteristics testing, such as high-speed transmission lines used to transmit high-speed signals. Wiring 112 is a wiring not subject to transmission characteristics testing, such as a ground wiring. A ground wiring is a wiring electrically connected to a ground layer (not shown) on the outer surface of the printed wiring board 110. Alternatively, wiring 112 may be a power supply line for transmitting power or a low-speed transmission line for which transmission characteristics testing is not required.

As shown in Figure 9B , wirings 111, 112, and 113 are formed in insulating substrate 119. Wirings 111, 112, and 113 comprise interconnecting elements such as lines and vias or through-holes formed on the inner layers of printed wiring board 110. Input terminals 111a, 112a, and 113a and output terminals 111b, 112b, and 113b are formed on the surface of insulating substrate 119. Wiring 111 electrically connects input terminal 111a and output terminal 111b. Wiring 112 electrically connects input terminal 112a and output terminal 112b. Wiring 113 electrically connects input terminal 113a and output terminal 113b. In other words, one end of the wirings 111, 112, 113 is electrically connected to the input terminals 111a, 112a, 113a of the printed wiring board 110, respectively, and the other end of the wirings 111, 112, 113 is electrically connected to the output terminals 111b, 112b, 113b, respectively.

Furthermore, the wiring to be inspected is not limited to wiring embedded in an insulating substrate, but may also be wiring formed on the surface of an insulating substrate in the form of a micro stripline structure.

Next, each printed wiring board 110 of product sheet S is inspected for open/short circuits (step S102). Specifically, wirings 111, 112, and 113 of printed wiring board 110 are individually inspected for open circuits (i.e., broken wiring) and short circuits (i.e., short circuits). This step is performed using the inspection structure shown in Figure 10. DC resistance meter 500 has measurement ports 510 and 520 for measuring DC resistance. Measurement port 510 is electrically connected to contact P1 of inspection tool 530 via cable 550. Similarly, measurement port 520 is electrically connected to contact P2 of inspection tool 540 via cable 560.

Inspection tool 530 includes inspection probes 531, 532, and 533. Inspection probe 531 contacts input terminal 111a of wiring 111. Similarly, inspection probe 532 contacts input terminal 112a of wiring 112, and inspection probe 533 contacts input terminal 113a of wiring 113.

Inspection tool 540 includes inspection probes 541, 542, and 543. Inspection probe 541 contacts output terminal 111b of wiring 111. Similarly, inspection probe 542 contacts output terminal 112b of wiring 112, and inspection probe 543 contacts output terminal 113b of wiring 113.

Inspection tool 530 includes a switch mechanism that selectively electrically connects any one of inspection probes 531, 532, and 533 to contact P1. Similarly, inspection tool 540 includes a switch mechanism that selectively electrically connects any one of inspection probes 541, 542, and 543 to contact P2. By controlling these switch mechanisms, the DC resistance of each of wirings 111, 112, and 113 on printed wiring board 110 is measured to check whether each wiring is open. For example, by controlling the switch mechanisms, contact P1 is electrically connected to inspection probe 531, and contact P2 is electrically connected to inspection probe 541. In this state, DC resistance is measured using DC resistance meter 500. If the measured DC resistance exceeds the specified open circuit detection threshold, it is determined that a break has occurred in wiring 111. The same inspection is performed on wirings 112 and 113.

This step also checks for short circuits between wires. For example, by controlling the switch mechanism, a state is established where contact P1 and test probe 531 are electrically connected, and contact P2 and test probe 542 are electrically connected. In this state, DC resistance is measured using DC resistance meter 500. If the measured DC resistance is lower than the specified short-circuit detection threshold, a short circuit is determined to have occurred between wires 111 and 112. Similar checks are performed between wires 111 and 113, and between wires 112 and 113.

Next, the appearance of the product sheet S is inspected (step S103).

Next, connectors 120 and 130 are mounted on printed wiring board 110, which has been determined to be normal after the open/short circuit inspection in step S102 and the visual inspection in step S103 (step S104). As shown in Figures 11A and 11B, connector 120 (the first connector) has connector terminals 121, 122, and 123. Connector 130 (the second connector) has connector terminals 131, 132, and 133.

Connector 120 is mounted on printed wiring board 110 such that connector terminals 121, 122, and 123 are electrically connected to input terminals 111a, 112a, and 113a, respectively. Similarly, connector 130 is mounted on printed wiring board 110 such that connector terminals 131, 132, and 133 are electrically connected to output terminals 111b, 112b, and 113b, respectively.

Next, the product sheet S is cut into individual FPCs (step S105). Specifically, the product sheet S is cut along the product outline to produce printed wiring boards 110 with connectors 120 and 130 mounted thereon. Hereinafter, the flexible printed wiring boards with connectors mounted thereon will also be referred to as "component-mounted FPCs."

Next, the printed wiring board 110 (component mounting FPC 100) with connectors 120 and 130 mounted thereon is inspected for open circuits and short circuits (step S106). In this step, the connector terminals of connector 120 and connector 130 are inspected for open circuits and short circuits.

Specifically, as shown in FIG12 , the DC resistance meter 500 is used to inspect the mounting portions of connectors 120 and 130 for short circuits or broken wires due to, for example, poor soldering. This inspection is performed with inspection probes 531, 532, and 533 of an inspection tool 530 in contact with connector terminals 121, 122, and 123, respectively, and with inspection probes 541, 542, and 543 of an inspection tool 540 in contact with connector terminals 131, 132, and 133, respectively. The subsequent inspections for open and short circuits are similar to those in step S102, and therefore a detailed description thereof will be omitted.

Next, the printed wiring board 110 (component mounting FPC 100) with the connector mounted thereon undergoes a transmission characteristic inspection (step S107). The transmission characteristic inspection is performed on the wiring to be inspected. Specifically, the transmission characteristics of wirings 111 and 113, which serve as high-speed transmission lines, are measured.

During the inspection in step S107, as shown in FIG13 , a vector network analyzer 600 is used. Vector network analyzer 600 has measurement ports 610, 620, 630, and 640. Measurement port 610 is electrically connected to an inspection probe 651 of an inspection tool 650 via a coaxial cable 653. Similarly, measurement port 620 is electrically connected to an inspection probe 661 of an inspection tool 660 via a coaxial cable 663. Measurement port 630 is electrically connected to an inspection probe 652 of an inspection tool 650 via a coaxial cable 654. Measurement port 640 is electrically connected to an inspection probe 662 of an inspection tool 660 via a coaxial cable 664.

During the inspection in step S107, as shown in Figure 13 , inspection probe 651 is brought into contact with connector terminal 121, inspection probe 652 is brought into contact with connector terminal 123, inspection probe 661 is brought into contact with connector terminal 131, and inspection probe 662 is brought into contact with connector terminal 133. The transmission characteristics of wiring 111 and wiring 113 are then measured using vector network analyzer 600.

After the transmission characteristics are evaluated, the component mounting FPC 100 is inspected for appearance (step S108). The component mounting FPC 100 that is judged to be normal in the appearance inspection becomes a finished product assembled in an electronic device.

As described above, in the comparative example printed wiring board inspection method, the printed wiring board with the connector mounted must be inspected for open/short circuits and transmission characteristics separately. This inevitably leads to reduced inspection efficiency. In contrast, in the printed wiring board inspection method according to the embodiment of the present invention, as described later, based on the measurement results of a vector network analyzer, not only the transmission characteristics of the wiring subject to the transmission characteristics inspection are inspected, but also the open and short circuit states of the wiring are inspected. This eliminates the need for separate open/short circuit inspections of the wiring subject to the transmission characteristics inspection. Consequently, inspection efficiency can be significantly improved.

Below, the embodiment of the present invention is described with reference to the accompanying drawings.

(First Implementation)

Referring to FIG1 , the inspection system according to the first embodiment will be described.

The inspection system 1 of this embodiment is an inspection system for inspecting a component-mounted FPC 100.

As described above, component mounting FPC 100 to be inspected includes printed wiring board 110 and connectors 120 and 130 mounted on printed wiring board 110. Printed wiring board 110 includes wiring 111, which is the target of transmission characteristics inspection; wiring 112, which is adjacent to wiring 111 and is not the target of transmission characteristics inspection; and wiring 113, which is adjacent to wiring 111 and is the target of transmission characteristics inspection.

As shown in Figure 1, the inspection system 1 of this embodiment includes a vector network analyzer 2, a DC resistance meter 3, a signal processing device 4, an inspection tool (first inspection tool) 5, and an inspection tool (second inspection tool) 6. Furthermore, the inspection system 1 may also include a retaining mechanism (not shown) for retaining the component-mounted FPC 100.

The following describes in detail the components of the inspection system 1.

Vector network analyzer 2 measures the transmission characteristics of wiring in the same manner as vector network analyzer 600. Vector network analyzer 2 of this embodiment has measurement ports 21, 22, 23, and 24, and measures the transmission characteristics of wiring 111 and wiring 113. As the transmission characteristics, at least one of reflection characteristics and transmission loss is measured.

Furthermore, as a transmission characteristic, the crosstalk between the wiring 111 and the wiring 113 can also be measured. In addition, the number of measurement ports of the vector network analyzer 2 is not limited to four, and may be six or eight.

The DC resistance meter 3 measures the DC resistance of the wiring in the same manner as the DC resistance meter 500. For example, a multimeter is used as the DC resistance meter 3.

The DC resistance meter 3 of this embodiment has a measurement port 31 electrically connected to one end (input terminal 112a) of the wiring 112 and a measurement port 32 electrically connected to the other end (output terminal 112b) of the wiring 112, and measures the DC resistance of the wiring 112. The number of measurement ports of the DC resistance meter 3 is not limited to two, and may also be four, six, or the like.

Inspection tool 5 includes an inspection probe 51 (first inspection probe) electrically connected to measurement port 21 (first measurement port) of vector network analyzer 2; an inspection probe 52 (second inspection probe) electrically connected to measurement port 31 (first measurement port) of DC resistance meter 3; and an inspection probe 53 electrically connected to measurement port 23 (third measurement port) of vector network analyzer 2. Inspection tool 6 includes an inspection probe 61 (first inspection probe) electrically connected to measurement port 22 (second measurement port) of vector network analyzer 2; an inspection probe 62 (second inspection probe) electrically connected to measurement port 32 (second measurement port) of DC resistance meter 3; and an inspection probe 63 electrically connected to measurement port 24 (fourth measurement port) of vector network analyzer 2.

Inspection probe 51 of inspection tool 5 is configured to be electrically connected to one end (input terminal 111a) of wiring 111. Inspection probe 52 is configured to be electrically connected to one end (input terminal 112a) of wiring 112. Inspection probe 53 is configured to be electrically connected to one end (input terminal 113a) of wiring 113.

Inspection probe 61 of inspection tool 6 is configured to be electrically connected to the other end (output terminal 111b) of wiring 111. Inspection probe 62 is configured to be electrically connected to the other end (output terminal 112b) of wiring 112. Inspection probe 63 is configured to be electrically connected to the other end (output terminal 113b) of wiring 113.

In this embodiment, a printed wiring board 110 (i.e., a component-mounted FPC 100) with connectors 120 and 130 mounted thereon is inspected. Therefore, the inspection probes 51, 52, and 53 of the inspection tool 5 are configured to be mounted on connector terminals 121, 122, and 123, respectively, of the connector 120 mounted on the printed wiring board 110. Similarly, the inspection probes 61, 62, and 63 of the inspection tool 6 are configured to be mounted on connector terminals 131, 132, and 133, respectively, of the connector 130 mounted on the printed wiring board 110. For example, if the connector terminals are concave, the inspection probes are inserted into the connector terminals when mounted thereon.

The vector network analyzer 2, DC resistance meter 3, and component mounting FPC 100 to be inspected are connected via the aforementioned inspection tools 5 and 6. As shown in Figure 1, measurement port 21 of vector network analyzer 2 is electrically connected to one end of wiring 111 (input terminal 111a). Measurement port 22 is electrically connected to the other end of wiring 111 (output terminal 111b). Similarly, measurement port 23 is electrically connected to one end of wiring 113 (input terminal 113a). Measurement port 24 is electrically connected to the other end of wiring 113 (output terminal 113b).

More specifically, measurement port 21 is electrically connected to connector terminal 121 of connector 120 via coaxial cable 54 and inspection probe 51 of inspection tool 5. Measurement port 22 is electrically connected to connector terminal 131 of connector 130 via coaxial cable 64 and inspection probe 61 of inspection tool 6. Similarly, measurement port 23 is electrically connected to connector terminal 123 of connector 120 via coaxial cable 55 and inspection probe 53 of inspection tool 5. Measurement port 24 is electrically connected to connector terminal 133 of connector 130 via coaxial cable 65 and inspection probe 63 of inspection tool 6.

The measurement port 31 of the DC resistance meter 3 is electrically connected to the connector terminal 122 of the connector 120 via the coaxial cable 55 and the inspection probe 52 of the inspection tool 5. The measurement port 32 is electrically connected to the connector terminal 132 of the connector 130 via the coaxial cable 65 and the inspection probe 62 of the inspection tool 6.

Next, the message processing device 4 is described.

The signal processing device 4 is connected to the vector network analyzer 2 and the DC resistance meter 3 via wired or wireless communication to enable communication with them. The signal processing device 4 simultaneously or sequentially transmits a trigger signal for starting measurement to the vector network analyzer 2 and the DC resistance meter 3. Furthermore, the signal processing device 4 receives measurement results from the vector network analyzer 2 and the DC resistance meter 3.

The information processing device 4 is configured to determine whether the component mounting FPC 100 is normal based on the measurement results received from the vector network analyzer 2 and the DC resistance meter 3. The information processing device 4 is, for example, a personal computer. Alternatively, the information processing device 4 may be a portable information terminal such as a tablet or smartphone.

The processing content of the message processing device 4 is further described in detail.

Signal processing device 4 checks the transmission characteristics of wiring 111 based on the transmission characteristics measured by vector network analyzer 2, and checks for open and short circuits in wiring 111. Signal processing device 4 similarly checks the transmission characteristics of wiring 113 based on the transmission characteristics of wiring 113, and checks for open and short circuits in wiring 113. Signal processing device 4 then displays the inspection results on a display.

First, the transmission characteristics inspection will be described. The signal processing device 4 inspects the transmission characteristics of the wiring 111 based on the characteristic impedance obtained by, for example, performing TDR conversion on the reflection characteristics measured by the vector network analyzer 2. For example, if the characteristic impedance in the time region corresponding to the area where the wiring 111 is formed (the wiring region) is within a predetermined range (e.g., 50 ± 5Ω), the signal processing device 4 determines that the transmission characteristics of the wiring are normal.

In addition, TDR conversion is usually performed by the vector network analyzer 2. However, this is not limited to this, and the signal processing device 4 can also perform TDR conversion.

In addition, the signal processing device 4 can also check the transmission characteristics of the wiring based on the voltage-to-wave ratio (VSWR) obtained by performing TDR conversion on the measured reflection characteristics.

In addition, the signal processing device 4 can also determine whether the transmission characteristics of the wiring 111 are good based on the transmission loss or crosstalk of the wiring 111 measured by the vector network analyzer 2 according to the inspection specifications.

Next, we will explain open/short circuit detection based on transmission characteristics. If the characteristic impedance obtained by TDR conversion of the reflection characteristics of wiring 111 is lower than a specified short circuit detection threshold, signal processing device 4 determines that wiring 111 is short-circuited. On the other hand, if the characteristic impedance exceeds the specified open circuit detection threshold, signal processing device 4 determines that wiring 111 is open.

The open/short circuit test is described in detail with reference to Figures 2A and 2B. Figure 2A shows an example of characteristic impedance in normal and short circuit states. Figure 2B shows an example of characteristic impedance in normal and open circuit states.

In a normal state, with no disconnection or short circuit, peaks appear at times corresponding to the positions of the tips of test probes 51 and 61, as shown by the solid lines in Figures 2A and 2B . The characteristic impedance between these peaks is approximately equal to the design value (50Ω) for impedance matching.

If a short circuit occurs in connector 120 (for example, when connector terminal 121 and connector terminal 122 are electrically connected due to excessive solder), the characteristic impedance begins to decrease rapidly at the time corresponding to the location of connector 120, reaching a low value throughout the entire wiring area, as shown by the dotted line waveform in FIG2A . Therefore, if the characteristic impedance in the wiring area falls below a predetermined short-circuit detection threshold, signal processing device 4 can determine that wiring 111 is short-circuited. In the case of FIG2A , the short-circuit detection threshold is, for example, 35Ω to 45Ω. Alternatively, the lower limit of the characteristic impedance detection threshold (for example, 45Ω) may be used as the short-circuit detection threshold.

If a break occurs in connector 120 (for example, if input terminal 111a and connector terminal 121 are not electrically connected due to insufficient solder), the characteristic impedance begins to increase and diverge rapidly at the time corresponding to the location of connector 120, as shown by the dotted line waveform in FIG2B . Therefore, if the characteristic impedance exceeds a predetermined open-circuit detection threshold in the wiring region, information processing device 4 can determine that wiring 111 is open. In the case of FIG2B , the open-circuit detection threshold is, for example, 65Ω or greater.

As described above, signal processing device 4 uses the characteristic impedance obtained from the reflection characteristics measured by vector network analyzer 2 to perform an open/short circuit check on wiring 111. Furthermore, signal processing device 4 also checks the transmission characteristics of wiring 113 based on its reflection characteristics in the same manner as for wiring 111, and also performs an open/short circuit check on wiring 113.

The signal processing device 4 is not limited to using reflection characteristics. It can also use other transmission characteristics (transmission loss, VSWR) measured by the vector network analyzer 2 to perform open/short circuit inspections on the wirings 111 and 113. The use of transmission loss is described below with reference to Figures 2C and 2D. Figure 2C shows an example of transmission loss in normal and short-circuit conditions. Figure 2D shows an example of transmission loss in normal and open-circuit conditions.

When a short circuit occurs in connector 120, the transmission loss waveform changes dramatically from normal operation, as shown by the dashed line in Figure 2C . At specific frequencies (e.g., approximately 3 GHz or 6.5 GHz), the transmission loss decreases dramatically. Therefore, if the transmission loss falls below the short-circuit detection threshold at a specific frequency, signal processing device 4 can determine that wiring 111 is short-circuited. In the case of Figure 2C , the short-circuit detection threshold is set to -5 dB at 3 GHz, for example.

Alternatively, the signal processing device 4 may determine whether a short circuit exists based on transmission loss values at multiple frequencies. For example, in the case of FIG2C , if the transmission loss is less than -5 dB at 3 GHz and less than -7 dB at 6.5 GHz, the wiring under inspection may be determined to be short-circuited.

If a wire break occurs in connector 120, transmission loss increases across all frequencies, as shown by the dashed line in Figure 2D. In particular, the transmission loss diverges toward infinity in the DC region (near 0 GHz). In the high-frequency region, due to capacitive coupling between traces, the transmission loss decreases. However, the transmission loss remains below -30 dB (above 30 dB). Therefore, if the transmission loss (or the absolute value of the transmission loss) exceeds a predetermined open-circuit detection threshold at at least one frequency (in the case of the transmission loss being below the open-circuit detection threshold in the graph of FIG2D ), the signal processing device 4 can determine that the wiring 111 is in an open-circuit state. For example, if the transmission loss is below -20 dB (i.e., above 20 dB) in the graph of FIG2D , the signal processing device 4 determines that the wiring 111 is in an open-circuit state.

Furthermore, in the open state, transmission loss decreases dramatically in the DC region. Therefore, if the transmission loss (or the absolute value of the transmission loss) exceeds a predetermined open-circuit determination threshold in the DC region, the signal processing device 4 may determine that the wiring 111 is in an open state.

Alternatively, the signal processing device 4 may perform an open/short inspection on the wiring 111 based on multiple transmission characteristics (e.g., reflection characteristics and transmission loss). In this case, if the signal processing device 4 determines that the wiring is normal through both the reflection characteristic inspection and the transmission loss inspection, the signal processing device 4 ultimately determines that the wiring under inspection is normal.

In addition to the open/short circuit detection described above, the information processing device 4 also checks for an open circuit in the wiring 112 based on the DC resistance of the wiring 112 measured by the DC resistance meter 3. Specifically, if the measured DC resistance of the wiring 112 exceeds a specified open circuit detection threshold, the information processing device 4 determines that a break has occurred in the wiring 112 (i.e., the wiring 112 is in an open circuit state). The information processing device 4 then displays the result of the detection on a display.

As described above, wirings 111 and 113 are inspected for open/short circuits based on transmission characteristics. Therefore, it is no longer necessary to inspect wirings 111 and 113 for open/short circuits using the DC resistance meter 3. In other words, there is no need to inspect wirings for open/short circuits using the DC resistance meter 3. This reduces the number of open/short circuit inspections using the DC resistance meter 3 compared to the comparative example, thereby improving inspection efficiency.

In printed wiring board 110, wirings 111 and 113 are inspected for short circuits based on transmission characteristics. Therefore, there is no need to inspect wiring 112, which is adjacent to wirings 111 and 113, for short circuits (to check whether wiring 112 is short-circuited). Furthermore, in printed wiring board 110B ( FIG. 5B ), described later, wiring 115, which is not subject to transmission characteristics inspection, is not adjacent to wirings subject to transmission characteristics inspection. Therefore, wiring 115 is inspected for short circuits.

As described above, the inspection system of the first embodiment not only inspects the transmission characteristics of the wiring being inspected, but also checks for open and short circuits, based on the transmission characteristics measured by the vector network analyzer 2. This significantly reduces the number of open/short circuit inspections performed by the DC resistance meter 3. Consequently, this embodiment improves the inspection efficiency of component-mounted FPC 100.

Furthermore, in this embodiment, all necessary inspections can be performed using inspection tools 5 and 6. That is, there is no need to prepare separate inspection tools 530 and 540 for open/short inspections and inspection tools 650 and 660 for transmission characteristics inspections, as in the comparative example. Consequently, this embodiment can reduce inspection costs.

Furthermore, in this embodiment, the relatively expensive vector network analyzer 2 and the relatively inexpensive DC resistance meter 3 are combined in a single inspection system. This reduces excessive use of the vector network analyzer compared to a scenario where all inspections are performed solely using the vector network analyzer, specifically, where the vector network analyzer is used to inspect wiring 112, which is not subject to transmission characteristic inspection. Consequently, the overall inspection system can be optimized for inspection costs.

＜Inspection Process＞

A method for manufacturing a printed wiring board including a step of inspecting the printed wiring board using the inspection system 1 will be described according to the flowchart of FIG. 3 .

First, a product sheet S including a plurality of flexible printed circuit boards (FPCs) is manufactured (step S1). This step is the same as step S101 described in the comparative example.

Next, each printed wiring board 110 of the product sheet S manufactured in step S1 is inspected for open circuits and short circuits (step S2). This step is the same as step S102 described in the comparative example.

Next, the appearance of the product sheet S is inspected (step S3). This step is the same as step S103 described in the comparative example.

Next, connectors 120 and 130 are mounted on the printed wiring board 110 that was determined to be normal in the open/short circuit inspection in step S2 and the appearance inspection in step S3 (step S4). This step is the same as step S104 described in the comparative example.

Next, the product sheet S is cut into individual pieces into a plurality of FPCs (step S5). This step is the same as step S105 described in the comparative example.

Next, the printed wiring board 110 (component mounting FPC 100) with the connectors 120 and 130 mounted thereon is subjected to a transmission characteristic inspection and an open/short circuit inspection (step S6). An example of this step will be described in detail with reference to FIG4 .

First, the transmission characteristics of the high-speed transmission line (wirings 111 and 113) are measured using a vector network analyzer 2 (step S61). Furthermore, the DC resistance of the ground wiring (wiring 112) is measured using a DC resistance meter 3 (step S62).

Next, based on the transmission characteristics of the high-speed transmission line measured in step S61, the transmission characteristics of the high-speed transmission line are checked, and an open/short circuit check is performed on the high-speed transmission line (step S63). In this step, based on the transmission characteristics measured by the vector network analyzer 2, the signal processing device 4 determines whether the transmission characteristics of the wirings 111 and 113 are good, and also determines whether the wirings 111 and 113 are open or shorted.

In addition, when checking for open/short circuits of the wirings 111 and 113, the reflection characteristic or the transmission loss may be used as the transmission characteristic. Alternatively, the wirings 111 and 113 may be checked for open/short circuits by using both the reflection characteristic and the transmission loss.

Thereafter, the ground wiring is checked for open circuit based on the DC resistance of the ground wiring measured in step S62 (step S64). In this step, the information processing device 4 determines whether the ground wiring is open circuit based on the DC resistance of the ground wiring as described above.

The inspection process in Figure 4 is merely an example. The order of the steps can be reversed within a consistent range. For example, the order of steps S61 and S62 can be reversed. Alternatively, steps S61 and S62 can be performed simultaneously. Alternatively, step S63 can be performed between steps S61 and S62.

After step S6, the appearance inspection of the component mounted FPC 100 is performed (step S7). This step is the same as step S108 described in the comparative example.

According to the above-described printed wiring board inspection method, it is not necessary to perform an open/short circuit inspection on the wirings 111 and 113, which are the target of the transmission characteristic inspection, using the DC resistance meter 3. Therefore, the inspection efficiency of the component-mounted FPC 100 can be significantly improved.

Other examples of flexible printed wiring boards

In the above embodiment, the inspection target is a printed wiring board 110 having wirings 111, 112, and 113. The following description also enables the effective inspection of printed wiring boards having a different wiring structure using this embodiment.

Figure 5A is a top view of a component mounting FPC 100A, which includes a printed wiring board 110A and connectors 120A and 130A mounted on the printed wiring board 110A. Printed wiring board 110A includes wirings 111 and 114, which are subject to transmission characteristics inspection, and wiring 112, which is not subject to transmission characteristics inspection. Wiring 112 is located between wirings 111 and 114. Compared to printed wiring board 110, printed wiring board 110A includes wiring 114 (a fourth wiring) adjacent to wiring 112, which is subject to transmission characteristics inspection, instead of wiring 113.

When inspecting component-mounted FPC 100A (printed wiring board 110A), the transmission characteristics of wirings 111 and 114 are measured using a vector network analyzer 2. Based on the measured transmission characteristics, wirings 111 and 114 are inspected for open and short circuits. The inspection method is the same as for wirings 111 and 113. When inspecting component-mounted FPC 100A, it is not necessary to inspect wirings 111 and 114 for open and short circuits using a DC resistance meter 3. Furthermore, since wirings 111 and 114 are inspected for short circuits based on the transmission characteristics, it is not necessary to inspect wiring 112 for short circuits.

Figure 5B is a top view of a component mounting FPC 100B, which includes a printed wiring board 110B and connectors 120B and 130B mounted on the printed wiring board 110B. Printed wiring board 110B has wirings 111 and 117, which are subject to transmission characteristics inspection, and wirings 112, 115, and 116, which are not subject to transmission characteristics inspection. Wirings 112, 115, and 116 are located between wiring 111 and wiring 117. Compared with the printed wiring board 110 , the printed wiring board 110A includes a wiring 115 (fifth wiring) adjacent to the wiring 112 and not subject to the transmission characteristic inspection, and wirings 116 and 117 adjacent to the wiring 115 instead of the wiring 113 .

When inspecting component-mounted FPC 100B (printed wiring board 110B), the transmission characteristics of wirings 111 and 117 are measured using vector network analyzer 2. Based on the measured transmission characteristics, wirings 111 and 117 are inspected for open and short circuits. The inspection method is the same as for wirings 111 and 113. When component-mounted FPC 100B is present, it is not necessary to inspect wirings 111 and 117 for open and short circuits using DC resistance meter 3. Furthermore, since wirings 111 and 117 are tested for short circuits based on transmission characteristics, there is no need to test wirings 112 and 116 adjacent to wirings 111 and 117 for short circuits. On the other hand, wiring 115 is not adjacent to wirings 111 and 117, which are the targets of transmission characteristics testing. Therefore, wiring 115 is tested for short circuits in addition to open circuits using DC resistance meter 3.

(Second Implementation)

Next, referring to Figure 6 , the inspection system of the second embodiment will be described. One of the differences between the first and second embodiments is the simultaneous inspection of multiple component-mounted FPCs. The following description of the second embodiment will focus on these differences. In Figure 6 , components identical to those of the first embodiment are assigned the same reference numerals as in Figure 1 .

As shown in FIG6 , the inspection system 1A of this embodiment is configured to simultaneously inspect a plurality of component-mounted FPCs 100C.

Inspection system 1A includes a vector network analyzer 2, DC resistance meters 3A and 3B, a signal processing device 4, inspection tools 5A and 5B, and multiple inspection tools 6A and 6B. Inspection system 1A may also include a retaining mechanism (not shown) for retaining component-mounted FPC 100C.

The component mounting FPC 100C to be inspected includes a printed wiring board 110C and connectors 120C and 130C mounted on the printed wiring board 110C. The printed wiring board 110C includes a wiring 111 to be inspected for transmission characteristics and a wiring 112 adjacent to the wiring 111 and not to be inspected for transmission characteristics.

Connector 120C includes connector terminal 121 welded to the input terminal of wiring 111 and connector terminal 122 welded to the input terminal of wiring 112. Connector 130C includes connector terminal 131 welded to the output terminal of wiring 111 and connector terminal 132 welded to the output terminal of wiring 112.

Inspection tool 5A includes inspection probe 51 electrically connected to measurement port 21 of vector network analyzer 2 and inspection probe 52 electrically connected to measurement port 31 of DC resistance meter 3A. Inspection tool 6A includes inspection probe 61 electrically connected to measurement port 23 of vector network analyzer 2 and inspection probe 62 electrically connected to measurement port 32 of DC resistance meter 3A.

Inspection tool 5B includes inspection probe 51 electrically connected to measurement port 24 of vector network analyzer 2 and inspection probe 52 electrically connected to measurement port 31 of DC resistance meter 3B. Inspection tool 6B includes inspection probe 61 electrically connected to measurement port 22 of vector network analyzer 2 and inspection probe 62 electrically connected to measurement port 32 of DC resistance meter 3B.

In this embodiment, the vector network analyzer 2 measures the transmission characteristics of the wiring 111 connected between the measurement port 21 and the measurement port 23, and also measures the transmission characteristics of the wiring 111 connected between the measurement port 24 and the measurement port 22.

DC resistance meters 3A and 3B are the same as DC resistance meter 3 described in the first embodiment. For example, a multimeter is used as DC resistance meter 3A and 3B. DC resistance meter 3A measures the transmission characteristics of wiring 112 connected between measurement port 31 and measurement port 32. Similarly, DC resistance meter 3B measures the transmission characteristics of wiring 112 connected between measurement port 31 and measurement port 32.

In this embodiment, the signal processing device 4 is connected to the vector network analyzer 2, DC resistance meter 3A, and DC resistance meter 3B in a manner that enables communication with them. The signal processing device 4 sends a trigger signal to the vector network analyzer 2 and DC resistance meter 3A and 3B simultaneously or sequentially to start measurement. Furthermore, the signal processing device 4 receives measurement results from the vector network analyzer 2 and DC resistance meter 3A and 3B. Based on these results, the signal processing device 4 determines whether the FPC 100C is properly mounted on each component. The signal processing device 4 displays the results on a display.

Based on the transmission characteristics of wiring 111 measured by vector network analyzer 2, signal processing device 4 inspects the transmission characteristics of wiring 111 for each component mounting FPC 100C, and also inspects wiring 111 for open and short circuit conditions. Furthermore, based on the DC resistance of wiring 112 measured by DC resistance meters 3A and 3B, signal processing device 4 inspects wiring 112 for open circuit conditions for each component mounting FPC 100C. The details of these inspection methods are the same as those of the first embodiment, and therefore their description will be omitted.

In the second embodiment, as in the first embodiment, wiring 111 is inspected for open/short circuits based on transmission characteristics. Therefore, it is no longer necessary to inspect wiring 111 for open/short circuits using DC resistance meters 3A and 3B. Thus, according to the second embodiment, the number of open/short circuit inspections using DC resistance meters 3A and 3B is reduced compared to the comparative example. This improves inspection efficiency.

Furthermore, the second embodiment enables simultaneous inspection of multiple component mounting FPCs. Furthermore, the measurement ports of the vector network analyzer 2 can be efficiently and flexibly utilized. In particular, if the vector network analyzer has many ports, vacant ports can be used to inspect other component mounting FPCs. This improves the efficiency of using the expensive vector network analyzer.

In addition, in this embodiment, the inspection object is a plurality of component mounting FPCs 100C having the same structure. However, the present invention is not limited to this, and the inspection object may also be a plurality of component mounting FPCs having mutually different structures.

In addition, in this embodiment, multiple DC resistance meters 3A and 3B are used. However, this is not limited to this. A single DC resistance meter with multiple measurement ports can also be used to measure the DC resistance of multiple component mounting FPCs.

Furthermore, in this embodiment, either or both printed wiring boards 110C may include a third wiring, such as wiring 113 shown in the first embodiment, for transmission characteristics inspection. In this case, the vector network analyzer 2 further includes a third measurement port electrically connected to one end of the third wiring and a fourth measurement port electrically connected to the other end of the third wiring, thereby also being able to measure the transmission characteristics of the third wiring.

Two embodiments of the present invention have been described above.

Furthermore, the present invention is not limited to the inspection of flexible printed wiring boards on which components such as connectors are mounted, but can also be applied to the inspection of flexible printed wiring boards before components are mounted.

Furthermore, the present invention is not limited to flexible printed wiring boards, but can also be applied to the inspection of rigid printed wiring boards.

Furthermore, the present invention can also be applied to the inspection of printed wiring boards on which components other than connectors are mounted, such as surface mount components such as chip capacitors, chip resistors, or chip inductors.

Furthermore, the present invention can also be applied to the inspection of printed wiring boards that only have wiring to be inspected for transmission characteristics. In this case, open/short circuit inspection of high-speed transmission lines using a DC resistance meter is no longer necessary, thereby improving inspection efficiency.

Based on the above description, those skilled in the art may be able to conceive of additional effects and various modifications of the present invention. The present invention is not limited to the above-described embodiments. Various additions, modifications, and partial deletions are possible without departing from the conceptual ideas and purpose of the present invention as derived from the claims and their equivalents.

1, 1A: Inspection system 2: Vector network analyzer 21, 22, 23, 24: Measurement port 3: DC resistance meter 31, 32: Measurement port 4: Signal processing device 5, 6: Inspection tool 51, 52, 53, 61, 62, 63: Inspection probe 54, 55, 64, 65: Coaxial cable 55, 65: Cable 100, 100A, 100B, 100C: Component mounting FPC 110, 110A, 110B: Printed wiring board 111, 112, 113: Wiring 111a, 112a, 113a: Input terminals 111b, 112b, 113b: Output terminals 119: Insulation substrate 120, 130: Connector 121, 122, 123, 131, 132, 133: Connector terminals 500: DC resistance meter 510, 520: Measurement port 530, 540: Inspection tool 550, 560: Cable 600: Vector network analyzer 610, 620, 630, 640: Measurement port P1, P2: Contact S: Product sheet

Figure 1 is a diagram schematically illustrating the configuration of an inspection system according to a first embodiment. Figure 2A is a diagram illustrating an example of characteristic impedance (normal state and short-circuit state) based on reflection characteristics measured by a vector network analyzer. Figure 2B is a diagram illustrating an example of characteristic impedance (normal state and open-circuit state) based on reflection characteristics measured by a vector network analyzer. Figure 2C is a diagram illustrating an example of transmission loss (normal state and short-circuit state) measured by a vector network analyzer. Figure 2D is a diagram illustrating an example of transmission loss (normal state and open-circuit state) measured by a vector network analyzer. Figure 3 is a flowchart illustrating the inspection method according to the embodiment. Figure 4 is a flowchart illustrating the details of the inspection method according to the embodiment. Figure 5A is a diagram showing another example of a printed wiring board to be inspected. Figure 5B is a diagram showing yet another example of a printed wiring board to be inspected. Figure 6 is a diagram showing the schematic configuration of an inspection system according to the second embodiment. Figure 7 is a flow chart showing a method for manufacturing a printed wiring board, including a printed wiring board inspection step, according to a comparative example. Figure 8 is a top view showing an example of a product sheet including multiple printed wiring boards. Figure 9A is a top view of the printed wiring board in the product sheet shown in Figure 8. Figure 9B is a cross-sectional view taken along line I-I in Figure 9A. Figure 10 is a diagram illustrating open/short circuit inspection using a DC resistance meter according to a comparative example. Figure 11A is a top view of a printed wiring board mounted as a component of a printed wiring board with a connector mounted thereon. Figure 11B is a cross-sectional view taken along line II-II in Figure 11A. Figure 12 illustrates an open/short circuit test using a DC resistance meter as a comparative example. Figure 13 illustrates a transmission characteristics test using a vector network analyzer as a comparative example.

1: Check the system

2: Vector Network Analyzer

21, 22, 23, 24: Measurement ports

3: DC resistance meter

31,32: Measurement ports

4: Message processing device

5,6: Inspection Tools

51,52,53,61,62,63: Check the probe

54,55,64,65: Coaxial cable

55,65: Cable

100: Component Installation FPC

110: Printed wiring board

111, 112, 113: Wiring

120,130: Connector

121, 122, 123, 131, 132, 133: Connector terminals

Claims (15)

A method for inspecting a printed wiring board includes a first wiring whose transmission characteristics are to be inspected, and a second wiring adjacent to the first wiring and not to be inspected. The method includes: measuring the transmission characteristics of the first wiring using a vector network analyzer; measuring the DC resistance of the second wiring using a DC resistance meter; inspecting the transmission characteristics of the first wiring based on the transmission characteristics of the first wiring, and inspecting the first wiring for open circuit and short circuit conditions; and inspecting the second wiring for an open circuit based on the DC resistance of the second wiring. The inspection method as described in claim 1, wherein measuring the transmission characteristics of the first wiring includes measuring the reflection characteristics of the first wiring as the transmission characteristics using the vector network analyzer, and inspecting the open circuit state and the short circuit state of the first wiring includes: if a characteristic impedance obtained by performing TDR transformation on the reflection characteristics of the first wiring is lower than a specified short circuit judgment threshold, determining that the first wiring is in the short circuit state; and if the characteristic impedance exceeds the specified open circuit judgment threshold, determining that the first wiring is in the open circuit state. The inspection method as described in claim 1, wherein measuring the transmission characteristics of the first wiring includes measuring the transmission loss of the first wiring as the transmission characteristics using the vector network analyzer, and inspecting the open circuit state and the short circuit state of the first wiring includes: if the transmission loss of the first wiring is lower than a specified short circuit judgment threshold at at least one frequency, determining that the first wiring is in the short circuit state; and if the transmission loss exceeds the specified open circuit judgment threshold, determining that the first wiring is in the open circuit state. The inspection method according to any one of claims 1 to 3, further comprising not inspecting the short-circuit state of the second wiring using the DC resistance meter. The inspection method according to any one of claims 1 to 3, wherein the first wiring is a high-speed transmission line, and the second wiring is a power supply line, a ground wiring, or a low-speed transmission line. The inspection method as described in any one of claims 1 to 3, wherein the printed wiring board further has a third wiring adjacent to the first wiring and serving as an object of transmission characteristic inspection, the inspection method further comprising: measuring the transmission characteristics of the third wiring using the vector network analyzer; and inspecting the transmission characteristics of the third wiring based on the transmission characteristics of the third wiring, and inspecting the open circuit state and the short circuit state of the third wiring. The inspection method as described in any one of claims 1 to 3, wherein the printed wiring board further has a fourth wiring adjacent to the second wiring and serving as an object of transmission characteristic inspection, the inspection method further comprising: measuring the transmission characteristics of the fourth wiring using the vector network analyzer; and inspecting the transmission characteristics of the fourth wiring based on the transmission characteristics of the fourth wiring, and inspecting the open circuit state and the short circuit state of the fourth wiring. The inspection method of any one of claims 1 to 3, wherein the printed wiring board further includes a fifth wiring adjacent to the second wiring and not subject to transmission characteristic inspection, the inspection method further comprising: measuring a DC resistance of the fifth wiring using the DC resistance meter; and inspecting the fifth wiring for an open circuit based on the DC resistance of the fifth wiring. The inspection method according to any one of claims 1 to 3, wherein the printed wiring board is a flexible printed wiring board having a first connector and a second connector mounted thereon, the first connector being electrically connected to an input terminal of the first wiring and an input terminal of the second wiring, and the second connector being electrically connected to an output terminal of the first wiring and an output terminal of the second wiring. The inspection method according to any one of claims 1 to 3, wherein the printed wiring board is a flexible printed wiring board without a connector mounted thereon and included in a product sheet together with other printed wiring boards. An inspection system for inspecting a printed wiring board, the printed wiring board having a first wiring as a transmission characteristic inspection target and a second wiring adjacent to the first wiring and not being the transmission characteristic inspection target, the inspection system comprising: a vector network analyzer having a first measurement port electrically connected to one end of the first wiring and a second measurement port electrically connected to the other end of the first wiring, for measuring the transmission characteristics of the first wiring; a DC resistance meter having a first measurement port electrically connected to one end of the second wiring and a second measurement port electrically connected to the other end of the second wiring, a second measurement port electrically connected to the vector network analyzer to measure the DC resistance of the second wiring; and a signal processing device connected to the vector network analyzer and the DC resistance meter so as to be communicative, the signal processing device checking the transmission characteristics of the first wiring based on the transmission characteristics of the first wiring measured by the vector network analyzer, and checking the open circuit state and the short circuit state of the first wiring, the signal processing device checking the open circuit state of the second wiring based on the DC resistance of the second wiring measured by the DC resistance meter. The inspection system as described in claim 11 further includes: a first inspection tool, having a first inspection probe electrically connected to the first measurement port of the vector network analyzer and a second inspection probe electrically connected to the first measurement port of the DC resistance meter; and a second inspection tool, having a first inspection probe electrically connected to the second measurement port of the vector network analyzer and a second inspection probe electrically connected to the second measurement port of the DC resistance meter, the first inspection probe of the first inspection tool being configured to be electrically connected to the one end of the first wiring, the second inspection probe of the first inspection tool being configured to be electrically connected to the one end of the second wiring, the first inspection probe of the second inspection tool being configured to be electrically connected to the other end of the first wiring, and the second inspection probe of the second inspection tool being configured to be electrically connected to the other end of the second wiring. An inspection system as described in claim 12, wherein the first and second inspection probes of the first inspection tool are configured to be mounted on connector terminals of a first connector mounted on the printed wiring board, and the first and second inspection probes of the second inspection tool are configured to be mounted on connector terminals of a second connector mounted on the printed wiring board. An inspection system as described in any one of claims 11 to 13, wherein the inspection system not only inspects the printed wiring board, but also inspects a printed wiring board different from the printed wiring board, the different printed wiring board having a third wiring as an object of transmission characteristic inspection, and the vector network analyzer further has a third measurement port electrically connected to one end of the third wiring of the different printed wiring board and a fourth measurement port electrically connected to the other end of the third wiring, for measuring the transmission characteristics of the third wiring. A method for inspecting a printed wiring board having a wiring as a transmission characteristic inspection target includes: measuring the transmission characteristics of the wiring using a vector network analyzer; and inspecting the transmission characteristics of the wiring based on at least either voltage-to-peak ratio (VSR) or transmission loss as the transmission characteristic of the wiring, and inspecting the wiring for open circuit and short circuit conditions.