JP2004037219A - Impedance measuring method and wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable the measurement of characteristic impedance and differential impedance by using a space of a wiring board efficiently. <P>SOLUTION: About one out of two conductors constituting a differential impedance test pattern 104, conductor of a characteristic impedance test pattern 105 is connected. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a wiring board used for an information processing apparatus, and more particularly to a wiring board having an impedance measuring method for confirming impedance accuracy and a test pattern for measurement.
[0002]
[Prior art]
In recent years, the processing speed of information processing apparatuses has been remarkably improved. This is largely due to an increase in the operating frequency of an electronic element represented by a CPU mounted on a wiring board built in the information processing device. Efforts have been made to suppress the generation of noise on the wiring board in a personal computer for such a stable operation as the speed of the electric signal is increased. In particular, it is known that matching the characteristic impedance value of the wiring board is important for reducing noise.
[0003]
In addition, it is expected that the influence of noise on a signal will increase more than ever due to an increase in the operating frequency and a decrease in the operating voltage of the electronic element. In order to reduce the influence of noise, use of a differential signal line is being studied when transmitting signals between electronic elements. The differential signal lines use two pairs of signal lines to transmit one signal. Similar to the characteristic impedance of one signal line, the differential impedance is defined for the differential signal line.
[0004]
In printed wiring boards, the characteristic impedance and differential impedance vary depending on the thickness of the insulating layer, the width of the wiring pattern, etc., and tests to see if this value is within the guaranteed range of product accuracy are shipped from the printed wiring board manufacturer. At this time, the test is performed using a test pattern provided on a product or a scrap material portion.
[0005]
In such a test pattern, a test pattern for measuring characteristic impedance and a test pattern for measuring differential impedance are separately provided.
[0006]
As an example of the invention relating to such a test pattern of a wiring board, Japanese Patent Application Laid-Open No. 2001-251061, which aims to measure the impedance of two data transmission patterns in a single measurement operation, is disclosed. The disclosed invention is mentioned.
[0007]
[Problems to be solved by the invention]
Conventionally, as described above, the pattern for measuring characteristic impedance and the pattern for measuring differential impedance for confirming the product accuracy of the wiring board were separately provided, so when there is little room for wiring board space was there.
[0008]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a wiring board capable of measuring characteristic impedance and differential impedance and efficiently using space.
[0009]
[Means for Solving the Problems]
The present invention provides a first wiring comprising a pair of parallel wirings arranged on a wiring board and electrically isolated from other circuits, and a pair of parallel wirings forming the first wiring. An impedance measuring method for measuring impedance using one of the wirings and a second wiring that is electrically connected and disposed, wherein the length of the first wiring and the length of the second wiring are measured. And an input step of inputting the first wiring, a first measuring step of measuring the differential impedance in the range of the length of the first wiring input in the input step, and the second wiring of the second wiring input in the input step A second measuring step of measuring the characteristic impedance in the range of the length.
[0010]
According to such a configuration, it is possible to measure the characteristic impedance and the differential impedance by efficiently using the space of the wiring board.
[0011]
Also, the present invention provides a first wiring comprising a pair of parallel wirings electrically isolated from a circuit for mounting an electronic element, and a pair of parallel wirings constituting the first wiring. , And one of the wirings and a second wiring electrically connected thereto.
[0012]
According to such a configuration, it is possible to measure the characteristic impedance and the differential impedance by efficiently using the space of the wiring board.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a notebook computer as an example of an information processing apparatus according to an embodiment of the present invention. The information processing apparatus 1 mainly includes a main body 2 and a display 3, and the main body 2 and the display 3 are rotatably connected by a hinge 4. The inside of the main body 2 includes a wiring board on which a CPU chip described later and a memory are mounted.
[0014]
FIG. 2 is a diagram illustrating a wiring board before being mounted on the information processing apparatus 1. This wiring board is a so-called printed wiring board and has a multiplex structure as described later. This embodiment corresponds to an example of a four-layer wiring board. In the shipping state of the wiring board, the product part 101, which is a part actually incorporated in the information processing apparatus 1, and the other end part 102 are often shipped in a state where they are not separated yet. The impedance test pattern 103 is provided on the offcut portion 102 of the wiring board 100.
The impedance test pattern 103 is electrically isolated from circuits and wiring for mounting various electronic elements provided on the wiring board 100, and is used for impedance measurement. In this embodiment, it is assumed that the impedance test pattern 103 is cut off when the wiring board is mounted. However, the impedance test pattern 103 may be provided in the product unit 101. When priority is given to miniaturization at the time of mounting, it is preferable to separate them.
[0015]
The impedance test pattern 103 will be described below with reference to FIGS. FIG. 3 is an enlarged view of the periphery of the impedance test pattern 103 in the wiring board 100. The impedance test pattern 103 includes signal pads 301 to 304 and V / G pads 401 to 404 described later with reference to FIG. 4, a differential impedance test pattern 104, and a characteristic impedance test pattern 105. The differential impedance test pattern 104 includes a pair of signal lines. This is a pattern for measuring the differential impedance of the pair of signal lines and measuring the accuracy of the differential signal lines of the wiring board 100. The length is about 100 mm.
[0016]
The characteristic impedance test pattern 105 is electrically connected to one of the differential impedance test patterns 104, and extends linearly. The length is about 100 mm similarly to the differential impedance test pattern. Although the characteristic impedance test pattern 105 is a portion indicated by a thick line in FIG. 3, the thickness of an actual wiring may vary depending on the impedance accuracy or the like according to a wiring board to be manufactured. The signal layer and the like provided with these wirings will be described later.
[0017]
FIG. 4 is an enlarged view of the impedance test pattern 103 centering on the pad portion. The wiring board 1 is provided with a differential impedance test pattern 104 and a characteristic impedance test pattern 105 on a first signal layer described later. The wiring board 1 is provided with signal pads 301 and 302 electrically connected to the differential impedance test pattern 104 and reference V / G pads 401 and 402 connected to a power supply layer and a ground layer described later. Have been. When measuring the differential impedance or the characteristic impedance of the first signal layer, a pair of the signal pad 301 and the V / G pad 401 and a pair of the signal pad 302 and the V / G pad 402 are respectively measured by a measuring device. Connecting. The signal pads 301 and 302 and the V / G pads 401 and 402 are provided with through holes 501, 502, 503 and 504, respectively.
[0018]
A signal line 202 indicated by a dotted line indicates a signal line provided on the back side of the wiring board 100 and a second signal layer described later. This signal line is electrically connected to the signal pads 303 and 304 via through holes 505 and 506, respectively. Further, reference V / G pads 403 and 404 connected to a power supply layer and a ground layer described later are provided. When measuring the differential impedance or the characteristic impedance of the second signal layer, the pair of the signal pad 303 and the V / G pad 403 and the pair of the signal pad 304 and the V / G pad 404 are respectively measured by a measuring device. Connecting. The signal pads 303 and 304 and the V / G pads 403 and 404 are provided with through holes 505, 506, 507 and 508, respectively.
[0019]
FIG. 5 is a cross-sectional view showing a cross section of the wiring board 100 of the present embodiment cut along the line 1-1 ′ shown in FIG. 4, showing the configuration of a four-layer wiring board. The uppermost layer is the first signal layer 601 on the surface. Since no signal line is provided on the cutting line, no copper foil or the like is present except for the signal pad 304. An insulating layer 602 is provided below this. The signal layer 601 and the power supply layer 603 are insulated by the insulating layer 602. Similarly, an insulating layer 604 is provided between the power supply layer 603 and the ground layer 605. Similarly, an insulating layer 606 is provided between the ground layer 605 and the second signal layer 607 on the rear surface of the wiring board.
[0020]
The power supply layer 603 is a layer for supplying power to various elements mounted on the wiring board when the wiring board 100 is built in the information processing apparatus 1. The ground layer 605 is a layer for providing a ground to various elements mounted on the wiring board when the wiring board 100 is built in the information processing device 1. In the present embodiment, the power supply layer 603 is disposed on the ground layer 605, but the arrangement may be reversed. Since the power supply layer 603 and the ground layer 605 serve as a layer for providing a reference when measuring the differential impedance and the characteristic impedance in the present invention, they are collectively referred to as a reference layer for convenience.
[0021]
A through-hole 506 is provided in such a wiring board. The through-hole literally penetrates the wiring board, and serves as a wiring for connecting elements mounted on the front surface of the wiring board and elements mounted on the back surface, for example. In order to prevent a short circuit, a clearance is provided between reference layers such as the power supply layer 603 and the ground layer 605.
[0022]
FIG. 6 is a cross-sectional view showing a cross section of the wiring board 100 of the present embodiment cut along the line 2-2 ′ shown in FIG. This corresponds to the cross section of the V / G pad. As in FIG. 5, it includes signal layers 601, 607, insulating layers 602, 604, 606, a power supply layer 603, and a ground layer 604. The difference from FIG. 5 is that there is no clearance between the through holes 508 and reference layers such as the power supply layer 603 and the ground layer 604, and they are electrically connected. This is for use as a reference for measuring the characteristic impedance.
[0023]
FIG. 7 is a diagram illustrating an example of a probe of a measuring device that actually performs measurement on the impedance test pattern 103. The probe of the measuring device is provided with two signal pins 701 for contacting a signal pad and two ground pins 702 for contacting a V / G pad. In order to measure the differential impedance and the characteristic impedance using this measuring device, the signal pins 701 are inserted into the through holes 501 of the signal pads 301 and the signal pads 302 described above, and the ground pins are also used for grounding. Pins 702 are inserted into through holes 503 provided in V / G pad 401 and through holes 504 provided in V / G pad 402.
[0024]
With reference to FIG. 8, a flow of measurement of differential impedance and characteristic impedance of a wiring board, which is one embodiment of the present invention, will be described below. First, the user inputs information on the length of the differential impedance test pattern and the length of the characteristic impedance test pattern to the measurement device (step S101). In the example of the present embodiment, a differential impedance test pattern length of 100 mm and a characteristic impedance test pattern length of 100 mm are input. These values are used to switch the program used when the measuring device calculates the impedance value, as described later.
[0025]
After inputting the information on the length of each test pattern, the measuring device calculates the differential impedance (step S102). This is performed by calculating an impedance value at a position corresponding to the distance from the measurement device based on the measured value of the incident voltage from the measurement device and the reflected voltage from the circuit.
[0026]
Subsequently, the measuring apparatus determines whether or not this measurement has reached the differential impedance test pattern length (step S103). This determination is made by comparing the value input in step S101 with the distance actually measured. Here, if it is determined that the differential impedance test pattern length has not yet been reached, the measuring device continues the measurement of the operating impedance (No from step S104 to step S103). When it is determined that the length of the differential impedance test pattern has been reached, the measurement apparatus switches the program (Yes in step S103 to step S104).
[0027]
The switching of the program is executed by switching from the program for calculating the differential impedance to the program for calculating the characteristic impedance. After switching the program, the measuring device continues measuring the characteristic impedance (step S105). Subsequently, the measuring apparatus determines whether or not the measurement has reached the characteristic impedance test pattern length (step S106). This determination is performed by comparing the value input in step S101 with the distance actually measured, as in the case of the differential impedance. Here, when it is determined that the characteristic impedance test pattern length has not yet been reached, the measuring apparatus continues the measurement of the characteristic impedance (No from step S106 to step S105). When it is determined that the length of the characteristic impedance test pattern has been reached, the measurement device ends the measurement.
[0028]
FIG. 9 is a diagram illustrating an example of a result of a measurement test of the differential impedance and the characteristic impedance using the present invention. The horizontal axis indicates the distance from the measuring device, and the vertical axis indicates the characteristic impedance value. In the graph, in order from the left, a region indicating the probe portion including the tip of the signal pin of the measuring device, a region indicating the measurement portion of the differential impedance test pattern, and a region indicating the measurement portion of the characteristic impedance test pattern. After passing through the measurement area of the characteristic impedance test pattern, the measurement device recognizes the characteristic impedance in an infinite form. FIG. 8 shows an example of a measurement result of a wiring board in which the differential impedance is larger than the characteristic impedance.
[0029]
As described above, according to the first embodiment of the present invention, the characteristic impedance and the differential impedance can be measured, and the space can be used efficiently.
[0030]
FIG. 9 shows a top view of a wiring board according to the second embodiment of the present invention. The second embodiment of the present invention is an example in which a part of a characteristic impedance test pattern connected to a differential impedance test pattern is curved in a U-shape.
[0031]
A part of the characteristic impedance test pattern 105 that is connected to the differential impedance test pattern is curved in a U-shape, and is arranged so as to be substantially parallel to the differential impedance measurement wiring. Here, in order to suppress adverse effects such as noise at the time of measurement, it is preferable to leave at least about 0.5 mm between the characteristic impedance pattern 105 and the differential impedance pattern 104. From the viewpoint of securing such a clearance, it is preferable that the characteristic impedance test pattern 105 be disposed not to be between the two wirings of the differential impedance test pattern 104 but to extend outward.
[0032]
When the characteristic impedance test pattern 105 linearly extends from the differential impedance test pattern 104 as in the first embodiment, depending on the size of the wiring board and the wiring pattern, only the characteristic impedance test pattern is arranged. In some cases, it is difficult to secure the length. According to the second embodiment, since a part of the characteristic impedance test pattern 105 is curved in a U-shape, even if it is difficult to secure a length for arranging the linearly extended wiring, It is possible to respond. This curved connection may use a part of the differential impedance test pattern 104.
[0033]
FIG. 10 shows a top view of the wiring board according to the third embodiment. The second embodiment of the present invention is an example in which a part of the characteristic impedance test pattern 105 connected to the differential impedance test pattern 104 is curved in an L shape. This curved connection may use a part of the differential impedance test pattern 104. Like the second embodiment, the present embodiment is applicable to the case where the arrangement is difficult as in the first embodiment, and is particularly suitable for the case where a test pattern is formed at a corner portion of a wiring board or the like.
[0034]
In the second and third embodiments, examples are shown in which the curved portions are curved in a U-shape or an L-shape, but the number of the curved portions is one each. The number of the curved portions can be increased, and a test pattern can be set according to the wiring pattern. However, an increase in the number of curved portions may cause noise during impedance measurement. It is preferable that the number of the curved portions is small.
[0035]
Although the above embodiments have been described with reference to a four-layer multilayer printed wiring board, the present invention can, of course, be applied to a wiring board having a structure other than four layers.
[0036]
【The invention's effect】
As described above, according to the present invention, the characteristic impedance and the differential impedance can be measured by efficiently using the space of the wiring board.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an example of an information processing apparatus according to each embodiment of the present invention.
FIG. 2 is a top view showing an example of a wiring board according to each embodiment of the present invention.
FIG. 3 is a top view showing an impedance test pattern according to the first embodiment of the present invention.
FIG. 4 is a top view showing an example of a pad portion of the impedance test pattern according to the first embodiment of the present invention.
FIG. 5 is a sectional view showing a section of the wiring board according to each embodiment of the present invention.
FIG. 6 is a sectional view showing a section of the wiring board according to each embodiment of the present invention.
FIG. 7 is a perspective view showing a probe portion of a measuring device used in each embodiment of the present invention.
FIG. 8 is a flowchart showing the operation of the measuring device during measurement.
FIG. 9 is a diagram showing a measurement example of characteristic impedance.
FIG. 10 is a top view showing an impedance test pattern according to the second embodiment of the present invention.
FIG. 11 is a top view showing an impedance test pattern according to a third embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Information processing apparatus, 2 ... Body part, 3 ... Display part, 4 ... Hinge part,
Reference numeral 100: wiring board, 101: product part, 102: remnant part, 103: impedance test pattern, 104: differential impedance test pattern, 105: characteristic impedance test pattern, 201, 202: signal line, 301, 302, 303, 304 ... signal pad, 401, 402, 403, 404 ... V / G pad, 501, 502, 503, 504, 505, 506, 507, 508 ... through hole, 601, 607 ... signal layer, 602, 604, 606 ... Insulating layer, 603: power supply layer, 604: ground layer, 701: signal pin, 702: ground pin

Claims (5)

A first wiring composed of a pair of parallel wirings arranged on a wiring board and electrically isolated from other circuits, and one of a pair of parallel wirings forming the first wiring An impedance measurement method for measuring impedance using a second wiring arranged electrically connected to the wiring,
An input step of inputting a length of the first wiring and a length of the second wiring,
A first measurement step of measuring the differential impedance in the range of the length of the first wiring input in the input step,
A second measuring step of measuring a characteristic impedance in a range of the length of the second wiring input in the inputting step. A first wiring including a pair of parallel wirings electrically isolated from a circuit for mounting the electronic element,
A wiring board, comprising: one of a pair of parallel wirings constituting the first wiring and a second wiring electrically connected to the wiring. 3. The wiring board according to claim 2, wherein the second wiring is linearly connected to an end of one of the first wirings so as to extend the first wiring. 4. The wiring board according to claim 2, wherein the wiring board further comprises a U-shaped connection portion for electrically connecting one of the first wirings and the second wiring. . The wiring board according to claim 2, wherein the wiring board includes an L-shaped connection portion that electrically connects one of the first wirings and the second wiring.

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