JP2014229865A - Printed wiring board and electronic apparatus - Google Patents

Abstract

A high-speed signal transmission is realized without increasing a signal transmission loss at a low frequency at a stub end. A multilayer wiring printed circuit board is connected to signal wiring patterns formed on a plurality of wiring layers and different wiring layers, and a through hole that forms a signal transmission path is formed on the back surface of the multilayer wiring printed circuit board. It has the insulator 23 to be formed and the electric conductor 24 to be formed on the surface of the insulator 23. The insulator 23 is connected to the power / ground wiring pattern 20 formed in the wiring layer, and is formed so as to cover the end surface of the stub 21a that does not form the signal transmission path in the through hole 21. [Selection] Figure 1

Description

  The present invention relates to a printed wiring board and an electronic device, and more particularly to a technique effective for high-speed signal transmission of a multilayer wiring board.

  Electrical transmission devices such as servers, routers, and storage devices exchange data at high speed internally, and in terms of device performance, it is required to increase the amount of data exchanged per second.

  On the other hand, a device that exchanges such data usually employs a printed wiring board (hereinafter referred to as a multilayer board) that realizes a circuit board with a laminated structure of a patterned copper foil and a resin plate. .

  In a multilayer substrate, there is a structure called a through hole or via formed by plating a drill hole in order to connect the patterned copper foil wirings of each layer. However, in the multilayer substrate, several problems occur when the signal speed is increased, and for example, the voltage pulse waveform deterioration phenomenon due to reflection at a through-hole via is one of them.

  In the through-hole, a stub branched from the signal transmission path is formed, and the voltage pulse signal that has traveled to the stub is reflected back and becomes noise for the signal that travels on the transmission path.

  In particular, it is known that, at a specific frequency, the wavelength of the wave reflected and returned to the branch point is offset by about 180 ° from the original wave and increases the insertion loss of the through hole. Noise caused by reflection at the stub is difficult to remove by a functional element that compensates for the loss of the transmission line such as a signal conditioner, and the printed circuit board itself is designed and manufactured so that the influence is reduced. .

  As a design technique, for example, it is known to minimize the influence of a stub by using a surface layer of a multilayer substrate or an inner layer near the surface as a transmission line for transmitting a high-speed signal. However, this method restricts the layers that can be wired, making it difficult to design the pattern of the printed circuit board.

  Further, as a manufacturing technique, a back drill technique or a build-up technique is generally used. The back drill technique is a method of removing a stub portion from a through hole structure once made by a drill. The build-up technology is a method for forming a non-penetrating via structure by depositing a thin film.

  As another manufacturing technique, for example, a stub termination technique is known in which the end of a branched stub is terminated with a resistor. As a specific structure in this type of stub termination technology, a thin film material having a certain resistivity fills the space between the through hole and the ground pattern (see, for example, Patent Document 1), or chip resistance is defined as a through hole. A device mounted so as to be connected to a ground pattern (for example, see Patent Documents 2 and 3) is known.

JP 2004-146810 A Japanese Patent No. 4880360 Japanese Patent No. 4006447

  The above-described back drill technique must leave a stub of a certain length in order to prevent the drill depth from being incorrect and the signal wiring from being cut in the printed circuit board. With the current level of back drill technology, it is difficult to sufficiently reduce the influence of stubs at the next-generation electric signal speed of about 25 Gb / s. In addition, the build-up technology is expensive and makes it difficult to spread the product.

  In addition, the stub termination technology disclosed in Patent Documents 1, 2, and 3 can reduce the influence of the stub at high frequencies, but increases the loss at low frequencies of the transmission line due to the DC current flowing from the stub. It was a problem.

  An object of the present invention is to provide a stub termination technique capable of realizing high-speed signal transmission without increasing a signal transmission loss at a low frequency.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.

  That is, the outline of a typical one is applied to a printed wiring board and an electronic device, and has the following characteristics.

  The printed wiring board is connected to a plurality of wiring layers, signal wiring patterns formed on different wiring layers, and forms a signal transmission path, an insulator formed on the wiring layer on the surface layer, and an insulator And a first electric conductor formed on the surface of the substrate.

  The insulator is connected to the ground wiring formed in the wiring layer, and is formed so as to cover the end face of the stub that does not form the signal transmission path among the through holes.

  In addition, the electronic device is connected to a plurality of wiring layers, signal wiring patterns formed on different wiring layers, and forms a signal transmission path, an insulator formed on the wiring layer on the surface layer, and an insulating layer. And a printed wiring board having a first electric conductor formed on the surface of the body.

  In this printed wiring board, the insulator is connected to the ground wiring formed in the wiring layer, and is formed so as to cover the end face of the stub that does not form the signal transmission path in the through hole.

  Among the inventions disclosed in the present application, effects obtained by typical ones will be briefly described as follows.

  (1) An increase in transmission loss in the low frequency region can be prevented.

  (2) With the above (1), the performance of the electronic device can be improved.

3 is a cross-sectional view showing an example of a multilayer wiring printed board according to Embodiment 1. FIG. It is explanatory drawing which shows the equivalent circuit in the signal wiring pattern of FIG. 1, a through hole, and a termination circuit. It is explanatory drawing which showed an example of the phase change in a stub resonance frequency. It is explanatory drawing which shows an example of the frequency characteristic of the insertion loss of the wave which advances through a through hole. It is sectional drawing which shows the other example of a multilayer wiring printed circuit board. 6 is an explanatory diagram showing an example of a phase change at a stub resonance frequency according to Embodiment 2. FIG. It is explanatory drawing which shows an example of the frequency characteristic of the insertion loss of the wave which advances the through hole to which the termination circuit made into resistance value which satisfy | fills Formula 5 was connected. It is sectional drawing which shows an example of the multilayer wiring printed circuit board by this Embodiment 3. It is sectional drawing which shows the other example of a multilayer wiring printed circuit board. It is sectional drawing which shows an example of the multilayer wiring printed circuit board by this Embodiment 4. It is explanatory drawing which shows an example of the server of the blade structure by this Embodiment 5.

  In the following embodiments, when it is necessary for the sake of convenience, the description will be divided into a plurality of sections or embodiments. However, unless otherwise specified, they are not irrelevant to each other. There are some or all of the modifications, details, supplementary explanations, and the like.

  Further, in the following embodiments, when referring to the number of elements (including the number, numerical value, quantity, range, etc.), especially when clearly indicated and when clearly limited to a specific number in principle, etc. Except, it is not limited to the specific number, and may be more or less than the specific number.

  Further, in the following embodiments, the constituent elements (including element steps and the like) are not necessarily indispensable unless otherwise specified and apparently essential in principle. Needless to say.

  Similarly, in the following embodiments, when referring to the shape, positional relationship, etc. of components, etc., the shape of the component is substantially the case unless it is clearly specified and the case where it is clearly not apparent in principle. And the like are included. The same applies to the above numerical values and ranges.

  In all the drawings for explaining the embodiments, the same members are denoted by the same reference symbols in principle, and the repeated explanation thereof is omitted. In order to make the drawings easy to understand, even a plan view may be hatched.

(Embodiment 1)
<Summary of invention>
The outline of the present invention is a printed wiring board (multilayer wiring printed board 10). This printed wiring board has a plurality of wiring layers, a through hole (through hole 21), an insulator (insulator 23), and a first electric conductor (electric conductor 24).

  The through holes are connected to signal wiring patterns (signal wiring patterns 11 and 16) formed in different wiring layers to form a signal transmission path. The insulator is formed on the wiring layer on the front surface layer (back surface). The first electrical conductor is formed on the surface of the insulator.

  The insulator is connected to the ground wiring (power supply / ground wiring pattern 20) formed in the wiring layer, and is formed so as to cover the end surface of the stub (stub 21a) that does not form the signal transmission path among the through holes. The

<Configuration example of multilayer printed circuit board>
Hereinafter, the embodiment will be described in detail based on the above-described outline.

  FIG. 1 is a cross-sectional view showing an example of a multilayer wiring printed board according to the first embodiment.

  As shown in FIG. 1, for example, eight first to eighth wiring pattern layers are formed on the multilayer wiring printed board 10 from the upper side as the main surface to the lower side as the back surface. On the first wiring pattern layer formed on the main surface of the multilayer wiring printed board 10, a signal wiring pattern 11 and a power / ground wiring pattern 12 are formed.

  A second wiring pattern layer is formed below the first wiring pattern layer. A power / ground wiring pattern 13 is formed in the second wiring pattern layer. Similarly, a third wiring pattern layer is formed below the second wiring pattern layer, and a fourth wiring pattern layer is formed below the third wiring pattern layer.

  A fifth wiring pattern layer is formed below the fourth wiring pattern layer, and a sixth wiring pattern layer is formed below the fifth wiring pattern layer. A seventh wiring pattern layer is formed below the sixth wiring pattern layer, and an eighth wiring pattern layer is formed below the seventh wiring pattern layer.

  Power supply / ground wiring patterns 14 and 15 are also formed in the third wiring pattern layer and the fourth wiring pattern layer, respectively. In the fifth wiring pattern layer, a signal wiring pattern 16 and a power / ground wiring pattern 17 are formed. Power supply / ground wiring patterns 18, 19, and 20 are formed in the sixth wiring pattern layer, the seventh wiring pattern layer, and the eighth wiring pattern layer, respectively.

  These signal wiring patterns 11 and 16 and power / ground wiring patterns 12 to 15 and 17 to 20 are formed, for example, by etching copper foil or the like.

  A through hole 21 formed so as to penetrate from the main surface to the back surface of the multilayer wiring printed board 10 is provided at the center of the multilayer wiring printed board 10. The through hole 21 has a structure in which a hole is formed in the multilayer printed circuit board 10 by a rotary drill, and then a metal film is formed inside the hole after drilling by plating.

  Therefore, the through hole 21 has, for example, a hollow cylindrical shape, and one end is connected to the signal wiring pattern 11 formed on the main surface of the multilayer wiring printed board 10. The signal wiring pattern 16 formed in the fifth wiring pattern layer is connected to the outer peripheral surface of the through hole 21. These signal wiring patterns 11 and 16 are wiring patterns for transmitting signals input / output from an electronic circuit or the like.

  In the through hole 21, a portion branched from the signal transmission path, that is, a portion from the signal, that is, the portion where the signal wiring pattern 16 is connected to the lower back surface becomes the stub 21 a.

  Further, the power supply / ground wiring patterns 12 to 15 and 17 to 19 are so-called solid grounds in which the entire surface of the wiring layer is a ground pattern ground wiring, or a power supply voltage that is an operation power supply for electronic components to be mounted. It is a planar pattern for supplying VDD or the like, that is, a so-called power plane. The power / ground wiring patterns 12 to 15 and 17 to 19 may be other than a solid ground or a power plane. Further, the power supply / ground wiring pattern 20 is a ground wiring having a planar pattern on the entire surface of the wiring layer, so-called solid ground.

  A first wiring pattern layer and a second wiring pattern layer; a second wiring pattern layer and a third wiring pattern layer; a third wiring pattern layer and a fourth wiring pattern layer; and a fourth wiring pattern layer; Insulating layers 22 are respectively formed between the fifth wiring pattern layers.

  Similarly, between the fifth wiring pattern layer and the sixth wiring pattern layer, the sixth wiring pattern layer and the seventh wiring pattern layer, and the seventh wiring pattern layer and the eighth wiring pattern layer, Insulating layers 22 are respectively formed. By this insulating layer 22, each pattern layer is electrically insulated. The insulating layer 22 is made of, for example, a glass cloth, which is a cloth woven of glass fibers, dipped in a thermosetting resin.

  Further, the layer configuration or the number of layers of the multilayer printed circuit board 10 shown in FIG. 1 is an example, and the present invention is not limited to this. The layer on which the signal wiring patterns 11 and 16 are formed is also arbitrary.

  In FIG. 1, for the sake of simplicity, the signal wiring pattern 16 is disposed in the inner layer, the signal wiring pattern 11 is disposed in the front surface layer, and as a result, the stub 21a is formed from the signal wiring pattern 16 to the lower back surface. Is shown.

  An insulator 23 is formed on the entire back surface, which is the eighth wiring pattern layer, that is, the surface layer of the multilayer wiring printed board 10. The insulator 23 is made of, for example, solder resist or resin. The insulator 23 is used for protecting the back surface of the multilayer wiring printed board 10 and preventing bleeding at the time of soldering.

  An electric conductor 24 is formed on the entire surface of the insulator 23. According to this configuration, the termination circuit 25 shown in FIG. 2 described later can be formed by the capacitance formed by the insulator 23 and the resistance of the electric conductor 24. The termination circuit 25 attenuates noise caused by reflection at the stub 21a.

  The insulator 23 is made of an insulator such as an epoxy resin. The insulator 23 changes its capacitance value by changing its thickness, dielectric constant, and the like. The electric conductor 24 is made of, for example, carbon. For example, carbon is formed into a sheet shape, thereby facilitating adhesion with the insulator 23. For example, the sheet-like electric conductor 24 is thermocompression bonded to an insulator 23 made of an epoxy resin.

  In addition, in order to obtain a sufficient termination effect, the electrical conductor 24 is suitably a substance having an electrical conductivity with respect to the thickness of the following formula (1).

  The electric conductor 24 may be other than carbon, and may be any substance as long as the electric conductivity with respect to the thickness is about the above-described formula 1. For example, the structure which mixed metal powder, such as iron, aluminum, or copper, with insulators, such as an epoxy resin, may be sufficient.

  In this case, as with sheet-like carbon, an epoxy resin mixed with metal powder may be formed on the sheet and attached by thermocompression bonding, or formed by a technique similar to solder resist silk printing. You may make it do.

  In order to form the electrical conductor 24 by printing, for example, a liquid epoxy resin mixed with metal powder is applied to the back surface of the multilayer wiring printed board 10 and the excess epoxy resin is removed by a squeegee or the like.

<Equivalent circuit of termination circuit>
FIG. 2 is an explanatory diagram showing an equivalent circuit in the signal wiring patterns 11, 16, the through hole 21, and the termination circuit 25 of FIG. 1.

  In FIG. 2, the uppermost wiring path 26 shows the signal line of the signal wiring pattern 11, and the lower wiring path 27 shows the signal line of the through hole 21 excluding the stub 21a.

  A wiring path 28 below the left side of the wiring path 27 indicates a signal path of the signal wiring pattern 16, and a wiring path 29 below the wiring path 27 indicates a signal path of the stub 21a. A termination circuit 25 is connected below the wiring path 29. The termination circuit 25 is formed by the capacitance of the insulator 23 and the resistance of the electric conductor 24 as described above. The ground connected via the capacitor is the power supply / ground wiring pattern 20.

  A signal output from the wiring path 28 that is the wiring path of the signal wiring pattern 16 is branched at a signal branch point between the wiring path 27 that is a through hole and the wiring path 29 that is a stub 21a, and a part of the signal is stubbed. Proceed to the 21a side, that is, to the wiring path 29.

  Then, the signal that has advanced to the wiring path 29 is terminated by the termination circuit 25. In other words, the signal that has traveled to the stub 21a is terminated by an impedance that is constituted by the capacitance formed by the insulator 23 and the resistance formed by the electric conductor 24 at the end of the stub 21a.

  In this way, by terminating the stub 21a with the capacitance and the resistance, signal reflection at the end of the stub 21a can be greatly reduced. As a result, the influence of the reflected signal returning to the signal branch point and superimposed on the signal waveform as noise can be reduced.

  On the other hand, in the case of a multilayer wiring board with no stub termination, the stub end is an open stub, but the signal at the stub end is reflected and the reflected signal returns to the signal branch point as noise. It will be superimposed on the signal waveform.

  In addition, the termination circuit 25 can be formed at low cost because it is only necessary to affix the sheet-like electric conductor 24 such as carbon to the insulator 23 such as solder resist.

<Phase change of stub resonance frequency>
FIG. 3 is an explanatory diagram showing an example of a phase change at the stub resonance frequency.

  FIG. 3 shows the phase of the traveling wave at the branch point at the resonance frequency and the phase of the wave returning to the branch point without being terminated at the stub end.

  As shown in FIG. 3, the phase difference between the wave reflected and returned from the end of the stub and the traveling wave at the branch point shown in FIG. 2 is about 180 °, which cancel each other. In such a relationship, the insertion loss of the wave traveling through the through-hole, that is, the signal degradation increases, but the influence of the reflected wave is small because the amplitude of the reflected wave is small because of the termination.

  In the present embodiment, the termination of the stub 21a is the presence of the insulator 23, whereby the ground and the stub 21a are insulated in a DC manner, and an increase in transmission loss at low frequencies can be prevented.

<Example of frequency characteristics>
FIG. 4 is an explanatory diagram showing an example of frequency characteristics of insertion loss of a wave traveling through a through hole. FIG. 4 shows the result of comparing the loss of the signal transmitted through the through hole with and without the capacitance in the equivalent circuit of FIG.

  In FIG. 4, the solid line indicates the frequency characteristic of the open stub, the alternate long and short dash line indicates the frequency characteristic of the stub terminated only by the resistor, and the dotted line indicates the frequency characteristic of the stub 21a terminated by the capacitance and the resistance.

  In the case of an open stub in which the stub is not terminated, loss at a resonance frequency of about 12.5 GHz, for example, is increased. However, a stub terminated by only a resistor and a stub 21a terminated by a capacitor and a resistor is used. Then, the loss at the resonance frequency of about 12.5 GHz is reduced in any case.

  However, as can be seen from FIG. 4, by stub termination, the loss is greater in the case of stub termination other than the resonance frequency. In the case of the stub termination with only the resistor, the loss is larger when the stub termination is performed up to about 0 Hz. However, in the case of the stub termination with the capacitance and the resistance, there is no loss increase penalty due to the stub termination at frequencies of about 100 MHz or less. I can confirm.

  In the example of FIG. 4, the characteristic impedances of the signal wiring, the through hole, and the stub in FIG. 2 are all the same, and the resistance value of the resistor used for the stub termination is the same as the characteristic impedance.

  Here, when the reflection at the termination circuit 25 is suppressed to 10% or less, the resistance value R of the resistor in FIG. 2 is expressed by Equation 2 with respect to the characteristic impedance Z0 of the stub 21a. Moreover, the capacity | capacitance needs the capacitance value C of Formula 3 grade.

  As described above, by forming the termination circuit 25 composed of a capacitor and a resistor on the multilayer wiring printed board 10, an increase in transmission loss at a low frequency of, for example, about 100 MHz or less can be prevented.

  In addition, since the chip resistor or the like serving as a termination resistor is not necessary, the cost of the multilayer wiring printed board 10 can be reduced. Furthermore, since it is not necessary to mount a chip resistor, it is possible to prevent a defect caused by a defect of the chip resistor or a connection failure.

<Other examples of multilayer printed circuit board>
In the first embodiment, the insulator 23 and the electric conductor 24 are formed on the entire back surface of the multilayer wiring printed board 10. However, the insulator 23 and the electric conductor 24 are formed as follows. It is not limited to this.

  For example, as shown in FIG. 5, the insulator 23 and the electric conductor 24 are formed not at the entire back surface of the multilayer wiring printed board 10 but at, for example, the end of the stub 21 a on the back surface of the multilayer wiring printed board 10 and the vicinity thereof. You may make it do. Thereby, since the area which forms the insulator 23 and the electrical conductor 24 can be made small, the cost of the multilayer wiring printed circuit board 10 can be reduced.

  Furthermore, in the first embodiment, the case where one stub 21a is formed in one through hole 21 has been described. However, for example, the signal wiring pattern 11 of FIG. 1 is not wired to the surface layer of the main surface of the multilayer wiring printed board 10 but may be wired to the inner layer of the multilayer wiring printed board 10.

  In that case, the stubs 21a are respectively formed at the upper and lower ends of the through hole 21, and by forming two termination circuits 25 accordingly, an increase in transmission loss can be more effectively prevented. .

  When the two termination circuits 25 are formed, the same structure as the insulator 23 and the electric conductor 24 formed on the back surface of the multilayer wiring printed board 10 may be formed on the main surface of the multilayer wiring printed board 10. .

<Selection of electrical conductor material>
The resistances of the above formulas 1 and 2 are realized by the electric conductor 24 between the end of the stub 21a and the surrounding pattern 20. When the radius of the end of the stub 21a is a, the distance from the center of the end to the surrounding pattern 20 is b, and the thickness of the electric conductor 24 is h, the resistance is expressed as shown in Equation 4.

  Here, σ is the electric conductivity of the electric conductor 24. In Equation 4, when a and b are about 100 μm to about 1 mm and h is about 10 μm to about 30 μm, the electrical conductivity of the electrical conductor is about 10 S / m to about 10,000 S / m in order to make the resistance about 50Ω. m must be present.

(Embodiment 2)
<Modification of stub end>
In the first embodiment, the disadvantage that the loss becomes large up to about 0 Hz at a frequency other than the stub resonance when terminated only by the resistor is compensated by adding a capacitor.

  The second embodiment is also the same as the first embodiment, and has a configuration in which a capacitor and a resistor are connected in series to the stub end with respect to the ground, and the termination circuit 25 is the same as that in FIG. However, the resistance value of the termination circuit 25 in FIG. 2 of the first embodiment satisfies the following expression (5).

  The difference from the first embodiment is that the reflection at the stub end becomes fixed-end reflection by using a resistance value that satisfies the following formula, and a 180 ° phase shift is used. .

  FIG. 6 is an explanatory diagram showing an example of a phase change at the stub resonance frequency.

  FIG. 6 shows the phase change until the wave that has advanced to the stub returns to the signal branch point again at the resonance frequency at the time of the open stub.

  In FIG. 6, the phase change from the signal branch point to the stub end is the same as that in the case of the termination shown in FIG. Shift 180 °.

  The wave reflected by the stub end returns to the signal branch point again has a phase difference of 360 ° from the original wave, and is in a reinforcing relationship. By such a principle, stub resonance at the time of open stub can be avoided.

<Example of frequency characteristics>
FIG. 7 is an explanatory diagram showing an example of the frequency characteristic of the insertion loss of the wave traveling through the through hole to which the termination circuit 25 having a resistance value satisfying Equation 5 is connected.

  Also in FIG. 7, the solid line indicates the frequency characteristic of the open stub, the one-dot chain line indicates the frequency characteristic of the stub terminated only by the resistor, and the dotted line indicates the frequency characteristic of the stub 21a terminated by the capacitance and the resistance. Yes.

  From the insertion loss graph shown in FIG. 7, it can be confirmed that the insertion loss is remarkably reduced at the resonance frequency of about 12.5 GHz at the time of the open stub regardless of the presence or absence of the capacitance. At a low frequency of about 100 MHz or less, the loss with the capacity is smaller than that without the capacity.

  In this way, loss at a resonance frequency of about 12.5 GHz can be further reduced, and transmission loss can be further reduced.

  When the 180 ° phase shift of the fixed end reflection is used, an increase in loss due to stub resonance during open stub can be avoided as described above. On the other hand, since the stub is connected to the ground with a low impedance, there is a risk that even if a capacitor is used, the insertion loss increases at a low frequency.

  In the example of FIG. 7, when the capacitance and resistance are terminated in series, there is a loss peak at about 1.6 GHz. However, such an increase in loss can be recovered by using a peaking amplifier or the like having a high amplification factor for a signal of a specific frequency.

  Also, as shown in FIG. 6, the reflected wave overlaps with the original wave with a phase difference of 360 °, thereby causing intersymbol interference. However, since data transmission such as communication interface and high-speed serial interface is known to always interfere with the code after 2 bits, the signal is output on the transmission side or the recovery is performed on the reception side. Can be made. Alternatively, the influence can be avoided by using coding that has a lower limit in the band to be used, such as 8B10B.

(Embodiment 3)
<Overview>
In the first and second embodiments, the technology for preventing an increase in signal transmission loss at a low frequency by using a capacitor at the end has been described. When the capacitance value to be terminated is small, the impedance becomes high, and there is a possibility that a sufficient termination effect cannot be obtained. Therefore, in order to obtain the effects described in the first and second embodiments, it is necessary to secure a sufficient capacity.

  In the third embodiment, a technique for securing a larger capacity in the termination circuit 25 will be described.

<Configuration example of multilayer printed circuit board>
FIG. 8 is a sectional view showing an example of a multilayer wiring printed board according to the third embodiment.

  The multilayer printed circuit board 10 shown in FIG. 8 has the same configuration as that of FIG. 1 of the first embodiment. The difference from FIG. 1 is that an electric conductor 31 is provided at the end of the stub 21a. It is a point.

  The through hole 21 has a hollow cylindrical shape as described in the first embodiment. Therefore, the stub 21a has a hollow portion as compared with the case where the end surface of the stub 21a is covered with an electric conductor. The stub end has a smaller capacity.

  In order to prevent this, an electric conductor 31 is provided and covered so as to fill a hollow hole in the end face of the stub 21a. The electric conductor 31 may be any conductive material, such as a solder ball. The solder ball is buried by being pushed into a hollow hole in the end face of the stub 21a, or the hole is filled by heating.

  As a result, the surface area of the end face of the stub 21a electrically connected to the electric conductor 31 is increased, and as a result, the area where the end face of the stub 21a is in contact with the insulator 23 is increased, thereby increasing the capacitance value. it can.

  The electric conductor 31 may be a conductor material as described above, and the shape thereof may be other than a spherical shape, and the end face of the hollow stub 21a can be in contact with the lid. Any shape is acceptable.

  Further, by making the through hole 21 have a pad-on-via structure, the same effect can be obtained without using the electric conductor 31. In this case, as shown in FIG. 9, the hollow portion of the through hole 21 is filled with resin 32, and the plating 26 is formed on the end surface of the stub 21a.

  Furthermore, although not shown in the figure on the surface of the plating 26, it is possible to increase the surface area, thereby increasing the capacity.

  As described above, since a sufficient capacitance value in the termination circuit 25 can be secured, an increase in transmission loss can be prevented more stably.

(Embodiment 4)
<Summary of invention>
The outline of the fourth embodiment is a printed wiring board (multilayer wiring printed board 10). This printed wiring board has a plurality of wiring layers, a through hole (through hole 21), an insulator (insulator 23), and a first electric conductor (electric conductor 24).

  The through holes are connected to signal wiring patterns (signal wiring patterns 11 and 16) formed in different wiring layers to form a signal transmission path. The first electric conductor is connected to the ground wiring (power supply / ground wiring pattern 18) formed in the inner wiring layer, and is formed in the same wiring layer as the ground wiring.

  The insulator is formed so as to cover the end face of the stub (stub 21a) that does not form a signal transmission path among the through holes.

  Hereinafter, the embodiment will be described in detail based on the above-described outline.

<Overview>
In the first to third embodiments, the termination circuit 25 is formed on the back surface of the multilayer wiring printed board 10. However, the termination circuit 25 is not necessarily formed in such a configuration.

  In the fourth embodiment, a configuration in which the termination circuit 25 is formed in the inner layer of the multilayer wiring printed board 10 will be described. Here, the termination technique in the through hole 21 formed by, for example, the back drill technique will be described.

  The back drill technique is to remove a stub portion from a through-hole structure once made by a drill. In this back drill technique, a stub having a certain length is left in order to prevent the signal wiring from being cut in the printed circuit board. Therefore, noise caused by reflection on the remaining stub will adversely affect signal transmission.

<Configuration example of multilayer printed circuit board>
FIG. 10 is a cross-sectional view showing an example of a multilayer wiring printed board according to the fourth embodiment.

  As shown in the figure, the multilayer wiring printed board 10 includes signal wiring patterns 11 and 16, power / ground wiring patterns 12, 13, 14, 15, 17, 18, 19, 20, a through hole 21, and an insulating layer 22. Each is formed. These wiring configurations are the same as those in FIG. 1 in the first embodiment.

  10 is different from FIG. 1 in that the power / ground wiring pattern 18 is a ground wiring, the electric conductor 24 is formed below the power / ground wiring pattern 18, and the stub 21a is described above. It is the point removed by the back drill.

  The stub 21a is removed by back drilling. A hole 21b is formed in the portion removed by back drilling. In the through hole 21, a stub 21a having a certain length is left to prevent the signal wiring pattern 16 from being cut during back drilling.

  The insulating layer 22 interposed between the remaining stub 21a and the electric conductor 24 becomes a capacity. Further, the electric conductor 24 connected to the power supply / ground wiring pattern 18 which is the ground wiring becomes a resistor, and the termination circuit 25 shown in FIG. 2 is formed.

  As described above, the termination circuit 25 including the capacitance and the resistance can be formed on the multilayer wiring printed board 10 even with the back-drilled through hole 21. Thereby, for example, an increase in transmission loss at a low frequency of about 100 MHz or less can be prevented.

  In addition, the cost of the multilayer printed circuit board 10 can be reduced, and defects caused by defects in the chip resistance, connection defects, and the like can be prevented.

(Embodiment 5)
<Summary of invention>
The outline of the present embodiment is an electronic device (server 40) having a printed wiring board (multilayer wiring printed board 10). The printed wiring board has a plurality of wiring layers, a through hole (through hole 21), an insulator (insulator 23), and a first electric conductor (electric conductor 24).

  The through holes are connected to signal wiring patterns (signal wiring patterns 11 and 16) formed in different wiring layers to form a signal transmission path. The insulator is formed on the wiring layer on the front surface layer (back surface). The first electrical conductor is formed on the surface of the insulator.

  The insulator is connected to the ground wiring (power supply / ground wiring pattern 20) formed in the wiring layer, and is formed so as to cover the end surface of the stub (stub 21a) that does not form the signal transmission path among the through holes. The

  Hereinafter, the embodiment will be described in detail based on the above-described outline.

<Example of server configuration>
In the fifth embodiment, an example in which the multilayer wiring printed board 10 in the first to fourth embodiments is used as a server will be described.

  FIG. 11 is an explanatory diagram showing an example of a server having a blade structure according to the fifth embodiment.

  As shown in FIG. 11, the server 40 is provided with a backboard 41 which is an interconnect installed in a direction perpendicular to the floor which is the installation surface. The backboard 41 is connected to a plurality of multilayer printed wiring boards 10 serving as a mother board.

  The server 40 has a so-called blade structure in which the required number of multilayer printed circuit boards 10 is increased or decreased according to required performance and connected to the backboard 41. Various electronic components such as a CPU (Central Processing Unit) and a memory (not shown) are mounted on the multilayer wiring printed board 10.

  These multilayer wiring printed boards 10 are connected to the mounting surface of the backboard 41 in the vertical direction, that is, orthogonal to the mounting surface. The multilayer printed wiring board 10 is connected at substantially equal intervals in the horizontal (X) direction, that is, the long side direction, and in the vertical (Y) direction, that is, the short side direction in the backboard 41 of FIG. The CPU mounted on the multilayer wiring printed board 10 is connected to the CPU mounted on another multilayer wiring printed board 10 via the back board 41.

  11 shows an example in which the multilayer wiring printed board 10 is arranged and connected in the horizontal direction and the vertical direction, but the connection of the multilayer wiring printed board 10 is not limited to this. . For example, the multilayer printed circuit board 10 may be arranged only in the horizontal (X) direction of the backboard 41 or may be arranged only in the vertical (Y) direction of the backboard 41.

  In the server 40, the signal transmission speed of the multilayer wiring printed circuit board 10 which is a mother board is a key as a factor for improving performance, and it is required to increase the amount of data exchanged per second.

  Therefore, by using the multilayer wiring printed board 10 having the configuration of the first to fourth embodiments as the motherboard of the server 40, it is possible to reduce the voltage pulse waveform deterioration phenomenon due to reflection at the through hole.

  Moreover, in the multilayer printed circuit board 10, as described in the first to fourth embodiments, not only the signal insertion loss at high frequency is reduced by the termination circuit 25 of FIG. 2, but also the insertion loss at low frequency is adjusted. Can be made smaller.

  Thereby, since the transmission speed of a signal can be raised, the performance of the server 40 can be improved. Moreover, since the noise resulting from reflection of a stub can be reduced, the reliability of the server 40 can be improved.

  In the fifth embodiment, the server 40 is described as an example of the electronic device using the multilayer wiring printed board 10. However, the electronic device is not limited to this and uses a multilayer wiring printed board. If it is.

  The multilayer wiring printed board 10 can obtain a greater effect when used in an electronic device that exchanges data at high speed. Electronic devices that exchange data at high speed include, for example, routers and storage devices other than servers.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

  In addition, this invention is not limited to above-described embodiment, Various modifications are included. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to one having all the configurations described.

  Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. . In addition, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

10 multilayer wiring printed circuit board 11 signal wiring pattern 12 power supply / ground wiring pattern 13 power supply / ground wiring pattern 14 power supply / ground wiring pattern 15 power supply / ground wiring pattern 16 signal wiring pattern 17 power supply / ground wiring pattern 18 power supply / ground wiring pattern 19 Power supply / ground wiring pattern 20 Power supply / ground wiring pattern 21 Through hole 21a Stub 22 Insulating layer 23 Insulator 24 Electric conductor 25 Termination circuit 26 Wiring path 27 Wiring path 28 Wiring path 29 Wiring path 31 Electric conductor 32 Resin 40 Server 41 Backboard

Claims (15)

Multiple wiring layers;
A through hole connected to a signal wiring pattern formed in a different wiring layer and forming a signal transmission path;
An insulator formed in the wiring layer of the surface layer;
A first electrical conductor formed on a surface of the insulator;
Have
The printed circuit board, wherein the insulator is connected to a ground wiring formed in the wiring layer and covers an end surface of a stub that does not form the signal transmission path in the through hole. In the printed wiring board of Claim 1,
The end surface of the stub and the ground wiring are formed in the wiring layer of the surface layer in the printed wiring board,
The printed circuit board, wherein the insulator is formed so as to cover the entire surface layer. In the printed wiring board of Claim 1,
The end surface of the stub and the ground wiring are formed in the wiring layer of the surface layer in the printed wiring board,
The printed circuit board, wherein the insulator is formed so as to cover an end face of the stub and a part of the ground wiring. In the printed wiring board of Claim 1,
The printed wiring board, wherein the first electrical conductor has an electrical conductivity of 1 to 10000 s / m. In the printed wiring board of Claim 1,
Furthermore, the printed wiring board which has a 2nd electrical conductor which plugs up the end surface of the said stub. In the printed wiring board of Claim 1,
Furthermore, the through hole is a printed wiring board in which a hollow portion of the through hole is filled with resin, and plating is formed on an end surface of the stub. Multiple wiring layers;
A through hole connected to a signal wiring pattern formed in a different wiring layer and forming a signal transmission path;
A first electrical conductor connected to the ground wiring formed in the wiring layer of the inner layer and formed in the wiring layer of the same layer as the ground wiring;
An insulator formed so as to cover an end surface of the stub that does not form the signal transmission path among the through holes;
A printed wiring board. The printed wiring board according to claim 7,
The end surface of the stub is a printed wiring board, which is a portion left when the stub that does not form the signal transmission path is removed by a drill in the through hole. The printed wiring board according to claim 7,
The printed wiring board, wherein the first electrical conductor has an electrical conductivity of 1 to 10000 s / m. Multiple wiring layers;
A through hole connected to a signal wiring pattern formed in a different wiring layer and forming a signal transmission path;
An insulator formed in the wiring layer of the surface layer;
A first electrical conductor formed on a surface of the insulator;
Have
The electronic device includes a printed wiring board that is connected to a ground wiring formed in the wiring layer and has a printed wiring board formed so as to cover an end surface of a stub that does not form the signal transmission path among the through holes. The electronic device according to claim 10.
The end surface of the stub and the ground wiring are formed in the wiring layer of the surface layer in the printed wiring board,
The said insulator is an electronic device formed so that the whole surface of the said surface layer may be covered. The electronic device according to claim 10.
The end surface of the stub and the ground wiring are formed in the wiring layer of the surface layer in the printed wiring board,
The said insulator is an electronic device formed so that the end surface of the said stub and a part of said ground wiring may be covered. The electronic device according to claim 10.
The electronic device, wherein the electric conductivity of the first electric conductor is 1 to 10,000 s / m. The electronic device according to claim 10.
Furthermore, the electronic apparatus which has a 2nd electrical conductor which plugs up the end surface of the said stub. The electronic device according to claim 10.
Further, in the electronic device, the through hole is filled with a resin in a hollow portion of the through hole, and plating is formed on an end surface of the stub.

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