JP2016018837A - Printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printed wiring board in which deterioration of signal transfer characteristics based on the difference of signal amplitude before and after reflection can be suppressed.SOLUTION: A printed wiring board 1 includes a first via hole 21 and a second via hole 22 penetrating a multilayer board 10, first wiring 31 connecting a transmission unit 5 and the first via hole 21 electrically, second wiring 32 connecting the first via hole 21 and second via hole 22 electrically, third wiring 33 connecting the second via hole 22 and a reception unit 6 electrically, first stub wiring 41 connecting the first via hole 21 electrically, second stub wiring 42 connecting the second via hole 22 electrically, a first termination 45 connecting the first stub wiring 41 electrically, and a second termination 46 connecting the second stub wiring 42 electrically.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a printed wiring board using a multilayer board.

  As a conventional technique, a multilayer substrate, a via hole penetrating the multilayer substrate, a surface layer wiring that is wired to a surface layer of the multilayer substrate and connected to a first tip portion that is one tip portion of the via hole, and the interior of the multilayer substrate At least one inner layer wiring connected to a portion other than the upper and lower tip portions of the conductive portion of the via hole is connected to the surface layer wiring on the opposite side of the first tip portion of the conductive portion of the via hole. 2. Description of the Related Art A printed wiring board including a conductive member connected to a second tip that is not provided is known (see, for example, Patent Document 1).

  The conductive member of the conventional printed wiring board has an impedance at a predetermined frequency when the conductive member side is viewed from the first connection point closest to the second tip portion among the connection points between the inner layer wiring and the conductive portion of the via hole. The electric length is such that the value of becomes larger than a predetermined value. When the tip of the conductive member is open, the sum of the electrical length from the first connection point to the second tip and the electrical length of the conductive member is substantially n of the wavelength corresponding to the predetermined frequency. / 2 times (n is a natural number). When the tip of the conductive member is grounded, the sum of the electrical length from the first connection point to the second tip and the electrical length of the conductive member is substantially equal to the wavelength corresponding to the predetermined frequency. Upper (2n-1) / 4 times (n is a natural number) is set.

JP 2004-146810 A

  However, since the conventional printed wiring board does not consider the difference in signal amplitude before and after reflection, the signal that is not canceled may interfere with the signal propagating through the conductive portion of the via hole, and the signal transmission characteristics may be degraded. There is.

  An object of the present invention is to provide a printed wiring board capable of suppressing deterioration in signal transmission characteristics based on a difference in signal amplitude before and after reflection.

  The present invention provides a multilayer substrate in which substrates and wiring layers are alternately arranged, a propagation part that is part of a path through which the signal propagates, and a signal separated from the path propagates. A via hole that is divided in the thickness direction of the multilayer substrate in the stub portion, a first wiring that is connected to the propagation portion exposed on the surface of the multilayer substrate, the signal propagates, and the propagation portion and the stub portion The second wiring through which the signal propagates, the stub wiring connected to the stub portion exposed on the back surface of the multilayer substrate, and the path that is connected to the stub wiring and propagates through the stub wiring. A printed wiring board is provided that includes a termination portion that reflects a part of the signals separated from each other.

  The length of the stub part and the length of the stub wiring are a length normalized by the wavelength of the signal separated from the path propagating through the stub part, and a part of the signal separated from the path propagating through the stub wiring. It may be determined according to the condition that the lengths normalized at the wavelengths are equal.

The impedance of the termination portion is a condition T ₁₂ = T ₂₃ (1-T) determined by a reflection coefficient T ₁₂ between the stub portion and the stub wiring and a reflection coefficient T ₂₃ between the stub wiring and the termination portion. ₁₂ ).

  According to the present invention, it is possible to suppress deterioration in signal transfer characteristics based on a difference in signal amplitude before and after reflection.

FIG. 1A is a cross-sectional view of a main part of a printed wiring board according to an embodiment of the present invention, and FIG. 1B is a schematic diagram for explaining signal paths. FIG. 2A is a schematic diagram for explaining connection of the first wiring, the first via hole, and the first stub wiring of the printed wiring board according to the embodiment of the present invention. ) Is a schematic diagram for explaining the connection of the third wiring, the second via hole, and the second stub wiring. FIG. 3 is an equivalent circuit diagram of the printed wiring board according to the embodiment of the present invention.

[Embodiment]
(Overall configuration of printed wiring board 1)
FIG. 1A is a cross-sectional view of a main part of a printed wiring board according to an embodiment of the present invention, and FIG. 1B is a schematic diagram for explaining signal paths. Note that, in each drawing according to the embodiment described below, the ratio between figures may be different from the actual ratio.

  As shown in FIG. 1A, the printed wiring board 1 includes a multilayer board 10 in which boards and wiring layers are alternately arranged, a transmitter 5 and a receiver 6 mounted on a surface 110 of the multilayer board 10. It is equipped with. As an example, the multilayer substrate 10 includes first to third substrates 11 to 13 and first to fourth wiring layers 14 to 17.

  Further, the printed wiring board 1 includes a first via hole 21 and a second via hole 22 that penetrate the multilayer substrate 10, a first wiring 31 that electrically connects the transmission unit 5 and the first via hole 21, and A second wiring 32 that electrically connects the first via hole 21 and the second via hole 22; a third wiring 33 that electrically connects the second via hole 22 and the receiving unit 6; A first stub wiring 41 electrically connected to the via hole 21, a second stub wiring 42 electrically connected to the second via hole 22, and a first electrically connected to the first stub wiring 41. , And a second terminal portion 46 that is electrically connected to the second stub wiring 42. In the following description, connection is used to mean electrical connection unless otherwise specified.

(Configuration of the first to third substrates 11 to 13)
As an example, the first to third substrates 11 to 13 are rigid substrates such as a glass epoxy substrate.

  On the surface 110 of the first substrate 11, the transmission unit 5 and the reception unit 6 are disposed, and the first wiring 31 and the third wiring 33 are formed. The transmission unit 5 is, for example, an FPGA (Field Programmable Gate Array), and the reception unit 6 is, for example, an optical transceiver. The transmission unit 5 outputs a high-frequency signal 7 having a frequency of 1 GHz or more, for example.

  On the back surface 130 of the third substrate 13, the first stub wiring 41 and the second stub wiring 42 are formed, and the first termination portion 45 and the second termination portion 46 are disposed. .

  A first wiring layer 14 is formed on the surface 110 of the first substrate 11. A second wiring layer 15 is formed between the first substrate 11 and the second substrate 12. A third wiring layer 16 is formed between the second substrate 12 and the third substrate 13. A fourth wiring layer 17 is formed on the back surface 130 of the third substrate 13.

(Configuration of the first to fourth wiring layers 14 to 17)
In the first wiring layer 14, a first wiring 31 and a third wiring 33 are formed.

  In the second wiring layer 15, a second wiring 32, a wiring 35, and a wiring 36 are formed. The wiring 35 and the wiring 36 are electrically independent of the second wiring 32, the first via hole 21, and the second via hole 22.

  In the third wiring layer 16, wirings 37 and wirings 38 are formed. The wiring 37 and the wiring 38 are electrically independent of the first via hole 21 and the second via hole 22.

  A first stub wiring 41 and a second stub wiring 42 are formed in the fourth wiring layer 17.

  The 1st thru | or 3rd wiring 31-33, the 1st stub wiring 41, and the 2nd stub wiring 42 are formed using the metal material which has electroconductivity, such as copper and silver, as an example. In addition, the wirings 35 to 38 are formed using the same metal material as the first to third wirings 31 to 33, the first stub wiring 41, and the second stub wiring 42 as an example.

(Configuration of the first wiring 31)
The first wiring 31 is connected to the transmitter 5 disposed on the surface 110 of the first substrate 11 and the end 215 of the first via hole 21 exposed on the surface 110 of the first substrate 11. As illustrated in FIG. 1B, the first wiring 31 constitutes a part of a path 70 that is a propagation path of the signal 7 output from the transmission unit 5.

(Configuration of the second wiring 32)
The second wiring 32 is connected to the first via hole 21 and the second via hole 22 and constitutes a part of the path 70.

(Configuration of the third wiring 33)
The third wiring 33 is connected to the receiving unit 6 disposed on the surface 110 of the first substrate 11 and the end 225 of the second via hole 22 exposed on the surface 110 of the first substrate 11. As illustrated in FIG. 1B, the third wiring 33 constitutes a part of the path 70 of the signal 7 output from the transmission unit 5.

(Configuration of first via hole 21 and second via hole 22)
The first via hole 21 penetrates through the multilayer substrate 10, one end 215 is connected to the first wiring 31, and the other end 216 is connected to the first stub wiring 41. One end 215 is exposed on the surface 110 of the multilayer substrate 10. The other end 216 is exposed on the back surface 130 of the multilayer substrate 10.

  The first via hole 21 is formed by forming a conductive metal material such as copper on the inner wall of a through hole provided so as to penetrate the multilayer substrate 10.

  The second via hole 22 penetrates through the multilayer substrate 10, one end 225 is connected to the third wiring 33, and the other end 226 is connected to the second stub wiring 42. The end 225 is exposed on the surface 110 of the multilayer substrate 10. Further, the end 226 is exposed on the back surface 130 of the multilayer substrate 10.

  FIG. 2A is a schematic diagram for explaining connection of the first wiring, the first via hole, and the first stub wiring of the printed wiring board according to the embodiment of the present invention. ) Is a schematic diagram for explaining the connection of the third wiring, the second via hole, and the second stub wiring. FIG. 3 is an equivalent circuit diagram of the printed wiring board according to the embodiment of the present invention.

  Further, as shown in FIG. 2A, the first via hole 21 has a propagation part 210 that is a part of the path 70 through which the signal 7 propagates, and a stub part 211 through which the signal 7a separated from the path 70 propagates. The multilayer substrate 10 is divided in the thickness direction.

  The propagation unit 210 and the stub unit 211 are separated by the second wiring 32. From the portion where the second wiring 32 is connected to the portion where the first wiring 31 is connected is the propagation unit 210, and the first stub wiring 41 is connected from the portion where the second wiring 32 is connected. The portion up to the portion is the stub portion 211. In FIG. 1A, as an example, the boundary between the propagation unit 210 and the stub unit 211 is indicated by a dotted line.

  Further, as shown in FIG. 2B, the second via hole 22 has a propagation part 220 that is a part of the path 70 through which the signal 7 propagates and a stub part 221 through which the signal 7 c separated from the path 70 propagates. The multilayer substrate 10 is divided in the thickness direction.

  The propagation unit 220 and the stub unit 221 are separated by the second wiring 32. From the portion where the second wiring 32 is connected to the portion where the third wiring 33 is connected is the propagation part 220, and the second stub wiring 42 is connected from the portion where the second wiring 32 is connected. The portion up to the portion is the stub portion 221. In FIG. 1A, as an example, the boundary between the propagation unit 220 and the stub unit 221 is indicated by a dotted line.

  The first via hole 21 and the second via hole 22 are formed by forming a conductive metal material such as copper on the inner wall of a through hole provided so as to penetrate the multilayer substrate 10.

The length of the stub portion 211 of the first via hole 21 is L _{1 as} shown in FIG. The length of the stub portion 221 of the second via hole 22 is set to L ₁ which is the same as that of the stub portion 221 as shown in FIG. The significance of the length _{L 1} of the stub portion 211 and the stub 221 will be described later.

  As shown in FIG. 1B and FIG. 2A, the stub portion 211 of the first via hole 21 propagates the signal 7a separated from the path 70 and transmits a signal at the boundary with the first stub wiring 41. 7a is reflected to form a first reflection path 71.

  Further, as shown in FIGS. 1B and 2B, the stub portion 221 of the second via hole 22 propagates the signal 7c separated from the path 70 and has a boundary with the second stub wiring 42. Thus, the signal 7c is reflected to form the third reflection path 73.

The impedance of the stub portions 211 and 221 is Z _{1 as} shown in FIG.

(Configuration of the first and second stub wirings 41 and 42)
The length of the first stub line 41, as shown in FIG. 2 (a), and _{L 2.} The length of the second stub wiring 42 is set to L ₂ which is the same as that of the first stub wiring 41 as shown in FIG. The significance of the length L ₂ of the first stub line 41 and the second stub line 42, described later.

  In the first stub wiring 41, a part of the signal 7a propagating through the stub portion 211 of the first via hole 21 is transmitted and propagated as the signal 7b, and the signal 7b is transmitted at the boundary with the first termination portion 45. A second reflection path 72 is formed by reflection.

  In addition, a part of the signal 7c propagating through the stub portion 221 of the second via hole 22 is transmitted to the second stub wiring 42 and propagated as the signal 7d, and the signal at the boundary with the second termination portion 46 is transmitted. 7d reflects and the 4th reflective path | route 74 is formed.

The impedance of the first and second stub line 41, as shown in FIG. 3, and _{Z 2.}

(Configuration of the first and second terminal portions 45 and 46)
The first and second terminal portions 45 and 46 are configured to reflect the signals 7 b and 7 d propagating through the first and second stub wirings 41 and 42. Impedance of the first and second end portions 45 and 46, as shown in FIG. 3, and _{Z 3.}

  As shown in FIG. 3, the first and second terminal portions 45 and 46 include, for example, a resistor having one end grounded.

(A second condition for determining the first condition and _{Z 3} for determining the _{L 2)}
When an electronic component or the like is arranged on the multilayer substrate, for example, the degree of freedom of arrangement of the electronic component or the like may be improved if a part of the wiring is arranged inside the multilayer substrate. As an example, the printed wiring board 1 has a first via hole 21 for electrical connection between the first wiring 31 formed on the surface 110 of the multilayer substrate 10 and the second wiring 32 formed inside. A second via hole 22 is formed in order to establish electrical connection between the third wiring 33 and the second wiring 32 formed on the surface 110. Hereinafter, a first condition for determining the length L ₂ of the first stub line 41, and the first second condition for determining the impedance Z ₃ of the terminal unit 45 will be described. The condition for determining the length L ₂ of the second stub line 42, and conditions for determining the impedance Z ₃ of the second end portion 46 is the same as the first and second conditions. The impedance _Z 1 to Z _{3 is} a _{Z 1 <Z} 2 _{<Z 3} or _Z 3 _<Z 2 _<either satisfy the condition of _{Z 1,} the impedance _{Z 1} is greater in adjustable range Better. This is because canceling the reflected wave results in energy loss, so that the energy flowing to the stub portions 211 and 221 is preferably small. In addition, the ratio of signals flowing to the stub units 211 and 221 is the same as that of the parallel circuit. The transmission path through the first wiring 31, the propagation unit 210, the second wiring 32, the propagation unit 220, and the third wiring 33 determined by the impedance and the ratio of the impedance Z _1.

  A part of the signal 7 propagating downward in the first via hole 21 from one end 215 toward the other end 216 is partially reflected by the end 216 through the stub part 211 and propagates through the propagation part 210. Interfering with the signal 7

In order to mitigate interference with the signal 7 propagating through the propagation unit 210, for example, the stub unit 211 is arranged so that the signal 7a propagating toward the end 216 and the signal reflected by the end 216 cancel each other. it is conceivable to adjust the length L _1. However, since the length of the stub portion 211 mainly depends on the thickness of the multilayer substrate 10, it is difficult to adjust it in accordance with the wavelength of the signal 7a to be propagated. Moreover, the method of removing the stub part 211 so that reflection does not occur is more difficult because the stub part 211 must be removed accurately.

  The first stub wiring 41 is provided in order to mitigate interference of the signal 7 a reflected at the end 216 of the first via hole 21. In the first stub wiring 41, the signal 7 b that is a part of the signal 7 a propagating through the stub portion 211 propagates, and reflection also occurs in the first stub wiring 41.

  When the first stub wiring 41 is an open stub (open end), the signal 7b propagating through the first stub wiring 41 is totally reflected and amplified at the end to propagate through the first stub wiring 41, and the stub Interfering with the signal 7a of the unit 211. However, even if the phase of the signal 7b is opposite to that of the signal 7a, the amplitudes are different from each other, making it difficult to cancel the signal 7a. Therefore, the printed wiring board 1 according to the present embodiment is provided with the first termination portion 45 at the end portion of the first stub wiring 41 for adjusting the reflection amount for adjusting the amplitude and the like.

(The first of the conditions that determine the _{L 2)}
The length L ₁ of the stub portion 211 and the length L ₂ of the first stub wiring 41 propagate through the first stub wiring 41 and the length normalized by the wavelength λ ₁ of the signal 7 a propagating through the stub portion 211. It is determined using the first condition expressed by the following formula (1) that the lengths normalized by the wavelength λ ₂ of the signal 7 b are equal.
L ₁ / λ ₁ = L ₂ / λ ₂ (1)

The first condition is a condition for matching the phase of the signal 7 a propagating through the stub portion 211 with the phase of the signal 7 b propagating through the first stub wiring 41. The length L ₁ of the stub portion 211, since the length determined by the thickness of the multilayer substrate 10 and the like, the length L ₂ of the first stub line 41 is adjusted in accordance with the first condition.

(Second condition for determining the _{Z 3)}
As shown in FIG. 3, when the impedance of the stub portion 211 is Z ₁ , the impedance of the first stub wiring 41 is Z ₂ , and the impedance of the first termination portion 45 is Z ₃ , the stub portion 211 and the first The reflection coefficient T ₁₂ between the stub wirings 41 and the reflection coefficient T ₂₃ between the first stub wiring 41 and the first terminal end 45 are expressed using the following expressions (2) and (3).
T ₁₂ = (Z ₂ −Z ₁ ) / (Z ₂ + Z ₁ ) (2)
_{T 23 = (Z 3 -Z 2} ) / (Z 3 + Z 2) ··· (3)
Based on the above equations (2) and (3), the condition that the amplitude of the signal 7a propagating through the stub portion 211 and the amplitude of the signal 7b propagating through the first stub wiring 41 is equal is as follows: This is the second condition represented by (4).
T ₁₂ = T ₂₃ (1 + T ₁₂ ) (4)

The second condition is that the impedance Z ₁ and the impedance Z ₂ are also determined by the length L ₁ of the stub portion 211 obtained by the first condition and the length L _{2 of} the first stub wiring 41. It is used to adjust the impedance Z ₃ of the terminal portion 45.

The lengths L ₁ and L ₂ and the impedances Z _{1 to} Z ₃ of the stub portion 221, the second stub wiring 42, and the second termination portion 46 of the second via hole 22 are determined according to the first and second conditions. Is done.

  When the printed wiring board 1 has a configuration satisfying the first and second conditions, when the frequency of the signal 7 is 7 GHz, the signal transmission characteristic of about +5 dB per via hole is improved.

(Operation of printed circuit board 1)
Hereinafter, an example of the operation of the printed wiring board 1 will be described with reference to the drawings.

  As illustrated in FIG. 1B, when the transmission unit 5 of the printed wiring board 1 outputs a signal 7 to the first wiring 31, the signal 7 is transmitted through the transmission unit 5 and the first wiring 31. It propagates to the propagation part 210 of the via hole 21. When the signal 7 propagates through the propagation unit 210, a part of the signal 7 propagates to the stub portion 211 of the first via hole 21 as a signal 7 a. A part of the signal 7a is transmitted through the first stub wiring 41 and propagated as the signal 7b, and the other is reflected at the boundary with the first stub wiring 41, and the stub part 211 is directed toward the propagation part 210. Propagate.

  The signal 7 b is reflected at the boundary between the first stub wiring 41 and the first terminal end 45, propagates to the stub portion 211, and cancels out by interfering with the signal 7 a propagating through the stub portion 211.

  As described above, the signal 7 in which the signals 7 a and 7 b cancel each other due to the interference caused by the signals 7 a and 7 b propagates to the propagation part 220 of the second via hole 22 through the second wiring 32. Similarly to the first via hole 21, the signal 7 propagated to the propagation unit 220 cancels the signals 7 c and 7 d due to interference by the signals 7 c and 7 d and reaches the reception unit 6 through the third wiring 33. The receiving unit 6 performs a predetermined process based on the signal 7 with improved signal transfer characteristics.

(Effect of embodiment)
The printed wiring board 1 according to the present embodiment adjusts the amplitudes of the signals 7 b and 7 d that reflect the first and second stub wirings 41 and 42, so that the stub portion 211 and the first stub wiring 41 are connected. The reflected signal 7a, the signal 7b reflected between the first stub wiring 41 and the first terminal end 45 are canceled out, and the signal 7c reflected between the stub part 221 and the second stub wiring 42, the second stub. Since the signal 7d reflected between the wiring 42 and the second terminal portion 46 can be canceled, deterioration of the transmission characteristic of the signal 7 based on the difference in signal amplitude before and after the reflection can be suppressed.

Further, the printed wiring board 1 can determine the length L ₁ of the stub wiring and the impedance Z _{3 of the} terminal end according to the first and second conditions.

[Other embodiments]
The embodiments of the present invention are not limited to the above-described embodiments, and various embodiments are possible. For example, in the above embodiment, the case where two via holes are provided in the signal path between the transmission unit 5 and the reception unit 6 has been described. However, one via hole is provided in the signal path between the transmission unit 5 and the reception unit 6. And an electronic circuit corresponding to the transmitter 5 or the receiver 6 may be formed inside the multilayer substrate 10.

  Further, the printed wiring board 1 may be formed with three or more via holes.

DESCRIPTION OF SYMBOLS 1 ... Printed wiring board, 5 ... Transmission part, 6 ... Reception part, 7, 7a-7d ... Signal,
DESCRIPTION OF SYMBOLS 10 ... Multilayer board | substrate, 11-13 ... 1st thru | or 3rd board | substrate, 14-17 ... 1st thru | or 4th wiring layer,
21 ... 1st via hole, 22 ... 2nd via hole, 31-33 ... 1st thru | or 3rd wiring,
35, 36, 37, 38 ... wiring, 41 ... first stub wiring, 42 ... second stub wiring,
45 ... first termination, 46 ... second termination, 70 ... path,
71-74 ... 1st thru | or 4th reflective path | route, 110 ... front surface, 130 ... back surface, 210 ... propagation part,
211 ... Stub part, 215 ... End part, 216 ... End part, 220 ... Propagation part, 221 ... Stub part,
225 ... End, 226 ... End

Claims (3)

A multilayer board in which boards and wiring layers are alternately arranged;
A via hole that penetrates the multilayer substrate in the thickness direction and includes a propagation part that forms part of a path through which a signal propagates and a stub part through which a signal separated from the path propagates;
A first wiring that is connected to the propagation part exposed on the surface of the multilayer substrate and through which the signal propagates;
A second wiring that is connected to a boundary between the propagation portion and the stub portion and that propagates the signal;
Stub wiring connected to the stub portion exposed on the back surface of the multilayer substrate;
A termination that is connected to the stub wiring and reflects a signal that is separated from the path and propagates through the stub wiring through the stub wiring;
Printed wiring board with The length of the stub portion and the length of the stub wiring are standardized by the length normalized by the wavelength of the signal propagating through the stub portion and the wavelength of a part of the signal propagating through the stub wiring separated from the path. Determined by the condition that the converted lengths are equal,
The printed wiring board according to claim 1. The impedance of the termination portion is a condition T ₁₂ = T ₂₃ (1 + T ₁₂ ) determined by a reflection coefficient T ₁₂ between the stub portion and the stub wiring and a reflection coefficient T ₂₃ between the stub wiring and the termination portion. Determined by
The printed wiring board according to claim 2.

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