JP2005302799A - Multilayer printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the radiation of electromagnetic noise of an inner layer wiring in a multilayer printed wiring board and greatly reduce the influence of electromagnetic noise due to induction from the outside or other wiring.
In a multilayer printed wiring board, ground or wiring fixed to a power supply potential is arranged on the upper and lower layers of a signal line arranged in an inner layer, and further, ground or power supply on both sides or one side of the same layer as the signal line. A shield strip line, a through hole or a via hole fixed at a potential is arranged.
[Selection] Figure 1

Description

  The present invention relates to a multilayer printed wiring board having high electromagnetic compatibility (EMC).

  Various EMC countermeasures have been taken so that electronic devices can coexist in the intended electromagnetic environment without causing functional degradation or damage.

  As the most general countermeasure, the layer configuration of the printed wiring board is changed and the insulator thickness is reduced.

  An example of a four-layer printed wiring board that is often used for a main board of a personal computer will be described.

  FIG. 8 shows the outer shape of a four-layer printed wiring board, and FIG. 9 shows a perspective view with the insulator removed.

  Reference numeral 1 denotes a first layer, 2 denotes a second layer, 3 denotes a third layer, 4 denotes a fourth layer, and each wiring layer is insulated by 5, 6 and 7 insulating layers. The thickness of the wiring layer is about 10 μm to 40 μm, and the thickness of the insulator layer is about 100 μm to 200 μm.

  In the case of a four-layer substrate, signal layers are arranged on the first and fourth layers, and two inner layers are used as a ground layer and a power supply layer. For this reason, electromagnetic noise was radiated from the surface layer of the printed wiring board.

  Therefore, as a measure for improving the radiated electromagnetic noise characteristics in the printed wiring board, the surface of the 1st and 4th layers of the printed wiring board is a ground layer or a power supply layer, and signal wiring is performed in 2 or 3 layers, Layer structure that confines electromagnetic noise generated from signal wiring inside.

  In order to reduce the loop area of the current formed by the signal line and the ground layer and reduce the electric field strength of the radiation noise, the thicknesses of the insulating layers 5, 6 and 7 are reduced.

  Etc. have been adopted.

For example, as a prior art, there is JP-A-8-148832.
JP-A-8-148832

  FIG. 10 shows lines of electric force generated when the first and fourth layers of the printed wiring board are ground layers and the three-layer signal wiring of the printed wiring board is wired to the edge of the substrate. In the figure, 8 is a signal wiring, and 11 is a line of electric force.

  When the front and back of the printed wiring board are covered with the ground power supply layer, the radiated electromagnetic noise from the front and back of the board can be greatly reduced, but it seems that the signal wiring is arranged at the edge of the printed wiring board. In such a case, the opening forms a slot antenna in terms of high frequency. Therefore, radiated electromagnetic noise from the end face direction of the substrate becomes a problem.

  FIG. 11 shows the lines of electric lines of force when the signal wiring is placed largely inside from the edge of the printed wiring board. It can be seen that most of the lines of electric force generated from the signal wiring 8 are confined in the printed wiring board.

  In general, when wiring a high-speed signal on the inner layer as described above, the wiring is placed at a distance of 20 to 100 times the thickness of the insulating layer from the ground of the substrate or the edge of the power supply layer. It is possible to reduce the electric field lines leaking into the screen. Therefore, it is possible to realize a printed wiring board that hardly emits radiation noise. However, since the insulating layer thickness between the layers of the multilayer substrate is about 100 to 200 μm, if the previous rule is applied to the inner layer peripheral portion of the substrate, a wiring prohibited region of about 2 to 20 mm is generated outside the signal wiring. This has been a problem at the time of designing a printed wiring board for a device that is particularly required to be downsized.

  The intensity of radiated electromagnetic noise is proportional to the square of the frequency and the current and current loop area. Therefore, reducing the thickness of the insulating layer of the printed wiring board is a very effective measure for reducing radiated electromagnetic noise because the current loop area is reduced.

  However, when the thickness of the printed wiring board insulating layer is reduced, the thickness of the printed wiring board becomes thin and the rigidity becomes low. For this reason, the disconnection of the wiring of a printed wiring board, the crack of a board | substrate, etc. have also become a problem.

  An object of the present invention is to provide a printed wiring board having high rigidity, small size, and greatly reducing radiated electromagnetic noise.

  For shields in which wiring fixed to ground or power supply potential is placed on the upper and lower layers of signal lines placed on the inner layer of a multilayer printed wiring board, and also connected to ground or power supply potential on both sides or one side of the same layer as the signal lines It is characterized in that it has a function of preventing the emission of electromagnetic noise by arranging strip lines, through holes, or via holes.

  Further, by providing the shielding strip line, through hole, or via hole in this way, it is possible to greatly reduce the influence of electromagnetic noise due to induction from the outside or other wiring in the printed wiring board.

  As described above, according to the present invention, in the multilayer printed wiring board, wiring fixed to the ground or the power supply potential is disposed on the upper and lower layers of the signal line disposed on the inner layer, and further, both sides or one side of the same layer as the signal line. Electromagnetic noise radiation can be prevented by arranging a shield strip line connected to the ground or power supply potential.

  Further, by providing the shield electrode in this way, it is possible to greatly reduce the influence of electromagnetic noise caused by induction from the outside or other wiring in the printed wiring board.

  These effects can be realized without significant changes in the thickness and size of the printed wiring board. Furthermore, a more complete shield can be realized by using a conductive paste or the like.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a perspective view of a multilayer printed wiring board according to an embodiment of the present invention. In the figure, 1 is the first layer, 2 is the second layer, 8 and 9 are the third layer, 4 is the fourth conductive layer, 8 is the signal wiring, 9 is the shield wiring, and 12 is the potential of the shielding wiring. The through-hole for fixing to the ground is shown.

  FIG. 2 shows a state of electric lines of force generated from the signal wiring 8 in the configuration of FIG. Despite the fact that the signal wiring is arranged near the edge of the printed wiring board, the electric lines of force generated from the signal wiring are placed in the printed wiring board by the shield wiring 9 and the first and fourth layer ground layers. You can see that you are trapped.

  Generally, when signal wirings are arranged in parallel, there is a change in the characteristic impedance of the signal wirings. In this embodiment, if the wiring width is W, the influence on the impedance of the signal wirings by taking 2 W from the shield wiring. Can be reduced to about 5%.

  Therefore, when the signal wiring width is 0.15 mm, the required area on one side of the signal wiring is about 0.45 mm, and the radiated electromagnetic noise is greatly reduced without changing the signal wiring constants with a small printed wiring board. It can be reduced.

In order to prevent the shield wiring from resonating with the harmonics of the signal flowing in the signal wiring, the interval T _p between the through holes in FIG. 1 is the wavelength of the highest harmonic frequency of the signal transmitted to the signal wiring. Must be less than half of Therefore, the following relational expression holds.

ｆ_m：信号線に伝送される信号の最大高調波周波数（Ｈｚ）
λ：最大高調波の波長
ε_r：プリント配線板の比誘電率
Ｃ：３×１０⁸（ｍ／ｓ）
ここで、１００ＭＨｚのクロックを信号配線に伝送した場合のスルーホールの間隔を求めてみる。

f _m : Maximum harmonic frequency (Hz) of the signal transmitted to the signal line
λ: wavelength of maximum harmonic ε _r : relative dielectric constant of printed wiring board C: 3 × 10 ⁸ (m / s)
Here, an interval between through holes when a 100 MHz clock is transmitted to the signal wiring is obtained.

In general, a rectangular wave needs to contain a harmonic component of about 3 to 10 times, so when calculating as f _m = 1 GHz,
The maximum pitch of the necessary through holes is 64 mm.

  A second embodiment according to the present invention will be described below with reference to FIG.

  FIG. 3 is a perspective view of a multilayer printed wiring board according to the second embodiment of the present invention. In the figure, 1 is the first layer, 2 is the second layer, 8 is the third layer, 4 is the fourth conductive layer, 8 is the signal wiring, and 12 is an alternative through hole for the shield wiring.

  FIG. 4 shows a view of the electric lines of force generated from the signal wiring 8 in the configuration of FIG. 3 as seen from the thickness direction of the printed wiring board. It can be seen that the electric lines of force generated from the signal wiring are confined in the through-hole 12 printed wiring board.

Since the thickness of the printed wiring board is sufficiently small with respect to the wavelength of the highest harmonic frequency of the signal transmitted to the signal wiring, the through hole interval T _{p is set} to the wavelength of the highest harmonic frequency of the signal transmitted to the signal wiring. By setting it to ½ or less, a signal having a frequency equal to or lower than the highest harmonic frequency can be cut off. Therefore, the following relational expression holds.

ｆ_m：信号線に伝送される信号の最大高調波周波数（Ｈｚ）
λ：最大高調波の波長
ε_r：プリント配線板の比誘電率
Ｃ：３×１０⁸（ｍ／ｓ）
ここで、１００ＭＨｚのクロック信号配線に伝送した場合のスルーホールの間隔を求めてみる。

f _m : Maximum harmonic frequency (Hz) of the signal transmitted to the signal line
λ: wavelength of maximum harmonic ε _r : relative dielectric constant of printed wiring board C: 3 × 10 ⁸ (m / s)
Here, the interval between the through holes in the case of transmission to the clock signal wiring of 100 MHz is obtained.

In general, a rectangular wave needs to contain a harmonic component of about 3 to 10 times, so when calculating as f _m = 1 GHz,
The maximum pitch of the necessary through holes is 64 mm.

  On the other hand, the change in characteristic impedance of the signal wiring due to the through hole is very small and can be ignored. Therefore, the interval can be reduced to the wiring reference level determined from the manufacturing process capability of the printed wiring board. In a general printed wiring board, an interval of about the minimum wiring width is taken. Therefore, when the signal wiring width is 0.15 mm, a necessary area on one side of the signal wiring is about 0.30 mm. Therefore, the radiated electromagnetic noise can be greatly reduced without changing the signal wiring constants and hardly affecting the printed wiring board size.

  FIG. 5 is a perspective view of a multilayer printed wiring board according to the third embodiment of the present invention. In the figure, 1 is the first layer, 2 is the second layer, 8 is the third layer, 4 is the fourth conductive layer, 8 is the signal wiring, and 12 is a shield with a conductive material such as conductive paste. Show.

  By covering the entire end face of the printed wiring board with a conductive material fixed to the ground or the power supply potential, radiation of electromagnetic noise can be prevented.

  FIG. 6 shows a case where a part of the end surface is covered with a conductive material fixed to the ground or the power supply potential.

  By keeping the interval expressed by the following relational expression, the radiated electromagnetic noise can be greatly reduced.

ｆ_m：信号線に伝送される信号の最大高調波周波数（Ｈｚ）
λ：最大高調波の波長
ε_r：プリント配線板の比誘電率
Ｃ：３×１０⁸（ｍ）
図７は、本発明の第４の実施の形態に係る多層プリント配線板の透視図である。同図において１は第１層、２は第２層、８は第３層、４は第４層の導電層であり、８は信号配線、９はシールド配線、１２はシールド配線の電位をグランドに固定する為のスルーホールを１５は信号配線層の上下の層に設けたシールド配線を示す。

f _m : Maximum harmonic frequency (Hz) of the signal transmitted to the signal line
λ: wavelength of maximum harmonic ε _r : relative dielectric constant of printed wiring board C: 3 × 10 ⁸ (m)
FIG. 7 is a perspective view of a multilayer printed wiring board according to the fourth embodiment of the present invention. In the figure, 1 is the first layer, 2 is the second layer, 8 is the third layer, 4 is the fourth conductive layer, 8 is the signal wiring, 9 is the shield wiring, and 12 is the ground potential of the shield wiring. Reference numeral 15 denotes a through hole for fixing to the shield wiring provided in the upper and lower layers of the signal wiring layer.

  When the upper and lower layers of the signal wiring are not fixed to the ground or the power supply layer, as shown in FIG. 7, the ground or power supply wiring is arranged in the upper and lower layers so as to cover the signal wiring and the shield wiring. The function of preventing noise emission and the influence of electromagnetic noise due to induction from other wiring in the printed wiring board can be greatly reduced.

  As shown in FIG. 3, the configuration of the shield wiring and the through hole or via hole may be a configuration of only the through hole or via hole in which the shield wiring is omitted.

1 is a perspective view of a printed wiring board according to a first embodiment of the present invention. The figure which shows the electric lines of force in the said printed wiring board. The perspective view of the printed wiring board which concerns on the 2nd Embodiment of this invention. The figure which shows the electric lines of force in the said printed wiring board. The perspective view of the printed wiring board which concerns on the 3rd Embodiment of this invention. The perspective view of the printed wiring board which concerns on the 3rd Embodiment of this invention. The perspective view of the printed wiring board which concerns on the 4th Embodiment of this invention. The external view of the 4-layer printed wiring board by a prior art. FIG. 9 is a perspective view of FIG. 8. FIG. 10 is a diagram showing lines of electric force generated in FIG. 9. The figure which shows the electric force line | wire which generate | occur | produces when a radiation electromagnetic noise countermeasure is performed in a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st layer of a printed wiring board 2 2nd layer of a printed wiring board 3 3rd layer of a printed wiring board 4 4th layer of a printed wiring board 5 Insulating layer between the 1st layer and 2nd layer of a printed wiring board 6 Printed wiring Insulating layer between the second layer and the third layer of the board 7 Insulating layer between the third layer and the fourth layer of the printed wiring board 8 Signal wiring 9 Shield wiring 11 Electric field lines 12 Through hole or via hole 13 Shielding with conductive material 14 Shielding with conductive material

Claims (5)

  For shields in which wiring fixed to ground or power supply potential is placed on the upper and lower layers of signal lines placed on the inner layer of a multilayer printed wiring board, and also connected to ground or power supply potential on both sides or one side of the same layer as the signal lines A multilayer printed wiring board characterized by arranging strip lines.   A multilayer printed wiring board in which the shield strip line is connected to a ground or a power source through a through hole or a via hole. A multilayer printed wiring board in which a through hole or via hole connection interval T _p is expressed by the following equation.

f _m : Maximum harmonic frequency (Hz) of the signal transmitted to the signal line
ε _r : dielectric constant of printed wiring board C: 3 × 10 ⁸ (m / s)   In the multilayer printed wiring board, wiring fixed to the ground or the power supply potential is arranged on the upper and lower layers of the signal line arranged in the inner layer, and the end surface of the printed wiring board is surrounded by a conductive material such as conductive paste or solder or all around. A multilayer printed wiring board characterized by a partially covered structure. 2. A structure according to claim 1, wherein only through holes or via holes are arranged at intervals T _p as follows instead of the strip line for shielding.

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