WO2010103722A1

WO2010103722A1 - Circuit board

Info

Publication number: WO2010103722A1
Application number: PCT/JP2010/000659
Authority: WO
Inventors: 及川昭; 栗林宏行
Original assignee: 住友ベークライト株式会社
Priority date: 2009-03-10
Filing date: 2010-02-04
Publication date: 2010-09-16
Also published as: TWI492674B; TW201038149A

Abstract

In a circuit board (1) having the ground layer (5) and the signal wiring (3A, 3B) arranged on the ground layer with an insulator layer (2) interposed therebetween, a shield layer (7) composed of a conductive material is formed on an insulation coating layer (4) covering the signal wiring on the side opposite to the ground layer (5). The portion which is above the insulator layer and faces the singnal wiring (3A) requiring a control of a characteristic impedance is configured as an opening (7a) in the shield layer where there is no shield layer arranged. When the signal wiring fulfils the function of single end transmission, the distance U between the opposite outsides of the signal wiring (3A) and the opening edge (7b) of the shield layer is set in the range of 3t1≤U≤20t1, where the thickness of the insulator layer (2) is t1. With such structure, a circuit board which can control the characteristic impedance of the signal wiring (3A) and can exhibit the effect also in EMI countermeasure is provided.

Description

Circuit board

The present invention relates to a ground layer and a circuit board in which signal wirings are arranged with respect to the ground layer via an insulator layer.

For example, a circuit board on which a device operating in a high frequency band is mounted has a characteristic impedance (hereinafter also referred to as Zo) of a signal transmission path (hereinafter also referred to as signal wiring) in order to suppress signal reflection and waveform distortion. It is necessary to match the input / output impedance of the device.
In order to match the characteristic impedance of the signal transmission path described above, a microstrip structure in which a ground layer is opposed to a signal transmission path (strip line) having an appropriate pattern width with an insulating layer having an appropriate thickness interposed therebetween is employed. Yes.

The ground layer in the circuit board structure described above serves as an electrical reference plane that defines the characteristic impedance of the signal transmission path. In general, the characteristic impedance is often selected to be around 50Ω for single-ended transmission and around 100Ω for differential transmission. Note that Zo in the circuit board described above is a ratio of reactance L per unit length of the signal transmission path and capacitance C per unit area between the signal transmission path and the ground layer (reactance L / electrostatic capacity). It is a value approximated by the square root of the capacitance C).

By the way, in recent years, thin rigid boards and flexible circuit boards are frequently used as circuit boards for mounting the above-described devices. When such circuit boards are adopted, of course, the signal transmission path for the ground layer is naturally used. The interlayer is narrow (thin), and the value of the capacitance C between them increases almost in inverse proportion to the dimension between the layers.
Therefore, in the above-described thin multilayer circuit board, in order to obtain the desired Zo, the width of the signal transmission path is narrower (thinner) than that of a conventional circuit board with a thick interlayer, A means for suppressing the increase in the capacitance C must be employed.

In this way, in order to obtain a desired Zo, when the signal wiring is to be formed thin, there is a case where the signal wiring has to be made so thin that it is difficult to process. Even if signal wiring can be processed, the thinner the signal wiring, the higher the ratio of circuit processing accuracy and line width variation, and the Zo variation increases accordingly.

For this reason, there arises a problem that signal reflection and waveform distortion occur in the signal wiring portion where the change of Zo is large. Furthermore, since the wiring resistance value of the signal wiring is increased, there is a problem that the higher the signal frequency supplied to the signal wiring, the worse the transmission characteristics.

Therefore, in order to solve the above-described technical problem, the ground layer formed as a so-called solid electrode layer is removed in a mesh shape so that the opposing area between the ground layer and the signal wiring per unit area is substantially reduced. Proposals have been made to ensure the width of the signal wiring by making it smaller. This is disclosed in the following prior art documents.

JP 7-32463 A

By the way, in the circuit board of the microstrip structure disclosed in the above-described prior art document, although the above-described ground layer side effectively acts as an EMI (electromagnetic wave interference) countermeasure, on the signal wiring side on the opposite side, The effect cannot be expected.
Therefore, it is conceivable that the outer surface layer (insulating coating layer) of the signal wiring that requires EMI countermeasures is covered with a conductive shield layer made of, for example, silver paste to substantially form a strip structure.

However, when the shield layer described above is disposed on the surface layer side of the signal wiring, a capacitive coupling newly occurs between the signal wiring and the shield layer on the insulating coating layer. That is, the capacitance between the signal wiring and the ground layer is added to the capacitance between the signal wiring and the shield layer, making it difficult to properly control Zo of the signal transmission path.

The present invention has been made by paying attention to the technical problems described above, and can sufficiently control the characteristic impedance of the signal transmission path, and also exhibits the effect in the above-mentioned EMI countermeasures. It is an object of the present invention to provide a circuit board having a signal wiring capable of performing single-ended transmission and a circuit board having a pair of signal wirings capable of performing differential transmission.

The circuit board according to the present invention, which has been made to solve the above-described problems, includes a ground layer and a signal wiring disposed through an insulator layer with respect to the ground layer, and capacitive coupling between the ground layer and the signal wiring. By controlling the characteristic impedance of the signal wiring, an insulating coating layer is formed on the signal wiring disposed on the insulator layer, Further, a shield layer made of a conductive material is formed, and an opening of the shield layer where the shield layer is not laid is formed on the insulating coating layer facing the signal wiring.

In the case where the signal wiring on which the characteristic impedance is controlled is a signal wiring on which single-ended transmission is performed, the signal wiring on which the characteristic impedance is controlled when the thickness of the insulator layer is t1. It is preferable that the distance U between both outer sides of the shield layer and the opening edge of the shield layer is set in a range of 3t1 ≦ U ≦ 20t1.

Further, when the signal wiring for which characteristic impedance control is performed is a pair wiring that is differentially transmitted, when the distance between the pair wirings is S, both outer sides of the pair wiring and the shield It is desirable that the distance U from the opening edge of the layer is set in a range of 3S ≦ U ≦ 20S.

In this case, the ground layer facing the signal wiring whose characteristic impedance is controlled is formed in a mesh-shaped conductor portion provided with a number of holes, and a solid electrode that is not provided with holes outside the mesh-shaped conductor portion. Preferably, the boundary between the mesh-like conductor portion and the solid electrode region coincides with the opening edge of the shield layer in a direction perpendicular to the substrate surface.

This is because the insulating layer between the ground layer and the signal wiring and the insulating coating layer between the signal wiring and the shielding layer are each made of a thin circuit board having a thickness of 100 μm or less. The effect can be exhibited remarkably.

In addition, a linear guard pattern having the same potential as that of the ground layer is disposed on the insulator layer along both outer sides of the signal wiring for which characteristic impedance is controlled, and the linear guard is provided. A circuit board configured so that the central portion in the width direction of the pattern is positioned at the opening edge of the shield layer can also be suitably employed.

In this case, in a preferred embodiment, the ground layer and the guard pattern are connected via a via hole, and the guard pattern and the shield layer are connected via an opening formed in the insulating coating layer. .

According to the circuit board described above, the insulating coating layer facing the signal wiring that needs to be controlled by Zo is formed in the opening portion of the shield layer where the shield layer is not laid. The degree of capacitance coupling between the two can be greatly reduced. Thereby, appropriate control of the characteristic impedance of the signal wiring can be achieved.

On the other hand, the signal wiring is provided with a circuit board capable of exhibiting a sufficient effect for the above-mentioned EMI countermeasures although the shield effect is slightly lowered by forming the opening of the shield layer. can do.

It is the laminated structure figure which showed 1st Embodiment of the circuit board provided with the signal wiring by which single end transmission is made with sectional drawing. It is the top view which showed the signal wiring part on the insulator layer shown to FIG. 1A. It is the top view which showed a preferable example of the ground layer in the circuit board provided with the signal wiring by which single end transmission is made. It is a characteristic diagram which shows the relationship between the distance U of the signal wiring and shield layer opening edge in which single end transmission is made, and interlayer thickness t1. It is the laminated structure figure which showed 2nd Embodiment of the circuit board provided with the signal wiring by which single-ended transmission is made with sectional drawing. It is the top view which showed the signal wiring part on the insulator layer shown to FIG. 4A. It is the laminated structure figure which showed 3rd Embodiment of the circuit board provided with the signal wiring by which single end transmission is made with sectional drawing. It is the top view which showed the signal wiring part on the insulator layer shown to FIG. 5A. It is the laminated structure figure which showed 1st Embodiment of the circuit board provided with the pair signal wiring transmitted differentially with sectional drawing. It is the top view which showed the signal wiring part on the insulator layer shown to FIG. 6A. It is the top view which showed a preferable example of the ground layer in the circuit board provided with the pair signal wiring transmitted differentially. It is a characteristic diagram which shows the relationship between the distance U of the pair signal wiring and shield layer opening edge which are differentially transmitted, and the distance S between lines. It is the laminated structure figure which showed 2nd Embodiment of the circuit board provided with the pair signal wiring transmitted differentially with sectional drawing. It is the top view which showed the signal wiring part on the insulator layer shown to FIG. 9A. It is the laminated structure figure which showed 3rd Embodiment of the circuit board provided with the pair signal wiring transmitted differentially with sectional drawing. It is the top view which showed the signal wiring part on the insulator layer shown to FIG. 10A.

Hereinafter, a circuit board provided with signal wiring for single-end transmission according to the present invention will be described with reference to FIGS. 1 to 5, and a circuit with pair signal wiring for differential transmission according to the present invention will be described below. The substrate will be described later with reference to FIGS. *

FIG. 1A shows the laminated structure of the first embodiment of the circuit board provided with the signal wiring for performing the above-mentioned single-end transmission, and FIG. 1B shows the signal wiring on the insulator layer shown in FIG. 1A. It is the top view which showed the part at the substantially same scale.

The circuit board shown in FIGS. 1A and 1B is provided with a ground layer and a signal wiring for performing single-ended transmission with respect to the ground layer through an insulator layer, and a signal wiring that requires control of characteristic impedance. Is configured with a microstrip structure, and a signal wiring that does not require control of characteristic impedance is provided with a shield layer to form a strip structure.

In this embodiment, a film-like base substrate is employed as the insulator layer 2, and the

signal wirings

3A and 3B are provided on one surface (the upper side in FIG. 1A) of the base substrate 2. The insulating coating layer 4 is laminated on the upper surface (the upper side in FIG. 1A) of the

signal wirings

3A and 3B through an adhesive layer (not shown).
On the other hand, a ground layer 5 is formed on the other surface (lower side in FIG. 1A) of the base substrate 2, and a second insulating coating layer is formed on the lower surface of the ground layer 5 via an adhesive layer (not shown). 6 are stacked.

A shield layer 7 made of a conductive material is formed on the insulating coating layer 4 covering the

signal wirings

3A and 3B on the surface opposite to the ground layer 5 through the base substrate 2, and has a characteristic impedance. On the insulating coating layer 4 facing the signal wiring 3A that needs to be controlled, an opening 7a of the shield layer where the shield layer is not laid is formed. *

The base substrate 2 that functions as a central insulator layer in which the signal wiring is disposed has a function as a core of the circuit board 1. The material of the base substrate 2 includes a resin film, a fiber substrate, and the like. Materials etc. can be mentioned.

Examples of the material constituting the resin film include polyimide resins such as polyimide resins, polyamide resins, and polyamideimide resins, thermosetting resins such as epoxy resins, and thermoplastic resins such as liquid crystal polymers.
Among these, a polyimide resin or a liquid crystal polymer is preferable. For example, in the case of a polyimide resin, it is excellent in heat resistance and mechanical properties and is easy to obtain. In the case of a liquid crystal polymer, it is suitable for high-speed signal transmission due to its low relative dielectric constant, and it has excellent dimensional stability due to its low hygroscopicity.

Examples of the fiber base material used for the insulating layer include glass fiber base materials such as glass fiber cloth and glass non-fiber cloth, or inorganic fiber base materials such as fiber cloth and non-fiber cloth containing inorganic compounds other than glass, aromatic And organic fiber base materials composed of organic fibers such as aromatic polyamide resins, polyamide resins, aromatic polyester resins, polyester resins, polyimide resins, and fluororesins. Among these base materials, glass fiber base materials represented by glass fiber fabric are preferable in terms of strength and water absorption.

When a fiber base material is used for the insulator layer, it is preferably used in a state where the fiber base material is impregnated with a resin. As the resin impregnated in the fiber base material, a thermosetting resin such as an epoxy resin or an acrylic resin is preferably used, and among these, an epoxy resin is preferable from the viewpoint of heat resistance.

The thickness t1 of the base substrate 2 is preferably in the range of 1 to 100 μm, more preferably in the range of 5 to 50 μm, and more preferably in the range of 10 to 30 μm.
By setting the thickness of the base substrate 2 to be equal to or greater than the lower limit value, it becomes easy to make the signal line width equal to or greater than the processing limit. On the other hand, by setting the thickness to be equal to or less than the upper limit value, rigidity is high. It is possible to suppress the occurrence of excessive thickness and retain the characteristics of a thin substrate such as a flexible circuit board that is flexible.

The

signal wirings

3A and 3B arranged on one surface of the base substrate 2 may be provided directly on the base substrate 2, or may be provided via an adhesive. Then, at the end portion of each signal wiring or an appropriate intermediate portion, it is bonded to a mounting pad such as a semiconductor device (not shown) and functions as the circuit board 1.

It is preferable that the insulating coating layer 4 covering the

signal wirings

3A and 3B via an adhesive layer (not shown) is made of a resin material. Examples of the resin material include polyester resins, polyimides, and liquid crystal polymers. Among these, polyimide is preferable. Thereby, heat resistance and flexibility can be improved.

The thickness t2 of the insulating coating layer 4 is preferably 1 to 100 μm, more preferably 5 to 50 μm, more preferably 10 to 30 μm.
By setting the thickness t2 of the insulating coating layer 4 to be equal to or greater than the lower limit value, it becomes easy to maintain the strength of the resin layer within a practical range, and by setting the thickness t2 or less to the upper limit value, the slidability and the flexibility are maximized. It becomes easy to make it exhibit.

In addition, as a material constituting an adhesive layer (not shown) interposed between the base substrate 2 and the insulating coating layer 4, for example, an acrylic resin, an epoxy resin, a polyimide resin, or the like may be used. it can. Among these, an epoxy resin is preferable, and thereby heat resistance and flexibility can be improved.

The conductive portion as the ground layer 5 disposed on the other surface (back surface) of the base substrate 2 is made of a conductor made of a copper material. In this conductor, a large number of holes formed in a parallelogram opening are formed in a portion facing the signal wiring 3A that requires impedance control. A specific configuration of the ground layer 5 will be described later in detail with reference to FIG.

The second insulating coating layer 6 laminated on the lower surface of the ground layer 5 (the lower side in FIG. 1A) via an adhesive layer (not shown) is preferably made of a resin material. Examples of the resin material include polyester resin, polyimide, liquid crystal polymer, and the like.
Among these, polyimide is preferable. Thereby, heat resistance and flexibility can be improved.

The thickness of the second insulating coating layer 6 is not particularly limited, but is preferably 5 to 50 μm, and particularly preferably 10 to 30 μm. This makes it easy to maintain the strength of the resin layer within a practical range by setting the thickness of the insulating coating layer 6 to be equal to or greater than the lower limit, and maximizing slidability and flexibility by reducing the thickness to the upper limit or less. It is easy to make it to the limit.

The material constituting the adhesive layer (not shown) interposed between the ground layer 5 and the second insulating coating layer 6 is interposed between the base substrate 2 and the insulating coating layer 4. For example, an acrylic resin, an epoxy resin, a polyimide resin, or the like can be used in the same manner as the material constituting the adhesive layer (not shown). Among these, an epoxy resin is preferable, and thereby heat resistance and flexibility can be improved.

The shield layer 7 made of a conductive material formed on the insulating coating layer 4 is formed by printing with a conductive paste (silver paste) or by sticking a conductive shield film, and the characteristic impedance can be controlled. The portion facing the required signal wiring 3A is formed in the opening 7a of the shield layer where the shield layer 7 is not laid as described above.

FIG. 2 is a partially enlarged view of one preferred configuration of the ground layer 5 described above. In FIG. 2, a state in which the signal wiring 3A that requires control of characteristic impedance is superimposed on the ground layer 5 is shown as seen through from a direction perpendicular to the surface. As described above, the ground layer 5 is made of a conductor made of a copper material, and the position of the conductor facing the signal wiring 3A constitutes a mesh-like conductor portion 5B in which a large number of holes are formed. .

That is, the hole in this embodiment is formed as a parallelogram (rhombus) opening by intersecting a plurality of lines in two directions. Each of the plurality of lines in the two directions is preferably inclined with respect to the signal wiring 3A within a range of 5 to 40 degrees. In addition, the longer diagonal line of the rhomboid opening has a mesh pattern that matches the wiring direction of the signal wiring 3A.

In addition, although each above-mentioned opening may have a mutually different magnitude | size (opening area), Preferably, it is made into the opening area of the same magnitude | size. Thereby, the characteristic impedance of the signal wiring 3A can be controlled with high accuracy.

On the other hand, the outside of the mesh-like conductor portion 5B is a solid electrode region 5A made of a copper material in which no hole is formed. The signal wiring 3B that does not require the characteristic impedance control is arranged opposite to the solid electrode region 5A.
According to the configuration shown in FIG. 2, the mesh-like conductor portion 5B is configured only in the portion where the characteristic impedance needs to be controlled, and the rest is the solid electrode region 5A, thereby avoiding an increase in the overall impedance of the ground layer 6. be able to.

In this case, the boundary between the mesh-like conductor portion 5B and the solid electrode region 5A is configured to substantially coincide with an opening edge 7b in the opening 7a of the shield layer described later in a direction orthogonal to the substrate surface.

In order to control the characteristic impedance of the signal wiring, it is effective to provide the mesh conductor portion 5B in the ground layer 5 as described above. However, the characteristic impedance of the signal wiring is determined by the line width and the insulating layer. It is also possible to control the thickness and further by selecting the dielectric constant of the insulating layer. In the present invention, it is not essential to provide the mesh-like conductor portion 5B.

In this embodiment, the thickness t1 of the base substrate 2 and the thickness t2 of the insulating coating layer 4 are both 100 μm or less, and the entire laminated structure is applied to a very thin circuit board. Therefore, the distance U between the signal wiring 3A that needs to control the characteristic impedance and the opening edge 7b of the opening 7a formed in the shield layer dominates the degree of capacitive coupling between them.

In this case, the signal wiring 3A whose characteristic impedance is controlled has the function of single-end transmission as described above, and when the thickness of the insulator layer 2 is t1, It is desirable that the distance U from the opening edge of the shield layer is set in the range of 3t1 ≦ U ≦ 20t1, more preferably 3t1 ≦ U ≦ 10t1.

FIG. 3 shows the ratio between the outer side of the signal wiring 3A and the opening edge 7b of the shield layer 7 as U, and the ratio of both when the thickness of the insulator layer 2 is t1, that is, U / t1. Is a horizontal axis and the characteristic impedance Zo of the signal wiring 3A is shown by a vertical axis.
The characteristic example shown in FIG. 3 is obtained when the line width L of the signal wiring 3A is 100 μm, the interlayer thickness t1 of the insulator layer 2 is 25 μm, and the copper (conductor) residual ratio of the mesh-like conductor portion 5B is 30%. Is. In addition, this is because the boundary between the mesh-like conductor portion 5B and the solid electrode region 5A is configured to coincide with the opening edge 7b of the opening 7a of the shield layer in a direction perpendicular to the substrate surface. .

In this case, the thickness (interlayer thickness) t1 of the insulator layer 2 separating the signal wiring 3A and the ground layer 5 dominates the degree of capacitive coupling between them. Therefore, it is desirable to manage the control of the characteristic impedance using the thickness t1 of the insulator layer 2 as a parameter.

When the distance U between the signal wiring 3A and the opening edge 7b of the shield layer 7 is less than a certain level, capacitive coupling between the signal wiring 3A and the shield layer 7 is increased, and the characteristics of the signal wiring are increased. Impedance control becomes difficult. That is, as shown in the characteristic diagram of FIG. 3, when the value of U is less than 3t1, the capacitive coupling increases rapidly, and this must be avoided.

On the contrary, when the value of U exceeds 3t1, the capacitive coupling of the shield layer 7 with respect to the signal wiring 3A that needs to control the characteristic impedance decreases rapidly, and the impedance control of the signal wiring by the mesh-like conductor portion 5B. Accuracy can be improved.

Although the same measurement was attempted under the condition that the thickness t2 of the insulating coating layer 4 was 100 μm or less, the capacitive coupling of the shield layer 7 to the signal wiring 3A was abrupt when the value of U was less than 3t1. It has been verified that the characteristic impedance of the signal wiring is lowered, and in all cases, it is recognized that the result is almost the same as the characteristic shown in FIG.

On the other hand, if the value of U is set large, the degree of influence on the setting of the characteristic impedance of the signal wiring is reduced, but on the other hand, the shield effect is reduced and cannot be overlooked in the EMI countermeasure.
Therefore, in order to ensure the shielding effect for the signal wiring, the value of U is desirably set to 20 t1 or less, preferably 10 t1 or less.

Therefore, the relationship between the distance U between the outer sides of the signal wiring 3A having the function of single-end transmission and the opening edge 7b of the shield layer and the thickness t1 of the insulator layer 2 is set within the above range. Thus, it is possible to provide a circuit board capable of achieving both adjustment of the characteristic impedance of the signal wiring and measures against EMI.

FIG. 4A shows a laminated structure of a circuit board according to the second embodiment of the present invention in which single-ended transmission is performed, and FIG. 4B shows signal wiring portions on the insulator layer shown in FIG. 4A at substantially the same scale. It is the top view shown by.

In FIG. 4A and FIG. 4B, parts that perform the same functions as the parts shown in FIG. 1A and FIG. 1B already described are denoted by the same reference numerals, and thus detailed description thereof is omitted. The relationship between the distance U between the outer sides of the signal wiring 3A and the opening edge 7b of the shield layer and the thickness t1 of the insulator layer 2 is also the same as described above based on FIG. 1A. Yes.

In this embodiment, linear guard patterns 8 having the same potential as that of the ground layer 5 are arranged on the base substrate 2 along both outer sides of the signal wiring 3A whose characteristic impedance is controlled. It is installed. And the center part of the width direction of the linear guard pattern 8 is comprised so that it may be located in the opening edge 7b of the said shield layer 7. FIG.

According to the configuration described above, the upper surface of the signal wiring 3A requiring control of the characteristic impedance is opened by the opening 7a of the shield layer, but below the signal wiring 3A as viewed in cross section as shown in FIG. 4A. Since both sides and the upper sides are surrounded by a sufficiently close ground, attenuation of the EMI shield characteristic can be minimized.

Further, FIG. 5A shows a laminated structure of the circuit board according to the third embodiment of the present invention in which single-ended transmission is performed, and FIG. 5B shows almost the same signal wiring portion on the insulator layer shown in FIG. 5A. It is the top view shown on a reduced scale.
The configuration shown in FIGS. 5A and 5B is obtained by further adding the configuration requirements to the above-described second embodiment shown in FIGS. 4A and 4B. The ground layer 5 and the guard pattern 8 include: The guard pattern 8 and the shield layer 7 are connected through an opening 4 a formed in the insulating coating layer 4. The guard pattern 8 and the shield layer 7 are connected through a via hole 2 a formed in the insulating base 2.

Via holes 2a connecting the ground layer 5 and the guard pattern 8 are formed at a plurality of locations along the longitudinal direction of the guard pattern 8 as shown in FIG. 5B, and both are connected via the via holes 2a. Has been.
The openings 4a formed in the insulating coating layer 4 are also formed at a plurality of locations along the longitudinal direction of the guard pattern 8, and the guard pattern 8 and the shield layer 7 are formed through the openings 4a. And are connected.

The above-described configuration can be suitably employed in a portion where the circuit board is not bent. According to this configuration, the gap between the grounds on both outer sides of the signal wiring 3A is filled, and the ground layer 5 functions as a ground potential. Further, the mechanical coupling of the guard pattern 8 and the shield layer 7 is strengthened, and it can contribute to further improving the EMI shield characteristics.

Next, a circuit board provided with differential signal transmission pair signal wiring according to the present invention will be described with reference to FIGS.
FIG. 6A shows the laminated structure of the first embodiment of the circuit board provided with the pair signal wiring for differential transmission as described above, and FIG. 6B shows the signal wiring on the insulator layer shown in FIG. 6A. It is the top view which showed the part at the substantially same scale.

In the circuit board 1 shown in FIGS. 6A and 6B, a signal wiring is disposed via a ground layer and an insulator layer with respect to the ground layer, and the signal wiring that requires control of characteristic impedance (see FIG. 6B). A microstrip structure is formed for the part (pair wiring indicated by symbol A), and a shield layer is added to the part of the signal wiring (pair wiring indicated by symbol B in FIG. 6B) that does not require control of the characteristic impedance. is doing.

In this embodiment, a film-like base substrate is employed as the insulator layer 2, and signal wiring that is differentially transmitted is provided on one surface (the upper side in FIG. 6A) of the base substrate 2. 3a and 3b are formed, and an insulating coating layer 4 is laminated on the upper surface (the upper side in FIG. 6A) of the

signal wirings

3a and 3b via an adhesive layer (not shown).
On the other hand, a ground layer 5 is formed on the other surface of the base substrate 2 (lower side in FIG. 6A), and a second insulating coating layer is formed on the lower surface of the ground layer 6 via an adhesive layer (not shown). 6 is formed.

A shield layer 7 made of a conductive material is formed on the insulating coating layer 4 that covers the signal wiring on the opposite side of the ground layer 5 through the base substrate 2, and the characteristic impedance needs to be controlled. On the insulating coating layer 7 facing the

signal wirings

3a and 3b (a pair wiring indicated by a symbol A in FIG. 6B), an opening 7a of the shield layer where the shield layer is not laid is formed.

6A and 6B, the circuit board 1 provided with the differential signal transmission pair signal wiring is the same as the circuit board provided with the signal wiring shown in FIG. 1A and FIG. Each layer having the same structure as that of the laminated structure and performing the same function is indicated by the same reference numeral. Therefore, the details of each layer and an adhesive layer (not shown) will not be described.

FIG. 7 is an enlarged view of a part of one preferred configuration of the ground layer 5 shown in FIG. 6A. FIG. 7 shows a state in which the

signal wirings

3a and 3b that need to control the characteristic impedance described above are superimposed on the ground layer 5 as seen through from a direction orthogonal to the surface. The ground layer 5 shown in FIG. 7 has the same configuration as that of the ground layer 5 shown in FIG. 2, and portions that perform the same function are indicated by the same reference numerals. Therefore, the detailed description of the ground layer 5 is also omitted.

In the embodiment shown in FIGS. 6 and 7, the thickness t1 of the base substrate 2 and the thickness t2 of the insulating coating layer 4 are both 100 μm or less, and the entire laminated structure is extremely thin. Therefore, the distance U between the

signal wirings

3a and 3b that need to be controlled in the characteristic impedance and the opening edge 7b of the opening 7a formed in the shield layer is a capacitive coupling between them. Will dominate the degree.

In this case, the signal wiring for which the characteristic impedance is controlled is a pair wiring that is differentially transmitted. As shown in FIG. 6A, when the distance between the

pair wirings

3a and 3b is S, the signal wiring The distance U between the outer sides of the pair wiring and the opening edge 7b of the shield layer at the position of the line distance S may be set in the range of 3S ≦ U ≦ 20S, more preferably 3S ≦ U ≦ 10S. desirable.

FIG. 8 shows a characteristic example in which the ratio of the distance U to the line-to-line distance S, that is, the value of U / S is shown on the horizontal axis, and the characteristic impedance Zo of the

signal wirings

3a and 3b is shown on the vertical axis. is there.
The characteristic example shown in FIG. 8 is such that the

differential signal lines

3a and 3b have a line width L / interline distance S = 100 μm / 100 μm, an interlayer thickness t1 of the insulator layer 2 = 25 μm, and the copper of the mesh conductor portion 5B. (Conductor) Residual rate = 30%.

When the distance U between the

signal wirings

3a and 3b and the opening edge 7b of the shield layer 7 is below a certain level, the capacitive coupling between the signal wiring and the shield layer is increased, and the characteristic impedance of the signal wiring is reduced. It becomes difficult to control. That is, as shown in the characteristic diagram of FIG. 8, when the value of U is less than 3S, the capacitive coupling increases rapidly, and this must be avoided.

On the contrary, when the value of U exceeds 3S, the capacitive coupling of the shield layer 7 to the

signal wirings

3a and 3b that need to control the characteristic impedance decreases rapidly, and the signal wiring of the mesh-like conductor portion 5B is reduced. Impedance control accuracy can be improved.

The same measurement was attempted under the condition that the thickness t2 of the insulating coating layer 4 was 100 μm or less. However, when the value of U was less than 3S, the capacitive coupling of the shield layer 7 to the signal wiring was abrupt. It has been verified that the characteristic impedance of the signal wiring increases and the characteristic impedance of the signal wiring decreases, and it is recognized that the results are almost the same as the characteristics shown in FIG.

On the other hand, if the value of U is set large, the degree of influence on the setting of the characteristic impedance of the signal wiring is reduced.
Therefore, in order to ensure the shielding effect on the signal wiring, the value of U is desirably set to 20S or less, preferably 10S or less.

Therefore, the characteristic impedance of the signal wiring can be reduced by setting the relationship between the line spacing S of the paired signal wirings and the distance U between the outer sides of the pair wirings and the opening edge 7b of the shield layer within the above range. It is possible to provide a circuit board capable of achieving both adjustment and EMI countermeasures.

As described above, in the case where the signal wiring is a pair wiring that is differentially transmitted, the distance U between the outer sides of the pair wiring and the opening edge 7b of the shield layer is set using the line spacing S of the pair wiring as a parameter. It is appropriate to set and manage the above-mentioned range.

The reason is that the distance between the pair wirings affects the characteristic impedance of the signal wiring next to the shield layer. Therefore, the distance from the signal wiring to the opening edge of the shield layer with respect to the distance between the lines is reduced to the characteristic impedance. This is because the magnitude of the impact is determined.

This can be considered that there is a virtual ground (GND) plane in the center between the lines of the pair wiring, and considering the area of the side surface of the signal line, the distance is the signal next to the shield layer. It is easily determined that the characteristic impedance of the wiring is affected. Therefore, the characteristic impedance of the signal line is determined by the coupling between the wirings, and the distance that the shield layer beyond the opening edge is separated so as not to affect the characteristic impedance can be described in relation to the distance between the signal lines. It depends.

FIG. 9A shows the laminated structure of the second embodiment of the circuit board provided with the differential signal transmission pair signal wiring, and FIG. 9B shows almost the same signal wiring portion on the insulator layer shown in FIG. 9A. It is the top view shown on a reduced scale. The configuration shown in FIGS. 9A and 9B shows an example in which the signal wiring that needs to control the characteristic impedance is a pair wiring that is differentially transmitted, similarly to the example shown in FIGS. 6A and 6B. .

In FIGS. 9A and 9B, parts that perform the same functions as those shown in FIGS. 6A and 6B described above are denoted by the same reference numerals, and therefore detailed description thereof is omitted. The distance U between the outer sides of the pair wiring and the opening edge 7b of the shield layer has the above-described relationship using the line spacing S of the pair wiring as a parameter.

In this embodiment, a linear guard pattern 8 having the same potential as the ground layer 5 is formed along the outer sides of the

signal wirings

3a and 3b whose characteristic impedance is controlled. It is arranged on the top. And the center part of the width direction of the linear guard pattern 8 is comprised so that it may be located in the opening edge 7b of the said shield layer 7. FIG.

According to the configuration described above, the upper surfaces of the

signal wirings

3a and 3b that require control of the characteristic impedance are opened by the opening 7a of the shield layer, but the signal wiring 3a viewed in a cross section as shown in FIG. 9A. , 3b, and the upper and lower sides are surrounded by a sufficiently close ground, so that the attenuation of the EMI shield characteristic can be minimized.

Further, FIG. 10A shows a laminated structure according to the third embodiment of a circuit board having a pair signal wiring for differential transmission, and FIG. 10B shows a signal wiring portion on the insulator layer shown in FIG. 10A. It is the top view shown on substantially the same scale.
The configuration shown in FIGS. 10A and 10B is obtained by further adding the configuration requirements to the second embodiment shown in FIGS. 9A and 9B. The ground layer 5 and the guard pattern 8 are The guard pattern 8 and the shield layer 7 are connected through an opening 4 a formed in the insulating coating layer 4. The guard pattern 8 and the shield layer 7 are connected through a via hole 2 a formed in the insulating base 2.

The via holes 2a connecting the ground layer 5 and the guard pattern 8 are formed at a plurality of locations along the longitudinal direction of the guard pattern 8 as shown in FIG. 10B, and both are connected via the via holes 2a. Has been.
The openings 4a formed in the insulating coating layer 4 are also formed at a plurality of locations along the longitudinal direction of the guard pattern 8, and the guard pattern 8 and the shield layer 7 are formed through the openings 4a. And are connected.

The above-described configuration can be suitably employed in a portion where the circuit board is not bent or the like. According to this configuration, a gap between the grounds on both outer sides of the signal wiring is filled, and the ground layer 5 functions as a ground potential. The mechanical coupling between the guard pattern 8 and the shield layer 7 is strengthened, and it can contribute to further improving the EMI shield characteristics.

The ground layer in the circuit board provided with the signal wiring that performs single-ended transmission and the pair signal wiring that is differentially transmitted as described above is configured to be applied with a reference potential of the circuit. In some cases, the operating power supply of each device may be superimposed. Therefore, the potential applied to the ground layer is not particularly limited.

The circuit board according to the present invention can be used for a printed wiring board, a flexible printed wiring board, a multilayer flexible printed wiring board, and the like, and can be suitably used particularly for a circuit board on which a device operating in a high frequency band is mounted.

1 Circuit board 2 Insulator layer (base material)

2a Via hole

3A,

3B Signal wiring

3a, 3b Signal wiring (pair wiring)
DESCRIPTION OF SYMBOLS 4 Insulation coating layer 4a Insulation coating layer opening 5 Ground layer 5A Solid electrode area 5B Mesh-like conductor part 6 Insulation coating layer 7 Shield layer 7a Shield layer opening part 7b Opening edge 8 Guard pattern

Claims

A circuit board for controlling characteristic impedance of the signal wiring by arranging a signal wiring through an insulator layer with respect to the ground layer and the ground layer and controlling capacitive coupling between the ground layer and the signal wiring. Because
An insulating coating layer is formed on the signal wiring disposed in the insulator layer, and a shield layer made of a conductive material is further formed through the insulating coating layer, and the insulating coating facing the signal wiring is formed. The circuit board is characterized in that the layer is formed in an opening of the shield layer on which the shield layer is not laid.
The signal wiring on which the characteristic impedance is controlled is a signal wiring on which single-ended transmission is performed, and when the thickness of the insulator layer is t1, both outer sides of the signal wiring on which the characteristic impedance is controlled 2. The circuit board according to claim 1, wherein a distance U between the opening edge of the shield layer and the shield layer is set in a range of 3t1 ≦ U ≦ 20t1.
The signal wiring for which characteristic impedance control is performed is a pair wiring for differential transmission, and when the distance between the pair wirings is S, both outer sides of the pair wiring and the opening edge of the shield layer The circuit board according to claim 1, wherein the distance U is set in a range of 3S ≦ U ≦ 20S.
The ground layer facing the signal wiring, whose characteristic impedance is controlled, is formed in a mesh-shaped conductor portion having a large number of holes, and the outside of the mesh-shaped conductor portion is a solid electrode region where no holes are formed. The boundary between the mesh-shaped conductor portion and the solid electrode region is configured to coincide with the opening edge of the shield layer in a direction orthogonal to the substrate surface. Circuit board.
2. The circuit board according to claim 1, wherein the insulator layer between the ground layer and the signal wiring has a thickness of 100 μm or less.
2. The circuit board according to claim 1, wherein the insulating coating layer between the signal wiring and the shield layer has a thickness of 100 μm or less.
A linear guard pattern having the same potential as that of the ground layer is disposed on the insulator layer along both outer sides of the signal wiring through which the single transmission is performed, and the width direction of the linear guard pattern is 7. The circuit board according to claim 1, wherein a central portion is configured to be positioned at an opening edge of the shield layer. 8.
The ground layer and the guard pattern are connected through a via hole, and the guard pattern and the shield layer are connected through an opening formed in the insulating coating layer. Circuit board.
A linear guard pattern having the same potential as that of the ground layer is disposed on the insulator layer along both outer sides of the pair wiring to which the differential transmission is performed, and the width direction of the linear guard pattern 7. The circuit board according to claim 2, wherein a central portion of the shield layer is positioned at an opening edge of the shield layer. 8.
The ground layer and the guard pattern are connected through a via hole, and the guard pattern and the shield layer are connected through an opening formed in the insulating coating layer. Circuit board.