TWI492674B - Circuit board - Google Patents

Description

Circuit substrate

The present invention relates to a circuit board in which a signal circuit is disposed on the ground layer by a ground layer and a transmission insulator layer.

For example, in order to suppress signal reflection and waveform distortion, a circuit substrate on which a component operating in a high frequency band is mounted must integrate a characteristic impedance (hereinafter referred to as Zo) of a signal transmission path (hereinafter referred to as a signal circuit) into the aforementioned components. Input and output impedance.

In order to integrate the characteristic impedance of the aforementioned signal transmission path, a microstrip structure is adopted which is opposed to the ground layer by sandwiching an appropriate thickness of the insulator layer on a signal transmission path (strip line) of a suitable pattern width.

The ground layer of the circuit board structure described above serves as an electrical reference surface for characterizing the characteristic impedance of the signal transmission path. Then, in general, the characteristic impedance is selected to be 50Ω or more in the case of single-ended transmission, and 100Ω in the case of differential transmission.

Further, in the Zo of the circuit board, the value is the square root of the ratio of the reactance L per unit length of the signal transmission path to the capacitance C per unit area between the signal transmission path and the ground layer (reactance L/electrostatic capacitance C). approximation.

In recent years, a thin rigid substrate or a flexible circuit substrate is often used for a circuit board on which the above-mentioned components are mounted. When such a circuit board is used, the layers of the signal transmission path to the ground layer are narrow (thin), and two The electrostatic capacitance C value between the two increases almost in inverse proportion to the size of the aforementioned layer.

Therefore, in the above-described thin multilayer circuit board, in order to obtain the aforementioned Zo, it is necessary to adopt a method in which the signal transmission path width is made narrower (thinner) than the conventional thick circuit board to suppress the aforementioned capacity. The rise of C.

Thus, in order to obtain the required Zo, when a thin signal circuit is to be formed, the signal circuit is slender and difficult to process. Moreover, even if the signal circuit can be processed, the finer the signal circuit, the higher the processing precision and the unevenness of the line width, and the worse the Zo is.

Therefore, in the signal circuit portion where the Zo changes greatly, the problem of signal reflection and waveform distortion will be caused. Further, since the circuit impedance value of the signal circuit becomes high, the signal frequency supplied thereto is higher, which is a cause of deterioration in transmission characteristics.

Therefore, in order to solve the above-mentioned technical problems, it is proposed that the ground layer formed as a so-called beta electrode layer is hollowed out into a mesh shape, so that the opposing area of the ground layer and the signal circuit per unit area is substantially reduced to ensure the width of the signal circuit. The technique is disclosed in Japanese Laid-Open Patent Publication No. Hei 7-321463.

However, in the circuit board of the microstrip structure disclosed in the above prior art, the ground layer side can effectively serve as a countermeasure against EMI (electromagnetic wave obstacle), but the effect on the opposite side of the signal circuit side is not as expected.

Then, it is considered that the outer surface layer (insulating coating layer) of the signal circuit requiring EMI countermeasures is covered with a conductive shielding layer made of, for example, silver paste, and is substantially formed into a strip structure.

However, in the case where the shielding layer is disposed on the surface layer side of the signal circuit, capacitive coupling occurs again between the signal circuit and the shielding layer on the insulating coating layer.

That is, the electrostatic capacitance between the signal circuit and the ground layer is added to the electrostatic capacitance between the shielding layer, and therefore, it is difficult to control the Zo of the signal transmission path.

The present invention has been made in view of the above-mentioned technical problems, and it is an object of the present invention to provide a signal circuit capable of performing single-ended transmission, which has a characteristic impedance that can surely sufficiently perform a signal transmission path and which has an effect in the aforementioned EMI countermeasures. A circuit board and a circuit board having a differentially coupled line pair signal circuit.

In the present invention, a circuit board for solving the above problem is formed by disposing a signal circuit on the ground layer by a ground layer and a transmission insulator layer, and controlling capacitive coupling between the ground layer and the signal circuit. Controlling the characteristic impedance of the signal circuit; forming an insulating coating layer on the signal circuit disposed on the insulator layer, and further forming a shielding layer with a conductive material through the insulating coating layer, and facing the signal circuit The shielding layer opening portion on which the shielding layer is not laid is formed on the insulating coating layer.

Next, in the case where the signal circuit for controlling the characteristic impedance is a single-ended signal circuit, when the thickness of the insulator layer is t1, both outer sides of the signal circuit for controlling the characteristic impedance and the shielding layer are provided. The distance U between the opening edges is preferably set at 3t1 ≦ U ≦ 20 t1.

Further, in the case where the signal circuit for performing the characteristic impedance control is differentially transmitted, when the distance between the lines of the pair of circuits is S, the outer sides of the pair of circuits and the opening edge of the shielding layer are The distance U is preferably set at 3S≦U≦20S.

In this case, the ground layer facing the signal circuit for controlling the characteristic impedance is a mesh conductor portion to which a plurality of hollow holes are applied, and the outer side of the mesh conductor portion is a beta electrode to which no void is applied. In the field, it is preferable that the boundary between the mesh conductor portion and the β electrode region is orthogonal to the substrate surface in a direction orthogonal to the substrate surface.

A thin circuit board having a thickness of 100 μm or less is formed in the insulating layer between the ground layer and the signal circuit, and the insulating coating layer between the signal circuit and the front shielding layer, respectively, and exhibits a remarkable effect.

Further, a circuit board in which a linear protection pattern having the same potential as the ground layer is disposed on both sides of the signal circuit for performing the single-ended transmission, and the linear layer is disposed on the insulating layer The central portion of the protective pattern in the width direction is tied to the opening edge of the shielding layer.

In a preferred aspect of the above aspect, the ground layer is connected to the linear protection pattern through the through hole, and the linear protection pattern and the shielding layer are connected to an opening formed in the insulating coating layer.

According to the circuit board described above, since the shielding layer opening portion in which the shielding layer is not disposed is formed on the insulating coating layer facing the signal circuit in which the control of Zo is required, the signal circuit can be significantly reduced between the shielding layer and the shielding layer. The degree of electrostatic capacitance coupling, whereby the control of the characteristic impedance of the signal circuit can be surely performed.

On the other hand, in the signal circuit, since the opening portion is formed in the shielding layer, the shielding effect is slightly lowered. However, it is possible to provide a circuit board capable of exhibiting a satisfactory effect in the EMI countermeasure.

The following is a circuit board of a signal circuit capable of single-ended transmission according to the present invention, which is described in the first to fifth figures, and the circuit board of the line-to-signal circuit with differential transmission according to the present invention is sixth. The figure is illustrated in the tenth figure.

1A is a cross-sectional view showing a laminated structure of a first embodiment of a circuit board having a signal circuit capable of single-ended transmission, and FIG. 2B is a view showing an insulator layer shown in FIG. A plan view of the signal circuit portion.

The circuit board shown in FIG. 1A and FIG. B is a signal circuit for performing single-ended transmission on the ground layer by a ground layer and a transmission insulator layer, and a signal circuit system for controlling characteristic impedance is required. The microstrip structure is formed; a signal circuit that does not require control of the characteristic impedance is added with a shielding layer to form a stripline structure.

In the present embodiment, a film-shaped base substrate is used as the insulator layer 2, and the signal circuits 3A and 3B and the upper surface of the signal circuits 3A and 3B are formed on the other surface of the insulator layer 2 (on the upper side of the first A-picture). (Upper side of the first A diagram), the insulating coating layer 4 is laminated through an adhesive layer not shown in the drawings.

On the other hand, a ground layer 5 is formed on the other surface of the insulator layer 2 (the lower side of the first A-picture), and a second insulating coating is laminated on the lower surface of the ground layer 5 through an adhesive layer not shown in the drawing. Layer 6.

Next, the shielding layer 7 is formed of a conductive material via the insulating layer 2, that is, the insulating coating layer 4 covering the signal circuits 3A and 3B on the reverse side of the ground layer 5, and is controlled by characteristic impedance. The shielding layer opening portion 7a on which the shielding layer is not laid is formed on the insulating coating layer 4 of the surface of the signal circuit 3A.

The insulator layer 2 on which the central insulator layer of the signal circuit is disposed has a function as a core of the circuit board 1. The material of the insulator layer 2 may be a resin film or a fiber substrate.

The material constituting the resin film may, for example, be a polyimide resin such as a polyimide resin, a polyamide resin or a polyimide resin, a thermosetting resin such as an epoxy resin, or a thermoplastic such as a liquid crystal polymer. Resin.

Among them, it is preferred to use a polyimine resin or a liquid crystal polymer. For example, a polyimide resin is excellent in heat resistance and mechanical properties, and is easily available. Further, the liquid crystal polymer has a lower specific dielectric ratio and is suitable for high-speed signal transmission, and has low stability due to low hygroscopicity.

In addition, the fiber base material used for the insulator layer may be a glass fiber base material such as a glass woven fabric or a glass non-woven fabric, or an inorganic fiber base material such as a woven fabric or a non-woven fabric containing inorganic compounds other than glass, or a polyarylamine. An organic fiber base material composed of an organic resin such as a resin, a polyamide resin, a polyarylate resin, a polyester resin, a polyimide resin, or a fluororesin. Among the above-mentioned base materials, a glass fiber base material typified by selection of a glass woven fabric is preferable in terms of strength and water absorption.

When a fibrous base material is used for the insulator layer, it is preferred to use the resin in a state in which the resin is impregnated into the fibrous base material. For the resin impregnated into the fiber base material, a thermosetting resin such as an epoxy resin or an acrylic resin can be used, and from the viewpoint of heat resistance, an epoxy resin is preferable among the above.

The thickness t1 of the insulator layer 2 is preferably in the range of 10 to 30 μm, preferably in the range of 5 to 50 μm, and more preferably in the range of 1 to 100 μm.

When the thickness of the insulating layer 2 is equal to or higher than the lower limit value, the signal line width is likely to be equal to or higher than the processing limit. On the other hand, if the thickness is equal to or less than the upper limit value, the rigidity can be suppressed from being excessively high. The characteristics of a thin substrate such as a flexible circuit board are kept soft.

The signal circuits 3A, 3B arranged on one side of the insulator layer 2 may be provided directly on the insulator layer 2 or may be provided through an adhesive. Then, at the end of each signal circuit or an appropriate intermediate portion, a dummy pad such as a semiconductor element not shown in the drawing is bonded to the circuit board 1.

It is preferable to cover the insulating coating layer 4 of the signal circuits 3A and 3B via an adhesive layer not shown in the drawings. The resin material may, for example, be a polyester resin, a polyimide, a liquid crystal polymer or the like. Among the above, polyienimine is preferred, whereby heat resistance and flexibility can be improved.

The thickness t2 of the insulating coating layer 4 is preferably 10 to 30 μm, more preferably 5 to 50 μm, and even more preferably 1 to 100 μm.

By setting the thickness t2 of the insulating coating layer 4 to be equal to or higher than the lower limit value, the strength of the resin layer can be easily maintained in a practical range, and the slidability and the flexibility can be easily maximized below the upper limit.

Further, an adhesive layer which is not shown in the drawings between the insulating layer 2 and the insulating coating layer 4 may be, for example, an acrylic resin, an epoxy resin, a polyimide resin or the like. Among the above, an epoxy resin is preferred, whereby heat resistance and flexibility can be improved.

The other surface (back surface) of the insulating layer 2 is disposed as a conductive portion of the ground layer 5, and is formed of a conductor of a copper material. The conductive system is formed with a plurality of hollow holes having a parallelogram opening in a portion opposite to the signal circuit 3A having the characteristic impedance control. Further, the specific structure of the ground layer 5 will be described in detail in the second diagram. Rear.

The second insulating coating layer 6 laminated on the lower side surface of the ground layer 5 (the lower side of the first A drawing) via an adhesive layer not shown in the drawings is preferably made of a resin material. The resin material may, for example, be a polyester resin, a polyimide, a liquid crystal polymer or the like.

Among the above, polyienimine is preferred, whereby 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, particularly preferably 10 to 30 μm.

By setting the thickness t2 of the insulating coating layer 6 to be equal to or higher than the lower limit value, the strength of the resin layer can be easily maintained in a practical range, and the slidability and the flexibility can be easily maximized below the upper limit.

Further, an adhesive layer which is not shown in the drawings between the ground layer 5 and the second insulating coating layer 6 is composed of a material interposed between the insulator layer 2 and the insulating coating layer 4 The constituent materials of the adhesive layer not shown in the middle are the same, and an acrylic resin, an epoxy resin, a polyimide resin, or the like can be used. Among them, an epoxy resin is preferred, whereby heat resistance and flexibility can be improved.

Further, the shielding layer 7 formed on the insulating coating layer 4 and formed of a conductive material can be formed by printing or posting a conductive mask film with a conductive paste (silver paste); and the aforementioned control for controlling the characteristic impedance The portion of the signal circuit 3A facing the crucible is formed as the shielding layer opening portion 7a in which the shielding layer 7 is not laid as described above.

The second figure shows a part of the preferred structure of the ground layer 5 in a magnified manner. In the second figure, the signal circuit 3A having the characteristic impedance control is superimposed on the ground layer 5, and State representation of the perspective of the face orthogonal direction. The ground layer 5 is made of a conductor of a copper material as described above, and a mesh conductor portion 5B that forms a plurality of hollow holes is formed at a position facing the signal circuit 3A in the conductor.

That is, the hollow hole of this embodiment forms an opening of a parallelogram (diamond) in which a plurality of lines intersect in a bidirectional direction. Preferably, the two-way plurality of lines are inclined with respect to the signal circuit 3A by a range of 5 to 40 degrees. Further, it is a mesh pattern in which the long diagonal line of the rhombic opening coincides with the circuit direction of the signal circuit 3A.

Further, the sizes (opening areas) of the respective openings may be different from each other, but it is preferable to form an opening area of the same size, whereby the characteristic impedance of the signal circuit 3A can be accurately controlled.

On the other hand, the outer side of the mesh conductor portion 5B is formed as a beta electrode region 5A formed of a copper material in which no void holes are formed. The signal circuit 3B, which does not require special control of the characteristic impedance, is disposed opposite to the above-described β electrode field 5A.

According to the configuration shown in the second figure, only the portion where the characteristic impedance is to be controlled constitutes the mesh conductor portion 5B, and the other portion is the β electrode region 5A, so that the impedance of the entire ground layer 6 can be prevented from rising.

At this time, the boundary between the mesh conductor portion 5B and the β electrode region 5A is formed in a direction orthogonal to the substrate surface, and is configured to substantially coincide with the opening edge 7b of the shielding layer opening portion 7a to be described later.

Further, in order to control the characteristic impedance of the signal circuit, it is effective that the ground layer 5 has the mesh conductor portion 5B, but the characteristic impedance of the signal circuit may be the line width or the thickness of the insulator layer, or the specific dielectric of the insulator layer is selected. In the present invention, the mesh conductor portion 5B is not required.

In this embodiment, the thickness t1 of the insulating layer 2 and the thickness t2 of the insulating coating layer 4 are all 100 μm or less, which is suitable for a circuit board having an extremely thin laminated structure. Therefore, it is necessary to perform characteristic impedance. The distance U between the controlled signal circuit 3A and the opening edge 7b forming the shielding layer opening 7a governs the degree of capacitive coupling between the two.

In this case, the signal circuit 3A for controlling the characteristic impedance has a single-ended transmission function, and when the thickness of the insulator layer 2 is set to t1, the distance between the outer sides of the signal circuit 3A and the opening edge of the shielding layer is U is set in the range of 3t1≦U≦20t1, and more preferably set to 3t1≦U≦10t1.

The third diagram is a characteristic example in which the distance between the outer sides of the signal circuit 3A and the opening edge 7b of the shielding layer 7 is U, and when the thickness of the insulator layer 2 is t1, the ratio of the two is shown, that is, The horizontal axis represents U/t1, and the vertical axis represents the characteristic impedance Zo of the signal circuit 3A.

In the characteristic example shown in the third diagram, the line width L of the signal circuit 3A is 100 μm, the interlayer thickness t1 of the insulator layer 2 is 25 μm, and the residual ratio of copper (conductor) of the mesh conductor portion 5B is 30%. Further, the boundary between the mesh conductor portion 5B and the β electrode region 5A is formed in a direction orthogonal to the substrate surface, and is configured to substantially coincide with the opening edge 7b of the shielding layer opening portion 7a to be described later.

At this time, the thickness (interlayer thickness) t1 of the insulator layer 2 of the segment signal circuit 3A and the ground layer 5 governs the degree of capacitive coupling between the two. Therefore, it is preferable to manage the control of the characteristic impedance by using the thickness t1 of the insulator layer 2 as a parameter.

Further, when the distance between the signal circuit 3A and the opening edge 7b of the shielding layer 7 is less than a certain degree, the capacitive coupling between the signal circuit 3A and the shielding layer 7 becomes large, and the characteristic impedance of the signal circuit is performed. The control will also become difficult. In other words, as shown in the characteristic diagram of the third figure, when the value of U is less than 3t1, the capacitive coupling is rapidly increased, so it must be avoided.

On the other hand, when the value of U exceeds 3t1, the capacitive coupling of the shielding layer 7 with respect to the signal circuit 3A having the characteristic impedance control is rapidly reduced, and the mesh conductor portion 5B can be obtained at this time. The accuracy of the control of the impedance of the signal circuit is improved.

Further, when the thickness of the insulating coating layer 4 is less than or equal to 100 μm, the same test is performed, and it is verified that when the value of U is less than 3t1, the capacitive coupling of the shielding layer 7 with respect to the signal circuit 3A will be With a rapid increase, the characteristic impedance of the signal circuit will also deteriorate, and the result will be almost the same as that shown in the third figure.

On the other hand, if the U value is set to a large value, the degree of influence on the characteristic impedance setting of the signal circuit becomes small, but the shielding effect is lowered, and the EMI countermeasure cannot be ignored.

Further, in order to secure the shielding effect on the signal circuit, the value of U is preferably 20 t1 or less, preferably 10 t1 or less.

Therefore, the relationship between the distance between the outer side of the signal circuit 3A having the single-ended transmission function and the opening edge 7b of the shielding layer and the thickness t1 of the insulating layer 2 is set in the above range, thereby providing an adjustment signal. A circuit board that balances both circuit characteristic impedance and EMI countermeasures.

4A is a view showing a laminated structure of a circuit board according to a second embodiment of the present invention for performing single-ended transmission, and FIG. 4B is a view showing a portion of the signal circuit on the insulator layer shown in FIG. Floor plan.

In addition, in the fourth A diagram and the fourth diagram B, the functions denoted by the same reference numerals are the same as those in the first A diagram and the first B diagram, and the detailed description thereof will be omitted. Next, the relationship between the distance U between the outer sides of the signal circuit 3A and the opening edge 7b of the shielding layer and the thickness t1 of the insulator layer 2 is also in the above-described relationship according to the first A diagram.

In this embodiment, the linear protection pattern 8 having the same potential as the ground layer 5 is disposed on the insulator layer 2 along both outer sides of the signal circuit 3A for controlling the characteristic impedance. Next, the linear protective pattern 8 is positioned at the central portion of the width direction in the opening edge 7b of the shielding layer 7.

According to the above configuration, the signal circuit 3A having the characteristic impedance control needs to be in an open state due to the opening portion 7a of the shielding layer. However, as shown in FIG. 4A, the signal circuit 3A seen in the cross section is below, The sides and upper sides are surrounded by a very close grounding, thus minimizing the attenuation of EMI shielding characteristics.

Fig. 5A is a plan view showing a laminated structure of a circuit board according to a third embodiment of the present invention relating to single-ended transmission, and Fig. 5B is a plan view showing a portion of the signal circuit on the insulator layer shown in Fig. 5A at substantially the same scale. .

The structures shown in the fifth A and fifth B are further incorporated in the second embodiment shown in the fourth A and fourth B, and the ground layer 5 and the linear protective pattern 8 are formed. The via hole 2a of the insulator layer 2 is connected, and the linear protection pattern 8 and the shielding layer 7 are connected to the opening 4a formed in the insulating coating layer 4.

The through hole 2a connecting the ground layer 5 and the linear protection pattern 8 is formed at a plurality of places along the longitudinal direction of the linear protection pattern 8 as shown in FIG. 5B, and is connected through the respective through holes 2a. .

Moreover, the opening 4a formed in the insulating coating layer 4 is also formed in a plurality of places along the longitudinal direction of the linear protective pattern 8, and the linear protective pattern 8 is connected to the shielding layer 7 through the respective openings 4a.

The above structure can be suitably employed in a portion where the circuit substrate is not bent, and according to the configuration, the gap between the two outer grounds of the signal circuit 3A can be filled, and the ground layer 5, the linear protection pattern 8, and the shielding layer 7 which are applied to the ground potential. The mechanical bond will also become stronger, which will also help improve EMI shielding characteristics.

Next, a circuit board having a signal transmission circuit of the differential transmission of the present invention will be described with reference to FIGS. 6 to 10.

6A is a view showing a laminated structure of a circuit board having the differential signal transmitting circuit of the first embodiment, and FIG. 6B is a view showing a portion of the signal circuit on the insulator layer shown in FIG. Floor plan.

The circuit board 1 shown in FIG. 6A and FIG. 6B is configured to transmit a signal circuit to the ground layer and the ground layer through an insulator layer, and the signal circuit for controlling the characteristic impedance is required (FIG. 6B The pair of circuits shown by the symbol A is formed by a microstrip structure, and a signal circuit for controlling the characteristic impedance is not required (the sixth B is shown by the symbol B), and the additional shielding layer constitutes a strip line structure.

In this embodiment, a film-shaped base substrate is used as the insulator layer 2, and differential signal circuits 3a and 3b are formed on the other surface (upper side of FIG. AA) of the insulator layer 2, and the signal circuit 3a is formed in the signal circuit 3a. The upper surface of 3b (upper side of the sixth drawing A) is laminated with the insulating coating layer 4 through an adhesive layer not shown in the drawing.

On the other hand, on the other surface of the insulator layer 2 (the lower side of the sixth A diagram), the ground layer 5 is formed, and the lower surface of the ground layer 5 is further formed into a second insulating coating layer 6 through an adhesive layer not shown in the drawing.

Next, the shielding layer 7 is formed of a conductive material via the insulating layer 2, that is, the insulating coating layer 4 covering the signal circuit opposite to the ground layer 5, and the signal circuit 3a is controlled by the characteristic impedance. 3b (the sixth circuit in Fig. B is indicated by the symbol A) is formed on the insulating coating layer 7 of the crucible, and the shielding layer opening portion 7a on which the shielding layer is not laid is formed.

Further, in the circuit board 1 having the differential transmission pair signal circuit shown in FIGS. 6A and 6B, the laminated structure is the same as that shown in the first A diagram and the first B diagram. The circuit board of the single-ended transmission signal circuit is the same, and the layers having the same function are denoted by the same symbols. Therefore, the detailed description of each layer and the subsequent layer not shown in the drawings will be omitted.

The seventh figure is a partially enlarged view showing a preferred structure of the ground layer 5 shown in Fig. A. Further, in the seventh diagram, the state in which the signal circuits 3a and 3b which are required to control the characteristic impedance are superimposed on the ground layer 5 is shown in a state of seeing from the plane orthogonal direction. The ground layer 5 shown in the seventh embodiment has the same structure as the ground layer 5 shown in the second figure, and therefore the same portions are denoted by the same reference numerals. Therefore, the detailed structure of the ground layer 5 is also omitted.

In the embodiment shown in the sixth and seventh embodiments, the thickness t1 of the insulating layer 2 and the thickness t2 of the insulating coating layer 4 are set to 100 μm or less, and the entire laminated structure is applied to an extremely thin circuit substrate. Therefore, the signal circuits 3a and 3b which are required to control the characteristic impedance and the opening edge 7b formed in the opening portion 7a of the shielding layer have a distance U which governs the degree of capacitive coupling therebetween.

In this case, the signal circuit for controlling the characteristic impedance is a differential transmission pair circuit, as shown in FIG. 6A, when the line-to-line distance between the signal circuits 3a and 3b is S, the bit is located on the line. The distance between the two outer sides of the signal circuit S and the opening edge 7b of the shielding layer is preferably set at 3S≦U≦20S, preferably 3S≦U≦10S.

In the eighth diagram, the horizontal axis represents the ratio of the distance U to the line S, that is, the value of U/S, and the vertical axis represents the characteristic impedance Zo of the signal circuits 3a and 3b.

The characteristic example shown in the eighth figure is the line width L/line distance S=100 μm/100 μm of the signal circuits 3a and 3b which are formed as differential signal lines, the interlayer thickness t1 of the insulator layer 2 is 25 μm, and the mesh conductor portion 5B. The case where the residual ratio of copper (conductor) = 30%.

When the distance U between the signal circuits 3a and 3b and the opening edge 7b of the shielding layer 7 is less than a certain level, the capacitive coupling between the signal circuit and the shielding layer becomes large, and the control of the characteristic impedance of the signal circuit becomes difficult. In other words, as shown in the characteristic diagram of the eighth figure, when the value of U is less than 3S, the capacitive coupling is rapidly increased, so it is necessary to avoid it.

On the other hand, when the value of U exceeds 3S, the capacitive coupling of the signal layer 3a, 3b having the characteristic impedance control by the shielding layer 7 is rapidly reduced, and the mesh conductor portion 5B can be obtained. The control accuracy of the impedance of the signal circuit is improved.

Further, when the thickness of the insulating coating layer 4 was measured under the condition of t2 = 100 μm or less, it was verified that when the value of U was less than 3 S, the capacitive coupling of the shielding layer 7 to the signal circuit was rapidly changed. Large, the characteristic impedance of the signal circuit will become lower, and the result will be almost the same as that shown in the eighth figure.

On the other hand, if the U value is set large, the degree of influence on the setting of the characteristic impedance of the signal circuit becomes small, but the shielding effect is lowered, and the EMI countermeasure cannot be ignored.

Therefore, in order to ensure the shielding effect on the signal circuit, the U value is preferably 20 S or less, preferably 10 S or less.

Therefore, the relationship between the line S of the pair of signal circuits and the distance U between the outer sides of the pair of circuits and the opening edge 7b of the shielding layer is set to the above range, thereby providing a balance between the characteristics of the adjustment signal circuit. Circuit board for impedance and EMI countermeasures.

As described above, in the case where the signal circuit is a differential transmission pair circuit, the distance S between the both outer sides of the circuit and the opening edge 7b of the shielding layer is set in the foregoing range with the line S of the circuit as a parameter. It can be properly managed.

The reason is that the distance between the lines of the circuit is affected by the characteristic impedance of the shielding layer to the signal circuit. Therefore, the distance from the signal circuit to the opening edge of the shielding layer relative to the line distance determines the influence on the characteristic impedance. degree.

This is based on the fact that there is an imaginary ground (GND) plane in the center of the line between the lines, and considering the relationship of the area of the side of the signal line, it is easy to judge that the distance will affect the characteristic impedance of the signal circuit in accordance with the shielding layer. Therefore, the characteristic impedance of the signal line is determined by the coupling between the aforementioned circuits, and the relationship between the shielding layer in front of the opening edge and the characteristic impedance is hardly affected by the relationship with the distance between the signal lines.

9A is a view showing a laminated structure of a second embodiment of a circuit board having a differential signal transmission circuit, and FIG. 9B is a view showing a signal circuit portion on the insulator layer shown in FIG. Floor plan. The structures shown in FIGS. 9A and 9B are the same as the examples shown in FIGS. 6A and 6B, showing that the signal circuit for which the characteristic impedance is to be controlled is a differential transmission pair circuit. example.

In addition, in the ninth A diagram and the ninth diagram, the functions of the same reference numerals are the same as those of the parts shown in the sixth A diagram and the sixth diagram B, and the detailed description thereof will be omitted. Next, the distance U between the outer sides of the circuit and the opening edge 7b of the shielding layer is the aforementioned relationship with respect to the line S of the circuit.

In this embodiment, the linear protection pattern 8 having the same potential as the ground layer 5 is disposed on the insulator layer 2 along both outer sides of the signal circuits 3a and 3b for controlling the characteristic impedance. Next, the central portion of the linear protection pattern 8 in the width direction is located at the opening edge 7b of the shielding layer.

According to the above configuration, the upper surfaces of the signal circuits 3a and 3b which are required to control the characteristic impedance are opened by the shielding layer opening portion 7a. However, as shown in FIG. 9A, the signal circuits 3a and 3b as seen in the cross section are The bottom, sides and upper sides are surrounded by a very close ground, so the attenuation of EMI shielding characteristics can be minimized.

Further, FIG. 10A shows a laminated structure of a circuit board of a circuit board having a differential transmission signal circuit, and FIG. 10B shows a signal circuit on the insulator layer shown in FIG. Part of the floor plan.

The structure shown in the tenth embodiment A and the tenth figure is that the constituent elements are further added to the second embodiment shown in the ninth A and ninth diagrams, and the ground layer 5 and the linear protection pattern 8 are transmitted through. The through holes 2a formed in the insulator layer 2 are connected, and the linear protective pattern 8 and the shielding layer 7 are connected to the opening 4a formed in the insulating coating layer 4.

The through hole 2a connecting the ground layer 5 and the linear protection pattern 8 is formed in a plurality of places along the longitudinal direction of the linear protection pattern 8 as shown in FIG. 10B, and is transmitted through each of the through holes 2a. connection.

Further, the opening 4a formed in the insulating cover layer 4 is formed in a plurality of places along the longitudinal direction of the linear protective pattern 8, and the linear protective pattern 8 and the shielding layer 7 are connected through the respective openings 4a.

The above structure can be suitably employed in a portion where the circuit board is not bent, and according to the configuration, the gap between the two outer grounds of the signal circuit can be filled, and the ground layer 5, the linear protection pattern 8, and the shielding layer 7 which are applied by the ground potential can be filled. The mechanical bond also becomes stronger, which also helps to improve EMI shielding characteristics.

Further, the circuit board having the single-ended transmission signal circuit described above and the ground layer of the circuit board having the differential transmission signal circuit may be configured to apply a circuit reference potential or may overlap each component. Action power. Therefore, the potential applied to the ground layer is not particularly limited.

The circuit board of the present invention can be used for a printed circuit board, a flexible printed circuit board, a multilayer flexible printed circuit board, etc., and is particularly suitable for assembling a circuit board of an element operating in a high frequency band.

1. . . Circuit substrate

2. . . Insulator layer

2a. . . Through hole

3A, 3B. . . Signal circuit

3a, 3b. . . Signal circuit

4. . . Insulating coating

4a. . . Insulating coating opening

5. . . Ground plane

5A. . . Beta electrode field

5B. . . Mesh conductor

6. . . Insulating coating

7‧‧‧shading layer

7a‧‧‧Shading layer opening

7b‧‧‧Opening edge

8‧‧‧Linear protection pattern

Fig. 1A is a cross-sectional view showing a laminated structure diagram of a first embodiment of a circuit board having a single-ended transmission signal circuit.

Figure 1B is a plan view showing the portion of the signal circuit on the insulator layer shown in Figure A.

The second drawing shows a plan view of one of the preferred examples of the ground layer on the circuit substrate having the single-ended transmission signal circuit.

The third figure is a characteristic line diagram showing the relationship between the distance U between the single-ended transmission signal circuit and the opening edge of the shielding layer, and the relationship between the interlayer thicknesses t1.

Fig. 4A is a cross-sectional view showing a laminated structure diagram of a second embodiment of a circuit board having a single-ended transmission signal circuit.

Figure 4B is a plan view showing a portion of the signal circuit on the insulator layer shown in Figure 4A.

Fig. 5A is a cross-sectional view showing a laminated structure diagram of a third embodiment of a circuit board having a single-ended transmission signal circuit.

Figure 5B is a plan view showing a portion of the signal circuit on the insulator layer shown in Figure 5A.

Fig. 6A is a cross-sectional view showing a laminated structure diagram of a first embodiment of a circuit board having a differential transmission versus signal circuit.

Figure 6B is a plan view showing a portion of the signal circuit on the insulator layer shown in Figure 6A.

The seventh drawing is a plan view showing one of preferred examples of the ground layer of the circuit substrate having the differential transmission signal circuit.

The eighth figure shows a characteristic line diagram showing the relationship between the distance U of the differential transmission pair signal circuit and the opening edge of the shielding layer, and the relationship between the line distances S.

Figure 9 is a cross-sectional view showing a laminated structure diagram of a second embodiment of a circuit board having a differential transmission versus signal circuit.

Figure IX is a plan view showing a portion of the signal circuit on the insulator layer shown in Figure IX.

Fig. 10A is a view showing a laminated structure of a third embodiment of a circuit board having a differential transmission line pair signal circuit.

Fig. 10B is a plan view showing a portion of the signal circuit on the insulator layer shown in Fig. A.

1. . . Circuit substrate

2. . . Insulator layer

3A, 3B. . . Signal circuit

4. . . Insulating coating

5. . . Ground plane

5B. . . Mesh conductor

6. . . Insulating coating

7. . . Masking layer

7a. . . Occlusion layer opening

7b. . . Opening edge

Claims (6)

A circuit board formed by disposing a signal circuit on the ground layer by a ground layer and a transmission insulator layer, and controlling the characteristic impedance of the signal circuit by controlling capacitive coupling between the ground layer and the signal circuit Further, an insulating coating layer is formed on the signal circuit disposed on the insulator layer, and the insulating coating layer is further formed to form a shielding layer by a conductive material, and on the insulating coating layer facing the signal circuit. Forming an opening of the shielding layer in which the shielding layer is not laid, the signal circuit for controlling the characteristic impedance is a signal circuit for single-ended transmission, and when the thickness of the insulating layer is t1, the signal circuit for controlling the characteristic impedance is formed. The distance U between the outer sides of the shielding layer and the opening edge of the shielding layer is set at 3t1≦U≦20t1. The circuit board according to claim 1, wherein the ground layer opposite to the signal circuit for controlling the characteristic impedance is a mesh conductor portion to which a plurality of hollow holes are applied, and the mesh conductor portion is The outer side is in the field of the β electrode to which the vacant hole is not applied, and the boundary between the mesh conductor portion and the β electrode region is in a direction orthogonal to the substrate surface, and coincides with the opening edge of the shielding layer. The circuit board according to claim 1, wherein the insulator layer between the ground layer and the signal circuit has a thickness of 100 μm or less. The circuit board according to the first aspect of the invention, wherein the insulating coating layer between the signal circuit and the pre-masking layer has a thickness of 100 μm or less. a circuit substrate as described in claim 1 or 4, wherein The linear protection pattern of the ground layer having the same potential is disposed on the outer side of the signal circuit along the single-ended transmission, and the central portion of the linear protection pattern in the width direction is located in the foregoing The opening edge of the shielding layer. The circuit board according to claim 5, wherein the ground layer is connected to the linear protection pattern through the through hole, and the linear protection pattern and the shielding layer are connected to an opening formed in the insulating coating layer.