JP2012023275A - Crosstalk suppression circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crosstalk suppression circuit board which can suppress crosstalk sufficiently without inhibiting high density of the circuit board.SOLUTION: The crosstalk suppression circuit board 2 comprises an insulating substrate 4 made of resin, a ground layer located on one surface of the insulating substrate 4, and a wiring circuit 12 located on the opposite surface of the insulating substrate 4 from the ground layer 8. The wiring circuit 12 includes a signal line 16 formed in a prescribed pattern, a coating material 14 consisting of a magnetic body covering the outside surface of the signal line 16, and a protective insulation layer 18 made of resin which buries the signal line 16 and the coating material 14.

Description

  The present invention relates to a crosstalk suppressing circuit board having a structure capable of suppressing crosstalk generated between signal lines arranged in parallel.

  In a circuit board including a signal line forming a wiring pattern, a magnetic field is generated around the signal line every time a signal passes through the signal line. Here, when the two signal lines are arranged close to each other, the two magnetic fields act on each other, so that signal coupling occurs between the signal lines, and so-called crosstalk occurs. When such crosstalk occurs, an operation failure may occur in an electronic component incorporated in the circuit.

This crosstalk increases as the distance between the signal lines is narrower, the signal line length is longer, and the signal frequency is higher. Accordingly, the circuit board has higher density, larger scale, and higher speed. The problem of crosstalk becomes obvious. For this reason, in order to increase the density of circuit boards and the like, it is necessary to take measures against crosstalk.
Here, as a circuit board to which measures against crosstalk are taken, for example, a crosstalk noise reduction multilayer wiring circuit board as shown in Patent Document 1 can be cited.
This multilayer circuit board that reduces crosstalk noise has a concave ground in cross-sectional view to surround the signal lines included in the circuit board to suppress signal leakage from the signal lines and reduce crosstalk noise. Yes.

JP 2003-209367 A

By the way, the circuit board of Patent Document 1 has a concave ground so as to surround the signal line. Therefore, the structure in the circuit board becomes complicated, and it takes time to manufacture. For this reason, there exists a problem that manufacturing cost increases.
In addition, a space for arranging the concave ground with a space from the signal line in the circuit board is required, and there is a limit in increasing the density of the circuit board.

  The present invention has been made on the basis of the above circumstances, and the object of the present invention is to provide a simple structure that does not require much time for manufacturing, and does not hinder the high density of the circuit board. An object of the present invention is to provide a crosstalk suppressing circuit board that can be suppressed.

  In order to achieve the above object, a crosstalk suppressing circuit board according to the present invention includes a resin insulating substrate, a ground layer provided on one surface of the insulating substrate, and the ground layer of the insulating substrate opposite to the ground layer. A wiring circuit provided on a side surface, the wiring circuit comprising: a signal line formed in a predetermined pattern; a covering material made of a magnetic material covering an outer surface of the signal line; and the signal line and And a protective insulating layer made of a resin in which the covering material is embedded (Claim 1).

The crosstalk suppressing circuit board of the present invention preferably includes a multilayer circuit having a multilayer structure in which a plurality of the wiring circuits are stacked (claim 2).
Preferably, the covering material is Ni-P plating.
Specifically, the P content in the Ni-P plating is preferably 0 to 15% by weight (Claim 4).
Moreover, it is preferable that the Ni—P plating has a thickness of 1 μm to 10 μm.

  According to the crosstalk suppressing circuit board of the present invention, since the magnetic field shielding effect by the covering material made of a magnetic material covering the signal lines is high, leakage of the magnetic field from the signal lines can be suppressed, It is very effective in suppressing crosstalk. Since a conventionally used method such as a plating method can be employed for forming the coating material made of a magnetic material, the coating material can be easily formed. In addition, since the covering material is in close contact with the signal line, no significant design change is required for the circuit board. For this reason, the manufacturing cost of the substrate can be reduced.

It is sectional drawing which shows the crosstalk suppression circuit board concerning 1st Embodiment. It is sectional drawing which shows the crosstalk suppression circuit board concerning 2nd Embodiment. It is a perspective view which shows a part of evaluation board | substrate. It is a perspective view which shows the board | substrate for evaluation. It is a graph which shows the frequency characteristic of the far end crosstalk amount when changing phosphorus content of a coating | covering material. It is a graph which shows the frequency characteristic of the far end crosstalk amount when changing the thickness of a coating | covering material.

(First embodiment)
FIG. 1 shows a cross section of a crosstalk suppressing circuit board 2 according to the first embodiment.
As shown in FIG. 1, the crosstalk suppressing circuit board 2 according to the present invention includes an insulating substrate 4 as a base material. The insulating substrate 4 is not particularly limited as long as it is an insulating resin, but a glass epoxy resin substrate in which an epoxy resin is impregnated with glass fiber as a reinforcing material is preferably used.

A ground layer 8 is formed on one surface (lower end surface 6) of the insulating substrate 4. The ground layer 8 is made of copper foil and has a thickness of 12 to 105 μm, for example.
A wiring circuit 12 including a signal line 16 and a protective insulating layer 18 in which the signal line 16 is embedded is formed on the surface (outer surface 10) opposite to the surface on which the ground layer 8 is formed of the insulating substrate 4. Is provided. Hereinafter, the wiring circuit 12 will be described in detail.

  First, a plurality of signal lines 16 formed in a predetermined pattern are disposed on the outer surface 10 of the insulating substrate 4. As is clear from FIG. 1, the signal line 16 has a rectangular cross section, and its lower surface 20 is in close contact with the outer surface 10 of the insulating substrate 4. The both side surfaces 22 and the upper surface 24 of the signal line 16 are covered with a covering material 14 made of a magnetic material.

  Here, the covering material 14 is in close contact with the periphery of the signal line 16 with a predetermined thickness. As described above, the covering material made of a magnetic material closely attached to the periphery of the signal line 16 forms a magnetic path. Therefore, the flow of the magnetic field, that is, the magnetic flux passes through the covering material 14 as indicated by the arrow m in FIG. For this reason, since the magnetic field generated due to the signal passing through the signal line 16 flows in the covering material 14, leakage is suppressed. As a result, a shielding effect is exhibited and crosstalk between signal lines is suppressed. In the present invention, since the covering material 14 made of a magnetic material is in close contact with the signal line 16, the interval between the adjacent signal lines 16 can be narrowed, and the density of the wiring pattern is not hindered.

The covering material 14 is preferably formed by Ni-P plating.
Here, it is preferable that the Ni-P plating has a P content in the range of 0 wt% to 15 wt% because the effect of suppressing crosstalk is exhibited. A more preferable content of P is 2 to 10% by weight.
Moreover, when the thickness of the Ni—P plating is in the range of 1 μm to 10 μm, it is preferable because the effect of suppressing crosstalk is exhibited. A more preferable thickness of the Ni—P plating is 2 μm to 6 μm.

  As described above, the signal line 16 having the covering material 14 is preferably protected by the protective insulating layer 18 such as a solder resist. The protective insulating layer 18 is made of an insulating resin such as an epoxy resin and is formed with a predetermined thickness so as to completely cover the signal line 16 on the outer surface 10 of the insulating substrate 4.

Next, a method for manufacturing the crosstalk suppressing circuit board 2 (four-layer board) of the present invention will be described.
First, a double-sided plate (core material) 7 in which a copper foil is bonded to an insulating substrate 9 made of a glass epoxy resin substrate is prepared. Here, the double-sided plate is preferable because copper foil is already formed on both sides, and this copper foil can be used as the ground layer 8.
Thereafter, a prepreg (insulating substrate 4) and a copper foil are laminated on both surfaces of the double-sided plate 7 under normal lamination press conditions to form a four-layer substrate. The signal lines 16 made of copper are formed in a predetermined pattern on both outermost surfaces by a conventional method such as a subtractive method.

Next, a plating resist is formed on portions other than the signal lines 16 on the insulating substrate 4 on which the signal lines 16 having a predetermined pattern are formed, and Ni-P plating is applied to the outer surface of the signal lines 16 without the plating resist. Apply. Specifically, the outer surface of the signal line 16 is covered with Ni—P plating as follows.
Ni-P plating is performed by performing electroless nickel plating using diaphosphate as a reducing agent, and the outer surface of the signal line 16 is covered with Ni-P plating.

  Next, a protective insulating layer 18 is formed on the outer surface 10 of the insulating substrate 4 having a predetermined pattern of the signal line 16 whose outer surface is covered with Ni-P plating so as to cover the entire pattern of the signal line 16. Form. The protective insulating layer 18 may be formed by a general method for forming a solder resist. For example, it is formed as follows.

First, an insulating resin ink is prepared. This insulating resin ink is made of an epoxy resin and a solvent, and is adjusted to a predetermined viscosity. And this insulating resin ink is apply | coated to the outer surface 10 side of the insulating substrate 4, and an insulating resin ink layer is formed. At this time, the insulating resin ink is filled in a gap between the patterns of the signal lines 16 and is applied with a predetermined thickness so as to completely cover the signal lines 16. Next, the entire insulating substrate 4 is heated to evaporate the solvent in the insulating resin ink and cure the insulating resin ink. Thus, the insulating resin ink layer is used as the protective insulating layer 18.
As described above, the crosstalk suppression circuit board 2 (four-layer board) of the first embodiment is manufactured.

(Second Embodiment)
FIG. 2 shows a crosstalk suppression circuit board 32 (six-layer board) of the second embodiment. The crosstalk suppressing circuit board 32 is different from the first embodiment only in that the crosstalk suppressing circuit board 32 is changed to a configuration including a laminated circuit 33 having a two-layer structure in which two wiring circuits 12 (34, 36) are laminated. . In the description of the second embodiment, the same reference numerals are given to those that exhibit the same functions as those of the components and parts already described, and the description thereof is omitted.

  The crosstalk suppression circuit board 32 according to the second embodiment includes a laminated circuit 33 including a lower wiring circuit 34 and an upper wiring circuit 36. This laminated circuit 33 is obtained by repeatedly forming the wiring circuit 12 (see FIG. 1) in the first embodiment on the upper and lower surfaces on the insulating substrate 4.

According to the crosstalk suppression circuit board 32 of the second embodiment, as indicated by the arrow n in FIG. 2, the magnetic flux around the signal line 16a in the upper wiring circuit 36 is covered by the signal line 16a. The coating material 14 passes through a part of the coating material 14 covered with the signal line 16b in the lower wiring circuit 34 positioned inside the signal line 16a. For this reason, crosstalk between the signal lines 16a and 16b can also be effectively suppressed.
Note that the present invention is not limited to the crosstalk suppression circuit board having the multilayer circuit having the two-layer structure as in the second embodiment, and a multilayer circuit having a multilayer structure in which more wiring circuits are stacked. May be provided.

Example 1
An evaluation substrate 40 for measuring crosstalk was produced as follows. In addition, the specific numerical value described below is an example.
First, as shown in FIG. 3, two signal lines 44 extending in parallel with each other are formed on both surfaces of a four-layer substrate 42 having a ground layer 48 formed on the inner layer. The four-layer board 42 is a double-sided board (core material) 7 formed by sticking, for example, a copper foil (ground layer 48) having a thickness h2 of 35 μm on both sides of a prepreg (insulating board 9) having an insulating layer thickness of 400 μm. The glass epoxy resin (insulating substrate 46) having a thickness h1 of 100 μm and a copper foil of 12 μm are stacked on both sides of the double-sided plate 7 and laminated by a laminating press. Further, electroless copper plating and electrolytic copper plating were performed, and when the thickness reached 30 μm, a circuit was formed by a subtractive method, and the two signal lines 44 described above were formed. For example, the thickness H1 of the signal line 44 is 30 μm. For example, the signal line 44 has a length L of 25 cm, a width W of 130 μm, and a thickness H1 of 30 μm, and an interval G between the two signal lines is set to 50 μm.

  Next, as shown in FIG. 4, Ni—P plating 54 was applied to the outer surface of the signal line 44. The conditions for Ni-P plating at this time are as follows.

  Ni-P plating is performed by performing electroless nickel plating using diaphosphate as a reducing agent, and the outer surface of the signal line 16 is covered with Ni-P plating.

Here, the content of P in the Ni—P plating was set to 2% by weight, and the plating thickness H2 was set to 6 μm, for example. Note that both end portions of the signal line 44 in the longitudinal direction are not subjected to Ni-P plating, and the signal line 44 is exposed.
Next, an insulating resin ink made of an epoxy resin and a solvent is applied to both surfaces 50 of the rectangular substrate 52, and an insulating resin ink layer is formed so as to cover the entire signal line 44 subjected to Ni-P plating. did. Thereafter, the solvent in the insulating resin ink was evaporated by heating at 150 ° C. for 1 hour, the insulating resin ink was cured, and the insulating resin ink layer was used as the protective insulating layer 56. The protective insulating layer 56 is indicated by a two-dot chain line in FIG.

The frequency characteristics of far end crosstalk (S ₄₁ ) were measured for the evaluation substrate 40 thus obtained. Here, far-end crosstalk means that when a signal in the same direction is transmitted to signal lines arranged in parallel, a signal transmitted through one signal line is combined with a signal transmitted through the other signal line. Say. Specifically, the amount of the far-end crosstalk is determined by using one signal line 44a of the evaluation substrate 40 as a main line and the other signal line 44b as a sub line, and a four-port high-frequency network between the main line and the sub line. The measurement was performed by using an analyzer (R3767CG OPT14 manufactured by Advantest). This result is shown by a solid line a in FIGS. 5 and 6 as a frequency characteristic of the far-end crosstalk (S ₄₁ ) between the main line and the sub line. Here, in FIGS. 5 and 6, the vertical axis represents the far-end crosstalk (S ₄₁ ) amount [dB], and the horizontal axis represents the frequency f [GHz].

(Example 2)
A substrate for evaluation was produced in the same manner as in Example 1 except that the content of P in the Ni—P plating was 7% by weight.
The frequency characteristics of the far-end crosstalk (S ₄₁ ) were measured on the evaluation substrate of Example 2 in the same manner as in Example 1, and the result is shown by a one-dot chain line b in FIG.

(Example 3)
An evaluation substrate was produced in the same manner as in Example 1 except that the content of P in the Ni-P plating was 10% by weight.
The frequency characteristic of far end crosstalk (S ₄₁ ) was measured for the evaluation substrate of Example 3 in the same manner as in Example 1, and the result is shown by a two-dot chain line c in FIG.

Example 4
A substrate for evaluation was produced in the same manner as in Example 1 except that the thickness H2 of the Ni—P plating was 4 μm.
The frequency characteristics of the far-end crosstalk (S ₄₁ ) were measured on the evaluation substrate of Example 4 in the same manner as in Example 1, and the result is shown by a one-dot chain line d in FIG.

(Example 5)
An evaluation substrate was produced in the same manner as in Example 1 except that the thickness H2 of the Ni—P plating was 2 μm.
The frequency characteristics of the far-end crosstalk (S ₄₁ ) were measured on the evaluation substrate of Example 5 in the same manner as in Example 1, and the result is shown by a two-dot chain line e in FIG.

(Comparative Example 1)
An evaluation substrate was produced in the same manner as in Example 1 except that Ni-P plating was not applied.
The frequency characteristic of the far-end crosstalk (S ₄₁ ) was measured for the evaluation substrate of Comparative Example 1 in the same manner as in Example 1, and the result is shown by the dotted line g in FIGS.

The following is clear from FIGS.
First, as shown in FIG. 5, the amount of far-end crosstalk in Examples 1, 2, and 3 subjected to Ni-P plating is lower than that in Comparative Example 1 where Ni-P plating is not performed. It can be seen that far-end crosstalk is suppressed by applying Ni-P plating. Here, the far-end crosstalk amount of Example 1 having a P content of 2% by weight was the smallest, and the far-end crosstalk amount of Comparative Example 1 without Ni-P plating was the largest. Since the difference in the amount of crosstalk between Example 1 and Comparative Example 1 near 1 GHz is about 10 dB, Ni-P plating with a P content of 2% by weight is compared with the case where Ni-P plating is not applied. It can be seen that the far-end crosstalk suppression amount in the vicinity of 1 GHz when applied is 10 dB.

  Next, FIG. 6 shows that the amount of far-end crosstalk when the Ni-P plating is not performed (Comparative Example 1) is the largest, and the thickness of the Ni-P plating is 2 μm, 4 μm, and 6 μm (Example 5). 4 and 1), the far-end crosstalk amount decreases as the thickness increases. Since the difference in crosstalk amount around 1 GHz between Example 1 where the thickness of Ni-P plating is 6 μm and Comparative Example 1 where Ni-P plating is not applied is about 10 dB, the thickness of Ni-P plating It can be seen that the far-end crosstalk suppression amount in the vicinity of 1 GHz when 10 μm is 10 μm is 10 dB.

2 Crosstalk suppression circuit board 4 Insulating board 6 Lower end face 8 Ground layer 10 Outer side face 12 Wiring circuit 14 Coating material 16 Signal line 18 Protective insulating layer 20 Lower face 22 Side face 24 Upper face 26 Upper face 33 Multilayer circuit

Claims (5)

A resin insulating substrate;
A ground layer provided on one surface of the insulating substrate;
A wiring circuit provided on a surface opposite to the ground layer of the insulating substrate,
The wiring circuit is
A signal line formed in a predetermined pattern;
A coating material made of a magnetic material covering the outer surface of the signal line;
A crosstalk suppressing circuit board comprising: a protective insulating layer made of a resin in which the signal line and the covering material are embedded.   The crosstalk suppression circuit board according to claim 1, further comprising a multilayer circuit having a multilayer structure in which a plurality of the wiring circuits are stacked.   The crosstalk suppressing circuit board according to claim 1, wherein the covering material is Ni—P plating.   4. The crosstalk suppressing circuit board according to claim 3, wherein the content of P in the Ni—P plating is 0 wt% to 15 wt%.   The crosstalk suppression circuit board according to claim 4, wherein the Ni—P plating has a thickness of 1 μm to 10 μm.

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