JP5139750B2 - Multilayer printed circuit board - Google Patents

Description

  The present invention is a printed circuit board on which electronic components such as semiconductor elements are mainly mounted, and includes a multilayer including at least one of a conductor layer functioning as a ground layer and a conductor layer functioning as a power supply layer as an internal conductor layer. The present invention relates to a printed wiring board.

  In the power supply layer and the ground layer, which are supposed not to flow a high-frequency current, a high-frequency current flows in these layers in recent years, which causes a new problem. Specifically, high-frequency current also flows through the power supply layer and the ground layer due to electromagnetic coupling between the power supply layer and the signal layer, weakening of the ground layer, and the length of the return current path, resulting in a relatively large current loop. Therefore, the problem of noise emission has arisen.

  Since these noise emissions are generated in the inner layer of the multilayer printed wiring board, for example, an effect cannot be expected even if a noise suppression sheet is attached to the outer surface of the board. On the other hand, conventionally, a method has been proposed in which a prepreg of a multilayer substrate itself or a part of the prepreg is made of a magnetic material to suppress noise (for example, see Patent Document 1 or Patent Document 2).

JP 2006-100608 A JP 2006-019590 A

  However, as proposed in Patent Document 1 or Patent Document 2, when a part of the substrate is composed of a composite magnetic body, the magnetic permeability of the composite magnetic body is not so large, and a thermal machine as a prepreg is used. Since the ratio of the polymer, which is the binder component in the composite magnetic material, cannot be made very small because it is necessary to maintain a typical performance, it has magnetism that can be expected to have a sufficient noise suppression effect at a thickness that does not interfere with practical use. It was extremely difficult to realize a prepreg.

  A multilayer printed wiring board is usually provided with a large number of via holes for electrically connecting the conductor layers. The wiring formed between the via holes and the conductor layers is bent by 90 degrees or impedance. This misalignment can induce noise radiation, particularly in the high frequency region. However, with the technique described in Patent Document 1 or Patent Document 2, it is difficult to suppress this type of noise emission.

  Under such circumstances, a new high-frequency noise countermeasure means that exhibits a high noise suppression effect while requiring almost no mounting space, and a new noise suppression material having a two-dimensional structure and mountability used therefor are desired.

  Therefore, an object of the present invention is to realize and provide a multilayer printed wiring board having a magnetic material and a mounting form that are most effective for reducing radiation noise generated by the operation of a circuit.

  The inventors have analyzed and studied in detail the effects and factors of noise suppression means using magnetic loss of magnetic materials, and by using the material and material mounting means of the present invention, the thickness and volume of the multilayer substrate can be reduced. The inventors have reached the present invention that can effectively suppress noise emission with little increase. Therefore, before explaining the details of the contents of the present invention, the noise suppression means using the magnetic loss of the magnetic material will be explained.

The noise suppression effect brought about by the noise suppression material (generally a sheet-like magnetic body) arranged directly above the transmission line, such as a signal pattern on a printed wiring board, is the magnitude of the effect per unit line length P _loss / P _in is represented by the following formula (1).

Here, M is a coupling coefficient between the high-frequency magnetic flux generated by the current flowing through the transmission line and the noise suppression material, and δ is the thickness of the noise suppression material. The coupling coefficient M in the formula (1) includes the influence of the thickness of the adhesive tape entering between the transmission line and the noise suppression material and the slight gap, and the slight gap causes the coupling coefficient M to be greatly deteriorated. Therefore, in order to obtain a large noise suppression effect, it is extremely important to eliminate a gap generated between the noise suppression material and the line. However, in general, a composite structure noise suppression material having self-adhesiveness has been developed, but an adhesive tape is inevitably used in order to ensure adhesive strength. Further, for example, when a magnetic body having a composite structure composed of magnetic powder and polymer as disclosed in Patent Document 1 or Patent Document 2 is applied to a prepreg, the polymer present around the magnetic powder is formed between the magnetic powder and the wiring conductor. Since a substantial gap is formed between them, this gap, that is, a film made of a polymer is also a major factor for reducing the coupling coefficient M. In order to obtain a high noise suppression effect, it is necessary to increase P _loss / P _{in represented} by the equation (1). Therefore, when using a magnetic material having a composite structure, a small coupling coefficient due to the presence of a gap. It is necessary to cover M with the size and thickness δ of the imaginary part permeability μ ″ of the magnetic material.

Further, from the equation (1), it can be understood that the size of the imaginary part permeability μ ″ and the frequency dependence thereof, that is, the design of the dispersion profile of μ ″ are also important factors that greatly influence the noise suppression performance. Particularly important elements in permeability dispersion profile of the noise suppressing material is the following three: 1) the product mu _i · f _r of initial permeability mu _i and the resonant frequency f _r is large; 2) the resonant frequency f _r Can be controlled over a wide frequency range; and 3) the resonance rises sharply. The size of the product mu _i · f _r of initial permeability mu _i and the resonant frequency f _r 1), in addition to the intrinsic material anisotropy field H _a saturation magnetization M _s, depending on the material shape. The initial permeability μ _i and the resonance frequency _fr are expressed by the following equations (2) and (3), respectively, and the relationship of the following equation (4) is established between the two.

Here, μ ₀ is the permeability of vacuum.

As can be understood from the equation (4), since the μ _i · f _r product is proportional to the saturation magnetization M _s of the material, the value is constant in a material system having the same M _s (Snoek's law), and more Large μ _i · _fr products are not feasible. However, when the material shape is added as another factor, the demagnetizing field N _d (z) · M _{s in} the thickness direction works to increase the precession kinetic energy of the spin. 5) Changes to the relationship of the formula.

Because here is a _{H a · M s / μ 0} »1, shape demagnetizing field in the thickness direction is increased, the resonance frequency f _r as compared with the bulk material of the same composition will be increased remarkably in other words a thin film. For the reasons described above, the ferrite plated film can provide a μ _i · _fr product that is nearly an order of magnitude larger than that of bulk sintered ferrite or thick film magnetic material.

In addition, in many cases, a noise suppressor made of a composite magnetic material containing a binder such as a polymer or a prepreg using part of the noise suppressor is in the direction in which the magnetic flux passes, that is, the surface of the sheet or plate-like composite magnetic material. A magnetic field of demagnetizing field N _d (x) · M in the magnetic path direction depending on the shape of the magnetic powder acts inward. Here, the effective magnetic permeability μ _e of the magnetic material in the open magnetic path is expressed by the following equation (6), and the demagnetizing coefficient N _d (in the magnetic path direction is independent of the initial magnetic permeability μ _i inherent to the material. x). Therefore, in a noise suppressor made of a composite magnetic material containing a binder such as a polymer and a prepreg using a part thereof, the effective magnetic permeability (μ _e ) in the magnetic path direction becomes extremely small.

  This is because magnetic particles are sequestered by non-magnetic inclusions such as polymers, so that strong interaction such as exchange interaction does not work between the magnetic particles. For this reason, the thickness δ of the magnetic material can only be increased to exhibit a sufficient noise suppression effect. However, in multilayer printed wiring boards, it is known that noise radiation increases when the distance between conductor layers, that is, the prepreg layer is thickened. When the magnetic layer is thickened, the noise suppression effect and conductivity of the magnetic layer are increased. The increase in noise emission accompanying the increase in the body-to-body distance is offset. As described above, the technique as described in Patent Document 1 or Patent Document 2 cannot incorporate the magnetic layer without substantially changing the thickness of the multilayer printed wiring board.

  Therefore, in order to provide an electronic circuit with less noise emission by adding a magnetic layer to the internal conductor layer of the multilayer printed wiring board, which is the object of the present invention, it is necessary to include 2 non-magnetic inclusions such as polymers. It is necessary to form a dimensional structure, that is, a magnetic layer having a sufficiently large ratio of surface size and thickness (aspect ratio) and a large μ ″ on the conductor layer without any gap. One means for realizing the structure is, for example, a method in which a ferrite thin film having a thickness of about several μm is directly plated on a printed wiring pattern of a power supply layer or a ground layer, and the thickness of the magnetic layer is about several μm. If so, the thickness is about one-hundred of the thickness of a general multilayer wiring board, and is sufficiently smaller than the thickness tolerance of the wiring board. Even if it is arranged on the inner layer surface, the substrate thickness will be substantially Not give Hibiki. The present invention is based on the viewpoint as described above, specifically, it has the following configuration.

  That is, according to the present invention, as the first multilayer printed wiring board, at least one of a conductor layer functioning as a ground layer and a conductor layer functioning as a power supply layer is provided as an internal conductor layer, and the internal conductor In a multilayer printed wiring board comprising a dielectric layer formed on the layer and a conductor layer functioning as a signal layer formed on the dielectric layer, a magnetic layer made of magnetic components is further provided as an inner layer In addition, a multilayer printed wiring board can be obtained.

  Furthermore, according to the present invention, as the second multilayer printed wiring board, in the first multilayer printed wiring, the magnetic layer is provided in close contact with the internal conductor layer. can get.

  Furthermore, according to the present invention, as the third multilayer printed wiring board, in the second multilayer printed wiring, the magnetic layer is formed on a surface of the internal conductor layer facing the signal layer. A multilayer printed wiring board is obtained.

  Furthermore, according to the present invention, as the fourth multilayer printed wiring board, in the second multilayer printed wiring, the magnetic layer is formed on a surface of the internal conductor layer that does not face the signal layer. A multilayer printed wiring board is obtained.

  Further, according to the present invention, as the fifth multilayer printed wiring board, in any one of the first to fourth multilayer printed wirings, a via hole for electrically connecting at least two of the conductor layers is further provided. Thus, a multilayer printed wiring board is obtained in which the via hole includes a via hole conductor and the magnetic layer formed on at least one of the inner surface and the outer surface of the via hole conductor.

  Furthermore, according to the present invention, as the sixth multilayer printed wiring board, in any one of the first to fourth multilayer printed wirings, the magnetic layer has a thickness t and an in-plane of the magnetic layer. When the minimum length in L is L, the thickness is so thin that t ≦ 50 μm and L / t ≧ 1000, and the imaginary part permeability μ ″ in the in-plane predetermined direction of the magnetic layer and the thickness of the magnetic layer A multilayer printed wiring board having a product μ ″ · t of 10 μm or more can be obtained.

  Furthermore, according to the present invention, as the seventh multilayer printed wiring board, in any one of the first to sixth multilayer printed wirings, the magnetic layer is formed by a chemical bond or van der Waals force. A multilayer printed wiring board which is a film to be obtained is obtained.

  Furthermore, according to the present invention, as the eighth multilayer printed wiring board, in any one of the first to seventh multilayer printed wirings, the first magnetic permeability that is the magnetic permeability in the first direction in the plane of the magnetic layer. A multilayer printed wiring board satisfying 0.5 ≦ x ≦ 2 is obtained, where x is the ratio of the second magnetic permeability which is the magnetic permeability in the second direction orthogonal to the first direction in the same plane. It is done.

  Furthermore, according to the present invention, as the ninth multilayer printed wiring board, in any one of the first to eighth multilayer printed wirings, the magnetic layer is composed of unit components that exhibit magnetism of the magnetic layer. A multilayer printed wiring board formed can be obtained by magnetically coupling each other by strong interaction in the plane.

  Furthermore, according to the present invention, as the tenth multilayer printed wiring board, in any one of the first to ninth multilayer printed wirings, the DC specific resistance of the magnetic layer is 0.1 Ω · cm or more. A wiring board is obtained.

  Furthermore, according to the present invention, as the eleventh multilayer printed wiring board, in any one of the first to tenth multilayer printed wirings, the magnetic layer has a magnetic permeability dispersion characteristic derived from ferromagnetic resonance. A wiring board is obtained.

  Furthermore, according to the present invention, as the twelfth multilayer printed wiring board, in any one of the first to eleventh multilayer printed wirings, a multilayer printed wiring board in which the magnetic layer is a ferrite film can be obtained.

  Furthermore, according to the present invention, as a thirteenth multilayer printed wiring board, in the twelfth multilayer printed wiring, the ferrite film is directly formed on the internal conductor layer by an electroless plating method. A multilayer printed wiring board is obtained in which the magnetic layer is a ferrite film.

Further, according to the present invention, as the fourteenth multilayer printed wiring board, in the twelfth or thirteenth multilayer printed wiring, the composition ratio Fe _a Ni _b Zn _c Co _d of the metal ions in the ferrite film is 2.1. ≦ a ≦ 2.7, 0.1 ≦ b ≦ 0.3, 0.1 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.15 (provided that a + b + c = 3.0) Is obtained.

  According to the present invention, a magnetic body layer in which unit components that express magnetism are arranged without gaps like a ferrite thin film is formed in close contact with the inner surface of a ground layer, a power supply layer, or a hollow via wiring included in a multilayer printed wiring board. By doing so, the loss performance which has frequency selectivity can be provided to the whole board | substrate. Therefore, according to the present invention, noise generated in a high frequency region of several hundred MHz or more or several GHz or more and a low frequency signal component or a drive current component can be selectively separated to suppress only noise. Therefore, a multilayer printed wiring board in which noise emission is suppressed can be obtained.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

In the following, a ferrite thin film produced by a ferrite plating method is used as a magnetic layer built in a multilayer printed wiring board. With the ferrite plating method, for example, as shown in Japanese Patent No. 1475891, an aqueous solution containing at least ferrous ions as magnetic metal ions is brought into contact with the surface of the object to be plated, and the surface of the object to be plated is contacted. Fe ²⁺ or this and other metal hydroxide ions are adsorbed, followed by oxidation of the adsorbed Fe ²⁺ to obtain Fe ³⁺ , which causes a ferrite crystallization reaction with the metal hydroxide ions in the aqueous solution. Is a means for forming a ferrite thin film on the surface of an object to be plated.

  The ferrite plating film can be easily formed if the surface of the object to be formed is resistant to the above-mentioned aqueous solution, and since it is an aqueous solution reaction, the temperature is relatively low (room temperature to below the boiling point of the aqueous solution). ) Can form a spinel ferrite film. Therefore, there are fewer restrictions on the film formation compared to other ferrite film creation techniques, and the multilayer printed wiring board of the present invention naturally has damage to the surface of the semiconductor encapsulant, various conductor surfaces, and silicon wafers. It is possible to form a film directly without imparting.

As in the present invention, means for suppressing high frequency noise by arranging a magnetic layer in the vicinity of the transmission line is achieved by frequency domain separation that attenuates only noise components using magnetic resonance that occurs in a specific frequency domain. Therefore, there should be no loss due to magnetic resonance in the frequency region of the signal or drive current, and conversely, a large resonance loss is required in the noise region. The sharpness of the rise of magnetic resonance means that there is little variation (dispersion) in the anisotropic magnetic field of each component that bears magnetism, such as crystal grains in the magnetic material. The elemental columnar crystal has high homogeneity (see Fig. 1), and adjacent crystals are strongly coupled by exchange interaction, so the variation in anisotropic magnetic field is small and there is no exchange interaction. Compared to a composite noise suppression sheet, the resonance rises sharply. Moreover, since the demagnetizing field in the in-plane direction is negligibly small due to the exchange interaction, the effective magnetic permeability is as close as possible to the magnetic permeability inherent to the material. That is, in the composite type magnetic sheet, the effective magnetic permeability significantly deteriorates due to the demagnetizing field in the in-plane direction that appears depending on the shape of the sheet. However, in the ferrite film used in the present invention, the demagnetizing field in the in-plane direction Since it is negligibly small, the magnetic permeability does not deteriorate, and the effective magnetic permeability has the same value as the magnetic permeability of the material. Therefore, even a thin magnetic material can be effective. Fig. 2 shows a typical magnetic permeability (μ ") profile of a ferrite plated film and a composite type noise suppression sheet. From the comparison between the two, the sharpness of the rise of the magnetic permeability (μ") dispersion of the ferrite plated film and a large magnetic permeability are shown. It can be seen that (μ ″) is suitable for suppressing high-frequency noise. Further, as shown in the equation (1), the noise suppressing effect is caused by the current flowing through the signal wiring, the power supply wiring, and the line such as the ground. Although it is proportional to the coupling coefficient between the high-frequency magnetic flux and the noise suppressor, non-magnetic inclusions such as binders and non-magnetic additives create substantial gaps in complex magnetic materials such as existing noise suppression sheets. , The coupling coefficient M does not increase, and as a result, the composite magnetic material requires a thickness that is not negligible relative to the thickness of the substrate in order to obtain effective noise suppression. It can be said that it is practically impossible to mount it as an inner layer of a layer substrate.The ferrite film used in the present invention can be mounted on a wiring substrate without a gap by using a film forming method such as a plating method. Becomes a value close to the maximum value (M _max = 1), and acts synergistically with the contribution of the above-described sharpness of the permeability (μ ″) dispersion and the large permeability (μ ″), so that an extremely thin magnetic material is used. Demonstrate effectiveness.

In order to evaluate the effect of suppressing conduction noise when a ferrite film is mounted on a multilayer printed wiring board by a plating method without any gaps, refer to IEC 62333-2, which is a performance evaluation standard for noise suppression sheets established by the IEC. Evaluation was performed using a microstrip line (hereinafter abbreviated as MSL) formed by processing a wiring board.

FIG. 3A shows a schematic diagram of a ferrite plating film forming apparatus. FIG. 3B is a layout view when a base body such as a printed wiring board, which is an object to be plated, is viewed from a direction perpendicular to the surface. In FIG. 3A, the base body 104 on which the ferrite film is formed is installed on the turntable 107. The solution stored in the tanks 105 and 106 for storing the liquid necessary for plating is supplied to the substrate 104 through the nozzles 101 and 102. At that time, for example, after the solution is supplied to the substrate 104 via the nozzle 101, a step of removing excess solution by centrifugal force due to rotation, and the solution supplied to the substrate 104 via the nozzle 102 are supplied. After that, the step of removing by centrifugal force due to rotation is repeated. Here, the illustrated permanent magnet 103 is for inducing and controlling the magnetic anisotropy in the film surface of the ferrite film. By changing the strength of the magnetic field generated by the permanent magnet 103, the surface of the base 104 is changed. Can apply a magnetic field of 0 to 50 Oe substantially parallel to the film surface, and the magnitude of the magnetic anisotropy can be controlled by its strength. On the rotating plate 107 of the ferrite plating apparatus having the configuration shown in FIG. 3, an MSL or an 8 cm square polyimide sheet having a thickness of 25 μm is installed as the base 104 and supplying deoxygenated ion exchange water while rotating at 150 rpm. Heated to ° C. Here, the MSL is a 1.6 mm thick, 80 mm square glass epoxy board with a central conductor with a width of about 3 mm formed at the center of the front surface over the entire width of 80 mm, and the back is a solid pattern (uniform pattern) The ground conductor was made with a characteristic impedance of 50Ω, and the ground conductor side surface was in contact with the rotating plate. Next, N ₂ gas was introduced into the plating apparatus to create a deoxygenated atmosphere. A desired amount of FeCl ₂ · 4H ₂ O, NiCl ₂ · 6H ₂ O, ZnCl ₂ and CoCl ₂ · 6H ₂ O is dissolved in deoxygenated ion exchange water as a reaction solution, and NaNO ₂ and CH ₃ are dissolved in deoxygenated ion exchange water. An oxidizing solution in which a desired amount of COONH ₄ was dissolved and the above-mentioned reaction solution were supplied from a nozzle at a flow rate of about 40 ml / min. A black ferrite film was formed on the substrate taken out after the above operations. The frequency characteristics of the permeability of the obtained ferrite film were measured by a permeability meter using a shielded loop coil method.

The noise suppression effect of the ferrite thin film was measured as transmission loss ΔP _loss / P _in using the evaluation system shown in FIG. In FIG. 4, 202 is an MSL used as a base and a transmission line when forming the ferrite thin film 204. In FIG. 4, 203 is a network analyzer. In the measurement, both ends of the MSL 202 are connected to the network analyzer 203 via the coaxial cable 201, and the transmission characteristics when the ferrite thin film 204 is disposed on the MSL 202 on the basis of the transmission characteristics of the MSL 202 alone are obtained. When the ferrite thin film 204 was formed on the polyimide sheet, the sheet was placed so that the surface of the ferrite thin film 204 was in contact with the MSL 202, and measurement was performed in a state where a uniform weight was applied to the entire sheet with a weight of 500 g. . The measurement results of various characteristics are shown in Table 1 below. In Table 1, “Fe”, “Ni”, “Zn”, and “Co” in the “Film composition (mol ratio)” column are “Fe ions”, “Ni ions”, “ The composition (mol ratio) of “Zn ions” and “Co ions”.

In the table, μa ′ and μb ′ respectively indicate the real part permeability in an arbitrary in-plane direction a of the ferrite thin film and the permeability in a direction b orthogonal to the a direction in the plane. The transmission loss ΔP _loss / P _in due to the ferrite film was calculated by the following formulas (7) and (8).

  Here, Γ and T are a reflection coefficient and a transmission coefficient, which are defined by the following equations (9) and (10), respectively.

Ferrite films # 1, # 3, # 4, # 5, # 7, the reflection characteristic of the # 8及 Beauty # 14 _{(S 11)} is despite high specific resistance [rho _DC forming a ferrite thin film in a large area It is a sufficiently low value to reflect, and it can be determined that the transmission signal is not adversely affected even if it is used for an actual multilayer printed wiring board. Moreover film # 1, # 3, # 4 , # 5, # 7, ΔP loss / P in the # 8及 beauty # 14 is low at relatively low frequencies of about 50 MHz, i.e. without attenuating the signal, the GHz band In the frequency band of conduction noise, an ideal characteristic having a large loss is shown. This seems to be an overall effect due to the following four points: a) Since the ferrite film does not contain non-magnetic elements such as a binder, it exhibits an ideal μ ″ characteristic as shown in FIG. , (1) μ ″ is large; b) As a result of large μ ″, the product μ ″ · t of the imaginary part permeability μ ″ and the thickness t of the magnetic layer is obtained despite the small film thickness. C) There is no gap because the magnetic layer not containing a non-magnetic component such as a binder is in close contact with the wiring conductor by a chemical bond, and as a result, the coupling coefficient of equation (1) M is sufficiently large; and d) It is sufficiently large when the ratio L / t between the thickness t of the magnetic layer and the length L in the shortest direction in any direction within the plane of the magnetic layer is 1000 or more. The fr · μ ″ product is derived from the fact that the demagnetizing field in the in-plane direction is negligibly small and has a two-dimensional shape. It is enhanced. Furthermore, the thin film # 1, # 3, # 4, # 5, # 7, # 8 since 及 beauty # 14 or no magnetic anisotropy in the film plane is small, in any plane of the magnetic layer The ratio x of the permeability μa in the direction a and the permeability μb in the direction b orthogonal to the a direction in the plane is 0.5 ≦ x ≦ 2, and as a result, the dispersion of μ ″ appears in the GHz band. In addition, since the effect on the transmission characteristics is almost isotropic, it exhibits excellent characteristics with little directionality of the noise suppression effect in the circuit board, and the thin films # 1, # 3, # 4, # 5, # 7, # 8及 beauty # 14 exhibit excellent permeability characteristics and noise suppression effect as described above, the composition ratio of metal ions in the membrane _Fe a _Ni b _Zn c Co _d is 2.1 ≦ a ≦ 2.7, 0.1 ≦ b ≦ 0.3, 0.1 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.15 (provided that a + b + c = 3.0) By that, the size and the dispersion characteristic of mu "is because it is a suitable for high-frequency noise suppression.

On the other hand, in the experiment using thin film # 2 formed on the polyimide sheet, the product of the magnetic permeability and the film thickness (μ ″ × t) is slightly higher than that of film # 1, but ΔP _{loss in} the GHz band. The value of / P _in is remarkably low because the ferrite film directly formed on the MSL is chemically bonded to a functional group such as OH group or CO group on the surface of the printed wiring board, and there is no gap on the surface of the printed wiring board. It is estimated that the magnetic coupling coefficient M between the high-frequency current and the film is sufficiently large, whereas when the film formed on the polyimide sheet is placed on the conductor, the ferrite film and the conductor It is considered that M is greatly reduced due to a slight gap between the two.
Thin film # 6 also has a very low ΔP _loss / P _{in in the} GHz band. This is presumably because the film thickness is extremely thin and μ ″ × δ in equation (1) is too small.

The thin films # 11 and # 12 have extremely low ΔP _loss / P _{in in} the GHz band in either the a direction or the b direction. This is because the ratio x of the magnetic permeability μa in an arbitrary in-plane direction a of the magnetic layer and the permeability μb in the direction b orthogonal to the a-direction in the plane exceeds the range of 0.5 ≦ x ≦ 2. This is probably because the direction dependency of the conduction noise suppression effect is too large.

In the thin film # 13, μ ″ × t is 10 μm or less because μ ″ is low, and as a result, ΔP _loss / P _in is remarkably low. This by Co 2 ₊ amount which has the effect of enhancing magnetocrystalline anisotropy is too large, the permeability is estimated to be due to decreased.

Since ΔP _loss / P _in of the thin film # 15 is a relatively high value even at a relatively low frequency of about 50 MHz, it is considered that there is an extremely high risk of deteriorating the signal quality. This is presumably because the loss due to the eddy current in the film is added from the low frequency region in addition to the loss due to the magnetic resonance because the specific resistance of the thin film # 15 is lower than 0.1 Ωcm. In other words, in the present invention, by setting the specific resistance of the magnetic layer to 0.1 Ωcm or more, loss resulting from ferromagnetic resonance can be used effectively, so only high-frequency noise can be obtained without degrading signal quality. In addition, even if the film contacts the via hole, leakage current to other wiring layers can be suppressed.

  In order to investigate the influence of the ratio L / t of the film thickness t on the magnetic permeability characteristic responsible for the noise suppression effect of the ferrite thin film and the length L in the shortest direction in any direction within the surface of the magnetic layer, Example A ferrite film was formed on the microstrip line by the same method as in Example 1, and this was cut into 4 mm square, and the magnetic permeability was measured using a shielded loop coil method. The measurement results are shown in Table 2 below.

  As understood from Table 2, films # 16 and # 17 having a film aspect ratio L / t of 1000 or more show relatively large magnetic permeability, whereas film # 18 has films # 16 and # 17. Despite the equal composition, the permeability is remarkably small. This is because the L / t of the films # 16 and # 17 is sufficiently large as 1000 or more, and the demagnetizing field in the in-plane direction of the film is so small that the effective magnetic permeability is almost as close as possible to the magnetic permeability inherent to the material. On the other hand, it is considered that the permeability of the film # 18 is lowered due to the influence of the demagnetizing field in the in-plane direction.

  In the present invention, the thickness of the magnetic layer is defined as t ≦ 50 μm because the L / t value is 1000 or more and the thickness of the multilayer substrate is substantially the same even when mounted as the inner layer of the multilayer substrate. Is within the error range.

  FIG. 5 is a schematic cross-sectional view of a four-layer printed wiring board (a), (b) and (c) provided with an inner layer of a ferrite film having the same composition and thickness as the film # 16 of Example 2 of the present invention. It shows in FIG.6 and FIG.7.

  As shown in FIG. 5, the wiring board (a) has a signal layer 351 and a signal layer 352 arranged in the first layer and the fourth layer, respectively, and a ground layer (conductor layer) 321 in which a ferrite film 331 is formed. Is a printed wiring board having a four-layer structure in which a power source layer (conductor layer) 322 having a ferrite film 332 formed thereon is arranged in the third layer. Reference numeral 310 indicates a dielectric layer for a core material, and reference numerals 341 and 342 indicate dielectric layers for a prepreg. The dielectric layers 310, 341, and 342 in this embodiment are all made of glass epoxy.

  As shown in FIG. 6, the wiring board (b) includes a ground layer in which a signal layer 451 and a signal layer 452 including power supply wiring are arranged in the first layer and the fourth layer, respectively, and ferrite films 431 and 432 are formed. (Conductor layers) 421 and 422 are printed wiring boards having a four-layer structure in which the second and third layers are arranged, respectively. Reference numeral 410 indicates a dielectric layer for the core material, and reference numerals 441 and 442 indicate dielectric layers for the prepreg. The dielectric layers 410, 441, and 442 in this embodiment are all made of glass epoxy. Here, in the wiring board (b), a via hole 470 penetrating the core material is formed. Via hole 470 according to the present embodiment includes a cylindrical via hole conductor 472 as a main part, and ferrite plating films 474 and 476 formed on the outer surface and the inner surface, respectively. Among these, the ferrite plating film 476 formed on the inner surface of the via hole conductor 472 extends to the ferrite films 431 and 432 in the thickness direction of the wiring board (b) rather than the via hole conductor 472. In the wiring board (b) shown in FIG. 6, the ferrite plating films 474 and 476 are formed on both the outer surface and the inner surface of the via hole conductor 472. However, only one of them is formed. Also good.

  As shown in FIG. 7, in the wiring board (c), the signal layer 551 and the signal layer 552 are arranged in the first layer and the fourth layer, respectively, and the ground layer (conductor layer) 531 in which the ferrite film 521 is formed. Is a printed wiring board having a four-layer structure in which a power source layer (conductor layer) 532 having a ferrite film 521 formed thereon is arranged in the third layer. Reference numeral 510 indicates a dielectric layer for the core material, and reference numerals 541 and 542 indicate dielectric layers for the prepreg. The dielectric layers 510, 541 and 542 in this embodiment are all made of glass epoxy.

(Procedure for producing wiring boards (a) and (b))
First, as a core material (inner layer substrate) of the wiring board (a), a double-sided glass epoxy printed wiring board a1 (0.96 mm thick glass epoxy material) on which conductor patterns of the ground layer 321 and the power supply layer 322 are formed is formed. A copper foil having a thickness of 0.035 mm) is prepared. Similarly, double-sided glass epoxy printed wiring board b1 (thickness 0.96 mm) on which ground layers 421 and 422, ferrite plating film 474 and via hole conductor 472 are formed as a core material (inner layer board) of wiring board (b). A glass epoxy material having a 0.035 mm thick copper foil on both sides) is prepared.

Next, the magnet is removed from the ferrite film forming apparatus used in Example 1, and the prepared double-sided glass epoxy printed wiring boards a1 and b1 are placed on a rotating plate in a state in which a magnetic field is not applied to the film formation object. The plate was heated to 90 ° C. while supplying deoxygenated ion exchange water while rotating the plate at 150 rpm. Next, N ₂ gas was introduced into the apparatus to form a deoxygenated atmosphere. Desired amounts of FeCl ₂ · 4H ₂ O, NiCl ₂ · 6H ₂ O and ZnCl ₂ are dissolved in deoxygenated ion-exchanged water as reaction solutions, and desired amounts of NaNO ₂ and CH ₃ COONH ₄ are each dissolved in deoxygenated ion-exchanged water. The dissolved oxidizing solution and the above-mentioned reaction solution were each supplied at a flow rate of about 40 ml / min through a nozzle. Thereafter, a black ferrite thin film was formed on the substrate taken out. This operation is performed on both sides of the two types of double-sided glass epoxy printed wiring boards a1 and b1, and the ferrite films 331, 332, 431, and 432 having a thickness of about 3 μm are closely attached to both sides of the double-sided glass epoxy printed wiring boards a1 and b. A film was formed. In the case of the wiring board (b), a ferrite plating film 476 is formed on the inner surface of the via hole conductor 472 in this ferrite film forming process.

  Epoxy prepregs (thickness: 0.2 mm) 341, 342, 441, 442 and copper foils 351, 352, 451, 452 (thickness) are formed on both surfaces of the core material a1 and b1 with ferrite film thus produced. : 0.012 mm) is thermocompression-bonded to form a hole for via hole, and then copper plating with a thickness of 0.01 mm is applied to provide via hole conductors 363, 364, 461, 462, and a wiring pattern is formed. Four-layer printed wiring boards (a) and (b) for evaluation were obtained.

(Procedure for production of wiring board (c))
On the other hand, in the case of the wiring board (c), unlike the case of the wiring boards (a) and (b), the upper and lower two substrates which are the main parts other than the core material are prepared roughly, and the ferrite plating film is formed on the surface thereof. After the formation of these, they were bonded to a dielectric 510 serving as a core material.

  Specifically, first, the conductor pattern of the signal layer 551 (with a copper foil having a thickness of 0.012 mm) is formed on one surface, and the conductor pattern (thickness 0. 0 mm) of the ground layer 531 is formed on the other surface. A double-sided glass epoxy printed wiring board c1 (having a copper foil on both sides of a glass epoxy material having a thickness of 0.2 mm) on which a signal layer 522 is formed on one side. Both sides on which a conductor pattern (with a copper foil having a thickness of 0.012 mm) is formed and the conductor pattern of the power supply layer 532 (with a copper foil having a thickness of 0.035 mm) is formed on the other surface Two glass epoxy printed wiring boards of glass epoxy printed wiring board c2 (with a copper foil provided on both sides of a 0.2 mm thick glass epoxy material) were prepared.

Next, the magnet is removed from the ferrite film forming apparatus used in Example 1, and the prepared two double-sided glass epoxy printed wiring boards are placed on the rotating plate in a state where no magnetic field is applied to the film formation target. Was heated to 90 degrees while supplying deoxygenated ion exchange water while rotating at 150 rp. Here, both the double-sided glass epoxy printed wiring board c1 and the double-sided glass epoxy printed wiring board c2 were installed so that the signal layer faced the rotating plate. Next, N ₂ gas was introduced into the apparatus to form a deoxygenated atmosphere. As reaction solutions, desired amounts of FeCl ₂ .4H ₂ O, NiCl ₂ .6H ₂ O, and ZnCl ₂ were dissolved in deoxygenated ion-exchanged water. Further, an oxidizing solution in which a desired amount of NaNO ₂ and CH ₃ COONH ₄ were dissolved in deoxygenated ion-exchanged water and the above-described reaction solution were supplied as nozzles at a flow rate of about 40 ml / min. Thereafter, a black ferrite thin film was formed on the substrate taken out.

  After inserting the epoxy prepreg 510 (thickness: 0.96 mm) between the double-sided glass epoxy printed wiring board c1 and c2 thus obtained, they were thermocompression bonded. Next, after forming a hole for a via hole, copper plating with a thickness of 0.01 mm is performed to provide via hole conductors 563 and 564, and a wiring pattern is formed to evaluate a four-layer printed wiring board (c). Got.

(Measurement and evaluation of radiation noise)
Printed wiring boards (a), (b) and (c) provided with a ferrite film as an inner layer, and six types of printed wiring boards (a ′), (b ′) and (c ′) for comparison The evaluation circuit was configured by mounting a PLD (Programmable Logic Device) with a clock of 75 MHz, four driver ICs, and resistance elements, capacitors, and the like necessary for these operations. Here, each of the comparative wiring boards (a ′), (b ′) and (c ′) is the wiring board (a) except that the ferrite film is removed from the wiring boards (a), (b) and (c). ), (B) and (c).

  6 types of printed wiring boards (a), (b) and (c) and (a '), (b') and (c ') are installed in an anechoic chamber, and each is operated under the same conditions. The intensity of radiated noise was measured.

  FIGS. 8 and 9 show radiation spectra at frequencies of 1 to 8 GHz of the four-layer printed wiring board (a ′) and (a) on which electronic components are mounted. As can be understood by comparing FIG. 8 and FIG. 9, the printed wiring board (a) in which the ferrite film is embedded has a significantly suppressed emission spectrum compared to the wiring board (a ′) without the ferrite film. It is apparent that the radiation noise can be effectively suppressed by the configuration in which the ferrite film of the present invention is provided in the power supply layer and the ground layer.

  FIGS. 10 and 11 show the emission spectra at frequencies of 1 to 8 GHz of the four-layer printed wiring board (b ′) and (b) on which electronic components are mounted. As can be understood by comparing FIG. 10 and FIG. 11, the emission spectrum is greatly suppressed even in the printed wiring board (b) in which the ferrite film is embedded, compared to the wiring board (b ′) without the ferrite film. Clearly, even when the inner layer is only the ground layer, it is clear that the radiation noise can be greatly reduced by the configuration provided with the ferrite film of the present invention.

  FIGS. 12 and 13 show the emission spectra of the 4-layer printed wiring board (c ′) and (c) on which electronic components are mounted at a frequency of 1 to 8 GHz. As can be understood by comparing FIG. 12 and FIG. 13, even in the printed wiring board (c) in which the ferrite film is embedded, the emission spectrum is greatly suppressed as compared with the wiring board (c ′) without the ferrite film. Radiation noise can be effectively suppressed even by the configuration in which the ferrite film according to the present invention is provided on the surface of the power supply layer or the ground layer not facing the signal layer.

  Here, the reason why the four-layer printed wiring boards (a ′), (b ′), and (c ′) having no ferrite film are different from each other is because the arrangement of components and the wiring pattern are different.

  In the present invention, the magnetic layer provided on the surface facing the signal layer of the wiring conductor constituting the ground layer or power supply layer, or on the surface not facing the signal layer of the wiring conductor constituting the ground layer or power supply layer Is preferably a ferrite film directly formed by electroless plating. In this embodiment, the case where a so-called batch type apparatus as shown in FIG. 3 is used for forming the ferrite plating film has been described as an example. However, the present invention is not particularly limited to this. A continuous film forming apparatus having the above may be used.

  According to the present invention, in a multilayer printed wiring board having a power source layer and / or a ground layer as an inner layer, for example, suppression and radiation of high-frequency electromagnetic interference inside and outside the device accompanying high-speed and high-density mounting. Since noise suppression can be realized without substantially increasing the thickness of the printed wiring board, an electronic circuit free from noise problems can be easily manufactured, which is an industrially extremely effective means.

It is the figure which showed typically the magnetic interaction in the ferrite film by embodiment of this invention. It is an example of the imaginary part magnetic permeability (μ ″) characteristic of the ferrite film and the composite type noise suppression sheet according to the embodiment of the present invention. FIG. 3A is a schematic diagram of a film forming apparatus for a ferrite plating film used in an example of the present invention. FIG. 3B is a layout view when the substrate is viewed from a direction perpendicular to the surface. It is a schematic diagram of the evaluation system of the electromagnetic noise suppression effect used for the Example of this invention. 2 is a cross-sectional structure of a four-layer printed wiring board used in an example of the present invention. 3 is a cross-sectional structure of another four-layer printed wiring board used in an example of the present invention. It is a cross-sectional structure of still another four-layer printed wiring board used in the examples of the present invention. It is a figure which shows the radiation spectrum of the 4-layer printed wiring board (a ') as a comparative example. It is a figure which shows the radiation noise spectrum of the 4-layer printed wiring board (a) by the Example of this invention. It is a figure which shows the radiation spectrum of the 4-layer printed wiring board (b ') as a comparative example. It is a figure which shows the radiation noise spectrum of the 4-layer printed wiring board (b) by the Example of this invention. It is a figure which shows the radiation spectrum of the 4-layer printed wiring board (c ') as a comparative example. It is a figure which shows the radiation noise spectrum of the 4-layer printed wiring board (c) by the Example of this invention.

Explanation of symbols

101, 102 Nozzle 103 Permanent magnet 104 Base 105, 106 Tank 107 Turntable 201 Coaxial cable 202 Microstrip line (MSL)
203 Network analyzer 204 Ferrite thin film

Claims (16)

At least one of a conductor layer functioning as a ground layer and a conductor layer functioning as a power supply layer is provided as an internal conductor layer, and a dielectric layer formed on the internal conductor layer and formed on the dielectric layer In a multilayer printed wiring board provided with a conductor layer functioning as a signal layer,
A multilayer printed wiring board further provided with a magnetic layer made of magnetic components as an inner layer,
The magnetic layer is a ferrite film,
The composition of the metal ions contained in the ferrite film _is made of _{Fe a Ni b Zn c Co d} ,
The composition ratio of the metal ions is 2.1 ≦ a ≦ 2.7, 0.1 ≦ b ≦ 0.3, 0.1 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.15 (where a + b + c = 3.0),
Multilayer printed wiring board. A via hole electrically connecting at least two of the conductor layers is further provided;
The via hole includes a via hole conductor and at least the magnetic layer formed on the inner surface of the via hole conductor.
The multilayer printed wiring board according to claim 1. The magnetic layer is thin enough to satisfy t ≦ 50 μm and L / t ≧ 1000, where t is the thickness and L is the shortest length in the plane of the magnetic layer.
The product μ ″ · t of the imaginary part permeability μ ″ in the predetermined direction in the plane of the magnetic layer and the thickness t of the magnetic layer is 10 μm or more.
The multilayer printed wiring board according to claim 1. The ferrite film is a ferrite plating film formed directly on the internal conductor layer by an electroless plating method.
The multilayer printed wiring board according to any one of claims 1 to 3. At least one of a conductor layer functioning as a ground layer and a conductor layer functioning as a power supply layer is provided as an internal conductor layer, and a dielectric layer formed on the internal conductor layer and formed on the dielectric layer In a multilayer printed wiring board provided with a conductor layer functioning as a signal layer,
A multilayer printed wiring board further provided with a magnetic layer made of magnetic components as an inner layer,
A via hole electrically connecting at least two of the conductor layers is further provided;
The via hole includes a via hole conductor and at least the magnetic layer formed on the inner surface of the via hole conductor.
Multilayer printed wiring board. The magnetic layer is a ferrite film,
The multilayer printed wiring board according to claim 5. The ferrite film is a ferrite plating film formed directly on the internal conductor layer by an electroless plating method.
The multilayer printed wiring board according to claim 6. The composition of the metal ions contained in the ferrite film _is, Fe _a Ni b _Zn c Co consist _d the composition ratio of the metal ions, 2.1 ≦ a ≦ 2.7,0.1 ≦ b ≦ 0.3 0.1 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.15 (provided that a + b + c = 3.0)
The multilayer printed wiring board according to claim 6 or 7. The magnetic layer is provided in close contact with the internal conductor layer.
The multilayer printed wiring board according to any one of claims 1 to 8. The magnetic layer is formed on a surface of the internal conductor layer facing the signal layer;
The multilayer printed wiring board according to claim 9. The magnetic layer is formed on a surface of the internal conductor layer that does not face the signal layer.
The multilayer printed wiring board according to claim 9. The magnetic layer is a film that can be formed by the action of chemical bonds or van der Waals forces.
The multilayer printed wiring board according to any one of claims 1 to 11. The ratio between the first magnetic permeability that is the magnetic permeability in the first direction in the plane of the magnetic layer and the second magnetic permeability that is the magnetic permeability in the second direction orthogonal to the first direction in the same plane is x. When satisfying 0.5 ≦ x ≦ 2,
The multilayer printed wiring board according to any one of claims 1 to 12. The magnetic layer is formed by magnetically coupling unit constituent elements expressing magnetism with each other by a strong interaction in the plane of the magnetic layer.
The multilayer printed wiring board according to any one of claims 1 to 13. The DC specific resistance of the magnetic layer is 0.1 Ω · cm or more,
The multilayer printed wiring board according to any one of claims 1 to 14. The magnetic layer has a magnetic permeability dispersion characteristic derived from ferromagnetic resonance,
The multilayer printed wiring board according to any one of claims 1 to 15.

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