JP4503583B2 - Adhesive sheet for capacitor and method for manufacturing printed wiring board with built-in capacitor using the same - Google Patents

Description

  The present invention relates to a capacitor adhesive sheet and a method for manufacturing a capacitor built-in type printed wiring board manufactured using the sheet, and more particularly to a capacitor adhesive applicable to a multilayer flexible printed wiring board having a flexible cable portion. The present invention relates to a sheet and a method for producing a printed wiring board using the sheet.

  In recent years, there has been an increasing demand for miniaturization and higher density of mounting substrates mounted on small electronic devices. As part of this, there is an increasing demand for high-density mounting on the surface of wiring boards such as CSP (chip size package), chip resistors, and chip capacitors, mainly in mobile phones.

  In multilayer printed wiring boards on which components such as CSP are mounted, capacitors are provided for various purposes such as decoupling capacitors, but so-called built-in components are required to cope with increased mounting costs, increased component costs, and high-density mounting. A wiring board has been devised.

  For example, a capacitor is provided between the wiring layers in order to reduce the number of surface-mounted components (see Patent Document 1). That is, an insulating layer of an organic resin containing a dielectric filler is provided between adjacent thin film wiring patterns to form a capacitor. As a result, the number of capacitors mounted on the surface can be reduced, so that the number of mounted components can be reduced.

  However, the method described in Patent Document 1 is not suitable for switching noise reduction applications that require a large capacity (see Patent Document 2). This Patent Document 2 also describes a method of increasing the capacitance of a capacitor by forming a metal foil to be an electrode in an uneven shape and increasing the electrode area.

  However, in these methods, no special consideration is given regarding application to a multilayer flexible printed wiring board.

  In this connection, a method has been proposed in which an electrode is formed on a base insulating material together with a wiring pattern, a dielectric is formed thereon by a method such as printing or electrodeposition, and an opposing electrode is further formed thereon. (See Patent Document 3).

  However, this method has a drawback in that it is difficult to stably form a thin film of the dielectric and the process is complicated. In addition, the flatness of the substrate is required for use as the inner core substrate of the multilayer flexible printed wiring board. However, since the flatness cannot be ensured by the above method, it is difficult to apply to the flexible printed wiring board. is there.

  Further, Patent Document 4 describes a double-sided copper-clad laminate in which a conductor layer provided on both sides of an insulating resin layer containing dielectric powder can form a pattern by etching. By using this method, the dielectric constant can be stabilized.

  However, if the organic resin layer is formed to a thickness of 50 μm or less, it is difficult to maintain the shape of the resin layer during the above pattern formation, and it is difficult to reduce the thickness of the capacitor, which is advantageous for increasing the capacity of the capacitor. For these reasons, a thin capacitor applicable to a component-embedded multilayer flexible printed wiring board is desired.

  FIG. 4 is a cross-sectional view showing the structure of the capacitor described in Patent Document 4. As shown in FIG. 4, copper foils 22 and 23 serving as electrodes are formed on both surfaces of an insulating resin layer 21 containing dielectric powder. It is a double-sided copper-clad laminate in which a conductor layer is bonded via an adhesive.

  However, since the insulating resin layer 21 has a thickness of about 0.3 mm, it is too thick to be incorporated in a multilayer flexible printed wiring board that is desired to be thin. On the other hand, if the thickness of the insulating resin layer 21 is 50 μm or less, the insulating resin layer 10 containing the dielectric powder cannot retain its shape when forming a pattern by etching, and it is difficult to flow the process stably.

  Further, as a printed wiring board, it is desirable that the insulating resin layer between the wirings has a low dielectric constant in order to ensure high frequency characteristics such as reduction of crosstalk generated between the wiring patterns and improvement of the resonance frequency band.

However, the insulating resin layer 21 contains a dielectric powder for forming a capacitor, and there is a problem that it is difficult to reduce the dielectric constant.
Japanese Patent Laid-Open No. 10-93246 JP 2001-177004 A Japanese Patent Laid-Open No. 2001-15883 JP 5-7063 A (Patent No. 3019541)

  As described above, the conventional capacitor for a printed wiring board with a built-in component has a problem in insulation between wirings arranged between layers as a printed wiring board and high frequency characteristics.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above points, and has a capacitor built-in multilayer flexible printed wiring board using a sheet for forming a thin capacitor applicable to a component built-in multilayer flexible printed wiring board. An object of the present invention is to provide a method for stably and inexpensively producing a product.

  In order to achieve the above object, the present invention provides the following inventions.

The first invention is
In the method of manufacturing a capacitor - embedded printed wiring board, in which a capacitor having electrodes bonded to both surfaces of a dielectric layer is built in the printed wiring board ,
A dielectric layer having a high dielectric constant and made of a material that does not substantially deform at a predetermined pressure and temperature in a press for bonding the electrode to the dielectric layer, and has both adhesive surfaces; and the electrode preparing an adhesive sheet for a capacitor having an adhesive resin layer for filling the surrounding,
A metal substrate in which the electrode is formed on a metal foil or a flexible resin film that can be peeled and removed.
Prepare two,
The electrodes face each other with the electrode-side surface of the metal substrate facing the adhesive sheet for capacitors.
To overlap,
The electrode and the dielectric layer that are opposed to each other by heating and pressurizing are adhered to each other so that the electrode is in contact with the dielectric layer.
Forming a counter electrode on the surface of the dielectric layer in a state of being embedded in the resin layer;
After the capacitor is formed, the metal foil or the flexible resin film is peeled and removed,
A metal layer to be a seed layer is formed on the surface from which the metal foil or the flexible resin film is peeled and removed, and a wiring pattern is formed by a semi-additive method.
A method of manufacturing a printed wiring board with a built-in capacitor ,
It is.

The second invention is
In the method of manufacturing a capacitor-embedded printed wiring board, in which a capacitor having electrodes bonded to both surfaces of a dielectric layer is built in the printed wiring board,
A dielectric layer having a high dielectric constant and made of a material that does not substantially deform at a predetermined pressure and temperature in a press for bonding the electrode to the dielectric layer, and has both adhesive surfaces; and the electrode Prepare an adhesive sheet for capacitors having an adhesive resin layer for filling the periphery of
Preparing a first conductive layer and a second conductive layer of the same kind of metal, and a metal foil having a dissimilar metal layer between the two conductive layers;
Two metal base materials on which a circuit wiring pattern including a capacitor electrode is formed by selective etching with respect to the different metal layer in the first conductive layer are prepared,
The electrode-side surface of the metal substrate is overlaid so that the electrode faces the adhesive sheet for capacitors,
Bonding the electrode and the dielectric layer facing each other by the press, and burying the electrode in the adhesive resin layer to form a counter electrode on the surface of the dielectric layer,
A method of manufacturing a printed wiring board with a built-in capacitor, wherein the wiring pattern is formed by selectively etching the second conductive layer after the formation of the capacitor;
It is.

The third invention is
In the manufacturing method of the printed wiring board with a built-in capacitor according to claim 1 or 2,
The method of manufacturing a capacitor-embedded printed wiring board, wherein the adhesive resin layer for filling the periphery of the electrode is a liquid crystal polymer ,
It is.

  Due to these features, the present invention has the following effects.

According to the method of manufacturing a printed wiring board with a built-in capacitor according to the present invention, since an adhesive sheet for a capacitor suitable for constituting a capacitor is used, it is difficult to achieve with a conventional manufacturing method. A built-in capacitor type printed wiring board having good insulation between the arranged wirings and high frequency characteristics can be manufactured inexpensively and stably.

  Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS.

(Example 1)
FIG. 1 is a cross-sectional process diagram illustrating a method for manufacturing a capacitor adhesive sheet in Example 1 of the present invention. First, as shown in FIG. 1 (1), a base material having adhesive resin layers 2 and 3 having high fluidity on both surfaces of a dielectric layer 1 having high dielectric constant and low fluidity is prepared. Here, the dielectric layer 1 is a film-like molded product containing about 60 to 85% by weight of barium titanate having a dielectric constant of about 2000 and about 15 to 40% by weight of a solvent and an epoxy resin.

  The relative dielectric constant of the film-like molded product is about 20 to 60. The thickness is preferably as thin as possible without causing film defects such as pinholes, and a thickness of 5 to 30 μm is also preferable because it has flexibility. However, since it is fragile or torn easily by itself, various process flows and mechanical characteristics as an insulating resin of the substrate are not sufficient as it is.

  As the dielectric material, in addition to the above-mentioned barium titanate, a material containing powders of titanic acid, aluminum oxide, strontium titanate, calcium titanate, magnesium titanate and the like can be applied. As for the resin component, a dielectric material powder can be dispersed and flexibility is required, and as a material that is difficult to be deformed in a subsequent press process, a thermosetting adhesive is suitable. Thermosetting polyimide, acrylic resin, etc., and mixtures thereof can be applied.

  The adhesive resin layers 2 and 3 are required to have a thickness, fluidity and flexibility that allow filling of the electrode part in a later step. From these, epoxy resins, thermoplastic and thermosetting polyimides, acrylic resins, liquid crystal polymers, etc., and mixtures thereof can be applied. Since it is necessary to fill the electrode portion without deforming the dielectric layer 1, the adhesive resin layers 2 and 3 are also required to have a softening temperature lower than that of the dielectric layer 1.

  In order to satisfy these requirements, it is desirable that the dielectric layer 1 is thermosetting and the adhesive resin layers 2 and 3 are thermoplastic. Since the thickness of the electrode part was set to 18 μm, the adhesive resin layers 2 and 3 were made of a liquid crystal polymer which is a thermoplastic resin having a thickness of 20 μm.

  The thickness of the adhesive resin layers 2 and 3 is sufficient to fill the electrode part, and also serves to supplement the mechanical properties of the dielectric layer 1 including the dielectric material. The physical properties may not be satisfied. Therefore, it is necessary to set the thickness in consideration of these points.

  By adopting such a multilayer structure, an adhesive resin layer having high fluidity and low fluidity is disposed on both sides of the dielectric layer, so that the process flow of the printed wiring board is difficult because it is fragile by itself. The dielectric material can be flowed without using a special device or the like.

  In the actual production of a three-layer material composed of dielectric layers 1, 2, and 3, a dielectric material including a dielectric material is coated on an adhesive resin 3 on a carrier such as a releasable metal or resin. A method of applying the layer 1 and further applying the adhesive resin 2 thereon can be employed.

  Next, as shown in FIG. 1 (2), a base material having a metal foil 5 to be an electrode on a peelable metal foil 4 is prepared, and an electrode portion 5a is formed by a photofabrication method or the like. Although not shown, opposing electrode portions 5 b are formed on the metal foil 4. The metal foil 4 can be a nickel foil or the like that can be removed by selective etching. As the resin material, it is possible to use a Teflon (registered trademark) -based resin having high releasability with respect to the adhesive resin layers 2 and 3 and having an electrode portion formed by sputtering, vapor deposition, or electrolytic plating.

  In addition, when the adhesive resin layers 2 and 3 are made of epoxy or acrylic and polyimide resin is used instead of the metal foil 4, the polyimide resin can be removed by selective resin etching. Here, the electrode part is formed of 18 μm thick copper, and the metal foil 4 is a 25 μm thick nickel foil.

  Next, as shown in FIG. 1 (3), the base material on which the electrodes 5a and 5b are formed on the metal foil 4 is aligned so as to face both surfaces of the dielectric layer 1 having a high dielectric constant and low fluidity. Then, they are laminated by hot pressing on the base material having the adhesive resin layers 2 and 3 having high fluidity.

  First, using a vacuum flat plate press in which surface accuracy is ensured, the adhesive resin layers 2 and 3 are flowed, and the dielectric layer 1 is heated to a high temperature region where adhesiveness is expressed and pressed. At this time, the parallelism of the upper and lower heating plates is maintained, the height is controlled according to the thickness of the base material, and the electrodes 5a and 5b and the dielectric layer 1 are bonded. Then, it cools to the temperature which the adhesive resin layers 2 and 3 which are thermoplastic resins harden | cure, maintaining the height of an up-and-down heating board.

  If such a press is performed in a vacuum, the adhesives 2 and 3 can be filled around the electrodes 5a and 5b because the fluidity is high. On the other hand, the dielectric layer 1 having a high dielectric constant has a low fluidity. Electrodes 5a and 5b are arranged on both sides without a gap. As a result, the distance between the electrodes is defined by the thickness of the dielectric layer 1. Although not shown, if the size of the opposing electrodes is set to a different size in consideration of the positional deviation at the time of stacking, the capacitance of the capacitor can be defined by an electrode having a small area.

As a design example of the capacitor, the capacitance when the dielectric layer 1, that is, the electrode having a thickness of 5 μm and a thickness of 100 mm ² is formed from the following formula (1) is approximately 0.005 μF.
C = ε ₀ × ε × s / d (1)
Where C: capacitance (F), ε ₀ : vacuum dielectric constant 8.85 × 10 ¹² (F / m), ε: relative dielectric constant (here 60), s: area (m ² ) , D: thickness (m).

  If it is this size, it is built directly under the chip parts such as QFP (quad flat package: surface mount parts with lead pins pulled out from the four sides of the IC package) mounted on the board, or CSP if it is the inner layer of the multilayer board Since it can be built in the inner layer side, it does not hinder high density.

  Further, the capacitance value on the substrate can be arbitrarily controlled by changing the thickness and area of the dielectric. For example, the capacitance of high-frequency small capacitors used in mobile phones and the like is about 0.1-1 pF, so it can be manufactured to a size of 0402 chips (size 0.4mm long x 0.2mm wide x 0.2 high) or less. it can. For example, a dielectric layer 1, that is, a dielectric layer having a thickness of 5 μm and an electrode diameter of φ50 μm can provide a capacitance of 0.2 pF. Therefore, the mounting area can be greatly reduced.

  Thereafter, as shown in FIG. 1 (4), the nickel foil of the metal foil 4 is removed by selective etching to obtain a capacitor 6. By adopting such a structure, even in a capacitor using a fragile dielectric material, the resin part other than the capacitor can be given flexibility enough to bend at the time of incorporation into a device.

  Although not shown, by stacking a plurality of capacitors 6, the capacitance can be further increased without increasing the substrate area. In addition, since the adhesive resin layers 2 and 3 have a thickness of 20 μm, the insulation between the layers can be sufficiently secured, and the electrical characteristics are superior to the conventional structure in which the dielectric material is sandwiched between the electrodes. Become.

  Also, in order to ensure high frequency characteristics between wiring patterns between layers other than the electrodes of the capacitor, it is desirable that the insulating resin layer between them has a low dielectric constant. This can be achieved by using a material having a low dielectric constant and low dielectric loss tangent such as the above.

  Further, although not shown, a fine printed wiring containing the capacitor by a so-called semi-additive method in which a metal layer is formed on the capacitor 6 by a method such as electroless plating, sputtering, or vapor deposition, and this is used as a seed layer. A board can be constructed.

  With such a structure, since the adhesive resin layers 1, 2, and 3 are present between the wiring layers, it is possible to ensure high insulating characteristics as compared with the dielectric material alone. Further, by using the capacitor 6 as an inner core substrate and building up a copper-clad laminate thereon, a capacitor-embedded multilayer printed wiring board can be obtained.

(Example 2)
FIG. 2 is a cross-sectional process diagram illustrating a method of manufacturing a capacitor in Example 2 of the present invention. First, as shown in FIG. 2 (1), adhesive resin layers 2 and 3 having high fluidity are formed on both surfaces of a dielectric layer 1 having high dielectric constant and low fluidity, as shown in FIG. 1 (1). A base material is prepared.

  Next, as shown in FIG. 2 (2), a metal substrate having a three-layer structure of copper foil 4a (for example, 18 μm thick) / nickel foil 7 (for example 2 μm thick) / copper foil 5 (for example 18 μm thick). And the electrode portion 5a is formed by selective etching in the photofabrication method.

  Although not shown, the opposing electrode portion 5b is formed on the copper foil 4a. The exposed nickel foil other than the electrode part is removed by selective etching, and a roughening process is performed to increase the adhesion strength between the copper foil and the adhesive in a later step.

  Next, as shown in FIG. 2 (3), the pair of devices having the electrodes 5a and 5b formed on the copper foil 4a are positioned so as to face both surfaces of the dielectric layer 1 having a high dielectric constant and low fluidity. These are laminated together by hot pressing on the base material having the adhesive resin layers 2 and 3 having high fluidity. Specific steps are the same as those in the first embodiment.

  Subsequently, as shown in FIG. 2 (4), a wiring pattern 4b is formed on the copper foil 4a by selective etching using a photofabrication technique. By using a structure in which a brittle dielectric material is sandwiched between adhesive resin layers having high fluidity as shown in the figure, there is no damage to the substrate due to conveyance or the like during the formation process of the wiring pattern. As the selective etching at this time, a chemical solution for etching copper with respect to nickel is used.

  Thereby, the wiring pattern 4b can be formed without damaging the electrode portions 5a and 5b. If necessary, the nickel foil is removed by selective etching to obtain a double-sided printed wiring board 8 incorporating a capacitor.

By adopting such a structure, even in a capacitor using a fragile dielectric material, it is possible to impart flexibility enough to bend the resin portion other than the capacitor when it is incorporated into a device. For this reason, it can be set as the flexible printed wiring board which has a cable part. In addition, since the adhesive resin layers 2 and 3 have a thickness of 20 μm, sufficient insulation between the layers can be secured, which is electrically superior to a conventional structure in which a dielectric material is simply sandwiched between electrodes.

  The interlayer connection can be performed, for example, by forming a conduction hole at a desired location with an NC drill or the like after stacking in FIG. In addition, after forming a wiring pattern on both surfaces of FIG. 2 (4), a conductive hole may be formed at a desired location with an NC drill or the like, and partial plating may be performed.

  Furthermore, a double-sided printed wiring board 8 with a built-in capacitor is used as a core substrate, a build-up layer is laminated, a conduction hole is formed at a desired location with an NC drill or the like, and through-hole plating processing including conductive treatment is performed. It can be carried out. At this time, via-hole connection can also be made from the surface layer to the electrode or the inner layer circuit.

(Example 3)
FIG. 3 is a cross-sectional process diagram illustrating a method for manufacturing a capacitor in Example 3 of the present invention. First, as shown in FIG. 3 (1), a base having adhesive resin layers 2 and 3 having high fluidity on both surfaces of the dielectric layer 1 having high dielectric constant and low fluidity shown in FIG. 1 (1). Prepare the materials.

  Next, as shown in FIG. 3 (2), a so-called double-sided copper-clad laminate having copper foils 10 and 11 on both sides of a polyimide film 9 having a thickness of 25 μm is prepared and selectively etched by a photofabrication technique. The electrode part 10a is formed. Although not shown, the opposing electrode portion 10 b is formed on the polyimide film 9. And the roughening process for raising the adhesive strength of copper foil and an adhesive material in a later process is performed.

  Next, as shown in FIG. 3 (3), the base material on which the electrodes 10a and 10b are formed on the polyimide film 9 is aligned so as to face both surfaces of the dielectric layer 1 having a high dielectric constant and low fluidity. Then, it is laminated by hot pressing on the base material having the adhesive resin layers 2 and 3 having high fluidity. The specific process is the same as that in Examples 1 and 2.

  Next, as shown in FIG. 3 (4), a wiring pattern 11a is formed on the copper foil 11 by selective etching using a photofabrication technique. Note that the interlayer connection can be performed, for example, by forming a conduction hole at a desired location with an NC drill or the like after stacking in FIG.

  Then, if necessary, surface treatment such as solder plating, nickel plating, gold plating, etc. is performed on the surface of the board, formation of a photo solder resist layer, and a shield layer on the outer layer side of the cable using silver paste, film, etc. The multilayer printed wiring board 13 having the cable portion 12 in the outer layer is obtained by performing the outer shape processing.

1 is a conceptual cross-sectional configuration diagram illustrating Example 1 of the present invention. The conceptual cross-sectional block diagram which shows Example 2 of this invention. The conceptual cross-sectional block diagram which shows Example 3 of this invention. The conceptual cross-sectional block diagram of the manufacturing method of the double-sided printed wiring board which incorporated the capacitor by the conventional construction method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dielectric layer 2 with high dielectric constant and low fluidity Adhesive resin layer 4 with high fluidity 4 Metal foil or flexible resin film 5 which can be removed Metal foil 5a used as an electrode part First electrode part 5b First 2 Electrode part 6 Capacitor according to the present invention 7 Nickel foil 8 Double-sided printed wiring board 9 incorporating the capacitor according to the present invention Copper foil 10a First electrode part 10b Second electrode part 11 Copper foil 12 Cable part 13 Capacitor according to the present invention Multilayer printed wiring board 21 having a cable portion with a built-in dielectric material 22, 23 copper foil

Claims (3)

In the method of manufacturing a capacitor - embedded printed wiring board, in which a capacitor having electrodes bonded to both surfaces of a dielectric layer is built in the printed wiring board ,
A dielectric layer having a high dielectric constant and made of a material that does not substantially deform at a predetermined pressure and temperature in a press for bonding the electrode to the dielectric layer, and has both adhesive surfaces; and the electrode Prepare an adhesive sheet for capacitors having an adhesive resin layer for filling the periphery of
A metal substrate in which the electrode is formed on a metal foil or a flexible resin film that can be peeled and removed.
Prepare two,
The electrodes face each other with the electrode-side surface of the metal substrate facing the adhesive sheet for capacitors.
To overlap,
The electrode and the dielectric layer opposed to each other by heating and pressurization are bonded to each other so that the electrode
Forming a counter electrode on the surface of the dielectric layer in a state of being embedded in the resin layer;
After the capacitor is formed, the metal foil or the flexible resin film is peeled and removed,
A metal layer to be a seed layer is formed on the surface from which the metal foil or the flexible resin film is peeled and removed, and a wiring pattern is formed by a semi-additive method.
A method of manufacturing a printed wiring board with a built-in capacitor. In the method of manufacturing a capacitor-embedded printed wiring board, in which a capacitor having electrodes bonded to both surfaces of a dielectric layer is built in the printed wiring board,
A dielectric layer having a high dielectric constant and made of a material that does not substantially deform at a predetermined pressure and temperature in a press for bonding the electrode to the dielectric layer, and has both adhesive surfaces; and the electrode Prepare an adhesive sheet for capacitors having an adhesive resin layer for filling the periphery of
Preparing a first conductive layer and a second conductive layer of the same kind of metal, and a metal foil having a dissimilar metal layer between the two conductive layers;
Two metal base materials on which a circuit wiring pattern including a capacitor electrode is formed by selective etching with respect to the different metal layer in the first conductive layer are prepared,
The electrode-side surface of the metal substrate is overlaid so that the electrode faces the adhesive sheet for capacitors,
Bonding the electrode and the dielectric layer facing each other by the press, and burying the electrode in the adhesive resin layer to form a counter electrode on the surface of the dielectric layer,
A method of manufacturing a printed wiring board with a built-in capacitor, wherein after the capacitor is formed, the second conductive layer is selectively etched to form a wiring pattern . In the manufacturing method of the printed wiring board with a built-in capacitor according to claim 1 or 2,
The method for manufacturing a printed wiring board with a built-in capacitor, wherein the adhesive resin layer for filling the periphery of the electrode is a liquid crystal polymer.

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