The present invention relates to a method of manufacturing a printed wiring board, and the printed wiring board, and in particular to a method of manufacturing a printed wiring board having a core containing a carbon fiber reinforced plastic, and the printed wiring board.
In recent years, it has become desirable for printed wiring boards to include a substrate with good heat dissipation properties, as electronic components are mounted in higher density. A metal core substrate has been known as a printed wiring board excellent in heat dissipation properties, and has already been put to practical use. The metal core substrate uses a metal having high thermal conductivity as a core material, and thereby can dissipate heat from a heat-generating component throughout the printed wiring board and suppress an increase in the temperature of the heat-generating component. Above all, aluminum, which has a low specific gravity, is generally used as a core material.
However, aluminum has a high thermal expansion coefficient of about 24 ppm/K, whereas a ceramic component has a low thermal expansion coefficient of about 7 ppm/K. Therefore, there arises a problem that when a heat cycle test is conducted, a crack occurs at a solder joint portion due to a difference in thermal expansion coefficient between aluminum and the ceramic component, failing to achieve mounting reliability.
As a core material capable of solving the above problem, carbon fiber reinforced plastics (hereinafter also referred to as CFRPs) have been known (for example, see Japanese Patent Laying-Open No. 11-40902 (Patent Literature 1)). A CFRP is a composite material made of carbon fiber and a resin. The carbon fiber has a low thermal expansion coefficient of ±2 ppm/K. Some of carbon fibers have a thermal conductivity of not less than 500 Wm−1K−1 In addition, the carbon fiber has a low specific gravity of about 2 g/cm3. If a core substrate can be fabricated using a CFRP, a substrate with high thermal conductivity and more excellent in mounting reliability than aluminum can be obtained. The CFRP has an in-plane thermal expansion coefficient of about 0 ppm/K, and an out-of-plane thermal expansion coefficient of about 30 ppm/K.
Since the CFRP is electrically conductive, the CFRP is insulated from a penetrating through hole for connecting wirings above and below a core. After the CFRP is insulated from the penetrating through hole, a predetermined circuit is formed on at least one of a front surface and a back surface of the core. After the circuit is formed, a predetermined component is mounted.
PTL 1: Japanese Patent Laying-Open No. 11-40902
Some components to be mounted on the core may be affected by a stray capacitance due to the CFRP. To avoid influence of the stray capacitance, it is necessary to remove a portion of the CFRP which includes a region in which a component is to be mounted when viewed in a plan view. However, as a result of removing the CFRP, the core has an uneven front surface (or back surface). A printed wiring board also has an uneven front surface (or back surface), and thus it becomes difficult to form a circuit.
A first object of the present invention is to provide a method of manufacturing a printed wiring board in which a mounted component is not affected by a stray capacitance due to a CFRP, and in which it is not difficult to form a circuit, and the printed wiring board. Further, another object of the present invention is to provide a method of manufacturing a printed wiring board in which a component-mounting surface in a front surface or a back surface of the printed wiring board at a portion from which the CFRP is removed does not become uneven, and the printed wiring board.
Generally, after a circuit is formed on a core, an outer edge of the core is cut to obtain a printed wiring board having a predetermined size. When the outer edge of the core is cut, a CFRP is exposed at side surfaces of the core. The CFRP includes carbon fiber, and carbon powder is scattered from the exposed CFRP. Since the carbon powder is electrically conductive, if it adheres between fine wirings on the circuit, it may cause a short circuit or the like.
A second object of the present invention is to provide a method of manufacturing a printed wiring board in which a CFRP is not exposed at side surfaces of a core even if an outer edge of the core is cut after a circuit is formed on the core, and the printed wiring board.
A method of manufacturing a printed wiring board in accordance with a first aspect of the present invention is a method of manufacturing a printed wiring board on which a predetermined component is to be mounted on at least one of a front surface side and a back surface side, including the following steps: preparing a core containing a carbon fiber reinforced plastic; forming a first through hole so as to penetrate the core from the front surface side to the back surface side and include a region in which the component is to be mounted when viewed in a plan view; closing the back surface side of the first through hole; arranging a fiber reinforced plastic having insulating properties so as to be included in the first through hole; and embedding the fiber reinforced plastic within the first through hole by filling the first through hole with a resin having insulating properties and curing the resin.
A printed wiring board in accordance with a second aspect of the present invention is a printed wiring board having a mounting surface on which a predetermined component is to be mounted on at least one of a front surface side and a back surface side, including: a core containing a carbon fiber reinforced plastic; a fiber reinforced plastic having insulating properties embedded so as to include a region in which the component is to be mounted when viewed in a plan view, and penetrate the core from the front surface side to the back surface side; a resin containing an inorganic filler formed between the region and the fiber reinforced plastic; and an insulating layer laminated on at least one of a front surface side and a back surface side of the core, and provided with the mounting surface or a predetermined wiring pattern.
A method of manufacturing a printed wiring board in accordance with a third aspect of the present invention is a method of manufacturing a printed wiring board, including the following steps: preparing a core having a front surface and a back surface and containing a carbon fiber reinforced plastic; forming a first through hole penetrating the core from a side having the front surface to a side having the back surface; filling the first through hole with a resin containing an inorganic filler; forming a second through hole which defines, together with the first through hole, an outer edge of a region to serve as the printed wiring board, by penetrating the core from the side having the front surface to the side having the back surface and partially overlapping the first through hole when viewed in a plan view; filling the second through hole with another resin containing an inorganic filler; and cutting the core along the outer edge defined by the first through hole and the second through hole.
According to the method of manufacturing a printed wiring board in accordance with the first aspect of the present invention and the printed wiring board in accordance with the second aspect of the present invention, it is possible to obtain a method of manufacturing a printed wiring board in which a mounted component is not affected by a stray capacitance due to a CFRP, and in which it is not difficult to form a circuit, and the printed wiring board.
Further, according to the method of manufacturing a printed wiring board in accordance with the first aspect of the present invention and the printed wiring board in accordance with the second aspect of the present invention, it is possible to obtain a method of manufacturing a printed wiring board in which a component-mounting surface in a front surface or a back surface of the printed wiring board at a portion from which the CFRP is removed does not become uneven, and the printed wiring board.
According to the method of manufacturing a printed wiring board in accordance with the third aspect of the present invention, it is possible to obtain a method of manufacturing a printed wiring board in which a CFRP is not exposed at side surfaces of a core even if an outer edge of the core is cut after a circuit is formed on the core.
Hereinafter, a method of manufacturing a printed wiring board, and the printed wiring board in an embodiment in accordance with the present invention will be described with reference to the drawings. For convenience of illustration,
(Laminated Body 100)
A method of manufacturing a printed wiring board will be described with reference to
Content rates of the carbon fiber and the resin constituting CFRP core 10 are not particularly limited. The structure (an unidirectional material, a cross material, or the like) of the carbon fiber constituting CFRP core 10 is not particularly limited. The resin constituting CFRP core 10 is, for example, epoxy, polyimide, bismaleimide, cyanate ester, or the like. Copper foils 20 are respectively bonded to a front surface and a back surface of CFRP core 10.
Referring to
Referring to
In the printed wiring board obtained by the method of manufacturing a printed wiring board, a predetermined component 90 is to be mounted above or below a region in which through hole 1 is formed (see
Through holes 5 are provided to form a penetrating through hole 5c1 (see
Referring to
Referring to
The size of GFRP core 30 when viewed in a plan view is set to be smaller than that of through hole 1a (see
Referring to
Referring to
Resin 32 contains a resin such as epoxy, polyimide, bismaleimide, or cyanate ester, and an inorganic filler. Preferably, resin 32 contains an epoxy resin and silica.
Since resin 32 contains an inorganic filler, an elastic modulus of GFRP core 30 in a planar direction can be decreased. Since resin 32 contains an inorganic filler, a stress caused by a difference in thermal expansion coefficient between GFRP core 30 and CFRP core 10 into which GFRP core 30 is to be embedded (the details will be described below) is relieved. From the viewpoint of relieving the stress, resin 32 preferably has a thermal expansion coefficient of about 30 ppm/K.
After resin 32 is formed, resin 32 adhering to an unnecessary portion (for example, a front surface of GFRP core 30) is polished. An unnecessary portion of resin 32 is removed.
Referring to
Referring to
By curing the resin paste, a resin 24 having insulating properties is formed inside each of through hole 1a (the gap between through hole 1a and GFRP core 30), through holes 3a, and through holes 5a. Resin 24 contains a resin such as epoxy, polyimide, bismaleimide, or cyanate ester, and an inorganic filler. Preferably, resin 24 contains an epoxy resin and silica.
When resin 24 contains silica, through holes 4 (see
Preferably, each of resin 24 and above resin 32 has an elasticity lower than that of the core containing a fiber reinforced plastic having insulating properties prepared for example as GFRP core 30. Further, preferably, each of resin 24 and above resin 32 has an elasticity lower than those of an insulating layer 52 (see
CFRP core 10 has an in-plane elastic modulus of about 205 GPa. GFRP core 30 as an example of the core containing a fiber reinforced plastic having insulating properties has an in-plane elastic modulus of about 38 GPa. Copper has an elastic modulus of about 129 GPa. When each of resins 24, 32 has an elastic modulus of, for example, about 5 GPa, the elastic modulus is decreased, although the thermal expansion coefficient is increased. A stress as a whole can be reduced.
GFRP core 30 is embedded in through hole 1 (through hole 1a) using resin 24. Resin 24 adhering to an unnecessary portion (for example, the front surface of GFRP core 30) is polished. An unnecessary portion of resin 24 is removed.
Referring to
Since copper foils 20 are removed in the portions subjected to the patterning, a stress caused between CFRP core 10 and plating 22 is relieved. Further, laminated body 100 has a lighter mass. Thus, laminated body 100 is obtained. By performing the steps described above with reference to
(Inner Layer Core 200)
Steps of preparing an inner layer core 200 (see
Referring to
Referring to
After inner layer core 200 and above laminated bodies 100 are laminated as described below, they are pressurized under vacuum at a high temperature. Since inner layer core 200 (insulating layer 52) has flat front and back surfaces, there is no step difference in the vicinity of inner layer copper wirings 54 even if a high pressure is applied during pressurization. Buckling of CFRP core 10 during pressurization can be prevented. Thus, inner layer core 200 is obtained. Inner layer core 200 has an in-plane thermal expansion coefficient of about 16 ppm/K, and an out-of-plane thermal expansion coefficient of about 60 ppm/K.
(Laminated Body 300)
Referring to
Referring to
(Outer Edge Processing)
Referring to
Referring to
By curing the resin paste, a resin 70 having insulating properties is formed inside each of through holes 4. Resin 70 contains a resin such as epoxy, polyimide, bismaleimide, or cyanate ester, and an inorganic filler. After resin 70 is formed, resin 70 adhering to an unnecessary portion (for example, a front surface of copper foil 60) is polished. An unnecessary portion of resin 70 is removed.
Referring to
Referring to
Referring to
Referring to
Similarly, penetrating through hole 5c1 is formed inside one through hole Sb (on the left side in the paper plane). Penetrating through hole 5c1 has an inner diameter of, for example, 0.3 mm. Penetrating through hole 5c1 is insulated from CFRP cores 10. Short-circuit through hole 5c2 is formed inside the other through hole 5b (on the right side in the paper plane). Short-circuit through hole 5c2 has an inner diameter of, for example, 0.3 mm. Short-circuit through hole 5c2 is in conduction with each CFRP core 10 through copper foil 60, via 65, and copper foil 20.
Since CFRP core 10 is connected to copper foil 60 (conductor layer) through via 65, there is no need to immerse the laminated body having CFRP cores 10 and copper foils 60 laminated therein into a plating bath to form a via. Contamination of the plating bath due to carbon powder can be suppressed. It is also possible to form short-circuit through hole 5c2 by opening a through hole in CFRP cores 10 and thereafter directly performing plating treatment on the through hole, although there is a possibility that carbon powder may enter the plating bath during the plating treatment.
Referring to
Next, router processing is performed along an outer shape processing line 80 (corresponding to the outer edge of the printed wiring board). Outer shape processing line 80 is defined so as to follow insulating resin 24 formed inside each through hole 3a and insulating resin 70 formed inside each through hole 4. Even if laminated body 300 is cut along outer shape processing line 80, CFRP cores 10 are not exposed in a cut portion (the outer edge of the printed wiring board). In the portion, only insulating resin 24 and insulating resin 70 are exposed.
Even if a plurality of printed wiring boards 400 are formed from one laminated body 300, no carbon powder is scattered from an outer edge of each printed wiring board 400, suppressing a short circuit in a fine wiring and the like on a circuit.
Referring to
Predetermined component 90 is to be mounted on printed wiring board 400. Component 90 is to be mounted above GFRP cores 30 embedded in through holes 1. Both GFRP core 30 and resin 24 formed inside through hole 1 have insulating properties. In other words, there is no CFRP core 10 having conductivity below a region in which component 90 is to be mounted.
Even if component 90 is mounted on printed wiring board 400, component 90 is not affected by a stray capacitance due to CFRP core 10. GFRP core 30 is embedded inside through hole 1 formed in CFRP core 10. Since printed wiring board 400 does not have an uneven front surface, it is not difficult to form a circuit on the front surface of printed wiring board 400.
(Another Configuration of Embodiment)
Although the plurality of through holes 3 (see
When one through hole 3 is provided, through hole 4 (see
Even if router processing is performed along outer shape processing line 80, the CFRP core is not exposed at the outer edge of the printed wiring board. No carbon powder is 10 scattered from the outer edge, suppressing a short circuit in a fine wiring and the like on a circuit.
Although the above embodiment has been described based on a method of manufacturing a six-layer printed wiring board, and the six-layer printed wiring board, the present invention is not limited thereto. The present invention can also be used for a method of manufacturing a printed wiring board having a desired number of layers by changing the number of layers in inner layer core 200 (see
Although the embodiment for carrying out the invention in accordance with the present invention has been described above, it should be understood that the embodiment disclosed herein is illustrative and non-restrictive in every respect. The scope of the present invention is defined by the scope of the claims, and is intended to include any modifications within the scope and meaning equivalent to the scope of the claims.
The present invention is particularly advantageously applicable to a method of manufacturing a printed wiring board having a core containing a CFRP, and the printed wiring board.
1, 1a, 1b, 2, 3, 3a, 4, 5, 5a, 5b: through hole, 1c, 5c1: penetrating through hole, 5c2: 30 short-circuit through hole, 10: CFRP core, 20, 50, 60: copper foil, 24, 32, 70: resin, 26: pattern, 30: GFRP core, 40: film, 52: insulating layer, 54: inner layer copper wiring, 56: inner layer connection, 62: prepreg, 64, 66: opening, 65: via, 69: copper wiring, 80: outer shape processing line, 90: component, 100, 300: laminated body, 200: inner layer core, 400: printed wiring board.
Number | Date | Country | Kind |
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2010-042906 | Feb 2010 | JP | national |
This application is a divisional of and claims the benefit of priority under 35 U.S.C. §120 from U.S. application Ser. No. 13/520,812, filed Jul. 6, 2012, which is a National Stage Application of PCT/JP2011/054015, filed Feb. 23, 2011, which claims the benefit of priority under 35 U.S.C. §119 from Japanese Application No. 2010-042906, Feb. 26, 2010; the entire contents of which are incorporated herein by reference.
Number | Date | Country | |
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Parent | 13520812 | Jul 2012 | US |
Child | 15299996 | US |