JP2002329959A - Printed wiring board and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printed wiring board for a high frequency circuit, which reduces transmission loss. SOLUTION: The printed wiring board has an insulating resin layer and a wiring conductor made on this insulating resin layer. The surface roughness of the boundary face between the wiring conductor and the insulating resin layer is not less than 0.01 μm and not more than 1.2 μm. Preferably, the surface roughness is not more than 0.4 μm, and more preferably, it is not more than 0.2 μm. It is desired that the wiring conductor is the wiring pattern composed of the conductor film made by combining a drive process such as deposition, sputtering, etc., and plating treatment. The lamination composed of the insulating resin layer and the wiring conductor of such surface roughness can also be used as the inner-layer circuit or outer-layer circuit of a multilayer printed wiring board.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board used for a high-frequency circuit and a method for manufacturing the same, and more particularly to a high-frequency printed wiring board with reduced transmission loss and a method for manufacturing the same.

[0002]

2. Description of the Related Art In the age of advanced information technology, the frequency band used in information communication technology, especially in wireless communication technology, is shifting to higher and higher frequency bands. In particular, with the spread of mobile phones and broadband communication network systems, high-frequency printed wiring boards used at several hundred MHz to several tens of GHz are required.

[0003] A specific circuit wiring pattern including passive elements such as capacitors, inductors, and resistors is formed on a printed wiring board. At a high frequency, current flows intensively on the surface of the conductor. Transmission loss from the contacting substrate surface increases. In order to reduce the loss of substrate material for high frequency / high speed systems, excellent dielectric properties in the GHz band, namely dielectric loss (or dielectric loss tangent tan)
δ) is small, and a substrate having a characteristic that the dielectric constant is constant over a wide range has been developed. Recently, fluoroplastics and P
A glass cloth copper-clad laminate using a PO (polyphenylene oxide) resin has been put to practical use, and has a good characteristic of a dielectric loss tangent of 0.005 or less at 10 GHz.

[0004] However, the transmission loss depends on the wiring conductor pattern,
It is also related to the surface roughness of the interface between the conductor pattern and the insulating resin layer. It is generally known that the larger the surface roughness, the greater the loss.However, the subtractive method, which is currently the mainstream method of manufacturing printed wiring boards, uses copper-clad laminates and uses copper foil in areas where copper foil is not needed. Is selectively removed by, for example, etching to form a conductor pattern. In copper-clad laminates, a surface roughening treatment is applied to increase the adhesive strength between the prepreg resin and the copper foil, and the surface roughness of the boundary surface between the copper foil and the resin of a general copper-clad laminate is About 6-8 μm, 2-3 for low profile foil
It is about μm. For this reason, even if the dielectric loss tangent is reduced by the substrate material, there is a limit in reducing the transmission loss due to the concentration of the high-frequency current on the conductor surface.

Further, wiring boards used for mobile communication devices such as mobile phones and mobile phones have a long wiring length, so that there is a problem that the transmission loss is cumulatively increased as a whole, and the transmission loss on the surface of the board is large. It is desired to reduce as much as possible.

Accordingly, the present invention provides a high-frequency printed wiring board in which transmission loss from the board surface is effectively reduced, and a method of manufacturing the same.

[0007]

In order to achieve the above object, a high-frequency printed circuit board according to the present invention has an insulating resin layer and a wiring conductor in contact with the insulating resin layer. Provided is a printed wiring board in which the surface roughness of the insulating resin layer is 0.01 μm or more and 1.2 μm or less, preferably 0.4 μm or less, and more preferably 0.2 μm or less.

When the surface roughness of the insulating resin layer is 0.01 μm or less, the surface treatment of the resin layer becomes difficult, and the production cost of the printed wiring board increases. On the other hand, the upper limit of the surface roughness varies depending on the frequency band to be used.
If m or more, the loss of the strip line or microstrip line in the GHz band increases, which is not preferable. For example, at a frequency of 2 GHz, by setting the surface roughness to 1.2 μm, the rate of loss can be reduced to 50%.
%, But if the roughness is further increased, the loss cannot be sufficiently reduced.

By setting the upper limit to 0.4 μm or less, transmission loss can be sufficiently reduced even at a high frequency of about 20 GHz.
Transmission loss can be effectively reduced even at a high frequency of 80 GHz or more.

In order to achieve such surface roughness, an insulating resin layer is formed by a press molding method, a compression molding method, a transfer molding method, or the like using a film, a plate, a molding die or the like having a smooth surface.

The surface of the insulating resin plate having a surface roughness of more than 1.2 μm may be subjected to a smoothing treatment. As a treatment method, a method of applying a liquid resin or a resin varnish to the surface of the insulating resin plate is preferable, and a known method such as coating, dipping, stamping, or casting can be used. Further, a method of obtaining a smooth surface by molding or pressing using a mold or a mirror plate having a mirror surface is also suitable. Furthermore, a method of bonding a film or a thin film having a smooth surface in advance through thermocompression bonding or an adhesive can also be used. The resin for coating used in the surface treatment may be a thermosetting resin or a thermoplastic resin, but when heat resistance is required, a resin having a network structure by a crosslinking reaction such as a thermosetting resin or a photocurable resin. Is preferred.

In order to form a conductive pattern on the surface of the insulating resin layer having a surface roughness in the above-mentioned range with good adhesion, first, a metal is formed on the above-mentioned insulating resin by sputtering, CVD, vapor deposition or the like. A conductor film is formed. The metal at this time is not particularly limited, but a metal having good electric conductivity is preferable. Next, a resist film is formed on the formed conductor film, patterned by photolithography, and a predetermined conductor pattern is formed by etching or the like.

As described above, by forming a conductor pattern by a dry process on an insulating resin layer having a predetermined range of surface roughness, a printed wiring board which ensures adhesion and reduces transmission loss at high frequencies. Can be provided.

As described above, by mounting an IC chip or the like operating in a high frequency band on a printed wiring board capable of coping with a sufficiently high frequency, it is possible to manufacture an electronic device with high operation reliability.

[0015]

FIG. 1 is a schematic sectional view of an electronic device in which an IC package 12 is mounted on a printed wiring board 11 of the present invention. FIG. 2 is a structural example of the printed wiring board shown in FIG. FIG. The printed wiring board of the present invention has an insulating resin layer 21 and a conductor pattern 22 formed on the insulating resin layer. The surface roughness of the interface between the insulating resin 21 and the wiring conductor is 1 μm in the example of FIG.

FIG. 2A shows an example of the configuration of a multilayer printed wiring board including, as an inner layer circuit, a conductor pattern 22 formed on an insulating resin 21 having a surface roughness of 1 μm.
Shows a configuration example in which a conductor pattern formed on an insulating resin having a similar surface roughness is used for an outer layer circuit. In the example shown in FIG. 2, the thickness of the insulating resin 21 is about 0.2 mm, the thickness of the conductor pattern 22 is about 18 μm, and the line width of the conductor pattern 22 is about 0.4 mm. An epoxy resin was used as the insulating resin 21, and the conductor pattern 22 was a copper (Cu) wiring pattern.

As shown in FIG. 2 (a), when used as an inner layer circuit, although not shown, the conductor pattern 22 is connected to an outer layer circuit formed by processing a copper foil 25 through a through hole. Is done. As a feature of the present invention, the conductor pattern 22 is a pattern formed of a conductor film directly formed by sputtering or the like on a very smooth resin surface having a surface roughness of 1 μm. The copper foil 25 as the material of the inner layer circuit and the outer layer circuit is formed by lamination through the prepreg 23.

FIG. 2B shows an example that can be applied to an outer layer circuit as a printed wiring board for mounting high frequency electronic components. The effect of reducing loss by using the printed wiring board of the present invention will be described later.

It should be noted that the insulating resin 21 is not limited to the above-described example, and other thermosetting resins or thermoplastic resins can be used. As thermosetting resins, phenolic resins, urea resins, melamine resins, alkyd resins,
Alkyl resin, unsaturated polyester resin, diallyl phthalate resin, epoxy resin, silicone resin, resin synthesized from cyclopentadiene, resin containing tris (2-hydroxyethyl) isocyanurate, resin synthesized from aromatic nitrile, trimerized aromatic A group dicyanamide resin, a resin containing triallyl trimethacrylate, a crosslinkable polybenzocyclobutene, a furan resin, a geton resin, a xylene resin, a thermosetting resin containing a condensed polycyclic aromatic, or the like can be used.

Examples of the thermoplastic resin include polyethylene, polypropylene, polyolefin resins such as 4-methylpentene-1 resin, polybutene-1 resin, and high-pressure ethylene copolymer; styrene resins, polyvinyl chloride;
Polyvinylidene chloride, polyvinyl alcohol, polyacrylonitrile, polyacrylic plastic, diene plastic, polyamide, polyester, polycarbonate, polyacetal, polybenzocyclobutene,
Fluorine-based resin, polyurethane-based plastic; and polystyrene-based thermoplastic elastomer, polyalefin-based thermoplastic elastomer, polyurethane-based thermoplastic elastomer, polyester-based thermoplastic elastomer, polyamide-based thermoplastic elastomer, low-crystalline 1,2-polybutadiene, chlorinated A thermoplastic elastomer such as a polymer-based thermoplastic elastomer, a fluorine-based thermoplastic elastomer, or an ion-crosslinked thermoplastic elastomer can be used.

Examples of the film or plate having a smooth surface used for forming the insulating resin layer include 4-methylpentene-
Preferred are resins having heat resistance and good releasability, such as resin 1, Tedlar resin, fluororesin, release-treated polyester resin, release-treated metal foil and metal plate. As a molding die, a die subjected to hard chromium plating is preferable.

As the resin used for smoothing the surface of the resin plate, the same thermosetting resin or thermoplastic resin as the above-mentioned insulating resin plate can be used.

FIG. 3 is a graph showing the relationship between the surface roughness Δ of the insulating resin in the printed wiring board shown in FIG. 2 and the increase rate Δαc of the transmission loss. FIG. 4 shows that the surface roughness Δ was 1.
Frequency f and skin depth at 2 μm
6 is a graph showing a relationship between δ and a relationship between a frequency f and a transmission loss increase rate Δαc. To obtain the data in FIG.
Insulating resin having different surface roughness is prepared as a sample, and a copper microstrip having a volume resistivity ρ = 1.74 × 10 ⁻⁸ Ωm and a magnetic permeability μ = 1.26 × 10 ⁻⁶ H / m is provided on the insulating resin. A line was formed. The rate of increase in transmission loss when the surface roughness was changed was measured at various frequencies with reference to the transmission loss when the surface roughness was 0.01 μm.

As is clear from the graph, for example, 2GH
In order to suppress the rate of increase in transmission loss in the z band to 50% or less, it is necessary to reduce the surface roughness to about 1.2 μm or less. In this case, the surface roughness Δ and the loss increase rate Δ
There is a relationship between αc and Δαc = (2 / π) tan ⁻¹ {1.4 (Δ / δ) ² }.

More specifically, when the upper limit of the loss increase rate Δαc is set to 50%, the roughness Δ
Are 1.253 μm at 2 GHz, 0.396 μm at 20 GHz, 0.280 μm at 40 GHz, 80 G
It is 0.198 μm in Hz. The band used by PHS is 1.
Since the frequency is 9 GHz, the surface roughness at the boundary between the insulating resin layer and the conductive circuit pattern is preferably 1.2 μm or less. Further, in consideration of application to a mobile communication system using a geostationary satellite or a case where a high-frequency transistor of several GHz or more is mounted, the surface roughness is desirably 0.4 μm or less. Further, considering future higher frequency, the surface roughness is more preferably 0.2 μm or less.

The lower limit of the standard surface roughness of 0.01 μm is because if the surface roughness is lower than this value, the production cost becomes disadvantageous. The reason is that the surface processing cost of the release film, the end plate, and the mold at the time of molding the insulating resin plate becomes extremely high. Further, when the surface is smoothed, fine irregularities may be generated on the surface of the processing resin, and a long time is required in a processing step for suppressing this.

Next, a method of manufacturing the printed wiring board shown in FIG. 1 and an electronic device in which an electronic component such as an IC chip is mounted on such a printed wiring board will be described with reference to FIGS.

(A) First, the surface roughness is 0.01 μm or more.
An insulating resin plate of 1.2 μm is prepared. As a method of forming such an insulating resin plate, (i) a method of forming an insulating resin plate by press molding, compression molding, or the like with a smooth film having a surface roughness in the above-described range as the uppermost layer; A method of performing a smoothing process on the surface of an insulating resin plate having a surface roughness of 1.2 μm or more so that the surface roughness finally falls within a range of 0.01 μm to 1.2 μm. is there. In the example of FIG. 3A, the latter method is adopted. That is, a glass cloth 53 impregnated with a phenol-cured epoxy resin is sandwiched between a 4-methylpentene-1 resin film (TPX manufactured by Mitsui Chemicals, Inc.) 54 and a stainless steel end plate 52, and is pressed to a thickness of 0.1 mm. 2
mm of the insulating resin layer was obtained. Since the surface roughness of the insulating resin layer is 0.2 μm, a polybenzocyclobutene resin 5 is further added to the surface of the insulating resin layer in order to smooth the surface.
5 was spin-coated to a film thickness of 5 μm to obtain an insulating resin plate 51. The surface roughness of this insulating resin plate is 0.01μ
m.

(B) Next, a Cr thin film 56 having a thickness of 0.05 μm is formed on the insulating resin plate by using RF sputtering at a gas pressure of 0.2 Pa and an RF power of 1 kW. A Cu film having a thickness of 0.5 μm was formed. By using such a dry process, the base of the conductor pattern can be formed on a smooth resin surface with good adhesion. A 5 μm-thick electrolytic copper plating was further performed on the Cu film to finally form a Cu conductor film 57.

(C) A dry film resist (Fotech H-W42 manufactured by Hitachi Chemical Co., Ltd.) is formed on the Cu conductor film 57.
5) After laminating 58 and forming a wiring pattern by photolithography, copper was etched with a ferric chloride etching solution.

(D) After the resist 58 has been stripped, the Cr thin film 56 is further diluted with an alkaline potassium ferricyanide solution.
Was etched to form a conductor pattern of the inner layer circuit.
Such an inner layer circuit has a smooth surface roughness of 0.1 μm at the boundary between the insulating resin plate 51 and the conductor pattern, and can significantly reduce transmission loss even at high frequencies.
Through the steps so far, a single-layer printed wiring board is realized.

(E) Obtained wiring board, glass cloth 60 impregnated with phenol-cured epoxy resin and copper foil 6
1 and press-formed. The copper foil 61 will be processed in a later step as a conductor pattern of the outer layer circuit.

(F) Laminating a dry film resist (not shown) on the surface copper foil 61, forming a wiring pattern by photolithography, etching the copper foil 61 with a ferric chloride etching solution, and removing the resist. Thus, a conductor pattern 61 was formed. Through the steps up to the individual steps, a multilayer printed wiring board including a high frequency compatible internal circuit is manufactured.

(G) On the surface of the obtained multilayer printed wiring board, a solder resist is screen-printed on a portion other than a portion to be soldered, and the resist is cured by irradiating ultraviolet rays. 63 was screen printed, electronic components such as an IC package 65 were mounted, and soldering was performed by an infrared reflow device to obtain an electronic device. Although not shown, the conductor pattern 57 of the inner layer circuit and the (surface) conductor pattern 61 of the outer layer circuit are connected by through holes. The electronic components to be mounted are not limited to the flat package as shown, but may be leadless chip components, lead components, or the like.
Further, a BGA type package may be mounted. In this case, a flip chip method in which solder bumps are fused is adopted instead of directly mounting the surface on the printed wiring board by reflow.

[0035]

According to the present invention, a printed wiring board is realized which reduces the transmission loss by sufficiently smoothing the surface roughness of the interface between the insulating resin plate and the conductor pattern formed on the insulating resin plate. By mounting an electronic component on such a printed wiring board, an electronic device capable of sufficiently suppressing transmission loss even at a high frequency is provided.

The present invention is particularly effective when the mounted electronic components operate at a high frequency. However, the effect of reducing transmission loss is similarly achieved when mounting components having an operation band of 1 GHz or less. You.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an electronic device using a printed wiring board according to an embodiment of the present invention.

FIG. 2 is a diagram showing a substrate in which a conductor pattern is formed on an insulating resin layer having a predetermined surface roughness for an inner layer circuit of a multilayer printed wiring board;
FIG. 3 is a diagram illustrating a configuration example used for an outer layer circuit.

FIG. 3 is a graph showing the relationship between the surface roughness of the interface between the insulating resin layer and the wiring conductor and the rate of increase in transmission loss.

FIG. 4 is a graph showing a relationship between a frequency and a skin depth, and a relationship between a frequency and an increase rate of a transmission loss.

FIG. 5 is a diagram showing a manufacturing process of the printed wiring board of the present invention.

FIG. 6 is a process for manufacturing the printed wiring board of the present invention,
FIG. 6 is a diagram illustrating a process following the process in FIG. 5.

[Explanation of symbols]

 12, 65 IC package 21, 51 Insulating resin plate 22, 57 Conductor pattern 25, 61 Copper foil

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masanori Yamaguchi 1500 Oji Ogawa, Shimodate City, Ibaraki Prefecture Inside Hitachi Chemical Co., Ltd. Within the Research Institute (72) Inventor Yoshiki Hirata 1500 Oji Ogawa, Shimodate City, Ibaraki Prefecture Inside the Hitachi Chemical Co., Ltd. F term (reference) 5E343 AA16 AA17 AA18 AA19 BB16 BB24 BB38 BB54 BB72 CC67 DD03 DD25 DD43 DD76 GG13 5E346 AA12 AA15 AA35 CC04 CC08 CC09 CC10 CC12 CC13 CC14 CC32 CC40 DD02 DD03 DD17 DD24 DD48 GG22 HH02H06H

Claims (7)

[Claims] 1. An insulating resin layer, and a wiring conductor in contact with the insulating resin layer, wherein a surface roughness of a boundary surface between the insulating resin layer and the wiring conductor is 0.01 μm or more and 1.2 μm or less. A printed wiring board characterized by the above. 2. An insulating resin layer, and a wiring conductor in contact with the insulating resin layer, wherein a surface roughness of a boundary surface between the insulating resin layer and the wiring conductor is 0.01 μm or more and 0.4 μm or less. A printed wiring board characterized by the above. 3. The surface roughness is not less than 0.01 μm and not more than 1.2 μm.
A multilayer printed wiring board including an inner layer circuit having an insulating resin layer having a thickness of not more than m and a wiring conductor formed on the insulating resin layer. 4. A surface roughness of not less than 0.01 μm and not more than 1.2 μm.
A multilayer printed wiring board including an outer layer circuit having an insulating resin layer having a thickness of not more than m and a wiring conductor formed on the insulating resin layer. 5. An insulating resin layer, and a wiring conductor directly contacting the insulating resin layer, wherein a surface roughness of a boundary surface between the insulating resin layer and the wiring conductor is 0.01 μm or more and 1.2 μm or less. An electronic device comprising: a printed wiring board; and one or more electronic components mounted on the printed wiring board. 6. The surface roughness is not less than 0.01 μm and not more than 1.2 μm.
m, forming a conductive thin film on the insulating resin plate by a dry process, and forming a conductive thin film on the conductive thin film using the same metal material as the conductive thin film. Forming a film; forming the wiring conductor by processing the conductive film;
And a method for manufacturing a printed wiring board. 7. A step of forming an insulating resin plate; and treating the surface of the insulating resin plate to have a surface roughness of 0.01.
forming an insulating resin layer of not less than μm and not more than 1.2 μm, forming a conductive film on the insulating resin layer by a dry process and a subsequent plating process, and processing the conductive film. Forming a wiring conductor;
And a method for manufacturing a printed wiring board.