JP2001358415A - Printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a board wherein mechanical strength is excellent, thermal expansion coefficient is low, dimensional stability and through hole reliability are excellent, relative permittivity is extremely low at 2.1 at most, and application to a communication apparatus using radio wave of millimeter wave band is sufficiently enabled. SOLUTION: In a printed circuit board 1, a prescribed circuit pattern 3 is formed by using copper foil on at least a single side of a sheet-shaped insulating layer 2 wherein silica fine hollow members are compounded in fluororesin at a rate of 10-70 vol.%. The printed circuit board is constituted by using the silica fine hollow member wherein the volume ratio of silica part and air in a hollow part is set as 1:6-1:3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed circuit board used as a wiring board for various electronic devices using a high frequency band.

[0002]

2. Description of the Related Art Printed circuit boards of various electronic devices using a high frequency band require a low dielectric constant and a low dielectric loss tangent as electrical characteristics corresponding to a high frequency. Conventionally, as a printed circuit board that meets this requirement, a circuit board in which a predetermined circuit pattern is formed of a metal foil on at least one side of a fluorine resin as an insulating layer is often used.

That is, in a printed circuit board, the signal transmission speed and the transmission loss of the circuit largely depend on the dielectric constant and the dielectric loss tangent of the substrate itself. The smaller the dielectric constant of the substrate, the higher the signal transmission speed. The smaller the dielectric loss tangent, the smaller the transmission loss. Therefore, substrates for electronic devices that require high speed and high efficiency of signal transmission such as computers are required to have a low dielectric constant and a low dielectric loss tangent, and fluorine is used as an insulating layer in a conventional printed circuit board. The reason why resin is often used is that the dielectric constant and dielectric loss tangent of fluororesin are phenol resin or epoxy resin,
This is because it is smaller than a polyimide resin or the like.

Meanwhile, with the recent development of information communication technology, the conventional microwave band (several hundred MHz to 20 GHz) has been used.
z) Even higher millimeter wave band (20 GHz to 30 GHz)
z) New applications such as mobile communication devices and radio wave transmission / reception devices (antennas) for radio waves are required, and ultra-high-speed operation is required more and more. And a low dielectric loss tangent are required.

[0005]

However, in a conventional printed circuit board using a fluororesin as an insulating layer, PTFE (polytetrafluoroethylene) having the lowest relative dielectric constant of 2.1 among the fluororesins itself is used. Even when the substrate is used, the relative dielectric constant of the entire substrate is limited to about 2.1 at the maximum, and the substrate having a relative dielectric constant of 2.1 or less required for the above-described device using the millimeter wave band radio wave is I can't get it.

Further, as a substrate having a relative dielectric constant of 2.1 or less, there is known a substrate using a porous fluororesin having pores as an insulating layer as disclosed in, for example, JP-A-5-243697. Have been. When the porous fluororesin has, for example, 80% of the pores, the relative dielectric constant of the porous fluororesin itself is very low at about 1.1 and the dielectric loss is also 1 MHz.
The measured value is about 0.00002, which is suitable for lowering the dielectric constant and the dielectric loss tangent of the substrate, but is a thin dielectric such as 400
Since it is extremely difficult to use as a dielectric (insulating layer) of μm or less, it is difficult to apply to a circuit board of a mobile phone or the like where high frequency, especially a millimeter wave band radio wave is used and thin and small size is desired. Also, there are few such applications. This is because a thin sheet-like insulating layer formed of a porous fluororesin has a very low mechanical strength, is a fluffy sheet due to the presence of vacancies, has no stiffness at all, and further has a high thermal resistance. The expansion coefficient is as high as 90 × 10 ⁻⁶ / ° C.
This is because even if heat of only ° C is applied, the material shrinks greatly, the dimensional stability against heat is poor, and the reliability of through holes is poor.

On the other hand, a printed circuit board using a fluororesin as an insulating layer generally has a high thermal expansion coefficient due to the thermal expansion coefficient of the fluororesin itself. The most general thermal expansion coefficient of the fluororesin laminate in the thickness direction is 80 to 100 × 1.
At 0 ^-6 / ° C, the thermal expansion coefficient in the thickness direction of a laminate of an epoxy resin, a polyimide resin or the like is larger than 20 to 40 × 10 ^-6 / ° C. In addition, since the dimensional stability is naturally poor, there is a problem that the reliability of the through hole is reduced.

In order to solve these problems, there is known a technique of adding particles of an inorganic filler having a low coefficient of thermal expansion such as silica powder to a fluorine resin to reduce the coefficient of thermal expansion in the thickness direction. In a fluororesin substrate containing inorganic particles, the relative permittivity of the inorganic particles is high (4% in the case of silica).
Therefore, the dielectric constant of the substrate is also increased, and the relative dielectric constant of 2.1 or less required for a circuit substrate of a mobile phone or the like using radio waves in the millimeter wave band cannot be achieved at all. is there.

The present invention has been made in view of the above situation, and has excellent mechanical strength, low thermal expansion coefficient, excellent dimensional stability and through-hole reliability, and a relative dielectric constant of 2 or more. It is an object of the present invention to provide a printed circuit board which is extremely low, such as 0.1 or less, and can be sufficiently applied to communication equipment using radio waves in the millimeter wave band.

[0010]

In order to achieve the above object, a printed circuit board according to the present invention comprises a metal foil on at least one side of a sheet-like insulating layer made of a mixture of a fluororesin and a hollow silica fine body. Wherein the volume ratio between the silica portion and the air in the hollow portion is set to 1: 6 to 1: 3. The mixing ratio of the silica micro hollow body to the fluororesin is 10 to 70 VOL.%
Is set to.

According to the present invention having the above-described structure, the silica fine hollow body is added to the fluororesin in an amount of 10 to 70 vol.%.
By forming the insulating layer by blending, even with a thin sheet-like insulating layer, it is possible to obtain a substrate that ensures sufficient mechanical strength, is strong, and has no warpage. The coefficient of thermal expansion in the thickness direction of the substrate is lower than the coefficient of thermal expansion of the fluororesin itself (70 to 95 × 10 ⁻⁶ / ° C.), and dimensional stability and through-hole reliability can be improved; and Since the difference in the coefficient of thermal expansion between the component connected to the circuit pattern on the board is also small, there is no cracking or peeling at the component connection due to thermal stress during actual use, and connection reliability Can also be increased.

[0012] By the way, when the mixing ratio of the silica micro hollow body to the fluororesin is less than 10 VOL.%, Sufficient mechanical strength cannot be ensured and the thermal expansion coefficient becomes large, so that the dimensional stability and the reliability of the through hole are not improved. Lack. On the other hand, when the blending ratio of the silica micro hollow body to the fluororesin exceeds 70 VOL.%, Many gaps are generated in the blend due to insufficient resin or insufficient resin flow, so that the sheet-like insulating layer made of the blend has The water absorption rate is increased and the solder heat resistance of the substrate is reduced, and the adhesion to the metal foil forming the circuit pattern is deteriorated, so that delamination or the like is easily caused.

In addition, by mixing a silica micro hollow body having a volume ratio of silica part to air in the hollow part of 1: 6 to 1: 3 with a fluororesin, the air existing in the hollow part of the silica micro hollow body is mixed. By averaging the relative permittivity (= about 1) and the relative permittivity of the silica part (= about 4), the relative permittivity of the silica micro hollow body itself becomes lower than that of the fluororesin, and as a result, the insulating layer, and hence the substrate Has a very low relative dielectric constant of 2.1 or less, so that a printed circuit board having a low dielectric constant and a low dielectric loss tangent that can be sufficiently applied to communication equipment using millimeter wave band radio waves can be obtained. .

Here, the mixing ratio of the silica micro hollow body to the fluororesin is set to be 40 to 6 as described in claim 2.
By setting to 0 VOL.%, The mechanical strength can be further improved, and the coefficient of thermal expansion can be reduced to further enhance the dimensional stability and the reliability of the through-hole.

As the fluorine resin used in the present invention, as described in claim 3, PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene /
Hexafluoropropylene copolymer) and PFA (tetrafluoroethylene / perfluoroalkylvinyl ether copolymer) may be one selected from
In particular, in order to lower the relative dielectric constant of the substrate, it is preferable to use PTFE having the smallest relative dielectric constant of the material itself.

The hollow silica microparticles used in the present invention may be of any shape, for example, spherical, needle-like or the like.
It is desirable that the particles have a spherical shape with a particle diameter of 0 μm. By using silica micro hollow spheres having such a particle diameter range, fluororesin particles of about 0.2 to 0.5 μm uniformly surround and cover the silica micro hollow spheres, and silica micro hollow spheres and fluoro resin particles And no void is formed in the insulating layer. When a silica micro hollow sphere having a particle diameter of less than 5 μm is used, it is difficult to infiltrate the fluororesin particles between the silica micro hollow spheres, so that a gap is easily generated between the silica micro hollow sphere and the fluororesin particle. In some cases, voids are generated in the insulating layer. Further, when the particle diameter is 2
When silica micro hollow spheres exceeding 0 μm are used, the particles may be too large to be easily settled, and cannot be uniformly dispersed and mixed with the fluororesin. As a result, the relative dielectric constant of the insulating layer may vary. Easy to occur. Further, since the silica micro hollow sphere is broken by the molding pressure, it causes voids and it is difficult to achieve a low dielectric constant.

Furthermore, the printed circuit board according to the present invention is
According to a fifth aspect of the present invention, the sheet-like insulating layer may be constituted by a laminated plate formed by laminating a plurality of the sheet-like insulating layers. It may be configured by laminating a plurality of substrates having a predetermined circuit pattern formed of metal foil on at least one side.

Further, the metal foil used in the present invention includes metals such as copper, aluminum, iron, stainless steel, nickel and the like and alloy foils thereof, and among them, the use of copper foil is most preferable. Moreover, you may use the shirasu micro hollow body which has the same effect as a silica micro hollow body.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional structural view of a printed circuit board according to the present invention.
The circuit patterns 3 and 3 are formed on both surfaces of the sheet-like insulating layer 2 with copper foil as an example of a metal foil.

As shown in FIG. 2, the sheet-like insulating layer 2 has a particle diameter of 5 to 20 μm in a fluororesin 4 selected from PTFE, FEP and PFA, and
The volume ratio between the silica portion 5a and the air in the hollow portion 5b is 1: 6.
The spherical silica micro hollow body 5 set to に 1: 3 is uniformly dispersed and mixed with a solvent at a ratio of 10 to 70 VOL.%, Preferably 40 to 60 VOL.% To prepare a paste-like compound. The paste-like compound is spread out into a sheet having a predetermined thickness using an extruder or the like, and the solvent is heated and evaporated. Then, after arranging copper foil in a predetermined pattern on both sides of the sheet-like insulating layer 2, 380 ° C., 980 × 1
^{0 4 Pa (100kgf / cm 2} ), by hot pressing at 60 minutes of conditions, and to produce a printed circuit board 1 having a predetermined circuit pattern 3, 3.

In the printed circuit board 1 manufactured as described above, the bending strength of the sheet-shaped insulating layer 2 and the printed circuit board 1 is enhanced by the reinforcing effect of the silica micro hollow body 5 uniformly dispersed and mixed in the fluororesin 4. In addition to improving the mechanical strength of the printed circuit board 1, the coefficient of thermal expansion in the thickness direction of the printed circuit board 1 can be improved by the coefficient of thermal expansion of the fluororesin 4 itself (95 ×
10 ⁻⁶ / ° C.) and uniform in the plane direction,
As a result, the occurrence of warpage due to heat when forming the predetermined circuit patterns 3 and 3 such as a hot press can be suppressed, and dimensional stability, through-hole reliability, and component connection reliability can be improved. In addition, the hollow part 5 of the silica micro hollow body 5
Due to the weighted average of the relative permittivity of air (= about 1) and the relative permittivity (= about 4) of the silica portion 5a, the relative permittivity of the silica minute hollow body 5 itself becomes the relative permittivity of the fluororesin 4. As a result, the relative dielectric constant of the sheet-like insulating layer 2 and thus the entire substrate 1 can be made as very low as 2.1 or less, and communication using radio waves in the millimeter wave band is possible. The printed circuit board 1 having a low relative dielectric constant and a low dielectric loss tangent that can be sufficiently applied to equipment can be obtained.

Next, the present invention will be described in more detail with reference to examples. As described in Table 1, in the substrates of Examples 1 to 5 corresponding to the product of the present invention, the mixing ratio of the hollow silica microspheres to the fluororesin (PTFE) was 10, 2 respectively.
0, 40, 60, 70 VOL.%
The volume ratios of the silica part of the silica micro hollow sphere and the air in the hollow part were respectively 1: 6, 1: 6, 1: 4, 1: 3,
1: 3 is set. As a result, the relative dielectric constant of the silica micro hollow spheres in Examples 1 to 5 is a weighted average of the relative dielectric constant (= about 1) of the air existing in the hollow part and the relative dielectric constant (= about 4) of the silica part. , 1.4, 1.4, 1.
6, 1.7 and 1.7.

On the other hand, in the substrate of Comparative Example 1, the porous fluororesin was used as the insulating layer, and neither silica fine hollow spheres nor silica powder was blended. In the substrate of Comparative Example 2, 50 VOL.% Of silica powder was blended with the fluororesin (PTFE). In the substrate of Comparative Example 3, 5 VOL.
%, And the volume ratio of the silica part of the silica micro hollow sphere to the air in the hollow part is set to 1: 4. Thereby, the relative permittivity of the hollow silica microspheres in Comparative Example 3 is 1.6.

[0024]

[Table 1]

Under the above conditions, the relative dielectric constant and the coefficient of thermal expansion of the substrates of Examples 1 to 5 and Comparative Examples 1 to 3 (× 10 ⁻⁶ /
C), mechanical strength and through-hole reliability were measured according to a predetermined test method, and the results shown in Table 2 were obtained.

[0026]

[Table 2]

As is clear from Table 2, the printed circuit boards of Examples 1 to 5 corresponding to the products of the present invention have a relative dielectric constant of 2.1 or less and a thermal expansion coefficient of only fluororesin. Is considerably lower than the thermal expansion coefficient (70-95 × 10 ⁻⁶ / ° C.), has excellent dimensional stability against heat and reliability of through-holes, and uses millimeter wave band radio waves in terms of mechanical strength. Thin suitable for communication equipment (for example, 40
(0 μm thickness or less) The strength required for a substrate having a sheet-like insulating layer is sufficiently ensured.

On the other hand, in the printed circuit board of Comparative Example 1 in which the porous fluororesin was used as the insulating layer, the relative dielectric constant was low as described above, but the thermal expansion coefficient was extremely high, and the dimensional stability against heat was high. In addition to very poor through-hole reliability and low mechanical strength, it is difficult to use it as a thin sheet-like insulating layer, and it can be applied to communication equipment that uses radio waves in the millimeter wave band. Can not. Also,
The printed circuit board of Comparative Example 2 can reduce the coefficient of thermal expansion and improve the mechanical strength, but has a high relative dielectric constant (=
Approximately 4) The relative permittivity of the whole substrate becomes very high due to the compounding of the silica powder, so that it cannot be practically used as a substrate for a communication device using a millimeter-wave band radio wave from the viewpoint of electrical characteristics with respect to a high frequency. . Furthermore, in the printed circuit board of Comparative Example 3, although the relative dielectric constant can be reduced, the reinforcing effect of the hollow silica microspheres is insufficient, and the mechanical strength required for forming the insulating layer into a thin sheet is ensured. And the coefficient of thermal expansion is still high, the reliability of through-holes is inferior, and the difference in coefficient of thermal expansion between the parts connected to the board and the parts is large. It is not suitable as a substrate for communication equipment using millimeter-wave band radio waves, which lacks the connection reliability of components such as cracks or peeling at the connection portion with the device and requires thinning and miniaturization.

In the above-described embodiment, the predetermined circuit patterns 3 and 3 are formed on both surfaces of the single sheet-like insulating layer 2 with copper foil.
3 has been described.
A substrate in which the circuit pattern 3 is formed only on one surface of the sheet-like insulating layer 2 may be used.

The printed circuit board 1 may be a laminated board. That is, as shown in FIG. 3, a compound obtained by uniformly dispersing and mixing a spherical silica micro hollow body 5 at a ratio of 10 to 70 VOL.%, Preferably 40 to 60 VOL. A plurality of insulating layers 2 formed in a sheet shape having a thickness of (three sheets are shown in the drawing, but two or more sheets are sufficient), and a predetermined layer of copper foil is formed on both sides or one side of the laminated plate 2A. A circuit pattern 3 may be formed.

Further, the printed circuit board 1 may be of a multilayer type. That is, as shown in FIG. 4, a plurality of laminated circuit boards 1 formed by forming a predetermined circuit pattern 3 of copper foil on one surface of a laminated board 2A in which a plurality of the sheet-shaped insulating layers 2 are laminated. And the top substrate 1
A multilayer circuit board 1 'may be formed by forming a predetermined circuit pattern 3' of a copper foil on the surface of the multi-layer printed circuit board 1 '.

[0032]

As described above, according to the present invention, the insulating layer is formed by mixing 10 to 70 vol.%, Preferably 40 to 60 vol. Even with a thin sheet-like insulating layer, it is possible to obtain a substrate that has sufficient mechanical strength and is stiff and does not warp, and has a coefficient of thermal expansion in the thickness direction of the substrate that is the thermal expansion of the fluororesin itself. Lower than the coefficient of thermal expansion to improve the dimensional stability against heat and the reliability of through-holes, and the difference in the coefficient of thermal expansion with the components connected to the circuit pattern on the board is reduced. Thus, it is possible to obtain a printed circuit board having high connection reliability without causing cracks or peeling at the component connection portions due to the thermal stress.

In addition, by using a silica fine hollow body having a volume ratio between the silica part and the air in the hollow part set to 1: 6 to 1: 3 as the silica fine hollow body to be mixed with the fluororesin, the silica fine hollow body is used. The relative dielectric constant of itself can be made lower than the relative dielectric constant of the fluororesin, so that the relative dielectric constant of the insulating layer, and thus the substrate, can be very small, such as 2.1 or less.
It is possible to provide a printed circuit board having a low relative dielectric constant and a low dielectric loss tangent that can be sufficiently applied to communication devices using radio waves in the millimeter wave band.

[Brief description of the drawings]

FIG. 1 is a sectional structural view of a printed circuit board according to the present invention.

FIG. 2 is an enlarged view of a main part of the printed circuit board.

FIG. 3 is a cross-sectional structural view of a laminated printed circuit board according to the present invention.

FIG. 4 is a sectional structural view of a multilayer printed circuit board according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Printed circuit board 1 'Multilayer type printed circuit board 2 Sheet-shaped insulating layer 3, 3' Predetermined circuit pattern 4 Fluororesin 5 Spherical silica micro hollow body 5a Silica part 5b Hollow part

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C08L 27/18 H05K 3/46 T H05K 3/46 C04B 35/00 108 F term (reference) 4F071 AA26 AB26 AD04 AF40 AF54 AH13 BA03 BB03 BB06 BC01 4G030 AA37 AA61 AA66 BA09 BA12 BA20 BA24 CA03 CA04 CA07 CA08 GA14 GA17 GA19 GA29 PA21 4J002 BD151 BD161 DJ016 FA106 GQ00 5E346 AA12 AA15 AA22 AA23 AA25 BB01 CC14 CC16 CC32 GG02 HH06H11

Claims (6)

[Claims] 1. A printed circuit board in which a predetermined circuit pattern is formed by a metal foil on at least one side of a sheet-like insulating layer comprising a blend of a fluororesin and a silica fine hollow body, The volume ratio of the silica part to the air in the hollow part is set to 1: 6 to 1: 3, and the mixing ratio of the silica micro hollow body to the fluororesin is set to 10 to 70 VOL.%. A printed circuit board. 2. The printed circuit board according to claim 1, wherein the compounding ratio of the silica micro hollow body to the fluororesin is set to 40 to 60 VOL.%. 3. The method according to claim 1, wherein the fluororesin is PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene /
The printed circuit board according to claim 1, which is one selected from hexafluoropropylene copolymer) and PFA (tetrafluoroethylene / perfluoroalkylvinyl ether copolymer). 4. 4. The printed circuit board according to claim 1, wherein the hollow silica microparticle has a particle diameter of 5 to 20 μm. 5. The printed circuit board according to claim 1, wherein the printed circuit board comprises a laminated plate formed by laminating a plurality of the sheet-shaped insulating layers. 6. The printed circuit board according to claim 1, wherein a substrate having a predetermined circuit pattern formed of metal foil on at least one side of the sheet-like insulating layer is laminated in multiple layers.