JP2001358416A - Printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a board which has low thermal expansion coefficient and superior dimensional stability and through hole reliability, ensures permitivity equivalent to the conventional one, reduces irregularity of permitivity remarkably, and improve surliness of communication function remarkably. SOLUTION: Fluororesin dispersion is compounded with 10-60 vol.% of fine hollow bodies of silica. A glass cloth 2 is impregnated with the compound and a sheet type insulating layer 3 is formed. On at least a single surface side of the insulating layer 3, a copper foil 4 for forming a prescribed circuit pattern is arranged in a printed circuit board 1. The fine hollow bodies of silica whose volume ratio of the silica part to air in the hollow part is set as 1:2-2:1 are used, and the circuit board 1 is constituted.

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.

On the other hand, in a printed circuit board using a fluororesin as an insulating layer, the thermal expansion coefficient of the substrate is generally high 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 has been proposed a technique of adding and mixing inorganic particles having a low coefficient of thermal expansion such as silica powder to a fluororesin matrix to reduce the coefficient of thermal expansion in the thickness direction.

[0007]

However, in a conventionally proposed printed circuit board having a fluororesin obtained by adding and mixing inorganic particles as an insulating layer, the specific gravity of the inorganic particles (4.9 for silica powder) is reduced. Specific gravity of the dispersion (Since the specific gravity of the fluororesin is 2.13 and the specific gravity of water as the solvent is about 1, the dispersion is about 1.5.
), It is difficult to settle the inorganic particles due to the difference in specific gravity and to uniformly disperse them in the fluororesin dispersion. As a result, when glass cloth is used as the insulating layer base material, the relative permittivity of the obtained printed circuit board varies because the glass cloth cannot be uniformly impregnated and held in the glass cloth. If the variation of the relative dielectric constant becomes ± 0.05 or more, high-frequency radio waves cannot be sufficiently introduced into the substrate, and there is a problem that the reliability of transmission and reception functions is reduced.

In addition, the dielectric constant of the printed circuit board itself increases due to the high dielectric constant of the inorganic particles (about 4 in the case of silica powder). Subsequent shrinkage is small, and shrinkage after heating is large in a portion having a small amount of inorganic particles. Therefore, there has been a problem that the substrate is deformed after heating or, in the case of a multilayer type, delamination occurs.

The present invention has been made in view of the above circumstances, and has a low coefficient of thermal expansion, excellent dimensional stability and excellent through-hole reliability, and has a relative dielectric constant equivalent to that of the related art. It is an object of the present invention to provide a printed circuit board capable of significantly reducing the variation in rate and significantly improving the reliability of a communication function.

[0010]

In order to achieve the above object, a printed circuit board according to the present invention comprises a glass cloth, a mixture of a fluororesin and a hollow silica fine body, and impregnates and retains the glass cloth. A printed circuit board comprising an insulating layer and a metal foil disposed so as to form a predetermined circuit pattern on at least one side of the insulating layer, wherein the silica micro hollow body has a silica portion. The volume ratio with the air in the hollow portion is set to 1: 2 to 2: 1.

According to the present invention having the above-described structure, the insulating layer is formed by impregnating and holding a mixture of a fluororesin and a hollow silica fine body in a glass cloth.
The coefficient of thermal expansion of the substrate is determined by the coefficient of thermal expansion of the fluororesin itself (70 to 9).
(5 × 10 ⁻⁶ / ° C.) to improve the dimensional stability of the substrate and the reliability of the through-holes, and the difference in the coefficient of thermal expansion from the components connected to the circuit pattern on the substrate is small. As a result, it is possible to prevent the occurrence of cracks or peeling at the component connection portions due to thermal stress during actual use, and to improve connection reliability.

In addition, the volume ratio of the silica portion of the silica micro hollow body mixed with the fluororesin to the air in the hollow portion is 1: 2.
By setting the specific gravity of the silica fine hollow body to a value (about 0.8 to 1.7) close to the specific gravity (about 1.5) of the fluororesin dispersion by setting the ratio to about 2: 1, It is possible to impregnate and hold the glass cloth in a state where the silica micro hollow body is uniformly dispersed and mixed, and as a result, the variation in the relative dielectric constant of the insulating layer and thus the substrate is suppressed to ± 0.02 or less, and the high frequency By sufficiently introducing radio waves into the substrate, the reliability of transmission and reception functions can be significantly improved. Further, the relative dielectric constant of the silica micro hollow body itself is determined by the weighted average of the relative dielectric constant (= about 1) of the air existing in the hollow part of the silica micro hollow body and the relative dielectric constant (= about 4) of the silica part. By making the dielectric layer lower than the resin, the relative dielectric constant of the insulating layer and, consequently, the substrate can be made as low as that of the conventionally proposed substrate containing inorganic particles or lower.

Here, the mixing ratio of the silica fine hollow body to the fluororesin is 10 to 6 as described in claim 2.
By setting to 0 VOL.%, The mechanical strength of the printed circuit board can be increased, and the coefficient of thermal expansion can be further reduced to further increase the dimensional stability and the reliability of the through hole.

As the fluorine resin used in the present invention, 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.

[0015] The silica micro hollow body used in the present invention may be of any shape such as a sphere or a needle, but in particular, as described in claim 4, 5 to 20 µm.
It is desirable that the particles have a spherical particle diameter. 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. And generate voids in the insulating layer. In addition, when using silica micro hollow spheres having a particle size of more than 20 μm, the particles are too large and the silica micro hollow spheres float in the fluororesin dispersion, and cannot be uniformly dispersed and mixed with the fluororesin dispersion, As a result, the relative permittivity of the insulating layer and the substrate tends to vary. Further, the hollow silica microspheres are broken by the molding pressure to cause voids, and it is difficult to achieve a low dielectric constant.

Further, the printed circuit board according to the present invention comprises:
According to a fifth aspect of the present invention, even when the insulating layer is constituted by a laminated plate obtained by laminating a plurality of the insulating layers, as described in the sixth aspect, at least one side of the insulating layer is provided. It may be configured by laminating a plurality of substrates on each of which a predetermined circuit pattern is formed by metal foil.

Further, examples of the metal foil used in the present invention include metals such as copper, aluminum, iron, stainless steel, nickel and the like and alloy foils thereof. Of these, use of copper foil is most preferable. Further, as the silica micro hollow sphere, a Shirasu micro hollow sphere having the same function may be used.

[0018]

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.
A sheet-like insulating layer 3 made of a mixture of a glass cloth 2, a fluororesin and a silica hollow microsphere and impregnated and held in the glass cloth 2, and a predetermined circuit pattern is formed on both sides of the sheet-like insulating layer 3. And copper foils 4 and 4 which are examples of metal foils arranged so as to be arranged.

As shown in FIG. 2, the sheet-like insulating layer 3 has a particle diameter of 5 to 20 μm and a silica resin dispersion 5 selected from PTFE, FEP and PFA. The silica micro hollow sphere 6 in which the volume ratio of the part 6a and the air in the hollow part 6b is set to 1: 2 to 2: 1 is 10 to 60 vol.%, Preferably 20 to 40 vol.
VOL.% Of the mixture is uniformly dispersed and mixed with a solvent, and the silica fine hollow spheres 6 mixed fluororesin dispersion 5
Is impregnated and held in a glass cloth 2 and then dried and fired. Then, after arranging copper foils 4 and 4 for forming a predetermined circuit pattern on both surfaces of the sheet-like insulating layer 3, 380 ° C., 980 × 10 ⁴ Pa (100 kgf / c
m ² ), by hot pressing for 60 minutes
A printed circuit board 1 on which a predetermined circuit pattern is formed is manufactured.

In the printed circuit board 1 manufactured as described above, the sheet-like insulating layer 3 and the printed insulating layer 3 are formed by the reinforcing effect of the silica micro hollow body 6 and the glass cloth 2 uniformly dispersed and mixed in the fluororesin dispersion 5. Not only the mechanical strength such as the bending strength of the circuit board 1 can be improved, but also the coefficient of thermal expansion in the plane (XY) direction of the printed circuit board 1 is the coefficient of thermal expansion of the fluororesin itself (70 to 95 × 10 ^−6).
/ ° C), the dimensional stability of the circuit board 1 and the reliability of the through-holes can be improved, and the difference in the coefficient of thermal expansion with the components connected to the circuit pattern is small.
It is possible to prevent the occurrence of cracks or peeling at the component connection part due to thermal stress during actual use, and to improve the connection reliability of the component.

The hollow portion 6b of the silica micro hollow sphere 6
Relative permittivity (= 1) of air existing in the inside and silica part 6
Due to the weighted average of the relative permittivity (= about 4) of a, the relative permittivity of the silica micro hollow sphere 6 itself becomes lower than the relative permittivity of the fluororesin and the glass cloth 2, and as a result, the sheet-like insulating layer 3, As a result, the relative dielectric constant of the entire substrate 1 can be reduced, and the printed circuit board 1 having a low relative dielectric constant and a low dielectric loss tangent, which can be sufficiently applied to communication devices using radio waves in the millimeter wave band, can be obtained. .

In addition, by setting the volume ratio between the silica portion 6a and the air in the hollow portion 6b of the silica micro hollow sphere 6 to be mixed with the fluororesin dispersion 5, from 1: 2 to 2: 1. The specific gravity of the hollow sphere 6 becomes a value (approximately 0.8 to 1.7) close to the specific gravity (approximately 1.5) of the fluororesin dispersion 5, and the fluororesin dispersion 5 and the silica micro hollow sphere 6 are uniformly formed. In a state of being dispersed and mixed, the glass cloth 2 can be impregnated and held. As a result, the variation in the relative dielectric constant of the insulating layer 3 and the circuit board 1 is suppressed to ± 0.02 or less, and the communication using the millimeter wave band radio wave by sufficiently introducing the high frequency radio wave into the circuit board 1 is performed. It is possible to significantly improve the reliability of the transmission and reception functions of the device.

Next, the present invention will be described in more detail with reference to examples. As described in Table 1, the substrates of Examples 1 to 4 corresponding to the product of the present invention were prepared such that the mixing ratio of the silica micro hollow spheres to the fluororesin (PTFE) dispersion was 10, 20, 40, and 60 VOL. %, And the insulating layer composed of this proportion is 80 VO with respect to the glass cloth.
L.% impregnation and the volume ratio between the silica part of the silica micro hollow sphere and the air in the hollow part was 2:
1, 2: 1, 1: 1, and 1: 2. Thereby, the specific gravity of the silica micro hollow spheres in Examples 1 to 4 becomes 1.7, 1.7, 1.3, 0.8, and the relative permittivity of the silica micro spheres exists in the hollow portion. The weighted average of the relative permittivity of air (= about 1) and the relative permittivity of the silica portion (= about 4) results in 3.0, 3.0, 2.5, and 2.0.

On the other hand, the substrate of Comparative Example 1 was obtained by impregnating and holding a glass cloth with an insulating layer made of only a fluororesin dispersion, and contained neither silica fine hollow spheres nor silica powder. The substrate of Comparative Example 2 was prepared by adding 50 pieces of silica powder to a fluororesin (PTFE) dispersion.
VOL.% Blended. In the substrate of Comparative Example 3, 5 VOL.% Of silica fine hollow spheres were blended with a fluororesin (PTFE) dispersion, and the volume ratio between the silica portion of the silica fine hollow spheres and the air in the hollow portion was set to 1: 1. The specific gravity of the hollow silica microspheres in Comparative Example 3 was 1.3, and the dielectric constant of the hollow silica microspheres was 2.5.

[0025]

[Table 1]

Under the above conditions, the relative dielectric constants of the substrates of Examples 1 to 4 and Comparative Examples 1 to 3 and the coefficient of thermal expansion in the X and Y directions (× 1
0 ⁻⁶ / ° C.), variation in relative dielectric constant, and through-hole reliability were measured according to a predetermined test method, and the results shown in Table 2 were obtained. In the variation test of the relative permittivity of the substrate, the relative permittivity was measured at nine arbitrary positions on the substrate of 500 mm × 700 mm, and the difference between the average value and the actually measured value at each position was measured.

[0027]

[Table 2]

As is clear from Table 2, the printed circuit boards of Examples 1 to 4 corresponding to the product of the present invention have the relative permittivity reduced to about the same level as Comparative Examples 1 and 3 corresponding to the conventional product. , The thermal expansion coefficient in the XY directions is extremely low, not only is the dimensional stability against heat and the reliability of the through hole excellent, but also the variation in the relative dielectric constant is suppressed to ± 0.02 or less, and the When applied to a communication device using radio waves, it is possible to sufficiently improve the reliability of the transmission and reception functions of the communication device by sufficiently introducing radio waves in the millimeter wave band into the substrate.

On the other hand, in the printed circuit board of Comparative Example 1 in which an insulating layer made of only a fluororesin dispersion is impregnated and held in a glass cloth, the relative dielectric constant is low and the variation is small. The coefficient of thermal expansion is extremely high, and dimensional stability to heat and through-hole reliability are very poor. The printed circuit board of Comparative Example 2 has a high relative dielectric constant, a very large variation, and a high coefficient of thermal expansion in the X and Y directions. It cannot be used practically as a substrate. Further, in the printed circuit board of Comparative Example 3, although the decrease in the relative dielectric constant and its variation can be reduced, the coefficient of thermal expansion is still high, the dimensional stability against heat and the reliability of the through-hole are inferior, and the printed circuit board is connected to the board. Due to the large difference in the coefficient of thermal expansion between components and parts, the connection between the components and the board may crack or peel off due to thermal stress during actual use. It is not suitable as a substrate for a communication device that uses radio waves of the above.

In the above embodiment, the printed circuit board 1 provided with the copper foils 4 and 4 for forming a predetermined circuit pattern with copper foil on both surfaces of the single sheet-like insulating layer 3 has been described. The printed circuit board may be provided with the copper foil 4 only on one side of the insulating layer 3.

Further, the printed circuit board 1 may be a laminated board. That is, as shown in FIG. 3, a silica micro hollow sphere 6 is
L.%, preferably a plurality of sheet-like insulating layers 3 made by impregnating and holding a composition uniformly dispersed and mixed at a ratio of 20 to 40 VOL. The laminate may be a laminate in which copper foils 4 and 4 are arranged so as to form a predetermined circuit pattern on both sides or one side of the laminated plate 3A.

Further, the printed circuit board 1 may be of a multilayer type. That is, as shown in FIG. 4, a copper foil 4 is formed on one side of a laminate 3A in which a plurality of the sheet-like insulating layers 3 are laminated.
A multilayer printed circuit board 1 is formed by laminating a plurality of laminated circuit boards 1, and a copper foil 4 ′ is also arranged on the surface of the uppermost board 1 so as to form a predetermined circuit pattern. The circuit board 1 ′ may be configured.

[0033]

As described above, according to the present invention, a glass cloth is impregnated with an insulating layer made by mixing 10 to 60 vol.
The dimensional stability and reliability of through-holes can be increased by lowering the coefficient of thermal expansion of the substrate than the coefficient of thermal expansion of the fluororesin itself, and the coefficient of thermal expansion of components connected to the circuit pattern on the substrate can be reduced. By making the difference small, it is possible to eliminate the occurrence of cracks or peeling at the component connection parts due to thermal stress during actual use, and to improve connection reliability.

Further, by using a silica micro hollow body having a volume ratio between the silica part and the air in the hollow part set to 1: 2 to 2: 1,
The specific gravity of the silica micro hollow body is approximated to the specific gravity of the fluororesin dispersion, so that the glass cloth can be impregnated and held in a state in which the fluororesin dispersion and the silica micro hollow body are uniformly dispersed and mixed. layer,
In addition, the dispersion of the relative dielectric constant of the board is kept to ± 0.02 or less, and the high-frequency radio waves are sufficiently introduced into the board to significantly improve the reliability of the transmission and reception functions of communication devices that use radio waves in the millimeter wave band. can do. In addition, the relative dielectric constant of the air present in the hollow portion of the silica micro hollow body and the relative permittivity of the silica portion make the relative dielectric constant of the silica micro hollow body itself lower than that of the fluororesin, so that the insulating layer, and thus the substrate, A printed circuit board can be provided in which the relative dielectric constant of the printed circuit board is suppressed to a low relative dielectric constant equivalent to or lower than that of the conventionally proposed substrate containing inorganic particles.

[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 Glass cloth 3 Sheet-shaped insulating layer 4, 4' Copper foil (metal foil) 5 Fluororesin dispersion 6 Silica fine hollow sphere 6a Silica part 6b Hollow part

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C08J 5/04 CEW C08K 7/00 C08K 7/00 7/22 7/22 C08L 27/12 C08L 27/12 H05K 3 / 46 TH05K 3/46 C04B 35/00 108 F term (reference) 4F072 AA08 AB28 AD07 AE22 AF06 AH02 AH22 AL13 4F100 AA20A AB01B AG00A AK17A AK18 AL01 BA02 BA03 BA06 BA13 DD23A DE04A DG12A EJ82AGB43 JB04A05 AA66 BA09 BA12 BA24 CA03 CA04 CA07 CA08 GA14 GA17 GA19 GA29 PA21 4J002 BD121 BD151 BD161 BE041 DJ016 DL007 FA106 FA117 GQ05 5E346 AA05 AA06 AA12 AA15 AA22 AA23 AA25 BB01 CC04 CC14 CC16 CC32 GG02 HH06 HH11 HH21

Claims (6)

[Claims] 1. An insulating layer comprising a glass cloth, a mixture of a fluororesin and a silica micro hollow body, impregnated and held in the glass cloth, and a predetermined circuit pattern is formed on at least one side of the insulating layer. And a metal foil arranged as described above, wherein the silica micro hollow body has a volume ratio between the silica portion and the air in the hollow portion set to 1: 2 to 2: 1. A printed circuit board, characterized in that: 2. The printed circuit board according to claim 1, wherein the mixing ratio of the silica micro hollow body to the fluororesin is set to 10 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 insulating layers. 6. The printed circuit board according to claim 1, wherein a substrate having a predetermined circuit pattern formed of a metal foil on at least one side of the insulating layer is laminated in multiple layers.