JP2005276926A - Printed circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an inexpensive printed circuit board, while controlling dielectric constant and tanδ to low levels, and to reduce the occurrence of continuity failures by enhancing adhesion strength of through hole plating. <P>SOLUTION: The printed circuit board comprises an insulating layer (4) including a fluororesin sheet (2), and a conductor layer (8) formed at least on one side of the insulating layer (4). The fluororesin sheet (2) has a thickness of 50-300 μm and is mixed with fine particles (11) of inorganic material, e.g. glass beads, glass filament or hollow glass beads, while the dispersion uniformly. The content of the fine particles (11) to the fluororesin sheet (2) is set in the range of 15 wt% or lower. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a printed circuit board used as a wiring board of various electronic devices using radio waves in a high frequency band, such as a millimeter wave antenna.

  In this type of printed circuit board, the smaller the dielectric constant of the board, the faster the signal transmission speed of the circuit, and the smaller the dielectric loss tangent, the smaller the transmission loss. Therefore, a printed circuit board using a fluororesin having a smaller dielectric constant and dielectric loss tangent has been widely used as a substrate for high-frequency electronic devices.

  As a printed circuit board using the above fluororesin, a prepreg made by impregnating a fluororesin into a woven cloth such as glass cloth is used, and a predetermined circuit pattern is formed on the outer surface of the prepreg by a metal foil such as a copper foil. Is known. This prepreg can reduce the dielectric constant and dielectric loss tangent of the substrate by increasing the impregnation ratio of the fluororesin to the woven fabric such as glass cloth. However, in order to reduce the dielectric constant to, for example, 2.2 or less, it is necessary to increase the impregnation ratio of the fluororesin to 91.5% by weight or more. For this purpose, the fluororesin impregnation step is repeated over a plurality of times. There is a need. For this reason, it is not easy to obtain a prepreg having a high impregnation ratio of the fluororesin, and there is a problem that the printed circuit board cannot be implemented at a low cost.

  Therefore, conventionally, a printed circuit board has been proposed in which a polytetrafluoroethylene resin (PTFE) sheet having the lowest dielectric constant among the fluororesins is used and the dielectric constant and dielectric loss tangent of the board are kept low ( For example, see Patent Document 1.)

  That is, in this prior art, a prepreg made of a glass cloth impregnated and held with a fluororesin is disposed on at least one side of the fluororesin sheet, and an insulating layer is formed by the fluororesin sheet and the prepreg. A conductor layer made of a metal foil is formed on the outer surface of the prepreg, and a predetermined circuit pattern is formed on the conductor layer. In this prior art, it seems that the insulating layer can be formed at a low cost, and the ratio of the fluororesin in the whole substrate can be easily increased. For example, a cellular phone using a radio wave in the millimeter wave band (20 GHz to 30 GHz) There is an advantage that the dielectric constant can be set to 2.2 or less so that it can be applied to other devices.

JP 2002-158415 A

  In the above prior art, the dielectric constant of the substrate can be lowered by increasing the ratio of the fluororesin to the entire substrate by increasing the thickness of the fluororesin sheet. However, among PTFE, especially PTFE with a low dielectric constant, the adhesion strength of plating is low. Therefore, when plating is performed on the through holes formed in this printed circuit board, the above fluororesin sheet portion There is a problem that the through-hole plating does not adhere, or the adhesion strength is weak and easy to peel off. In particular, when the fluororesin sheet is thick, the influence is large, and there is a problem that poor conduction is likely to occur.

  An object of the present invention is to provide a printed circuit board that solves the above-mentioned problems, can be implemented at low cost while keeping the dielectric constant and dielectric loss tangent low, and can increase the adhesion strength of through-hole plating and reduce the occurrence of conduction failure. Is a technical issue.

In order to solve the above-described problems, the present invention is configured as follows, for example, based on FIG. 1 and FIG. 2 showing an embodiment of the present invention.
That is, the present invention relates to a printed circuit board, which comprises an insulating layer (4) including a fluororesin sheet (2) and a conductor layer (8) formed on at least one side of the insulating layer (4). In the fluororesin sheet (2), fine particles (11) made of an inorganic material are contained in an amount of 15% by weight or less.

  Since the fluororesin sheet contains inorganic fine particles, when a through hole is formed in the printed circuit board, the inorganic fine particle is exposed on the inner surface of the through hole. As a result, when the through hole is plated, the plating adheres well to the inner surface of the through hole through the inorganic fine particles in the fluororesin sheet portion.

  The inorganic fine particles generally have a dielectric constant larger than that of the fluororesin, so that when the content increases, the dielectric constant of the entire substrate also increases. For example, when the content of the inorganic fine particles with respect to the fluororesin sheet is about 20% by weight, the dielectric constant becomes larger than 2.4, which is not suitable for a high-frequency printed circuit board. Therefore, the content of the inorganic fine particles is set to 15% by weight or less, preferably 12% by weight or less, more preferably 10% by weight or less. If the content of the inorganic fine particles is excessively reduced, the adhesion strength of the plating is weakened. Therefore, the content of the inorganic fine particles is preferably set to 1% by weight or more, more preferably 5% by weight or more.

  The inorganic fine particles may be granular or short fiber. The material of the inorganic fine particles only needs to have high adhesion strength of plating, and a material having a low dielectric constant is preferable, but glass peas, glass filaments, hollow glass beads, etc. are low in dielectric constant and can be implemented at low cost. More preferred.

  As the conductor layer, a copper foil is most preferably used, but a metal such as aluminum, iron, stainless steel, nickel, or an alloy foil thereof can also be used.

  The insulating layer including the fluororesin sheet may include a prepreg made of a glass cloth impregnated and held with a fluororesin. Further, between the insulating layer and the conductive layer, a fluororesin such as tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA) is used so that the conductive layer is satisfactorily bonded to the insulating layer. An adhesive layer may be provided as necessary.

  Although the thickness of said fluororesin sheet | seat is not specifically limited, Usually, it sets to 50-300 micrometers. The fluororesin used for this fluororesin sheet is not limited to a specific type, PTFE, PFA, tetrafluoroethylene / hexafluoropropylene / perfluoroalkyl vinyl ether copolymer (FEPPFA), FEP, polychlorotrifluoroethylene (PCTFE) , Vinylidene fluoride resin (PVDF), vinyl fluoride resin (PVF), ethylene / tetrafluoroethylene copolymer (ETFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), etc. can be used alone or A plurality of types can be used as a mixture, but among these, PTFE having a low dielectric constant and dielectric loss tangent and excellent heat resistance, chemical resistance and the like is preferable.

  Since the present invention is configured and operates as described above, the following effects can be obtained.

  (1) Since the fluororesin sheet contains inorganic fine particles, when plating is performed on the through holes formed in the printed circuit board, the plating passes through the inorganic fine particles in the fluororesin sheet portion. It adheres well to the inner surface of the through hole. As a result, the adhesion of the plating to the inner surface of the through hole can be increased to prevent the peeling of the plating, and the occurrence of poor conduction in the through hole can be reduced.

  (2) Moreover, since the content of the above-mentioned inorganic fine particles is set to 15% by weight or less, the dielectric constant and dielectric loss tangent of the entire printed circuit board can be kept low, and the above-mentioned inorganic fine particles are added to the fluororesin sheet. What is necessary is just to contain in the state disperse | distributed uniformly, and the printed circuit board suitable for high frequency can be implemented at low cost.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a first embodiment of the present invention, FIG. 1 (a) is a sectional structural view of a printed circuit board, and FIG. 1 (b) is an enlarged sectional view of a portion B of FIG. 1 (a).

  As shown in FIG. 1 (a), this printed circuit board (1) has an insulating layer (4) formed by disposing two prepregs (3) on both sides of a PTFE resin sheet (2). . The prepreg (3) is obtained by impregnating and holding a fluororesin (6) such as PTFE in a glass cloth (5) as shown in FIG. 1 (b).

  A conductor layer (8) made of copper foil is formed outside the insulating layer (4) via an adhesive layer (7) made of PFA, and a predetermined circuit is formed on the conductor layer (8). A pattern is formed. In the printed circuit board (1), through holes (9) are formed at necessary portions, and a copper plating layer (10) is formed on the inner surface of the through holes (9).

  In the PTFE resin sheet (2), inorganic fine particles (11) made of glass beads or the like are dispersed and mixed. The content of the inorganic fine particles (11) with respect to the PTFE resin sheet (2) is set to 15% by weight or less, for example, about 10% by weight. A part of the inorganic fine particles (11) is exposed on the inner surface of the part formed in the PTFE resin sheet (2) in the through hole (9). For this reason, the copper plating layer (10) Is well adhered to the inner surface of the through hole (9) through the inorganic fine particles (11).

  In the first embodiment, two prepregs (3) are arranged on both sides of the PTFE resin sheet (2) to form the insulating layer (4). However, in the present invention, the number of prepregs stacked is one or Three or more sheets may be used, and the prepreg may be omitted.

  That is, in the second embodiment shown in FIG. 2, the insulating layer (4) is formed of a single PTFE resin sheet (2) in which inorganic fine particles (11) are dispersed and mixed, and outside the insulating layer (4), Similar to the first embodiment, a conductor layer (8) made of copper foil is formed through an adhesive layer (7) made of PFA. Since the prepreg is omitted, the printed circuit board (1) of the second embodiment can be implemented at low cost, and the inorganic fine particles (11) are formed on the inner surface of the through hole (9) as in the first embodiment. Since a part is exposed, the copper plating layer (10) adheres well.

  Next, in the first embodiment, the dielectric constant and the plating adhesion on the inner surface of the through hole when the content of the inorganic fine particles was changed were measured. The PTFE resin sheet used had a thickness of 150 μm, and glass beads were dispersed and mixed therein. The prepreg used was a fluorine resin content of 91.5% by weight. Among the measurement results, the adhesion of the plating was determined from the conduction failure rate in the through hole. The measurement results are shown in the physical property comparison table of FIG.

  As is apparent from the above measurement results, Comparative Example 1 in which the inorganic fine particles (glass beads) are not contained in the PTFE resin sheet has a problem that the conduction failure rate at the through hole is large, and PTFE In Comparative Example 2 in which 20% by weight of inorganic fine particles were contained in the resin sheet, there was a problem that the dielectric constant was larger than 2.4, which was not suitable as a printed circuit board for high frequency. On the other hand, in Examples 1 to 5 in which 1 to 15% by weight of inorganic fine particles are contained in the PTFE resin sheet, the dielectric constant is 2.4 or less, and the conduction failure rate in the through hole is low. I was able to suppress it.

  In each of the above embodiments, a printed circuit board using only one fluororesin sheet has been described. However, the printed circuit board described in the above embodiment is exemplified for embodying the technical idea of the present invention, and the material, dimensions, shape, number of layers, etc. of the insulating layer and the conductor layer are described. The present invention is not limited to the embodiment described above, and various modifications can be made within the scope of the claims of the present invention.

  For example, although one fluororesin sheet is used in each of the above embodiments, a plurality of fluororesin sheets may be laminated and used in the present invention. In the above embodiment, the conductor layer is formed on both sides of the printed circuit board. However, the printed circuit board of the present invention may be formed only on one side, or the conductor layer may be formed on the printed circuit board. It may be a multilayer printed circuit board that is also provided in the inside.

  The printed circuit board of the present invention can be implemented at a low cost while keeping the dielectric constant and dielectric loss tangent low, and also can increase the adhesion strength of through-hole plating to reduce the occurrence of conduction failure, so that it can be used in portable communication devices and transmission / reception devices. It is suitably used for high-frequency printed wiring such as millimeter-wave antenna components used in the semiconductor, high-density wiring of semiconductors such as IC packages, and small wiring boards such as measuring instruments.

1A and 1B show a first embodiment of the present invention, FIG. 1A is a sectional view of a printed circuit board, and FIG. 1B is an enlarged sectional view of a portion B in FIG. It is a sectional structure figure of a printed circuit board of a 2nd embodiment of the present invention. It is a physical property comparison table | surface when content of an inorganic fine particle of the printed circuit board of this invention is changed.

Explanation of symbols

1 ... Printed circuit board 2 ... Fluorine tree sheet (PTFE resin sheet)
4 ... Insulating layer 8 ... Conductor layer
11… Inorganic fine particles

Claims (3)

A printed circuit board comprising an insulating layer (4) including a fluororesin sheet (2) and a conductor layer (8) formed on at least one side of the insulating layer (4),
A printed circuit board, wherein the fluororesin sheet (2) contains fine particles (11) made of an inorganic material in an amount of 15% by weight or less.   The printed circuit board according to claim 1, wherein the inorganic fine particles (11) include any one of glass peas, glass filaments, and hollow glass beads. The printed circuit board according to claim 1 or 2, wherein the fluororesin sheet (2) is a PTFE resin sheet.

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