JP2002158415A - Printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circuit board in which a specified performance can be ensured stably by reducing the dimensional variation rate substantially uniformly in two orthogonal directions at the time of etching or annealing while achieving a production target as well as the mechanical strength and permittivity. SOLUTION: A prepreg 3, 3 composed of a glass cloth arranged on each side of a PTFE sheet 2 comprises a set of two sheets of prepreg 3-1, 3-2 each laminated crosswise by 90 deg. in the warpwise direction, and a specified circuit pattern is formed of a copper foil 4, 4 on the outer surface of the prepreg 3, 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 radio waves in a high frequency band, such as portable communication devices and transmission / reception devices.

[0002]

2. Description of the Related Art In a printed circuit board of this type, the signal transmission speed and transmission loss of the circuit largely depend on the dielectric constant and the dielectric loss tangent of the substrate itself. The smaller the dielectric loss tangent, the smaller the transmission loss. Therefore, a substrate for an electronic device that requires high speed and high efficiency of signal transmission of a computer or the like is required to have low dielectric constant and low dielectric loss tangent electrical characteristics so as to correspond to a high frequency. In order to meet this demand, a printed circuit board using a fluorine resin having a smaller dielectric constant and a smaller dielectric loss tangent than other resins such as ceramic, phenol resin, epoxy resin, and polyimide resin has been frequently used.

As an example of a printed circuit board using a fluororesin, a prepreg made by impregnating a woven cloth such as a glass cloth with a fluororesin, as disclosed in, for example, Japanese Patent Application Laid-Open No. 8-148780, is used. Layers, or
There is known a fluororesin printed circuit board in which a plurality of sheets are laminated and used, and a predetermined circuit pattern is formed on the outer surface of the prepreg with a metal foil such as a copper foil.

In the above-mentioned fluororesin printed circuit board, the permittivity and dielectric loss tangent of the substrate can be reduced by increasing the impregnation ratio of the fluororesin into the woven fabric such as glass cloth constituting the prepreg. It is possible. However, in order to obtain a prepreg having a high fluororesin impregnation ratio, a plurality of impregnation steps are required, so that a large amount of the surfactant added to the fluororesin dispersion remains in the prepreg. The remaining surfactant causes an adverse effect such as an increase in the dielectric loss tangent.

Further, without using a prepreg obtained by impregnating a woven fabric such as a glass cloth with a fluororesin, only a PTFE (polytetrafluoroethylene) sheet having the lowest dielectric constant among the fluororesins is used. A printed circuit board in which a metal foil is adhered to the outer surface of the PTFE sheet has conventionally existed, but such a board has extremely low mechanical strength such as bending strength and cannot be put to practical use.

Therefore, the millimeter wave band (20 GHz to 30 G
(Hz), and aiming at manufacturing a substrate having a dielectric constant of 2.2 or less and a high mechanical strength so as to be applicable to a device such as a mobile phone in which thinner and smaller size is desired. Prepreg consisting only of glass cloth and the above-mentioned PT
A circuit board in which both are laminated by combining FE sheets is considered.

[0007]

However, in the case of a circuit board in which a prepreg and a PTFE sheet are simply laminated, heat treatment is performed at the time of etching for forming a circuit pattern and after the etching for mounting components such as soldering. At the time (at the time of annealing), furthermore, a large dimensional change occurs due to the thermal expansion and contraction of the PTFE sheet accompanying a change in the environmental temperature during actual use. At this time, due to the property of the prepreg laminated on the PTFE sheet, that is, it is difficult to move in the direction of the warp yarn to which tension is applied, but tends to expand and contract in the direction of the weft to which tension is hardly applied. However, the dimensional change in the prepreg warp direction is suppressed, but the dimensional change in the prepreg weft direction is not suppressed.

When the dimensional change rates in the two directions orthogonal to each other are different as described above, a compressive residual stress remains in one direction inside the substrate and a tensile residual stress remains in the other direction, causing warpage and distortion of the substrate. As a result, the width, length, shape, and impedance of the circuit pattern greatly fluctuate with respect to design values, and the performance as a circuit board becomes very unstable.

Further, at the time of designing a circuit board in consideration of the above-mentioned dimensional change and the like, it is conceivable to take measures such as correcting each variable element in advance.
When the amount of dimensional change of the sheet greatly changes, the dimensional change rate in two directions becomes larger, and the performance as a circuit board may become more unstable.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has a basic configuration in which a prepreg is combined with a fluororesin sheet such as PTFE, while achieving a production target with both mechanical strength and dielectric constant. The purpose of the present invention is to provide a printed circuit board capable of reducing a dimensional change rate in two orthogonal directions substantially at the time of etching or annealing by making effective use of the properties of the above, and stably ensuring predetermined performance without variation. And

[0011]

In order to achieve the above object, a printed circuit board according to the present invention is provided with a prepreg made of glass cloth on at least one side of a fluororesin sheet, and a metal prepreg formed on an outer surface of the prepreg. A printed circuit board on which a predetermined circuit pattern is formed by a foil, wherein the prepreg is at least one of a pair of prepregs laminated with their warp directions crossed at 90 ° with each other.
It is characterized by being composed of a set.

According to the present invention having the above structure, a prepreg obtained by impregnating a woven fabric such as a glass cloth with a fluororesin by using a fluororesin sheet and a prepreg together in a laminated state is used. As described above, there is no rise in dielectric loss tangent due to a large amount of surfactant added in the fluororesin dispersion remaining in the prepreg, and it is possible to obtain a target low dielectric constant, low dielectric loss tangent circuit board. In addition, it is possible to sufficiently secure mechanical strength such as bending strength as compared with the case where the PTFE sheet is used alone.

In addition, as a prepreg disposed on the surface of the fluororesin sheet, a prepreg composed of a pair of prepregs laminated so that the warp directions cross each other at 90 ° C. is used, so that the prepreg can be used for etching or annealing. Thermal expansion and shrinkage of the fluororesin sheet in two orthogonal directions due to temperature changes such as time are greatly reduced by reducing the dimensional change rate by suppressing the thermal expansion and contraction by the property of the prepreg, that is, the warp yarn tension. Can be made substantially uniform. Since the residual stress inside the substrate is extremely small due to such a remarkable decrease in the dimensional change rate in the two orthogonal directions, warpage and distortion hardly occur, the width, length, shape and impedance of the circuit pattern are maintained as designed. As a result, the predetermined performance as the circuit board can be stably secured.

In the present invention, the warp directions are set to 90
Although a set of two prepregs that are crossed and crossed by ° C. may be disposed on only one side of the fluororesin sheet, particularly,
By arranging a set of prepregs on both sides of the fluororesin sheet, the dimensional change rate can be further reduced and the occurrence of warpage can be suppressed.

Further, in the present invention, one or several other prepregs may be further laminated on the outer surface of a pair of prepregs which are laminated so that the warp directions are crossed.
Further, another set of prepregs obtained by laminating a pair of two may be provided. In these cases, the mechanical strength of the circuit board can be further improved in addition to the dimensional stability.

As the fluororesin used in the present invention, as described in claim 4, PTFE (polytetrafluoroethylene), PFA (tetrafluoroethylene / perproloalkyl vinyl ether copolymer), F
EP (tetrafluoroethylene / hexafluoropropylene copolymer), ETFE (ethylene / tetrafluoroethylene copolymer), PVDF (polyvinylidene fluoride), ECTFE (ethylene chlorotrifluoroethylene), PCTFE (polychlorinated trifluoroethylene) ), PVF (polyvinyl fluoride) or a mixture thereof, but it may be any one selected from the group consisting of PTFE, which has the lowest dielectric constant of the material itself in lowering the dielectric constant of the substrate. Is most preferred.

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.

[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.
The prepregs 3 and 3 made of glass cloth are stacked on both surfaces of a PTFE sheet 2 which is an example of a fluororesin sheet.
Copper foils 4 and 4, which are examples of metal foils, are stacked on the outer surface of each of them, and are heated and pressed under predetermined temperature conditions and surface pressure conditions to form them into a predetermined thickness and predetermined dimensions. A predetermined circuit pattern is formed on the foils 4 and 4 by etching.

The prepregs 3 on both sides are respectively
As clearly shown in FIG. 2, two prepregs 3-1 and 3-2 made of only glass cloth in which warp yarns 3a to which tension is applied and weft yarns 3b to which tension is not applied are woven in length and width.
It is configured by being stacked up and down as a set. These upper and lower 2
One set of prepregs 3-1 and 3-2 is composed of those warp yarns 3.
They are arranged so that the directions of “a” cross each other at 90 ° C.

The printed circuit board 1 manufactured as described above has a prepreg formed by impregnating a woven fabric such as a glass cloth with a fluororesin by using a PTFE sheet 2 and prepregs 3 and 3 in a laminated state. Compared to those using, there is no increase in dielectric loss tangent due to the remaining surfactant in the fluororesin dispersion, low dielectric constant,
Low dielectric loss tangent can be achieved and PTF
It is possible to ensure a sufficiently large mechanical strength such as bending strength as compared with the case where the E sheet is used alone.

In addition, as prepregs 3, 3 disposed on both sides of the PTFE sheet 2, the warp yarns 3a
Since the prepregs 3-1 and 3-2 consisting of only a pair of glass cloths stacked one above the other so as to intersect at 0 ° C. are used, the prepregs are used for etching or annealing for circuit formation, Thermal expansion and thermal contraction in two orthogonal directions of the PTFE sheet 2 due to a change in environmental temperature during actual use of a device incorporating the circuit board 1 are caused by a pair of prepregs 3 constituting the double-sided prepregs 3. 1,3-2 warp yarn 5
a, 5a, thereby suppressing the dimensional change of the circuit board 1 in two orthogonal directions.
And it is reduced substantially equally. As a result, the residual stress inside the substrate is extremely small, and warpage and distortion hardly occur.
By maintaining the width, length, shape, and impedance of the circuit pattern as designed, predetermined performance as the circuit board 1 can be stably secured.

Next, the present invention will be described in more detail with reference to examples. Example 1 corresponding to the present invention: As shown in FIG. 3A, two sets of prepregs 3-1 are provided as prepregs 3 on both sides of a PTFE sheet 2 having a thickness of 400 μm. , 3-2, their warp directions are 90
3C, and the warp direction of the prepreg 3-1 on the side close to the PTFE sheet 2 is as shown in FIG.
The E-sheet 2 is vertically laminated in a direction perpendicular to the thickness stretching direction, and copper foil is stacked on the outer surfaces of the double-sided prepregs 3, respectively, followed by hot press molding to produce a circuit board. This circuit board is 510mm long x 340mm wide
The substrate cut into pieces is prepared as a sample substrate of Example 1.

Embodiment 2 corresponding to the product of the present invention: FIG.
As shown in FIG. 2, as prepregs 3 and 3 disposed on both sides of a PTFE sheet 2 having a thickness of 400 μm, a pair of prepregs 3-1 and 3-2 each intersect at 90 ° in the warp direction. 4B, the warp direction of the prepreg 3-2 on the side farther from the PTFE sheet 2 is vertically stacked with respect to the thickness stretching direction of the PTFE sheet 2, and 3,3
The circuit board is manufactured by stacking copper foil on the outer surface of each of the above and hot pressing. A sample substrate of Example 2 was prepared by cutting this circuit board into a 510 mm long × 340 mm wide.

Comparative Example 1: As shown in FIG.
1 μm each on both sides of a 0 μm thick PTFE sheet 2
The prepregs 3, 3 have their respective warp directions shown in FIG.
As shown in (b), the PTFE sheet 2 is arranged along the thickness stretching direction, and
A circuit board is manufactured by stacking copper foil on the outer surface of each of No. 3 and hot pressing. 510mm ×
A sample cut to a width of 340 mm is prepared as a sample substrate of Comparative Example 1.

Comparative Example 2: As shown in FIG.
1 μm each on both sides of a 0 μm thick PTFE sheet 2
As shown in FIG. 6 (b), the prepregs 3 and 3 are arranged such that the warp direction of one prepreg 3 is along the thickness stretching direction of the PTFE sheet 2 and the warp direction of the other prepreg 3 is the PTFE sheet 2 A circuit board is manufactured by arranging the prepregs 3 and 3 in a state perpendicular to the thickness stretching direction, stacking copper foils on the outer surfaces of the prepregs 3 and 3 and performing hot press molding. This circuit board is 510 mm long x 340 mm wide.
A substrate cut into mm is prepared as a sample substrate of Comparative Example 2. 3 (a) to 6 (a), only the warp direction of the prepreg is shown, and the weft direction is not shown.

As shown in FIG. 7, the sample substrates of Examples 1 and 2 and Comparative Examples 1 and 2 are each provided with four holes H at the apexes of 250 mm square.
1, X2, Y1, and Y2 are measured in advance, and after removing the copper foil on both surfaces by etching and after performing a heat treatment (annealing) at 150 ° C. for 30 minutes, the distance X between the holes is respectively determined.
1, X2, Y1 and Y2 were measured to confirm the dimensional changes in the X (vertical) direction and the Y (horizontal) direction due to etching and annealing. As a result, a dimensional change (shrinkage) rate as shown in FIG. 8 and Table 1 was obtained after etching, and a dimensional change (shrinkage) rate as shown in FIG. 9 and Table 2 was obtained after annealing.

[0027]

[Table 1]

[0028]

[Table 2]

As is clear from FIG. 8 and Table 1, FIG. 9 and Table 2, in the printed circuit boards of Examples 1 and 2 corresponding to the product of the present invention, dimensional shrinkage (change) due to etching.
Rate and dimensional shrinkage due to annealing are very small, there is almost no residual compressive stress or no tensile residual stress in the PTFE sheet 2, and no warping or distortion occurs regardless of the environmental temperature change during production as well as during actual use. Therefore, it can be seen that the predetermined function as the circuit board is stably maintained over a long period of time. On the other hand, in the printed circuit boards of Comparative Examples 1 and 2, the rate of dimensional shrinkage (change) due to etching and annealing is several times that of Examples 1 and 2.
A large difference occurs in the rate of change between the X direction and the Y direction. Therefore, a lot of residual stress remains inside the board, and the performance as a circuit board is extremely unstable due to warpage and distortion, especially as a board for communication equipment using radio waves in the millimeter wave band. It turned out to be unsuitable.

In the above embodiment, the prepregs 3-1 and 3-2 consisting of only one pair of glass cloths are used.
Their warp directions cross each other at 90 ° C., and one of the prepregs 3-1 or 3-2 has a warp direction of P.
Although a description has been given of the case where the TFE sheet 2 is vertically stacked in a state orthogonal to the thickness stretching direction of the TFE sheet 2, if the warp directions cross each other at 90 ° C., it is oblique to the thickness stretching direction of the PTFE sheet 2. They may intersect.

[0031]

As described above, according to the present invention, the PTF
By using a fluororesin sheet such as E or PAF and a prepreg together in a laminated state, it is possible to sufficiently cope with high frequencies as compared with a prepreg obtained by impregnating a woven fabric such as a glass cloth with a fluororesin. A low dielectric constant of .2 or less;
A circuit board having a low dielectric loss tangent can be obtained, and P
It is possible to ensure a sufficiently high mechanical strength such as bending strength as compared with the case where the TFE sheet is used alone.

Furthermore, a pair of prepregs laminated so that the warp directions to which tension is applied cross each other at 90 ° C. are used by laminating them on a PTFE sheet.
Not only can the thermal expansion and thermal shrinkage of the fluororesin sheet caused by temperature changes during etching and annealing be suppressed using the warp tension, and the dimensional change rate can be significantly reduced, but also the dimensions in two orthogonal directions The amount of change in the rate of change can also be made substantially uniform, making the residual stress inside the substrate extremely small,
In addition, since the occurrence of warpage and distortion can be almost eliminated, the width, length, shape and impedance of the circuit pattern are maintained as designed without the need for complicated countermeasures such as pre-correction at the time of design. As a result, there is an effect that predetermined performance as a circuit board can be stably secured even in long-term use.

[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 a schematic configuration diagram of a main part showing a configuration of a prepreg in the printed circuit board;

3A and 3B show a configuration of a sample substrate according to a first embodiment corresponding to a printed circuit board according to the present invention, wherein FIG. 3A is a schematic perspective view and FIG.

FIGS. 4A and 4B show a configuration of a sample substrate according to a second embodiment corresponding to a printed circuit board according to the present invention, wherein FIG. 4A is a schematic perspective view and FIG.

5A and 5B show a configuration of a sample substrate of Comparative Example 1, in which FIG. 5A is a schematic perspective view, and FIG. 5B is an enlarged sectional structural view.

6A and 6B show a configuration of a sample substrate of Comparative Example 2, in which FIG. 6A is a schematic perspective view, and FIG. 6B is an enlarged sectional structural view.

FIG. 7 is a diagram illustrating an arrangement of holes formed in each sample substrate for measuring a dimensional change rate of each sample substrate.

FIG. 8 is a graph illustrating a dimensional change state after etching of each sample substrate.

FIG. 9 is a graph illustrating a dimensional change state of each sample substrate after annealing.

[Description of Signs] 1 Printed circuit board 2 PTFE sheet 3,3 Double-sided prepreg 3-1, 3-2 Laminated prepreg 3a Warp yarn 3b Weft yarn 4,4 Copper foil

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Satoshi Hashimoto 541-1, Shimouchi Shinto bat, Mita City, Hyogo Prefecture Inside the Mita Plant of Nippon Pillar Industry Co., Ltd. (72) Inventor Yasuhiko Ichino Shimouchijin, Mita City, Hyogo Prefecture No. 541 of character hitting ground In the Mita factory of Nippon Pillar Industry Co., Ltd. (72) Inventor Toshimitsu Yai No. 541 of Shimiuchi shrine type hitting ground of Mita City, Hyogo Prefecture F-term (reference) 4F100 AB01D AB33D AG00B AG00C AG00E AK17A AK18A AK19A BA04 BA05 BA10A BA10D BA22 DH01B DH01C DH01E GB43 JG05 JK01

Claims (4)

[Claims] 1. A printed circuit board having a prepreg made of glass cloth disposed on at least one side of a fluororesin sheet, and a predetermined circuit pattern formed of a metal foil on an outer surface of the prepreg. A printed circuit board comprising at least one set of two prepregs laminated in such a manner that the warp directions cross each other at 90 ° C. 2. The printed circuit board according to claim 1, wherein the prepreg is provided on both surfaces of a fluororesin sheet. 3. The prepreg according to claim 1, wherein one or several other prepregs are further laminated on the outer surface of a pair of prepregs which are laminated with the warp direction intersecting. A printed circuit board according to claim 1. 4. The above-mentioned fluororesin sheet is made of PTFE (polytetrafluoroethylene), PFA (tetrafluoroethylene / perproloalkylvinyl ether copolymer), FEP (tetrafluoroethylene / hexafluoropropylene copolymer), ETFE (polytetrafluoroethylene / hexafluoropropylene copolymer). Ethylene / tetrafluoroethylene copolymer), PVDF (polyvinylidene fluoride), ECTFE (ethylene chlorotrifluoroethylene), PCTFE (polychlorinate trifluoroethylene), PVF (polyvinyl fluoride) or a mixture thereof. 4. The printed circuit board according to claim 1, wherein the printed circuit board is one selected from the group consisting of: