JP2010016076A - Flexible printed board and rigid flexible printed board provided therewith - Google Patents

Abstract

The present invention provides a flexible printed circuit board with excellent high-frequency characteristics capable of reducing costs.
A differential signal transmission coplanar line comprising a pair of ground conductors (GND patterns) 6A and 6B and a pair of center conductors (signal lines) 6C and 6D formed therebetween, and a conductive top coat layer 3 And a shield made of silver paste layer 4 and a GND pattern of the transmission line and a laser via hole 10 for electrically connecting the shield.
[Selection] Figure 3

Description

  The present invention relates to a flexible printed circuit board (hereinafter also referred to as FPC) and a rigid flexible printed circuit board including the same, and more particularly to an FPC that transmits a high frequency signal and a rigid flexible printed circuit board including the FPC.

  The FPC is a substrate in which a laminated plate in which a flexible heat-resistant insulating film and a metal foil (for example, copper foil) are bonded together with an adhesive is used as a core, and the substrate and the cable are integrated. In addition, FPC is light, thin, and bendable, so it is widely used in small mobile devices such as mobile phones and digital still cameras (for example, Patent Document 1, Patents). Reference 3 and Patent Document 4).

  In recent years, devices mounted on small mobile devices have been speeded up, so that improvement of transmission characteristics (rise / fall time) on FPC, which has not been a problem in the past, has been demanded. . If the transmission characteristics on the FPC are inferior, problems such as distortion in the eye pattern occur due to the rising delay of the transmission signal waveform.

  In particular, in a serial interface or the like whose transmission speed is increased to about Gpbs, transmission loss and impedance mismatch of harmonic components as well as the fundamental wave of the transmission signal occur. For this reason, as a measure for improving transmission characteristics, there are many developments of materials and connectors having a low dielectric constant and a low dielectric loss tangent.

JP 2007-234500 A (paragraph 0002) JP 2000-77802 A JP 2006-179821 A (paragraph 0002) Japanese Patent Laid-Open No. 10-271048 (paragraph 0004) JP 2003-133660 A

  However, compared to polyimide, which is currently the mainstream heat-resistant insulating film, heat-resistant insulating materials with excellent high-frequency characteristics (for example, liquid crystal polymers) are still expensive, such as mobile phones that are demanding lower costs. In many cases, it is difficult to adopt in FPCs installed in consumer devices.

  An object of this invention is to provide the flexible printed circuit board excellent in the high frequency transmission characteristic (for example, signal integrity) which can aim at cost reduction, and a rigid flexible printed circuit board provided with the same in view of said situation.

  In order to achieve the above object, a flexible printed board according to the present invention comprises a transmission line, a shield, a GND pattern of the transmission line, and a via hole that electrically connects the shield.

  According to such a configuration, since the GND pattern of the transmission line and the shield are electrically connected, it is possible to prevent a high-frequency component from becoming a leakage current through the GND pattern of the transmission line, and excellent high-frequency transmission. Characteristics can be obtained. In addition, since it is possible to obtain excellent high-frequency transmission characteristics without using an expensive heat-resistant insulating material (for example, a liquid crystal polymer) having excellent high-frequency characteristics, cost reduction can be achieved.

  In the conventional flexible printed circuit board, no via hole is provided in order to improve the high frequency transmission characteristics. In flexible printed circuit boards that require flexibility, there is a possibility that the flexibility may be lost by providing via holes. Therefore, the number of via holes is usually reduced as much as possible, and the problem of high-frequency transmission characteristics has begun to attract attention recently. The reason is the content.

  In addition, it is desirable to provide a plurality of the via holes at intervals of 1/8 or less of the wavelength of the signal transmitted through the transmission line.

  By arranging the via holes at an interval of 1/8 or less of the wavelength of the signal transmitted through the transmission line, the via hole does not become an antenna, and the interval between the via holes does not generate a resonance mode at the frequency of the signal transmitted through the transmission line. Since the area near the signal line of the GND pattern of the transmission line can be regarded as the same ground potential at the wavelength of the signal transmitted through the transmission line, reflection of the transmission signal is reduced, and the influence of radiation and return current is reduced. Therefore, even more excellent high frequency transmission characteristics can be obtained.

  As the transmission line, for example, a differential signal transmission coplanar line, a microstrip line, or the like can be employed.

Further, as the via hole, for example, a laser via hole can be adopted.
Laser via holes are conventionally used for multilayer wiring and can be manufactured without changing the conventional manufacturing process.

  Also, from the viewpoint of cost reduction, it is desirable that the material of the substrate on which the transmission line is formed be a polyimide resin.

  In order to achieve the above object, a rigid flexible printed circuit board according to the present invention includes a flexible printed circuit board part and a rigid part connected to the flexible printed circuit board part, and the flexible printed circuit board part has any one of the above configurations. The configuration is a flexible printed circuit board.

  According to the present invention, since the GND pattern of the transmission line and the shield are electrically connected, it is possible to prevent a high-frequency component from becoming a leakage current through the GND pattern of the transmission line, and to obtain excellent high-frequency characteristics. be able to. In addition, since it is possible to obtain excellent high-frequency transmission characteristics without using an expensive heat-resistant insulating material (for example, a liquid crystal polymer) having excellent high-frequency characteristics, cost reduction can be achieved.

  Embodiments of the present invention will be described below with reference to the drawings. A top view of a multilayer rigid flexible printed circuit board according to the present invention is shown in FIG. 1, and an exploded sectional view is shown in FIG.

  The multilayer rigid flexible printed circuit board according to the present invention includes a flexible printed circuit board part (hereinafter referred to as an FPC part) 1 and rigid parts 2A and 2B connected to both ends of the FPC part 1, respectively. By providing the rigid portions 2A and 2B, it is possible to mount the connector of the multilayer rigid flexible printed circuit board according to the present invention.

  As shown in FIG. 2, the multilayer rigid flexible printed circuit board according to the present invention has a conductive top coat layer 3, a silver paste layer 4, a solder resist layer 5 for preventing adhesion of solder, and a pattern formed by etching. The laminated structure has a copper foil 6 that is formed and functions as a signal line or a GND pattern, a polyimide layer 7, a cover lay 8, and a prepreg layer 9 that is a thermosetting resin composition. The conductive top coat layer 3 and the silver paste layer 4 are provided from the viewpoint of EMC (Electro-Magnetic Compatibility) and function as a shield.

  Here, the characteristic part of the present invention will be described with reference to FIG. 3 which is a sectional view of the region R1 shown in FIG. 2 and FIG. 4 which is an exploded perspective view of the region R1 shown in FIG. 3 and 4, the same reference numerals are given to the same portions as those in FIG.

  On one surface of the polyimide layer 7, a differential signal transmission coplanar line comprising a pair of ground conductors (GND patterns) 6A and 6B and a pair of center conductors (signal lines) 6C and 6D formed therebetween. Is formed. A polyimide layer 8B covering the differential signal transmission coplanar line is fixed to one surface of the polyimide layer 7 by an adhesive 8A. In addition, a shield made of a conductive top coat layer 3 and a silver paste layer 4 is formed on the other surface of the polyimide layer 7.

  A feature of the present invention is that, in an FPC and a rigid flexible printed circuit board including the FPC, a shield and a GND pattern of a transmission line are electrically connected through a laser via hole. 3 and 4, the shield made of the conductive top coat layer 3 and the silver paste layer 4 and the GND patterns 6A and 6B of the differential signal transmission coplanar line are electrically connected through the laser via hole 10. Has been.

  Even in the conventional FPC, both the shield and the GND pattern of the transmission line are GND, and originally have the same potential. The laser via hole is purposely provided so as to obtain electrical continuity with the GND pattern of the transmission line. With such a configuration, it is possible to prevent a high frequency component from becoming a leakage current through the GND pattern of the transmission line, and to obtain excellent high frequency transmission characteristics. In addition, since leakage current can be suppressed, it leads to improvement of crosstalk between signal lines, that is, improvement of EMC.

  As shown in FIG. 4, the laser via holes are arranged in the vicinity of the transmission line along the longitudinal direction of the transmission line at intervals of 1/8 or less of the wavelength λ of the signal transmitted through the transmission line. Is desirable. For example, in FIG. 4, when the signal transmitted through the coplanar line for differential signal transmission is a high frequency signal of 2 GHz, the wavelength λo in vacuum is 150 mm. Therefore, when the dielectric constant εr of polyimide is 3.3, The wavelength λ (= λo / √εr) on the polyimide substrate 7 is 83 mm. Therefore, in FIG. 4, when the signal transmitted through the differential signal transmission coplanar line is a high-frequency signal of 2 GHz, the interval between the laser via holes 10 is preferably 10 mm (≈λ / 8) or less.

  By arranging laser via holes in the vicinity of the transmission line along the longitudinal direction of the transmission line at intervals of 1/8 or less of the wavelength λ of the signal transmitted through the transmission line, the laser via hole does not become an antenna. The distance between the laser via holes is the interval at which the resonance mode is not generated at the frequency of the signal transmitted through the transmission line, and the region near the signal line of the GND pattern of the transmission line can be regarded as the ground potential at the wavelength λ, so the transmission signal is less reflected. Therefore, the influence of radiation and return current is reduced. Therefore, even more excellent high frequency transmission characteristics can be obtained.

  In addition, the FPC according to the present invention and the rigid flexible printed circuit board including the FPC are not electrically connected to the shield and the GND pattern of the transmission line by a through hole penetrating the board, but a laser via hole that does not penetrate the board. Therefore, the structure is relatively flexible. As described above, in the FPC according to the present invention and the rigid flexible printed circuit board including the FPC, the deterioration in flexibility due to the structure in which the shield and the GND pattern of the transmission line are electrically connected is reduced. .

  In the above-described embodiment, the configuration (see FIGS. 3 and 4) in which the differential signal transmission coplanar line is employed as the transmission line has been described, but a configuration in which a microstrip line is employed as the transmission line may be employed.

  FIG. 5 and FIG. 6 show a sectional view and an exploded perspective view of the region R1 shown in FIG. 2 when a single-ended signal transmission microstrip line is adopted as the transmission line. 5 and 6, the same parts as those in FIG. 2 are denoted by the same reference numerals.

  A single-end signal transmission microstrip line comprising a pair of ground conductors (GND patterns) 6E and 6F and one central conductor (signal line) 6G formed therebetween is formed on one surface of the polyimide layer 7. Has been. Then, the polyimide layer 8B covering the single-end signal transmission microstrip line is fixed to one surface of the polyimide layer 7 by the adhesive 8A. In addition, a shield made of a conductive top coat layer 3 and a silver paste layer 4 is formed on the other surface of the polyimide layer 7. Further, the shield made of the conductive top coat layer 3 and the silver paste layer 4 and the GND patterns 6E and 6F of the single-end signal transmission microstrip line are electrically connected through the laser via hole 10.

  The high-frequency transmission characteristics and the interval between the laser via holes 10 are the same as when a differential signal transmission coplanar line is employed as the transmission line, and thus description thereof is omitted.

  In the above-described embodiment, the multilayer rigid flexible printed circuit board has been described. However, it is naturally possible to implement the flexible printed circuit board alone.

  In the above-described embodiment, the laser via hole is used as the via hole. However, another via hole (for example, a photo via hole) may be used.

These are the top views of the multilayer rigid flexible printed circuit board concerning the present invention. These are exploded sectional views of the multilayer rigid flexible printed circuit board according to the present invention. These are the fragmentary sectional views of the multilayer rigid flexible printed circuit board concerning the present invention. These are the partial exploded perspective views of the multilayer rigid flexible printed circuit board concerning the present invention. These are the fragmentary sectional views of the multilayer rigid flexible printed circuit board concerning the present invention which has a microstrip line. These are the partial exploded perspective views of the multilayer rigid flexible printed circuit board which concerns on this invention which has a microstrip line.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 FPC part 2A, 2B rigid part 3 Topcoat layer 4 Silver paste layer 5 Solder resist layer 6 Copper foil 6A, 6B Grounding conductor (GND pattern)
6C, 6D Center conductor (signal line)
6E, 6F Grounding conductor (GND pattern)
6G center conductor (signal line)
7 Polyimide layer 8 Coverlay 8A Adhesive 8B Polyimide layer 9 Prepreg layer 10 Laser via hole

Claims (7)

A transmission line;
A shield,
A flexible printed circuit board comprising: a GND pattern of the transmission line; and a via hole that electrically connects the shield.   The flexible printed circuit board according to claim 1, wherein a plurality of the via holes are provided at intervals of 1/8 or less of a wavelength of a signal transmitted through the transmission line.   The flexible printed circuit board according to claim 1, wherein the transmission line is a coplanar line for differential signal transmission.   The flexible printed circuit board according to claim 1, wherein the transmission line is a microstrip line.   The flexible printed circuit board according to claim 1, wherein the via hole is a laser via hole.   The flexible printed circuit board according to any one of claims 1 to 5, wherein a material of a substrate on which the transmission line is formed is a polyimide resin. A flexible printed circuit board part, and a rigid part connected to the flexible printed circuit board part,
A rigid flexible printed circuit board, wherein the flexible printed circuit board part is the flexible printed circuit board according to any one of claims 1 to 6.

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