JP2009130265A - Flexible printed wiring board, method of manufacturing the same, and electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve transmission loss which is a problem in a high-frequency zone signal transmission line by a differential transmission system including a ground layer coated with a conductive paste. <P>SOLUTION: The flexible printed wiring board 1A includes: a signal layer 20 embedded between a base layer 10 and a cover layer 30; and a metal spatter film 33 coated with the cover layer 30 while covering the signal layer 20. A grand line 21 is conductively joined in a spot manner to the metal spatter film 33 via an opening (CH). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a flexible printed wiring board suitable for application to a circuit that handles high-frequency band signals of a differential transmission system.

  In information processing equipment, a flexible printed wiring board having a high degree of freedom of wiring that can be mounted in a bent state in a casing is often used. With the increase in processing speed and circuit density in information processing equipment, the flexible printed wiring board mounted in the casing of the equipment is also changed from the microwave (UHF) band to the centimeter wave (SHF) band and further to the centimeter wave. From the viewpoint of the transition from the millimeter wave (EHF) band to the millimeter wave (EHF) band, there is a demand for a transmission line forming technique using printed wiring of high frequency band signals in consideration of transmission loss.

  In circuits where the signal transmission speed is not high, single-ended transmission lines are often used, but when transmitting signals in the high frequency band of several hundred MHz or more, the combination of low signal voltage and differential transmission methods A transmission line of a signal transmission form is frequently used. The differential transmission system changes one signal into two signals of the order phase and the opposite phase and transmits each signal through two parallel transmission lines, and is excellent in signal transmission by low voltage and noise resistance. It has the characteristics.

  A conventional flexible printed wiring board having a signal transmission line by a differential transmission method is provided with a ground layer coated with a conductive paste (for example, silver paste) to form a differential transmission line with a specified rated impedance. ing. As for the signals transmitted on the signal transmission line of the differential transmission system, the frequency band of the signals handled as described above becomes higher and the formation of the transmission line considering the millimeter wave band is required. When a transmission line for transmitting such a high-frequency band signal (for example, a signal of about several hundred Mbps) is formed by the ground layer made of the conductive paste and the copper printed wiring layer, the transmission loss increases. there were.

As a flexible printed wiring technology that constitutes a high-frequency transmission line as described above, conventionally, in a flexible printed wiring board having a microstrip line structure, openings are provided at predetermined intervals in a ground conductor layer that forms a ground line. There has been a technique for reducing the transmission loss of signal current and improving the transmission characteristics of high-frequency signals.
JP2007-123740

  As described above, in a flexible printed wiring board that forms a transmission line for transmitting a signal in a high frequency band by a differential transmission method, conventionally, signal transmission loss has become a problem as the frequency band handled increases. .

  It is an object of the present invention to provide a flexible printed wiring board that solves the above-described problems and improves transmission loss in a transmission line that transmits a high-frequency band signal by a differential transmission method.

  The present invention covers a base layer, a cover layer laminated on the base layer, a signal layer embedded between the base layer and the cover layer, and the signal layer covered with the cover layer. A flexible printed wiring board comprising a metal sputtered film is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the improvement of the transmission loss used as the problem in the signal transmission line of the high frequency band by the differential transmission system provided with the ground layer coated with the electrically conductive paste can be aimed at.

Embodiments of the present invention will be described below with reference to the drawings.
The structure of the principal part of the flexible printed wiring board which concerns on embodiment of this invention is shown in FIG.
A flexible printed wiring board 1 </ b> A according to the embodiment of the present invention shown in FIG. 1 includes a base layer 10, a signal layer 20, and a cover layer 30. The signal layer 20 forms a copper-pattern signal line, and is embedded between the base layer 10 and the cover layer 30 laminated on the base layer 10.

  The base layer 10 is composed of a base polyimide 11 and an adhesive 12. The surface of the adhesive 12 becomes the pattern formation surface of the signal layer 20 and forms a wiring layer with a copper pattern.

  The signal layer 20 uses the adhesive 12 of the base layer 10 as an insulating base, and forms a pair of signal lines 22a and 22b and a ground line 21 parallel to the signal lines 22a and 22b on the base. . The signal lines 22a and 22b are composed of two wiring patterns (copper patterns) parallel to each other on the surface of the base layer 10 (on the surface of the adhesive 12), and a differential transmission type signal transmission line (differential) Signal transmission line). The ground line 21 is provided on both sides of the signal lines 22a and 22b along the signal lines 22a and 22b with a certain distance from the signal lines 22a and 22b (see FIG. 4).

  The cover layer 30 includes a coverlay polyimide 31, a coverlay adhesive 32, and a metal sputter film 33 that forms a ground layer. In the cover layer 30, a protective layer 34 is formed on the metal sputtered film 33.

  The sputtered metal film 33 provided on the cover layer 30 is provided in place of the ground layer coated with the conductive paste in the existing flexible printed wiring board structure described above, and covers the signal layer 20.

  The metal sputtered film 33 is formed by sputtering coating using, for example, a metal (such as copper (Cu), silver (Ag), gold (Au), aluminum (Al), nickel (Ni)) or an alloy thereof as a raw material (target). It is formed by.

  The ground line 21 provided in the signal layer 20 is conductively joined to the metal sputter film 33 at a predetermined interval along the wiring (wire) direction of the signal lines 22a and 22b forming the differential transmission line. . In this embodiment, an opening (CH) for conductive bonding at which the copper pattern of the ground line 21 is exposed is provided in a region of the cover layer 30 located on the ground line 21 at a predetermined interval. The ground line 21 is spot-conductively bonded to the metal sputtered film 33 through the gap (see FIG. 4). Due to the conductive bonding between the ground line 21 and the metal sputtered film 33, the ground line 21 is held in a low resistance (low impedance) and same potential state in the extending direction. After the formation of the film of the metal sputtered film 33, the recess in the conductive bonding opening (CH) is filled with a member forming the protective layer 34, and a flat protective film is formed on the surface of the cover layer 30. ing.

  The metal sputtered film 33 has smaller surface irregularities and can be formed flat (smooth) as compared with the ground layer film made of the conductive paste described above. When a high-speed operation signal is transmitted, the transmission loss is improved as compared with the case where the ground layer is formed of the conductive paste. In signal transmission exceeding several hundreds Mbps, it is known that signal loss increases due to the surface shape of the transmission line because the signal current concentrates on the surface of the transmission line. The coating of the ground layer by the conductive paste has a rougher surface (larger surface irregularities) than the metal sputtered film 33 formed by vapor deposition by sputter evaporation, and therefore the resistance loss due to the skin effect described above in the signal transmission line described above. The increase in transmission loss is remarkable.

On the other hand, in the transmission line which uses the metal sputtered film 33 as the ground layer according to the above-described embodiment. Compared with the coating of the ground layer made of a conductive paste, the surface unevenness is small and the surface is flat (smooth). Therefore, the resistance loss due to the skin effect described above is small, and the transmission loss can be reduced.

  For this reason, when the metal sputter film 33 is provided on the differential transmission system transmission line instead of the conductive paste film, and a high-speed operation signal of, for example, about several hundred Mbps is transmitted on the transmission line. The transmission loss is improved as compared with the film made of the conductive paste.

  FIG. 2 illustrates a state where the flexible printed wiring board 1 </ b> A shown in FIG. 1 is mounted on an electronic device. Moreover, the structure of the whole flexible printed wiring board 1A is shown in FIG. 3, and the partial area | region (1s) shown in FIG. 3 is expanded and shown in FIG.

  FIG. 2 shows a configuration example in which the flexible printed wiring board 1A according to the above-described embodiment is applied to a small electronic device, for example, a handy type portable computer.

  In FIG. 2, a main body 51 of a portable computer 50 is provided with a display unit casing 52 so as to be rotatable via a hinge mechanism. The main body 51 is provided with a keyboard 53 serving as an operation input unit. The display housing 52 is provided with a display device 54 using a liquid crystal panel, for example.

  The main body 51 is a rigid board which is connected to the above-described flexible printed wiring board 1A and the flexible printed wiring board 1A, and performs signal transmission by the differential transmission method through the flexible printed wiring board 1A. Configured circuit boards 2A and 2B are provided. The circuit boards 2A and 2B are provided with transmission / reception end circuit elements PA and PB constituting signal input / output ports by a differential transmission method. The transmission / reception end circuit elements PA and PB transmit and receive signals (differential transmission signals) based on a differential transmission system via signal lines (differential transmission lines) 22a and 22b provided on the flexible printed wiring board 1A.

  As shown in FIG. 1, the flexible printed wiring board 1A for connecting the circuit boards 2A and 2B to each other includes a signal layer 20 embedded between the base layer 10 and the cover layer 30, and a cover layer 30. And a sputtered metal film 33 covering the signal layer 20. Furthermore, as shown in FIG. 4, openings (CH) for conductive bonding in which the copper pattern of the ground line 21 is exposed are provided at predetermined intervals in a region portion of the cover layer 30 located on the ground line 21. The ground line 21 is conductively bonded to the metal sputter film 33 in a spot shape through the opening (CH). Due to the conductive bonding of the ground line 21 and the metal sputtered film 33, the ground line 21 is held in a low resistance and the same potential state in the extending direction.

  The above-described transmission line using the metal sputtered film 33 as a ground layer (transmission line formed with a copper pattern on the signal layer 20) has a smaller surface irregularity and a smooth surface compared to the coating of the ground layer made of a conductive paste. Therefore, the resistance loss due to the skin effect described above is small, and good signal transmission with low transmission loss is possible for high-speed signal transmission of about several hundred Mbps.

The manufacturing process of the flexible printed wiring board 1A described above is shown in FIGS.
In step A shown in FIG. 5, an opening (CH) for conductive bonding is formed in the cover layer 30 constituted by the coverlay polyimide 31 and the coverlay adhesive 32. A plurality of openings (CH) for conductive bonding are formed at predetermined intervals in a region of the cover layer 30 located on the ground line 21.

  In step B shown in FIG. 6, the wiring pattern (copper pattern) of the signal layer 20 is formed on the insulating base formed of the adhesive 12 of the base layer 10. Here, a pair of parallel signal lines (differential transmission lines) 22a and 22b and a ground line 21 parallel to the signal lines 22a and 22b are formed on the insulating base. The ground line 21 is disposed in the direction in which the signal lines 22a and 22b extend so as to sandwich the signal lines 22a and 22b with a certain distance from the signal lines 22a and 22b.

  In Step C shown in FIG. 7, the cover layer 30 is laminated on the base layer 10 on which the signal layer 20 is formed, and the adhesive 12 of the base layer 10 and the coverlay adhesive 32 are adhered to each other. It is embedded between the base layer 10 and the cover layer 30. By laminating the base layer 10 and the cover layer 30, the surface of the partial pattern of the ground line 21 formed in the signal layer 20 is exposed from the opening (CH) for conductive bonding formed in the cover layer 30 in the above step A. It is in a state.

  In step D shown in FIG. 8, a metal sputtered film 33 is formed on the cover layer 30 laminated on the base layer 10 in the above step C by vapor deposition means by sputtering. By forming the metal sputtered film 33, the signal layer 20 is covered with the metal sputtered film 33, and the ground line 21 formed in the signal layer 20 is electrically connected to the metal sputtered film 33 through the opening (CH) for conductive bonding. Be joined.

  In step E shown in FIG. 9, the metal sputtered film 33 formed on the cover layer 30 is covered with a protective layer 34 including the conductive bonding opening (CH).

  Through this manufacturing process, the flexible printed wiring board 1A according to the embodiment is manufactured. Since the flexible printed wiring board 1A is a transmission line having the metal sputtered film 33 as a ground layer as described above, the surface unevenness is small and the surface is smooth as compared with the coating of the ground layer made of a conductive paste. Therefore, the resistance loss due to the skin effect described above is small, and good signal transmission with low transmission loss is possible for high-speed signal transmission of about several hundred Mbps.

  In the above-described embodiment, a belt-like flexible printed wiring board is taken as an example, and two signal lines (differential transmission lines) and two parallel to the same signal line so as to sandwich the two signal lines are sandwiched. Although the signal layer including the ground line is shown, the present invention is not limited to this, and in the implementation stage, the components can be modified or changed without departing from the gist of the present invention.

The sectional side view which shows the structure of the principal part of the flexible printed wiring board which concerns on embodiment of this invention. The sectional side view which shows the structure of the electronic device which mounted the flexible printed wiring board which concerns on the said embodiment. The top view which shows the structure of the flexible printed wiring board which concerns on the said embodiment. The top view which shows the structure of the principal part of the flexible printed wiring board which concerns on the said embodiment. The figure which shows the manufacturing process of the flexible printed wiring board which concerns on the said embodiment. The figure which shows the manufacturing process of the flexible printed wiring board which concerns on the said embodiment. The figure which shows the manufacturing process of the flexible printed wiring board which concerns on the said embodiment. The figure which shows the manufacturing process of the flexible printed wiring board which concerns on the said embodiment. The figure which shows the manufacturing process of the flexible printed wiring board which concerns on the said embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1A ... Flexible printed wiring board, 2A, 2B ... Circuit board, 10 ... Base layer, 11 ... Base polyimide, 12 ... Adhesive, 20 ... Signal layer, 21 ... Ground line, 22a, 22b ... Signal line (Differential transmission line) ), 30 ... cover layer, 31 ... coverlay polyimide, 32 ... coverlay adhesive, 33 ... metal sputtered film, CH ... opening for conductive bonding.

Claims (7)

The base layer,
A cover layer laminated on the base layer;
A signal layer embedded between the base layer and the cover layer;
A metal sputtered film covering the signal layer, covered with the cover layer;
A flexible printed wiring board comprising:   The flexible printed wiring board according to claim 1, wherein the signal layer includes a differential transmission line and a ground line parallel to the differential transmission line.   The flexible printed wiring board according to claim 2, wherein the ground line is conductively bonded to the metal sputter film at a predetermined interval along a wiring direction of the differential transmission line.   The flexible printed wiring board according to claim 3, wherein the ground line is conductively bonded to the metal sputtered film in a spot shape through an opening for conductive bonding provided in the cover layer.   The flexible printed wiring board according to claim 4, wherein the sputtered metal film is covered with a protective layer including the conductive joint portion. In the method of manufacturing a flexible printed wiring board for forming a differential transmission line and a ground line parallel to the differential transmission line in a signal layer embedded between a base layer and a cover layer,
Drilling a plurality of openings at predetermined intervals along the differential transmission line in the surface portion of the cover layer located on the ground line;
Forming a metal sputter film on the cover layer using the plurality of openings as conductive junctions;
The manufacturing method of the flexible printed wiring board characterized by comprising. An electronic device body,
A high-frequency circuit for handling a differential signal provided in the electronic device body;
A flexible printed circuit board connected to the signal transmission path of the high-frequency circuit,
The flexible printed circuit board is
A base layer; a cover layer laminated on the base layer; a signal layer having a differential transmission line and a ground line parallel to the differential transmission line embedded between the base layer and the cover layer; A sputtered metal film covering the signal layer and covered with the cover layer, and the ground line and the sputtered metal film are conductively joined at a predetermined interval along a wiring direction of the differential transmission line. An electronic device characterized by being configured.

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