Patent Application
20090244859
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2008-081015, filed Mar. 26, 2008, the entire contents of which are incorporated herein by reference.
1. Field
One embodiment of the invention relates to a flexible printed circuit board configured to transmit high-frequency signals, and to an electronic apparatus.
2. Description of the Related Art
Flexible printed circuit boards are often used for information processing apparatuses; the flexible printed circuit board can be mounted in a housing of the information processing apparatus in a bent condition, and offers a high degree of configurability. With the increased processing speed of the information processing apparatus and the increased density of circuits in the apparatus, even for the flexible printed circuit board, mounted in the housing of the apparatus, there has been a demand for a transmission line forming technique using printed circuitry for high-frequency-band signals with a transmission loss taken into account, in view of a change from a microwave (UHF) band to a centimeter wave (SHF) band, and further from the centimeter wave band to a millimeter wave (EHF) band.
For circuits with lower signal transmission rates, single end transmission lines are often used. In order to transmit signals in a high-frequency band of at least several hundred MHz, transmission lines are often used through which signals are transmitted based on a combination of the reduced voltage of the signal and a differential transmission scheme.
A conventional flexible printed circuit board with a transmission line based on the differential transmission scheme comprises a ground (GND) layer coated with a conductive paste (for example, a silver paste) so as to form a differential transmission line with a specified rated impedance.
On the flexible printed circuit board which comprises a ground layer formed using conductive paste, a conducting means should be provided to connect electrically the ground layer to the ground pattern portion (ground lines) formed on the signal layer. The conducting means is constituted by conductive junctions (conductive parts) that have been made by first making round openings in the cover layer covering the ground lines at arranged at regular intervals, each exposing the ground pattern layer, and then by applying and filling conductive paste in the round openings thus made.
The conductive junctions have been formed by applying the conductive paste by printing to the cover layer, filling the openings with the conductive paste. Inevitably, voids may be formed in the cover layer or the paste may overflow the openings made in the cover layer. To avoid this from happening, openings as large as 0.8 to 1 mm must be made in the cover layer, each exposing a ground line. The ground lines therefore need to have a width of about 2 mm (pad diameter), each at that part where a conductive junction will be formed. Consequently, traces cannot be formed in such large numbers as desired, in the limited area. Hence, a pattern of such a high density as expected can hardly be provided.
Techniques of forming conductive junctions are known, as disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2005-109101. The technique discloses making openings for conduction in an insulating layer, forming conductive metal pillars in the openings for conduction, and electrically connecting a conductive shielding layer to a ground circuit.
However, the conventional techniques, wherein a ground layer is formed, can hardly achieve a high-density pattern. This is because openings as large as about 1 mm must be made in order to form the conductive junctions by applying conductive paste.
A general architecture that implements the various feature of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention.
Various embodiments according to the invention will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment of the invention, there is provided a flexible printed circuit board, comprising: a base layer, a signal layer formed on the base layer, a cover layer covering the signal layer, a conductive pattern portion provided in the signal layer, a plurality of bumps formed by repeatedly applying conductive paste to the conductive pattern portion, a plurality of bump-guiding openings provided in the cover layer to align with the plurality of bumps, a plurality of crushed portions formed by crushing heads of the plurality of bumps protruding from the cover layer through the bump-guiding openings, and a ground layer formed on the cover layer, the ground layer being electrically connected to the plurality of crushed portions.
As shown in
The base layer la comprises a base-layer polyimide 11 and a base-layer adhesive 12a. The base layer 1a is an insulating base on which the signal layer 1b is formed.
The signal layer 1b comprises the ground lines 21 and the signal transmission lines 22a and 22b forming conductive patterns made of copper foil, as shown in
A plurality of solid bumps 31, each of which is shaped in form of a cone, are provided on the ground lines 21 and spaced apart at prescribed intervals, as shown in
The cover layer 1c comprises a cover-layer polyimide 15 and a cover-layer adhesive 12b. The cover-layer adhesive 12b covers the signal layer 1b and sticks to the base-layer adhesive 12a. The cover layer 1c has spot-shaped bump-guiding openings CH aligned with the bumps 31 formed on the ground lines 21.
Each bump 31 comprises a circular flange-shaped crushed portion 31a that is formed by crushing flatly the head of the bump 31 protruding from the cover layer 1c though a bump-guiding opening CH. The crushed portion 31a achieves the electrical connection of the bump 31 and ground layer 1d.
The ground layer 1d comprises a metal film 16. The ground layer 1d is formed by applying, for example, conductive paste on the upper surface of the cover layer 1c. In this embodiment, the ground layer 1d is formed by applying silver paste on the cover layer 1c and on the crushed portions 31a of the bumps 31, which protrude from the cover layer 1c.
The protective layer 1e comprises an overcoat 17. The protective layer 1e covers the upper surface and sides of the ground layer 1d.
As described above, conductive paste is repeatedly applied, forming the bumps 31 at prescribed intervals on the ground lines 21, bump-guiding openings CH are made in the cover layer 1c, in alignment with the bumps 31, the heads of the respective bumps 31 are crushed flatly, forming the crushed portions 31a, so that the crushed portions 31a are electrically connected to the ground layer 1d. The bumps 31 have a small diameter of about 0.15 to 0.20 mm. This ensures the electrical connection of the ground lines 21 to the ground layer 1d. The ground lines 21 can have a small width of about 0.2 to 0.3 mm. The signal transmission lines 22a and 22b can therefore be arranged at high density in the signal layer 1b.
A method of manufacturing the flexible printed circuit board 1A will be explained, with reference to
In Step A shown in
In Step B shown in
In Step C shown in
In Step D shown in
In Step E shown in
In Step F shown in
In Step G shown in
In Step H shown in
According to the above-described method of manufacturing the flexible printed circuit board 1A, conductive paste is repeatedly applied, forming the bumps 31 at prescribed intervals on the ground lines 21, bump-guiding openings CH are made in the cover layer 1c, in alignment with the bumps 31, the heads of the respective bumps 31 are crushed flatly, forming the crushed portions 31a, so that the crushed portions 31a are electrically connected to the ground layer 1d. Thus, it is possible to realize the bumps 31 having a small diameter (about 0.15 to 0.20 mm), ensuring the electrical connection of the ground lines 21 to the ground layer 1d.
Consequently, it is possible to realize the flexible printed circuit board 1A, in which the ground lines 21 can be thin, increasing the density at which lines are arranged in the signal layer 1b.
In the first embodiment described above, the metal film 16 of the ground layer 1d is formed by applying electrically conductive paste (silver paste), and the overcoat 17 of the protective layer 1e is formed to cover the upper surface and sides of the ground layer 1d. Instead, a shielding film may be applied to form the ground layer 1d comprising a conductive adhesive 52 and a metal foil 53, and the protective layer 1e comprising an insulating film (overcoat) 54, as shown in
The shielding film 50 shown in
In the step shown in
In the step shown in
Next, in the step shown in
As indicated above, according to the first embodiment of the invention, the ground layer 1d is formed using the conductive paste or shielding film, in flexible printed circuit board. Each opening achieving the electrical connection therefore has a small diameter, which increases the density of the trace pattern can therefore be high.
The electronic apparatus shown in
As shown in
The first housing 110 comprises a pair of display support portions 114a and 114b located in the rear of the first housing 110 and separated from each other in the width direction.
The display unit 103 comprises a second housing 120 and for example, a liquid crystal display device 121 as a display device. The second housing 120 is formed in form of a flat box, and a display screen 121a of the liquid crystal display device 121 is exposed in a display opening 122.
The second housing 120 comprises a pair of leg portions 123a and 123b. The leg portions 123a and 123b are pivotally movably supported in the display support portions 114a and 114b of the first housing 110 via hinges (not shown). This pivotally moving mechanism allows the display unit 103 to move pivotally between a closed position where the display unit 103 covers the palm rest 111 and the keyboard 113 from above and an open position where the display unit 103 is raised upright to expose the palm rest 111 and keyboard 113.
As shown in
The motherboard 170 and the hard disk drive 151 are mounted in the space S in the main body 102. The hard disk drive 151 and the motherboard 170 perform data read and write accesses via transmission lines for differential signals at a communication speed conforming to the Serial ATA-2.
As shown in
A CPU controlling the system and a peripheral circuit for the CPU are mounted on the motherboard 170. For example, a south bridge IC 175 mounted in the peripheral circuit for the CPU; the south bridge IC 175 makes up an I/O hub to which the hard disk drive 151 is connected so as to form a circuit. A connecter 170 (which comprises, for example, a crimping terminal of a lead insertion type) is mounted on the motherboard 170; the connecter 170 connects the hard disk drive 151 to the south bridge IC 175 so as to form a circuit.
The hard disk drive 151 comprises a connector (in this example, a connector receptacle) 152 making up an external connection interface mechanism.
The connector (connector receptacle) 152 of the hard disk drive 151 is connected to the connector (which comprises the crimping terminal of the lead insertion type) 171, mounted on the motherboard 170, via the flexible printed circuit board 1A shown in
In the second embodiment, the flexible printed circuit board 1A connects an external connection interface of the hard disk drive 151 to an I/O connection interface of the motherboard 170 as transmission ends of information processing elements so as to form a circuit. The external connection interface of the hard disk drive 151 is the connector (connector receptacle) 152. The I/O connection interface of the motherboard 170 is the connector (which comprises the crimping terminal of the lead insertion type) 171, connected to the south bridge IC 175 so as to form a circuit.
The flexible printed circuit board 1A applied to the second embodiment offers a trace length from one side portion of the first housing 110 to a substantial center of the housing. The flexible printed circuit board 1A is located in the space S in the first housing 110 and between the hard disc 151 and the motherboard 170 so as to extend along a rear surface of the hard disk drive 151 and through a narrow space (a narrow gap corresponding to the entire space excluding component mounting areas) formed behind the hard disk drive 151 and serving as an installation path.
The flexible printed circuit board 1A comprises a connector (connector plug) 153 located at one end in a connection direction and coupled to a connector (connector receptacle) 152 of the hard disk drive 151. The flexible printed circuit board 1A also comprises a connecting lead terminal portion 172 located at one end in the connection direction and fittingly attached to the connector (which comprises the crimping terminal of the lead insertion type) 171, mounted on the motherboard 170.
The flexible printed circuit board 1A is installed in the installation path so that the connector (connector receptacle) 153, provided at one end of the flexible printed circuit board 1A in the connection direction, is coupled to the connector (connector receptacle) 152 of the hard disk drive 151 and so that the connecting lead terminal 172, provided at the other end of the flexible printed circuit board 1A in the connection direction, is fittingly attached (pressure bonded) to the connector (which comprises the crimping terminal of the lead insertion type) 171, mounted on the motherboard 170.
High-speed transmission of read and write data complying with the Serial ATA-2 specifications is performed between the hard disk drive 151 and the south bridge IC 175, mounted on the motherboard 170, via the flexible printed circuit board 1A.
This flexible printed circuit board 1A comprises the base layer 1a, the signal layer 1b formed on the base layer 1a, the cover layer 1c covering the signal layer 1b, the ground layer 1d formed on the cover layer 1c, and the protective layer 1e, as shown in
As described above, conductive paste is repeatedly applied, forming the bumps 31 at prescribed intervals on the ground lines 21, bump-guiding openings CH are made in the cover layer 1c, in alignment with the bumps 31, the heads of the respective bumps 31 are crushed flatly, forming the crushed portions 31a, so that the crushed portions 31a are electrically connected to the ground layer 1d. The bumps 31 have a small diameter. This ensures the electrical connection of the ground lines 21 to the ground layer 1d. The ground lines 21 can have a small width. The signal transmission lines 22a and 22b can therefore be arranged at high density in the signal layer 1b. This contributes to reducing the size and weight of the apparatus.
As has been described, the embodiments of the invention can allow the trace-pattern elements to be arranged at high density in a flexible printed circuit board which has a ground layer formed using conductive paste or shielding film.
While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-081015 | Mar 2008 | JP | national |
