JP4922465B2 - Electronics - Google Patents

Description

  The present invention relates to an electronic device provided with a flexible printed wiring board.

  Flexible printed wiring boards that can be bent freely are widely used as wiring components for electronic devices such as portable computers. In recent electronic devices, high-speed transmission standards such as S-ATA (Serial Advanced Technology Attachment) have been adopted in accordance with the increase in data transmission speed and capacity. For this reason, also in the flexible printed wiring board for electronic devices, it exists in the tendency for the high-speed transmission characteristic which is not currently requested | required newly to be calculated | required.

  As a flexible printed wiring board that can cope with high-speed transmission characteristics, a double-sided flexible printed wiring board as disclosed in Patent Document 1 is known. A conventional double-sided flexible printed wiring board includes a first shield layer, a conductor layer having a signal line and a ground line laminated on the first shield layer, and a second shield laminated on the conductor layer. With layers.

  The first and second shield layers are composed of a conductive adhesive and a metal foil, and sandwich the conductor layer from both sides along the thickness direction of the flexible printed wiring board. The conductive adhesive is interposed between the metal foil and the ground line, and electrically connects the metal foil and the ground line.

  According to the conventional double-sided flexible printed wiring board, since the metal foil is laminated on both sides sandwiching the conductor layer, it is inevitable that the thickness dimension of the double-sided flexible printed wiring board increases. As a result, the double-sided flexible printed wiring board becomes heavy and the flexibility is impaired, and workability when the double-sided flexible printed wiring board is routed in a narrow space in the electronic device is deteriorated.

  On the other hand, in a single-sided flexible printed wiring board based on a single-sided copper-clad laminate, a conductor layer having signal lines and ground lines is covered with an insulating layer, and a conductive paste is applied on the insulating layer. Yes. The insulating layer has a plurality of openings that open above the ground line. The conductive paste is filled in the opening of the insulating layer and electrically connected to the ground line.

  According to such a single-sided flexible printed wiring board, since the conductive paste functions as a ground layer covering the signal line, the number of metal foils that are disadvantageous in terms of mass can be reduced. Therefore, the weight and thickness can be reduced in comparison with the double-sided flexible printed wiring board, and the handling becomes easy.

JP-A-8-125380

  The conductive paste used for the conventional single-sided flexible printed wiring board has a volume resistivity of about 100 to 50 μΩ · cm. Due to the inherent resistance of the conductive paste, it cannot be denied that a signal transmission loss occurs at the transmission end of the high-frequency signal.

  In this case, for example, according to a single-sided flexible printed wiring board having a differential transmission system transmission path, at the current data transmission speed in differential transmission, for example, S-ATA1 (transmission speed 1.5 Gbit / S), transmission loss is reduced. Normal data transmission is possible without deteriorating.

  However, when S-ATA 2 (transmission speed: 3.0 Gbit / S), which can be handled by the double-sided flexible printed wiring board disclosed in Patent Document 1, transmission loss begins to have a large effect, and data transmission speeds up. It becomes impossible to cope with.

  As a countermeasure, the present inventor has attempted to use a conductive paste having a volume resistivity of 30 μΩ · cm or less, for example, instead of the conventional conductive paste. By using a conductive paste having a small volume resistivity, the resistance of the conductive paste that causes transmission loss can be reduced.

  However, a conductive paste having a small volume resistivity maintains a high viscosity state with a large thixo ratio. Therefore, when the conductive paste is applied onto the insulating layer by using, for example, a screen printing method, it is difficult to densely fill the conductive paste with the opening of the insulating layer.

  In other words, when the highly viscous conductive paste is filled into the opening, air is easily trapped, and this air becomes a void and remains inside the conductive paste filled in the opening. Come.

  As a result, it is necessary to pay close attention not to generate voids when applying the conductive paste, and workability when manufacturing a flexible printed wiring board becomes extremely poor.

  An object of the present invention is to obtain an electronic device equipped with a flexible printed wiring board that can be easily manufactured while improving the transmission loss and coping with speeding up of data transmission when forming the ground layer with a conductive paste. There is.

  In order to achieve the above object, an electronic apparatus according to an aspect of the present invention includes a housing and a flexible printed wiring board accommodated in the housing.

  The flexible printed wiring board is stacked on the first insulating layer, the signal line stacked on the first insulating layer, the ground line stacked on the first insulating layer, and the ground line. A second insulating layer provided with a plurality of openings opened on the ground line, a ground layer that covers the signal line and is electrically connected to the ground line, and covers the ground layer A third insulating layer. The ground layer includes a first conductive paste filled in the opening so as to cover the ground line exposed from the opening, the first conductive paste, and the second insulating layer. And the second conductive paste applied so as to cover, the volume resistivity of the second conductive paste is smaller than the volume resistivity of the first conductive paste. .

  According to the present invention, the transmission loss of the ground layer can be suppressed to a low level and the data transmission can be speeded up without difficulty. At the same time, generation of voids when filling the opening with the first conductive paste can be prevented, and workability during application of the conductive paste can be improved. Therefore, it is possible to easily manufacture the flexible printed wiring board accommodated in the casing of the electronic device.

1 is a perspective view of a portable computer according to a first embodiment of the present invention. The perspective view which shows the positional relationship of the printed circuit board accommodated in the inside of a housing | casing, the hard-disk drive device, and a flexible printed wiring board in the 1st Embodiment of this invention. The perspective view which shows the flexible printed wiring board accommodated in the housing | casing in the 1st Embodiment of this invention. The top view of the flexible printed wiring board which concerns on the 1st Embodiment of this invention. Sectional drawing which follows the F5-F5 line | wire of FIG. Sectional drawing of the single-sided copper clad laminated board used in the 1st Embodiment of this invention. Sectional drawing which shows the state which formed the conductor layer which has a signal line and a ground line on the single-sided copper clad laminated board in the 1st Embodiment of this invention. Sectional drawing of the laminated body in which the opening part was formed in the 1st Embodiment of this invention. Sectional drawing which shows the state which laminated | stacked the laminated body on the single-sided copper clad laminated board in which the conductor layer was formed in the 1st Embodiment of this invention. Sectional drawing which shows the state with which the 1st electroconductive paste was filled in the opening part of the 2nd insulating layer in the 1st Embodiment of this invention. Sectional drawing which shows the state which applied the 2nd conductive paste on the surface of the 2nd insulating layer, and the 1st conductive paste in the 1st Embodiment of this invention. Sectional drawing of the flexible printed wiring board which concerns on the 2nd Embodiment of this invention.

  A first embodiment of the present invention will be described below with reference to FIGS.

  FIG. 1 discloses a portable computer 1 which is an example of an electronic apparatus. The portable computer 1 includes a computer main body 2 and a display module 3.

  The computer main body 2 includes a first housing 4 made of synthetic resin. The first housing 4 has a flat box shape having an upper wall 4a, a bottom wall 4b, and a peripheral wall 4c. A palm rest 5 and a keyboard attachment portion 6 are formed on the upper wall 4 a of the first housing 4. The keyboard attachment portion 6 supports the keyboard 7.

  The display module 3 has a second housing 9. The second housing 9 has a flat box shape that is substantially the same size as the first housing 4 and accommodates the liquid crystal display panel 10. The liquid crystal display panel 10 includes a screen 10a that displays character information and image information. The screen 10 a is exposed from the front surface of the second housing 9 to the outside of the display module 3.

  The display module 3 is supported on the rear end portion of the computer main body 2 via a hinge device (not shown). Therefore, the display module 3 is in a closed position lying on the computer main body 2 so as to cover the palm rest 5 and the keyboard 7 from above, and from the rear end portion of the computer main body 2 so as to expose the palm rest 5, the keyboard 7 and the screen 10a. It can be rotated between the standing open position.

  As shown in FIGS. 2 and 3, the first housing 4 of the computer main body 2 accommodates main components such as a printed circuit board 12 as a motherboard and a hard disk drive device 13.

  The printed circuit board 12 and the hard disk drive 13 are arranged in the width direction of the first housing 4 below the keyboard 7. The hard disk drive 13 is accommodated in the first housing 4 so as to be removable through a disk mounting opening 14 formed in the keyboard mounting portion 6.

  A flexible printed wiring board 15 is disposed inside the first housing 4. The flexible printed wiring board 15 has a function of electrically connecting the printed circuit board 12 and the hard disk drive device 13. The flexible printed wiring board 15 has a belt-like shape having a connector 16 at one end, and is routed through a gap between the bottom wall 4 b of the first housing 4 and the hard disk drive device 13. A connector 16 positioned at one end of the flexible printed wiring board 15 is detachably connected to the hard disk drive device 13.

  As shown in FIG. 5, the flexible printed wiring board 15 includes a first insulating layer 18, a conductor layer 19, a second insulating layer 20, a ground layer 21, and a third insulating layer 22.

  The 1st insulating layer 18 is a part used as the base of the flexible printed wiring board 15, for example, is comprised with the polyimide film.

  The conductor layer 19 is laminated on the first insulating layer 18 via the adhesive 23. The conductor layer 19 includes a signal line 24 and a ground line 25. The signal line 24 has a pair of differential transmission lines 24a and 24b. The differential transmission lines 24a and 24b are arranged in parallel to each other with a constant interval. The ground line 25 is arranged in parallel with one differential transmission line 24a. The differential transmission lines 24 a and 24 b and the ground line 25 extend along the longitudinal direction of the flexible printed wiring board 15. The distal ends of the differential transmission lines 24 a and 24 b and the distal end of the ground line 25 are electrically connected to the connector 16.

  The second insulating layer 20 is laminated on the conductor layer 19 with an adhesive 26 interposed therebetween. The second insulating layer 20 is made of, for example, a polyimide film and covers the conductor layer 19 in cooperation with the adhesive 26.

  The second insulating layer 20 has a plurality of circular openings 28 at positions corresponding to the ground lines 25. As shown in FIG. 4, the openings 28 are arranged at intervals in the longitudinal direction of the ground line 25. Each opening 28 penetrates the second insulating layer 20 and the adhesive 26 and opens on the ground line 25. Therefore, a part of the ground line 25 is exposed at the bottom of the opening 28.

  The ground layer 21 is stacked on the second insulating layer 20. The ground layer 21 is configured by applying the first conductive paste 30 and the second conductive paste 31 to the second insulating layer 20.

  The first and second conductive pastes 30 and 31 are a mixture of conductive particles such as silver particles and a binder resin that holds the conductive particles. For example, a silver paste, a silver / carbon mixed paste, or the like is used. Can be used. As means for applying the first and second conductive pastes 30 and 31, for example, a screen printing method is used.

  The first conductive paste 30 fills the opening 28 without any gap and covers the ground line 25 exposed at the bottom of the opening 28. According to the present embodiment, the first conductive paste 30 has the conductive portion 32 that rises from the second insulating layer 20. The outer peripheral edge portion of the conducting portion 32 is a flange portion 33 that overlaps the second insulating layer 20. The flange portion 33 has a larger diameter than the opening portion 28.

  As shown in FIG. 5, the first conductive paste 30 filled in the opening 28 is separated from the portion of the second insulating layer 20 that covers the differential transmission lines 24a and 24b. There is no impact. Therefore, as the first conductive paste 30, a material having a volume resistivity of, for example, 140 μΩ · cm is used. The first conductive paste 30 having a high volume resistivity has a small thixotropy, and maintains a low viscosity state when the opening 28 is filled.

  The second conductive paste 31 continuously covers the surface of the second insulating layer 20 and the conductive portion 32 of the first conductive paste 31. The second conductive paste 31 serves as a ground layer by covering the differential transmission lines 24 a and 24 b from above the second insulating layer 20. Therefore, as the second conductive paste 31, a paste having a volume resistivity of, for example, 30 μΩ · cm or less is used.

  In other words, the second conductive paste 31 has a smaller volume resistivity than the first conductive paste 30. The second conductive paste 31 having a small volume resistivity has a large thixotropy, and maintains a high viscosity state when applied to the second insulating layer 20. In order to reduce the volume resistivity of the second conductive paste 31, for example, the proportion of the conductive particles is increased or the shape of the conductive particles is made larger than the conductive particles of the first conductive paste 30. Good. By forming the conductive particles into flakes, the shape of the conductive particles can be increased.

  Therefore, in the ground layer 21 of the present embodiment, the volume resistivity is different between the portion corresponding to the opening 28 and the portion outside the opening 28.

  The third insulating layer 22 is laminated on the ground layer 21 and covers the ground layer 21 entirely. Therefore, the ground layer 21 is protected by the third insulating layer 22.

  Next, a procedure for manufacturing the flexible printed wiring board 15 having the above configuration will be described with reference to FIGS.

  First, a single-sided copper-clad laminate 35 serving as a base is prepared. As shown in FIG. 6, the single-sided copper-clad laminate 35 includes a first insulating layer 18 made of a polyimide film, and a copper foil 36 laminated on the first insulating layer 18 via an adhesive 23. It has a three-layer structure.

  Next, as shown in FIG. 7, the conductor layer 19 having the signal line 24 and the ground line 25 is formed by etching the copper foil 36 of the single-sided copper clad laminate 35.

  Next, a sheet-like laminate 37 as shown in FIG. 8 is prepared. The laminated body 37 has a two-layer structure including a second insulating layer 20 made of a polyimide film and an adhesive 26 applied to the entire back surface of the second insulating layer 20.

  Next, a plurality of openings 28 are formed on the laminate 37 by, for example, laser processing or drilling. The openings 28 are arranged at a distance from each other so as to correspond to the position of the ground line 25.

  After forming the opening 28 in the laminated body 37, the laminated body 37 is overlaid on the single-sided copper-clad laminate 35 on which the conductor layer 19 is formed, and heated and pressurized. As a result, as shown in FIG. 9, the single-sided copper clad laminate 35 and the laminate 37 become an integral structure, and the conductor layer 19 is covered with the second insulating layer 20 and the adhesive 26. At the same time, the opening 28 coincides with the ground line 25, and a part of the ground line 25 is exposed to the outside of the second insulating layer 20 through the opening 28.

  Next, as shown in FIG. 10, the first conductive paste 30 is filled in the opening 28 of the second insulating layer 20. In the present embodiment, a predetermined amount of the first conductive paste 30 is filled in the opening 28 by screen printing so that the first conductive paste 30 rises from the second insulating layer 20. Thereby, the conductor portion 32 having the flange portion 33 is formed on the opening portion 28, and the ground line 25 exposed at the bottom of the opening portion 28 is covered with the first conductive paste 30.

  After the printing of the first conductive paste 30 is completed, the first conductive paste 30 is dried. Subsequently, as shown in FIG. 11, a second conductive paste 31 is applied on the second insulating layer 20. In the present embodiment, a predetermined amount of the second conductive paste 31 is applied on the second insulating layer 20 by screen printing so as to continuously cover the conductive portion 32 of the first conductive paste 30. is doing.

  When printing of the second conductive paste 31 is completed, the second conductive paste 31 is dried. As a result, the first and second conductive pastes 30 and 31 are cured, and the ground layer 21 is formed. Simultaneously with the formation of the ground layer 21, electrical connection is made between the ground layer 21 and the ground line 25 via the first conductive paste 30 filled in the opening 28.

  Finally, the surface and end of the ground layer 21 are covered with the third insulating layer 22. Through such a process, a series of manufacturing processes of the flexible printed wiring board 15 is completed.

  According to the first embodiment of the present invention, the ground layer 21 is formed by the second conductive paste 31 so that the signal lines 24 including the differential transmission lines 24 a and 24 b are covered with the second conductive paste 31. Are formed by the first conductive paste 30. The volume resistivity of the second conductive paste 31 is, for example, 30 μΩ · cm or less, which is much smaller than the volume resistivity of the first conductive paste 30.

  Therefore, the second conductive paste 31 becomes a ground line having a low electrical resistance over the entire length of the differential transmission lines 24a and 24b, and forms the ground layer 21 with a small transmission loss.

  As a result, signal transmission conforming to high-speed transmission standards such as S-ATA 2 (transmission speed 3.0 Gbit / S) and S-ATA 3 (transmission speed 6.0 Gbit / S), or this high-speed transmission standard. It is possible to cope with signal transmission at the same or higher speed without difficulty. Therefore, data transmission with stable operation is possible.

  Further, according to the above configuration, the volume resistivity of the first conductive paste 30 filled in the opening 28 is 140 μΩ · cm, which is equivalent to the volume resistivity of a general conductive paste conventionally used. is there. This type of conductive paste has a low thixotropy and maintains a low viscosity state when applied to the second insulating layer 20.

  For this reason, the fluidity of the first conductive paste 30 is improved and the opening 28 can be filled densely, and it is difficult to entrain air during the filling. As a result, it is possible to prevent a void from being generated inside the first conductive paste 30 filled in the opening 28.

  Therefore, the workability | operativity at the time of apply | coating the 1st electroconductive paste 30 can be improved, and the flexible printed wiring board 15 can be manufactured easily.

  Since the second conductive paste 31 has a higher silver particle content than the first conductive paste 30, it is inevitable that the cost of the second conductive paste 31 is increased. However, in the first embodiment, the volume resistivity of the opening 28 of the second insulating layer 20 that is out of the differential transmission lines 24a and 24b is not much different from that of the conventional conductive paste. By filling the conductive paste 30, the two types of conductive pastes 30 and 31 are properly used. For this reason, the amount of the expensive second conductive paste 31 used can be suppressed as much as possible, and the manufacturing cost of the flexible printed wiring board 15 can be reduced.

  The present invention is not limited to the first embodiment, and various modifications can be made without departing from the spirit of the invention.

  In the first embodiment, the conductive portion that protrudes on the second insulating layer is formed in the first conductive paste, but this conductive portion is not an essential component. For example, the surface of the first conductive paste and the surface of the second insulating layer may be positioned on the same plane.

  Further, the signal line is not limited to the signal line having a differential transmission line, and may be a signal line having a single-ended transmission line, for example.

  FIG. 12 discloses a flexible printed wiring board 15 according to a second embodiment of the present invention. In the second embodiment, the configuration of the ground layer 40 is different from that of the first embodiment, and the other configuration is the same as that of the first embodiment. Therefore, in the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  As shown in FIG. 12, the ground layer 40 includes a plating layer 41 and a conductive paste 42. The plated layer 41 fills the opening 28 of the second insulating layer 20 without any gap, and covers the ground line 25 exposed at the bottom of the opening 28. In the present embodiment, the plating layer 41 does not rise from the surface of the second insulating layer 20, and the surface of the plating layer 41 is located on the same plane as the surface of the second insulating layer 20.

  The conductive paste 42 continuously covers the surface of the second insulating layer 20 and the surface of the plating layer 41 by screen printing. The conductive paste 42 serves as a ground layer by covering the differential transmission lines 24a and 24b from above the second insulating layer 20. In the present embodiment, the volume resistivity is, for example, 30 μΩ · cm. The following are used. The conductive paste 42 having a small volume resistivity has a high thixo ratio, and maintains a high viscosity state when applied to the second insulating layer 20. The conductive paste 42 is electrically connected to the ground line 25 through the plating layer 41 filled in the opening 28.

  According to the second embodiment, the ground layer 40 has a portion covering the signal line 24 including the differential transmission lines 24 a and 24 b formed by the conductive paste 42, and a portion filled in the opening 28 is the plated layer 41. It is formed by. The volume resistivity of the conductive paste 31 is 30 μΩ · cm or less, which is much smaller than the volume resistivity of the conventional conductive paste.

  Therefore, the conductive paste 42 becomes a ground line having a low electrical resistance over the entire length of the differential transmission lines 24a and 24b, and forms the ground layer 40 with a small transmission loss.

  Therefore, as in the first embodiment, it conforms to high-speed transmission standards such as S-ATA 2 (transmission speed 3.0 Gbit / S) and S-ATA 3 (transmission speed 6.0 Gbit / S). Therefore, it is possible to easily cope with signal transmission that has been performed, or signal transmission that is equivalent to or faster than this high-speed transmission standard, and stable data transmission can be realized.

  Furthermore, since it is the plating layer 41 that fills the opening 28, air is not involved when filling the opening 28, and the occurrence of voids that have been a problem with the conductive paste is prevented. Can do. Therefore, workability when manufacturing the flexible printed wiring board 15 can be improved.

  DESCRIPTION OF SYMBOLS 4 ... Housing | casing (1st housing | casing), 15 ... Flexible printed wiring board, 18 ... 1st insulating layer, 19 ... Conductive layer, 20 ... 2nd insulating layer, 21, 40 ... Ground layer, 22 ... 1st 3 insulating layers, 24... Signal line, 25... Ground line, 28... Opening, 30... First conductive paste, 31.

Claims (10)

A housing,
A flexible printed wiring board housed in the housing,
The flexible printed wiring board is
A first insulating layer;
A signal line stacked on the first insulating layer;
A ground line laminated on the first insulating layer;
A second insulating layer stacked on the ground line and provided with a plurality of openings opened on the ground line;
A ground layer covering the signal line and electrically connected to the ground line;
A third insulating layer covering the ground layer,
The ground layer includes a first conductive paste filled in the opening so as to cover the ground line exposed from the opening, the first conductive paste, and the second insulating layer. And a second conductive paste applied so as to cover,
The electronic device in which the volume resistivity of the second conductive paste is smaller than the volume resistivity of the first conductive paste. A housing,
A flexible printed wiring board housed in the housing,
The flexible printed wiring board is
A first insulating layer;
A conductor portion overlaid on the first insulating layer;
A second insulating layer provided with an opening and sandwiching the conductor portion with the first insulating layer;
A first conductive paste filled in the opening and electrically connected to the conductor; and
A second conductive paste that is overlaid on the second insulating layer and is electrically connected to the first conductive paste and having a volume resistivity lower than that of the first conductive paste;
A third insulating layer covering the second conductive paste;
Including electronic equipment.   3. The electronic device according to claim 2, wherein the thixo ratio of the second conductive paste is larger than the thixo ratio of the first conductive paste.   3. The electronic device according to claim 2, wherein the conductor part includes a signal part including a pair of differential transmission lines, and the differential transmission line transmits data having a communication speed compliant with the serial ATA standard.   3. The method according to claim 2, wherein the first and second conductive pastes include conductive particles and a binder resin that holds the conductive particles, and the second conductive paste includes the first conductive paste. An electronic device having a larger filling amount of the conductive particles than the conductive paste. A first insulating layer;
A second insulating layer provided with an opening;
A conductor portion positioned between the first insulating layer and the second insulating layer;
A first conductive paste electrically connected to the conductor through the opening;
A second conductive paste electrically connected to the first conductive paste and having a volume resistivity smaller than that of the first conductive paste;
An electronic device provided with a flexible printed wiring board.   The electronic device according to claim 6, further comprising a housing in which the flexible printed wiring board is accommodated.   The electronic device according to claim 6, wherein a thixo ratio of the second conductive paste is larger than a thixo ratio of the first conductive paste.   7. The electronic device according to claim 6, further comprising a hard disk drive device to which the flexible printed wiring board is electrically connected.   The electronic device according to claim 6, wherein at least one of the first conductive paste and the second conductive paste contains silver.

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