METHOD FOR FORMING LAMINATED CIRCUIT BOARD, AND LAMINATED CIRCUIT BOARD FORMED USING SAME

Abstract

Research on practical realization of various types of printable devices has progressed, and the realization of devices in which these printable devices are integrated on a flexible board is expected. However, there is the problem that, if a plurality of printable devices are simply integrated on the same board, the area of the integrated device increases, and the yield ratio greatly decreases. An integration technique that solves the problem of an increase in the area and a decrease in the yield ratio is in demand. Electronic devices to be integrated are formed on individual boards, the boards are laid to overlap each other in a predetermined relationship, and then through-vias are formed at predetermined positions. With this, the electronic devices are electrically connected to each other, and function as an integrated device.

Claims

1-13. (canceled)

14. A method for forming a laminated circuit board in which a plurality of flexible circuit boards are laminated, each flexible circuit board being provided with a printable electronic device that is formed on a flexible film using a printing technique, wherein the flexible circuit boards are arranged so that one flexible circuit board overlaps, in a region in the vicinity of at least one side of peripheral sides thereof, another flexible circuit board, and so that the sides on the flexible circuit boards where the regions are located are in the same direction, and electrical connection of one flexible circuit board with another flexible circuit board is made via a through-via that is formed in an overlapping region, or via an electrically-conductive material arranged on end faces of the flexible circuit boards.

15. The method for forming a laminated circuit board according to claim 14, wherein the electrical connection is made by forming at least one through-hole that penetrates the plurality of flexible circuit boards in the regions in a state in which the flexible circuit boards overlap each other, embedding an electrically-conductive material in the through-hole to form the through-via, and laying out in advance circuit interconnects on the circuit boards so that parts of the circuit interconnects reach the regions in which the through-via is to be formed.

16. The method for forming a laminated circuit board according to claim 15, wherein an opening of the through-via that is formed in the plurality of laminated circuit boards increases toward a top layer.

17. The method for forming a laminated circuit board according to claim 14, wherein the electrical connection is made by forming the through-hole in advance in a process of forming each of the flexible circuit boards, embedding an electrically-conductive material in the through-hole in a state in which the flexible circuit boards overlap each other to form the through-via, and laying out in advance circuit interconnects on the circuit boards so that parts of the circuit interconnects reach the regions in which the through-via is to be formed.

18. The method for forming a laminated circuit board according to claim 17, wherein an opening of the through-via that is formed in the plurality of laminated circuit boards increases toward a top layer.

19. The method for forming a laminated circuit board according to claim 14, wherein the plurality of flexible circuit boards are classified into two or more groups, a flexible circuit board lamination in which a plurality of flexible circuit boards are laminated is formed for each group, and the plurality of flexible circuit board laminations are laminated.

20. The method for forming a laminated circuit board according to claim 14, wherein the electrical connection is made by forming a notch-shaped or semicircular recess in a peripheral end portion of each flexible circuit board, and arranging the electrically conductive material along the recesses to bring the electrically conductive material into contact with the circuit interconnects formed on the flexible circuit boards.

21. A laminated circuit board that is formed by the method according to claim 14.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0011] FIG. 1A is a perspective view illustrating a laminated integrated device 150 according to a first embodiment of the present invention. The laminated integrated device 150 is obtained by laminating circuit boards 110, 120, 130, and 140.

[0012] FIG. 1B is a top view of the laminated integrated device 150. Parts of the circuit boards 110 and 130, and the entire upper surface of the circuit board 140 are shown. The circuit board 120 is hidden by the circuit board 130 and cannot viewed. This figure also shows through-vias 301 for electrically connecting the circuit boards.

[0013] FIG. 2A is a diagram schematically illustrating a lamination process flow according to the first embodiment of the present invention, showing a situation in which the circuit boards 110, 120, 130, and 140 that are to be laminated are positioned in a predetermined positional relationship.

[0014] FIG. 2B is a diagram schematically illustrating the lamination process flow according to the first embodiment of the present invention, showing a state immediately after the laminated circuit boards 110, 120, 130, and 140 have been bonded to each other.

[0015] FIG. 2C is a diagram schematically illustrating the lamination process flow according to the first embodiment of the present invention, showing a state in which a plurality of through-holes 201 are formed in the bonded circuit boards at predetermined positions.

[0016] FIG. 2D is a diagram schematically illustrating the lamination process flow according to the first embodiment of the present invention, showing a state in which an electrically-conductive material is embedded in the through-holes 201 to form the through-vias 301.

[0017] FIG. 3 is a diagram illustrating the laminated integrated device 150 according to the first embodiment of the present invention, showing a region A, which is a region on the laminated integrated device 150, and a direction B along which a cross section of the region A is taken, the region A and the direction B being referenced in the description below.

[0018] FIG. 4 illustrates a top view of the region A (upper figure) immediately after the circuit boards 110, 120, 130, and 140 are bonded to each other in the lamination process of the first embodiment of the present invention, and a cross-sectional view of the region A (lower figure) that is taken along B. In the figures, the reference numerals 111, 112, 113, and 114 denote interconnects on the circuit board 110, the reference numerals 121, 122, 123, and 124 denote interconnects on the circuit board 120, the reference numerals 131, 132, 133, and 134 denote interconnects on the circuit board 130, and the reference numerals 141, 142, and 143 denote interconnects on the circuit board 140.

[0019] FIG. 5 illustrates a state immediately after the plurality of through-holes 201 are formed in the laminated circuit board obtained by bonding the circuit boards 110, 120, 130, and 140 to each other in the lamination process of the first embodiment of the present invention, with the upper figure showing a top view of the region A, and the lower figure showing a cross-sectional view of the region A taken along B.

[0020] FIG. 6 illustrates a state immediately after the electrically-conductive material is embedded in the through-holes 201 and the through-vias 301 are formed in the lamination process of the first embodiment of the present invention, with the upper figure showing a top view of the region A, and the lower figure showing a cross-sectional view of the region A taken along B.

[0021] FIG. 7 is a schematic diagram illustrating an example of the present invention in which no through-via is used.

DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Embodiment 1

[0023] FIGS. 2A, 2B, 2C, and 2D schematically show the present invention in which circuit boards 110, 120, 130, and 140 are laminated, through-holes 201 are formed at predetermined positions penetrating all of the boards, and an electrically-conductive material is embedded in the through-holes to form through-vias 301 for electrically connecting circuits provided on the circuit boards.

[0024] In the present embodiment, four flexible boards are laminated, the four flexible boards including: the board 110 on which illuminance sensors for monitoring illuminance are arranged in a line; the board 140 on which a temperature sensor is formed; and the boards 120 and 130 that are two separate boards on which circuits for controlling the illuminance sensors and the temperature sensor are formed divided between the two. Within the application range of the present invention, the number of boards is not limited.

[0025] FIG. 4 shows the four circuit boards immediately after they are bonded to each other, in a partial cross sectional view taken along a line (direction B) intersecting a row of the through-vias that are to be formed in the subsequent process, and in a top view thereof. Interconnects on the circuit boards are laid out in advance so that: in the range shown in this figure, interconnects 111 and 121 are connected to each other;

[0026] interconnects 131 and 141 are connected to each other; interconnects 112, 122, and 132 are connected to each other; interconnects 113, 123, 133, and 142 are connected to each other; and interconnects 114, 124, 134, and 143 are connected to each other.

[0027] Circuits, which are however not shown, on the circuit boards are each made of a plurality of interconnect layers, and only the interconnects of the uppermost layer are shown. Within the application range of the present invention, a layout configuration is possible in which only one circuit interconnect layer is provided on the circuit board, or in which an intermediate layer of multilayer interconnects is connected to a through-via.

[0028] FIG. 5 shows a cross sectional view and a top view of a part (region A) of the laminated circuit board immediately after the through-holes 201 are formed, at predetermined positions, in the laminated circuit board obtained by bonding the circuit boards 110, 120, 130, and 140 to each other. In the present embodiment, the through-holes are formed using a laser, but in the application range of the present invention, the means for forming the through-holes is not limited. Furthermore, in the figure, the through-holes are formed through the circuit board 110 of the lowermost layer as well, but the through-holes are not necessarily formed passing through the board of the lowermost layer.

[0029] FIG. 6 shows a cross sectional view and a top view of a part (region A) of the laminated circuit board immediately after an electrically-conductive material is embedded in the through-holes 201 formed in the previous step and the through-vias 301 are formed. As a result of the through-vias 301 being formed, the circuits on the circuit boards 110, 120, and 130 are connected to each other at necessary contacts, and all of the laminated boards function as an integrated device.

[0030] In the present embodiment, an electroless plating method is used to embed gold to form the through-vias, but within the application range of the present invention, another method may also be used to embed another electrically-conductive material. Furthermore, it is not essential to completely fill the through-holes with an electrically-conductive material. It is also possible to form an electrically-conductive material layer only on side walls of the through-vias using a plating method or the like. It is possible to connect circuits on the circuit boards to each other at necessary positions using an electrically-conductive material in the through-vias, which is an object of the present patent application.

[0031] Furthermore, in the present embodiment, the through-vias formed in the through-holes are used to connect the circuits on the circuit boards to each other, but it is also possible to form notch-shaped or semicircular recesses at peripheral ends of the circuit boards, and to bring the electrically-conductive material into contact with the circuit boards along the recesses, so that the circuits on the circuit boards are connected to each other. The recesses may not necessarily be formed if a large contact surface can be ensured between the circuits on the circuit boards and the electrically-conductive material that connects the circuit boards. As a method for ensuring such a large contact surface, it is also advantageous that the circuit boards are laid to overlap each other while being shifted little by little. FIG. 7 is a perspective view schematically showing this state.

Embodiment 2

[0032] The forgoing first embodiment has described an example in which four circuit boards are laminated, but as an application of the present invention, it is also possible that, when a plurality of circuit boards are laminated, the circuit boards are bonded to each other while being classified into several groups, through-holes are formed in each group of laminated boards, then these groups of laminated boards are laid to overlap each other, and through-vias are formed. Furthermore, it is also conceivable that the present invention is applied to each group of laminated boards to subject the group of laminated boards to processing until the formation of through-vias, and then the groups of laminated boards are further laminated. In the latter case, all of the positions of the through-vias of the groups of laminated boards are not necessarily aligned, and the groups of laminated boards may be arranged so that only through-vias that need to be connected to each other overlap each other when all of the laminated boards are bonded to each other. This makes it possible for the entire integrated device to function.

[0033] Laminated circuit boards to which the present invention was applied are formed in advance. For example, a first laminated circuit board may be obtained by laminating two circuit boards, a second laminated circuit board may be obtained by laminating four circuit boards, and a third laminated circuit board may be obtained by laminating five circuit boards. These laminated circuit boards have through-vias. These through-vias are arranged so as to be connected to each other as appropriate when the three laminated circuit board are stacked together.

[0034] A laminated integrated device is obtained by laminating these three laminated boards.

[0035] Functions and Effects

[0036] The present embodiment relates to an integration of illuminance sensor arrays, a temperature sensor, and an organic semiconductor circuit, but if these are formed on the same flexible board, the area of the integrated devices increases, and thus the yield ratio greatly decreases. In the experiment, the yield ratio never exceeded 20%. When the present invention was applied, it was observed that a yield ratio of about 80% could be achieved.