KR101580203B1 - Multilayer flexible printed circuit board, and method for fabricating the same - Google Patents

Abstract

There is a need for a multilayer flexible printed circuit board (multilayer FPC) that includes surface wiring layers each having a fine circuit configuration and allows higher density mounting. The first double-sided FPC 3 and the second double-sided FPC 4 are laminated through the bonding sheet 2. The first double-sided FPC 3 and the second double-sided FPC 4 have holes filled with the electrically conductive paste 11 and the electrically conductive paste 11 Are electrically connected to each other. Inner layer via holes 16 and 24 are formed in the first double-sided FPC 3 and the second double-sided FPC 4, respectively, and the inner layer via holes 16 and 24 are formed in the first double-sided FPC 3 and the second double- The size of the component mounting regions on the first wiring layer L1 and the fourth wiring layer L4 (external surface wiring layers) of the FPC 4 is not reduced.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a multilayer flexible printed circuit board and a method for manufacturing the same,

The present invention relates to a multilayer flexible printed circuit board for use in a mobile phone, a small mobile terminal or the like, and a method for manufacturing the same.

Flexible printed circuit boards (hereinafter referred to as "FPC") are thin foldable circuit boards that can be used in a variety of electronic devices. In particular, along with the recent trend toward smaller size and higher performance of electronic devices such as mobile phones, handheld mobile terminals, digital cameras and the like, FPCs to be mounted on electronic devices include fine wires and have higher There is an increasing demand for having a wiring density and a reduced thickness. There is now a growing demand for multi-layer FPCs made by laminating two double-sided FPCs, single-sided FPCs, or one single-sided FPC and one double-sided PFC have.

Patent Document 1 proposes that the printed circuit boards are laminated through a prepreg (sheet material) for the production of a multilayer printed circuit board. As proposed in Patent Document 1, through-holes are previously formed in the prepreg and filled with an electrically conductive paste, and the printed circuit boards are laminated through a prepreg. The use of prepregs simultaneously accomplishes the bonding of printed circuit boards and the formation of inner via-holes (IVH).

Patent Document 2 discloses an adhesive sheet which can be used for laminating FPCs. The adhesive sheet is composed of a base and a resin composition of a woven fabric and a nonwoven fabric and has a configuration suitable for laminating FPCs to an adhesive sheet inserted between FPCs.

Patent Document 3 discloses a resin adhesive sheet which can be used for laminating FPCs. The adhesive sheet has through holes filled with an electrically conductive paste.

Patent Document 4 discloses a bonding sheet which can be used for a multilayer FPC. The bonding sheet disclosed in Patent Document 4 is a prepreg multi-layer FPC bonded sheet prepared by impregnating a woven or nonwoven base with an epoxy resin composition, and serves to increase the rigidity of the multi-layer FPC.

Patent Document 5 discloses a multilayer FPC including an adhesive sheet (bonded sheet) in which a hollow portion for connecting FPCs to each other is formed.

[References]

[Patent Literature]

Patent Document 1: WO2007 / 46459

Patent Document 2: JP-4237726

Patent Document 3: JP-A-2005-347414

Patent Document 4: JP-A-2006-299209

Patent Document 5: JP-A-2006-179679

As already described in the background, a multilayer flexible printed circuit board (hereinafter referred to as a "multilayer FPC") must meet the requirements for higher wiring density and reduced thickness. As disclosed in Patent Document 1 and Patent Document 3, when a connection sheet, that is, a connection sheet having through-holes filled with an electrically conductive paste is used, a multilayer FPC obtained by laminating FPCs has a reduced thickness, There is an advantage of ensuring proper electrical connection between the interconnection layers provided on both sides.

However, in the prior art, the wiring density of the multilayer FPC is not sufficiently increased, leaving room for improvement. More specifically, electronic components and electronic devices are mounted on exposed wiring layers at the front surface of a multi-layer FPC. Therefore, if the front surface wiring layer does not have a fine circuit configuration, it is difficult to mount electronic parts or the like at a higher density. In the prior art, the front surface wiring layer has blind via-holes (BVH) and through-via-holes (BVH) extending from the front surface, Surrounding surfaces are also plated. This increases the thickness of the front surface wiring layer, thereby preventing the provision of a fine circuit structure in the front surface wiring layer. In addition, the provision of BVHs and TVHs (at the electronic component mounting surface) in the front surface layer reduces the size of the component mounting areas, thereby preventing higher density mounting. Therefore, it is desirable that the multilayer FPC be improved to allow higher density mounting.

In addition, it is desirable to improve the multilayer FPC manufacturing method so as to simplify the manufacturing steps of the multilayer FPC manufacturing method and reduce the number of manufacturing steps.

In view of the foregoing, it is a principal object of the present invention to provide a multilayer FPC suitable for mounting at higher densities.

It is another object of the present invention to provide a multilayer FPC produced by a simplified manufacturing process.

It is a further object of the present invention to provide an improved method for making multilayer FPCs.

According to an aspect of the invention of claim 1, there is provided a bonding sheet (2); A first double-sided flexible printed circuit board (3) provided on a surface of one of both surfaces of the bonding sheet; And a second double-sided flexible printed circuit board (4) provided on the other surface of the bonding sheet; The bonding sheet (2) has through holes (7, 8, 9, 10) which are provided at predetermined positions as penetrating from one surface to another surface, and the first both- Is filled with the electrically conductive paste (11) so as to electrically connect the printed circuit board (3) and the second double-sided flexible printed circuit board (4) with the electrically conductive paste (11); The first double-sided flexible printed circuit board 3 and the second double-sided flexible printed circuit board 4 are provided with insulating films 13 and 21 and internal surfaces respectively provided on both surfaces of the insulating films 13 and 21, Wiring layers (L2, L3) and external surface wiring layers (L1, L4), respectively; The external surface wiring layers (L1, L4) are positioned away from the bonding sheet (2) and function as a wiring layer on which electronic devices are mounted; The inner surface wiring layer (L2, L3) has an opening formed at a predetermined position in contact with the bonding sheet (2); The insulating film has an inner-layer via-hole (16, 24) extending through the inner surface wiring layer and the outer surface wiring layer so as to face the outer surface wiring layer in communication with the opening for electrical connection between the inner surface wiring layer and the outer surface wiring layer.

The parenthesized reference numerals after each component correspond to the reference numerals used in the embodiments described later. This definition is effective here.

According to an aspect of the invention of claim 2, the multilayer flexible printed circuit board according to claim 1 further comprises a hollow part (12), through which the first double-sided flexible printed circuit board (3) The flexible printed circuit board 4 is partially opposed to each other at the time of the absence of the bonding sheet 2.

According to an aspect of the invention as set forth in claim 3, the inner surface wiring layer is a part of the first double-sided flexible printed circuit board facing each other through the hollow part 12 in the multilayer flexible printed circuit board of claim 2, It does not exist in a part of the flexible printed circuit board.

According to an aspect of the invention of claim 4, the part of the first double-sided flexible printed circuit board and the part of the second double-sided flexible printed circuit board, which are opposed to each other through the hollow part 12, And have different lengths in the multilayer flexible printed circuit board.

According to an aspect of the invention of claim 5, the multilayer flexible printed circuit board of claim 1 is characterized in that the first double-sided flexible printed circuit board (3) provided on the one surface of the bonding sheet (2) A laminate portion 53 including the second double-sided flexible printed circuit board 4 provided on the other surface of the first double-sided flexible printed circuit board 4 ) Or a non-laminate including only the extension of the first double-sided flexible printed circuit board (3) or the second double-sided flexible printed circuit board (4) at the time of the absence of the first double-sided flexible printed circuit board and non-laminate portions 54,55.

According to an aspect of the invention of claim 6, there is provided a first double-sided flexible printed circuit including an insulating film (13), an internal surface wiring layer (L2) and an external surface wiring layer (L1) provided on both surfaces of the insulating film Wherein the external surface wiring layer (L1) functions as a wiring layer on which the electronic device is mounted, the internal surface wiring layer (L2) has an opening formed at a predetermined position, and the insulating film (13) Sided flexible printed circuit board (3) having an inner layer via hole (16) extending through the outer surface wiring layer and communicating with the opening for electrical connection between the inner surface wiring layer and the outer surface wiring layer, ; A second two-sided flexible printed circuit board (4) comprising an insulating film (21), an inner surface wiring layer (L5) provided on both surfaces of the insulating film (21) and an outer surface wiring layer (L6) The wiring layer L6 functions as a wiring layer on which the electronic device is mounted, the internal surface wiring layer L5 has an opening formed at a predetermined position, and the insulating film 21 covers the internal surface wiring layer and the external surface wiring layer The second double-sided flexible printed circuit board (4) having an inner layer via hole (24) communicating with the opening and extending through the outer surface wiring layer so as to face the outer surface wiring layer; And a multilayer structure (911) provided between the first double-sided flexible printed circuit board (3) and the second double-sided flexible printed circuit board (4), wherein the multilayer structure (911) (N is a natural number and is greater than or equal to 2) and N-1 double-sided printed circuit boards 92 and the outermost bond sheets of the bond sheets 2 are bonded to the outside of the multilayer structure 911 And the outermost bond sheets 2 extend through from one surface to the other surface and each have a hole formed at a predetermined position to fill the electrically conductive paste 11 , The first double-sided flexible printed circuit board (3) and the second double-sided flexible printed circuit board (4) are electrically connected to the circuit boards of the multilayer structure (911) through the electrically conductive paste (11) This, the multi-layer flexible printed circuit board comprising the multilayer structure 911 is to be connected is provided.

According to an aspect of the invention of claim 7, the multilayer flexible printed circuit board of claim 6 further comprises a hollow part (12) through which the first double-sided flexible printed circuit board and the second double- The circuit boards are partially opposed to each other in the absence of the multilayer structure.

According to an aspect of the invention of claim 8, the double-sided printed circuit boards 92 of the multi-layered structure 911 are made of a double-sided flexible printed circuit board, a double-sided rigid printed circuit board, a double-sided flexible printed circuit board, And a substrate selected from a multilayered structure including a combination of substrates.

According to an aspect of the invention of claim 9, the inner surface wiring layer is a part of the first double-sided flexible printed circuit board facing each other through the hollow part (12) in the multilayer flexible printed circuit board of claim 7 or claim 8, And is not present in a part of the second double-sided flexible printed circuit board.

According to an aspect of the invention of claim 10, a part of the first double-sided flexible printed circuit board and a part of the second double-sided flexible printed circuit board facing each other through the hollow part (12) Lt; / RTI > have different lengths in the multilayer flexible printed circuit board.

According to an aspect of the invention of claim 11, in a state in which the first double-sided flexible printed circuit board is stacked on one surface of both sides of the joint sheet and the second double-sided flexible printed circuit board is stacked on the other surface of the joint sheet, There is provided a method for manufacturing a multilayer flexible printed circuit board by laminating the first double-sided flexible printed circuit board and the second double-sided flexible printed circuit board through a bonding sheet, the method comprising the steps of: Sided flexible printed circuit board and the second double-sided flexible printed circuit board are laminated so as to be in contact with the bonding sheet, an opening is formed at a predetermined position in the internal surface wiring layer of the first double-sided flexible printed circuit board so as to be in contact with the bonding sheet, 1 < / RTI > flexible printed circuit board Sided flexible printed circuit board so as to communicate with the opening of the inner surface wiring layer of the first double-sided flexible printed circuit board and to face the external surface wiring layer of the first double-sided flexible printed circuit board for electrically connecting the wiring layer and the external surface wiring layer, Forming an inner layer via hole extending through the insulating film of the flexible printed circuit board; And a step of forming an opening at a predetermined position in the internal surface wiring layer of the second double-sided flexible printed circuit board so as to be in contact with the bonding sheet, and electrically connecting the internal surface wiring layer and the external surface wiring layer of the second double- Sided flexible printed circuit board so as to be in communication with the opening of the internal surface wiring layer of the second double-sided flexible printed circuit board to face the external surface wiring layer of the second double-sided flexible printed circuit board for connection, Forming an inner-layer via hole extending through the through-hole; And collectively laminating the first double-sided flexible printed circuit board and the second double-sided flexible printed circuit board through the bonding sheet.

According to an aspect of the invention according to claim 12, the method for manufacturing the multilayer flexible printed circuit board of claim 11 is characterized in that, prior to the collectively laminating step, the step of laminating the one Forming a hole extending through the bonding sheet from the surface to the other surface; And filling the hole of the bonding sheet with an electrically conductive paste.

According to an aspect of the invention of claim 1, the first double-sided flexible printed circuit board and the second double-sided flexible printed circuit board each have an inner layer via hole, and the inner surface wiring layer and the outer surface wiring layer are electrically Respectively. For the formation of the inner layer via hole, the inner peripheral surface of the inner layer via hole is plated with, for example, copper. However, the external surface wiring layer is not plated. This ensures the provision of a fine circuit structure in the external surface wiring layer, and otherwise, when the thickness of the external surface wiring layer is increased by plating of the external surface wiring layer.

The inner layer via hole does not extend through the outer surface wiring layer so that the size of the component mounting regions of the outer surface wiring layer to which the electronic devices and the electronic components are to be mounted thereon is not reduced. This ensures a higher density of mounting on the outer surface wiring layer.

The first double-sided flexible printed circuit board and the second double-sided flexible printed circuit board are laminated through a bonding sheet having holes filled with an electrically conductive paste. Therefore, the multilayer flexible printed circuit board has a reduced thickness. Thus, thickness reduction is achieved. Particularly, the first double-sided flexible printed circuit board and the second double-sided flexible printed circuit board are provided with the internal surface wiring layer, which is held in direct contact with the surfaces of the bonding sheet and is embedded in the bonding sheet from the surfaces of the bonding sheet, Are laminated. This arrangement is particularly effective for reducing the thickness of the multilayer flexible printed circuit board.

According to an aspect of the invention of claim 2, the multilayer flexible printed circuit board has a hollow portion in which the bonding sheet is not present. Since the hollow portion imparts excellent flexing resistance to the multilayer flexible printed circuit board, the multilayer flexible printed circuit board is suitable for use in a folding mobile phone or the like.

According to an aspect of the invention of claim 3, the internal surface wiring layer is not present in the hollow portion. This improves the flexibility around the hollow portion.

According to an aspect of the invention of claim 4, a part of the first double-sided flexible printed circuit board and a part of the second double-sided flexible printed circuit board facing each other through the hollow part have different lengths. Therefore, the multilayer flexible printed circuit board has excellent bending resistance around the hollow portion.

According to an aspect of the invention of claim 5, the multilayer flexible printed circuit board may have a partial multilayer structure as required. Therefore, the multilayer flexible printed circuit board can be appropriately accommodated in a smaller space without taking up unnecessarily much space in the apparatus in which the multilayer flexible printed circuit board is mounted.

According to an aspect of the invention of claim 6, a multilayer flexible printed circuit board comprising six or more wiring layers has a reduced thickness, allowing the provision of fine circuit configurations in the surface wiring layers and the mounting of higher density of components .

According to aspects of the invention of claims 7, 8, 9 and 10, as in aspects of the invention of claims 2, 3 and 4, the multilayer flexible printed circuit board comprises a hollow part, Flexibility.

The manufacturing method of claim 11 and claim 12 makes it possible to manufacture the multilayer flexible printed circuit board by a relatively small number of processing steps in a shorter time period.

Figure 1 is a schematic cross-sectional view illustrating three structural block layers of a multilayer flexible printed circuit board according to one embodiment of the present invention (the "flexible printed circuit board" will be abbreviated herein as "FPC"), .
Figure 2 shows a laminate structure of a multilayer FPC (1) of an embodiment manufactured by laminating the first double-sided FPC (3) and the second double-sided FPC (4) in contact with both surfaces of the laminate sheet Fig.
3 is a schematic cross-sectional view of the multi-layer FPC 1 as a finished product.
4A is a schematic cross-sectional view showing the structure of a prior art multi-layer FPC manufactured by a process of the prior art, and Fig. 4B is a schematic cross-sectional view of a multi-layer FPC 1 of an embodiment of the present invention, to be.
FIG. 5A is a view showing a process of the prior art for manufacturing a multilayer FPC of the prior art, and FIG. 5B is a diagram showing the process of the invention for manufacturing the multilayer FPC 1 according to the embodiment of the present invention.
6 is a schematic cross-sectional view showing the configuration of the multilayer FPC 51 according to another embodiment of the present invention.
7 is a schematic cross-sectional view showing a configuration of a multilayer FPC 71 according to another embodiment of the present invention.
8 is a schematic view for explaining the difference in length between the outer FPC and the inner FPC when the multilayer FPC is bent.
9 is a schematic cross-sectional view showing a configuration of a multilayer FPC 91 according to another embodiment of the present invention.

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

1 is a schematic cross-sectional view illustrating three structural block layers of a multilayer flexible printed circuit board (hereinafter referred to as "multilayer FPC") according to one embodiment of the present invention.

The multi-layer FPC 1 according to this embodiment comprises as structural block layers (structural parts) a first double-sided FPC 3 provided on one of both surfaces of the bonding sheet 2, And a second double-sided FPC 4 provided on the other surface of the bonding sheet 2.

Exemplary sheet materials for the bonding sheet 2 include a prepreg prepared by impregnating a glass fiber sheet with an epoxy resin, an adhesive such as an epoxy resin, a core film (for example, a polyimide film) ), And a coreless thermosetting resin film. ≪ RTI ID = 0.0 >

The multilayer FPC 1 has a reduced thickness because the bonding sheet 2 thus functions as an insulating layer and an adhesive layer. In this embodiment, the bonded sheet 2 has a thickness of about 100 to about 150 micrometers.

The bonding sheet 2 has holes 7, 8, 9 and 10 formed at predetermined positions, and each of the holes 7, 8, 9 and 10 has one surface 5 thereof. To another surface (6). The holes 7 to 10 are filled with the electrically conductive paste 11.

As the electrically conductive paste, an electrically conductive paste containing an electrically conductive filler (such as silver or copper or silver coated copper powder) together with an epoxy resin, for example, an electrically conductive paste disclosed in JP-4109156 Paste is available. Further, an electrically conductive paste containing a low melting point metal and a high melting point metal as the electrically conductive filler together with the epoxy resin, for example, the electrically conductive paste disclosed in JP-4191678 can be used.

The electrically conductive paste filled in the holes 7 to 10 and the holes 7 to 10 formed in the bonding sheet 2 acts as via-holes, and these via holes are electrically connected to the first double-sided FPC The inner layer circuit (second wiring layer L2) of the first double-sided FPC 4 and the inner layer circuit (third wiring layer L3) of the second double-sided FPC 4 are electrically connected.

In this embodiment, the bonding sheet 2 has a bonding sheet non-existing portion 12 located at the laterally intermediate portion. The bonding sheet absent portion 12 has a hollow portion, and the first double-sided FPC 3 and the second double-sided FPC 4 partially face each other via this hollow portion, as will be described later.

The first double-sided FPC 3 is formed by treating a copper clad laminate (CCL) comprising copper foils provided on both surfaces of a polyimide insulating base film 13, The first wiring layer L1 and the second wiring layer L2 are formed on the outer surface and the inner surface of the polyimide insulating base film 13, respectively.

Alternatively, the first wiring layer L1 and the second wiring layer L2 are formed by sputtering seed layers having a thickness of several hundred angstroms on both surfaces of the insulating base film 13 And by forming the wiring layer patterns on the seed layers by copper electrolytic plating. [0041] The method of the present invention can be applied to a semiconductor device using a semiconductor device.

The first double-sided FPC 3 is characterized in that the first double-sided FPC 3 is formed inside thereof and the first interconnection layer L1 (external surface interconnection layer) is formed from the second interconnection layer L2 (Inner surface layer wiring) and the second wiring layer L2 (inner surface wiring layer) are electrically connected to each other via the inner layer via holes 16. The first wiring layer L1 to be.

More specifically, the innerlayer via holes 16 are formed from the side surface of the second wiring layer L2 (inner surface wiring layer) and do not extend through the first wiring layer L1 (outer surface wiring layer) They do not function as via holes (TVH). The formation of the inner layer via holes 16 is performed by etching the copper foil portions from the opening forming regions of the second wiring layer L2 (inner surface wiring layer), and then forming the openings in the insulating film 13 For example, by a conformal method. ≪ RTI ID = 0.0 >

The inner layer via holes 16 are formed from the side surfaces of the second wiring layer L2 (inner surface wiring layer) in the first both-side FPC 3 and do not extend through the first wiring layer L1 (outer surface wiring layer). Therefore, when the inner peripheral surfaces of the inner layer via holes 16 are plated for formation of the interlayer conductive holes, the first wiring layer L1 (outer surface wiring layer) is not plated (i.e., the first wiring layer L1) Is not plated). This ensures the provision of a fine circuit configuration, and if not, the thickness of the finely processed first wiring layer L1 will increase when plated.

The size of the component mounting regions on the first wiring layer L1 is not reduced by the innerlayer via holes 16 since the innerlayer via holes 16 are not present in the first wiring layer L1. This allows higher density mounting.

The inner layer via holes 16 are thus formed from the second wiring layer L2 (inner surface wiring layer) so as not to extend through the first wiring layer L1 (outer surface wiring layer), so that the first wiring layer The inner peripheral surfaces of the inner layer via holes 16 are not affected by plating, and the reduction in the size of the component mounting regions is eliminated. This makes it possible to properly mount electronic devices and electronic components at a higher density over the finely processed first wiring layer L1.

The first double-sided FPC 3 has a second wiring layer L2 provided as an internal surface wiring layer on the inner side surface so as to face the bonding sheet 2 and as an external surface wiring layer on the external side in relation to the second wiring layer L2 And a first wiring layer L1 provided thereon. In the region of the first double-sided FPC 3 facing the bonding sheet absent portion 12, the inner surface 131 of the insulating film 13 is bonded to the bonding sheet non-existent portion 12 ). The first wiring layer 14L is provided as a signal line on the outer side surface of the insulating film 13 in this region.

The outer surface of the signal line 14L is covered with a cover layer 17 such as an adhesive 19 and a polyimide film.

The second double-sided FPC 4 basically has the same configuration as the first double-sided FPC 3 and is symmetrically disposed with respect to the first double-sided FPC 3 with respect to the bonding sheet 2. The second double-sided FPC 4 has an insulating film 21, a third wiring layer L3 as an internal surface wiring layer, a fourth wiring layer L4 as an external surface wiring layer, and inner layer via holes 24, a signal line 22L provided in the fourth wiring layer L4, an adhesive 20 and a cover layer 25 which are laminated on the insulating film 13 of the first double-sided FPC 3, L2, the first wiring layer L1, the inner layer via holes 16, the signal line layer 14L, the adhesive 19, and the cover layer 17, respectively. Since these parts have the same configuration as corresponding parts, respectively, redundant description will be omitted.

When the inner peripheral surfaces of the innerlayer via-holes 24 are plated, the fourth wiring layer L4 (outer surface wiring layer) is not plated with the second double-sided FPC 4 by plating. This ensures the provision of a fine circuit configuration in the fourth wiring layer L4. The size of the component mounting regions on the fourth wiring layer L4 is not reduced by the innerlayer via holes 24 because the innerlayer via holes 24 do not extend through the fourth wiring layer L4.

Fig. 2 is a cross-sectional view of an embodiment of this embodiment produced by laminating the first double-sided FPC 3 and the second double-sided FPC 4 described with reference to Fig. 1 in contact with both surfaces of the bonded sheet 2 by heat and pressure Sectional view of a laminated structure of the multi-layer FPC 1. Fig. Lamination of the first double-sided FPC 3 and the second double-sided FPC 4 through the bonding sheet 2 simultaneously and simultaneously collects the first double-sided FPC 3, the bonding sheet 2 and the second double- By heat and pressure treatment.

For example, the laminating process is performed at a pressure of about 3 MPa and a heating temperature of about 170 DEG C for a treatment period of about 30 minutes.

The first double-sided FPC 3 and the second double-sided FPC 4 are collectively laminated by heat and pressure through the bonding sheet 2 so that the respective double-sided FPCs 3, The electrically conductive paste 11 filled in the first double-sided FPC 3 is electrically connected to the circuit of the second wiring layer L2 of the first double-sided FPC 3 and the circuit of the third wiring layer L3 of the second double- do. That is, the holes 7 to 10 and the electrically conductive paste 11 are electrically connected to the first double-sided FPC 3, the second wiring layer L2 (internal surface wiring layer), and the third wiring layer L3 The inner surface wiring layer).

The first double-sided FPC 3 and the second double-sided FPC 4 are bonded to the bonding sheet 2 in a laminated state in which the resin component immersed in the bonding sheet 2 is once melted and reintroduced again in the laminating process using heat and pressure. Respectively. At this time, the first double-sided FPC 3 and the second double-sided FPC 4 are bonded to the second wiring layer L2 and the third wiring layer L3, which are embedded in the bonding sheet 2 from the surfaces of the bonding sheet 2 And laminated. That is, the thicknesses of the second wiring layer L2 and the third wiring layer L3 are accommodated by the bonding sheet 2 in which the second wiring layer L2 and the third wiring layer L3 are embedded. Therefore, the inter-layer distance between the first double-sided FPC 3 and the second double-sided FPC 4 of the multilayer FPC 1 is substantially equal to the thickness of the bonding sheet 2. Therefore, the multilayer FPC 1 has a reduced thickness.

Fig. 3 is a cross-sectional view of a completed product obtained by coating the outer surface of the multilayer FPC 1 of Fig. 2 with a cover coat for surface treatment and then subjecting the multilayer FPC 1 to a pretreatment step and an inspection step Fig. 3, in the completed product of the multilayer FPC 1, the upper surface portion of the first wiring layer L1 except for the component mounting regions is protected by the protection of the first wiring layer L1 having the cover coat 27 And is covered with a cover coat 27. [ Similarly, the surface portion of the fourth wiring layer L4 excluding the component mounting regions is covered with the cover coat 28 for protection of the fourth wiring layer L4 having the cover coat 28. [

4A and 4B are diagrams for comparison between a cross-sectional configuration of a multilayer FPC according to the prior art and a cross-sectional configuration of a multilayer FPC 1 according to an embodiment of the present invention.

As is apparent from the comparison between Figs. 4A and 4B, the prior art multilayer FPC of Fig. 4A is a multilayer FPC in which the second wiring layer L2 is covered with a polyamide cover lay film 31 and the third wiring layer L3 is covered with a coverlay film 32 bonded to the surface of the third wiring layer L3 by an adhesive 38. [ The second wiring layer L2 and the third wiring layer L3 are connected to each other through the coverlay films 31 and 32 by the bonding sheet 33. [

Therefore, the distance between the second wiring layer L2 and the third wiring layer L3 is different from the distance between the coverlay film 31 and the junction layer 33 because the second wiring layer L2 and the third wiring layer L3 are not embedded in the bonding sheet 33. Therefore, The thickness of the sheet 33 and the thickness of the cover layer film 32. [

The first wiring layer L1 and the second wiring layer L2 are electrically connected to each other through a so-called blind via-hole (BVH) 34 extending from an outer layer to an inner layer Respectively. Similarly, the third wiring layer L3 and the fourth wiring layer L4 are electrically connected to each other through the BVHs 34. [ Therefore, portions of the first wiring layer L1 and the fourth wiring layer L4 where the BVHs 34 are formed can not be used as component mounting regions. This reduces the size of the component mounting regions on the first wiring layer L1 and the fourth wiring layer L4.

The first wiring layer L1, the second wiring layer L2, the third wiring layer L3 and the fourth wiring layer L4 are electrically connected to each other through through-via holes (TVH) Therefore, the presence of the TVHs 35 also reduces the size of the component mounting regions on the first wiring layer L1 and the fourth wiring layer L4.

4B according to the embodiment of the present invention may be directly connected to the bonding sheet 2 such that the second wiring layer L2 and the third wiring layer L3 are embedded in the contact sheet 2 Respectively. Therefore, the distance between the first double-side FPC 3 and the second double-sided FPC 4 is substantially equal to the thickness of the bonding sheet 2. Thus, the thickness reduction of the multilayer FPC 1 is achieved. The second wiring layer L2 and the third wiring layer L3 are electrically connected to each other by the electrically conductive paste 11 filled in the holes formed in the bonding sheet 2 in advance. This eliminates the need for formation of through-via-holes (TVH).

Further, the inner layer via holes 16 and 24 are formed in the first both-side FPC 3 and the second two-side FPC 4 from the side surfaces of the inner surface wiring layers L2 and L3. This prevents a reduction in the size of the component mounting regions on the first wiring layer L1 and the fourth wiring layer L4, and thus permits a higher density of mounting. In addition, it is advantageous that fine circuit patterns of the first wiring layer L1 and the fourth wiring layer L4 are used in this state.

Figs. 5A and 5B are views for comparison between the manufacturing process for the multi-layer FPC of the prior art of Fig. 4A and the manufacturing process for the multi-layer FPC 1 of Fig. 4B according to the embodiment of the present invention.

The prior art multi-layer FPC manufacturing process of Fig. 5A includes ten steps for the fabrication of prior art multi-layer FPCs. Meanwhile, the multi-layer FPC manufacturing process of FIG. 5B according to the embodiment of the present invention includes eight steps for manufacturing the multi-layer FPC 1.

That is, the number of steps for manufacturing the multi-layer FPC 1 according to the embodiment of the present invention is two smaller than the steps for manufacturing the multi-layer FPC of the prior art. Thus, the manufacturing time can be reduced.

A more specific comparative explanation will be given. 5A, a first double-sided FPC board (flexible copper clad laminate) and a second double-sided FPC board are prepared (step A1), and on each double-sided FPC board, (Step A2). Next, the inner layer circuits are covered with inner layer cover layers (step A3). At the same time, a bonded sheet is prepared (step A3).

Next, a first double-sided FPC (defined herein as including an FPC substrate and a circuit formed on the FPC substrate) and a second double-sided FPC are laminated through a bonding sheet (step A4). This time, blind via holes BVH are formed in the first double-sided FPC and the second double-sided FPC from the external side by laser treatment (step A5), and the through via holes TVH are drilled to form the first double- , The bonding sheet, and the second double-side FPC (step A6). Next, the inner peripheral surfaces of the via holes are plated with copper (step A7), and the outer layer circuits are formed on the first both-side FPC and the second both-side FPC (step A8). Next, the cover coat layers are formed on the first double-sided FPC and the second double-sided FPC (Step A9), and the surface treatment (gold plating, etc.) is performed on the first double-sided FPC and the second double-sided FPC (Step A10). Thus, the multilayer FPC of the prior art is completed.

On the other hand, the multilayer FPC 1 of the embodiment of the present invention is manufactured in the following manner.

First, a first double-sided FPC board and a second double-sided FPC board are prepared (step B1) and inner-layer via-holes are formed in the second wiring layer L2 and the third wiring layer L3 by laser processing (step B2). Next, the inner layer via holes are plated with copper (step B3). This time, the inner layer circuits and the outer layer circuits are formed on the first both-side FPC board and the second both-side FPC board (step B4), and at the same time, the bonding sheet is prepared (step B4). Next, the outer layer circuits are covered with the cover layers (step B5), and at the same time, the holes are formed in the bonding sheet and filled with the electrically conductive paste. Next, the resulting first double-sided FPC and the resulting second double-sided FPC are laminated (step B6) through the bond sheet (step B6) and cover coat layers are formed on the first double-sided FPC and the second double-sided FPC (step B7). Next, surface treatment (gold plating, etc.) is performed on the first double-sided FPC and the second double-sided FPC (step B8). Thus, the multilayer FPC 1 is completed.

As is apparent from the above comparison, the number of steps of the manufacturing process for the multi-layer FPC 1 according to the embodiment of the present invention is two smaller than the number of steps of the manufacturing process for the conventional multi-layer FPC, Can be reduced.

6 is a schematic cross-sectional view showing the configuration of the multilayer FPC 51 according to another embodiment of the present invention.

The multi-layer FPC 51 shown in Fig. 6 is a so-called partial multi-layer FPC having a multi-layer structure provided at a desired position.

More specifically, the first double-sided FPC 52 includes a first wiring layer L1 and a second wiring layer L2 provided on both surfaces of the insulating base film 13. In Fig. 6, the first double-sided FPC 52 is connected to the double-sided circuit portion 53 via the signal line portion 54 provided on the right side and the single-sided circuit portion, And has a double-sided circuit portion 55. The second wiring layers L2 of the first double-side FPC 52 have inner layer via holes 16 formed at predetermined positions thereof, for example, by laser processing. The inner peripheral surfaces of the inner layer via holes 16 are plated with, for example, copper. However, since the first wiring layer L1 is not coated with copper plating, the fine circuit of the first wiring layer L1 is not affected by the plating.

In addition, the first wiring layer L1 has no reduction in the size of the component mounting regions on which the electronic parts and the like are mounted.

The second double-sided FPC 60 is provided only on the second wiring layer L2 existing in the double-sided circuit portion 53 of the first double-sided FPC 52. [ The second double-sided FPC 60 includes a third wiring layer L3 and a fourth wiring layer L4 provided on both surfaces of the insulating base film 21. The third wiring layer L3 has innerlayer via holes 24 through which the third wiring layer L3 and the fourth wiring layer L4 are electrically connected to each other.

The second double-sided FPC 60 and the double-sided circuit portion 53 of the first double-sided FPC 52 are laminated through the bonding sheet 2. Like the bonding sheet 2 already described, the bonding sheet 2 has through holes formed at predetermined positions and filled with the electrically conductive paste 11. The second wiring layer L2 and the third wiring layer L3 are electrically connected to each other by the electrically conductive paste 11.

Thus, the multilayer FPC of the present invention can be provided as a partial multilayer FPC 51 having a multilayer structure provided at a desired position. In Fig. 6, reference numerals 27 and 28 denote cover coat layers.

7 is a schematic cross-sectional view showing a configuration of a multilayer FPC 71 according to another embodiment of the present invention. The multi-layer FPC 71 shown in Fig. 7 has the same basic structure as the multi-layer FPC 1 shown in Fig. 3, and the same parts will be denoted by the same reference numerals.

The characteristic of the multilayer FPC 71 shown in Fig. 7 is that the signal line portion 72 of the first double-sided FPC 3 and the signal line portion 72 of the second double-sided FPC 4 facing each other via the hollow portion 12 The portion 73 has slightly different lengths than those measured laterally in Fig.

When the multilayer FPC 71 is a circuit board to be mounted, for example, in a folding mobile phone, the multilayer FPC 71 has a folded state in which the signal line portions 72 and 73 are bent by about 180 degrees, The portions 72 and 73 are frequently switched between a straight line state in which they extend in a generally straight line. Hence the multilayer FPC 71 is sufficient to withstand frequent switching between the folded and straight states while the signal line portions 72 and 73 remain parallel to each other with the hollow portion 12 inserted It is required to have a folding endurance. Thus, for example, if a multi-layer FPC 71 is positioned above the inner side of the signal line portion 72 and is bent so that the slewing portion 73 is positioned over the outer side, the multilayer FPC 71 is positioned over the inner side The signal line portion 72 is designed to have a length less than the signal line portion 73 located above the outer side. Thus, the signal line portions 72 and 73 will be difficult to receive compressive or tensile stresses during the bending of the multilayer FPC 71, so that the multilayer FPC 71 has improved bendability during bending.

8, the inner FPC 3 has a length M1, the outer FPC 4 has a length M2, the outer FPC 4 is bent to have a radius of curvature r, The FPC 3, and the FPC 4 have thicknesses D, t3 and t4, respectively. if so,

M1 = M +? X {r - t4 - D - (1/2) x t3}

M2 = M +? X {r - (1/2) x t4}

Here, M is a basic length of the FPC 3 and the FPC 4.

Thus, the difference between the lengths M1 and M2 is expressed as follows.

M2 - M1 =? X {(1/2) x (t3 + t4) + D}

At the end of this specification (embodiments of the invention), the data obtained during the bending of the FPC 3 and the FPC 4 while the lengths of the FPCs 4 are adjusted are shown in Table 1. As apparent from Table 1, the length-adjusted multilayer FPC is superior in flex resistance.

9 is a schematic cross-sectional view showing a configuration of a multilayer FPC 91 according to another embodiment of the present invention.

The multi-layer FPC 91 shown in Fig. 9 is a multi-layer FPC having a six-layer structure including six wiring layers. More specifically, the multilayer FPC 91 includes a first double-sided FPC 3 having a first wiring layer L1 and a second wiring layer L2, and a second double-sided FPC 3 having a fifth wiring layer L5 and a sixth wiring layer L6 2 double-sided FPC 4.

The multi-layer FPC 91 further includes a multi-layer structure 911 provided between the double-sided FPCs 3 and 4. The multilayered structure 911 includes two upper and lower bonding sheets 2 and one double-sided FPC 92 disposed between the two bonding sheets 2, i.e., a third double-sided FPC 92. The third double-sided FPC 92 includes a third wiring layer L3 and a fourth wiring layer L4.

The first double-sided FPC 3 and the second double-sided FPC 4 each have substantially the same configuration as the first double-sided FPC 3 and the second double-sided FPC 4 described with reference to Fig.

On the other hand, the multilayered structure 911 is divided into the right and left portions as shown in Fig. 9 in the absence of the lateral intermediate portion thereof, and the right portion and the left portion are separated from each other by the hollow portion 12. The right and left portions of the third double-sided FPC 92 have via holes 93 for electrical connection between the third wiring layer L3 and the fourth wiring layer L4. The bonding sheets 2 each have through holes filled with the electrically conductive paste 11 and are provided between the first double-sided FPC 3 and the third double-sided FPC 92 and between the third double-sided FPC 92 and the second double- Two-sided FPC 4, respectively. The first double-sided FPC 3, the second double-sided FPC 92 and the second double-sided FPC 4 are laminated via the bonding sheet 2.

As shown in Fig. 9, the multilayered structure 911 includes N bonding sheets (N is a natural number and N is greater than or equal to 2) and N-1 double-sided FPCs are bonded to the first double-sided FPC 3 and the second double- Layer FPCs 4 and the outermost ones of the bond sheets are configured to be located in the outer surfaces (upper and lower surfaces of FIG. 9) of the multilayered structure 911, And has a multilayer structure including six or more wiring layers.

In the case where the hollow portion 12 is provided, instead of the third double-sided FPC 92, a double-sided rigid printed circuit board or a substrate prepared by laminating a double-sided FPC and a double-sided rigid circuit board may be used. Even in this case, the resulting multilayer FPC 91 has a reduced thickness as in the first embodiment. It is also possible to provide fine circuit arrangements in the outer wiring layers L1 and L6 and achieve a higher density of mounting on the multilayer FPC without reducing the size of the component mounting areas.

Although the present invention relates to multi-layer FPCs each comprising a first double-sided FPC, a second double-sided FPC and a junction sheet, a single-sided FPC (with only outer layer circuits) can be used instead of one of the double sided FPCs. In this case, a multilayer FPC is manufactured by laser processing the base film, providing connection terminals on the base film for connection to the outer layer circuit, and connecting connection terminals to the electrically conductive paste plugs provided in the bonding sheet.

Although embodiments of the present invention are directed primarily to multi-layer FPCs having hollow portions each having no joint sheet, the multi-layer FPC of the present invention may not have a hollow portion.

It should be understood that the invention is not limited to the embodiments described above, but that various modifications may be made within the scope of the following claims.

[Table 1]

Length-adjustable multi-layer FPC Data obtained during the bending of

1. Layer structure of evaluation samples

2. Circuit wirings of evaluation samples

Parallel wirings (bendable portions of the double-sided FPC 1 and the double-sided FPC 2) arranged at an interval of 100 micrometers and each having a width of 100 micrometers,

3. Test conditions

As described in IPC 5016, a folding radius of 1.0 mm, a bending rate of 120 times / minute (times / minute), a stroke of 50 mm and a normal temperature environment were used as test conditions.

4. Test results (number of bends)

(Unit: Thousand)

In the present specification, the number of bends is defined as being observed when the conductor resistance of the circuit wiring is increased by 30% with respect to the initial resistance level at the time of testing.

In this specification, an equal length product is defined as a multi-layer FPC including an internal signal line portion 72 and an external signal line portion 73 having the same length in Fig.

In this specification, a length-controlled product is defined as a multi-layer FPC including an internal signal portion 72 and an external signal portion 73 having different lengths in Fig.

In the example of this invention, the length difference is 677 m calculated as follows.

? x {(1/2) x (t3 + t4) + D}

= π × ((65.5 + 65.5) / 2 + 150} = 677 μm

Here, t3 is the thickness of the double-side FPC 1, t4 is the thickness of the double-side FPC 2, and D is the thickness of the hollow portion 12. [

1, 51, 71, 91: Multilayer FPCs
2: Bonding sheet
3: First double-sided FPC
4: 2nd double-sided FPC
7, 8, 9, 10: Holes
11: electrically conductive paste
12: Part without the bonding sheet (hollow portion)
911: Multilayer structure
L1: first wiring layer (external surface wiring layer)
L2: second wiring layer (internal surface wiring layer)
L3: Third wiring layer (inner surface wiring layer)
L4: fourth wiring layer (outer surface wiring layer)

Claims (12)

A flexible printed circuit board comprising a first double-sided flexible printed circuit board and a second double-sided flexible printed circuit board laminated on one side of the bonded sheet, Wherein the bonding sheet is provided with a hole penetrating from one side to the other side of the bonded sheet in a predetermined position, the hole is filled with a conductive paste, and the conductive paste is applied to the first double- And the second double-sided flexible printed circuit board are electrically connected to each other,
Wherein the first double-sided flexible printed circuit board and the second double-sided flexible printed circuit board both have an insulating film and an inner surface wiring layer and an outer surface wiring layer respectively provided on both surfaces of the insulating film, Wherein the external surface wiring layer constitutes a wiring layer on which an electronic element can be mounted and an opening is formed in the internal surface wiring layer in contact with the junction sheet at a predetermined position, An inner layer via hole for electrically connecting the inner surface wiring layer and the outer surface wiring layer is formed facing the outer surface wiring layer,
Wherein the first double-sided flexible printed circuit board and the second double-sided flexible printed circuit board are provided with a hollow portion in which the bonding sheet does not exist and the first double-sided flexible printed circuit board and the second double- And the internal surface wiring layer is not provided on both of the second double-sided flexible printed circuit board and the second double-sided flexible printed circuit board. The multilayer flexible printed circuit board according to claim 1, wherein a length of the first double-sided flexible printed circuit board in the hollow portion is different from a length of the second double-sided flexible printed circuit board. A flexible printed circuit board comprising a first double-sided flexible printed circuit board and a second double-sided flexible printed circuit board laminated on one side of the bonded sheet, Wherein the bonding sheet is provided with a hole penetrating from one side to the other side of the bonded sheet in a predetermined position, the hole is filled with a conductive paste, and the conductive paste is applied to the first double- And the second double-sided flexible printed circuit board are electrically connected to each other,
Wherein the first double-sided flexible printed circuit board and the second double-sided flexible printed circuit board both have an insulating film and an inner surface wiring layer and an outer surface wiring layer respectively provided on both surfaces of the insulating film, The external surface wiring layer constitutes a wiring layer on which the electronic element can be mounted. An opening is formed in the internal surface wiring layer contacting the junction sheet at a predetermined position. The external surface wiring layer is connected to the opening, An inner layer via hole facing the outer surface wiring layer for electrically connecting the inner surface wiring layer and the outer surface wiring layer is formed,
Wherein the laminated portion including the bonding sheet, the first double-sided flexible printed circuit board and the second double-sided flexible printed circuit board, and the bonding sheet and the first double-sided flexible printed circuit board or the second double- And the second double-sided flexible printed circuit board alone or the first double-sided flexible printed circuit board alone is extended. The multi-layer flexible printed circuit board according to claim 1, A flexible printed circuit board for use as a first double-sided flexible printed circuit board, comprising: an insulating film; and an inner surface wiring layer and an outer surface wiring layer respectively provided on both surfaces of the insulating film, wherein the outer surface wiring layer constitutes a wiring layer, An inner layer via hole for electrically connecting the inner surface wiring layer and the outer surface wiring layer is formed in the surface wiring layer so as to face the outer surface wiring layer through the insulating film, The first double-sided flexible printed circuit board,
A second double-sided flexible printed circuit board comprising: an insulating film; and an inner surface wiring layer and an outer surface wiring layer provided on both surfaces of the insulating film, wherein the outer surface wiring layer constitutes a wiring layer on which electronic elements can be mounted, An inner layer via hole for electrically connecting the inner surface wiring layer and the outer surface wiring layer is formed in the surface wiring layer so as to face the outer surface wiring layer through the insulating film, The second double-sided flexible printed circuit board,
(N is a natural number, N > / = 2) and N-1 pieces of flexible sheet-like flexible printed circuit boards are laminated on the first double-sided flexible printed circuit board and the second double- Wherein the double-sided printed circuit board has the multi-layer structure of a structure in which the junction sheets are alternately stacked so as to be located on the outside,
Wherein the bonding sheet located outside the multilayered structure is provided with a hole penetrating from one side to the other side of the bonding sheet at predetermined positions, the hole is filled with a conductive paste, Wherein the first double-sided flexible printed circuit board and the second double-sided flexible printed circuit board are electrically connected to the double-sided printed circuit board included in the multilayer structure, respectively, and
Wherein the multilayered structure is absent and the first double-sided flexible printed circuit board and the second double-sided flexible printed circuit board have hollow portions facing each other with a space therebetween,
Wherein the internal surface wiring layer is not provided on both the first double-sided flexible printed circuit board and the second double-sided flexible printed circuit board in the hollow portion.  5. The multilayer flexible printed circuit board according to claim 4, wherein the double-sided printed circuit board included in the multi-layer structure includes a double-sided flexible printed circuit board, a double-sided rigid printed circuit board, or a multilayered structure formed by combining them.  The multilayer flexible printed circuit board according to claim 4 or 5, wherein a length of the first double-sided flexible printed circuit board in the hollow portion is different from a length of the second double-sided flexible printed circuit board. delete delete delete delete delete delete

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