TW201808067A - Flexible circuit board and method for manufacturing same - Google Patents

Abstract

The present invention relates to a flexible circuit board. The flexible circuit board includes an inner circuit substrate, two bonding layers and two outer circuit substrates. The inner circuit substrate includes a first conductive circuit layer. The first conductive circuit layer includes at least a signal circuit. The bonding layer includes a first insulating layer, a first pure rubber layer and a second pure rubber layer. The first pure rubber layer and the second pure rubber layer are formed on two opposite surfaces of the first insulating layer respectively. The first pure rubber layer is formed on the surface of the inner circuit substrate. The bonding layer also includes two first openings through the first insulating layer, the first pure rubber layer and the second pure rubber layer. The first opening is corresponding to the signal circuit. The two first openings, the two outer circuit substrates define an airtight cavity. The airtight cavity is full of air. The air covers the signal circuit. The present invention also relates to a method for manufacturing the flexible circuit board.

Description

Flexible circuit board and manufacturing method thereof

The invention relates to a printed circuit board technology, in particular to a flexible circuit board and a method for manufacturing a flexible circuit board.

The signal attenuation of high-frequency transmission signal lines mainly comes from the attenuation caused by dielectric loss. Among them, the dielectric loss is proportional to the dielectric loss factor and the relative dielectric constant. A common manufacturing method of an RF circuit board in the industry is to use a liquid crystal polymer (LCP), Teflon, or low-relative-dielectric-constant pure glue as a substrate layer for covering a signal circuit. However, the dielectric loss of the above materials is still relatively large, resulting in a large signal attenuation of the transmission line of the circuit board made of the above materials.

In view of this, the present invention provides a flexible circuit board with both ultra-low signal attenuation and low cost, and a manufacturing method thereof.

A flexible circuit board includes: an inner-layer circuit substrate, the inner-layer circuit substrate including a first conductive circuit layer, the first conductive circuit layer including at least one signal line, and two adhesive layers, the adhesive layer including a A first insulating layer and two first pure adhesive layers and a second pure adhesive layer formed on opposite surfaces of the first insulating layer, respectively, and the first pure adhesive layer is bonded to the surface of the inner-layer circuit board. The bonding layer further includes a first opening penetrating the first insulating layer, the first pure rubber layer, and the second pure rubber layer, and a position of the first opening corresponds to a position of the signal line; and Two outer circuit substrates respectively formed on the bonding layer, two of the first openings and two outer circuit substrates form a closed cavity, and the closed cavity is filled with air, and the air covers the signal line.

A method for manufacturing a flexible circuit board includes the steps of providing an inner layer circuit substrate, two adhesive layers, and two outer layer circuit substrates. The inner layer circuit substrate includes a first conductive circuit layer, and the first conductive circuit layer includes at least A signal line; the bonding layer includes a first insulating layer and two first pure adhesive layers and a second pure adhesive layer respectively formed on opposite surfaces of the first insulating layer, the first pure adhesive layer The adhesive layer is adhered to the surface of the inner-layer circuit board. The adhesive layer further includes a first opening penetrating the first insulating layer, the first pure adhesive layer, and the second pure adhesive layer. Corresponds to the position of the signal line; the outer circuit substrate, the bonding layer, the inner circuit substrate, the bonding layer, and the outer circuit substrate are sequentially stacked and pressed together to form a closed cavity, and further The flexible circuit board is formed; the closed cavity is filled with air, and the air covers the signal line.

The flexible circuit board provided by the present invention and a manufacturing method thereof cover conventional linear Teflon or liquid crystal polymer as a dielectric layer by replacing air with a dielectric constant of 1 F / m available around the linear signal line. The signal of the flexible circuit board is almost lossless as if transmitted in the air 81, so as to achieve ultra-low loss signal transmission, thereby improving the transmission quality, and the flexible circuit board can be made by the current process without using special materials The flexible circuit board greatly reduces the overall manufacturing cost.

FIG. 1 is a cross-sectional view of a flexible circuit board according to a first embodiment of the present invention.

2 is a cross-sectional view of an inner-layer circuit substrate, two adhesive layers, and two outer-layer circuit substrates provided by the first embodiment of the present invention for manufacturing a flexible circuit board.

FIG. 3 is a cross-sectional view of steps involved in manufacturing the inner-layer circuit board shown in FIG. 2.

FIG. 4 is a plan view of the inner-layer circuit board shown in FIG. 3.

FIG. 5 is a cross-sectional view of steps involved in producing the adhesive layer shown in FIG. 2.

FIG. 6 is a cross-sectional view of a step involved in manufacturing the outer-layer circuit board shown in FIG. 2.

FIG. 7 is a cross-sectional view of a flexible circuit board according to a second embodiment of the present invention.

FIG. 8 is a cross-sectional view of a flexible circuit board according to a third embodiment of the present invention.

FIG. 9 is a cross-sectional view of a flexible circuit board according to a fourth embodiment of the present invention.

In order to further explain the technical means and effects adopted by the present invention to achieve the intended purpose of the present invention, the specific implementation, structure, features, and effects of the flexible circuit board of the present invention and its manufacturing method are described in detail below with reference to the accompanying drawings and preferred embodiments. described as follows.

Referring to FIG. 1, a first embodiment of the present invention discloses a flexible circuit board 100 including an inner-layer circuit substrate 20 and two bonds formed on opposite sides of the inner-layer circuit substrate 20 respectively. The layer 40 and two outer-layer circuit boards 50 are formed on the surfaces of the two adhesive layers 40 that are remote from the inner-layer circuit board 20. It can be understood that the flexible circuit board 100 of the present invention can also be applied to a rigid-flex board.

The inner-layer circuit substrate 20 includes a first conductive circuit layer 13. The first conductive circuit layer 13 is made of pure copper. The first conductive line layer 13 includes at least one signal line 131, at least two ground lines 132, and at least two through grooves 133 on two sides of the signal line 131. In this embodiment, at least two of the ground lines 132 are parallel to each other, and the signal line 131 and the ground line 132 are parallel to each other. Specifically, the signal line 131 is an electrically independent wire for transmitting signals and is electrically isolated from the ground line 132. The through slot 133 penetrates the first conductive circuit layer 13, and the signal line 131 and the ground line 132 are separated by the through slot 133.

In this embodiment, there is one signal line 131, two ground lines 132, and two through slots 133.

The adhesive layer 40 includes a first insulating layer 31, a first pure glue layer 32 and a second pure glue layer 33. The first pure rubber layer 32 and the second pure rubber layer 33 are respectively formed on opposite sides of the first insulating layer 31. The first pure adhesive layer 32 is adhered to a surface of the ground circuit 132.

The bonding layer 40 further includes a first opening 34. The position of the first opening 34 corresponds to the position of the signal line 131. The length of the first opening 34 along the extending direction of the signal line 131 is substantially equal to the length of the signal line 131. The width of the first opening 34 is not less than the width of the signal line 131. That is, the projection of the signal line 131 on the bonding layer 40 in a direction perpendicular to the surface of the inner-layer circuit substrate 20 completely falls within the first opening 34.

Wherein, the first insulating layer 31 is flexible. Generally, the material of the first insulating layer 31 may be polyimide (PI), polyethylene terephthalate (PET), or polyethylene naphthalate. Polyethylene Naphthalate (PEN), polyethylene (PE), Teflon, liquid crystal polymer (LCP), polyvinyl chloride polymer (PVC) and other materials Kind of.

The bonding layer 40 further includes a plurality of first conductive holes 37. The first conductive holes 37 pass through the bonding layer 40 and correspond to the ground line 132. In this embodiment, a plurality of the first conductive holes 37 are equally spaced along the two ground lines 132. In other embodiments, a plurality of the first conductive holes 37 may also be distributed at non-equal intervals to meet different design requirements.

The outer-layer circuit substrate 50 includes a second copper foil layer 51 and a solder resist layer 52. The second copper foil layer 51 is formed on the surface of the second pure rubber layer 33 away from the first insulating layer 31, and the solder resist layer 52 is formed on the second copper foil layer 51 far from the second pure rubber layer. 33 on the surface. The solder mask layer 52 includes at least one second opening 53, and a portion of the second copper foil layer 51 is exposed from the second opening 53. A nickel-gold layer 54 is formed on the surface of the second copper foil layer 51 exposed from the second opening 53. The nickel-gold layer 54 is composed of a nickel layer and a gold layer. The second opening 53 and the nickel-gold layer 54 are used for carrying active components or passive components as required and grounded.

The first conductive via 37 is electrically connected to the ground circuit 132 and the second copper foil layer 51.

The flexible circuit board 100 further includes a closed cavity 80 formed by two of the through grooves 133 and two of the first openings 34. Preferably, the closed cavity 80 is filled with air 81, and the closed cavity 80 covers the signal line 131. Because the closed cavity 80 is filled with air 81, and the dielectric constant of the air 81 is 1.0 Farad / meter (F / m), which is smaller than the dielectric constant of Teflon or liquid crystal polymer or pure glue. When transmitting through the signal line 131 of the present invention, the transmitted signal can approach a lossless state.

Please refer to FIGS. 1, 2 to 6. A first embodiment of the present invention provides a method for manufacturing a flexible circuit board 100. The steps include:

In the first step, referring to FIG. 2, an inner circuit board 20, two adhesive layers 40 and two outer circuit boards 50 are provided.

Please refer to FIGS. 3 to 4. The method for manufacturing the inner-layer circuit substrate 20 includes the following steps: First, a copper-clad substrate 10 is provided. The copper-clad substrate 10 includes a first copper foil layer 11 and a substrate 12 formed on a surface of the first copper foil layer 11. Next, the first copper foil layer 11 is fabricated to form a first conductive circuit layer 13. The first conductive line layer 13 includes at least one signal line 131, at least two ground lines 132, and at least two through grooves 133 on two sides of the signal line 131. Specifically, the first conductive circuit layer 13 is made of the pure copper through an image transfer process and an etching process. Again, the substrate 12 is removed to form the inner-layer circuit substrate 20.

Referring to FIG. 5, the method for manufacturing the adhesive layer 40 includes the following steps: First, an adhesive sheet 30 is provided. The adhesive sheet 30 includes a first insulating layer 31, a first pure adhesive layer 32, and a second Pure rubber layer 33. The first pure rubber layer 32 and the second pure rubber layer 33 are respectively formed on opposite sides of the first insulating layer 31, and the first pure rubber layer 32 is adhered to a surface of the ground line 132. Next, a plurality of first openings 34 and a plurality of first through holes 35 are formed in the adhesive sheet 30 and penetrate the adhesive sheet 30. The first through hole 35 and the first opening 34 can be formed by mechanical drilling or laser etching. The position of the first opening 34 corresponds to the position of the signal line 131. The first through holes 35 correspond to the ground line 132. In this embodiment, a plurality of the first through holes 35 are equally spaced along the two ground lines 132. In other embodiments, a plurality of the first through holes 35 may be distributed at non-equidistant intervals. Again, the first through hole 35 is filled with a first conductive paste 36 to form a first conductive hole 37, and then the bonding layer 40 is formed. The first conductive paste 36 may be a copper conductive paste.

Referring to FIG. 6, the method for manufacturing the outer-layer circuit substrate 50 includes the following steps: First, a second copper foil layer 51 is provided. Next, a solder resist layer 52 covering the second copper foil layer 51 is formed on one surface of the second copper foil layer 51 and a second opening 53 is formed on the solder resist layer 52, part of the second copper foil. The layer 51 is exposed from the second opening 53. Again, a nickel-gold layer 44 is formed on the surface of the second copper foil layer 51 exposed from the second opening 53 to form the outer-layer circuit substrate 50. The nickel-gold layer 44 can be formed by a gold plating process. The nickel-gold layer 54 is composed of a nickel layer and a gold layer.

In the second step, referring to FIG. 1, the outer circuit substrate 50, the adhesive layer 40, the inner circuit substrate 20, the adhesive layer 40 and the outer circuit substrate 50 are sequentially stacked and pressed together to form The cavity 80 further forms the flexible circuit board 100.

The position of the first opening 34 corresponds to the position of the signal line 131. The first conductive hole 37 is electrically connected to the ground line 132 and the second copper foil layer 51. The closed cavity 80 is filled with air 81, and the closed cavity 80 covers the signal line 131.

Please refer to FIG. 7, a second embodiment of the present invention provides a flexible circuit board 200. The structure of the flexible circuit board 200 is basically the same as that of the flexible circuit board 100. The difference is that the inner circuit board 60 of the flexible circuit board 200 It includes a first conductive circuit layer 13 and a second insulating layer 61 formed between the first conductive circuit layer 13 and the first pure rubber layer 32. The second insulating layer 61 is further formed with a plurality of second vias. The second conductive hole 611 is filled in the second through hole 611 to form a second conductive hole 613. The position of the second through hole 611 corresponds to the position of the first through hole 35. The second conductive hole 613 is used to electrically connect the ground line 132 and the first conductive hole 37.

Referring to FIG. 8, a third embodiment of the present invention provides a flexible circuit board 300. The structure of the flexible circuit board 300 is basically the same as that of the flexible circuit board 100. The difference is that the outer circuit substrate 70 of the flexible circuit board 300 is also The third insulating layer 73 includes a third insulating layer 73 formed on a surface of the second copper foil layer 51 of the outer circuit substrate 70, and the third insulating layer 73 and the solder mask layer 72 of the outer circuit substrate 70. Opposites. A plurality of third through holes 731 are also formed on the third insulating layer 73, and a third conductive paste 732 is filled in the third through holes 731 to form a third conductive hole 733. The position of the third through hole 731 corresponds to the position of the first through hole 35. The third conductive hole 733 is used to electrically connect the second copper foil layer 51 and the first conductive hole 37.

Referring to FIG. 9, a fourth embodiment of the present invention provides a flexible circuit board 400. The structure of the flexible circuit board 400 is basically the same as that of the flexible circuit board 300. The difference is that the copper-clad substrate of the flexible circuit board 400 is similar to the copper-clad substrate of the flexible circuit board 400. The structure of the copper-clad substrate 60 of the flexible circuit board 200 is the same. The outer circuit substrate of the flexible circuit board 400 is the same as the outer circuit substrate 70 of the flexible circuit board 300.

The flexible circuit board provided by the present invention and a manufacturing method thereof, 1) A cavity 80 is formed around the signal line 131 of the flexible circuit board 100, and the dielectric constant of the air 81 in the closed cavity 80 is 1F / m, Air 81 replaces traditional Teflon or liquid crystal polymer or pure glue to cover the signal line as a dielectric layer, so that the signal of the flexible circuit board 100 is almost lossless as if transmitted in air 81 to achieve Ultra-low signal attenuation signal transmission; 2) Adhesive layer 40 is formed by a layered structure of pure glue layer + insulation layer + pure glue layer, which can increase the volume of the closed cavity 80 so that it can accommodate more low-media The electric constant air 81 further reduces the attenuation of the signal for signal transmission in the signal line 131; 3) because the process cost of forming the first opening 34 in the adhesive sheet 30 is relatively low, it can reduce the production of flexible circuit boards the cost of.

In summary, the present invention has indeed met the requirements for an invention patent, and a patent application was filed in accordance with the law. However, the above are only preferred embodiments of the present invention, and the scope of patent application in this case cannot be limited by this. For example, those who are familiar with the skills of this case and equivalent modifications or changes made according to the spirit of the present invention should be covered by the following patent applications.

100, 200, 300, 400

Flexible circuit board:

10‧‧‧ Copper-clad substrate

11‧‧‧The first copper foil layer

12‧‧‧ substrate

13‧‧‧ the first conductive circuit layer

131‧‧‧Signal line

132‧‧‧ ground line

133‧‧‧through groove

20,60‧‧‧Inner circuit board

30‧‧‧Adhesive sheet

31‧‧‧first insulating layer

32‧‧‧The first pure rubber layer

33‧‧‧Second pure rubber layer

34‧‧‧ first opening

35‧‧‧First through hole

36‧‧‧The first conductive paste

37‧‧‧First conductive hole

40‧‧‧ Adhesive layer

50, 70‧‧‧ Outer circuit board

51‧‧‧Second copper foil layer

52, 72‧‧‧solder resist

53‧‧‧Second opening

54‧‧‧ nickel-gold layer

61‧‧‧Second insulation layer

611‧‧‧second through hole

612‧‧‧Second conductive paste

613‧‧‧Second conductive hole

73‧‧‧ third insulating layer

731‧‧‧Third through hole

732‧‧‧Third conductive paste

733‧‧‧Third conductive hole

80‧‧‧ Cavity

81‧‧‧ air

no

100‧‧‧flexible circuit board

13‧‧‧ the first conductive circuit layer

131‧‧‧Signal line

132‧‧‧ ground line

133‧‧‧through groove

31‧‧‧first insulating layer

32‧‧‧The first pure rubber layer

33‧‧‧Second pure rubber layer

34‧‧‧ first opening

37‧‧‧First conductive hole

20‧‧‧Inner circuit board

40‧‧‧ Adhesive layer

50‧‧‧ Outer circuit board

51‧‧‧Second copper foil layer

52‧‧‧Solder Mask

53‧‧‧Second opening

54‧‧‧ nickel-gold layer

80‧‧‧ Cavity

81‧‧‧ air

Claims (10)

A flexible circuit board includes:
An inner-layer circuit substrate, the inner-layer circuit substrate including a first conductive circuit layer, the first conductive circuit layer including at least one signal line;
Two adhesive layers. The adhesive layer includes a first insulating layer and two first pure adhesive layers and a second pure adhesive layer respectively formed on opposite surfaces of the first insulating layer. An adhesive layer is adhered to the surface of the inner-layer circuit substrate. The adhesive layer further includes a first opening penetrating the first insulating layer, the first pure adhesive layer, and the second pure adhesive layer. The first opening Corresponding to the position of the signal line; and two outer circuit substrates respectively formed on the bonding layer, the two first openings and the two outer circuit substrates forming a closed cavity, and the closed cavity It is filled with air, which covers the signal line. The flexible circuit board according to claim 1, wherein a position of the first opening corresponds to a position of the signal line, and the signal line is bonded to the surface in a direction perpendicular to a surface of the inner-layer circuit substrate. The projection on the layer falls completely within the first opening. The flexible circuit board according to claim 2, wherein the first conductive line layer further includes at least two ground lines on both sides of the signal line, and the bonding layer further includes a plurality of first conductive holes. The first conductive holes are equally spaced along the two ground lines. The outer circuit board includes a second copper foil layer formed on the second pure rubber layer away from the first insulation layer. On the surface, the first conductive hole is electrically connected to the ground line and the second copper foil layer. The flexible circuit board according to claim 3, wherein the inner-layer circuit substrate further includes a second insulating layer formed between the first conductive circuit layer and the first pure rubber layer, and the second insulating layer A plurality of second conductive holes is formed on the layer. The positions of the second conductive holes are opposite to the positions of the first conductive holes. The second conductive holes are used to electrically connect the ground line and the first conductive hole. The flexible circuit board according to claim 3, wherein the outer circuit board further includes a third insulating layer formed between the second copper foil layer and the second pure adhesive layer, and the third insulating layer The third insulating layer is formed on a surface of the second copper foil layer, the third insulating layer is opposite to the solder resist layer, and a plurality of third conductive holes are formed on the third insulating layer. The first conductive holes are opposite to each other, and the third conductive hole is electrically connected to the second copper foil layer and the first conductive hole. The flexible circuit board according to claim 3, wherein the inner-layer circuit substrate further includes a second insulating layer formed between the first conductive circuit layer and the first pure rubber layer, and the second insulating layer A plurality of second conductive holes are formed on the layer, the positions of the second conductive holes are opposite to the positions of the first conductive holes, and the second conductive holes are used to electrically connect the ground line and the first conductive hole; the outer layer circuit The substrate further includes a third insulating layer formed between the second copper foil layer and the second pure adhesive layer. The third insulating layer is formed on a surface of the second copper foil layer. The third insulating layer Opposite the solder resist layer, a plurality of third conductive holes are also formed on the third insulating layer. The position of the third conductive hole is opposite to the position of the first conductive hole, and the third conductive hole is electrically connected to the first conductive hole. Two copper foil layers and the first conductive hole. A method for manufacturing a flexible circuit board includes steps:
An inner circuit substrate, two adhesive layers, and two outer circuit substrates are provided. The inner circuit substrate includes a first conductive circuit layer, the first conductive circuit layer includes at least one signal line, and the adhesive layer includes a A first insulating layer and two first pure adhesive layers and a second pure adhesive layer formed on opposite surfaces of the first insulating layer, respectively, and the first pure adhesive layer is bonded to the surface of the inner-layer circuit board. Preferably, the bonding layer further includes a first opening penetrating the first insulating layer, the first pure rubber layer, and the second pure rubber layer, and a position of the first opening corresponds to a position of the signal line;
The outer circuit substrate, the adhesive layer, the inner circuit substrate, the adhesive layer and the outer circuit substrate are sequentially stacked and pressed together to form a cavity, thereby forming the flexible circuit board; the closed cavity The air is filled with air, which covers the signal line. The method for manufacturing a flexible circuit board according to claim 7, wherein the position of the first opening corresponds to the position of the signal line, and the projection of the signal line on the adhesive layer completely falls on the first opening. Inside. The method for manufacturing a flexible circuit board according to claim 7, wherein the first conductive line layer further includes at least two ground lines on both sides of the signal line, and the bonding layer further includes a plurality of first conductive holes. The outer circuit substrate includes a second copper foil layer formed on a surface of the second pure rubber layer away from the first insulating layer, and the first conductive hole is electrically connected to the ground line and the The second copper foil layer. The method for manufacturing a flexible circuit board according to claim 7, wherein the method for manufacturing the adhesive layer includes the steps of: providing an adhesive sheet; and forming a plurality of first adhesive sheets on the adhesive sheet through the adhesive sheet. An opening and a plurality of first through-holes, the first through-holes corresponding to the ground line; the first through-holes are filled with a first electrical paste to form a first conductive hole, and then the bonding layer is formed.