TWI665949B - Flexible printed circuit board and method for making the same - Google Patents

Abstract

A flexible circuit board includes a copper-clad substrate and a first conductive circuit layer formed on one surface of the copper-clad substrate. The copper-clad substrate is provided with at least one conductive hole penetrating therethrough, and a portion of the first conductive circuit layer is filled in each In the conductive hole, the first conductive line layer includes a pair of signal lines and a plurality of ground lines on both sides of the signal line. A surface of the first conductive line layer away from the copper-clad substrate is covered with a first adhesive layer. The first adhesive layer fills a gap formed by the first conductive circuit layer, wherein the first adhesive layer is provided with at least one through opening, the opening is filled with a conductive paste, and each opening is The conductive paste is in contact with and electrically connected to one of the ground wires, and the surface of the first adhesive layer away from the first conductive circuit layer is covered with an electromagnetic shielding layer.

Description

Flexible circuit board and manufacturing method thereof

The invention relates to the technical field of circuit boards, in particular to a flexible circuit board and a method for manufacturing the flexible circuit board.

Flexible circuit boards often produce electromagnetic interference during actual work, which affects signal transmission on the circuit boards. Therefore, an electromagnetic shielding layer needs to be provided in a flexible circuit board product. At present, the electromagnetic shielding layer usually includes a protective layer, a shielding layer, and an anisotropic conductive adhesive layer which are sequentially stacked. When manufacturing the flexible circuit board, a double-sided copper-clad substrate needs to be covered with a cover film having a through hole to expose the ground wire of the double-sided copper-clad substrate, and then the electromagnetic shield is laminated to On the cover film, a part of the anisotropic conductive adhesive layer flows and fills the through hole, so as to be electrically connected to the ground line. Therefore, on the flexible circuit board, the signal lines of the double-sided copper-clad substrate are not only covered with the cover film, but also covered with the anisotropic conductive adhesive layer.

Although the existing cover film can already be made of a material with a small dielectric constant D _k and a small dielectric loss D _f (D _k <3, D _f <0.005), the anisotropic conductive adhesive layer is usually not With a small dielectric constant D _k , the flexible circuit board cannot achieve high-frequency signal transmission impedance matching, which affects high-frequency and high-speed digitalization of signal transmission.

Therefore, it is necessary to provide a flexible circuit board and a manufacturing method thereof to solve the above problems.

A method for manufacturing a flexible circuit board includes providing a substrate unit including a copper-clad substrate and a copper-plated layer formed on at least one surface of the copper-clad substrate. At least one through-hole is provided, and the copper-plated layer is filled in the through-hole to form a conductive hole; a required conductive circuit is etched in one of the copper-plated layers by exposure and development technology, thereby obtaining a first A conductive circuit layer, the first conductive circuit layer includes a pair of signal lines and a plurality of ground lines on both sides of the signal line; and a surface of the first conductive circuit layer away from the copper-clad substrate is covered with a first An adhesive layer and an electromagnetic shielding layer, and pressing the first adhesive layer and the electromagnetic shielding layer to make the first adhesive layer flow to fill the gap formed by the first conductive circuit layer, wherein At least one penetrating opening is opened in the first adhesive layer, and the opening is filled with a conductive paste, and each of the openings is in contact with one of the ground wires through the conductive paste and is electrically conductive. connection.

A flexible circuit board includes a copper-clad substrate and a first conductive circuit layer formed on a surface of the copper-clad substrate. The copper-clad substrate is provided with at least one conductive hole penetrating therethrough, and part of the first conductive circuit layer is filled. In each conductive hole, the first conductive circuit layer includes a pair of signal lines and a plurality of ground lines on both sides of the signal line. A surface of the first conductive circuit layer away from the copper-clad substrate is covered with a A first adhesive layer, the first adhesive layer filling a gap formed by the first conductive circuit layer, wherein the first adhesive layer is provided with at least one penetrating opening, and the opening is filled with conductive Paste, each of the openings is in contact with one of the ground wires through the conductive paste and is electrically connected, and a surface of the first adhesive layer away from the first conductive circuit layer is covered with an electromagnetic shielding layer.

In the flexible circuit board according to the preferred embodiment of the present invention, because the signal line is covered with the first adhesive layer and is not covered with an anisotropic conductive adhesive, the material of the first adhesive layer may be selected from an existing dielectric. The electrical constant D _k and the dielectric loss D _f are made of a material having a small dielectric constant, so it is advantageous for the flexible circuit board to achieve high-frequency signal transmission impedance matching.

100‧‧‧flexible circuit board

10‧‧‧ double-sided copper-clad substrate

11‧‧‧ Grassroots

12‧‧‧ Copper foil layer

20‧‧‧through hole

30‧‧‧Organic conductive film

40‧‧‧ copper plating

41‧‧‧ conductive hole

42‧‧‧ substrate unit

51‧‧‧The first conductive circuit layer

52‧‧‧Second conductive circuit layer

53‧‧‧Photosensitive layer

61‧‧‧The first adhesive layer

62‧‧‧Second glue layer

70‧‧‧ electromagnetic shielding layer

71‧‧‧protective layer

72‧‧‧ conductive silver layer

510‧‧‧Signal cable

511‧‧‧ ground wire

530‧‧‧ pattern

610‧‧‧Opening

611‧‧‧ conductive paste

FIG. 1 is a cross-sectional view of a double-sided copper-clad substrate provided by a preferred embodiment of the present invention.

FIG. 2 is a cross-sectional view after a through hole is opened on the double-sided copper-clad substrate shown in FIG. 1.

3 is a cross-sectional view after an organic conductive film is formed in the through hole shown in FIG. 2.

FIG. 4 is a cross-sectional view after copper plating on the surface of the double-sided copper-clad substrate shown in FIG. 3 to form a copper plating layer. Illustration.

FIG. 5 is a cross-sectional view after covering the photosensitive layer on the copper-plated layer shown in FIG. 4.

6 is a cross-sectional view after a pattern is formed in the photosensitive layer shown in FIG. 5.

FIG. 7 is a cross-sectional view after etching the copper plating layer shown in FIG. 6 to form a conductive circuit layer.

8 is a cross-sectional view of the conductive circuit layer shown in FIG. 7 after being covered with a first adhesive layer, a second adhesive layer, and an electromagnetic shielding layer.

FIG. 9 is a cross-sectional view of a flexible circuit board prepared by laminating the first adhesive layer, the second adhesive layer, and the electromagnetic shielding layer shown in FIG. 8.

Please refer to FIGS. 1 to 9. A method for manufacturing a flexible circuit board 100 according to a preferred embodiment of the present invention includes the following steps:

Step 1. Referring to FIG. 1, a double-sided copper-clad substrate 10 is provided.

The double-sided copper-clad substrate 10 includes an insulating base layer 11 and two copper foil layers 12 formed on two opposite surfaces of the base layer 11. The material of the base layer 11 may be selected from polyimide (PI), polyethylene terephthalate (PET), and polyethylene naphthalate (PEN). ) And so on.

Step two, referring to FIG. 2, at least one through hole 20 penetrating the base layer 11 and each copper foil layer 12 is formed on the double-sided copper-clad substrate 10. The through hole 20 is formed by laser drilling, and the diameter of the through hole 20 is approximately 0.15 mm.

Step three, referring to FIG. 3, an organic conductive film 30 is formed on an inner wall of each through hole 20 and a region corresponding to the base layer 11.

Step four, referring to FIG. 4, copper is plated on the surface of each copper foil layer 12 away from the base layer 11 to form a copper plating layer 40 on the copper foil layer 12, and a portion of the copper plating layer 40 is filled. A conductive hole 41 for electrically connecting the two copper-plated layers 40 is formed in the through hole 20 in which the organic conductive film 30 is formed, so as to obtain a substrate unit 42.

Step five, referring to FIG. 5 to FIG. 7, an exposure and development technique is used to etch a required conductive circuit in the two copper plating layers 40 of the substrate unit 42, so as to obtain a first conductive circuit layer 51 and a first conductive circuit layer 51. Two conductive circuit layer 52. The first conductive circuit layer 51 includes a pair of signal lines 510 and a plurality of ground lines 511 on both sides of the signal line 510.

Specifically, firstly, two photosensitive layers 53 (see FIG. 5) are covered on the surfaces of the two copper-plated layers 40 away from the copper foil layer 12, and a desired pattern is formed in each photosensitive layer 53 by exposure and development technology. 530 (see FIG. 6); etching the two copper-plated layers 40 using the photosensitive layer 53 having the pattern 530 as a photomask to form the first conductive circuit layer 51 and the second conductive circuit 52, The photosensitive layer 53 is then removed (see FIG. 7). The photosensitive layer 53 may be a dry film.

Step 6: Referring to FIG. 8 and FIG. 9, a surface of the first conductive circuit layer 51 and the second conductive circuit layer 52 far from the copper foil layer 12 is covered with a first adhesive layer 61 and a second An adhesive layer 62, covering the surface of the first adhesive layer 61 away from the first conductive circuit layer 51 with an electromagnetic shielding layer 70 (see FIG. 8), and laminating the first adhesive layer 61 and the second The adhesive layer 62 and the electromagnetic shielding layer 70 allow the first adhesive layer 61 and the second adhesive layer 62 to flow to fill a gap formed by the first conductive circuit layer 51 and the second conductive circuit layer 52 ( (See Figure 9). The first adhesive layer 61 is provided with at least one penetrating opening 610, and the opening 610 is filled with a conductive paste 611. Each of the openings 610 communicates with the conductive paste 611 and one of the openings 610. The ground wire 511 is in contact with and electrically connected. Wherein, the material of the first glue layer 61 and the second glue layer 62 may be pure glue. The conductive copper paste 511 may be a conductive copper paste.

It can be understood that the first adhesive layer 61 and the second adhesive layer 62 are in a semi-cured state, so that they can flow during the lamination process.

The first adhesive layer 61 may be formed by providing a first cover film (not shown). The first cover film includes an original adhesive layer and two original adhesive layers respectively formed on the original adhesive layer. Two insulating layers on opposite surfaces; openings 610 penetrating the original adhesive layer and each insulating layer in the first cover film; and filling the conductive paste 611 in each of the openings 610 ; Remove said Two insulating layers form the first adhesive layer 61. Wherein, the material of the insulating layer may be polyethylene terephthalate (PET).

In this embodiment, the electromagnetic shielding layer 70 includes a protective layer 71 and a conductive silver layer 72 which are sequentially stacked, and the conductive silver layer 72 is formed on the protective layer 71 and the first adhesive layer 61. between. The conductive silver layer 72 may be formed by gravure coating silver ink on the protective layer 71. In this embodiment, the thickness of the conductive silver layer 72 is 0.15 μm to 0.3 μm. The conductive silver layer 72 includes silver particles having an average particle diameter of less than 100 nanometers. The material of the protective layer 72 may be polyimide (PI).

In other embodiments, the double-sided copper-clad substrate 10 may be replaced by a single-sided copper-clad substrate.

Because the signal line 510 is covered with the first adhesive layer 61 and is not covered with an anisotropic conductive adhesive, the material of the first adhesive layer 61 can be selected from the existing dielectric constant D _k and dielectric loss. D _f is made of a smaller material, so it is beneficial for the flexible circuit board 100 to achieve high-frequency signal transmission impedance matching. In addition, the diameter of the through-hole 20 is much smaller than the diameter of the through-hole formed by the conventional punching method (greater than 0.6 mm), which is beneficial to reducing the overall size of the flexible circuit board.

Referring to FIG. 9, the flexible circuit board 100 includes a double-sided copper-clad substrate 10. The double-sided copper-clad substrate 10 includes an insulating base layer 11 and two copper foil layers 12 formed on two opposite surfaces of the base layer 11. The first conductive circuit layer 51 and the second conductive circuit layer 52 are respectively formed on the surfaces of the two copper foil layers 12 away from the base layer 11. The double-sided copper-clad substrate 10 is provided with at least one conductive hole 41 penetrating the base layer 11 and the two copper foil layers 12 for electrically connecting the first conductive circuit layer 51 and the second conductive circuit layer 52. Each of the conductive holes 41 includes a through hole 20 and an organic conductive film 30 formed on a region of the inner wall of the through hole 20 corresponding to the base layer 11, and part of the first conductive circuit layer 51 and the second conductive layer. The circuit layer 52 is filled in the conductive hole 41. The first conductive circuit layer 51 includes a pair of signal lines 510 and a plurality of ground lines 511 on both sides of the signal line 510.

The surfaces of the first conductive circuit layer 51 and the second conductive circuit layer 52 remote from the copper foil layer 12 are respectively covered with a first adhesive layer 61 and a second adhesive layer 62. The first adhesive layer 61 and the second The adhesive layer 62 fills a gap formed by the first conductive circuit layer 51 and the second conductive circuit layer 52. The first adhesive layer 61 is provided with at least one penetrating opening 610, and the opening 610 is filled with a conductive paste 611. Each of the openings 610 communicates with the conductive paste 611 and one of the openings 610. The ground wire 511 is in contact with and electrically connected. The surface of the first adhesive layer 61 away from the first conductive circuit layer 51 is covered with an electromagnetic shielding layer 70.

Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solution of the present invention and are not limiting. Although the present invention has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be carried out. Modifications or equivalent replacements should not depart from the spirit and scope of the technical solution of the present invention.

Claims (7)

A method for manufacturing a flexible circuit board includes providing a substrate unit including a copper-clad substrate and a copper-plated layer formed on at least one surface of the copper-clad substrate. The copper-clad substrate is provided with at least one through hole. Holes, the copper-plated layer is filled in the through-holes to form conductive holes; a desired conductive circuit is etched in one of the copper-plated layers by exposure and development technology, thereby obtaining a first conductive circuit layer, the The first conductive circuit layer includes a pair of signal lines and a plurality of ground lines on both sides of the signal lines; and a surface of the first conductive circuit layer away from the copper-clad substrate is covered with a first adhesive layer and an electromagnetic A masking layer, and pressing the first adhesive layer and the electromagnetic shielding layer to make the first adhesive layer flow to fill a gap formed by the first conductive circuit layer, wherein the first adhesive layer The layer is provided with at least one penetrating opening, and the opening is filled with a conductive paste. Each of the openings is in contact with one of the ground wires through the conductive paste and is electrically connected. The cover layer includes one And a sheath layer of conductive silver, the silver conductive layer is formed between the protective layer and the first adhesive layer, the electromagnetic shield layer does not include anisotropic conductive adhesive. The method for manufacturing a flexible circuit board according to item 1 of the scope of patent application, wherein the method for manufacturing the substrate unit comprises: providing the copper-clad substrate, which includes an insulating base layer and is formed on at least one surface of the base layer A copper foil layer on top; opening the through hole penetrating the base layer and the copper foil layer on the copper-clad substrate; forming an organic conductive film on an inner wall of each through hole and a region corresponding to the base layer ; And copper-plating a surface of the copper foil layer away from the base layer to form the copper-plated layer, and filling the copper-plated layer with the through-holes in which the organic conductive film is formed to form conductive holes, Thereby, the substrate unit is obtained. The method for manufacturing a flexible circuit board according to item 2 of the scope of patent application, wherein the method for manufacturing the first conductive circuit layer further comprises: covering a surface of the copper plating layer away from the copper foil layer with a photosensitive layer Forming a desired pattern in the photosensitive layer by exposure and development technology; etching the copper plating layer using the photosensitive layer having the pattern as a photomask to form the first conductive circuit layer; and removing The photosensitive layer. The method for manufacturing a flexible circuit board according to item 1 of the scope of patent application, wherein the method for manufacturing the first adhesive layer includes: providing a first cover film, the first cover film includes an original adhesive layer, and Two insulating layers formed on two opposite surfaces of the original adhesive layer; openings in the first cover film penetrating through the original adhesive layer and each insulating layer; in each of the openings Filling the conductive paste; and removing the two insulating layers to form the first adhesive layer. The method for manufacturing a flexible circuit board according to item 1 of the scope of the patent application, wherein the through hole is formed by laser drilling, and the diameter of the through hole is 0.15 mm. The method for manufacturing a flexible circuit board according to item 1 of the scope of patent application, wherein the conductive silver layer is formed by gravure coating silver ink on the protective layer, and the thickness of the conductive silver layer is 0.15 microns to 0.3 microns. A flexible circuit board includes a copper-clad substrate and a first conductive circuit layer formed on a surface of the copper-clad substrate. The copper-clad substrate is provided with at least one conductive hole penetrating therethrough, and part of the first conductive circuit layer is filled. In each conductive hole, an improvement is that the first conductive circuit layer includes a pair of signal lines and a plurality of ground lines on both sides of the signal line, and the first conductive circuit layer is far from the copper-clad substrate. The surface of is covered with a first adhesive layer, and the first adhesive layer fills the gap formed by the first conductive circuit layer, wherein the first adhesive layer is provided with at least one through-opening, and the opening A conductive paste is filled therein, and each of the openings is in contact with and electrically connected to one of the ground wires through the conductive paste, and the surface of the first adhesive layer away from the first conductive circuit layer is covered with an electromagnetic A shielding layer, the electromagnetic shielding layer comprising a protective layer and a conductive silver layer which are sequentially stacked, the conductive silver layer is formed between the protective layer and the first adhesive layer, and the electromagnetic mask The layer does not include an anisotropic conductive glue.