TWI676404B - Hollow flexible circuit board and method for manufacturing same - Google Patents

Abstract

A hollow flexible circuit board includes a conductive circuit layer and a photosensitive resin layer formed on one surface of the conductive circuit layer. The conductive circuit layer includes at least a first solder pad, and the photosensitive resin layer includes a first A surface and a second surface opposite to the first surface, the first surface facing the conductive circuit layer, at least one first opening is formed on the photosensitive resin layer, and each of the first solder pads extends from the first surface An opening is exposed, and the first surface is flush with an end surface of the first pad away from the conductive circuit layer. The invention also relates to a method for manufacturing a hollow flexible circuit board.

Description

Hollow flexible circuit board and manufacturing method

The invention relates to the field of circuit board manufacturing, in particular to a hollow flexible circuit board and a manufacturing method thereof.

With the increasingly strict requirements on quality, lightness, and shortness of mid-to-high-end consumer electronics products (Smart Phone, Tablet, UltraBook, etc.), the design of circuit boards is becoming thinner and the circuits are becoming more refined. Ordinary single-sided FPC has only one side for component and assembly. Without increasing the wiring density of the product, in order to improve the convenience of component and assembly placement, the design and application of the hollow board (relief board); ) Is a single-sided FPC with two-sided PAD, which can be attached to components or assembled at the same time. However, the traditional hollow-out board is prone to produce circuit defects and creasing marks.

In view of this, the present invention provides a hollow flexible circuit board capable of reducing the defective rate of lines and avoiding creasing, and a manufacturing method thereof.

A hollow flexible circuit board includes a conductive circuit layer and a photosensitive resin layer formed on a surface of the conductive circuit layer. The conductive circuit layer includes a plurality of first pads, at least one conductive circuit, and at least one second For a solder pad, the photosensitive resin layer includes a first surface and a second surface opposite to the first surface. The first surface faces the conductive circuit layer. A plurality of first resin layers are formed on the photosensitive resin layer. An opening, each of the first pads is exposed from each of the first openings, and the photosensitive resin layer is protected between the adjacent first pads, and the first surface is away from the first pads One end surface of the conductive circuit layer is flush with each other; the conductive circuit and the second bonding pad are both formed on the first surface, and the conductive line The thickness of the road is less than the thickness of the first pad and greater than the thickness of the second pad. The thickness of the first pad is equal to the sum of the thickness of the photosensitive resin layer and the conductive line.

A method for manufacturing a hollow flexible circuit board includes the following steps: providing a double-sided copper-clad substrate including a base layer and two copper foil layers respectively formed on two opposite surfaces of the base layer; and two copper foils A photosensitive resin layer is formed on the surface of the layer. The photosensitive resin layer includes a first surface and a second surface opposite to the first surface. The first surface faces the copper foil layer. The photosensitive resin layer A plurality of first openings are formed on the layer; a copper plating layer is formed on the second surface of the photosensitive resin layer and the plurality of first openings; two copper plating layers are formed to form a conductive circuit layer; The conductive circuit layer includes a plurality of first solder pads, at least one conductive circuit, and at least one second solder pad. Part of the first solder pads are located in the first opening, and the photosensitivity is provided between adjacent first solder pads. Type resin layer protection, the conductive line and the second bonding pad are both formed on the first surface, and the thickness of the conductive line is smaller than the thickness of the first bonding pad and greater than the thickness of the second bonding pad. The thickness of the pad is equal to the photosensitive resin layer and the The sum of the thickness of the electrical circuit; removing the base layer to form two flexible circuit substrates; the flexible circuit substrate including the conductive circuit layer, the photosensitive resin layer, and a copper foil layer; and removing the copper foil layer, making the first The surface is flush with an end surface of the first pad away from the conductive circuit layer.

The hollow flexible circuit board provided by the present invention and a manufacturing method thereof are protected by a photosensitive resin layer between the first solder pads (circuits), which can not only enhance the toughness of the hollow flexible circuit board, reduce creasing marks, improve product quality, but also This makes the hollow flexible circuit board difficult to delaminate during the thermal process, reduces the defective rate of the circuit, and increases the reliability of the product.

100, 200‧‧‧ Hollow flexible circuit board

10‧‧‧ double-sided copper-clad substrate

11‧‧‧ basal layer

12‧‧‧ Copper foil layer

13‧‧‧ Photosensitive resin layer

131‧‧‧ the first surface

132, 232‧‧‧Second surface

133‧‧‧First opening

14‧‧‧ Copper plating

15‧‧‧Photoresist layer

151‧‧‧Second opening

16‧‧‧ conductive circuit layer

161‧‧‧ conductive line

162,262‧‧‧The first pad

163,263‧‧‧Second welding pad

17‧‧‧ Cover film

171, 271‧‧‧th third opening

20‧‧‧flexible circuit board

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

FIG. 2 is a cross-sectional view of a double-sided copper-clad substrate provided by the first embodiment of the present invention.

3 is a cross-sectional view after a photosensitive resin layer is formed on two opposite surfaces of the double-sided copper-clad substrate shown in FIG. 2.

FIG. 4 is a cross-sectional view after a copper plating layer is formed on the photosensitive resin layer shown in FIG. 3.

FIG. 5 is a cross-sectional view after a dry film layer is formed on the surface of the copper plating layer shown in FIG. 4.

FIG. 6 is a cross-sectional view after the copper exposed from the opening of the dry film layer shown in FIG. 5 is etched away and the dry film layer is removed to form a conductive circuit layer.

FIG. 7 is a cross-sectional view after forming a cover film layer on the surface of the conductive circuit layer shown in FIG. 6.

FIG. 8 is a cross-sectional view of one of the two separated circuit substrates formed by removing the substrate in FIG. 7.

FIG. 9 is a cross-sectional view of a hollow flexible circuit board according to a second 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, and structure of the hollow flexible circuit board and the manufacturing method provided by the present invention are described below with reference to FIGS. 1-10 and the preferred embodiments. The features and their effects are explained in detail below.

Referring to FIG. 1, a first embodiment of the present invention provides a hollow flexible circuit board 100. The hollow flexible circuit board 100 includes a conductive circuit layer 16 and a photosensitive resin layer 13 formed on one surface of the conductive circuit layer 16. And a cover film layer 17 formed on the surface of the conductive circuit layer 16 away from the photosensitive resin layer 13.

The conductive circuit layer 16 includes at least one conductive circuit 161, a plurality of first bonding pads 162 and at least one second bonding pad 163.

In this embodiment, the first pad 162 is a gold finger.

The photosensitive resin layer 13 includes a first surface 131 and a second surface 132 opposite to the first surface 131. The first surface 131 faces the conductive circuit layer 16. Specifically, the conductive line 161 and the second solder pad 163 are both formed on the first surface 131.

A plurality of first openings 133 are also formed on the photosensitive resin layer 13. The first openings 133 correspond to the first pads 162, and each of the first pads 162 is exposed from the first opening 133. That is to say, the adjacent first pad 162 is protected by a photosensitive resin layer 13, which can not only enhance the toughness of the hollow flexible circuit board 100, but also reduce the occurrence of the hollow flexible circuit board 100 in the manufacturing process. The chance of creases, thereby improving the quality of the product. It can also make the hollow flexible circuit board 100 difficult to delaminate during the thermal process, thereby increasing the reliability of the product.

An end surface of the first solder pad 162 away from the cover film layer 17 is flush with the second surface 132. Define the thickness of the conductive line 161 as H1, the thickness of the first pad 162 as H2, the thickness of the second pad 163 as H3, and the thickness of the photosensitive resin layer 13 as H4, then H2> H1> H3, Among them, H2 = H1 + H4.

The material of the photosensitive resin layer 13 may be a photosensitive flexible material such as a photosensitive polyimide (PI) or a photosensitive cover-lay (CVL). In this embodiment, the material of the photosensitive resin layer 13 is photosensitive polyimide.

The cover film layer 17 includes a third opening 171, and at least one of the second pads 163 is exposed from the third opening 171.

The first solder pad 162 and the second solder pad 163 are used for mounting electronic components.

In addition, the first embodiment of the present invention also provides a method for manufacturing a hollow flexible circuit board 100, which includes the following steps:

The first step, referring to FIG. 2, is to provide 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 opposite surfaces of the base layer 11 respectively.

Wherein, the base layer 11 is flexible, and its material is usually selected from polyimide (PI), polyethylene terephthalate (PET), or polyethylene naphthalate. (Polyethylene Naphthalate (PEN)), polyethylene (PE), Teflon, liquid crystal polymer (LCP), polyvinyl chloride polymer (PVC), etc. . In this embodiment, the material of the base layer 11 is PET.

An adhesive layer or a release film layer (not shown) is also formed between the two opposite surfaces of the base layer 11 and the copper foil layer 12.

In this embodiment, an adhesive layer is further formed between two opposite surfaces of the base layer 11 and the copper foil layer 12, and the adhesive layer is preferably a pressure-sensitive adhesive.

In the second step, referring to FIG. 2, a photosensitive resin layer 13 is respectively formed on the surfaces of the two copper foil layers 12 away from the base layer 11.

The photosensitive resin layer 13 includes a first surface 131 and a second surface 132 opposite to the first surface. The first surface 131 faces the copper foil layer 12.

A plurality of first openings 133 are formed in the photosensitive resin layer 13. The first openings 133 penetrate the photosensitive resin layer 13, and a portion of the copper foil layer 12 is exposed from the first openings.

The method for forming the photosensitive resin layer 13 includes the following steps: first, the photosensitive resin is formed on the surface of the copper foil layer 12 away from the base layer 11 by coating or printing; second, by pre-baking The photosensitive resin is cured in a manufacturing process; again, at least one first opening 133 is formed at a predetermined position (pad region) of the photosensitive resin through an exposure and development process, and then the photosensitive resin layer 13 is formed.

In the third step, referring to FIG. 4, a copper-plated layer 14 is formed on the surface of the photosensitive resin layer 13 away from the base layer 11 and in the first opening 133.

The copper plating layer 14 can be formed by electroless copper plating or copper electroplating.

Wherein, the thickness of the copper plating layer 14 is defined as H5, and the thickness of the copper foil layer 12 is H6, and H5 = H1> H6.

In the fourth step, referring to FIG. 5, a photoresist layer 15 is respectively formed on the surfaces of the two copper plating layers 14 away from the photosensitive resin layer 13.

The photoresist layer 15 includes a plurality of second openings 151. Part of the copper plating layer 14 is exposed from the second openings 151. A portion of the photoresist layer 15 corresponding to the pad region is opposite to at least one of the first pads 162.

The method for forming the photoresist layer 15 includes the following steps: First, two dry films are provided and the two dry films are attached to the surfaces of the two copper-plated layers 14 away from the photosensitive resin layer 13 respectively. Secondly, through exposure and development processes, a plurality of the second openings 151 are formed on the dry film to form the photoresist layer 15.

Fifth step, referring to FIG. 6, the copper plating layer 14 exposed from the second opening 151 is etched away by an etching process, and the photoresist layer 15 is removed to form the conductive circuit layer 16.

The conductive circuit layer 16 includes at least one conductive circuit 161, a plurality of first bonding pads 162, and at least one second bonding pad 163.

In this embodiment, the first pad 162 is a gold finger.

In the sixth step, referring to FIG. 7, a cover film layer 17 is formed on a surface of the two conductive circuit layers 16 away from the photosensitive resin layer 13.

The cover film layer 17 includes a third opening 171, and at least one of the second pads 163 is exposed from the third opening 171.

In a seventh step, referring to FIG. 8, the base layer 11 between the two copper foil layers 12 is removed to form two flexible circuit substrates 20.

The flexible circuit substrate 20 includes the conductive circuit layer 16, the photosensitive resin layer 13, the cover film layer 17 and the copper foil layer 12.

In the eighth step, referring to FIG. 1, the copper foil layer 12 is slightly etched away by a copper reduction process, so that the photosensitive resin layer 13 is exposed, thereby forming the hollow flexible circuit board 100.

Wherein, an end surface of the first solder pad 162 away from the cover film layer 17 is flush with the second surface 132.

During the copper reduction process, the second solder pad 163 is also slightly etched away, but because the thickness of the copper foil layer 12 is smaller than the thickness of the copper plating layer 14, the thickness of the second solder pad 163 is smaller than that The thickness of the conductive line 161. That is, H2> H1> H3, and H2 = H1 + H4.

The second embodiment of the present invention provides a hollow flexible circuit board 200. The structure and manufacturing method of the hollow flexible circuit board 200 are basically the same as the hollow flexible circuit board 100. The difference is that the third opening of the hollow flexible circuit board 200 The position of 271 is opposite to the position of the first solder pad 262 of the hollow flexible circuit board 200, and the second solder pad 262 of the hollow flexible circuit board 200 is far from the second of the photosensitive resin layer 23 of the hollow flexible circuit board 200. An end surface of the surface 232 is exposed from the third opening 271 of the hollow flexible circuit board 200. That is, the end surface of the first solder pad 262 of the hollow flexible circuit board 200 far from the second surface 232 of the photosensitive resin layer 23 is the second solder pad 263 of the hollow flexible circuit board 200.

Compared with the prior art, the hollow flexible circuit board provided by the present invention and the manufacturing method thereof are 1) a relatively short production process; 2) two hollow flexible circuit boards can be manufactured simultaneously, and the production efficiency is high; 3) the first welding at the hollow There is a dielectric layer (photosensitive resin layer) for protection between the pads (circuits), which can not only enhance the toughness of the hollow flexible circuit board, reduce creasing marks, improve product quality, but also make the hollow flexible circuit board difficult to undergo during thermal processing Layering reduces line failure rate and increases product reliability.

The above description is only the preferred embodiment of the present invention, and is not a limitation on the form of the present invention. Although the present invention is the preferred embodiment disclosed above, it is not intended to limit the present invention, and any skilled person familiar with the art Without departing from the scope of the technical solution of the present invention, when the above disclosed technical content can be used to make a few changes or modifications to equivalent equivalent implementations, any Any simple modifications, equivalent changes, and modifications made to the above embodiments according to the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims (9)

A hollow flexible circuit board includes a conductive circuit layer and a photosensitive resin layer formed on a surface of the conductive circuit layer. The conductive circuit layer includes a plurality of first pads, at least one conductive circuit, and at least one second For a solder pad, the photosensitive resin layer includes a first surface and a second surface opposite to the first surface. The first surface faces the conductive circuit layer, and a plurality of photosensitive resin layers are formed on the photosensitive resin layer. A first opening, each of the first pads is exposed from each of the first openings, and a photosensitive resin layer is protected between the adjacent first pads, the second surface and the first pads One end surface away from the conductive circuit layer is flush; the conductive circuit and the second pad are formed on the first surface, and the thickness of the conductive circuit is smaller than the thickness of the first pad and larger than the second pad The thickness of the first pad is equal to the sum of the thickness of the photosensitive resin layer and the thickness of the conductive circuit. The hollow flexible circuit board according to claim 1, wherein the hollow flexible circuit board further includes a cover film layer formed on a surface of the conductive circuit layer away from the photosensitive resin layer, and the cover film layer includes A third opening, and each of the second pads is exposed from the third opening. The hollow flexible circuit board according to claim 2, wherein a position of the third opening is opposite to a position of the first pad, and an end surface of the first pad away from the second surface is from the third opening. Inside exposed. A method for manufacturing a hollow flexible circuit board includes the following steps: providing a double-sided copper-clad substrate including a base layer and two copper foil layers respectively formed on two opposite surfaces of the base layer; and two copper foils A photosensitive resin layer is formed on the surface of the layer, and a plurality of first openings are formed on the photosensitive resin layer. The photosensitive resin layer includes a first surface and a second surface opposite to the first surface. The first surface faces the copper foil layer; a copper plating layer is formed on the second surface of the photosensitive resin layer and the plurality of first openings; two conductive copper plating layers are formed to form a conductive circuit layer; The conductive circuit layer includes a first solder pad, at least one conductive circuit, and at least one second solder pad. Part of the first solder pad is located in the first opening, and the photosensitive type is disposed between adjacent first solder pads. Protected by a resin layer, the conductive line and the second pad are both formed on the first surface. The thickness of the conductive line is less than the thickness of the first pad and greater than the thickness of the second pad. The first pad The thickness is equal to the photosensitive resin layer and the guide The sum of the thickness of the circuit; removing the base layer to form two flexible circuit substrates; the flexible circuit substrate including the conductive circuit layer, the photosensitive resin layer, and a copper foil layer; and removing the copper foil layer so that the second surface It is flush with an end surface of the first pad away from the conductive circuit layer. The method for manufacturing a hollow flexible circuit board according to item 4 of the claim, wherein the method for forming the photosensitive resin layer includes the following steps: forming the photosensitive resin on the copper foil layer away from the copper foil layer by coating or printing. On the surface of the base layer; curing the photosensitive resin through a pre-baking process; and forming at least one first opening in a predetermined position (pad region) of the photosensitive resin through an exposure and development process. The method for manufacturing a hollow flexible circuit board according to item 4 of the claim, wherein the thickness of the copper plating layer is greater than the thickness of the copper foil layer. The method for manufacturing a hollow flexible circuit board according to item 4 of the claim, wherein after the two steps of forming the copper plating layer to form the conductive circuit layer, the step of removing the base layer further includes steps: A covering film layer is formed on a surface of each of the conductive circuit layers away from the photosensitive resin layer; the covering film layer includes a third opening, and at least one second pad is exposed from the third opening. The method for manufacturing a hollow flexible circuit board according to claim 7, wherein the position of the third opening is opposite to the position of the first pad, and the end surface of the first pad away from the second surface is removed from the The third opening is bare. The method for manufacturing a hollow flexible circuit board according to item 4 of the claim, wherein the copper foil layer is removed by a copper reduction process.