CN108260302A - Multi-layer flexible circuit board and preparation method thereof - Google Patents

Abstract

The invention discloses a multilayer flexible circuit board and a preparation method thereof. The multi-layer flexible circuit board includes a base; N-layer conductive lines, the N-layer conductive lines are stacked on one side surface of the base in a direction away from the base and electrically interconnected with each other; N-1 layer isolation layer, and each layer of isolation layer is arranged between every two adjacent layers of conductive lines; wherein, when corresponding to the same electrical interconnection circuit, there is an opening on the N-1th layer of isolation layer for exposing the N-1st layer of conductive lines. A through hole for electrical interconnection, and the projection of the through hole on the isolation layer on the substrate at least partially overlaps; a conductive material is filled in the through hole to realize the electrical properties of the interlayer conductive circuit connect. The invention can be applied to the interconnection between adjacent or non-adjacent conductive lines, not only preventing circuit failure phenomena such as wire cracking and circuit breakage caused by the height difference of the wire layer in the through hole, but also improving the overall flatness of the flexible circuit board.

Description

Multilayer flexible circuit board and its preparation method

technical field

The invention belongs to the technical field of circuit boards, and in particular relates to a multilayer flexible circuit board and a preparation method thereof.

Background technique

Multilayer circuit board is the most basic electronic component in modern electronic equipment, which plays the role of connecting and carrying electronic components. With the continuous development of electronic technology, circuit boards are gradually developing towards high density and flexibility. (1) High density, the line width and line spacing of conductive lines are continuously reduced, the wiring is continuously densified, and the number of layers of circuit boards is also increasing; (2) Flexibility, using flexible films as circuit board substrates to achieve electrical conductivity The winding and bending performance of the line.

However, the current flexible circuit board is basically based on polyimide, and is produced by traditional circuit preparation technology. The production process includes dry film coating-exposure-removal-removal-removal-removal and other process steps. Not only the process is complicated, the waste of raw materials is large, but also it is easy to pollute the environment, which has aroused widespread concern of people. At the same time, the flexible circuit based on polyimide cannot realize the preparation of very thin circuit due to the technical problems in the preparation process, and the general thickness requirement is more than 50um. Modern electronic equipment is increasingly pursuing thinner and lighter, especially the sensitivity of personal consumer products such as mobile phones to thickness and weight, which makes major manufacturers continue to pursue thinner and lighter circuit boards, so flexible circuit boards are also widely used. The use of flexible boards such as Apple's iphone, ipad, Google Glass and other products. Secondly, due to its own folding and winding properties, the flexible circuit board can make the circuit wiring in the product more flexible and convenient, and the product volume and shape design also have greater freedom, which makes the flexible circuit board more and more popular in electronic equipment. more and more widely used.

Due to some limitations in the current process, equipment and technology of flexible circuit boards, it is still difficult to prepare thin and light multi-layer flexible circuits, which restricts the development of thin and light products to a certain extent. And with the development of electronic components in recent years, the components are continuously miniaturized, and the combination with flexible circuits to develop flexible circuit systems with high density, good flexibility and good heat dissipation performance has become an important research direction in this field.

The existing flexible circuit board preparation technology prepares multi-layer flexible circuits by lamination. However, due to the height difference between the upper and lower conductive layers at the point where the interlayer interconnection is conducted, there will be a risk of breaking the interconnection structure of the upper and lower conductive lines, thereby causing circuit failure. Therefore, how to develop a reliable multilayer flexible circuit interlayer interconnection structure and method is an important research content for the development of multilayer flexible circuit boards.

Contents of the invention

In order to solve the above-mentioned problems in the prior art, the object of the present invention is to provide a multi-layer flexible circuit board and a preparation method thereof which enable reliable electrical connection of each layer of conductive circuits.

The invention provides a multi-layer flexible circuit board, which includes: a base; N-layer conductive lines, the N-layer conductive lines are stacked on one side surface of the base in a direction away from the base and electrically connected to each other Interconnection; N-1 layer of isolation layer, each layer of isolation layer is arranged between every two adjacent layers of conductive lines; wherein, when corresponding to the same electrical interconnection circuit, there are holes on the N-1th layer of isolation layer for exposure The through hole used for electrical interconnection in the N-1th layer of conductive circuit, and the projection of the through hole on the isolation layer on the substrate at least partially overlaps; the conductive material is filled in the through hole to Realize the electrical connection of the conductive lines between the layers.

Further, the area of the via holes on the N-1th isolation layer corresponding to the same electrical interconnection path is greater than the area of the via holes on the N-2th isolation layer.

Further, the projection of the through hole on the N-2th isolation layer corresponding to the same electrical interconnection path on the substrate is located within the projection of the through hole on the N-1th isolation layer on the substrate .

Further, the projections of the through holes corresponding to the same electrical interconnection path on the substrate are concentric with each other.

Further, the through hole on the isolation layer has a circular shape, and the diameter of the through hole is 0.1mm˜8mm.

Further, the isolation layer is formed of a polymer film material with a dense structure and has electrical insulation, and/or the thickness of the isolation layer is 2um˜125um.

Further, the Nth layer conductive circuit is arranged around the through hole on the N-1th layer isolation layer.

Further, the difference between the edge thickness of the through hole on each isolation layer and the thickness of the isolation layer is less than 5um.

The present invention also provides a method for preparing the above-mentioned multilayer flexible circuit board, which includes:

forming N-layer conductive circuits on one side surface of the substrate, the N-layer conductive circuits are stacked in a direction away from the substrate and electrically interconnected with each other;

N-1 layers of isolation layers are formed, and each layer of isolation layers is arranged between every two adjacent layers of conductive circuits; wherein, when corresponding to the same electrical interconnection circuit, there are holes on the N-1 layer isolation layer for exposing the Nth layer. - through holes for electrical interconnection in layer 1 conductive lines, and the projections of the through holes on the isolation layer on the substrate at least partially overlap;

The conductive material is filled in the through hole to realize the electrical connection of the interlayer conductive circuit.

Further, the via hole technology is used to fill the conductive material in the through hole, so as to realize the electrical connection of different interlayer conductive lines.

Beneficial effects of the present invention: the multilayer flexible circuit and its preparation method of the present invention can realize the interconnection between multilayer conductive lines, not limited to the interconnection between adjacent upper and lower layer conductive lines, and make each layer of conductive lines have reliable The electrical connection reduces the risk of fracture failure of the interconnection structure due to the height difference between the upper and lower layers. In addition, the multi-layer flexible circuit and its preparation method can also realize the interconnection of lines between layers with a large depth, and improve the overall flatness of the flexible circuit board.

Description of drawings

The above and other aspects, features and advantages of embodiments of the present invention will become more apparent through the following description in conjunction with the accompanying drawings, in which:

Fig. 1 is the sectional view of the multilayer flexible circuit board of the embodiment of the present invention;

2 is a schematic structural view of a multilayer flexible circuit board according to an embodiment of the present invention;

3 is a flow chart of the steps of the method for preparing a multilayer flexible circuit board according to an embodiment of the present invention;

4 to 7 are the flow charts of the preparation of the multi-layer flexible circuit board according to the embodiment of the present invention.

Detailed ways

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the specific embodiments set forth herein. Rather, these embodiments are provided to explain the principles of the invention and its practical application, so that others skilled in the art can understand various embodiments of the invention and various modifications as are suited to particular intended uses. The same reference numerals may be used to refer to the same elements throughout the specification and drawings.

In the drawings, the thicknesses of layers and regions are exaggerated for clear illustration of components.

FIG. 1 is a cross-sectional view of a multilayer flexible circuit board according to an embodiment of the present invention. FIG. 2 is a schematic structural diagram of a multilayer flexible circuit board according to an embodiment of the present invention.

Referring to FIG. 1 , a multilayer flexible circuit board according to an embodiment of the present invention includes a substrate 1 , conductive lines 2 , isolation layers 3 , and conductive materials 4 .

The thickness of the substrate 1 is 15 μm. Preferably, in this embodiment, the thickness of the substrate 1 is 10 μm.

The N-layer conductive lines 2 are stacked on one side of the substrate 1 in a direction away from the substrate 1 and electrically interconnected with each other.

The number of isolation layers 3 is N-1 layers. Each layer of isolation layer 3 is disposed between every two adjacent layers of conductive circuits 2 . Wherein, when corresponding to the same electrical interconnection path, a through hole 3a for exposing the electrical interconnection part in the conductive circuit 2 of the N-1th layer is opened on the N-1th layer isolation layer 3, and the isolation layer 3 The projections of the through holes 3a on the substrate 1 at least partially overlap. Here, N is greater than or equal to 3, and N is a positive integer, that is to say, the number of isolation layers 3 may be two, three or more than three, and the present invention is not limited thereto. It should be noted that the "N-1th layer isolation layer 3 is provided with a through hole 3a for exposing the N-1th layer conductive circuit 2 for electrical interconnection" refers to the N-1st The through hole on the first layer of isolation layer 3 makes the part of the N-1th layer of conductive circuit 2 that is approximately parallel to the substrate and farther away from the substrate for electrical interconnection not isolated by the N-1th layer layer 3; in some embodiments, the multilayer flexible circuit board of the present application may be manufactured to have non-planar structural features in the initial state, and this similar situation is also applicable to the above-mentioned through holes and The characteristic definition of the structural relationship of the electrical interconnection part in the wire circuit.

In general, two or more isolation layers 3 are sequentially stacked and formed on the side of the first-layer conductive circuit 2 away from the substrate 1 . The through hole 3a is opposite to the conductive circuit that needs to be connected to expose the conductive circuit 2 that needs to be interconnected, and the area of the through hole on the N-1 layer isolation layer 3 corresponding to the same electrical interconnection circuit is larger than that of the N-2 layer isolation layer. The area of the via hole on layer 3, so that the conductive lines that need to be interconnected are partially exposed.

When interconnecting adjacent multilayer lines 2, the projection of the through hole 3a on the N-2th layer isolation layer 3 corresponding to the same electrical interconnection path on the substrate 1 is located on the N-1th layer isolation layer 3 The through hole 3a is within the projection on the substrate 1 . Preferably, in this embodiment, when adjacent multilayer circuits 2 are interconnected, the projections of the through holes 3 a corresponding to the same electrical interconnection path on the substrate 1 are concentric with each other. The through hole 3 a on the isolation layer 3 is in a circular shape, and the diameter of the through hole 3 a may be 0.1 mm˜8 mm. But the present invention is not limited thereto, and the through hole 3a may also be square or other. Specifically, through-holes 3 a are prepared on the isolation layer 3 by means of mechanical drilling for circuit interconnection, and the edges thereof are smooth and flat. The edge thickness of the through hole 3a may be due to abrasion or thinning during mechanical drilling. In order to ensure the flatness of the isolation layer 3 , in this embodiment, the difference between the edge thickness of the through hole 3 a and the thickness of the isolation layer 3 is less than 5 um.

The isolation layer 3 is made of a polymer film material with a dense structure and has electrical insulation properties, and its thickness is 2um-125um. The surface of the isolation layer 3 is coated with an easy-adhesion layer, the surface tension of which is greater than 45 dyne, and the thickness is less than 1um.

The N-th layer conductive circuit 2 is disposed around the through hole 3 a on the N-1-th layer isolation layer 3 . Generally, the conductive lines 3 of the Nth layer are just routed around the edge of the through hole 3a of the isolation layer of the N-1th layer, but the present invention is not limited thereto, and the conductive lines 3 can be laid out according to actual wiring needs. The conductive circuit 3 is made of nano-gold, nano-silver, nano-copper, nano-aluminum and metal alloy materials. The conductive circuit is patterned by printing technology, which can be formed by screen printing, gravure printing, inkjet printing, flexographic printing, transfer printing or aerosol printing.

It should be noted that through the through hole 3 a on the isolation layer 3 , the conductive lines of any layer can be electrically connected, not limited to the interconnection between the adjacent upper and lower layer conductive lines. As another embodiment of the present invention, for example, when it is necessary to realize the interconnection between the upper and lower conductive lines that are not adjacent, for example, when realizing the electrical connection of the conductive lines on the first isolation layer and the third isolation layer, Similarly, through holes are opened on the conductive lines on the first isolation layer, the second isolation layer and the third isolation layer, and the conductive lines are arranged in the adjacent places of the through holes on the first isolation layer and the third isolation layer. , but no conductive lines are laid on the adjacent through holes on the second isolation layer.

The conductive material 4 is filled in the through hole 3 a to realize the electrical connection of the conductive circuits on different isolation layers 3 . The conductive material 4 is specifically made of silver conductive paste with high solid content, and is filled in the interconnection blind hole by using the plug hole technology, so that the interconnection of the conductive lines between the upper and lower layers is electrically conducted, and prevents the gap between the layers of the conductive lines in the blind hole from being And the conductive material 4 is filled incorrectly to cause circuit failure.

FIG. 3 is a flow chart of the steps of the method for manufacturing a multilayer flexible circuit board according to an embodiment of the present invention.

Referring to FIG. 1 , FIG. 2 and FIG. 3 , the embodiment of the present invention also provides a method for connecting multilayer flexible circuit boards. Described method specifically comprises the following steps:

Step 210: forming N-layer conductive circuits on one side of the substrate, the N-layer conductive circuits are stacked in a direction away from the substrate and electrically interconnected with each other.

Step 220: Forming N-1 layers of isolation layers, each layer of isolation layers is arranged between every two adjacent layers of conductive lines; wherein, when corresponding to the same electrical interconnection circuit, there are holes on the N-1th layer of isolation layers for The via holes used for electrical interconnection in the N-1th layer of conductive circuits are exposed, and the projections of the via holes on the isolation layer on the substrate at least partially overlap.

Step 230 : Fill the via hole with conductive material to realize the electrical connection of the interlayer conductive circuit.

Preferably, the conductive material is filled in the through hole by plugging technology, so as to realize the electrical connection of different interlayer conductive lines.

In addition, another layer of isolation layer can be formed on the last layer of conductive lines to protect the conductive lines. But the present invention is not limited thereto.

The preparation process of the multi-layer flexible circuit board will be further described below in conjunction with specific examples. 4 to 7 are the flow charts of the preparation of the multi-layer flexible circuit board according to the embodiment of the present invention.

As shown in FIG. 4 , when preparing a three-layer flexible circuit board, firstly, the nano-silver conductive material is patterned and deposited on the substrate 1 by means of inkjet printing (Dimatix3000), and the material deposition thickness is controlled by the number of times of printing. After curing and sintering in a convection oven at 130° C. for 20 minutes, the first conductive circuit 21 is formed, and the thickness of the first conductive circuit 21 after sintering is 5 μm. The substrate is a flexible substrate, specifically a PET film with a thickness of 15um.

As shown in FIG. 5 , a first isolation layer 31 having through holes is formed on the first-layer conductive circuit 21 . The diameter of the through hole of the first isolation layer 31 is 0.1 mm. The through hole of the first isolation layer 31 is opposite to the first-layer conductive circuit 21 to be interconnected, so that the first conductive circuit 21 to be interconnected is exposed. On the first isolation layer 31 , the second layer of conductive lines 22 is formed after patterning the ink-jet conductive nano-silver material.

As shown in FIG. 6 , the second isolation layer 32 having through holes is attached. The diameter of the through hole of the second isolation layer 32 is larger than the diameter of the through hole of the first isolation layer 31 , and the diameter of the through hole of the second isolation layer 32 is larger than that of the first isolation layer 31 . Specifically, the diameter of the through hole of the second isolation layer 32 is 0.2 mm. Because the diameter of the through hole of the second isolation layer 32 is larger than the diameter of the through hole of the first isolation layer 31, the conductive circuit facing the second through hole on the first isolation layer 31 is exposed, which facilitates the interconnection of the interlayer circuit . After patterning the inkjet conductive nano-silver material on the second isolation layer 32 , the third layer of conductive circuit 23 is obtained.

Finally, the high-solid-content silver conductive paste is filled in the through holes of the above-mentioned two-layer isolation layer by plugging technology, so that the first layer of conductive lines 21, the second layer of conductive lines 22, and the third layer of conductive lines 23 are interconnected. Electrical conduction.

In the same principle, as shown in FIG. 7 , when preparing a four-layer conductive circuit board, after forming the third-layer conductive circuit 23 , continue to attach the third isolation layer 33 with through holes on the third-layer conductive circuit 23 . After the patterned inkjet conductive nano-silver material is passed on the third isolation layer 33 , the fourth layer of conductive circuit 24 is obtained. Finally, the high-solid-content silver conductive paste is filled into the blind interconnection holes formed by the through-holes of the above-mentioned three-layer isolation layer by using plug hole technology, so that the interconnection between the four-layer conductive lines is electrically conducted. It should be noted that the diameter of the through hole on the third isolation layer 33 is larger than the diameter of the through hole on the second isolation layer 32 , and its diameter is 0.3 mm. Whereas interlayer interconnection is not required, the first isolation layer 31 , the second isolation layer 32 and the third isolation layer 33 may be used to cover to form an insulating layer. Since the conductive circuit is prepared by ink-jet printing, its thickness is in the order of um, and there is a certain height difference in the through holes of the first isolation layer 31, the second isolation layer 32 and the third isolation layer 33. Ink-jet printing It is impossible to make the conductive material fill the interconnection blind holes, which may easily cause connection discontinuity, cracks and other phenomena when interlayer lines are interconnected, resulting in failure of circuit performance. Therefore, for multi-layer flexible circuits, plug hole technology is finally used to fill the high-solid silver conductive paste in the interconnection blind holes (as shown in Figure 1), so that the conductive paste fills the interconnection blind holes, so that each The conductive circuit layer realizes reliable electrical connection and prevents false filling caused by the height difference between the conductive circuit layers.

To sum up, the multi-layer flexible circuit and its preparation method according to the embodiment of the present invention use a flexible film as the material for the isolation layer between the substrate and adjacent circuit layers, and the prefabricated through holes on the isolation layer are used for the interconnection between the upper and lower conductive circuits; and At the interconnection of multi-layer conductive lines, the diameter of the through hole of the outer isolation layer is larger than the diameter of the through hole of the inner isolation layer, and exposes the conductive lines that need to be interconnected in the underlying circuit. The conductive circuit on the flexible circuit board is prepared by printing technology, and the conductive paste is filled in the through hole by plugging technology. The multilayer flexible circuit board prepared by this method can obtain reliable interlayer interconnection and prevent circuit failure phenomena such as wire cracking and circuit breakage caused by the height difference of the wire line in the through hole, and is suitable for interconnection of multilayer flexible circuit boards. in structure. In addition, the embodiments of the present invention are not limited to the interconnection between adjacent upper and lower layers of circuits, and can realize the interconnection of circuits between layers with a large depth, and improve the overall flatness of the flexible circuit board.

While the invention has been shown and described with reference to particular embodiments, it will be understood by those skilled in the art that changes may be made in the form and scope thereof without departing from the spirit and scope of the invention as defined by the claims and their equivalents. Various changes in details.

Claims (10)

1. A multilayer flexible circuit board, characterized in that, comprising: base; N-layer conductive lines, the N-layer conductive lines are stacked on one side surface of the base in a direction away from the base and electrically interconnected with each other; N-1 layer of isolation layer, each layer of isolation layer is arranged between every two adjacent layers of conductive lines; wherein, when corresponding to the same electrical interconnection circuit, there are holes on the N-1th layer of isolation layer for exposing the N-th A through hole for an electrical interconnection part in a layer 1 conductive circuit, and the projection of the through hole on the isolation layer on the substrate at least partially overlaps; The conductive material is filled in the through hole to realize the electrical connection of the interlayer conductive circuit. 2. The multilayer flexible circuit board according to claim 1, wherein the area of the through hole on the N-1th isolation layer corresponding to the same electrical interconnection path is larger than that on the N-2th isolation layer. Via area. 3. The multilayer flexible circuit board according to claim 2, wherein the projection of the through hole on the substrate on the N-2th isolation layer corresponding to the same electrical interconnection path is located at the N-th The vias on the 1-layer isolation layer are in projection on the substrate. 4 . The multilayer flexible circuit board according to claim 1 , wherein the projections of the through holes corresponding to the same electrical interconnection path on the substrate are concentric with each other. 5 . The multilayer flexible circuit board according to claim 1 , wherein the through hole is in a circular shape, and the diameter of the through hole is 0.1 mm˜8 mm. 6. The multilayer flexible circuit board according to claim 1, characterized in that, the isolation layer is formed by a polymer film material with a dense structure, and has electrical insulation, and/or the thickness of the isolation layer is 2um～125um. 7 . The multi-layer flexible circuit board according to claim 1 , wherein the Nth layer conductive circuit is arranged around the through hole on the N-1th layer isolation layer. 8 . 8 . The multilayer flexible circuit board according to claim 1 , wherein the difference between the edge thickness of the through hole on each isolation layer and the thickness of the isolation layer is less than 5 um. 9. A method for preparing the multilayer flexible circuit board according to any one of claims 1 to 8, characterized in that, comprising: forming N-layer conductive circuits on one side surface of the substrate, the N-layer conductive circuits are stacked in a direction away from the substrate and electrically interconnected with each other; N-1 layers of isolation layers are formed, and each layer of isolation layers is arranged between every two adjacent layers of conductive circuits; wherein, when corresponding to the same electrical interconnection circuit, there are holes on the N-1 layer isolation layer for exposing the Nth layer. - through holes for electrical interconnection in layer 1 conductive lines, and the projections of the through holes on the isolation layer on the substrate at least partially overlap; The conductive material is filled in the through hole to realize the electrical connection of the interlayer conductive circuit. 10 . The method for preparing a multi-layer flexible circuit board according to claim 9 , wherein the via hole technology is used to fill the conductive material into the through hole, so as to realize the electrical connection of the conductive circuits between different layers. 11 .