Flexible circuit board with gold fingers and method of making same

Abstract

This invention discloses a flexible circuit board with gold fingers and its manufacturing method. The method includes: providing a double-sided flexible substrate; setting a gold finger region on the double-sided flexible substrate and setting a copper retention region at the outer edge of the gold finger region on the waste area of ​​the double-sided flexible substrate; etching the double-sided flexible substrate based on the gold finger region and the copper retention region to form a first processed double-sided substrate; bonding protective films to both sides of the first processed double-sided substrate excluding the gold finger region to form a second processed double-sided substrate; and sequentially performing immersion gold plating and punching on the second processed double-sided substrate according to the gold finger region to obtain the target flexible circuit board. This invention reduces the etching stress on the gold finger outer edge by laying copper in the waste area at the edge of the gold finger, avoiding the fact that the waste area at the edge of the ZIF is all PI without copper, effectively solving the problem that PI with low tensile strength and tensile modulus is prone to breakage when used as FCCL to manufacture ZIF.

Description

Technical Field

[0001] This invention relates to the field of flexible circuit board manufacturing technology, specifically to a flexible circuit board with gold fingers and its manufacturing method. Background Technology

[0002] Flexible copper clad laminate (FCCL) is the substrate material for flexible printed circuits (FPCs), composed of a flexible insulating base film and metal foil. FCCLs using polyimide (PI) base film possess excellent electrical, thermal, and heat resistance properties. Its low dielectric constant (Dk) allows for rapid signal transmission; its good thermal properties facilitate component cooling; and its high glass transition temperature (Tg) allows for optimal component operation at higher temperatures. Therefore, PI-based FCCLs are widely used in the fabrication of flexible printed circuits.

[0003] In the field of flexible circuit board manufacturing, the connecting finger (ZIF) refers to the connecting component formed on the flexible circuit board for connecting slots. All signals are transmitted through the connecting finger, so the ZIF is crucial to the performance of the flexible circuit board.

[0004] ZIF (Zero-Insulated Interchange) is typically formed by electroplating or electroless plating onto a PI-based FCCL (Fused-Insulated Copper Cladding), followed by a gold coating. During ZIF formation, if the tensile strength and tensile modulus of the PI in the FCCL are low—for example, Kaneka's FRS (Fused-Insulated Steel Reinforced Plastic) with a 25µm thick PI and 35µm thick HA (High-Altitude Copper) FCCL has a tensile strength of 167MPa and a tensile modulus of 4.5Gpa—which is lower than other manufacturers like Arisawa, DuPont, and Doosan—then the PI in this type of FCCL is more brittle and less resistant to acid and alkali attacks. When this type of FCCL is used in ZIF fabrication, PI fractures are found at the ZIF edges after etching the circuitry. Figure 1 and Figure 2 As shown, in Figure 1 and Figure 2 In the diagram, 1 represents the copper foil, 2 represents the PI layer, 3 represents the gold fingers, and 4 represents the PI fracture point. After the protective film is applied, the PI fracture becomes more severe, with a 100% fracture rate. Optimizing the etching parameters cannot improve this anomaly.

[0005] Therefore, the problem of PI fracture that occurs when using PI with such low tensile strength and tensile modulus as FCCL to manufacture ZIF urgently needs to be solved. Summary of the Invention

[0006] In view of this, embodiments of the present invention provide a flexible circuit board with gold fingers and a method for manufacturing the same, in order to solve the problem of PI breakage that occurs when using PI with lower tensile strength and tensile modulus as FCCL to manufacture ZIF in the prior art.

[0007] This invention provides a method for manufacturing a flexible circuit board with gold fingers, comprising:

[0008] Provides double-sided flexible substrates;

[0009] A gold finger area is formed on the double-sided flexible substrate, and a copper retention area is formed on the waste area of ​​the double-sided flexible substrate at the outer edge of the gold finger area.

[0010] Based on the gold finger area and the copper retention area, the double-sided flexible substrate is etched to form a first processed double-sided substrate;

[0011] Protective films are attached to both sides of the first processed double-sided substrate, excluding the gold finger area, to form a second processed double-sided substrate.

[0012] According to the gold finger area, the second processed double-sided substrate is sequentially subjected to immersion gold plating and die cutting to obtain the target flexible circuit board.

[0013] Optionally, the gold finger region includes multiple parallel gold finger immersion gold areas, and each gold finger immersion gold area has the same length.

[0014] Optionally, the copper retention area includes a first sub-copper retention area, a second sub-copper retention area, and a third sub-copper retention area located at the outer edge of the gold finger area on the waste area of ​​the double-sided flexible substrate;

[0015] The first sub-copper retention area, the second sub-copper retention area, and the third sub-copper retention area are connected in sequence, and the first sub-copper retention area and the third sub-copper retention area are arranged opposite to each other.

[0016] Optionally, the length of the first sub-copper retention area and the length of the third sub-copper retention area are the same, and the length of the first sub-copper retention area and / or the length of the third sub-copper retention area are greater than the length of the gold finger immersion gold area.

[0017] Optionally, the difference between the length of the first sub-copper retention area and the length of the gold finger immersion gold area is greater than or equal to 0.5 mm, and / or the difference between the length of the third sub-copper retention area and the length of the gold finger immersion gold area is greater than or equal to 0.5 mm.

[0018] Optionally, the width of the first sub-copper retention area and the width of the third sub-copper retention area are the same, and the width of the first sub-copper retention area and / or the width of the third sub-copper retention area are greater than or equal to 0.3 mm.

[0019] Optionally, the distance between the first sub-copper retention area, the second sub-copper retention area and the third sub-copper retention area and the outer edge of the gold finger area is greater than or equal to 0.2 mm.

[0020] Optionally, the width of the second sub-copper region is greater than or equal to 0.3 mm.

[0021] Optionally, the etching of the double-sided flexible substrate based on the gold finger region and the copper retention region to form a first processed double-sided substrate includes:

[0022] Based on the gold finger area and the copper retention area, the copper layers on both sides of the double-sided flexible substrate are etched respectively, so that the copper layers on both sides of the double-sided flexible substrate, excluding the gold finger area and the copper retention area, are etched away to form the first processed double-sided substrate.

[0023] In addition, the present invention also provides a flexible circuit board with gold fingers, which is manufactured using the aforementioned manufacturing method.

[0024] The beneficial effects of this invention are as follows: A gold finger region is formed on a double-sided flexible substrate for fabricating the gold fingers of a flexible circuit board; a copper retention region is formed at the outer edge of the gold finger region on the waste area of ​​the double-sided flexible substrate, making full use of the copper layer in the waste area; etching is performed based on the gold finger region and the copper retention region, achieving copper retention at the outer edge of the gold finger; compared with traditional flexible circuit boards with gold fingers, it is easier to reduce the etching stress on the outer edge of the gold finger by laying copper in the waste area at the outer edge of the gold finger after subsequent immersion gold and die cutting, avoiding the phenomenon that the waste area at the edge of the ZIF is all PI without copper, and thus the stress concentration at the edge causes the PI to easily break during etching. This effectively solves the problem that PI is brittle and prone to breakage when using PI with lower tensile strength and tensile modulus as FCCL to make ZIF, and broadens the application range of using PI with lower tensile strength and tensile modulus as FCCL, with good application prospects. Attached Figure Description

[0025] The features and advantages of the invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the invention in any way. In the drawings:

[0026] Figure 1The diagram shows a top view of the PI fracture structure when using PI with lower tensile strength and tensile modulus as FCCL to fabricate ZIF in the prior art.

[0027] Figure 2 This diagram shows a cross-sectional view of the PI fracture structure when using PI with lower tensile strength and tensile modulus as FCCL to fabricate ZIF in the prior art.

[0028] Figure 3 A flowchart of a method for manufacturing a flexible circuit board with gold fingers according to Embodiment 1 of the present invention is shown;

[0029] Figure 4 This diagram shows a cross-sectional view of the double-sided flexible substrate in Embodiment 1 of the present invention.

[0030] Figure 5 This is a top view of the layout of the gold finger area and its corresponding multiple gold finger immersion gold areas in Embodiment 1 of the present invention.

[0031] Figure 6 This shows a schematic diagram of the copper-retaining area design in Embodiment 1 of the present invention;

[0032] Figure 7 This shows a top view of the structure of the first processed double-sided substrate after S3 etching in Embodiment 1 of the present invention.

[0033] Figure 8 This shows a top view of the structure of the second-processed double-sided substrate after S4 film application in Embodiment 1 of the present invention.

[0034] Figure 9 This shows a top view of the structure of the second-processed double-sided substrate after S5 immersion gold plating in Embodiment 1 of the present invention.

[0035] Figure 10 The diagram shows a top view of the target flexible circuit board obtained after the shape is punched by S5 in Embodiment 1 of the present invention.

[0036] Explanation of reference numerals in the attached figures:

[0037] 1. Copper foil, 2. PI layer, 3. Gold fingers, 4. PI fracture point, 5. Protective film;

[0038] 100. Gold finger area; 101. Gold finger gold-plated area; 102. The outer edge of the gold finger area;

[0039] 200. Waste Area;

[0040] 300, Copper Retention Area; 301, First Sub-Copper Retention Area; 302, Second Sub-Copper Retention Area; 303, Third Copper Retention Area. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Example 1

[0043] A method for manufacturing a flexible circuit board with gold fingers, such as... Figure 3 As shown, it includes the following steps:

[0044] S1 provides a double-sided flexible substrate.

[0045] Specifically, the double-sided flexible substrate is a flexible copper-clad laminate (FCCL) composed of double-layer copper foil and a flexible insulating base film (PI layer), with the double-layer copper foil located on both sides of the flexible insulating base film (PI layer), such as... Figure 4 As shown, in Figure 4 In the diagram, 1 represents copper foil and 2 represents the PI layer.

[0046] like Figure 3 As shown in Figure S2, a gold finger region is formed on the double-sided flexible substrate, and a copper retention region is formed on the waste area of ​​the double-sided flexible substrate at the outer edge of the gold finger region.

[0047] The above-mentioned S2 defines the gold finger area for subsequent gold plating to form the gold fingers in the target flexible circuit board, and also defines the copper retention area for etching on the double-sided flexible substrate, thereby leaving copper at the outer edge of the gold finger area, which helps to reduce the etching stress on the outer edge of the gold finger during punching, and avoids the phenomenon that the waste area at the edge of the ZIF is full of PI without copper, which causes stress concentration at the edge during etching and makes the PI easy to break.

[0048] Preferably, the gold finger region includes multiple parallel gold finger immersion gold areas, and each gold finger immersion gold area has the same length.

[0049] The gold-plating zones for the gold fingers, arranged in multiple parallel intervals as described above, facilitate the formation of gold fingers for flexible circuit boards of higher quality.

[0050] In this embodiment, the layout diagram of the gold finger area and its corresponding multiple gold finger immersion gold areas is shown below. Figure 5 As shown, in Figure 5 In the diagram, 100 represents the gold finger area, 101 represents the gold finger immersion gold area, 102 represents the outer edge of the gold finger area, and 200 represents the waste area.

[0051] Preferably, the copper retention area includes a first sub-copper retention area, a second sub-copper retention area, and a third sub-copper retention area located at the outer edge of the gold finger area on the waste area of ​​the double-sided flexible substrate;

[0052] The first sub-copper retention area, the second sub-copper retention area, and the third sub-copper retention area are connected in sequence, and the first sub-copper retention area and the third sub-copper retention area are arranged opposite to each other.

[0053] By leaving copper areas as described above, it is possible to lay as much copper as possible at the outer edge of the gold finger area to reduce etching stress and thus minimize the risk of PI breakage caused by etching stress concentration at the outer edge.

[0054] Specifically, the design of the copper-reserved area in this embodiment is as follows: Figure 6 As shown, in traditional technology, the outer edge of the gold finger area does not have a copper retention area, and its structure is as follows: Figure 5 As shown. In Figure 6 In the diagram, 300 represents the copper retention area, 301 represents the first sub-copper retention area, 302 represents the second sub-copper retention area, and 303 represents the third sub-copper retention area.

[0055] Preferably, such as Figure 6 As shown, the length of the first sub-copper retention area and the length of the third sub-copper retention area are the same, and the length of the first sub-copper retention area and / or the length of the third sub-copper retention area are greater than the length of the gold finger immersion gold area.

[0056] By setting the length as described above, it is possible to lay as much copper as possible at the outer edge of the gold finger area, ensuring that the PI at the edge of the gold finger formed after the subsequent gold plating will not break; and it is also possible to etch away as much waste area as possible, thereby improving the quality of the target flexible circuit board.

[0057] Specifically, the difference between the length of the first sub-copper retention area and the length of the gold finger immersion gold area is greater than or equal to 0.5 mm, and / or the difference between the length of the third sub-copper retention area and the length of the gold finger immersion gold area is greater than or equal to 0.5 mm.

[0058] In one specific embodiment, the difference between the length of the first sub-copper retention area and the length of the gold finger immersion gold area is 0.5mm, and the difference between the length of the third sub-copper retention area and the length of the gold finger immersion gold area is also 0.5mm.

[0059] Preferably, the width of the first sub-copper retention area and the width of the third sub-copper retention area are the same, and the width of the first sub-copper retention area and / or the width of the third sub-copper retention area are greater than or equal to 0.3 mm.

[0060] By using the first and / or third sub-copper retention areas with the aforementioned width range, the etching stress on the edge of the gold finger shape can be effectively reduced during punching.

[0061] In one specific embodiment, the width of both the first sub-copper region and the width of the third sub-copper region are 0.3 mm.

[0062] Preferably, the distance between the first sub-copper retention area, the second sub-copper retention area, and the third sub-copper retention area and the outer edge of the gold finger area is greater than or equal to 0.2 mm.

[0063] By using the above spacing, the etching stress on the edge of the gold finger shape can be reduced, avoiding the PI breakage problem caused by only PI and no copper at the edge of the gold finger, and ensuring that the copper foil in the copper-retaining area is not punched during subsequent shape cutting.

[0064] In one specific embodiment, the distance between the first sub-copper retention area, the second sub-copper retention area, and the third sub-copper retention area and the outer edge of the gold finger area is 0.2mm.

[0065] Preferably, the width of the second copper retention area is greater than or equal to 0.3 mm.

[0066] Similar to the first and third sub-copper retention areas, the second sub-copper retention area of ​​the above-mentioned width can better reduce the etching stress on the edge of the gold finger shape during punching. In addition, it can ensure better connection between the second sub-copper retention area and the first and third sub-copper retention areas, reducing the difficulty of etching copper retention.

[0067] In one specific embodiment, the width of the second sub-copper region is 1 mm.

[0068] like Figure 3 As shown, in step S3, based on the gold finger area and the copper retention area, the double-sided flexible substrate is etched to form a first processed double-sided substrate.

[0069] Preferably, S3 includes: etching the copper layers on both sides of the double-sided flexible substrate based on the gold finger region and the copper retention region, so that the copper layers on both sides of the double-sided flexible substrate, excluding the gold finger region and the copper retention region, are etched away to form the first processed double-sided substrate.

[0070] Based on the gold finger area and the copper retention area, etching is performed on both sides of the double-sided flexible substrate so that the copper layer on both sides of the double-sided flexible substrate, excluding the gold finger area and the copper retention area, is etched away. This is equivalent to leaving copper on both sides of the double-sided flexible substrate during the gold finger line etching process. There is no need to plate copper in the gold finger area and the copper retention area separately through a separate process. This simplifies the process and produces a gold finger flexible circuit board that can improve the edge PI breakage of ZIF.

[0071] In one specific embodiment, the top view of the first processed double-sided substrate after S3 etching is shown below. Figure 7 As shown, where Figure 7 Only one side of the first processed double-sided substrate is shown; the other side is the same and will not be shown here. Figure 7 It also shows the length and width of each sub-region in the copper retention area, as well as the spacing between each sub-region and the gold finger area.

[0072] like Figure 3 As shown, in step S4, protective films are applied to both sides of the first processed double-sided substrate, excluding the gold finger area, to form a second processed double-sided substrate.

[0073] Through step S4 above, a protective film is formed to protect the first processed double-sided substrate, thus protecting it. Specifically, applying the protective film to both sides of the first processed double-sided substrate, excluding the gold finger area, indicates that a protective film needs to be applied to the copper-retaining area. This not only improves the situation of ZIF edge PI breakage but also facilitates subsequent gold plating in the gold finger area, improving the gold plating effect and ensuring the quality of the gold fingers.

[0074] Specifically, in this embodiment, protective films are applied to both sides of the first processed double-sided substrate, excluding all gold finger immersion gold areas. That is, protective films are also applied to other areas of the gold finger region besides the gold finger immersion gold areas, which further enhances the protection.

[0075] In one specific embodiment of this example, the top view of the second-processed double-sided substrate after S4 film lamination is shown below. Figure 8 As shown, in Figure 8 In the middle, 5 represents a protective film.

[0076] like Figure 3 As shown, in step S5, according to the gold finger area, the second processed double-sided substrate is sequentially subjected to immersion gold plating and die cutting to obtain the target flexible circuit board.

[0077] By applying immersion gold only to the gold finger area of ​​the second-processed double-sided substrate, a higher quality gold finger can be formed. Then, by punching the shape of the immersion gold-plated double-sided substrate only to the gold finger area, the copper-containing areas and other waste areas can be punched out and discarded. This ensures that the PI at the edge of the ZIF will not break during the punching process, thus improving the yield. This effectively solves the problem that PI is brittle and prone to breakage when using PI with lower tensile strength and tensile modulus as FCCL to make ZIF, and broadens the application range of PI with lower tensile strength and tensile modulus as FCCL.

[0078] In one specific embodiment of this example, the top view of the double-sided substrate after the S5 immersion gold treatment is shown below. Figure 9 As shown, the top view of the target flexible circuit board obtained after S5 punching is as follows. Figure 10 As shown, in Figure 9 and Figure 10 In the middle, 3 represents the gold finger obtained after immersing gold in the gold finger area of ​​100.

[0079] Obviously, the manufacturing process of the target flexible circuit board in this embodiment also includes some conventional processes, such as laser engraving, copper plating, and dry film development. The specific operation processes of laser engraving, copper plating, and dry film development all adopt existing technologies, and the specific details will not be repeated here.

[0080] This embodiment sets a gold finger region on a double-sided flexible substrate to fabricate the gold fingers of the flexible circuit board. A copper retention region is set at the outer edge of the gold finger region on the waste area of ​​the double-sided flexible substrate, making full use of the copper layer in the waste area. Etching is performed based on the gold finger region and the copper retention region to achieve copper retention at the outer edge of the gold finger. Compared with traditional flexible circuit boards with gold fingers, it is easier to reduce the etching stress on the outer edge of the gold finger by laying copper in the waste area at the outer edge of the gold finger after subsequent immersion gold and die cutting. This avoids the phenomenon that the waste area at the edge of the ZIF is full of PI without copper, which causes stress concentration at the edge and makes the PI easy to break during etching. It effectively solves the problem that PI is brittle and prone to breakage when using PI with lower tensile strength and tensile modulus as FCCL to make ZIF. It broadens the application range of PI with lower tensile strength and tensile modulus as FCCL and has good application prospects.

[0081] Example 2

[0082] A flexible circuit board with gold fingers is manufactured using the method described in Example 1.

[0083] The flexible circuit board manufactured in this embodiment has higher quality gold fingers, which can effectively avoid ZIF edge PI breakage and improve the yield of the circuit board.

[0084] Similarly, the flexible circuit board described in this embodiment is manufactured using the manufacturing method described in Embodiment 1. Therefore, for any details not covered in this embodiment, please refer to Embodiment 1 and... Figures 1 to 10 The specific description is omitted here.

[0085] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A method for manufacturing a flexible circuit board with gold fingers, characterized in that, include: Provides double-sided flexible substrates; A gold finger area is formed on the double-sided flexible substrate, and a copper retention area is formed on the waste area of ​​the double-sided flexible substrate at the outer edge of the gold finger area. Based on the gold finger area and the copper retention area, the double-sided flexible substrate is etched to form a first processed double-sided substrate; Protective films are attached to both sides of the first processed double-sided substrate, excluding the gold finger area, to form a second processed double-sided substrate. According to the gold finger area, the second processed double-sided substrate is sequentially subjected to gold plating and die cutting to obtain the target flexible circuit board. The gold finger region includes multiple parallel gold finger immersion gold areas, and each gold finger immersion gold area has the same length. The copper retention area includes a first sub-copper retention area, a second sub-copper retention area, and a third sub-copper retention area located at the outer edge of the gold finger area on the waste area of ​​the double-sided flexible substrate. The first sub-copper retention area, the second sub-copper retention area, and the third sub-copper retention area are connected in sequence, and the first sub-copper retention area and the third sub-copper retention area are arranged opposite to each other; The distance between the first sub-copper retention area, the second sub-copper retention area, and the third sub-copper retention area and the outer edge of the gold finger area is greater than or equal to 0.2 mm.

2. The method for manufacturing a flexible circuit board with gold fingers according to claim 1, characterized in that, The length of the first sub-copper retention area is the same as the length of the third sub-copper retention area, and the length of the first sub-copper retention area and / or the length of the third sub-copper retention area is greater than the length of the gold finger immersion gold area.

3. The method for manufacturing a flexible circuit board with gold fingers according to claim 2, characterized in that, The difference between the length of the first sub-copper retention area and the length of the gold finger immersion gold area is greater than or equal to 0.5 mm, and / or the difference between the length of the third sub-copper retention area and the length of the gold finger immersion gold area is greater than or equal to 0.5 mm.

4. The method for manufacturing a flexible circuit board with gold fingers according to claim 1, characterized in that, The width of the first sub-copper retention area is the same as the width of the third sub-copper retention area, and the width of the first sub-copper retention area and / or the width of the third sub-copper retention area is greater than or equal to 0.3 mm.

5. The method for manufacturing a flexible circuit board with gold fingers according to claim 1, characterized in that, The width of the second copper retention area is greater than or equal to 0.3 mm.

6. The method for manufacturing a flexible circuit board with gold fingers according to any one of claims 1 to 5, characterized in that, The etching of the double-sided flexible substrate based on the gold finger area and the copper retention area to form a first processed double-sided substrate includes: Based on the gold finger area and the copper retention area, the copper layers on both sides of the double-sided flexible substrate are etched respectively, so that the copper layers on both sides of the double-sided flexible substrate, excluding the gold finger area and the copper retention area, are etched away to form the first processed double-sided substrate.

7. A flexible circuit board with gold fingers, characterized in that, It is manufactured using the manufacturing method described in any one of claims 1 to 6.

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