Double-sided flexible circuit board with special conduction structure and manufacturing process

Abstract

The application provides a double-sided flexible circuit board with a special conduction structure and a preparation process, and relates to the technical field of printed circuits. The double-sided flexible circuit board with the special conduction structure comprises a PET base material, a first circuit layer is etched in the middle part of an upper copper foil, a top protection layer is arranged on the upper surface of an upper solder resist layer, a second circuit layer is cut in the middle part of a lower copper foil by means of a UV laser cutting machine, the upper and lower ends of the PET base material are both formed with solder holes by means of laser, and the ends of the solder holes respectively extend to the surfaces of the first circuit layer and the second circuit layer, and the interiors of the solder holes are both provided with electroplated solder layers. The copper foil and the circuit layers are formed with a sandwich structure by means of a transparent adhesive layer and a solder resist layer, the copper foil does not directly contact the PET base material, the circuit patterns of the first circuit layer and the second circuit layer are more stable during subsequent lamination, a conduction ring is arranged around the electroplated solder layer, the strength of the electroplated solder layer during connection can be improved, material breakage caused by excessive stress concentration can be avoided, and practicality is improved.

Description

Technical Field

[0001] This invention relates to the field of printed circuit technology, specifically to a double-sided flexible circuit board with a special conductive structure and its fabrication process. Background Technology

[0002] With the continuous advancement of technology, consumer electronics products such as mobile phones and tablets are developing rapidly, and the demand for miniaturized and high-resolution displays is becoming increasingly urgent, which in turn increases the requirements for the fineness of the circuit lines on flexible circuit board packaging substrates.

[0003] In current production, the most common way to produce double-sided flexible circuit boards is to use two single-sided circuit boards. However, this requires more material costs and additional processing steps, resulting in lower processing efficiency. Furthermore, the circuit pattern stability of the surface layer of the double-sided flexible circuit board produced by combining the two boards is poor during the subsequent bonding process, and it is also inconvenient to position the board. In the subsequent soldering process, the solder layer may experience excessive stress concentration, which could lead to material damage. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a double-sided flexible circuit board with a special conductive structure and its fabrication process. This solves the problems of poor stability of the circuit pattern during subsequent bonding, inconvenience in positioning, and excessive stress concentration in the solder layer during the soldering process, which may lead to material damage.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a double-sided flexible circuit board with a special conductive structure, comprising a substrate, wherein the substrate is PET or PI, an upper copper foil is connected to the upper surface of the substrate through an upper transparent adhesive layer, a first circuit layer is etched in the middle of the upper copper foil, an upper solder resist layer is provided on the upper surface of the upper copper foil, a top protective layer is provided on the upper surface of the upper solder resist layer, a lower copper foil is connected to the lower surface of the substrate through a lower transparent adhesive layer, a second circuit layer is cut in the middle of the lower copper foil by a UV laser cutting machine, a lower solder resist layer is provided on the lower surface of the lower copper foil, a bottom protective layer is provided on the lower surface of the lower solder resist layer, and solder holes are formed at both the upper and lower ends of the substrate by laser forming, with the ends of the solder holes extending to the surfaces of the first and second circuit layers respectively, and an electroplated solder layer is provided inside each solder hole.

[0006] Preferably, the outer layer of the electroplated solder layer is provided with a conductive ring.

[0007] Preferably, positioning holes are provided on both sides of the interior of the substrate.

[0008] Preferably, both the top protective layer and the bottom protective layer are made of biaxially oriented polyester film, and both the top protective layer and the bottom protective layer have a thickness of 13 μm.

[0009] Preferably, both the upper and lower transparent adhesive layers are made of epoxy resin or polyethylene.

[0010] Preferably, both the upper and lower solder resist layers are made of polyimide film.

[0011] Preferably, the pad plating layer is made of a composite of electroplated nickel layer and electroless gold plating layer, wherein the thickness of the electroplated nickel layer is 0.5-2 μm and the thickness of the electroless gold plating layer is 0.05-1 μm.

[0012] A fabrication process for a double-sided flexible circuit board with a special conductive structure includes the following steps:

[0013] S1: Cut the substrate into a specific shape, apply a transparent adhesive layer to the top and bottom surfaces respectively, and then attach the upper and lower copper foils respectively;

[0014] S2: Apply a solder resist layer to the upper copper foil and apply a lower solder resist layer to the surface of the lower copper foil. Then, send it into a hot press for hot pressing and shaping, remove excess adhesive from the edges, and obtain copper-clad sheets.

[0015] S3: Make positioning holes on both sides of the copper-clad sheet, then use the positioning holes to fix the copper-clad sheet on the bracket, plan and set the distribution lines of the first circuit layer and the second circuit layer, use ferric chloride to etch the lines on the upper copper foil, and use a UV laser cutter to cut the lines on the lower copper foil to obtain a stack with the first circuit layer and the second circuit layer.

[0016] S4: Apply a top protective layer to the top of the laminate using hot melt adhesive, and apply a bottom protective layer to the bottom of the laminate using hot melt adhesive, leaving space for solder holes to obtain a flexible board;

[0017] S5: Prepare two steel plates, two silicone sheets, and two release films. Stack them on the press in the order of steel plate-silicone-release film-soft board-release film-silicone-steel plate. Pre-press for 15 minutes, then perform molding and pressing. After completion, cool the stack, remove the stack, and peel off the steel plate, silicone sheet, and release film layer by layer to obtain the pressed soft board.

[0018] S6: Use the positioning holes again to fix the lamination flexible board on the bracket, laser-drill the solder holes according to the reserved solder hole positions, and extend the ends of the solder holes to the surfaces of the first circuit layer and the second circuit layer respectively. Fill the solder holes with conductive rings and electroplated solder layers, and then perform drying curing, performance testing and surface treatment to obtain a double-sided flexible circuit board.

[0019] This invention provides a double-sided flexible circuit board with a special conductive structure and its fabrication process. It has the following beneficial effects:

[0020] This invention uses a transparent adhesive layer and a solder resist layer to form a sandwich between the copper foil and the circuit layer, preventing the copper foil from directly contacting the substrate. This makes the circuit patterns of the first and second circuit layers more stable during subsequent bonding. Positioning holes are opened on both sides of the circuit board, which not only facilitates subsequent installation and positioning but also allows the circuit board to be fixed on the bracket. Circuits can be built on both the top and bottom sides simultaneously, greatly improving the processing progress and efficiency of the double-sided flexible circuit board. Adding a conductive ring around the electroplated solder layer can improve the strength of the electroplated solder layer during connection, avoid material damage caused by excessive stress concentration, and improve practicality. Attached Figure Description

[0021] Figure 1 This is a cross-sectional view of the present invention;

[0022] Figure 2 for Figure 1 Enlarged view of point A in the middle;

[0023] Figure 3 This is a schematic diagram of the preparation process of the present invention.

[0024] The components are as follows: 1. Substrate; 2. Upper transparent adhesive layer; 3. Upper copper foil; 4. First circuit layer; 5. Upper solder resist layer; 6. Top protective layer; 7. Lower transparent adhesive layer; 8. Lower copper foil; 9. Second circuit layer; 10. Lower solder resist layer; 11. Bottom protective layer; 12. Solder hole; 13. Electroplated solder layer; 14. Conductive ring; 15. Positioning hole. Detailed Implementation

[0025] 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, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] Example:

[0027] Please see the appendix Figure 1 -Appendix Figure 3This invention provides a double-sided flexible circuit board with a special conductive structure, including a substrate 1, which is made of PET or PI. An upper copper foil 3 is connected to the upper surface of the substrate 1 via an upper transparent adhesive layer 2. A first circuit layer 4 is etched in the middle of the upper copper foil 3. An upper solder resist layer 5 is provided on the upper surface of the upper copper foil 3. A top protective layer 6 is provided on the upper surface of the upper solder resist layer 5 for outer protection and improved safety. A lower copper foil 8 is connected to the lower surface of the substrate 1 via a lower transparent adhesive layer 7. A second circuit layer 9 is cut in the middle of the lower copper foil 8 using a UV laser cutting machine. A lower solder resist layer 10 is provided on the lower surface of the lower copper foil 8 for insulation. A bottom protective layer 11 is provided on the lower surface of the lower solder resist layer 10. Solder holes 12 are formed at both the upper and lower ends of the substrate 1 by laser engraving, with the ends of the solder holes 12 extending to the surfaces of the first circuit layer 4 and the second circuit layer 9, respectively. An electroplated solder layer 13 is provided inside each solder hole 12. This basic structure of the circuit board is used for subsequent soldering connections of electronic components.

[0028] Furthermore, the outer layer of the electroplated solder layer 13 is provided with conductive rings 14. The conductive rings 14 can improve the strength of the electroplated solder layer during connection, avoid material damage caused by excessive stress concentration, and improve practicality. The inner sides of the substrate 1 are provided with positioning holes 15, which not only facilitates subsequent installation and positioning, but also fixes the circuit board on the bracket, so that the circuit board can be built on both the top and bottom sides at the same time, improving work efficiency.

[0029] Furthermore, both the top protective layer 6 and the bottom protective layer 11 are made of biaxially oriented polyester film, and both have a thickness of 13µm. Controlling the thickness of the protective layers can improve flexibility.

[0030] Furthermore, both the upper transparent adhesive layer 2 and the lower transparent adhesive layer 7 are made of either epoxy resin or polyethylene.

[0031] Furthermore, both the upper solder resist layer 5 and the lower solder resist layer 10 are made of polyimide film.

[0032] Furthermore, the pad plating layer 13 is made of a composite of electroplated nickel layer and electroless gold plating layer, with the electroplated nickel layer having a thickness of 0.5-2 μm and the electroless gold plating layer having a thickness of 0.05-1 μm.

[0033] A fabrication process for a double-sided flexible circuit board with a special conductive structure includes the following steps:

[0034] S1: Cut the substrate 1 into a specific shape, coat the top and bottom surfaces with transparent adhesive layer 2 and lower transparent adhesive layer 7 respectively, and attach the upper copper foil 3 and lower copper foil 8 respectively;

[0035] S2: Apply solder resist layer 5 to the upper copper foil 3 and apply lower solder resist layer 10 to the surface of the lower copper foil 8. Then, send it into a hot press for hot pressing and shaping, remove excess adhesive from the edges, and obtain copper-clad sheets.

[0036] S3: Make positioning holes 15 on both sides of the copper-clad sheet, then use the positioning holes 15 to fix the copper-clad sheet on the bracket, plan and set the distribution lines of the first circuit layer 4 and the second circuit layer 9, use ferric chloride to etch the lines on the upper copper foil 3, and use a UV laser cutter to cut the lines on the lower copper foil 8 to obtain a stack with the first circuit layer 4 and the second circuit layer 9.

[0037] Specifically, the upper part uses an etching process, while the lower part uses a laser cutting process, with both sides being processed simultaneously, which greatly improves processing efficiency.

[0038] S4: Apply the top protective layer 6 to the top of the stacked wafers using hot melt adhesive, and apply the bottom protective layer 6 to the bottom of the stacked wafers using hot melt adhesive, leaving the position of the solder hole 12 to obtain a flexible board;

[0039] S5: Prepare two steel plates, two silicone sheets, and two release films. Stack them on the press in the order of steel plate-silicone-release film-soft board-release film-silicone-steel plate. Pre-press for 15 minutes, then perform molding and pressing. After completion, cool the stack, remove the stack, and peel off the steel plate, silicone sheet, and release film layer by layer to obtain the pressed soft board.

[0040] Specifically, the molding and pressing temperature is controlled at 175±10℃, the pressing time is 30-60min, the pressure is 10-15Mpa, and the temperature is cooled to 80℃ after molding and pressing.

[0041] S6: Use the positioning hole 15 again to fix the press-fit flexible board on the bracket, and laser-drill the solder hole 12 according to the reserved solder hole 12 position. The end of the solder hole 12 extends to the surface of the first circuit layer 4 and the second circuit layer 9 respectively. Fill the solder hole 12 with the conductive ring 14 and the electroplated solder layer 13. Then, after drying and curing, performance testing and surface treatment, a double-sided flexible circuit board is obtained.

[0042] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A double-sided flexible circuit board with a special conductive structure, comprising a substrate (1), wherein the substrate (1) is PET or PI, an upper copper foil (3) is connected to the upper surface of the substrate (1) through an upper transparent adhesive layer (2), a first circuit layer (4) is etched in the middle of the upper copper foil (3), an upper solder resist layer (5) is provided on the upper surface of the upper copper foil (3), a top protective layer (6) is provided on the upper surface of the upper solder resist layer (5), a lower copper foil (8) is connected to the lower surface of the substrate (1) through a lower transparent adhesive layer (7), and the middle of the lower copper foil (8) is cut by a UV laser cutting machine. The second circuit layer (9) has a lower solder resist layer (10) on the lower surface of the lower copper foil (8), and a bottom protective layer (11) on the lower surface of the lower solder resist layer (10). The upper and lower ends of the substrate (1) are formed with solder holes (12) by laser and the ends of the solder holes (12) extend to the surfaces of the first circuit layer (4) and the second circuit layer (9) respectively. The inside of the solder holes (12) is provided with an electroplated solder layer (13). The outer layer of the electroplated solder layer (13) inside the solder holes (12) is provided with a conductive ring (14). The inside of the substrate (1) is provided with positioning holes (15) on both sides.

2. The double-sided flexible circuit board with a special conductive structure according to claim 1, characterized in that, The top protective layer (6) and the bottom protective layer (11) are both made of biaxially oriented polyester film, and the thickness of the top protective layer (6) and the bottom protective layer (11) is 13 μm.

3. The double-sided flexible circuit board with a special conductive structure according to claim 1, characterized in that, The upper transparent adhesive layer (2) and the lower transparent adhesive layer (7) are both made of either epoxy resin or polyethylene.

4. A double-sided flexible circuit board with a special conductive structure according to claim 1, characterized in that, The upper solder resist layer (5) and the lower solder resist layer (10) are both made of polyimide film.

5. A double-sided flexible circuit board with a special conductive structure according to claim 1, characterized in that, The electroplated solder layer (13) is made of a composite of electroplated nickel layer and electroless gold plating layer. The thickness of the electroplated nickel layer is 0.5-2 μm, and the thickness of the electroless gold plating layer is 0.05-1 μm.

6. A fabrication process for a double-sided flexible circuit board based on the special conductive structure described in any one of claims 1-5, characterized in that, The preparation steps include the following: S1: Cut the substrate (1) into a specific shape, coat the top and bottom surfaces with transparent adhesive layer (2) and lower transparent adhesive layer (7) respectively, and attach the upper copper foil (3) and lower copper foil (8) respectively; S2: Apply a solder resist layer (5) to the upper copper foil (3) and apply a lower solder resist layer (10) to the surface of the lower copper foil (8). Then, send it to a hot press for hot pressing and shaping, remove excess adhesive from the edges, and obtain a copper-clad sheet. S3: Make positioning holes (15) on both sides of the copper-clad sheet, and then use the positioning holes (15) to fix the copper-clad sheet on the bracket. Plan and set the distribution lines of the first circuit layer (4) and the second circuit layer (9). Use ferric chloride to etch the lines on the upper copper foil (3) above, and use a UV laser cutter to cut the lines on the lower copper foil (8) below, to obtain a stack with the first circuit layer (4) and the second circuit layer (9). S4: Apply a top protective layer (6) to the top of the stacked wafers using hot melt adhesive, and apply a bottom protective layer (6) to the bottom of the stacked wafers using hot melt adhesive, leaving a position for the solder hole (12) to obtain a flexible board; S5: Prepare two steel plates, two silicone sheets, and two release films. Stack them on the press in the order of steel plate-silicone-release film-soft board-release film-silicone-steel plate. Pre-press for 15 minutes, then perform molding and pressing. After completion, cool the stack, remove the stack, and peel off the steel plate, silicone sheet, and release film layer by layer to obtain the pressed soft board. S6: Use the positioning hole (15) again to fix the press-fit flexible board on the bracket, and laser-drill the solder hole (12) according to the reserved solder hole (12) position. The end of the solder hole (12) extends to the surface of the first circuit layer (4) and the second circuit layer (9) respectively. Fill the solder hole (12) with a conductive ring (14) and an electroplated solder layer (13). Then, after drying, curing, performance testing and surface treatment, a double-sided flexible circuit board is obtained.

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