Multilayer circuit board and processing method thereof

Abstract

The present invention discloses a multilayer circuit board and a processing method thereof. The processing method of the multilayer circuit board comprises the following steps: aligning and laminating an inner layer protective film on a double-sided board formed with an inner layer circuit to form a double-sided board with an inner layer protective film, laminating and baking a copper adhesive board and the double-sided board with the inner layer protective film, arranging an outer layer circuit on the single-sided board of the multilayer board, aligning and laminating the multilayer board after the above processing with the outer layer protective film, and baking until the outer layer protective film is completely solidified, wherein the outer layer protective film is provided with a second opening in an opening area, the shape of the second opening is the same as that of the opening area, and the width of a single side is smaller than a second preset length than the opening area, and the difference between the second preset length and the preset distance is greater than 0.

Description

Technical Field

[0001] The invention belongs to the technical field of flexible circuit boards, and in particular relates to a multilayer circuit board and a processing method thereof. Background Art

[0002] Flexible Printed Circuit (FPC) is a highly reliable and extremely flexible printed circuit board made of polyimide or polyester film as the substrate. It has the characteristics of high wiring density, light weight, thin thickness and good bending properties. Flexible circuit boards can move and stretch in three-dimensional space, realize three-dimensional wiring of circuits, improve the integration of component assembly and connection, reduce product volume while maintaining high stability, so FPC can be widely used in mobile phones, computers, mobile peripherals, automotive electronics and other industries.

[0003] With the upgrading of electronic products, the number of multi-layer FPCs with three layers or more is gradually increasing to meet the functional requirements of high density. As the number of layers and thickness of flexible circuit boards are higher, the bending performance is worse and the reliability cannot meet the requirements. In order to maintain a balance between versatility and bendability, local layer reduction design is usually developed at the location where the multi-layer FPC needs to be bent. The outer layer of the circuit board in a specific area is cut and peeled off through processes such as laser or punching, thereby achieving a local single-layer or double-layer structure and improving the bending performance of the circuit board. The layer reduction area is also called the de-cap area.

[0004] At present, the existing technology mainly adopts the post-opening process, that is, using picosecond laser to cut the outer copper foil. In order to avoid the inner layer glue (bonding glue) from melting due to heat during the laser process and causing glue flow, this technology usually shrinks the opening of the glue by 0.1mm before the outer layer is attached; after hot rolling glue, laminating machine pressing and laser opening process, the edge of the inner layer glue is 60-140um away from the edge of the opening area; after the protective film is quickly pressed, the filling with the inner layer circuit is better, and the risk of inner layer gap is small; however, if a lamination parameter with a higher pressure is used, the protective film glue is usually backfilled by 80-110um, and there is still the possibility that the two types of glue are not in contact and cause a gap, thereby affecting the insulation performance of the inner and outer layers of the FPC, and under long-term voltage load, there is a risk of copper ions migrating and growing in the gap, resulting in spark test (spark), short circuit and other functional malfunctions of the FPC. Summary of the invention

[0005] Therefore, the present invention aims to solve the technical problem in the prior art that a gap appears in the cover opening area of ​​the inner layer circuit of the flexible circuit board, resulting in spark test failure or short circuit and other functional malfunctions.

[0006] In order to solve the above technical problems, the present invention provides a method for processing a multilayer circuit board, and the method for processing a multilayer circuit board comprises the following steps:

[0007] Step S100, aligning and laminating the inner layer protective film on the double-sided board with the inner layer circuit formed thereon, to form a double-sided board with the inner layer protective film, wherein the outer shape of the inner layer protective film is the same as the shape of the cover opening area and the width of one side relative to the cover opening area is greater than a first preset length;

[0008] Step S200, laminating and baking the copper glue board and the double-sided board with the inner layer protective film, so that the inner layer glue in the copper glue board melts and overflows and fills the inner layer circuit together with the inner layer protective film in a molten state, to obtain a multilayer board, wherein the copper glue board includes the inner layer glue and the single-sided board pressed together, and the copper glue board is provided with a first opening, and the size and shape of the first opening are the same as the cover opening area;

[0009] Step S300, forming an outer layer circuit on the single-sided board of the multi-layer board, wherein the outer layer circuit is spaced a preset distance from the edge of the cover opening area;

[0010] Step S400, aligning and laminating the multilayer board processed in step S300 with the outer protective film, and baking until the outer protective film is completely cured, wherein the outer protective film has a second opening in the cover opening area, the shape of the second opening is the same as that of the cover opening area, and the width of one side is smaller than the second preset length than the cover opening area, and the difference between the second preset length and the preset distance is greater than 0.

[0011] Preferably, in the processing method of the multi-layer circuit board, the difference between the second preset length and the preset distance is ΔL, and ΔL is 0.2±0.1 mm.

[0012] Preferably, in the processing method of the multi-layer circuit board, the preset distance is D, and D is 0.45±0.1 mm.

[0013] Preferably, in the method for processing the multilayer circuit board, before step S100, the following steps are further included:

[0014] The protective film is laminated to the carrier film and punched to obtain an inner protective film having the same shape as the cover opening area and a width of a single side relative to the cover opening area of ​​a first preset length.

[0015] Preferably, in the processing method of the multi-layer circuit board, the first preset length is L1, and L1 is 0.70±0.1 mm.

[0016] Preferably, in the method for processing the multilayer circuit board, before step S200, the following steps are further included:

[0017] The inner layer adhesive and the single-sided board are sequentially attached and pressed to form the copper adhesive board, and a first opening is cut in the cover opening area of ​​the copper adhesive board, and the size and shape of the first opening are the same as those of the cover opening area.

[0018] Preferably, in the method for processing the multilayer circuit board, before step S400, the following steps are further included:

[0019] The outer protective film is cut in the cover opening area to form a second opening, the shape of the second opening is the same as that of the cover opening area, and the width of one side of the second opening is smaller than the second preset length than the cover opening area.

[0020] Preferably, in the processing method of the multi-layer circuit board, the second preset length is L2, and L2 is 0.25±0.1 mm.

[0021] The present invention also provides a multilayer circuit board, the multilayer circuit board comprising:

[0022] A double-sided board layer, comprising an inner protective film and a double-sided board with inner circuits formed thereon, which are sequentially attached and laminated from a first direction, wherein the outer shape of the inner protective film is the same as the shape of the cover opening area and the width of a single side relative to the cover opening area is greater than a first preset length;

[0023] A copper glue board is attached and laminated on the double-sided board layer along a first direction, the copper glue board includes an inner layer glue and a single-sided board which are attached and laminated in sequence along the first direction, the single-sided board is provided with an external circuit, the copper glue board is provided with a first opening, the size and shape of the first opening are the same as the cover opening area, the inner layer glue and the inner layer protective film are used to fill the internal circuit, wherein the outer layer circuit is spaced from the edge of the cover opening area by a preset distance;

[0024] The outer protective film is attached and laminated on the copper adhesive board along a first direction. The outer protective film has a second opening in the cover opening area. The shape of the second opening is the same as that of the cover opening area, and the width of one side of the second opening is smaller than the second preset length than the cover opening area. The second preset length is smaller than the preset distance.

[0025] Preferably, in the multilayer circuit board, the difference between the second preset length and the preset distance is ΔL, and ΔL is 0.2±0.1 mm; wherein,

[0026] The preset distance is D, D is 0.45±0.1 mm; and / or,

[0027] The second preset length is L2, L2 is 0.25±0.1 mm; and / or,

[0028] The first preset length is L1, and L1 is 0.70±0.1 mm.

[0029] The technical solution provided by the present invention has the following advantages:

[0030] The present invention adds an inner protective film to the cover opening area, cancels the inner glue shrinkage design, and processes after laminating with the outer single panel to ensure the fusion of the inner glue and the inner protective film glue, avoiding the gap in the inner circuit cover opening area, resulting in spark test failure or short circuit and other functional malfunctions;

[0031] Furthermore, the present invention forms a double-sided board with an inner layer protective film by aligning and laminating the inner layer protective film on a double-sided board formed with an inner layer circuit, wherein the outer shape of the inner layer protective film is the same as the shape of the cover opening area and the width of a single side relative to the cover opening area is greater than a first preset length, and the copper glue board and the double-sided board with the inner layer protective film are laminated and baked so that the inner layer glue in the copper glue board melts and overflows and fills the inner layer circuit together with the inner layer protective film in a molten state to obtain a multilayer board, wherein the copper glue board includes the inner layer glue and the single-sided board pressed together, and the copper glue board is provided with a first opening, the size and shape of the first opening are the same as the cover opening area, and the inner layer protective film is formed on the inner layer protective film of the multilayer board. An outer circuit is formed on the single-sided board, wherein the outer circuit is spaced from the edge of the cover opening area by a preset distance, the processed multi-layer board and the outer protective film are aligned and laminated, and baked until the outer protective film is completely cured, wherein the outer protective film is provided with a second opening in the cover opening area, the shape of the second opening is the same as that of the cover opening area, and the width of the single side of the second opening is less than the second preset length than the cover opening area, and the difference between the second preset length and the preset distance is greater than 0, so that the inner layer glue in the copper glue board melts and overflows and fills the inner layer circuit together with the inner layer protective film in the molten state, and the outer layer protective film is larger than the outer layer circuit by △L on one side, ensuring that the circuit is completely covered in the protective film;

[0032] Furthermore, by splitting the protective film into an inner layer and an outer layer, and processing it on the circuit board surface before and after the inner layer glue is attached, the filling stability of the glue in the open cover area of ​​the multi-layer flexible circuit board is improved, avoiding undesirable phenomena such as copper ion migration caused by incomplete glue filling, and improving the yield and stability of the product;

[0033] Furthermore, the present invention adds an opening design for the outer protective film, thereby reducing the overall thickness of the opening area of ​​the multilayer board. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0035] Figure 1 It is a cross-sectional view of a multi-layer circuit board in the prior art;

[0036] Figure 2 A cross-sectional view of an embodiment of a double-sided board provided by the present invention;

[0037] Figure 3 A cross-sectional view of an embodiment of a double-sided board with inner layer circuits provided by the present invention;

[0038] Figure 4 for Figure 3 A cross-sectional view of a double-sided board with inner circuit after the inner protective film is attached;

[0039] Figure 5 A cross-sectional view of a copper-coated plate after a first opening is provided in the present invention;

[0040] Figure 6 A cross-sectional view of an embodiment of a multilayer board provided by the present invention;

[0041] Figure 7 for Figure 6 A cross-sectional view of an embodiment of a middle multilayer board provided with outer layer circuits;

[0042] Figure 8 for Figure 7 Cross-sectional view of the middle layer board and the outer layer protective film after bonding;

[0043] Fig. 9 A schematic flow chart of an embodiment of a method for processing a multilayer circuit board provided by the present invention.

[0044] Description of prior art reference numerals:

[0045]

[0046] Description of the accompanying drawings of the present invention:

[0047]

[0048] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0049] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0050] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0051] In the present invention, unless otherwise specified, the directional words used, such as "up, down, top, bottom", usually refer to the directions shown in the drawings, or to the components themselves in the vertical, perpendicular or gravity directions; similarly, for ease of understanding and description, "inside and outside" refer to the inside and outside relative to the outline of each component itself, but the above-mentioned directional words are not used to limit the present invention.

[0052] Figure 1 The cross-sectional view of the multi-layer circuit board in the prior art is shown. Figure 1 The processing method of the multilayer circuit board in the prior art includes:

[0053] Step S100': Align and bond the inner layer adhesive 31' and the double-sided board 2' according to the alignment holes;

[0054] The double-sided board 2' in step S100' includes a first copper layer 21', a first substrate 22', and a second copper layer 23' which are stacked together in sequence.

[0055] Step S200': align and laminate the single-sided board 32' with the inner layer adhesive 31' and the double-sided board 2' after lamination in step S100', and cure the inner layer adhesive by high temperature and high pressure treatment in a laminator to form a multilayer board;

[0056] The single-sided board 32' includes a third copper layer 321' and a second substrate 322' which are stacked in sequence.

[0057] Step S300': laser processing blind holes, plasma etching to remove slag, carbon coating, copper plating to form via holes on the multilayer board, followed by film pressing, exposure, development, etching, and film stripping to form L3 layer circuit patterns;

[0058] Step S400': Uncovering process: locate the area to be uncovered according to the optical mark (Fiducial mark) etched on the L3 layer, and use picosecond laser to cut the pattern, and then use a machine to tear off the L3 layer substrate and copper above the glue opening to expose the L2 layer circuit. Then manually inspect whether there are defects such as substrate residue, delamination or damage in the uncovering area, and finally use plasma etching to remove glue residue.

[0059] After step S400', the multilayer board after opening the cover also undergoes optical inspection for glue flow and electrical inspection for open circuit, short circuit and other functional defects, conventional lamination of protective film 1', compression of protective film 1', solder mask treatment and surface treatment.

[0060] The processing method of the multi-layer circuit board is the aforementioned post-opening process, and a gap 4' appears in the open-cover area of ​​the inner layer circuit of the flexible circuit board, resulting in spark test failure or short circuit and other functional malfunctions.

[0061] Example 1

[0062] Figures 2 to 9 The schematic diagram of the steps of the processing method of the multilayer circuit board of the present invention is illustrated. The present invention provides a processing method of a multilayer circuit board, wherein the multilayer circuit board 100 can be three-layer, four-layer, ..., etc., and no specific limitation is made here. The present invention is described below by taking a three-layer circuit board as an example, and the three-layer circuit board includes a double-sided board 2, an inner layer glue 31 and a single-sided board 32, etc.

[0063] See also Fig. 9 The processing method of the multilayer circuit board comprises the following steps:

[0064] Step S100, aligning and laminating the inner layer protective film 1 on the double-sided board 2 formed with the inner layer circuit 5, to form the double-sided board 2 with the inner layer protective film 1, wherein the outer shape of the inner layer protective film 1 is the same as the shape of the cover opening area and the width of one side relative to the cover opening area is greater than a first preset length;

[0065] Specifically, in the step S100, the inner protective film 1 is aligned and bonded to the double-sided board 2 formed with the inner circuit 5, which may be done by using a clamp, and then cured by a fast press, and baked at high temperature to remove moisture. It can also be cured by lamination. This is all prior art and will not be described in detail. The first preset length is L1, L1 is 0.70±0.1mm, that is, L1 is 0.6mm~0.80mm, for example, L1 can be 0.65mm, 0.66mm, 0.68mm, 0.70mm, 0.72mm, 0.74mm, or 0.76mm.

[0066] In this example, see Figure 2The double-sided board 2 includes a first copper layer 21, a first substrate 22 (eg, polyimide), and a second copper layer 23 stacked along a first direction.

[0067] The manufacturing process step S110 of the inner protective film 1 may be, before step S100, to laminate the protective film on the carrier film and punch out to obtain the inner protective film 1 having the same shape as the cover opening area and a single side with a first preset length relative to the cover opening area, specifically including:

[0068] Step S111, laminating the unprocessed protective film to the carrier film;

[0069] The laminating process may be, but is not limited to, laminating the unprocessed protective film on the carrier film in a roll-to-roll process, and the carrier film may be, but is not limited to, made of transparent polyethylene terephthalate (PET) material.

[0070] Step S112, punching out the outer shape of the protective film in step S111, the outer shape of which is the same as the shape of the cover opening area, but increasing the first preset length on one side, to obtain an inner protective film 1 arranged on the surface of the carrier film;

[0071] Among them, see Figure 4 The punching process can be but is not limited to punching the shape in a half-cut manner, and its shape is the same as the shape of the cover opening area, but the first preset length L1 is increased on one side (it should be understood that the first preset length is increased on one side compared with the cover opening area, that is, the distance between each side and the cover opening area is increased by the same first preset length), and the cutting depth is consistent with that of the protective film. In other embodiments, the cutting depth can also be greater than the protective film, so that the shape of the protective film is cut completely.

[0072] Step S112 also includes steps such as tearing off waste materials after punching, which will not be described in detail here.

[0073] Among them, see Figure 3 The process of forming the double-sided board 2 with the inner layer circuit 5 can be a conventional method, for example, a roll-to-roll process of laser processing through blind holes, pressing dry film, exposure, development, etching, film stripping and other processes to form the L2 layer circuit.

[0074] Step S200, attaching and laminating the copper glue board 3 and the double-sided board 2 with the inner layer protective film 1, so that the inner layer glue 31 in the copper glue board 3 melts and overflows and fills the inner layer circuit 5 together with the inner layer protective film 1 in a molten state, to obtain a multilayer board, wherein the copper glue board 3 includes the inner layer glue 31 and the single-sided board 32 pressed together, and the copper glue board 3 is provided with a first opening 33, and the size and shape of the first opening 33 are the same as those of the cover opening area;

[0075] Specifically, see Figure 6After the copper glue board 3 and the double-sided board 2 with the inner layer protective film 1 are aligned and attached, they are laminated and baked to form a multi-layer board. The inner layer glue 31 in the copper glue board 3 melts and overflows under high temperature and high pressure, and merges with the inner layer protective film 1 in the molten state to fill the inner layer circuit 5, and finally solidifies together. The inner layer glue 31 is usually 0-0.125mm in width under high temperature and high pressure. Please refer to Figure 5 The single-sided board 32 includes a third copper layer 321 stacked along a first direction and a second substrate 322 (polyimide).

[0076] Before step S200, please refer to Figure 5 , further comprising the following steps:

[0077] Step S210 , sequentially attaching and pressing the inner layer adhesive 31 and the single-sided board 32 to form the copper adhesive board 3 , and forming a first opening 33 in the cover opening area of ​​the copper adhesive board 3 , wherein the size and shape of the first opening 33 are the same as those of the cover opening area.

[0078] Specifically, the unprocessed inner layer glue 31 and the single-sided board 32 are laminated and pressed into the copper glue board 3 by a roll-to-roll process. The copper glue board 3 is cut into single sheets, and the offset alignment holes and exhaust holes of the processing layer are cut by laser or die punching by a single sheet process, and the hole diameter is generally 2mm. At the same time, the shape of the laser cutting is made in the opening area, and the size and shape are the same as the opening area. Unlike the back opening process, the cutting depth does not need to be strictly controlled in the front opening process. After the opening is obtained by laser cutting, the carbon powder and glue residue are cleaned and removed.

[0079] Step S300, forming an outer layer circuit 6 on the single-sided board 32 of the multi-layer board, wherein the outer layer circuit 6 is spaced a preset distance from the edge of the cover opening area;

[0080] Specifically, the process of forming the outer layer circuit 6 on the single-sided board 32 of the multi-layer board is similar to the conventional process and will not be described in detail here. Figure 7 , the difference is that the outer layer circuit 6 is preset to a distance from the edge of the cover opening area. In this embodiment, the preset distance is D, D is 0.45±0.1mm, that is, D is 0.35mm~0.55mm. In this way, it can effectively ensure that after the protective film is attached, the protective film and the protective film's glue flow away from the cover area. The cover opening area is generally used for bending functions. If there is glue flow or the protective film covers the cover opening area, it will affect the reliability of the bending. In other embodiments, D can be 0.37mm, 0.39mm, 0.41mm, 0.43mm, 0.45mm, 0.47mm, or 0.5mm.

[0081] Step S400, aligning and laminating the multilayer board processed in step S300 with the outer protective film 4 until the outer protective film 4 is completely cured, wherein the outer protective film 4 has a second opening in the cover opening area, the shape of the second opening is the same as that of the cover opening area, and the width of one side of the cover opening area is less than the second preset length, and the second preset length is less than the preset distance, so that the outer protective film 4 can be larger than the circuit, and the outer protective film 4 is used to protect the circuit layer. For details, please refer to Figure 8 , the multilayer board processed in step S300 is aligned with the outer protective film 4 and laminated, which can be but not limited to alignment and lamination according to the alignment holes, and then the outer protective film 4 glue is completely cured by lamination. Since the single-side distance between the outer protective film 4 and the outer circuit 6 is greater than the preset value (that is, the difference △L between the second preset length and the preset distance), it can be ensured that the outer circuit 6 is completely covered in the outer protective film 4.

[0082] In this embodiment, △L is 0.2±0.1mm, that is, △L is 0.1mm~0.3mm. Since the matching tolerance of the outer protective film 4 is 0.2mm, if △L is too small, considering the fitting deviation of the outer protective film 4, the outer protective film 4 will not be able to cover the circuit layer. If it is too large, the outer protective film 4 will be too close to the cover opening area. The fitting deviation will cause the outer protective film 4 to deviate to the cover opening area, causing defects. In addition, for multilayer boards, it is also necessary to consider the expansion and contraction factors of the flexible board, the environmental factors in the production process, the stability of the equipment and other factors that affect the fitting accuracy. Therefore, in this embodiment, △L is 0.1mm~0.3mm, which has a better effect. In other embodiments, △L can be 0.14mm, 0.15mm, 0.16mm, 0.17mm, 0.18mm, 0.19mm, 0.20mm, 0.21mm, or 0.22mm.

[0083] In this embodiment, the second preset length is L2, and L2 is 0.25±0.1 mm.

[0084] Preferably, in the processing method of the multilayer circuit board 100, preferably, in the processing method of the multilayer circuit board 100, the first preset length is L1, L1 is 0.70±0.10mm, that is, L1 is 0.60mm~0.80mm, so that the copper glue board and the open cover area can have an overlap of at least 0.2mm to achieve better effect. For example, L1 can be 0.65mm, 0.72mm, 0.74mm, 0.76mm, or 0.78mm.

[0085] Preferably, in the method for processing the multilayer circuit board 100, before step S400, the following steps are further included:

[0086] Step S410 , forming a second opening in the cover opening area of ​​the outer protective film 4 , wherein the shape of the second opening is the same as that of the cover opening area, and the width of one side of the second opening is smaller than a second preset length than that of the cover opening area.

[0087] Specifically, the outer protective film 4 is cut into single sheets and then the alignment holes are processed by laser or punching process. At the same time, a second opening is cut in the opening area. The opening shape of the second opening is the same as that of the opening area, but the second preset length is reduced on one side. The laser process requires the use of alcohol to clean carbon powder or glue residue.

[0088] In addition, after step S400, solder mask processing and surface treatment are also included. Since the subsequent processes can be conventional processes in the prior art, they are not described in detail here.

[0089] The present invention adds an inner protective film 1 in the cover opening area, cancels the inner layer glue 31 shrinkage design, and processes it after being bonded with the outer single-layer panel 32, thereby ensuring the fusion of the inner layer glue 31 and the inner protective film 1 glue, and avoiding the gap in the cover opening area of ​​the inner layer circuit 5, which may cause spark test failure or short circuit and other malfunctions;

[0090] Furthermore, the present invention forms a double-sided board 2 with an inner layer protective film 1 by aligning and laminating the inner layer protective film 1 on the double-sided board 2 formed with the inner layer circuit 5, wherein the outer shape of the inner layer protective film 1 is the same as the shape of the cover opening area and the width of the single side relative to the cover opening area is greater than a first preset length, and the copper glue board 3 is laminated and baked with the double-sided board 2 with the inner layer protective film 1, so that the inner layer glue 31 in the copper glue board 3 melts and overflows and fills the inner layer circuit 5 together with the inner layer protective film 1 in the molten state, thereby obtaining a multilayer board, wherein the copper glue board 3 includes the inner layer glue 31 and the single-sided board 32 pressed together, and the copper glue board 3 is provided with a first opening 33, and the size and shape of the first opening 33 are the same as those of the cover opening area , an outer layer circuit 6 is formed on the single-sided board 32 of the multilayer board, wherein the outer layer circuit 6 is spaced from the edge of the cover opening area by a preset distance, and the processed multilayer board is aligned with the outer layer protective film 4 and laminated until the outer layer protective film 4 is completely solidified, wherein the outer layer protective film 4 is provided with a second opening in the cover opening area, the shape of the second opening is the same as that of the cover opening area, and the width of the single side is less than the second preset length than the cover opening area, and the second preset length is less than the preset distance, so that the inner layer glue 31 in the copper glue board 3 melts and overflows and fills the inner layer circuit 5 together with the inner layer protective film 1 in the molten state, and the outer layer protective film 4 is larger than the outer layer circuit 6 by △L on one side, so as to ensure that the circuit is completely covered in the protective film;

[0091] Furthermore, by splitting the protective film into an inner layer and an outer layer, and processing it on the circuit board surface before and after the inner layer glue 31 is attached, the filling stability of the glue in the open cover area of ​​the multi-layer flexible circuit board is improved, and the undesirable phenomenon such as copper ion migration caused by incomplete glue filling is avoided, thereby improving the yield and stability of the product;

[0092] Furthermore, the present invention adds an opening design for the outer protective film 4, thereby reducing the overall thickness of the opening area of ​​the multilayer board.

[0093] Furthermore, the present invention is different from the post-opening process mentioned in the prior art. The opening process is performed simultaneously with the inner layer of glue before the single-sided panel is bonded, and then the double-sided panel is bonded and pressed, thereby avoiding cumbersome post-processing processes such as tearing off after laser opening, manual inspection, and machine inspection. The inner layer protective film design is introduced to eliminate the risk of poor product function caused by the inner layer gap resulting from the incomplete contact between the inner layer glue and the outer layer protective film glue after opening the cover.

[0094] Example 2

[0095] The present invention also provides a multilayer circuit board 100, see Figures 2 to 8 The multilayer circuit board 100 includes a double-sided board layer, a copper glue board 3, and an outer protective film 4. The double-sided board layer includes an inner protective film 1 and a double-sided board 2 formed with an inner circuit 5, which are sequentially attached and laminated from a first direction. The outer shape of the inner protective film 1 is the same as the shape of the cover opening area, and the width of a single side relative to the cover opening area is greater than a first preset length. The copper glue board 3 is attached and laminated on the double-sided board 2 along the first direction. The copper glue board 3 includes an inner glue 31 and a single-sided board 32 sequentially attached and laminated along the first direction. The single-sided board 32 is provided with an external circuit. The rubber plate 3 is provided with a first opening 33, the size and shape of the first opening 33 are the same as those of the cover opening area, the inner layer glue 31 and the inner layer protective film 1 jointly fill the internal circuit, wherein the outer layer circuit 6 is spaced a preset distance from the edge of the cover opening area, the outer layer protective film 4 is attached and laminated on the copper rubber plate 3 along a first direction, and the outer layer protective film 4 is provided with a second opening in the cover opening area, the shape of the second opening is the same as that of the cover opening area, and the width of a single side of the cover opening area is less than a second preset length, and the second preset length is less than the preset distance.

[0096] The double-sided board 2 includes a first copper layer 21, a first substrate 22 (eg, polyimide), and a second copper layer 23 stacked along a first direction. The single-sided board 32 includes a third copper layer 321 and a second substrate 322 (polyimide) stacked along the first direction.

[0097] The multilayer circuit board 100 can be formed by the processing method of the multilayer circuit board 100 provided in Embodiment 1, or can be formed by other processing methods, which are not specifically limited here. The embodiment of the multilayer circuit board 100 can be all embodiments of the processing method of the multilayer circuit board 100 described above.

[0098] Preferably, the preset distance is D, and D is 0.45±0.1 mm, that is, D is 0.35 mm to 0.55 mm.

[0099] In this embodiment, the difference between the second preset length and the preset distance is △L is 0.2±0.1mm, that is, △L is 0.1mm~0.3mm, for example, △L can be 0.14mm, 0.15mm, 0.16mm, 0.17mm, 0.18mm, 0.19mm, 0.20mm, 0.21mm, or 0.22mm.

[0100] In this embodiment, the second preset length is L2, and L2 is 0.25±0.1 mm.

[0101] Obviously, the embodiments described above are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, ordinary technicians in this field can make other different forms of changes or modifications without creative work, which should fall within the scope of protection of the present invention.

Claims

1. A method for processing a multilayer circuit board, characterized in that: The steps include: Step S100, aligning and laminating the inner layer protective film on the double-sided board with the inner layer circuit formed thereon, to form a double-sided board with the inner layer protective film, wherein the outer shape of the inner layer protective film is the same as the shape of the cover opening area and the width of one side relative to the cover opening area is greater than a first preset length; Step S200, laminating and baking the copper glue board and the double-sided board with the inner layer protective film, so that the inner layer glue in the copper glue board melts and overflows and fills the inner layer circuit together with the inner layer protective film in a molten state, to obtain a multilayer board, wherein the copper glue board includes the inner layer glue and the single-sided board pressed together, and the copper glue board is provided with a first opening, and the size and shape of the first opening are the same as the cover opening area; Step S300, forming an outer layer circuit on the single-sided board of the multi-layer board, wherein the outer layer circuit is spaced a preset distance from the edge of the cover opening area; Step S400, aligning and laminating the multilayer board processed in step S300 with the outer protective film, and baking until the outer protective film is completely cured, wherein the outer protective film has a second opening in the cover opening area, the shape of the second opening is the same as that of the cover opening area, and the width of one side of the second opening is smaller than the second preset length than the cover opening area, and the difference between the second preset length and the preset distance is greater than 0; Before step S400, the following steps are also included: Cutting the outer protective film in the cover opening area to form a second opening, wherein the shape of the second opening is the same as that of the cover opening area, and the width of one side of the second opening is smaller than the second preset length than the cover opening area; The difference between the second preset length and the preset distance is △L, △L is 0.2±0.1mm; the preset distance is D, D is 0.45±0.1mm, the first preset length is L1, L1 is 0.70±0.1mm, and the second preset length is L2, L2 is 0.25±0.1mm.

2. The method for processing a multilayer circuit board according to claim 1, wherein: Before step S100, the following steps are also included: The protective film is attached to the carrier film and punched to obtain an inner protective film having the same shape as the cover opening area and a single side having a width larger than the cover opening area by a first preset length.

3. The method for processing a multilayer circuit board according to claim 1, wherein: Before step S200, the following steps are also included: The inner layer adhesive and the single-sided board are sequentially attached and pressed to form the copper adhesive board, and a first opening is cut in the cover opening area of ​​the copper adhesive board, and the size and shape of the first opening are the same as those of the cover opening area.

4. A multilayer circuit board, characterized in that: include: A double-sided board layer, comprising an inner protective film and a double-sided board with inner circuits formed thereon, which are sequentially attached and laminated from a first direction, wherein the outer shape of the inner protective film is the same as the shape of the cover opening area and the width of a single side relative to the cover opening area is greater than a first preset length; A copper glue board is attached and laminated on the double-sided board layer along a first direction, the copper glue board includes an inner layer glue and a single-sided board which are attached and laminated in sequence along the first direction, the single-sided board is provided with an external circuit, the copper glue board is provided with a first opening, the size and shape of the first opening are the same as the cover opening area, the inner layer glue and the inner layer protective film are used to fill the inner layer circuit, wherein the outer layer circuit is spaced from the edge of the cover opening area by a preset distance; An outer protective film is attached and laminated on the copper adhesive board along a first direction, the outer protective film has a second opening in the cover opening area, the shape of the second opening is the same as that of the cover opening area, and the width of a single side of the second opening is smaller than a second preset length than the cover opening area, and the second preset length is smaller than the preset distance; The difference between the second preset length and the preset distance is △L, and △L is 0.2±0.1mm; wherein, The preset distance is D, D is 0.45±0.1 mm; and / or, The second preset length is L2, L2 is 0.25±0.1 mm; and / or, The first preset length is L1, and L1 is 0.70±0.1 mm.

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