A high-precision solder resist pattern flexible circuit board manufacturing method

Abstract

The application discloses a high-precision solder resist pattern flexible circuit board manufacturing method, taking a first single-sided flexible copper-clad plate, manufacturing a first window pattern, and manufacturing a solder resist pattern, then a circuit pattern, including an IC pad pattern, the solder resist pattern is located between opposite pads of the IC pad pattern, taking a second single-sided flexible copper-clad plate, a second circuit pattern, manufacturing an intermittent through slot along the edge of the second circuit pattern, and forming a connecting position, aligning, pressing, cutting off the connecting position, uncovering, and forming a flexible circuit board; by manufacturing the solder resist pattern before manufacturing the circuit pattern, and then manufacturing the first circuit pattern, the solder resist pattern has high precision, thickness and flatness, the second single-sided flexible copper-clad plate is used to manufacture the second circuit pattern, plays a protection and release role on the solder resist pattern, prevents damage in pressing, improves the processing precision of the cover film, and improves the manufacturing quality of the high-precision flexible circuit board through cooperation of overall processing procedures.

Description

Technical Field

[0001] This invention relates to the field of circuit board processing, and in particular to a method for manufacturing flexible circuit boards with high-precision solder mask patterns. Background Technology

[0002] When soldering some IC chips, the height of the chip body is higher than the pin height, while the height of the corresponding IC pad on the circuit board is higher than the height of the empty space in the middle of the IC pad (corresponding to the chip body). Therefore, after soldering, there is a large gap between the chip body and the empty space, and the chip body is in a suspended state. This affects the stability of the chip during application and is prone to problems such as solder joint cracking. Therefore, it is necessary to make a filling layer in the empty space so that the chip body is "lifted" after soldering, thereby improving the stability of the chip.

[0003] For high-precision flexible circuit boards with the above characteristics, two methods are generally used to fabricate the filler layer:

[0004] Create a covering film for the area and attach it together with the surface covering film to form a filling layer.

[0005] The problem with this manufacturing method is that the cover film at the empty space is in an independent state and generally needs to be applied independently, making it difficult to form a reference for alignment. In addition, the size is small and the precision is high, so problems such as misalignment and displacement are easy to occur during application.

[0006] After the flexible circuit board is fabricated, a solder mask layer is applied to that location to form a filler layer.

[0007] The problem with this manufacturing method is that, for high-precision flexible circuit boards, on the one hand, the gaps in the middle of the high-precision IC pads are small, and the manufacturing of the solder mask layer requires high precision in processes such as alignment, exposure, and cover film lamination; on the other hand, the flexible circuit board is relatively soft, and the manufacturing of the solder mask layer is prone to problems such as misalignment and unevenness.

[0008] Based on the above background and problems, there is a need to provide a method for fabricating flexible circuit boards with high-precision solder resist patterns. Summary of the Invention

[0009] This invention addresses the problems of misalignment and displacement when using a cover film to create a fill layer for the empty space opposite the IC pads in existing flexible circuit boards, and the problems of misalignment and unevenness when using a solder resist layer to create the fill layer. The invention proposes a method for fabricating flexible circuit boards with high-precision solder resist patterns.

[0010] S10: Take a first single-sided flexible copper-clad laminate, create a first window pattern on the copper layer, apply ink to the first window pattern position, and bake and cure to form a solder mask pattern; then create a first circuit pattern, including creating an IC pad pattern; the area formed by the solder mask pattern and the IC pad pattern is the surface pattern area, and the solder mask pattern is located between the opposite pads of the IC pad pattern; the entire assembly is fabricated to form a circuit pattern core board;

[0011] S20: Take a second single-sided flexible copper-clad laminate, and make a second circuit pattern on the copper layer. The size of the second circuit pattern covers the surface pattern area. Along the edge of the second circuit pattern, make intermittent through grooves on the insulating dielectric layer of the second single-sided flexible copper-clad laminate. The non-through groove positions of the intermittent through grooves form connection positions. The whole assembly is made to form a cover film pattern board.

[0012] S30: Align the circuit pattern core board with the cover film pattern board, wherein the second circuit pattern is corresponding to and opposite to the surface pattern area; then press them together to form a press plate;

[0013] S40: Cut off the connection position of the pressing plate, remove the cover, and form the flexible circuit board.

[0014] Furthermore, before the ink is produced, the first windowed graphic position is subjected to plasma treatment.

[0015] Furthermore, the process of forming the circuit pattern core board further includes: after baking and curing, laser ablation of the solder resist pattern along the edge of the first window pattern to ablate the solder resist pattern that overflows the first window pattern.

[0016] Furthermore, after the laser ablation is performed, alkaline washing and water washing are carried out.

[0017] Furthermore, after the laser ablation is performed, micro-etching is then carried out.

[0018] Furthermore, the thickness of the copper layer in the micro-etching is 5 μm to 8 μm.

[0019] Furthermore, the width of the connection position is from 50 μm to 2.0 mm.

[0020] Furthermore, the second single-sided flexible copper-clad laminate contains an adhesive layer located between the copper layer and the insulating dielectric layer.

[0021] Furthermore, the copper layer of the second single-sided flexible copper-clad laminate is 5μm to 15μm.

[0022] Furthermore, the connection position of the pressed plate is cut off by laser ablation, followed by alkaline washing and water washing.

[0023] This invention's technical solution involves creating a solder mask pattern before creating the circuit pattern, thus confining the solder mask pattern within the first windowed pattern area. This eliminates the need for alignment, exposure, and development processes. Furthermore, the thickness of the solder mask pattern can be limited to the copper layer thickness, resulting in a smoother surface finish and effectively improving the processing precision and quality of the solder mask pattern. By using a second single-sided flexible copper-clad laminate as the cover film, the surface pattern area is protected during the lamination process, while also serving a crucial release function, preventing adhesion or damage to the solder mask layer during lamination. The second circuit pattern allows for higher precision alignment, resulting in a higher overall alignment accuracy than when using a windowed cover film, thus improving the processing quality of high-precision circuit boards. The entire manufacturing process, from high-precision solder mask fabrication to the use of the second circuit pattern to protect the solder mask pattern during lamination of the cover film layer, creates a coordinated processing flow, representing an innovation in the overall process flow and improving the manufacturing quality of high-precision flexible circuit boards. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0025] Figure 1 This is a flowchart illustrating the main processes included in the embodiments of the present invention;

[0026] Figure 2 This is a schematic diagram of the cross-sectional structure of the flexible core board with window in this embodiment;

[0027] Figure 3 for Figure 2 A schematic diagram of the cross-sectional structure of surface AA;

[0028] Figure 4 This is a schematic diagram of the cross-sectional structure of the ink layer core board in this embodiment;

[0029] Figure 5 for Figure 4 A schematic diagram of the cross-sectional structure of the BB surface;

[0030] Figure 6 This is a schematic diagram of the planar structure of the laser ablation solder resist pattern in this embodiment;

[0031] Figure 7 This is a schematic diagram of the planar structure of another ink layer core board in this embodiment;

[0032] Figure 8 for Figure 7 A schematic diagram of the cross-sectional structure of the C-plane;

[0033] Figure 9 This is a schematic diagram of the planar structure of the circuit pattern core board of this embodiment;

[0034] Figure 10 for Figure 9 A schematic diagram of the cross-sectional structure of the DD surface;

[0035] Figure 11 This is a schematic diagram of the planar structure of the graphic cover film of this embodiment;

[0036] Figure 12 for Figure 11 A schematic diagram of the cross-sectional structure of the EE surface;

[0037] Figure 13 This is a schematic diagram of the cross-sectional structure of the pressing plate in this embodiment;

[0038] Figure 14 This is a schematic diagram of the planar structure of the flexible circuit board according to this embodiment;

[0039] Figure 15 for Figure 14 A schematic diagram of the cross-sectional structure of the FF surface.

[0040] Explanation of icon numbers:

[0041]

[0042] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0043] 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 a part of the embodiments of the present invention, and not all of the 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.

[0044] It should be noted that all directional indications (such as up, down, left, right, front, back, inside, outside, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0045] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0046] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0047] Please see Figure 1 ; Figure 1 This is a flowchart illustrating the main processes involved in an embodiment of the present invention.

[0048] The method for fabricating a flexible circuit board with high-precision solder resist patterns according to embodiments of the present invention includes: Figure 1 The main manufacturing process is explained in detail step by step below.

[0049] Please see Figures 2 to 10 ; Figure 2 This is a schematic diagram of the cross-sectional structure of the flexible core board with window in this embodiment; Figure 3 for Figure 2 A schematic diagram of the cross-sectional structure of surface AA; Figure 4 This is a schematic diagram of the cross-sectional structure of the ink layer core board in this embodiment; Figure 5 for Figure 4 A schematic diagram of the cross-sectional structure of the BB surface; Figure 6 This is a schematic diagram of the planar structure of the laser ablation solder resist pattern in this embodiment; Figure 7 This is a schematic diagram of the planar structure of another ink layer core board in this embodiment; Figure 8 for Figure 7 A schematic diagram of the cross-sectional structure of the C-plane; Figure 9 This is a schematic diagram of the planar structure of the circuit pattern core board of this embodiment; Figure 10 for Figure 9 A schematic diagram of the cross-sectional structure of the DD surface.

[0050] Step S10:

[0051] Take a first single-sided flexible copper-clad laminate, which consists of a copper layer and a first flexible dielectric layer 130. Create a first window pattern 110 on the copper layer to form a windowed copper layer 120. The first single-sided flexible copper-clad laminate forms a windowed flexible core board 10. Figure 2 , Figure 3); Apply ink to the first window shaped position 110 and bake to cure, forming a solder resist pattern 210, and the entire process forms an ink layer core board 20 ( Figure 4 , Figure 5 Then, the first circuit pattern 310 is fabricated, including the IC pad pattern 3110; the area formed by the solder mask pattern 210 and the IC pad pattern 3110 is the surface pattern area 320, and the solder mask pattern 310 is located between the opposite pads of the IC pad pattern 3110; the entire circuit pattern core board 30 is fabricated.

[0052] This method first creates the first window pattern 110, and then directly creates the solder resist pattern 210 in that area. This eliminates the need for alignment, exposure, and development processes, avoiding the cumulative effects of alignment errors, exposure errors, and material expansion / contraction errors that can occur when creating the solder resist pattern 210 after creating the first circuit pattern 310. This avoids problems such as solder resist misalignment. In other words, this method creates the solder resist pattern 210 first, then the first circuit pattern 310, unlike existing technologies that create the first circuit pattern 310 first and then the solder resist pattern 210. Furthermore, the solder resist pattern 210 is created between the corresponding pads of the IC pad pattern 3110, corresponding to the area where the IC chip body is located after soldering, thus supporting the IC chip body.

[0053] In this embodiment, plasma treatment is applied to the first window pattern 110 position before ink is produced.

[0054] The position of the first windowed pattern 110 is the position where the copper layer is removed to expose the insulating dielectric layer of the first single-sided flexible copper-clad laminate, that is, the position where the first flexible dielectric layer 130 (generally polyimide material) is exposed. Plasma treatment can effectively improve the material activity of the first flexible dielectric layer 130 at the position of the first windowed pattern 110, improve the uniform roughness of the material surface, improve the adhesion between ink and material, and prevent problems such as ink peeling.

[0055] Please continue reading. Figure 6 and Figure 7 .

[0056] In this embodiment, forming the circuit pattern core board further includes: after baking and curing, laser ablation of the solder resist pattern 210 along the edge of the first window pattern 110 to ablate the solder resist pattern 210 that overflows the first window pattern 110.

[0057] Ink is generally produced by screen printing. In this embodiment, ink can be produced by creating a screen printing plate with a dotted screen. The screen printing plate window pattern is made at the position corresponding to the first window pattern 110. During screen printing, ink leaks from the screen printing plate window pattern to the position of the first window pattern 110. The ink will generally spread and overflow beyond the area outside the first window pattern 110. Therefore, laser ablation can be optionally used to cut off the overflowing solder resist pattern 210, leaving only the solder resist pattern 210 within the first window pattern 110. Since the copper layer is below the overflowing ink, the laser ablation energy can be adjusted to burn off the solder resist pattern 210 without damaging the copper layer.

[0058] Furthermore, after laser ablation, alkaline washing and water washing are performed.

[0059] Laser ablation produces impurities such as carbon powder, which can be cleaned with alkaline solutions such as KOH or NaOH, and then rinsed thoroughly with DI water.

[0060] Furthermore, after laser ablation, micro-etching is performed, with the copper layer thickness of the micro-etched layer being 5μm to 8μm, forming another ink layer core board 20A.

[0061] After laser ablation, there may still be solder resist patterns 210 covering the surface of the copper layer in a microscopic state. Micro-etching is used to etch away a certain thickness of the copper layer to completely remove the solder resist patterns 210 covering the surface of the copper layer.

[0062] Therefore, it is understandable that the copper layer of the first single-sided flexible copper-clad laminate in this embodiment needs to be pre-thickened by 5μm to 8μm compared to the prior art. The thickness is increased first, and then etched in that area to form the copper thickness required for the first circuit pattern 310. The reason for using laser ablation is that the flexible circuit board is relatively soft and inconvenient to remove by grinding.

[0063] In this embodiment, the ink is preferably a flexible solder resist ink, which is convenient for matching with the material of the flexible circuit board.

[0064] Please see Figures 11 to 13 ; Figure 11 This is a schematic diagram of the planar structure of the graphic cover film of this embodiment; Figure 12 for Figure 11 A schematic diagram of the cross-sectional structure of the EE surface.

[0065] Step S20:

[0066] Take a second single-sided flexible copper-clad laminate and create a second circuit pattern 410 on the copper layer. The size of the second circuit pattern 410 covers the surface pattern area 320. Along the edge of the second circuit pattern 410, create intermittent through grooves 430 on the insulating dielectric layer (i.e., the cover film layer 420) of the second single-sided flexible copper-clad laminate. The non-through groove positions of the intermittent through grooves 430 form connection positions 440. The entire assembly is then used to form the cover film pattern board 40.

[0067] This embodiment uses a second single-sided flexible copper-clad laminate to create patterns, instead of directly using a cover film (with openings) for lamination. By creating a second circuit pattern 410, the surface pattern area is protected during the lamination process. At the same time, it plays a more important role in release, preventing the solder mask layer from being adhered or damaged during lamination. Furthermore, the second circuit pattern 410 can be used to create a higher precision alignment effect, resulting in an overall cover film layer 420 with higher alignment precision than the cover film with openings, thus improving the processing quality of high-precision circuit boards.

[0068] First, intermittent through slots 430 are made to partially cut off the cover film layer corresponding to the second circuit pattern 410. This prevents subsequent simultaneous cutting from generating large amounts of laser-ablated carbon powder and impurities, contaminating the flexible circuit board surface, and causing potential hazards such as short circuits. At the same time, several connection positions 440 are retained to ensure the effective connection of the second circuit pattern 410 during lamination.

[0069] In this embodiment, the width of the connection position 440 is 50μm to 2.0mm; the connection position 440 is set with an appropriate size according to the size of the graphic and the application requirements to ensure that it can be connected.

[0070] In this embodiment, the second single-sided flexible copper-clad laminate contains an adhesive layer located between the copper layer and the insulating dielectric layer, and is an acrylic adhesive layer or an epoxy resin adhesive layer.

[0071] The adhesive layer can effectively act as an adhesive and create a difference in adhesion performance between it and the second circuit pattern 410, resulting in the effect that the adhesive layer effectively adheres while the second circuit pattern 410 does not adhere under pressing conditions.

[0072] In this embodiment, the copper layer (also the second circuit pattern 410) of the second single-sided flexible copper-clad laminate is 5μm to 15μm; this copper layer is only used for release and auxiliary alignment, so a thinner copper layer can meet the application requirements.

[0073] Please see Figure 13 ; Figure 13 This is a schematic diagram of the cross-sectional structure of the pressing plate in this embodiment.

[0074] Step S30:

[0075] The circuit pattern core board 30 and the cover film pattern board 40 are aligned, and the second circuit pattern 410 is set corresponding to and opposite the surface pattern area 320; then they are pressed together to form a pressed plate 50.

[0076] Please see Figure 14 and Figure 15 ; Figure 14 This is a schematic diagram of the planar structure of the flexible circuit board according to this embodiment; Figure 15 for Figure 14 A schematic diagram of the cross-sectional structure of the FF surface.

[0077] Step S40:

[0078] Cut the connection position 440 of the press plate 50, remove the cover, and form a patterned window 610 in the surface pattern area 320 to form a flexible circuit board 60.

[0079] In this embodiment, the connection position 440 of the press plate 50 is cut off by laser ablation, and then alkaline washing and water washing are performed.

[0080] After lamination is completed, the connection position 440 is cut off in the subsequent processing. Then the cover can be removed to expose the solder mask pattern 210 and IC pad pattern 3110.

[0081] It is worth noting that, due to the high precision of the circuit boards in the actual design and manufacturing process, the actual structural diagrams and dimensions such as the thickness of each layer and the width of the lines are at the micrometer level. For example, the thickness of each layer is generally between 5μm and 50μm. If the accompanying drawings in the instruction manual are made according to the actual scale, there will be a problem of unclear illustrations. Therefore, in order to more clearly show the implementation process of the manufacturing method, the accompanying drawings in this embodiment are all enlarged schematic diagrams of the technical features, and do not represent the size of the actual structural diagram, nor do they represent enlarged views of the actual structural diagram at the same scale.

[0082] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural transformations made using the contents of the specification and drawings of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the scope of patent protection of the present invention.

Claims

1. A method for fabricating a flexible circuit board with high-precision solder resist patterns, characterized in that: S10: Take a first single-sided flexible copper-clad laminate, create a first window pattern on the copper layer, apply ink to the first window pattern position, and bake and cure to form a solder mask pattern; then create a first circuit pattern, including creating an IC pad pattern; the area formed by the solder mask pattern and the IC pad pattern is the surface pattern area, and the solder mask pattern is located between the opposite pads of the IC pad pattern; the entire assembly is fabricated to form a circuit pattern core board; S20: Take a second single-sided flexible copper-clad laminate, and make a second circuit pattern on the copper layer. The size of the second circuit pattern covers the surface pattern area. Along the edge of the second circuit pattern, make intermittent through grooves on the insulating dielectric layer of the second single-sided flexible copper-clad laminate. The non-through groove positions of the intermittent through grooves form connection positions. The whole assembly is made to form a cover film pattern board. S30: Align the circuit pattern core board with the cover film pattern board, wherein the second circuit pattern is corresponding to and relative to the surface pattern area; Then they are pressed together to form a pressed plate; S40: Cut off the connection position of the pressing plate, remove the cover, and form the flexible circuit board.

2. The method for fabricating a flexible circuit board with a high-precision solder resist pattern as described in claim 1, characterized in that, Before the ink is produced, the first windowed graphic position is subjected to plasma treatment.

3. The method for fabricating a flexible circuit board with high-precision solder resist patterns as described in claim 1, characterized in that, The process of forming the circuit pattern core board further includes: after baking and curing, laser ablation of the solder resist pattern along the edge of the first window pattern to ablate the solder resist pattern that overflows the first window pattern.

4. The method for fabricating a flexible circuit board with high-precision solder resist patterns as described in claim 3, characterized in that, After the laser ablation is performed, alkaline washing and water washing are carried out.

5. A method for fabricating a flexible circuit board with a high-precision solder resist pattern as described in claim 3 or 4, characterized in that, After laser ablation, micro-etching is then performed.

6. The method for fabricating a flexible circuit board with a high-precision solder resist pattern as described in claim 5, characterized in that, The thickness of the copper layer obtained by micro-etching is 5 μm to 8 μm.

7. The method for fabricating a flexible circuit board with a high-precision solder resist pattern as described in claim 1, characterized in that, The width of the connection point is from 50 μm to 2.0 mm.

8. The method for fabricating a flexible circuit board with high-precision solder resist patterns as described in claim 1, characterized in that, The second single-sided flexible copper-clad laminate contains an adhesive layer, which is located between the copper layer and the insulating dielectric layer.

9. A method for fabricating a flexible circuit board with a high-precision solder resist pattern as described in claim 1 or 8, characterized in that, The copper layer of the second single-sided flexible copper-clad laminate is 5μm to 15μm.

10. A method for fabricating a flexible circuit board with a high-precision solder resist pattern as described in claim 1 or 8, characterized in that, The connection point of the pressed plate is cut off by laser ablation, followed by alkaline washing and water washing.

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