Circuit board micro-hole structure and processing method thereof

Abstract

The application provides a circuit board micro-hole structure and a processing method thereof. The circuit board micro-hole structure comprises a circuit board and a first solder resist layer. The circuit board comprises a substrate and a conductive micro-hole arranged on the substrate. The conductive micro-hole comprises a through hole penetrating through the substrate along the thickness direction of the substrate, a conductive layer arranged on the inner wall of the through hole, a first conductive disc and a second conductive disc. The first conductive disc is arranged on one side of the thickness direction of the substrate, and the first conductive disc is connected with the edge of one end of the conductive layer. The second conductive disc is arranged on the other side of the thickness direction of the substrate, and the second conductive disc is connected with the edge of the other end of the conductive layer. The conductive layer defines a conductive channel. The first solder resist layer covers one side of the thickness direction of the circuit board. The first solder resist layer is provided with a gas guide hole corresponding to the conductive channel. The gas guide hole is connected with the conductive channel. The diameter of the gas guide hole is equal to the diameter of the conductive channel, and the gas guide hole and the conductive channel are coaxially arranged.

Description

Technical Field

[0001] This invention relates to the field of circuit board processing, and in particular to a micro-hole structure for circuit boards and its processing method. Background Technology

[0002] In order to meet customer requirements in terms of appearance, circuit boards with conductive microvias in related technologies typically have one side with normal exposure and a window, while the other side is completely covered with solder mask and has no window at all.

[0003] However, when the pore size of the conductive micropores is extremely small, the solder resist ink is easily driven by capillary effect to seep and accumulate into the conductive micropores along the pore wall. Under the subsequent developing process conditions, the ink that has formed a closed state inside the pores is difficult to be completely removed by the developing solution, resulting in semi-closed or fully closed defects in the conductive micropores, which will seriously affect the quality of subsequent chemical gold processing. Summary of the Invention

[0004] This invention provides a microvia structure for a circuit board to solve the above-mentioned technical problems.

[0005] The circuit board microvia structure of this invention includes: A circuit board, comprising a substrate and conductive microvias disposed on the substrate, the conductive microvias comprising a through hole penetrating the substrate along the thickness direction, a conductive layer disposed on the inner wall of the through hole, a first conductive pad, and a second conductive pad, the first conductive pad being disposed on one side of the substrate along the thickness direction and connected to the edge of one end of the conductive layer; the second conductive pad being disposed on the other side of the substrate along the thickness direction and connected to the edge of the other end of the conductive layer; the conductive layer defining a conductive channel; A first solder mask layer covers one side of the circuit board in the thickness direction. The first solder mask layer has a vent hole corresponding to the conductive channel. The vent hole is connected to the conductive channel. The diameter of the vent hole is equal to the diameter of the conductive channel, and the vent hole and the conductive channel are coaxially arranged.

[0006] This invention creates vent holes on the first solder resist layer that are coaxial with and of equal diameter to the conductive channels. This ensures that both ends of the conductive channels are open and connected, eliminating the conditions for solder resist ink to accumulate inside the micropores and form closed dead cavities due to capillary effect. In other words, it is precisely because the vent holes provide micro-venting and drainage channels that the developing solution, as well as the micro-etching solution and immersion gold solution in subsequent electroless gold plating processes, can be fully replaced and rinsed out, avoiding liquid residue inside the micropores and eliminating defects such as incomplete electroless gold plating and uneven plating.

[0007] Meanwhile, because the conductive microvias are very small in size and the diameter of the conductive channels is also very small, meaning the diameter of the vent holes is also very small, the placement of the vent holes will not change the appearance of the first solder mask layer and will not be visible to the naked eye. At the same time, it will not affect the conductive microvias or the overall electrical performance of the circuit board, thus meeting the customer's appearance design requirements.

[0008] In some embodiments, the circuit board microvia structure of the present invention further includes a second solder resist layer, which covers the other side of the circuit board in the thickness direction. The second solder resist layer has a window corresponding to the second conductive pad to expose the second conductive pad.

[0009] In some embodiments, the inner edge of the window is spaced apart from the outer edge of the first conductive disk.

[0010] In some embodiments, the diameter of the through hole is 0.15~0.3mm.

[0011] The present invention also provides a method for fabricating micro-hole structures on circuit boards.

[0012] The fabrication method for the microvia structure of the circuit board according to this embodiment of the invention includes the following operations: A circuit board is obtained, the circuit board including a substrate and conductive microvias disposed on the substrate. The conductive microvias include a through hole penetrating the substrate along the thickness direction, a conductive layer disposed on the inner wall of the through hole, a first conductive pad and a second conductive pad. The first conductive pad is disposed on one side of the substrate in the thickness direction and is connected to the edge of one end of the conductive layer. The second conductive pad is disposed on the other side of the substrate in the thickness direction and is connected to the edge of the other end of the conductive layer. A first solder mask layer is processed on one side of the circuit board in the thickness direction. The first solder mask layer has a vent hole corresponding to the conductive channel. The vent hole is connected to the conductive channel. The diameter of the vent hole is equal to the diameter of the conductive channel, and the vent hole and the conductive channel are coaxially arranged.

[0013] In some embodiments, before processing the first solder mask layer, a stop point with a diameter equal to that of the conductive channel is provided on one side of the circuit board in the thickness direction.

[0014] In some embodiments, processing the first solder mask layer includes the following operations: Print solder resist ink on one side of the circuit board in the thickness direction; Expose the solder resist ink; Develop the solder resist ink; Curing of solder resist ink; The first solder resist layer is formed.

[0015] In some embodiments, the method for processing the micro-hole structure of the circuit board according to the present invention includes the following operations: processing a second solder resist layer on the other side of the circuit board in the thickness direction, wherein the second solder resist layer has an opening corresponding to the second conductive pad to expose the second conductive pad.

[0016] In some embodiments, processing the second solder mask layer includes the following operations: Print solder resist ink on the other side of the circuit board in the thickness direction; Expose the solder resist ink; Develop the solder resist ink; Curing of solder resist ink; A second solder resist layer is formed.

[0017] In some embodiments, the inner edge of the window is spaced apart from the outer edge of the first conductive disk. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention 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 these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the micro-hole structure of the circuit board according to an embodiment of the present invention.

[0020] In the picture: 100. Microvia structure of circuit boards; 1. Circuit board; 2. Substrate; 3. Conductive micropores; 301. Through holes; 302. Conductive layer; 303. First conductive pad; 304. Second conductive pad; 305. Conductive channel; 4. First solder mask layer; 401. Vent hole; 5. Second solder resist layer; 501. Open the window. Detailed Implementation

[0021] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0022] In the description of this invention, it should be understood that the terms "longitudinal," "radial," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0023] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal encapsulation of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0024] In traditional circuit boards 1, when processing microvia structures, one side is typically exposed with a window 501, while the other side is completely covered with a solder resist layer without any window 501. When the diameter of the conductive microvia 3 is small, the solder resist ink is driven by capillary effect to penetrate and accumulate along the wall of the conductive microvia 3. The developing process cannot completely remove the ink in the closed state inside the hole, resulting in semi-closed or fully closed defects in the conductive microvia 3. This leads to chemical residues in the subsequent gold plating process, incomplete gold plating on the inner wall of the microvia, and uneven plating thickness.

[0025] In response, the present invention proposes a microvia structure 100 for a circuit board, comprising a circuit board 1 and a first solder resist layer 4.

[0026] The circuit board 1 includes a substrate 2 and conductive microholes 3 disposed on the substrate 2. The conductive microholes 3 include a through hole 301 penetrating the substrate 2 along the thickness direction of the substrate 2, a conductive layer 302 disposed on the inner wall of the through hole 301, a first conductive pad 303 and a second conductive pad 304. The first conductive disk 303 is disposed on one side of the substrate 2 in the thickness direction, and the first conductive disk 303 is connected to the edge of one end of the conductive layer 302. The second conductive disk 304 is disposed on the other side in the thickness direction of the substrate 2, and the second conductive disk 304 is connected to the edge of the other end of the conductive layer 302; The conductive layer 302 defines the conductive channel 305; The first solder mask layer 4 covers one side of the circuit board 1 in the thickness direction. The first solder mask layer 4 is provided with a vent hole 401 corresponding to the conductive channel 305. The vent hole 401 is connected to the conductive channel 305. The diameter of the vent hole 401 is equal to the diameter of the conductive channel, and the vent hole 401 is coaxially arranged with the conductive channel.

[0027] For ease of understanding, the following explains some key terms in this embodiment: Conductive microvia 3: A micro-channel structure configured to extend along the thickness direction of substrate 2 to achieve electrical interconnection of interlayer circuits.

[0028] Conductive channel 305: A hollow flow space defined by a conductive layer 302 attached to the inner wall of the through hole 301.

[0029] Vent hole 401: It is formed on the first solder mask layer 4 and is axially aligned and connected with the conductive channel 305 to provide an opening structure for gas and liquid discharge.

[0030] Specifically, in the process of constructing the micro-hole structure 100 of the circuit board, the substrate 2 serves as the insulating support body of the overall structure, and the through hole 301 is opened through the thickness direction of the substrate 2. The through hole 301 can be formed by mechanical drilling or by laser ablation and other processes.

[0031] Furthermore, a conductive layer 302 is formed on the inner wall surface of the through-hole 301. The conductive layer 302 can be deposited by a combination of chemical copper plating and full-board copper plating. The inner wall surface of the conductive layer 302 defines an axially extending conductive channel 305. A first conductive pad 303 is formed on one side surface of the substrate 2 in the thickness direction and is connected to the first edge of the conductive layer 302. A second conductive pad 304 is formed on the other side surface of the substrate 2 in the thickness direction and is connected to the second edge of the conductive layer 302.

[0032] Based on this, a first solder mask layer 4 is coated and covers one side of the circuit board 1 in the thickness direction. A vent hole 401 is formed in the region of the first solder mask layer 4 corresponding to the conductive channel 305, and the vent hole 401 communicates with the conductive channel 305. The diameter of the vent hole 401 is machined to be consistent with the diameter of the conductive channel 305, and the geometric center axis of the vent hole 401 is configured to coincide with the geometric center axis of the conductive channel 305.

[0033] This invention provides a vent hole 401 on the first solder resist layer 4, coaxial with and of the same diameter as the conductive channel 305. This ensures that both ends of the conductive channel 305 are open and connected, eliminating the conditions for solder resist ink to accumulate inside the micropores and form a closed dead cavity due to capillary effect. In other words, it is precisely because the vent hole 401 provides a micro-venting and drainage channel that the developer and subsequent etching solution and gold plating solution in the electroless gold plating process can be fully replaced and rinsed out, avoiding liquid residue inside the micropores and eliminating defects such as incomplete electroless gold plating and uneven plating.

[0034] Meanwhile, since the conductive micro-hole 3 is very small in size and the conductive channel 305 is also very small in diameter, the vent hole 401 is also very small in diameter. Therefore, the setting of the vent hole 401 will not change the appearance of the first solder mask layer 4, and it cannot be seen with the naked eye. At the same time, it will not affect the overall electrical performance of the conductive micro-hole 3 and the circuit board 1, thus meeting the customer's appearance design requirements.

[0035] In some embodiments of the present invention, the circuit board micro-hole structure 100 further includes a second solder resist layer 5, which covers the other side of the circuit board 1 in the thickness direction. The second solder resist layer 5 has a window 501 corresponding to the second conductive disk 304 to expose the second conductive disk 304.

[0036] Specifically, the second solder mask layer 5 serves as an insulating protective structure disposed on the other side of the circuit board 1, and is used to protect the conductive lines on the other side of the substrate 2 from external oxidation, physical scratches, and bridging short circuits during assembly and soldering.

[0037] It is understandable that conductive lines are provided on both sides of the substrate 2 in the thickness direction, and the first conductive disk 303 and the second conductive disk 304 can be understood as part of the conductive lines on both sides of the substrate 2 in the thickness direction.

[0038] Furthermore, the window 501 serves as a through-hole area formed on the second solder resist layer 5, used to precisely expose the conductive surface of the second conductive disk 304.

[0039] In a specific implementation, the window 501 can be obtained through a photomask positioning exposure and a photolithographic development process that uses a weakly alkaline developer to dissolve the uncrosslinked ink.

[0040] Through the above technical solution, the second solder resist layer 5 and its window 501 structure provide a reliable electrical access interface for the second conductive disk 304, ensuring that the circuit board 1 can be soldered to external devices in the future.

[0041] More importantly, the opening 501 of the second solder resist layer 5 and the vent 401 on the first solder resist layer 4 on the other side ensure that the conductive channel 305 is no longer in a single-end restricted or closed state. During wet processes such as micro-etching, immersion gold, and subsequent water washing, the treatment solution and cleaning solution can smoothly enter the conductive channel 305 through the opening 501 of the second solder resist layer 5, and achieve internal and external pressure balance and sufficient displacement convection through the vent 401 at the first solder resist layer 4. This completely eliminates the problems of liquid retention and dead corner liquid accumulation caused by capillary effect, ensuring that the conductive layer 302 on the hole wall can fully contact the reaction solution and be thoroughly cleaned, effectively preventing process defects such as incomplete gold plating, uneven plating thickness, and local copper exposure.

[0042] In some embodiments, the inner edge of the window 501 is spaced apart from the outer edge of the first conductive disk 303.

[0043] Specifically, the spacing between the inner edge of the window 501 and the outer edge of the first conductive disk 303 means that, in the thickness projection direction of the substrate 2, the inner contour boundary of the window 501 and the outer contour boundary of the first conductive disk 303 do not contact each other in space, and a preset safe distance is maintained between them to form structural isolation.

[0044] In detail, regarding the implementation of this spacing setting, in one optional embodiment, the inner edge of the window 501 and the outer edge of the first conductive disk 303 can be designed as a coaxial and concentric geometric contour, so that a uniformly wide annular isolation area is formed between the inner edge of the window 501 and the outer edge of the first conductive disk 303 in the entire circumferential direction; in another optional embodiment, the inner edge of the window 501 can also adopt a polygonal, elliptical or asymmetrical contour design, so that the spacing in a specific direction is specifically expanded according to the circuit layout or process alignment margin, thereby forming an isolation area of ​​non-uniform width around the first conductive disk 303.

[0045] Through the above technical solution, the present invention completely blocks the direct interference between the second solder resist layer 5 and the first conductive disk 303 by making the inner edge of the window 501 and the outer edge of the first conductive disk 303 staggered and maintaining a gap in the spatial structure.

[0046] Meanwhile, given the inherent alignment tolerances and ink microflow characteristics in the printing, exposure alignment and curing processes of solder resist ink, the reserved gap space can serve as an effective process tolerance zone, preventing the solder resist ink from overflowing and climbing to the edge of the first conductive disk 303 during processing, and preventing the ink from seeping into the conductive micropores 3 due to capillary action, causing contamination of the pore walls or blockage of the channels.

[0047] Based on this, the physical separation of the inner edge of the window 501 and the outer edge of the first conductive disk 303 ensures a smooth flow channel between the conductive channel 305 and the external environment. This allows the micro-etching solution, gold plating solution, and cleaning solution to fully penetrate into the conductive channel 305 and achieve efficient replacement and complete drainage during the subsequent gold plating process. This fundamentally eliminates the hidden danger of residual solution accumulation inside the micropores, ensures the uniformity and integrity of the gold plating layer on the inner wall of the conductive layer 302, and effectively prevents defects such as missed plating and exposed copper.

[0048] In some embodiments, the diameter of the through hole 301 is 0.15~0.3mm.

[0049] Preferably, the diameter of the through hole 301 is any one value or a range of any two values ​​from 0.15mm, 0.17mm, 0.19mm, 0.21mm, 0.23mm, 0.25mm, 0.27mm, 0.28mm, and 0.3mm.

[0050] Specifically, through-hole 301 refers to a micro-channel structure that penetrates the substrate 2 along its thickness direction. The processing method of through-hole 301 can be selected according to the actual board thickness and process conditions. For example, it can be formed by mechanical drilling, laser drilling (such as ultraviolet laser drilling or carbon dioxide laser drilling), or plasma dry etching.

[0051] It is understandable that when the diameter of the through-hole 301 is between 0.15 and 0.3 mm, the conductive channel 305 and the coaxial, equal-diameter vent hole 401 cooperate to present an optimal hydrodynamic state. During the fabrication of the first solder resist layer 4, the vent hole 401 can smoothly connect to the outside, preventing the formation of localized negative pressure within the hole that would draw and accumulate the solder resist ink. Simultaneously, the appropriate hole diameter effectively weakens capillary climbing force, preventing the micropores from being too small and thus hindering the developer from effectively wetting and rinsing, while also avoiding the problem of excessively large vent holes 401, further preventing any impact on the appearance of the first solder resist layer 4 and thus meeting customer requirements for aesthetics.

[0052] Based on this, the aperture range also ensures that in the subsequent electroless gold plating process, the immersion gold solution, micro-etching solution and water washing liquid can achieve full and smooth dynamic replacement and convection cleaning inside the conductive channel 305. From the physical structure, it eliminates the phenomenon of solution interception and liquid accumulation residue, thereby reliably avoiding quality defects such as incomplete electroless gold plating, uneven plating thickness and local copper exposure on the inner wall of the conductive layer 302.

[0053] The present invention also provides a method for processing a micro-hole structure 100 on a circuit board.

[0054] The processing method of the circuit board microvia structure 100 of this embodiment includes the following operations: obtaining a circuit board 1, the circuit board 1 including a substrate 2 and conductive microvias 3 disposed on the substrate 2, the conductive microvias 3 including a through hole 301 penetrating the substrate 2 along the thickness direction of the substrate 2, a conductive layer 302 disposed on the inner wall of the through hole 301, a first conductive disk 303 and a second conductive disk 304, the first conductive disk 303 being disposed on one side in the thickness direction of the substrate 2, and the first conductive disk 303 being connected to the edge of one end of the conductive layer 302; the second conductive disk 304 being disposed on the other side in the thickness direction of the substrate 2, and the second conductive disk 304 being connected to the edge of the other end of the conductive layer 302; processing a first solder resist layer 4 on one side in the thickness direction of the circuit board 1, the first solder resist layer 4 being provided with a vent hole 401 corresponding to the conductive channel 305, the vent hole 401 being connected to the conductive channel 305, the diameter of the vent hole 401 being equal to the diameter of the conductive channel 305, and the vent hole 401 being coaxially disposed with the conductive channel 305.

[0055] Specifically, during the manufacturing process of circuit board 1, substrate 2 serves as the main insulating carrier, and through-holes 301 are formed in substrate 2 through mechanical drilling or laser ablation processes.

[0056] The conductive layer 302 is deposited on the inner wall of the through hole 301 through chemical copper plating and full-board electroplating copper processes, and its inner surface defines the conductive channel 305.

[0057] The first conductive disk 303 and the second conductive disk 304 are formed on both sides of the substrate 2 by subtractive etching or additive patterning electroplating processes, respectively, and are electrically connected to the end edge of the conductive layer 302.

[0058] Based on this, a first solder resist layer 4 is coated on one side of the circuit board 1. By precisely controlling the pattern of the exposure mask, a vent hole 401 is formed at the position corresponding to the conductive channel 305, ensuring that the vent hole 401 is coaxial with the conductive channel 305 and has the same aperture size.

[0059] Since the air vent 401 and the conductive channel 305 are coaxial and of equal diameter, the conductive microhole 3 remains open at both ends after the solder resist layer is applied, thereby eliminating the conditions for ink accumulation caused by capillary effect in the hole and preventing ink from seeping into and accumulating in the hole.

[0060] During the developing process, the developer can fully penetrate the hole to clean away residues; in the subsequent gold plating process, the micro-etching solution, gold plating solution and washing solution can be fully replaced and rinsed to completely remove accumulated liquid residues.

[0061] Through the above technical solution, the present invention effectively solves the problem of semi-closed or fully closed defects in conductive micro-holes 3, ensures the uniformity and integrity of gold plating on the inner wall of conductive micro-holes 3, and significantly improves the manufacturing quality and reliability of circuit board 1.

[0062] In some embodiments, before processing the first solder resist layer 4 on one side of the circuit board 1 in the thickness direction, a stop point with the same diameter as the conductive channel 305 is provided on one side of the circuit board 1 in the thickness direction corresponding to the conductive channel 305.

[0063] Specifically, a blocking point refers to a patterned barrier structure or shielding mark pre-set at the end of the opening of the conductive channel 305, used to locally block and optically or physically isolate the opening area of ​​the conductive channel 305.

[0064] Through the above technical solution, before processing the first solder resist layer 4, a blocking point with the same diameter as the conductive channel 305 is pre-set, blocking the path of solder resist ink into the conductive channel 305 from the source. During the subsequent printing of solder resist ink, the blocking point acts as a physical barrier, effectively preventing the solder resist ink from seeping and accumulating in the conductive channel 305 along the hole wall due to capillary effect. This ensures that the interior of the conductive channel 305 remains clean and unobstructed, completely avoiding the semi-closed or fully closed defects caused by residual ink in the hole that cannot be removed during the developing process.

[0065] Furthermore, since the stop point is equal in diameter and precisely aligned with the conductive channel 305, it not only ensures the integrity of the solder resist layer covering the area around the conductive channel 305, but also provides a reliable positioning reference for the subsequent precise formation of the vent hole 401, which is coaxial with the conductive channel 305 and has the same diameter.

[0066] In some embodiments, the step of processing the first solder mask layer 4 includes: Solder resist ink is printed on one side of the circuit board 1 in the thickness direction; Expose the solder resist ink; Develop the solder resist ink; Curing of solder resist ink; The first solder resist layer 4 is formed.

[0067] Specifically, printing solder resist ink on one side of the circuit board 1 in the thickness direction mainly serves to uniformly lay a layer of photosensitive polymer material film with insulating and protective functions on the outer surface of the circuit board 1, providing a material basis for subsequent patterning processing.

[0068] In practice, the solder resist ink can be printed using screen printing, where a squeegee is used to evenly coat the liquid solder resist ink onto the surface of the circuit board 1 through a screen with predetermined pores; or it can be printed using spraying or roller coating, where the solder resist ink is applied evenly to one side of the circuit board 1 using atomizing spraying equipment or a high-precision coating roller to obtain a uniform ink coating.

[0069] The main purpose of exposing solder resist ink is to cause the photosensitive ink in the target pattern area to undergo a cross-linking and curing reaction through photochemical action, thereby optically transferring and defining the retained area and the removed area.

[0070] In practice, exposure can be performed by a contact exposure machine in conjunction with an optical mask pre-drawn with the masking pattern of the vent hole 401, using ultraviolet light irradiation; alternatively, a laser direct imaging exposure system can be used, which selectively scans and exposes the solder resist ink surface using a focused laser beam based on a preset digital design pattern, in order to achieve maskless and precise optical pattern definition of the vent hole 401 position.

[0071] The main purpose of developing the solder resist ink is to use chemical solutions to dissolve and peel off the ink areas that have not undergone photocrosslinking and curing, thereby physically hollowing out the surface of the circuit board 1 to expose the preset pattern structure.

[0072] In practice, development can be achieved by using a spray-type developer to dissolve and clean the ink layer with a weakly alkaline developing solution under high pressure; alternatively, an immersion developing tank combined with ultrasonic vibration can be used to cause the ink in the unexposed areas to swell and peel off quickly in the developing solution, thereby ensuring that the residual ink at the corresponding air vent 401 position is thoroughly washed away.

[0073] The main purpose of curing solder resist ink is to enable the solder resist ink coating after development and molding to undergo thorough thermal cross-linking or deep photochemical curing through external energy input, thereby giving the solder resist layer sufficient mechanical strength, adhesion and chemical corrosion resistance.

[0074] In actual implementation, curing can be achieved by gradient heating and baking the circuit board 1 in a hot air circulating oven or tunnel baking oven; or by strong ultraviolet light irradiation of the solder resist layer with an ultraviolet light deep curing irradiation device, which promotes the complete cross-linking and overlapping of the solder resist resin molecular chains, and finally stabilizes the formation of the first solder resist layer 4.

[0075] In some embodiments, the processing method of the micro-hole structure 100 of the circuit board further includes processing a second solder resist layer 5 on the other side of the circuit board 1 in the thickness direction. The second solder resist layer 5 has a window 501 corresponding to the second conductive pad 304 to expose the second conductive pad 304.

[0076] Specifically, the second solder resist layer 5 serves as an insulating protective layer covering the other side of the circuit board 1 in the thickness direction. Its main function is to protect the insulating medium and non-soldering areas on the surface of the substrate 2 from external physical scratches, moisture and oxidizing media.

[0077] The window 501 refers to a partially through window formed by removing the solder resist material at a preset position on the second conductive disk 304 on the second solder resist layer 5. Its main function is to precisely expose the second conductive disk 304 so that subsequent processes can perform surface coating treatment or realize the soldering of components.

[0078] Through the above technical solution, the present invention adds a second solder resist layer 5 with a window 501 on the other side of the circuit board 1. The first solder resist layer 4 is designed with a vent hole 401 that is coaxial with the conductive channel 305 and of the same diameter. This eliminates the hole-sealing defect caused by the solder resist ink penetrating and accumulating due to capillary effect when the micropore diameter is extremely small. This ensures that the liquids such as micro-etching solution and gold immersion solution are fully replaced and rinsed out in subsequent gold immersion processes. Based on this, the second solder mask layer 5 fully covers and protects the surface of the substrate 2 on the other side of the circuit board 1, effectively preventing oxidation and corrosion of the circuit board 1 during process turnover and use environment. The opening 501 of the second solder mask layer 5 corresponding to the second conductive pad 304 precisely exposes the conductive contact surface, ensuring that the second conductive pad 304 can normally carry out electrical connection processes such as electroless gold plating, tin plating or surface mounting.

[0079] In some embodiments, the step of processing the second solder mask layer 5 includes: Solder resist ink is printed on the other side of the circuit board 1 in the thickness direction; Expose the solder resist ink; Develop the solder resist ink; Curing of solder resist ink; Form the second solder resist layer 5.

[0080] Specifically, during the process of printing solder resist ink on the other side of the thickness direction of the circuit board 1, liquid photosensitive solder resist ink can be uniformly transferred and coated onto the surface of the substrate 2 by screen printing.

[0081] During the exposure of solder resist ink, an ultraviolet light exposure machine can be used with a photomask with a preset pattern to selectively irradiate the solder resist ink. Alternatively, laser direct imaging technology can be used to perform patterned scanning of the solder resist ink. By changing the solubility of the solder resist ink in the target area through photochemical crosslinking reaction, the retention area and the windowed 501 area can be precisely defined.

[0082] During the development of solder resist ink, sodium carbonate solution can be used for high-pressure spray development, or a special organic alkaline developer can be used to dissolve and rinse the ink in the unexposed areas, thereby completely removing ink residue at the location to be opened (501), so that the preset window structure (501) is fully and clearly displayed.

[0083] During the curing process of solder resist ink, hot air circulation baking in an oven can be used to make the solder resist ink undergo a complete thermal cross-linking reaction. Alternatively, a dual curing method combining ultraviolet light irradiation and hot baking can be used to make the formed solder resist coating achieve the preset hardness and chemical stability, ultimately forming a structurally stable second solder resist layer 5.

[0084] Through the above technical solution, by using standardized coating, photosensitive imaging, developing and rinsing and cross-linking curing processes, high-precision control of the position and size of the second solder resist layer 5 window 501 is achieved, effectively avoiding defects such as blurred edges or residual adhesive of the window 501, ensuring that the second conductive disk 304 can be accurately and completely exposed, providing a clean and reliable contact interface for subsequent electrical connections.

[0085] In some embodiments, the inner edge of the window 501 is spaced apart from the outer edge of the first conductive disk 303.

[0086] Specifically, the interval between the inner edge of the window 501 and the outer edge of the first conductive disk 303 means that, in the projection direction parallel to the surface of the substrate 2, the inner peripheral edge contour of the window 501 formed by the second solder resist layer 5 is staggered in the horizontal plane from the outer peripheral edge contour of the first conductive disk 303 on the opposite side of the substrate 2, and a certain geometric gap is maintained.

[0087] In actual manufacturing, this spacing layout can be achieved in several ways: Firstly, when exposing the second solder resist layer 5, a mask light-blocking pattern with a preset size larger than the outer contour of the first conductive disk 303 is used, so that the inner diameter of the window 501 formed after exposure and development is completely expanded outward in the orthographic projection direction to the outer diameter edge of the first conductive disk 303, thereby forming an annular buffer gap between the two projections. Secondly, by adjusting the edge geometry of the window 501 pattern, the inner edge of the window 501 can be shifted outward, either entirely or partially, on the projection of the substrate 2 plane, so as to maintain a preset safety margin with the outer edge of the first conductive disk 303 in the horizontal direction, and avoid the edges of the two overlapping under tolerance fluctuations.

[0088] Through the above technical solution, the inner edge of the window 501 of the second solder resist layer 5 and the outer edge of the first conductive disk 303 are designed to be spaced out from the perspective of spatial layout, thereby avoiding direct contact or overlap between the edge of the solder resist layer and the edge of the conductive disk in the projected position from the structural level.

[0089] During the fabrication of the microporous structure, this spacing effectively prevents solder resist ink from overflowing onto the conductive pad surface due to edge effects during printing, exposure, or development, ensuring the cleanliness of the conductive pad area and thus providing good surface conditions for subsequent electroless gold processing.

[0090] Meanwhile, by maintaining a certain distance between the inner edge of the window 501 and the outer edge of the first conductive disk 303, the risk of local stress concentration, peeling, or cracking of the solder resist layer at the edge of the conductive disk can be reduced. While ensuring the effective connection area of ​​the conductive disk, the uniformity of the solder resist layer on the surface of the substrate 2 and the structural stability are optimized, and the gold plating quality of the area around the conductive microhole 3 is significantly improved.

[0091] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A microvia structure for a circuit board, characterized in that, include: A circuit board, comprising a substrate and conductive microvias disposed on the substrate, the conductive microvias comprising a through hole penetrating the substrate along the thickness direction, a conductive layer disposed on the inner wall of the through hole, a first conductive pad, and a second conductive pad, the first conductive pad being disposed on one side of the substrate along the thickness direction and connected to the edge of one end of the conductive layer; the second conductive pad being disposed on the other side of the substrate along the thickness direction and connected to the edge of the other end of the conductive layer; the conductive layer defining a conductive channel; A first solder mask layer covers one side of the circuit board in the thickness direction. The first solder mask layer has a vent hole corresponding to the conductive channel. The vent hole is connected to the conductive channel. The diameter of the vent hole is equal to the diameter of the conductive channel, and the vent hole and the conductive channel are coaxially arranged.

2. The microvia structure of the circuit board according to claim 1, characterized in that, It also includes a second solder mask layer, which covers the other side of the circuit board in the thickness direction. The second solder mask layer has a window corresponding to the second conductive pad to expose the second conductive pad.

3. The microvia structure of the circuit board according to claim 2, characterized in that, The inner edge of the window is spaced apart from the outer edge of the first conductive disk.

4. The microvia structure of the circuit board according to claim 1, characterized in that, The diameter of the through hole is 0.15~0.3mm.

5. A method for fabricating a micro-hole structure on a circuit board, characterized in that, This includes the following operations: A circuit board is obtained, the circuit board including a substrate and conductive microvias disposed on the substrate. The conductive microvias include a through hole penetrating the substrate along the thickness direction, a conductive layer disposed on the inner wall of the through hole, a first conductive pad and a second conductive pad. The first conductive pad is disposed on one side of the substrate in the thickness direction and is connected to the edge of one end of the conductive layer. The second conductive pad is disposed on the other side of the substrate in the thickness direction and is connected to the edge of the other end of the conductive layer. A first solder mask layer is processed on one side of the circuit board in the thickness direction. The first solder mask layer has a vent hole corresponding to the conductive channel. The vent hole is connected to the conductive channel. The diameter of the vent hole is equal to the diameter of the conductive channel, and the vent hole and the conductive channel are coaxially arranged.

6. The method for fabricating microvia structures on a circuit board according to claim 5, characterized in that, Before processing the first solder mask layer, a stop point with the same diameter as the conductive channel is set on one side of the circuit board in the thickness direction.

7. The method for fabricating micro-hole structures on a circuit board according to claim 5, characterized in that, Processing the first solder mask layer includes the following operations: Print solder resist ink on one side of the circuit board in the thickness direction; Expose the solder resist ink; Develop the solder resist ink; Curing of solder resist ink; The first solder resist layer is formed.

8. The method for fabricating micro-hole structures on a circuit board according to claim 5, characterized in that, It also includes the following operation: processing a second solder resist layer on the other side of the circuit board in the thickness direction, wherein the second solder resist layer has a window corresponding to the second conductive pad to expose the second conductive pad.

9. The method for fabricating micro-hole structures on a circuit board according to claim 8, characterized in that, Processing the second solder mask layer includes the following operations: Print solder resist ink on the other side of the circuit board in the thickness direction; Expose the solder resist ink; Develop the solder resist ink; Curing of solder resist ink; A second solder resist layer is formed.

10. The method for fabricating micro-hole structures on a circuit board according to claim 8, characterized in that, The inner edge of the window is spaced apart from the outer edge of the first conductive disk.

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