Soldering method based on half-plugged holes of circuit board and circuit board

Abstract

The application discloses a kind of based on circuit board half hole's tin spraying method and circuit board.The method includes the following steps: providing circuit board, wherein, the surface of circuit board is provided with circuit layer, and circuit board is provided with multiple through holes, the surface of circuit board is covered with solder resist layer, solder resist layer is provided with solder resist window, solder resist layer covers circuit layer, and the pad of circuit layer and each through hole are exposed through solder resist window;Each through hole is handled to hole, and half hole is formed;Hot melt resin is pre-coated at the hole mouth position of half hole, and hot melt resin layer is formed at the hole mouth position of half hole;Circuit board is immersed in molten tin to carry out tin spraying treatment, and the circuit board after tin spraying is obtained.The application is by setting hot melt resin layer at the hole mouth of half hole, using tin spraying heat to drive resin melt flow to form temporary sealing structure, reduce the risk of molten tin infiltration, improve the structural integrity of half hole and circuit board tin spraying reliability.

Description

Technical Field

[0001] This invention relates to the field of printed circuit technology, and in particular to a solder spraying method based on a partially plugged circuit board and a circuit board. Background Technology

[0002] Semi-plugged vias, due to their combined functions of conductivity, heat dissipation, ventilation, and positioning, are widely used in test points, heat dissipation holes, and back-drilled positioning holes. During circuit board manufacturing, semi-plugged via products typically undergo hot air leveling and tin plating to improve the solderability of the pads and surface protection. However, during tin plating, the circuit board is immersed in high-temperature molten solder and subjected to high-pressure hot air blowing. The opening of the semi-plugged via and the plugging ink are subjected to significant thermal and airflow impacts, easily leading to damage to the sealing structure of the via opening. This causes molten solder to seep into the via along the opening gaps, resulting in defects such as solder penetration, via bursting, and uncontrolled semi-plugging depth, severely affecting the reliability and product yield of the circuit board. Currently, existing technologies typically mitigate these defects by improving the heat resistance of the plugging ink, optimizing the tin plating temperature, or adjusting the air knife parameters. However, these measures mainly optimize single process parameters and are insufficient to effectively protect the opening gaps of the semi-plugged via during the tin plating process. When high-temperature molten solder and hot air work together, a solder penetration channel can easily form at the orifice, causing molten solder to penetrate into the half-plugged hole, resulting in poor solder spraying quality stability. Summary of the Invention

[0003] Therefore, the present invention needs to provide a solder spraying method and circuit board based on a circuit board with partially plugged holes, in order to solve at least one of the above-mentioned technical problems.

[0004] To achieve the above objectives, a solder spraying method based on a partially plugged via on a circuit board includes the following steps: A circuit board is provided, wherein a circuit layer is provided on the surface of the circuit board, and the circuit board has multiple vias. The surface of the circuit board is covered with a solder mask layer, and the solder mask layer is provided with solder mask windows. The solder mask layer covers the circuit layer, and the pads of the circuit layer and each via are exposed through the solder mask windows. Each through hole is plugged to form a partial plug; A hot-melt resin is pre-coated at the opening of the partially plugged hole to form a hot-melt resin layer. The circuit board is immersed in molten solder for solder spraying to obtain the solder-sprayed circuit board.

[0005] Preferably, a circuit board is also provided, which is manufactured using a solder spraying method based on a circuit board half-hole plugging method.

[0006] This invention pre-coats a hot-melt resin layer at the opening of a partially plugged via before soldering. This allows the resin to melt during the soldering process, utilizing the high temperature of the molten solder, and flow along the opening to form a temporary seal. This effectively prevents molten solder from seeping into the partially plugged via. By fully utilizing the heat generated during soldering, the invention actively seals the opening, transforming thermal shock from a negative factor into a favorable condition for seal formation. While ensuring normal soldering of the pads, it effectively reduces the probability of solder seepage, hole bursting, and partially plugged via failure, improving the structural integrity, processing consistency, circuit board reliability, and product yield after soldering. Attached Figure Description

[0007] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the steps of the solder spraying method based on the partial plugging of circuit board holes according to the present invention; Figure 2 for Figure 1 A detailed flowchart of step S2; Figure 3 for Figure 1 A detailed flowchart of step S3. Detailed Implementation

[0008] The technical method of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0009] Furthermore, the accompanying drawings are merely illustrative of the invention and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented in software, in one or more hardware modules or integrated circuits, or in different network and / or processor methods and / or microcontroller methods.

[0010] It should be understood that although the terms "first," "second," etc., may be used herein to describe various units, these units should not be limited by these terms. These terms are used merely to distinguish one unit from another. For example, without departing from the scope of the exemplary embodiments, a first unit may be referred to as a second unit, and similarly, a second unit may be referred to as a first unit. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0011] To achieve the above objectives, please refer to Figure 1 This invention provides a solder spraying method based on a partially plugged via on a circuit board, characterized by comprising the following steps: Step S1: Provide a circuit board, wherein the surface of the circuit board is provided with a circuit layer, and the circuit board has multiple vias. The surface of the circuit board is covered with a solder mask layer, the solder mask layer is provided with solder mask windows, the solder mask layer covers the circuit layer, and the pads of the circuit layer and each via are exposed through the solder mask windows. A circuit board with a predetermined circuit pattern is used as the processing object. A circuit layer is formed on the surface of the circuit board, and multiple through-holes are machined through the circuit board. A solder mask layer is covered on the circuit layer and the surface of the circuit board. Windows are made in the solder mask layer according to the positions of the pads and through-holes, so that the pads and through-holes are exposed from the solder mask windows, while the remaining areas of the circuit layer are covered by the solder mask layer. By defining the solder spraying area through the structure, the molten solder mainly acts on the exposed pads and through-hole areas, reducing the adhesion of molten solder to non-soldering areas.

[0012] Step S2: Plug each through hole to form a half-plugged hole; The circuit board is fed into a via-filling device, where via-filling ink enters the via through the opening. The filling depth of the ink is controlled so that it only fills a portion of the via's depth, leaving unfilled space inside. The ink is then cured, fixing it inside the via and creating a partial via. By creating a partial via, a portion of the via's cavity is preserved, providing a solution for sealing the via opening during the soldering process.

[0013] Step S3: Pre-coat the opening of the half-plugged hole with hot melt resin to form a hot melt resin layer at the opening of the half-plugged hole. After forming the partial plug, hot-melt resin is applied to the opening of the partial plug using a quantitative coating method, covering the edge of the opening and forming a continuous hot-melt resin layer around it. The hot-melt resin layer is then pre-cured to maintain its position at the opening of the partial plug. By pre-forming the hot-melt resin layer, the heat generated by tin spraying melts the resin layer, sealing the opening of the partial plug.

[0014] Step S4: Immerse the circuit board in molten solder for solder spraying to obtain the solder-sprayed circuit board.

[0015] The circuit board with the thermoplastic resin layer is fed into the solder molten area, bringing the exposed pads and vias into contact with the molten solder. Hot air is then used to blow away the molten solder from the circuit board surface, creating a continuous solder layer on the pads and vias. During the solder spraying process, the thermoplastic resin layer melts and flows along the edge of the partially plugged via opening towards the center, sealing the gap at the opening. This sealing action reduces the probability of molten solder entering the partially plugged via, while simultaneously achieving a smooth and continuous solder layer.

[0016] In one embodiment, after the step of exposing the circuit layer pads and vias through solder mask windows, the following method is further included: The walls of each through hole are micro-etched to form a uniformly distributed micro-pit structure on the surface of the hole wall. Low-pressure plasma is used to activate the pore walls, removing residues from the pore wall surface and increasing the opening size of the micropit structure.

[0017] In this embodiment, after the solder mask window is formed, the circuit board is placed in a micro-etching tank to ensure that the walls of each via are in full contact with the micro-etching solution. The micro-etching solution is an acidic solution capable of dissolving and removing a small amount of copper layer from the surface of the via walls. The amount of copper layer removed is controlled by adjusting the solution concentration, processing temperature, and processing time to create a uniformly distributed micro-pit structure on the via wall surface. During the process, the circuit board is kept submerged, and the micro-etching solution continuously flows through each via to reduce differences in the degree of micro-etching at different locations within the vias. After the micro-etching treatment is completed, the circuit board is removed and washed with water to remove residual micro-etching solution from the via walls, and then dried to retain the micro-pit structure formed by the micro-etching on the via wall surface.

[0018] Understandably, during the micro-etching process, a solder mask layer is used to cover and protect the circuit layers on the circuit board surface. Since the circuit layers on the circuit board surface are located within the solder mask coverage area, the micro-etching solution cannot directly contact the solder mask-covered circuit layers. However, the orifice openings of vias are exposed through the solder mask window, and the via wall is connected to the cavity. Therefore, the micro-etching solution can enter the cavity through the via opening and directly contact the via wall. Thus, the micro-etching solution mainly acts on the via walls not covered by the solder mask, while other copper layers on the circuit board surface are physically isolated by the solder mask and do not directly participate in the micro-etching reaction. During the micro-etching process, by controlling the concentration of the micro-etching solution, the processing temperature, the processing time, and the liquid flow state, only the shallow copper layer on the via wall dissolves, forming a micro-pit structure. Simultaneously, the micro-etching solution is prevented from entering the circuit layer surface from the edge of the solder mask, thereby maintaining the circuit dimensions and surface condition of other copper layers on the circuit board surface.

[0019] The circuit board, after micro-etching, is placed in a low-pressure plasma processing chamber with the orifice openings facing the plasma action area. The chamber is then evacuated to achieve a predetermined low-pressure state. A working gas is introduced into the chamber, generating plasma under low pressure. This plasma enters the orifices and acts on the orifice walls. By controlling the plasma processing power, chamber pressure, and processing time, organic residues on the orifice walls are decomposed and removed. Simultaneously, the edges of the micro-pit structures are further activated, expanding the pits from small openings to more easily accessible structures. After processing, plasma generation is stopped, the chamber pressure is restored, and the circuit board is removed.

[0020] By first micro-etching the via walls to create a uniform micro-pit structure, and then using low-pressure plasma to remove residues from the via walls and enlarge the opening size of the micro-pit structure, a clean, roughened surface structure with open micro-pits is formed on the via walls. This structure increases the actual contact area between the via-plugging ink and the via walls, improves the ink's ability to penetrate the micro-pit structure, and enhances the bonding stability between the cured semi-plugged vias and the via walls, thereby reducing the risk of detachment and cracking of the semi-plugged vias under subsequent tin-spraying heat treatment.

[0021] In one embodiment, see Figure 2 The steps for plugging each through hole to form a semi-plugged hole include: Step S21: Place the circuit board in the vacuum plugging device and evacuate it to a high vacuum state; Step S22: Use hole-filling ink to fill each via; Step S23: After the plugging ink is immersed in the through hole, the plugging pressure is controlled to make the plugging ink reach the target depth. When the plugging ink penetrates to the target depth, the plugging ink fills the micro-pit structure and is cured to form a semi-plugged hole.

[0022] In this embodiment, after micro-etching and low-pressure plasma activation, the circuit board is placed on the support platform of the vacuum plugging equipment, fixing it in the plugging position and aligning the orifice of the via with the plugging ink supply position. The cavity of the vacuum plugging equipment is closed, and a vacuum pump is used to evacuate the cavity, creating and maintaining a high vacuum state to fully remove any residual air from the vias. During the vacuuming process, the circuit board remains stationary until the cavity pressure reaches the preset high vacuum pressure, after which the plugging process begins.

[0023] The vacuum via-plugging device maintains a high vacuum state within its cavity, delivering via-plugging ink to the circuit board surface. This ink covers the openings of each via and is pushed into the vias by a scraper or pressing structure. Because the inside of the vias is already under low pressure, the ink enters under the pressure at the opening and penetrates inwards along the via wall. During this process, the ink makes full contact with the micro-pit structure, ensuring it enters the pit openings and cavities. After the ink penetration is complete, the circuit board and ink are kept stable, allowing the ink to form a continuous filling area within the vias.

[0024] After the via-hole plugging ink has penetrated the via, a preset plugging pressure is applied to the vacuum plugging device, causing the ink to continue moving inward along the axis of the via. The duration of the plugging pressure is controlled according to a preset target depth. When the ink penetration depth reaches the target depth, the plugging pressure is stopped, causing the leading edge of the ink to cease moving further into the via. At this point, the ink has filled the micro-pit structure on the via wall surface and formed an interlocking state with the micro-pit structure; simultaneously, unfilled cavities remain inside the via, thus forming a partial plug. The circuit board is then heated and cured, causing the ink to cross-link and solidify, fixing it inside the via and within the micro-pit structure, completing the formation of the partial plug.

[0025] By first establishing a high vacuum state, then introducing the via-filling ink into the via, and controlling the filling depth through via-filling pressure after the ink has immersed, the filling depth of the via-filling ink is stably controlled, forming a semi-filled via with a predetermined unfilled space inside the via. Simultaneously, the via-filling ink enters the micro-pit structure and forms an interlocking structure after curing, enhancing the adhesion between the via-filling ink and the via wall, and reducing the risk of loosening, cracking, and detachment of the semi-filled via under the heat of solder spraying.

[0026] In one embodiment, the pore-filling ink comprises one or more of epoxy resin, hydrophobic resin, or silane coupling agent.

[0027] In this embodiment, before the via-sealing process, via-sealing ink is prepared according to a predetermined ratio. The via-sealing ink includes one or more of epoxy resin, hydrophobic resin, or silane coupling agent. Specifically, when using epoxy resin, it is used as the main resin, and after adding the curing component, it is thoroughly stirred to form a uniform via-sealing ink. When using hydrophobic resin, it is added to the epoxy resin and thoroughly stirred to give the via-sealing ink hydrophobic properties. When using silane coupling agent, it is added to the epoxy resin or hydrophobic resin to uniformly disperse the silane coupling agent within the via-sealing ink. After preparation, the via-sealing ink is degassed to remove air bubbles generated during stirring, and the ink is kept in a sealed container for later use. By pre-mixing and degasing the via-sealing ink, it maintains a continuous state when entering the via, reducing the impact of air bubbles on the integrity of the semi-via filling.

[0028] The prepared via-hole plugging ink is added to the ink supply chamber of a vacuum via-hole plugging device. Under high vacuum, the ink covers the opening of the via and is pushed into the via using plugging pressure. After the ink enters the via, the epoxy resin fills the via and forms the main cured structure during the curing process; hydrophobic resin is distributed inside the ink and at the interface with the via wall; silane coupling agent migrates to the surface of the via wall and forms an interface bond with the via wall. The immersion position of the ink is controlled according to the target depth, so that the ink fills the micro-pit structure inside the via wall while leaving the unfilled area inside the via. Once the target depth is reached, the plugging pressure is stopped, and the ink is heated and cured according to the curing conditions to fix it inside the via, thus forming a partial plug.

[0029] After the via-filling ink forms a partial via, the circuit board is heat-cured to allow the epoxy resin to form a continuous cured structure and the silane coupling agent to form a stable interfacial bond between the via-filling ink and the via wall. When the via-filling ink includes a hydrophobic resin, the hydrophobic resin is cured and distributed within the partial via and at the via wall interface. During the curing process, the temperature is increased and maintained according to the curing temperature and time specified for the via-filling ink. After curing, the circuit board is allowed to return to room temperature. Through this curing process, the via-filling ink is fixed within the micro-pit structure, reducing ink movement within the partial vias and maintaining a stable filling depth.

[0030] By introducing epoxy resin, hydrophobic resin, or silane coupling agent into the via-filling ink, the ink can simultaneously perform molding and curing, interfacial bonding, and hydrophobic protection. Epoxy resin forms a stable cured structure, hydrophobic resin reduces the adsorption of moisture by the semi-filled via, and silane coupling agent enhances the interfacial bonding between the via-filling ink and the via wall. Combined with the aforementioned micro-pit structure, the via-filling ink is embedded in the via wall and cured stably, thereby improving the filling stability and heat resistance of the semi-filled via and reducing the risk of cracking or detachment of the semi-filled via during tin plating.

[0031] In one embodiment, after the step of plugging each via to form a half-plugged via, the method further includes: The circuit board is baked.

[0032] In this embodiment, after the via-sealing ink has cured to form partial vias, the circuit board is removed from the vacuum via-sealing equipment. The circuit board surface is cleaned to remove any remaining via-sealing ink, and the openings and filling status of the partial vias are inspected. The inspected circuit board is then placed flat on the support frame of the baking equipment, ensuring that all areas of the circuit board are in full contact with the hot air inside the baking equipment. Before baking, the circuit board is brought to room temperature, and the baking equipment is preheated to the preset baking temperature. The support frame is then placed into the baking equipment, and the circuit board begins to heat up. During the heating process, airflow is maintained inside the baking equipment to ensure uniform heating of all areas of the circuit board.

[0033] After placing the circuit board inside the baking equipment, it is heated in stages. First, the overall temperature of the circuit board gradually increases at a low rate. Once the circuit board reaches the preset baking temperature, it is held at that temperature to ensure the sealing ink inside the partially plugged vias continues to be heated. During baking, hot air is circulated inside the baking equipment, and the circuit board is kept flat to ensure that the sealing ink at different depths within the partially plugged vias receives continuous heating. After holding at that temperature for the preset time, heating is stopped, and the circuit board is allowed to cool naturally inside the baking equipment until it falls below the softening temperature of the sealing ink before being removed.

[0034] By adding a baking process after the semi-plugging is formed, the plugging ink inside the semi-plugging is further thermo-cured, and residual volatile components are released, reducing residual stress inside the plugging ink. Through staged heating, holding, and cooling, a stable cured structure is formed inside the semi-plugging, reducing the expansion, cracking, or displacement of the plugging ink caused by heat during the tin-spraying process, thereby improving the heat resistance stability of the semi-plugging.

[0035] In one embodiment, the step of baking the circuit board further includes: The circuit board is micro-etched to roughen it, and then flux is applied to the surface of the micro-etched and roughened circuit board to form a flux layer at the edge of the holes on the circuit board.

[0036] In this embodiment, after baking and cooling, the circuit board is placed in a micro-etching tank to ensure full contact between the board surface and the etching solution. The temperature and time of the etching solution are controlled to cause shallow dissolution of the copper layer on the board surface, forming a uniformly distributed roughened structure. During the micro-etching process, the board surface remains in continuous contact with the etching solution, maintaining a consistent processing state across all areas. After etching, the board is removed, washed with water to remove residual etching solution, and then dried. The micro-etching roughening process covers the copper layer around the pads and via openings, as well as the exposed circuit layers within the solder mask windows, allowing the applied flux to adhere to the board surface.

[0037] The micro-etched and roughened circuit board is fixed at the flux coating station with its surface facing the flux supply direction. Liquid flux is evenly coated onto the circuit board surface, covering the exposed pads and vias within the solder mask windows, and ensuring a continuous coating along the edges of the via openings. The flux supply is controlled during coating to form a continuous thin layer on the circuit board surface, preventing excessive flux accumulation inside the partially plugged vias. After coating, the circuit board is briefly preheated to allow the flux to adhere stably to the surface and form a flux layer at the edges of the via openings. At this point, the flux layer covers the edges of the via openings and contacts the roughened structure created by micro-etching, providing flux for wetting the molten solder between the pads and vias during the solder spraying process.

[0038] First, the circuit board is micro-etched to roughen the surface, creating a roughened surface at the edges of the pads and vias, increasing the actual contact area between the flux and the circuit board surface. Then, flux is applied and a continuous flux layer is formed at the edges of the vias, improving the adhesion stability of the flux before soldering. During soldering, the flux layer promotes the wetting and spreading of molten solder on the pads and vias, reducing the risk of local discontinuities or insufficient wetting in the solder layer, while ensuring a stable flux coverage at the edges of the vias.

[0039] In one embodiment, see Figure 3 The steps of pre-coating the orifice of the partially plugged hole with a hot-melt resin and forming a hot-melt resin layer at the orifice of the partially plugged hole include: Step S31: Apply hot melt resin to the opening of each half-plug hole by quantitative spraying, so that the hot melt resin covers the edge of the opening and extends outward from the opening. Step S32: Pre-curing treatment is performed on the sprayed hot melt resin to form a continuous covering structure in the edge area of ​​the semi-plugged hole, and the continuous covering structure extends towards the inside of the semi-plugged hole so that after being heated and melted during the tin spraying process, it flows along the edge of the hole towards the center of the hole and seals the gaps in the hole.

[0040] In this embodiment, after completing the aforementioned half-plugging hole formation and circuit board surface treatment, the circuit board is fixed at the hot-melt resin spraying station, with the openings of each half-plugging hole facing the spraying direction. Liquid hot-melt resin is added to a metering spraying device, and the hot-melt resin is sprayed onto the openings of each half-plugging hole through the nozzle. During the spraying process, the amount of resin sprayed per pass is controlled according to the opening area of ​​each half-plugging hole, so that the hot-melt resin first covers the edge of the half-plugging hole opening, and then extends from the opening edge to the outer perimeter of the opening, so that the hot-melt resin covers the circuit board surface around the opening. After the spraying is completed, the openings of each half-plugging hole are inspected to ensure that the hot-melt resin layer continuously covers the opening edge while retaining the internal opening structure of the opening.

[0041] After the hot-melt resin coating is completed, the circuit board is fed into a pre-curing device to pre-cur the hot-melt resin layer at a temperature lower than the solder spraying operating temperature. During the pre-curing process, the hot-melt resin layer gradually forms a continuous coverage structure. By controlling the pre-curing temperature and time, the hot-melt resin layer is kept in a state where it can be softened and melted again by heat during the solder spraying process. The pre-cured hot-melt resin layer covers the edge of the semi-plugged hole and extends from the edge of the hole towards the inside of the semi-plugged hole to form a continuous coverage structure, ensuring continuous contact between the hot-melt resin layer and the edge of the hole. After pre-curing, the circuit board is cooled to room temperature, fixing the hot-melt resin layer at the position of the semi-plugged hole. During the solder spraying process, the heat generated by the molten solder is transferred to the hot-melt resin layer, causing it to soften and melt. The molten hot-melt resin flows along the edge of the hole towards the center of the hole and enters the gap of the hole to form a sealing structure.

[0042] A precise amount of hot-melt resin is sprayed to concentrate and cover the edge of the semi-plugged orifice, extending outwards to create a continuous coverage area. Pre-curing fixes the resin layer at the orifice position while preserving its flowability during soldering. During soldering, the resin melts and flows from the orifice edge towards the center, actively filling the gaps and forming a temporary seal. This reduces the risk of molten solder entering the semi-plugged orifice along the gaps, while also preventing excessive resin from entering and affecting the orifice structure.

[0043] In one embodiment, the step of immersing a circuit board in molten solder for solder spraying to obtain a solder-sprayed circuit board includes: High-pressure hot air is used to blow the surface of the circuit board using a dual air knife or a variable angle air knife to flatten the solder. The surface tin layer is then rapidly cooled and solidified by cold air. Residual flux on the board surface is cleaned and removed, and the board is then dried.

[0044] In this embodiment, after the circuit board comes into contact with the molten solder, it is conveyed to a hot air cleaning station to make the molten solder on the circuit board surface flowable. High-pressure hot air is used to clean the opposite sides of the circuit board using dual air knives, or a variable-angle air knife is used to clean the molten solder from above the circuit board surface. The high-pressure hot air moves along the circuit board surface, blowing away excess solder adhering to the pads and vias. During the cleaning process, a predetermined distance is maintained between the air knife and the circuit board surface, and the air knife moves continuously along the circuit board conveying direction, allowing the molten solder to spread under the continuous airflow.

[0045] After high-pressure hot air purging, the circuit board is transported to the cooling station, where cold air is blown from the circuit board surface towards the solder layer. The cold air lowers the surface temperature of the solder layer, rapidly cooling the continuous solder layer formed by the hot air purging and transforming it from a molten state to a solid state. During the cooling process, the cold air is evenly applied to the pads, vias, and surrounding solder layer, ensuring the solder layer maintains its surface morphology during solidification. Once the solder layer is completely solidified, the cold air purging is stopped, and the circuit board is transported to the cleaning station.

[0046] The cooled and cured circuit board is placed in the cleaning station, where it is rinsed with cleaning fluid to remove residual flux from the pads, via openings, and solder mask. During cleaning, the cleaning fluid covers the entire circuit board surface and continuously washes the area around the via openings to fully dissolve or remove any flux adhering to the edges. After cleaning, the circuit board is rinsed with water to remove the cleaning fluid and residual flux, and then transferred to the drying station.

[0047] After cleaning, the circuit board is placed inside a drying device, allowing hot air to continuously flow over its upper and lower surfaces, as well as the via openings, removing moisture from the board's surface. During the drying process, the circuit board is kept flat, and the hot air continues to circulate, gradually evaporating moisture from the pads, via openings, and solder mask surface. Once no visible moisture remains on the circuit board surface, it is removed from the drying device and allowed to cool to room temperature.

[0048] High-pressure hot air is used to purge the circuit board surface using dual air knives or variable-angle air knives, causing the molten solder to spread evenly and form a continuous tin layer. Simultaneously, the molten state of the thermoplastic resin layer is maintained, promoting the sealing of gaps in partially plugged vias. Subsequently, rapid cooling with cold air ensures the tin layer morphology is promptly fixed. Cleaning and drying remove residual flux and moisture from the board surface, reducing the impact of residues on the tin layer and circuit board surface, thereby improving the continuity, surface stability, and cleanliness of the tin layer after plating.

[0049] In one embodiment, the step of using a dual-air knife or a variable-angle air knife to perform high-pressure hot air cleaning on the circuit board surface includes: The circuit board is divided into multiple purge control areas; Based on the heat capacity, half-plug hole distribution density, and hot air coverage of each purging control area, the air knife purging pressure, purging angle, and purging time of the corresponding area are determined respectively. The dual air knife or variable angle air knife is controlled to perform zoned blowing of the circuit board according to the blowing pressure, blowing angle and blowing time of the air knife corresponding to each blowing control area. This causes the hot melt resin layer of each blowing control area to be heated and melted and flow to the center of the corresponding half plug hole, so as to form a sealing structure that synchronously seals the gap of the hole.

[0050] In this embodiment, after the circuit board is soldered and enters the high-pressure hot air cleaning station, the surface of the circuit board is divided into multiple cleaning control areas using the length and width directions as the area division directions. Each cleaning control area includes corresponding pads, vias, and half-plugged vias. During division, adjacent cleaning control areas are continuously distributed at the boundary, and the position of each cleaning control area on the circuit board surface is recorded. For each cleaning control area, the number of half-plugged vias within the area is counted, and the distribution position of the half-plugged vias within the area is determined. Simultaneously, the heat capacity of the cleaning control area is determined based on the circuit board thickness, copper layer distribution, and surface structure. Furthermore, the coverage state of the hot air on the surface of each cleaning control area after soldering is determined, so that each cleaning control area corresponds to independent area parameters.

[0051] For each purge control area, the air knife purging pressure, purging angle, and purging time are determined based on the area's heat capacity, half-hole distribution density, and hot air coverage for soldering. For purge control areas with a large heat capacity, the air knife purging pressure and purging time are increased accordingly to ensure the hot-melt resin layer receives continuous heat. For purge control areas with a high half-hole distribution density, the air knife purging angle is directed towards the half-hole opening area, concentrating the hot air on the hot-melt resin layer. For purge control areas with insufficient hot air coverage for soldering, the air knife purging time is extended to compensate for the heat loss to the hot-melt resin layer. After determining the above parameters, the air knife purging pressure, purging angle, and purging time corresponding to each purge control area are used as the purging parameters for that area, and a correspondence between the purging parameters and the purge control areas is established according to the area location of the circuit board.

[0052] Based on the purging parameters corresponding to each purging control area, dual air knives or variable-angle air knives are used to sequentially purge each purging control area with high-pressure hot air. During the purging process, the air knives output hot air according to the purging pressure of the corresponding purging control area, and apply the hot air to the thermoplastic resin layer of that purging control area according to the corresponding purging angle, while maintaining the corresponding purging time. After the hot air acts on the thermoplastic resin layer, the thermoplastic resin layer reaches a molten state and flows along the edge of the semi-plugged orifice towards the center of the orifice under the action of the air knife airflow; when the molten thermoplastic resin enters the orifice gap, it continues to converge towards the center of the orifice under the action of hot air and surface tension, forming a sealing structure covering the orifice gap. The purging of all purging control areas is completed sequentially according to the purging parameters corresponding to each purging control area, so that the thermoplastic resin layer in different purging control areas completes melting and flow within the corresponding time period, and all semi-plugged orifices are synchronously sealed.

[0053] By dividing the circuit board into multiple purge control zones and determining the purge pressure, angle, and time based on the heat capacity, half-plug via distribution density, and hot air coverage of each zone, the purge knife achieves the appropriate hot air effect for each zone. This zoned purge process ensures the hot-melt resin layer fully melts and flows along the via edge towards the center, allowing multiple half-plug vias to simultaneously form a sealing structure. This reduces incomplete sealing caused by insufficient local heat and excessive resin flow caused by excessive heat, thereby improving the consistency of half-plug via sealing.

[0054] In one embodiment, the step of cleaning and removing residual flux from the board surface further includes: The circuit board is subjected to plasma cleaning to decompose and evaporate the residual hot melt resin on the surface of the circuit board. The cleaned circuit board is then rinsed with deionized water.

[0055] In this embodiment, after flux cleaning, cold air cooling, and drying, the circuit board is placed in the processing chamber of the plasma cleaning equipment with its surface facing the plasma action area. The processing chamber is closed and the air inside is evacuated to bring it to a predetermined low-pressure state. Then, working gas is introduced and radio frequency power is applied to generate plasma within the processing chamber. The plasma acts on the residual hot-melt resin on the surface of the circuit board, causing the surface of the hot-melt resin to be bombarded by high-energy particles, resulting in chain breakage and pyrolysis. The volatile components generated by pyrolysis detach from the surface of the circuit board and are discharged with the airflow in the processing chamber. The plasma cleaning time is controlled to gradually reduce and remove the hot-melt resin from the edge of the semi-plugged hole and the surrounding surface of the circuit board. After plasma cleaning is completed, the radio frequency power and working gas supply are stopped, the pressure in the processing chamber is restored, and the circuit board is removed.

[0056] The circuit boards that have undergone plasma cleaning are transported to the water washing station, where deionized water is used to continuously rinse the surface of the circuit boards. This process removes the pyrolysis products, particles, and soluble residues generated during plasma cleaning from the circuit board surface. During rinsing, deionized water covers the upper and lower surfaces of the circuit board, as well as the areas around the via openings, and continuously washes the surface around the partially plugged via openings. For the via opening areas, deionized water is ensured to fully contact the edges of the openings to remove any remaining hot-melt resin pyrolysis products from the plasma cleaning. After rinsing, the circuit boards are either spun dry or dried with hot air to remove and evaporate the deionized water from the surface, resulting in a clean circuit board surface.

[0057] Plasma cleaning breaks down and evaporates the hot melt resin remaining on the circuit board surface during the tin plating process, achieving complete removal of the hot melt resin as a temporary sealing material after tin plating. Then, deionized water rinsing removes the pyrolysis products and surface residues, reducing the impact of hot melt resin residue on the tin layer, pads, and solder mask, thereby improving the surface cleanliness of the circuit board after tin plating and avoiding damage to the tin layer and solder mask caused by mechanical scraping.

[0058] The present invention also provides a circuit board, characterized in that it is manufactured using the above-described solder spraying method based on the circuit board half-hole plugging.

[0059] Therefore, the embodiments should be considered as exemplary and non-limiting in all respects, and the scope of the invention is not limited by the foregoing description. Thus, all changes falling within the meaning and scope of the equivalents of the application are intended to be included within the scope of the invention.

[0060] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features of the invention herein.

Claims

1. A solder spraying method based on a partially plugged via on a circuit board, characterized in that, Includes the following steps: A circuit board is provided, wherein a circuit layer is provided on the surface of the circuit board, and the circuit board has multiple vias. The surface of the circuit board is covered with a solder mask layer, and the solder mask layer is provided with solder mask windows. The solder mask layer covers the circuit layer, and the pads of the circuit layer and each via are exposed through the solder mask windows. Each through hole is plugged to form a partial plug; A hot-melt resin is pre-coated at the opening of the partially plugged hole to form a hot-melt resin layer. The circuit board is immersed in molten solder for solder spraying to obtain the solder-sprayed circuit board.

2. The solder spraying method based on partial plugging of circuit board vias according to claim 1, characterized in that, Following the step of exposing the circuit layer pads and vias through solder mask windows, the following further steps are also included: The walls of each through hole are micro-etched to form a uniformly distributed micro-pit structure on the surface of the hole wall. Low-pressure plasma is used to activate the pore walls, removing residues from the pore wall surface and increasing the opening size of the micropit structure.

3. The solder spraying method based on partial plugging of circuit board vias according to claim 2, characterized in that, The step of plugging each through hole to form a semi-plugged hole includes: Place the circuit board in a vacuum plugging device and evacuate it to a high vacuum state; The vias are plugged using via-filling ink; After the via-hole is immersed in the via, the via-hole pressure is controlled to make the via-hole ink reach the target depth. When the via-hole ink penetrates to the target depth, the via-hole ink fills the micro-pit structure and is cured to form a semi-filled via.

4. The solder spraying method based on partial plugging of circuit board vias according to claim 3, characterized in that, The pore-filling ink includes one or more of epoxy resin, hydrophobic resin, or silane coupling agent.

5. The solder spraying method based on a partially plugged via in a circuit board according to claim 3, characterized in that, After the step of plugging each through hole to form a semi-plugged hole, the method further includes: The circuit board is baked.

6. The solder spraying method based on a partially plugged hole in a circuit board according to claim 4, characterized in that, The process of baking the circuit board is followed by: The circuit board is micro-etched to roughen it, and then flux is applied to the surface of the micro-etched and roughened circuit board to form a flux layer at the edges of the holes on the circuit board.

7. The solder spraying method based on a partially plugged via in a circuit board according to any one of claims 1 to 6, characterized in that, The step of pre-coating the opening of the partially plugged hole with hot-melt resin and forming a hot-melt resin layer at the opening of the partially plugged hole includes: Hot melt resin is sprayed onto the opening of each half-plug hole using a quantitative spraying method, so that the hot melt resin covers the edge of the opening and extends outward from the opening. The hot-melt resin after spraying is pre-cured to form a continuous covering structure in the edge area of ​​the semi-plugged hole, and the continuous covering structure extends towards the inside of the semi-plugged hole so that after being heated and melted during the tin spraying process, it flows along the edge of the hole towards the center of the hole and seals the gaps in the hole.

8. The solder spraying method based on a partially plugged via in a circuit board according to claim 1, characterized in that, The step of immersing the circuit board in molten solder for solder spraying to obtain a solder-sprayed circuit board includes: High-pressure hot air is used to blow the surface of the circuit board using a dual air knife or a variable angle air knife to flatten the solder. The surface tin layer is then rapidly cooled and solidified by cold air. Residual flux on the board surface is cleaned and removed, and the board is then dried.

9. The solder spraying method based on a partially plugged via in a circuit board according to claim 8, characterized in that, The step of using a dual-air knife or a variable-angle air knife to blow high-pressure hot air onto the circuit board surface includes: The circuit board is divided into multiple purge control areas; Based on the heat capacity, half-plug hole distribution density, and hot air coverage of each purging control area, the air knife purging pressure, purging angle, and purging time of the corresponding area are determined respectively. The dual air knife or variable angle air knife is controlled to perform zoned blowing of the circuit board according to the blowing pressure, blowing angle and blowing time of the air knife corresponding to each blowing control area. This causes the hot melt resin layer of each blowing control area to be heated and melted and flow to the center of the corresponding half plug hole, so as to form a sealing structure that synchronously seals the gap of the hole.

10. The solder spraying method based on a partially plugged via in a circuit board according to claim 8, characterized in that, The step of cleaning and removing residual flux from the board surface also includes: The circuit board is subjected to plasma cleaning to decompose and evaporate the residual hot melt resin on the surface of the circuit board. The cleaned circuit board is then rinsed with deionized water.

11. A circuit board, characterized in that, It is manufactured using the solder spraying method based on the partial plugging of the circuit board as described in any one of claims 1 to 10.

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