Manufacturing method of conductive silver paste hole plugging circuit board
Through mechanical drilling, oxygen plasma removal of slag and staged pouring and curing, the high cost, instability and crack risks of multi-layer circuit boards are solved, and more efficient and stable conductivity and thermal conductivity are achieved.
Patent Information
- Application Number
- CN202510409488.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-02
- Publication Date
- 2025-08-05
AI Technical Summary
The interlayer through-hole treatment of traditional multi-layer circuit boards has high costs, instability and crack risks, serious chemical copper pollution, and complex processing technology.
The step-type plug-in process is used to remove the glue slag with mechanical drilling combined with oxygen plasma, and to pour conductive silver paste in stages and perform two curings. Combined with surface leveling, the silver paste is evenly distributed and dense in the through holes.
Reduce production costs and processing cycles, improve electrical and thermal conductivity, avoid the risk of cracks caused by resin retraction and electroplating of copper, and improve the reliability and stability of circuit boards.
Smart Images
Figure CN120434898A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of circuit boards, and in particular to a method for manufacturing a conductive silver paste plugging circuit board. Background Art
[0002] Circuit boards can be divided into single-layer boards and multi-layer boards. Multi-layer boards require inter-layer vias to connect the circuits between layers. Traditional multi-layer boards mostly treat inter-layer vias by electroplating copper after chemical copper deposition. Because the copper layer thickness is insufficient after chemical copper deposition, it needs to be thickened again by electroplating, which will increase costs. In addition, resin plugging is required after copper deposition. After copper deposition, electroplating and plugging, when the circuit board is reflow soldering or thermal stress reliability testing, it is easy to produce cracks caused by resin shrinkage and electroplated copper. In addition, chemical copper has a large pollution, the process is unstable, and the copper layer itself has stress, which can cause cracks in the copper layer. Summary of the Invention
[0003] In view of this, the present invention provides a method for manufacturing a conductive silver paste plugged via circuit board, which has a simple process and can effectively improve plugging stability and yield.
[0004] The purpose of the present invention is achieved through the following technical solutions: A method for manufacturing a conductive silver paste plugged via circuit board comprises the following steps: S1: Inner layer board pretreatment, providing inner layer boards with completed inner layer circuit pattern production and lamination; S2: drilling, mechanically drilling the inner layer board to form a plurality of through holes penetrating each conductive layer; S3: hole wall treatment, removing the residual glue residue on the inner wall of the through hole; S4: Step-by-step silver paste plugging: Conductive silver paste is injected into the via hole through a staged filling process, wherein the staged filling process includes a first filling stage and a second filling stage. After the first filling stage, a first curing is performed; after the second filling stage, a second curing is performed. S5: Surface leveling treatment, polishing and removing the silver paste overflowing from the through hole, so that the surface of the through hole opening is leveled to obtain a circuit board with completed plugging.
[0005] In the above technical solution, mechanical drilling is combined with a slag removal process to prevent residues on the hole wall from interfering with the contact between the silver paste and the conductive layer, enhance the adhesion of the silver paste, and ensure the low impedance characteristics of the conductive path; and the stepped plugging process with staged infusion and two-time curing can effectively reduce the generation of bubbles and microcracks inside the silver paste, ensure the uniform distribution and density of the silver paste in the through-hole, thereby reducing the risk of oxidation in the hole and improving the conductivity reliability and long-term stability; and the staged curing strategy takes into account both the production rhythm and material properties. The first curing initially fixes the silver paste morphology, and the secondary curing achieves complete cross-linking, which not only shortens the single curing time, but also avoids excessive thermal stress damaging the substrate, adapting to large-scale production needs.
[0006] Therefore, compared with the traditional processing technology of copper plating, electroplating and resin plugging to make the through-hole conductive, the present invention only needs to be achieved through silver paste plugging, which can greatly reduce the production cost and processing cycle, and has better conductivity and thermal conductivity. The conductive cylinder formed after the silver paste plugging can also effectively avoid the risk of cracks caused by resin shrinkage and electroplated hole copper, making the reliability of the circuit board more stable.
[0007] Optionally, in a possible implementation, in step S3, the adhesive residue on the inner wall of the through hole is removed by a chemical desmearing process, wherein the chemical desmearing process is: ionizing oxygen into oxygen plasma, and allowing the oxygen plasma to chemically react with the adhesive residue to generate volatile gas.
[0008] In this technical solution, oxygen plasma, through both physical bombardment and chemical reaction, precisely removes residual adhesive residue from the hole walls, avoiding micro-etching or substrate damage caused by chemical solvent cleaning. Volatile products are vacuum-extracted, leaving no secondary residue, ensuring hole cleanliness and providing a highly reliable interface for subsequent silver paste filling.
[0009] Optionally, in a possible implementation, during the first filling stage, the silver paste is filled to the entire through hole, and after the first solidification is completed, the silver paste is shrunk to 75%-85% of the through hole volume; during the second filling stage, the silver paste is filled to the entire through hole and partially overflows the through hole.
[0010] In the above technical solution, after the initial filling, the silver paste shrinks to 75%-85% of the through-hole volume through precisely controlled curing conditions, forming a stable skeleton structure within the hole and providing an anchoring interface for the secondary filling. This stage releases the internal stress of the silver paste during curing, avoiding microcracks within the hole or peeling from the hole wall caused by excessive shrinkage during a single filling. During the secondary filling, the pore space after the initial curing is used for shrinkage compensation. The excess silver paste overflowing the hole mouth forms a uniform covering layer through surface tension, which can compensate for volume changes caused by curing shrinkage or temperature changes.
[0011] Optionally, in a possible implementation, when the silver paste is cured for the first time, the inner layer board is placed horizontally and baked at a temperature range of 140-160° C. for 10-20 minutes to put the silver paste in a semi-cured state.
[0012] In this technical solution, horizontal baking is performed within a temperature range of 140-160°C. This prevents both premature cross-linking and shrinkage of the resin caused by high temperatures and inadequate curing due to insufficient temperatures. A short baking time of 10-20 minutes forms a semi-cured silver paste layer, providing chemical bonding sites for the second stage of filling. This step-by-step cross-linking mechanism strengthens the interfacial bonding between the two filling layers.
[0013] Optionally, in a possible implementation, when the silver paste is being cured for the second time, the inner layer board is placed horizontally and baked at a temperature range of 140-160° C. for 55-65 minutes to fully cure the silver paste.
[0014] In the above technical solution, horizontal baking is maintained for 55-65 minutes in the temperature range of 140-160°C. By extending the heat action time, it is ensured that the first filling silver paste and the second filling silver paste can be completely cured, thereby improving the continuity of the conductive path and the mechanical bonding strength.
[0015] Optionally, in a possible implementation, the silver paste is formed by mixing silver powder, modified epoxy resin, DBE solvent and additives.
[0016] In the above technical solution, the silver paste formed by mixing multiple components has the characteristics of short curing time, wide curing temperature range, and strong bonding with the substrate, which can effectively improve processing efficiency and product quality.
[0017] Optionally, in a possible implementation, the silver paste needs to be frozen during storage, and needs to be thawed for 5-6 hours and stirred for 25-35 minutes before use.
[0018] In this technical solution, frozen storage effectively inhibits the pre-crosslinking reaction of the modified epoxy resin in the silver paste, while also reducing the volatilization rate of the DBE solvent and the tendency of the silver powder to settle, ensuring that the rheological and conductive properties of the silver paste remain stable during storage. The 5-6 hour thawing process slowly raises the temperature of the silver paste to the process temperature threshold, preventing rapid temperature changes that could lead to unstable performance.
[0019] Optionally, in a possible implementation, in step S4, when plugging the holes with silver paste, the plugging is performed by an auxiliary mechanism, and the auxiliary mechanism includes a pad and an aluminum mesh, and the inner layer plate is placed between the pad and the aluminum mesh, and the aluminum mesh is provided with positioning holes corresponding to the through holes.
[0020] In the above technical solution, the aluminum mesh ensures that there is no deviation or leakage during the silver paste filling process and also restricts the spread of silver paste at the hole opening. The backing plate can generate a certain elastic support force during the pressure application phase of the silver paste plugging, improving the plugging effect.
[0021] Optionally, in a possible implementation, the diameter of the positioning hole is 0.1-0.2 mm larger than the diameter of the corresponding through hole.
[0022] In the above technical solution, the aperture of the positioning hole is larger than that of the through hole, which can ensure that the through hole is completely located in the positioning hole. In this way, when the silver paste is screen-printed on the aluminum plate, it can be ensured that the silver paste can completely enter the through hole, and it can also effectively prevent the silver paste from diffusing outside the circuit board, thereby improving the accuracy of the silver paste plugging.
[0023] Optionally, in a possible implementation, in step S5, the surface of the inner layer board is polished by a grinding machine using a non-woven grinding brush.
[0024] In the above technical solution, the non-woven fabric brush can effectively grind off the excess solidified silver paste while achieving micron-level roughening of the board surface through evenly distributed abrasive particles, forming a honeycomb microstructure, which can effectively improve the adhesion of subsequent plating or ink. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.
[0026] Figure 1 It is an overall flow chart of an embodiment. DETAILED DESCRIPTION
[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Generally, the components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.
[0028] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application without making any creative efforts shall fall within the scope of protection of the present application.
[0029] Please refer to Figure 1 This embodiment provides a method for manufacturing a conductive silver paste plugged via circuit board, comprising the following steps: S1: Inner layer board pretreatment, providing an inner layer board with completed inner layer circuit pattern production and lamination. Electrolytic copper foil can be used to form the inner layer circuit pattern through a pattern transfer process, and then interlayer lamination is performed to form a composite inner layer board with a dielectric layer structure; S2: Drilling: Mechanically drill the inner layer board to form several through holes that penetrate each conductive layer. A carbide drill bit can be used to machine through holes with a diameter of 0.1-0.3mm on the inner layer board. S3: Hole wall treatment, remove the residual glue residue on the inner wall of the through hole, use a glue remover to remove the glue residue in the hole, improve the surface properties of the material, and promote the close bonding of the subsequent silver paste and the substrate; S4: Step-type silver paste plugging: Conductive silver paste is injected into the through-hole through a staged filling process. The staged filling process includes a first filling stage and a second filling stage. After the first filling stage, the first curing is performed; after the second filling stage, the second curing is performed. S5: Surface leveling treatment, polishing and removing the silver paste overflowing from the through-hole, making the surface of the through-hole mouth flat to obtain a completed plugged circuit board.
[0030] Specifically, a complete finished circuit board can be obtained by further performing outer layer circuit pattern production, solder mask, characterization, surface treatment, molding, electrical testing and other processes on the circuit board that has completed silver paste plugging.
[0031] This embodiment uses mechanical drilling combined with a slag removal process to prevent residues on the hole wall from interfering with the contact between the silver paste and the conductive layer, enhance the adhesion of the silver paste, and ensure the low impedance characteristics of the conductive path. The stepped plugging process with staged infusion and two-stage curing can effectively reduce the generation of bubbles and microcracks inside the silver paste, ensure the uniform distribution and density of the silver paste in the through-hole, thereby reducing the risk of oxidation in the hole and improving the conductivity reliability and long-term stability. In addition, the staged curing strategy takes into account both production rhythm and material properties. The first curing initially fixes the silver paste morphology, and the secondary curing achieves complete cross-linking, which not only shortens the single curing time but also avoids excessive thermal stress damage to the substrate, adapting to the needs of large-scale production. The silver paste overflowing from the hole mouth is also removed by grinding, so that the surface flatness meets the requirements of high-precision circuit boards, avoiding short circuits or cold solder joints caused by surface unevenness during subsequent lamination or welding, and improving the overall process compatibility.
[0032] Therefore, compared to the traditional copper plating, electroplating, and resin plugging process to make the through-holes conductive, this embodiment only requires silver paste plugging, which can greatly reduce production costs and processing time. It also has better electrical and thermal conductivity. The conductive cylinders formed after silver paste plugging can also effectively avoid the risk of cracks caused by resin shrinkage and electroplated copper holes, making the circuit board more reliable. More specifically, compared with the traditional process, this embodiment reduces costs by approximately 10 yuan per square meter and shortens the circuit board processing cycle by approximately 14 hours.
[0033] In step S3 of this embodiment, a chemical desmearing process is used to remove adhesive residue from the inner wall of the through-hole. The chemical desmearing process involves ionizing oxygen into oxygen plasma, which then reacts with the adhesive residue to generate volatile gases. Specifically, the oxygen plasma treatment parameters are: vacuum pressure of 180 mTorr, vacuum chamber temperature of 80-105°C, treatment time of 5-15 minutes, and gas flow rate of 3.0 SLN.
[0034] Oxygen plasma, through a dual action of physical bombardment and chemical reaction, precisely removes residual adhesive residue from the pore walls, avoiding micro-etching and substrate damage caused by chemical solvent cleaning. Volatile products are vacuum-extracted, eliminating any secondary residue, ensuring pore cleanliness and providing a highly reliable interface for subsequent silver paste filling. Furthermore, this process eliminates the need for organic solvents or strong acids or bases, reducing hazardous waste disposal costs and environmental risks, aligning with green manufacturing requirements. It also simplifies the cleaning process, shortens production cycles, and reduces overall energy consumption.
[0035] In this embodiment, during the first filling stage, the silver paste is filled to the entire through hole, and after the first solidification, the silver paste is allowed to shrink to 75%-85% of the through hole volume; during the second filling stage, the silver paste is filled to the entire through hole and partially overflows the through hole.
[0036] After the first filling, the volume of the silver paste is shrunk to 75%-85% of the through-hole volume through precisely controlled curing conditions, forming a stable skeleton structure in the hole and providing an anchoring interface for the secondary filling. This stage can release the internal stress of the silver paste during the curing process, avoiding microcracks in the hole or peeling from the hole wall caused by excessive shrinkage in a single filling. During the secondary filling, the pore space after the first curing is used for shrinkage compensation. The excess silver paste overflowing the hole mouth forms a uniform covering layer through surface tension, which can compensate for the volume change caused by curing shrinkage or temperature change. Staged curing allows the filling status in the hole to be detected after the first shrinkage, and targeted grouting is implemented for the holes that do not meet the shrinkage standards, thereby improving the overall hole filling qualification rate.
[0037] It should be noted that during the initial curing of the silver paste, the inner layer boards are placed horizontally and baked at a temperature range of 140-160°C for 10-20 minutes to semi-cure the silver paste, i.e., achieve initial solidification. In this embodiment, the inner layer boards are baked at 150°C for 15 minutes. Specifically, the inner layer boards are placed on a rack in a baking oven, where the rack has multiple horizontal layers. This allows for simultaneous baking of multiple inner layer boards, improving efficiency.
[0038] Horizontal baking within a temperature range of 140-160°C precisely matches the activation energy threshold of the silver paste polymerization reaction, preventing both premature cross-linking and shrinkage of the resin caused by high temperatures and insufficient curing due to insufficient temperatures. A short bake time of 10-20 minutes forms a semi-cured silver paste layer, which retains some active functional groups and provides chemical bonding sites for the second stage of filling. This step-by-step cross-linking mechanism enhances the interfacial bonding between the two filling layers. By regulating the semi-cured state, the volume shrinkage of the silver paste after the initial curing is stabilized within a range of 15%-25%, forming a transition layer with a porous skeleton structure, which reserves space for uniform expansion for the secondary filling. This process design effectively avoids the surface collapse or internal voids that are prone to occur with traditional single-stage curing.
[0039] Secondly, when the silver paste of this embodiment is cured for the second time, the inner layer board is placed horizontally and baked at a temperature range of 140-160°C for 55-65 minutes to fully cure the silver paste. For example, in this embodiment, the baking temperature is 150°C for 60 minutes.
[0040] Maintaining a horizontal bake at 140-160°C for 55-65 minutes ensures complete cure of both the first and second fills by extending the thermal exposure time, thereby improving the continuity and mechanical bond strength of the conductive path. The gradient thermal stress field created by the staged curing effectively alleviates shear stress concentration at the interface between the silver paste and the hole wall, preventing cracks between the paste and the hole wall.
[0041] In this embodiment, the silver paste is formed by mixing silver powder, modified epoxy resin, DBE solvent, and additives. This multi-ingredient mixture offers advantages such as a short curing time, a wide curing temperature range, and strong adhesion to the substrate, effectively improving processing efficiency and product quality. The modified epoxy resin forms a three-dimensional cross-linked network during the curing process, which not only enhances the interfacial bonding strength of the silver powder but also maintains the inherent low volume resistivity of the epoxy resin. The DBE (diacid ester) solvent has moderate permeability to the surface oxide layer of the silver powder and, in combination with an ionic dispersant, reduces the likelihood of silver powder agglomeration.
[0042] It should be noted that silver paste needs to be frozen during storage, with the freezing temperature ranging from -20°C to -5°C. It needs to be thawed for 5-6 hours and stirred for 25-35 minutes before use. Frozen storage effectively inhibits the pre-crosslinking reaction of the modified epoxy resin in the silver paste, while also reducing the volatilization rate of the DBE solvent and the tendency of the silver powder to settle, ensuring that the rheological and conductive properties of the silver paste remain stable during storage. The 5-6 hour thawing process slowly raises the temperature of the silver paste to the process temperature threshold, avoiding rapid temperature changes that could lead to unstable performance.
[0043] In step S4 of this embodiment, during silver paste plugging, the plugging is performed using an auxiliary mechanism comprising a backing plate and an aluminum mesh plate. The inner plate is positioned between the backing plate and the aluminum mesh plate, and the aluminum mesh plate is provided with positioning holes corresponding to the through-holes. The provision of the aluminum mesh plate ensures that there is no offset or leakage of the silver paste during the silver paste filling process and also restricts the diffusion of the silver paste at the hole opening. The backing plate can generate a certain elastic support force during the silver paste plugging pressure phase, thereby improving the silver paste plugging effect.
[0044] Specifically, the diameter of the locating hole is 0.1-0.2mm larger than the diameter of the corresponding through hole. The larger diameter of the locating hole can ensure that the through hole is completely located within the locating hole. In this way, when the silver paste is screen-printed on the aluminum plate, it can be guaranteed that the silver paste can completely enter the through hole. It can also effectively prevent the silver paste from diffusing outside the circuit board, thereby improving the accuracy of the silver paste plugging.
[0045] In step S5 of this embodiment, the inner layer board surface is polished by a grinding machine using a non-woven brush. The non-woven brush is a combination of 600 mesh and 800 mesh, the grinding current is set to 2.5 mA, and the grinding speed is 2.5-3.0 m / min.
[0046] The non-woven fabric abrasive brush can effectively remove excess solidified silver paste while achieving micron-level coarsening of the board surface through evenly distributed abrasive particles, forming a honeycomb microstructure, which can effectively improve the adhesion of subsequent plating or ink.
[0047] In the description of the present invention, it should be understood that terms such as "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.
[0048] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.
[0049] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.
Claims
1. A method for manufacturing a conductive silver paste plugged via circuit board, characterized in that: The following steps are involved: S1: Inner layer board pretreatment, providing inner layer boards with completed inner layer circuit pattern production and lamination; S2: drilling, mechanically drilling the inner layer board to form a plurality of through holes penetrating each conductive layer; S3: hole wall treatment, removing the residual glue residue on the inner wall of the through hole; S4: Step-by-step silver paste plugging: Conductive silver paste is injected into the via hole through a staged filling process, wherein the staged filling process includes a first filling stage and a second filling stage. After the first filling stage, a first curing is performed; after the second filling stage, a second curing is performed. S5: Surface leveling treatment, polishing and removing the silver paste overflowing from the through hole, so that the surface of the through hole opening is leveled to obtain a circuit board with completed plugging.
2. The method for manufacturing a conductive silver paste plugged via circuit board according to claim 1, characterized in that: In step S3, the adhesive residue on the inner wall of the through hole is removed by a chemical adhesive removal process. The chemical adhesive removal process is: oxygen is ionized into oxygen plasma, and the oxygen plasma is chemically reacted with the adhesive residue to generate volatile gas.
3. The method for manufacturing a conductive silver paste plugged via circuit board according to claim 1, characterized in that: During the first filling stage, the silver paste is filled to the entire through hole, and after the first solidification is completed, the silver paste is allowed to shrink to 75%-85% of the through hole volume; during the second filling stage, the silver paste is filled to the entire through hole and partially overflows the through hole.
4. The method for manufacturing a conductive silver paste plugged via circuit board according to claim 1, characterized in that: When the silver paste is cured for the first time, the inner layer board is placed horizontally and baked at a temperature range of 140-160° C. for 10-20 minutes to make the silver paste in a semi-cured state.
5. The method for manufacturing a conductive silver paste plugged via circuit board according to claim 1, characterized in that: When the silver paste is being cured for the second time, the inner layer board is placed horizontally and baked at a temperature range of 140-160° C. for 55-65 minutes to fully cure the silver paste.
6. The method for manufacturing a conductive silver paste plugged via circuit board according to claim 1, characterized in that: The silver paste is prepared by mixing silver powder, modified epoxy resin, DBE solvent and additives.
7. The method for manufacturing a conductive silver paste plugged via circuit board according to claim 6, characterized in that: The silver paste needs to be frozen during storage and needs to be thawed for 5-6 hours and stirred for 25-35 minutes before use.
8. The method for manufacturing a conductive silver paste plugged via circuit board according to claim 1, characterized in that: In step S4, when plugging the holes with silver paste, the plugging is performed by an auxiliary mechanism, which includes a pad and an aluminum mesh plate, and the inner layer plate is placed between the pad and the aluminum mesh plate, and the aluminum mesh plate is provided with positioning holes corresponding to the through holes.
9. The method for manufacturing a conductive silver paste plugged via circuit board according to claim 8, characterized in that: The diameter of the positioning hole is 0.1-0.2 mm larger than the diameter of the corresponding through hole.
10. The method for manufacturing a conductive silver paste plugged via circuit board according to claim 1, characterized in that: In the step S5, the surface of the inner layer board is polished by a grinding machine using a non-woven grinding brush.