Method for electroplating and filling through hole with height-to-width-depth ratio
By attaching copper foil to the second end face of the substrate and combining chemical cleaning and electroplating processes, the problem of uneven copper deposition in blind hole electroplating was solved, achieving high density and bubble-free via filling, thus improving the reliability and conductivity of the circuit board.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-19
- Publication Date
- 2026-04-10
AI Technical Summary
In the blind hole electroplating process, it is difficult to effectively control copper deposition, resulting in bubbles or voids inside the hole, which affects conductivity and causes welding or thermal cycling failure risks.
Copper foil is attached to the second end face of the substrate to form a single-end open structure. The adhesive residue and bottom copper are removed by chemical cleaning. A continuous copper layer is formed by chemical copper plating. Copper is then filled into the through holes by electroplating. By combining sprayed electroplating solution and controlling the current density, uniform copper deposition is ensured.
It significantly improves the density and integrity of copper inside the through-hole, avoids bubble formation, enhances electroplating reliability and hole filling quality, and ensures conductivity.
Smart Images
Figure CN121842990A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of chip packaging technology, and specifically to a method for electroplating and filling high aspect ratio through-holes. Background Technology
[0002] To meet the demands of miniaturization and high density in electronic products, high-density interconnect technology is widely used in the manufacturing process of printed circuit boards (PCBs). Blind vias are typically used to achieve electrical conductivity between multilayer boards, therefore their filling quality directly affects the conductivity of the PCB. In current manufacturing processes, copper plating is commonly used to fill blind vias, ensuring the formation of continuous and dense copper pathways.
[0003] However, during blind via electroplating, the filling ability of the plating solution makes it difficult to effectively control copper deposition, easily leading to residual gas or liquid within the via, forming bubbles or voids. These bubbles hinder the plating solution from fully penetrating the blind via, resulting in poor local filling and even quality problems such as empty plating, inclusions, and copper layer delamination within the via. The presence of bubbles not only affects the conductivity of the blind via but also poses a risk of open circuits and board failures during subsequent soldering or thermal cycling, severely reducing product reliability. Summary of the Invention
[0004] To overcome the above shortcomings, the purpose of this invention is to provide a method for electroplating and filling high aspect ratio through holes, which can effectively improve the density and integrity of copper filling in the through holes and significantly reduce or even avoid the generation of bubbles in the holes.
[0005] Technical solution: This invention discloses a method for electroplating and filling high aspect ratio through holes, comprising the following steps: 1. A substrate is provided, the substrate having a first end face and a second end face opposite to each other, and a through hole is formed on the substrate through the first end face and the second end face; 2. Use chemical agents to clean the adhesive residue inside the through holes of the substrate and remove the base copper on the surface of the substrate; 3. A layer of copper foil is attached to the second end face of the substrate, such that the copper foil can cover one end of the through hole, wherein the copper foil is rolled copper; Fourth, a first copper layer is deposited on the first end face of the substrate by chemical copper plating, and the first copper layer extends from the first end face to the inner wall of the through hole to form a second copper layer. 5. The through hole is filled with copper by electroplating, and an electroplating layer is attached to the side of the copper foil away from the substrate, and an electroplating layer is attached to the side of the first copper layer away from the substrate.
[0006] Furthermore, the diameter of the through hole is 30-200 μm, and the aspect ratio is 0.8-2.
[0007] Furthermore, in step five, the electroplating solution used for electroplating includes 200-250 g / L sulfuric acid, 60-100 g / L copper sulfate, 30-70 ppm chloride ions, and hydrogen peroxide, and the material of the electroplated layer is copper.
[0008] Furthermore, following step five, the following steps are also included: 6. Apply a film to the surface of the electroplated layer on both sides of the substrate.
[0009] Furthermore, following step six, the following steps are also included: 7. Exposure and development are performed on the substrate onto which the film is applied, thereby displaying the corresponding pattern on the substrate.
[0010] Furthermore, following step seven, the following steps are also included: 8. Etch the electroplated layer, copper foil and the first copper layer printed on the substrate, and remove the film layer attached to the surface of the electroplated layer.
[0011] Furthermore, in step five, the current density is 10-200 ASD during the electroplating filling process.
[0012] Furthermore, in step five, the electroplating solution is injected into the through hole by spraying at a pressure of 0.5-2 bar.
[0013] Furthermore, in step five, the substrate with the through hole is placed in an electroplating tank, and the electroplating solution is injected into the through hole by spraying pressure, and the temperature of the solution is 25-40°C.
[0014] Furthermore, step two also includes pretreatment of the substrate, namely spraying the substrate with a degreasing agent and / or alkaline solution for 1-5 minutes at a temperature of 25-40°C.
[0015] The beneficial effects of this invention are as follows: (1) By attaching copper foil to the second end face of the substrate, the through hole forms a single-end opening structure. During electroplating, the current is concentrated in one direction, so that copper can uniformly and densely fill the through hole from bottom to top during electroplating, which significantly improves the filling quality and avoids defects such as voids and poor contact in the hole. (2) The present invention removes the glue residue in the through hole and cleans the bottom copper at the same time, which significantly improves the cleanliness of the inner wall of the through hole and the adhesion of the electroplated metal, thereby facilitating copper deposition during subsequent electroplating and improving the reliability of electroplating. (3) The present invention forms a continuous first copper layer and a second copper layer on the first end face and the inner wall of the through hole, which provides a good conductive basis for electroplating and further improves the density of the electroplated copper filling. Attached Figure Description
[0016] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way. Furthermore, the shapes and proportions of the components in the drawings are merely illustrative to aid in understanding the invention and are not intended to specifically limit the shapes and proportions of the components. Those skilled in the art, guided by the teachings of this invention, can select various possible shapes and proportions to implement the invention according to specific circumstances. In the drawings: Figure 1 This is a schematic diagram of the process for electroplating and filling through-holes with a ground aspect ratio according to the present invention. Detailed Implementation
[0017] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments.
[0018] In the description of this invention, it should be understood that the terms "upper," "lower," "front," "rear," "left," "right," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for 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. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. The embodiments of this invention will now be described according to its overall structure.
[0019] like Figure 1 As shown, this invention discloses a method for electroplating and filling high aspect ratio through holes, comprising the following steps: 1. A substrate is provided, the substrate having a first end face and a second end face opposite to each other, and a through hole is formed on the substrate through the first end face and the second end face; 2. Use chemical agents to clean the adhesive residue inside the through holes of the substrate and remove the base copper on the surface of the substrate; 3. A layer of copper foil is attached to the second end face of the substrate, such that the copper foil can cover one end of the through hole, wherein the copper foil is rolled copper; Fourth, a first copper layer is deposited on the first end face of the substrate by chemical copper plating, and the first copper layer extends from the first end face to the inner wall of the through hole to form a second copper layer. 5. The through hole is filled with copper by electroplating, and an electroplating layer is attached to the side of the copper foil away from the substrate, and an electroplating layer is attached to the side of the first copper layer away from the substrate.
[0020] By employing the above method, this invention coats a layer of copper foil onto the second end face of the substrate, thereby creating a single-ended opening structure for the pre-drilled through-holes. During electroplating, the current is concentrated in a single direction, allowing copper to uniformly and densely fill the through-holes from bottom to top, significantly improving the filling quality and avoiding defects such as voids and poor contact within the holes. This effectively solves the problems of air bubbles, uneven filling, and voids in the holes that are common in traditional through-hole copper filling processes. This invention improves the filling quality and the reliability of the finished product.
[0021] A through-hole is formed on the substrate, penetrating the first and second end faces. Preferably, the through-hole has a large aspect ratio. Existing electroplating processes may encounter problems such as residual gas or impurities inside the through-hole, leading to uneven copper ion deposition and ultimately resulting in bubbles or localized empty plating within the through-hole. To avoid impurities inside the through-hole during electroplating, this invention performs a process to remove adhesive residue and base copper before electroplating. Chemical cleaning completely removes residual drilling adhesive residue from the through-hole, ensuring a clean inner wall and improving the subsequent copper plating effect. Simultaneously, base copper on the substrate surface is removed to prevent abnormal current distribution due to residual base copper, ensuring uniform copper deposition during subsequent electroplating.
[0022] In the process of removing resin residue and removing the bottom copper layer from the substrate, the substrate is first immersed in a swelling solution composed of organic amines and surfactants to fully swell and soften the resin residue in the through holes. Then, it is transferred to a strong oxidizing solution containing permanganate. The strong oxidizing effect of permanganate decomposes the resin residue, resin residue, and hard-to-remove carbides on the hole walls after drilling into easily detachable debris. After the oxidation treatment, a neutralizing solution containing sulfuric acid and hydrogen peroxide or oxalic acid is used to wash away the residual manganese oxides and neutralize the alkalinity of the hole walls, restoring the hole wall surface to a clean and stable state. Then, the substrate is immersed in a micro-etching solution containing sulfuric acid. The extremely thin chemical manganese oxide and metal oxide layer on the substrate surface are removed through gentle and controlled chemical etching, so that a brand-new active copper layer is exposed on the copper surface. This not only removes processing residues but also ensures that the subsequent electroless copper plating can be uniformly deposited and firmly bonded.
[0023] After removing the adhesive residue and the base copper on the substrate surface, this invention applies copper foil to the second end face of the through-hole, sealing one side of the through-hole with the copper foil. This facilitates control of the electric field and liquid flow direction during subsequent electroplating, allowing copper ions to preferentially enter the through-hole from the first end face and gradually deposit along the inner wall, thereby reducing the retention of bubbles within the through-hole during electroplating. This solution, through process flow design and adjustment of the hole structure, matches the conditions to existing electroplating processes and allows for better control of the copper reaction rate. Furthermore, this design has good versatility in electroplating processes, enabling existing electroplating lines to simultaneously perform through-hole and blind-hole processing without requiring additional capacity, allowing for direct continuous production. Simultaneously, the copper foil also participates in metal deposition during electroplating, forming a continuous electroplated layer of copper on the side of the copper foil facing away from the substrate.
[0024] In the copper plating step, a continuous first copper layer is formed on the first end face through chemical reduction or deposition, and the first copper layer extends to the inner wall of the through hole to form a second copper layer, providing a good conductive path and deposition basis for subsequent copper electroplating.
[0025] Ultimately, copper filling is achieved inside the through-hole through-plate. During this process, the electroplated copper layer at the top of the through-hole grows inward, working synergistically with the chemically deposited copper on the inner wall to gradually fill the through-hole space. Due to the sealing effect of the copper foil at the bottom, a closed cavity is formed during the electroplating process, effectively controlling the flow direction of the electroplating solution and the deposition trajectory of copper ions, thereby improving the density of the copper filling.
[0026] Furthermore, the diameter of the through-hole ranges from 30-200 μm, and the aspect ratio is 0.8-2. The through-hole exhibits a high aspect ratio, meaning a large diameter and relatively small depth. Because the opening of the through-hole is relatively large compared to its depth, it is less likely to cause columnar growth of the copper plating layer or internal voids during subsequent electroplating, thus avoiding structural problems that could affect the conductivity and structural reliability of the through-hole.
[0027] Furthermore, in step five, the electroplating solution used in the electroplating process contains 200-250 g / L sulfuric acid, 60-100 g / L copper sulfate, 30-70 ppm chloride ions, and hydrogen peroxide, ensuring that the final electroplated layer is made of copper. This electroplating solution results in a more uniform current distribution within the hole, a more sufficient supply of copper ions, and a more stable deposition at the bottom of the hole, thereby guaranteeing a dense, void-free, and continuous metal filling inside the through-hole.
[0028] Specifically, a higher concentration of sulfuric acid in the electroplating solution can significantly improve the conductivity of the solution, resulting in a lower resistivity. This allows the current to be smoothly conducted to the bottom of the hole, improving the common problems of insufficient deep current and excessive deposition at the top in through holes.
[0029] Copper sulfate, as the primary source of copper ions in the electroplating process, directly determines the replenishment rate of copper ions within the holes. This ensures a sufficient supply of copper ions even under high current density conditions deep within the holes, preventing defects such as voids, cracks, or pinholes due to copper ion depletion. Furthermore, the addition of 30-70 ppm chloride ions to the electroplating solution creates a micro-regulating environment at the electrochemical interface, resulting in finer copper grains and a more uniform deposition structure. The synergistic effect of chloride ions and organic components in the electroplating solution improves adsorption behavior at the cathode, leading to smoother deposits and significantly enhancing the flatness and density of copper filling within the through-holes. This is particularly beneficial for the bottom region, reducing the occurrence of shrinkage cavities or V-shaped voids.
[0030] Hydrogen peroxide in the electroplating solution mainly improves solution activity and promotes local micro-disturbance, inhibiting the growth of large grains during the deposition process within the pores, resulting in a denser filling structure. It also helps maintain the cleanliness and reactivity of the electroplating solution, making the copper deposition process more stable and smooth. This lays a solid foundation for achieving void-free, high-density electroplated pore filling.
[0031] Furthermore, step six involves attaching a film to the electroplated surface on both sides of the substrate, which effectively protects the integrity of the electroplated layer during subsequent pattern transfer, provides a clear circuit pattern, and enables the subsequent circuit pattern to have high resolution and clear edges.
[0032] Furthermore, it also includes step seven, exposing and developing the substrate with the dry film attached to form the opening area of the desired circuit in the dry film layer, so that subsequent etching can be performed on specific locations.
[0033] Furthermore, the process includes step eight, which involves selectively etching the substrate to remove unwanted electroplating layers, copper foil, and the first copper layer from the substrate surface, while also removing the film layer attached to the surface of the electroplating layer, retaining the metal conductors in the circuit pattern area, thereby achieving precise transfer of the metal pattern.
[0034] In step five, the current density is set to 10-200 ASD. This balances the copper ion deposition rate with the uniformity of the plating layer inside the via during the electroplating process of high aspect ratio vias. Since the electric field distribution inside high aspect ratio vias is typically uneven, the current density is higher at the via opening and lower at the bottom. If the current density is set too high, it can lead to rapid copper deposition at the via opening, premature sealing, and the formation of voids or bubbles before complete filling. If the current density is too low, the plating rate is slow, the filling efficiency is low, and plating porosity is likely to occur. By controlling the current density within the range of 10-200 ASD, a lower current density can be used initially to promote deposition inside the via, improving the flow and distribution of copper within the via. As the plating layer grows, the current density can be gradually increased, allowing the via to fill evenly from bottom to top, resulting in a dense, void-free filled structure.
[0035] Preferably, in step five, the electroplating solution is ejected using a spraying method, with the pressure controlled between 0.5 and 2 bar. During traditional static immersion electroplating, the liquid turnover within the holes is slow, resulting in insufficient copper ion supply and concentration polarization at the bottom of the holes, leading to uneven plating thickness or voids. By spraying the electroplating solution at a preset pressure into the vias of the substrate, the old solution within the holes is rapidly replaced, promoting continuous replenishment of copper ions and uniform distribution of the electric field. Spraying the electroplating solution reduces residual bubbles within the vias and creates a finer, denser plating structure on the hole walls, significantly improving the uniformity and reliability of the filling, ensuring complete copper filling and a smooth surface in the vias.
[0036] Preferably, in step five, the substrate with through-holes is placed in an electroplating tank, and the electroplating solution is injected into the through-holes by spraying. The temperature of the tank solution is 25-40°C. Using spraying to inject the electroplating solution into the through-holes effectively avoids the problem of dry plating, improves the electroplating conditions at the bottom of the hole, and thus forms a fine and dense plating structure on the hole wall. Maintaining the tank temperature at 25-40°C is a suitable temperature range for electroplating, thereby maintaining the activity balance of metal ions and preventing uncontrolled reactions at low or high temperatures.
[0037] Preferably, in step three, the copper foil attached to the second end face of the substrate is rolled copper, which can improve the density, bonding strength, and conductivity uniformity of the copper plating in the hole. Rolled copper is a high-density copper foil that has undergone mechanical stretching and surface compaction treatment. Its flexibility and conductivity are superior to electrolytic copper. Utilizing the heritable characteristics of crystal growth, the electroplated copper can also acquire good heritable characteristics after growth, that is, the growth direction of the copper plating can be controlled, thereby improving the reliability of the via filling. Due to the special crystal structure formed by the method provided in this application, grain growth is suppressed, and atomic diffusion can be suppressed in subsequent packaging processes, thus further extending the product's life cycle.
[0038] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.
Claims
1. A method for electroplating and filling high aspect ratio through holes, characterized in that, Includes the following steps:
1. A substrate is provided, the substrate having a first end face and a second end face opposite to each other, and a through hole is formed on the substrate through the first end face and the second end face; 2. Use chemical agents to clean the adhesive residue inside the through holes of the substrate and remove the base copper on the surface of the substrate; 3. A layer of copper foil is attached to the second end face of the substrate, such that the copper foil can cover one end of the through hole, wherein the copper foil is rolled copper; Fourth, a first copper layer is deposited on the first end face of the substrate by chemical copper plating, and the first copper layer extends from the first end face to the inner wall of the through hole to form a second copper layer.
5. The through hole is filled with copper by electroplating, and an electroplating layer is attached to the side of the copper foil away from the substrate, and an electroplating layer is attached to the side of the first copper layer away from the substrate.
2. The method for electroplating and filling high aspect ratio through holes according to claim 1, characterized in that, The diameter of the through hole is 30-200 μm, and the aspect ratio is 0.8-2.
3. The method for electroplating and filling high aspect ratio through holes according to claim 1, characterized in that, In step five, the electroplating solution used includes 200-250 g / L sulfuric acid, 60-100 g / L copper sulfate, 30-70 ppm chloride ions and hydrogen peroxide, and the material of the electroplated layer is copper.
4. The method for electroplating and filling high aspect ratio through holes according to claim 1, characterized in that, Following step five, the following steps are also included:
6. Apply a film to the surface of the electroplated layer on both sides of the substrate.
5. The method for electroplating and filling high aspect ratio through holes according to claim 4, characterized in that, Following step six, the following steps are also included:
7. Exposure and development are performed on the substrate onto which the film is applied, thereby displaying the corresponding pattern on the substrate.
6. The method for electroplating and filling high aspect ratio through holes according to claim 5, characterized in that, Following step seven, the following steps are also included:
8. Etch the electroplated layer, copper foil and the first copper layer printed on the substrate, and remove the film layer attached to the surface of the electroplated layer.
7. The method for electroplating and filling high aspect ratio through holes according to claim 1, characterized in that, In step five, the current density is 10-200 ASD during the electroplating filling process.
8. The method for electroplating and filling high aspect ratio through holes according to claim 1, characterized in that, In step five, the electroplating solution is injected into the through hole by spraying at a pressure of 0.5-2 bar.
9. The method for electroplating and filling high aspect ratio through holes according to claim 1, characterized in that, In step five, the substrate with the through hole is placed in an electroplating tank, and the electroplating solution is injected into the through hole by spraying. The temperature of the solution is 25-40°C.
10. The method for electroplating and filling high aspect ratio through holes according to claim 1, characterized in that, Step two also includes pretreatment of the substrate, which involves spraying the substrate with a degreasing agent and / or alkaline solution for 1-5 minutes at a temperature of 25-40°C.