Blind hole filling method
By employing multiple electroplating processes and controlling different current densities and time periods, the problem of filling hollow cavities in blind holes with large diameters was solved, achieving high-quality blind hole filling and signal transmission effects.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-09
- Publication Date
- 2026-04-07
AI Technical Summary
In existing technologies, blind vias with large depth-to-diameter ratios are prone to leaving incompletely filled cavities during filling, leading to signal attenuation and reduced thermal reliability, thus becoming a bottleneck in high-density PCB manufacturing.
A multi-stage electroplating method is used to fill blind holes with different current densities and time periods. The process includes forming a conductive substrate in the first stage, gradually increasing the current density in the second stage, closing the gap and dissolving the loose copper layer in the third stage with a pulsed current, and then performing a low-density electroplating to smooth the copper layer in the fourth stage to avoid the formation of cavities.
This effectively avoids the formation of cavities inside blind holes, improves the filling quality and signal transmission efficiency of blind holes, and enhances the structural stability and reliability of blind holes.
Smart Images
Figure CN121802500A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the technical field of circuit board manufacturing, and particularly relates to a method for filling blind vias. Background Technology
[0002] As printed circuit boards (PCBs) rapidly iterate towards higher density, miniaturization, and multilayer structures, blind vias, as the core structure for interlayer interconnection, directly determine the signal transmission efficiency and long-term reliability of the PCB due to their plating quality. Current technologies require blind vias to be completely filled with copper layers to achieve high-quality electrical interconnection and structural protection in multilayer PCBs.
[0003] In existing technologies, when filling blind vias with large diameters, problems such as large diameters, limited ion diffusion in the plating solution, and poor gas discharge within the vias can lead to incompletely filled cavities. These cavities can cause signal attenuation, decreased thermal reliability, and other malfunctions, becoming a bottleneck restricting the yield of high-density PCB manufacturing. Summary of the Invention
[0004] To address the issue of signal attenuation caused by incompletely filled cavities within blind holes when filling blind holes with large diameters. This invention proposes a method for filling blind holes.
[0005] The present invention solves the above problems through the following technical solutions: In a first aspect, the present invention proposes a method for filling blind holes, comprising: The blind via is first electroplated to fill it with a first current density at the first time to form a conductive substrate; The blind via is filled by a second electroplating at a second current density at a second time, and the second current density is gradually increased in an increasing trend during the second time to gradually fill the blind via. A third electroplating process is performed at a third current density and a third time to fill the holes, and the blind holes are closed and the gaps are filled and the loose copper layer is dissolved by pulses. The blind vias are filled with a fourth current density at a fourth time, and the copper layer is smoothed by using a low-density fourth current density.
[0006] During blind via filling, a first electroplating process is performed using a first current density at a first time to form a conductive substrate. A second electroplating process is then performed using a second current density at a second time, with the second current density gradually increasing within the second time to gradually fill the blind via. A third electroplating process is performed using a third current density at a third time, using pulses to close the gaps between the blind vias and dissolve loose copper layers. A fourth electroplating process is performed using a fourth current density at a fourth time, using a low-density fourth current density to achieve a smooth copper layer. This process avoids the formation of cavities inside the blind vias during the electroplating process, especially when filling blind vias with large diameters.
[0007] In some implementations, the first current density is 1.0-1.5 A / dm². 2 The first time is 0~5 minutes.
[0008] In some implementations, the second current density is 1.0-1.5 A / dm². 2 The second time is 5~25 minutes.
[0009] In some implementations, the improvement trend is an increase of 0.5 A / dm every 5 minutes. 2 .
[0010] In some implementations, the third current density includes both forward pulse density and reverse pulse density.
[0011] In some implementations, the positive pulse density is 3.0-3.5 A / dm. 2 Reverse current density 0.5-1.0 A / dm 2 .
[0012] In some implementations, the forward current density duty cycle is 60%-70%, and the reverse current density duty cycle is 10%-15%.
[0013] In some implementations, the frequencies of the forward pulse density and the reverse pulse density are 500-800 Hz.
[0014] In some implementations, direct current is used for the first, second, and fourth electroplating filling processes.
[0015] In some implementations, the fourth current density is 1.0-1.2 A / dm². 2 The fourth time is 35-40 minutes.
[0016] The beneficial effects of the blind hole filling method of the present invention are: During blind via filling, a first electroplating process is performed using a first current density at a first time to form a conductive substrate. A second electroplating process is then performed using a second current density at a second time, with the second current density gradually increasing within the second time to gradually fill the blind via. A third electroplating process is performed using a third current density at a third time, using pulses to close the gaps between the blind vias and dissolve loose copper layers. A fourth electroplating process is performed using a fourth current density at a fourth time, using a low-density fourth current density to achieve a smooth copper layer. This process avoids the formation of cavities within the blind vias during the electroplating process.
[0017] The above description is merely an overview of the technical solutions of the embodiments of the present invention. In order to better understand the technical means of the embodiments of the present invention and to implement them in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the embodiments of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description
[0018] Figure 1 This is a flowchart of the blind hole filling method of the present invention; Figure 2 This is a sectional view after hole filling using the conventional hole filling method; Figure 3 This is a cross-sectional view of the blind hole filling method of the present invention after filling the hole; Figure 4 This is a flowchart of the blind via filling process for a circuit board according to Embodiment 3 of the present invention. Detailed Implementation
[0019] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.
[0020] Example 1: like Figure 1 As shown, the present invention proposes a method for filling blind holes, comprising: Step 100: The blind via is filled by electroplating at a first current density at a first time to form a conductive substrate; Specifically, the blind via is first electroplated and filled with a first current density at the first time. The first electroplating slowly deposits a thin layer of copper (2-3 μm thick) on the wall of the blind via and the surface of the core, forming a conductive substrate to avoid the direct impact of high current causing the via to be quickly sealed. At the same time, the fluidity of the electroplating solution is enhanced under low current, and the residual air in the via is discharged with the electroplating solution. Step 100 can first remove the air and residue in the blind via, avoiding the formation of a cavity inside the blind via due to incomplete gas removal after complete molding.
[0021] Step 200: The blind via is electroplated for the second time using a second current density at a second time, and the second current density is gradually increased in an increasing trend during the second time to gradually fill the blind via; Specifically, the second current density is gradually increased in a step-like manner. As the current density increases stepwise, the deposition rate of copper ions in the annular gap of the blind via gradually accelerates from the bottom to the opening. Initially, a low current ensures preferential deposition of the copper layer at the bottom of the via, filling the tiny gap between the core and the bottom. Later, the current increases to promote copper layer growth at the opening, preventing the formation of cavities within the gap. This step-like control balances the concentration gradient of the plating solution, preventing localized copper ion depletion that could interrupt deposition. By gradually increasing the current density to match the shape of the blind via, the current density is slowly applied to gradually fill the interior of the blind via, avoiding the formation of cavities caused by incomplete removal of internal gas during rapid filling. Step 300: Perform a third electroplating to fill the holes using a third current density at a third time, and use pulses to close the gaps between the blind holes and dissolve the loose copper layer; Specifically, by further filling the annular gap until it is completely closed, and by dissolving any loose copper layer that may exist inside the hole, the porosity is reduced; at the same time, the pulsed current can promote the interfacial diffusion between the conductive paste on the core surface and the copper layer, thereby improving the bonding strength (the bonding strength can reach more than 25 MPa).
[0022] Step 400: The blind via is electroplated for the fourth time at a fourth current density, and the copper layer is smoothed by using a low-density fourth current density.
[0023] Specifically, the fourth current density uses a reduced current density so that after the blind via is filled with copper, the surface copper (thickness 3-5μm) is slowly deposited through a low current density, so that the surface of the blind via and the copper layer of the PCB board are smoothly transitioned, avoiding the stress concentration of the plating layer caused by the sudden drop in current, and improving the overall structural stability.
[0024] During blind via filling, a first electroplating process is performed using a first current density at a first time to form a conductive substrate. A second electroplating process is then performed using a second current density at a second time, with the second current density gradually increasing within the second time to gradually fill the blind via. A third electroplating process is performed using a third current density at a third time, using pulses to close the gaps between the blind vias and dissolve loose copper layers. A fourth electroplating process is performed using a fourth current density at a fourth time, using a low-density fourth current density to achieve a smooth copper layer. This process avoids the formation of cavities inside the blind vias during the electroplating process, especially when filling blind vias with large diameters.
[0025] Example 2: like Figures 2-3 As shown, this embodiment further explains and optimizes the steps proposed in Embodiment 1: In some specific implementations, the simulated product design features blind holes with a diameter of 100µm and a dielectric thickness of 85µm, or 90µm-120µm with a relatively large depth-to-diameter ratio. The product manufacturing steps are as follows: Based on an acidic copper sulfate electroplating solution (containing 50-70g / L sulfuric acid and 240-260g / L copper sulfate), a four-step control strategy as described in Example 1 is adopted: In some preferred embodiments, the first current density is 1.0-1.5 A / dm². 2 The first time is 0~5 minutes.
[0026] Specifically, the initial electroplating filling is used to form a thin electroplated layer inside the blind hole wall. The initial current density can be derived by considering parameters such as plating thickness and electroplating time, combined with Faraday's law of electrolysis and commonly used formulas. That is: ...(1) Among them, ASF is approximately equal to 0.0929 A / dm. 2 , This represents the required copper plating thickness, and t is the effective plating time. The initial copper plating thickness is approximately 2-3 mm. The first time took approximately 0-5 minutes, and the calculated ASF was approximately 16. This was then converted to A / dm. 2 Afterwards, the density is approximately 1.4 A / dm³. 2 The first current density can be adjusted according to the actual situation.
[0027] In some embodiments, the second current density is 1.0-1.5 A / dm². 2 The second time is 5~25 minutes.
[0028] Specifically, the initial value of the second current density can be 1.0-1.5 A / dm².2 Its intensity can be the same as the value of the first current density, or it can be slightly greater than the first current density. The second time is 5~25min. The second current density gradually increases with time according to the increasing trend in the second time. The current density can be calculated by substituting into formula (1).
[0029] Furthermore, in a preferred embodiment, the improvement trend is an increase of 0.5 A / dm every 5 minutes. 2 .
[0030] Specifically, the second stage employs a stepped increase to gradually accelerate the deposition rate of copper ions within the blind via pores from the bottom to the top. This stepped increase in current density effectively avoids incomplete copper ion deposition and incomplete gas removal caused by sudden increases in current density. This prevents cavities from forming within the blind vias after final filling. The increase is set at 0.5 A / dm every 5 minutes. 2 This allows the current to be reduced from 1.5 A / dm 2 Increased to 3.0A / dm 2 This fills the small gap between the core and the bottom of the hole, promotes the growth of the copper layer at the hole opening, and prevents local copper ion depletion from causing deposition interruption.
[0031] In some embodiments, the third current density includes a forward pulse density and a reverse pulse density.
[0032] Specifically, the third current is a pulse, and its third current density includes forward current density and reverse current density. The forward pulse further fills the annular gap until it is completely closed, while the reverse pulse can dissolve any loose copper layer that may exist inside the hole, reducing porosity. Furthermore, the forward pulse current density can efficiently deposit metal plating. During the forward pulse, the circuit board acts as the cathode, and metal ions in the plating solution (such as copper ions in copper plating) are reduced to metal atoms under the influence of the electric field and deposited on the board surface and hole walls. Compared to traditional DC electroplating, a properly set forward pulse current density can improve cathode polarization, accelerate crystal nucleation, and ensure plating efficiency while making the initial deposition of the plating layer more uniform, laying the foundation for subsequent plating thickness increase. Moreover, for high aspect ratio circuit board vias, the intermittent nature of the forward pulse can reduce the influence of concentration polarization. During the pulse shutdown phase, metal ions in the plating solution can quickly replenish the consumed areas within the holes, preventing the plating layer from being too thin or lacking copper due to ion depletion at the bottom of the holes. This improves deep plating capability and ensures the consistency of plating thickness between the hole wall and the board surface. The reverse pulse current density can remove plating burrs and protrusions, avoiding "dog-bone" defects. During the reverse pulse, the circuit board becomes the anode. This high current density preferentially dissolves protrusions, burrs, and excessively thick plating layers that easily appear at the hole openings. It effectively solves the "dog-bone" problem of excessively thick plating at the hole openings and insufficiently thin plating inside the holes in traditional electroplating, resulting in a more uniform plating thickness between the hole and the board surface. Furthermore, the reverse pulse current density can optimize the plating crystallization quality and help stabilize the plating solution environment.
[0033] Furthermore, a forward pulse can be used for electroplating deposition first, and a reverse pulse can be used to correct the copper plating quality, thereby improving the uniformity and density of the plating layer of blind holes and improving the filling quality of blind holes with large depth-to-diameter ratios.
[0034] In some preferred embodiments, the positive pulse density is 3.0-3.5 A / dm. 2 Reverse current density 0.5-1.0 A / dm 2 .
[0035] Specifically, the forward current density is typically between 1.0 and 10 A / dm². 2 The preferred forward current density is 3.0-3.5 A / dm², and the frequency is 500-800 Hz. Its intensity is calculated based on the required copper thickness and time, or it can be calculated using formula (1). The reverse current density is 0.5-1.0 A / dm², and the frequency is 500-800 Hz. The quality of the copper layer is corrected by the reverse current density.
[0036] In some embodiments, the forward current density duty cycle is 60%-70%, and the reverse current density duty cycle is 10%-15%.
[0037] Specifically, when the blind hole depth-to-diameter ratio is >0.8:1, the forward duty cycle is usually set to 60%~70%. A duty cycle higher than 70% will reduce the diffusion time of ions, resulting in a lack of ions at the bottom of the hole. A duty cycle lower than 60% will result in too low electroplating efficiency and the production capacity will not meet the standard. The duty cycle of the reverse current density is 10%-15%, which can be used to enhance the coating correction effect.
[0038] Furthermore, when electroplating blind holes with a large diameter, an interval time ratio can be set between the positive current density and the negative current density, which can be set to 5%~20%. The purpose is to allow copper ions in the plating solution to fully diffuse to the bottom of the hole, alleviate concentration polarization, and avoid the absence of copper at the bottom of the hole.
[0039] In some embodiments, the frequencies of the forward pulse density and the reverse pulse density are 500-800 Hz.
[0040] Specifically, high-frequency ion diffusion has low pressure, and high-frequency reverse can quickly optimize coating crystallization, making the coating denser.
[0041] In some embodiments, the first, second, and fourth electroplating filling processes all use direct current.
[0042] Specifically, the first, second, and fourth electroplating filling processes use direct current, which can reduce maintenance costs and material consumption. The process of direct current is mature and easy to control, ensuring stable production. The operation threshold of direct current is relatively low, which also makes the coating quality stable. In addition, direct current is more suitable for filling blind holes with larger diameters.
[0043] In some embodiments, the fourth current density is 1.0-1.2 A / dm². 2 The fourth time is 35-40 minutes.
[0044] Specifically, the fourth electroplating filling is usually 3-5μm thick, so that the blind hole and the copper layer on the PCB can be smoothly transitioned, avoiding stress concentration in the plating layer caused by a sudden drop in current, and improving the stability of the overall structure.
[0045] Furthermore, after electroplating, the PCB is subjected to reliability tests such as thermal stress, IR, TCT, and TCH to verify whether there are any quality risks. The inside of the blind vias can also be observed with a microscope to determine whether there are any voids or cavities inside the blind vias, so as to meet the reliability requirements.
[0046] Example 3: like Figure 4 As shown, this embodiment proposes a process flow for filling blind vias on a circuit board: This includes copper flash plating, degreasing, micro-etching, water washing, acid washing, hole filling, water washing, unloading, drying, and board collection. Among these steps, the hole filling uses the blind hole filling method of either Example 1 or Example 2, thereby avoiding cavities inside the blind holes when filling blind holes with a large depth-to-diameter ratio.
[0047] Specifically, when filling multiple copper slots, the slots can be filled sequentially, such as copper slot 1-copper slot 2-copper slot 3...copper slot 12. The purpose is to fill different depths and shapes of the copper slots separately, resulting in better filling effect. Alternatively, multiple copper slots can be filled simultaneously to improve filling efficiency.
[0048] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of the invention may be practiced without these specific details. Similarly, for the sake of brevity and to aid in understanding one or more aspects of the invention, in the description of exemplary embodiments of the invention above, various features of the embodiments are sometimes grouped together in a single embodiment, figure, or description thereof. The claims, which follow the detailed description, are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.
[0049] Those skilled in the art will understand that the modules in the device of the embodiment can be adaptively changed and placed in one or more devices different from that embodiment. Modules, units, or components in the embodiment can be combined into a single module, unit, or component, and further, they can be divided into multiple sub-modules, sub-units, or sub-components, except that at least some of such features and / or processes or units are mutually exclusive.
[0050] It should be noted that the above embodiments are illustrative of the invention and not restrictive, and that those skilled in the art can devise alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses should not be construed as limiting the claims. The word "comprising" does not exclude the presence of elements or steps not listed in the claims. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention can be implemented by means of hardware comprising several different elements and by means of a suitably programmed computer. In the unit claims enumerating several means, several of these means may be embodied by the same item of hardware. The use of the words first, second, and third, etc., does not indicate any order. These words can be interpreted as names. The steps in the above embodiments, unless otherwise specified, should not be construed as limiting the order of execution.
Claims
1. A method for filling blind holes, characterized in that, include: The blind via is first electroplated to fill it with a first current density at the first time to form a conductive substrate; The blind via is filled by a second electroplating at a second current density at a second time, and the second current density is gradually increased in an increasing trend during the second time to gradually fill the blind via. A third electroplating process is performed at a third current density and a third time to fill the holes, and the blind holes are closed and the gaps are filled and the loose copper layer is dissolved by pulses. The blind via is filled with a fourth current density at a fourth time, and the copper layer is smoothed by using the fourth current density at a low density.
2. The blind hole filling method according to claim 1, characterized in that, The first current density is 1.0-1.5 A / dm³. 2 The first time is 0~5min.
3. The blind hole filling method according to claim 1, characterized in that, The second current density is 1.0-1.5 A / dm². 2 The second time is 5~25 minutes.
4. The blind hole filling method according to claim 1, characterized in that, The improvement trend is an increase of 0.5 A / dm every 5 minutes. 2 .
5. The blind hole filling method according to claim 1, characterized in that, The third current density includes the forward pulse density and the reverse pulse density.
6. The blind hole filling method according to claim 5, characterized in that, The positive pulse density is 3.0-3.5 A / dm. 2 The reverse current density is 0.5-1.0 A / dm³. 2 .
7. The blind hole filling method according to claim 5, characterized in that, The forward current density duty cycle is 60%-70%, and the reverse current density duty cycle is 10%-15%.
8. The blind hole filling method according to claim 5, characterized in that, The frequencies of the forward pulse density and the reverse pulse density are 500-800Hz.
9. The blind hole filling method according to claim 1, characterized in that, The first, second, and fourth electroplating filling processes all use direct current.
10. The blind hole filling method according to claim 1, characterized in that, The fourth current density is 1.0-1.2 A / dm². 2 The fourth time is 35-40 minutes.