Process for electroplating via holes

Abstract

This invention discloses a process for electroplating and filling blind vias, comprising the following steps: determining a target blind via region and other regions on the surface of an upper copper foil layer; forming an etch-resistant mask layer in the other regions; etching the target blind via region to obtain a first blind via; removing the etch-resistant mask layer in the other regions; laser drilling through the insulating substrate layer at the location of the first blind via to form a second blind via; depositing a first copper layer in the second blind via to form a third blind via; electroplating a second copper layer in the third blind via until the copper layer is fully plated; and thickening the electroplating of the entire board. This process, without adding copper reduction and browning processes, can achieve blind via opening on single-sided copper substrates with an upper copper foil thickness ranging from 18μm to 70μm, reducing blind via diameter error, lowering the surface depression rate of the upper copper foil after electroplating and filling, and ensuring the heat dissipation performance of the single-sided copper substrate; it eliminates the need for copper reduction and browning processes in traditional methods, thus reducing production costs for enterprises.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board technology, and more specifically, to a process for electroplating and filling blind holes. Background Technology

[0002] In existing technologies, for single-sided copper substrates with a surface copper foil thickness exceeding the direct processing capability of conventional laser drilling machines (typically below 10μm), the common process route for fabricating blind vias and electroplating filling is as follows: copper reduction, browning, laser drilling, pretreatment for copper plating, copper plating, electroplating filling, and full-board electroplating. A typical process flow is as follows: First, a high-precision horizontal spray copper reduction line is used to thin the surface copper to 9-10μm using copper chloride etching solution; then, browning treatment is performed; next, a carbon dioxide laser drilling machine is used to drill through the surface copper and dielectric layer together to form blind vias; pretreatment for copper plating involves cleaning with dilute sulfuric acid and brush polishing; the copper plating process deposits a thin chemical copper layer on the via walls; finally, electroplating filling is used to fill the blind vias, supplemented by full-board electroplating to meet the copper thickness requirements of the finished product.

[0003] When the thickness of the surface copper foil exceeds the processing capacity of a conventional laser drilling machine, it is necessary to purchase additional copper reduction wire to thin the surface copper foil and perform browning and passivation treatment, which significantly increases the equipment procurement cost. The copper foil after copper reduction is also prone to large hole diameter errors during laser processing, with blind hole diameter errors as high as ±Φ25μm, which directly affects the subsequent hole filling quality.

[0004] Meanwhile, due to the aforementioned process constraints, blind hole electroplating filling generally results in obvious surface depressions, see [reference needed]. Figure 1 , Figure 1 This is a cross-sectional image of the recessed blind via locations on a single-sided copper substrate after using a traditional blind via electroplating filling process. The upper copper foil layer of the single-sided copper substrate is 18μm thick, the middle insulating layer is 80μm thick, and the overall board thickness is 1.20mm. Figure 1 The observed indentation value at the blind via location is 28.742 μm, exceeding 25 μm. Simultaneously, the high proportion of voids within the vias severely weakens the heat dissipation performance of the PCBA, resulting in a low overall product yield. Furthermore, to ensure laser machinability, the surface copper foil of the single-sided copper substrate is kept relatively thin, necessitating a significant increase in the thickness of the finished single-sided copper substrate through full-board electroplating, leading to a substantial increase in electroplating costs.

[0005] It is evident that the existing single-sided copper substrate blind hole electroplating filling process is difficult to balance between equipment investment, processing accuracy, filling quality and production cost. Among these issues, the problems of excessively large electroplating filling depressions and high void ratios are particularly prominent, and have become an industry bottleneck restricting the application of single-sided copper substrates in the field of high-efficiency heat dissipation.

[0006] To address the aforementioned issues, the existing traditional process of blind hole electroplating filling urgently needs improvement. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a process for electroplating and filling blind holes, comprising the following steps: S10. Determine the target blind hole area and other areas on the surface of the upper copper foil of the single-sided copper substrate, and form an etch-resistant mask layer in the other areas. S20. Perform chemical etching on the target blind hole region to remove the copper foil in the target blind hole region and obtain a plurality of first blind holes; S30. Remove the etch-resistant mask layer from the other areas; S40. Laser drilling is performed at the location of the first blind hole to penetrate the insulating substrate layer and form a second blind hole; S50. A copper plating process is performed on a single-sided copper substrate, and a first copper layer is deposited in the second blind via to form a third blind via. S60. Perform pulse electroplating on a single-sided copper substrate, depositing a second copper layer in the first copper layer of the third blind hole until the third blind hole is fully plated with copper layer. S70. Thicken the copper plating layer on the entire single-sided copper substrate.

[0008] Preferably, in the process of electroplating and filling blind holes, the diameter of the target blind hole is 80μm~170μm; the ratio of the diameter to the depth of the target blind hole is between 1.0 and 1.2.

[0009] Preferably, step S50 specifically includes: The single-sided copper substrate after copper plating is placed in the electroplating solution, and alternating positive and reverse pulse currents are applied to the electroplating solution to cause copper to be preferentially deposited at the bottom of the third blind hole and filled from bottom to top, forming a dense second copper layer within the first copper layer of the third blind hole.

[0010] Preferably, step S10 specifically includes: S11. Coat the surface of the upper copper foil of the single-sided copper substrate with photoresist ink to form a wet film layer; S12. Pre-curing the wet film layer to form a semi-solid film layer; S13. Based on the target blind hole area pattern preset on the surface of the upper copper foil, expose and develop the semi-solid film layer to remove the semi-solid film layer in the target blind hole area, retain the semi-solid film layer in other areas, and form an anti-etching mask layer in other areas.

[0011] Preferably, step S12 specifically includes: A single-sided copper substrate with a wet film layer coated on the surface of the upper copper foil is fed into a tunnel furnace. The single-sided copper substrate is controlled to pass through multiple temperature control zones in the tunnel furnace in sequence to achieve pre-curing of the wet film layer and form a semi-solid film layer on the surface of the upper copper foil.

[0012] Preferably, step S20 specifically includes: Spray etching is used, with copper chloride solution as the etching solution, to etch the target blind hole area on the surface of the upper copper foil of the single-sided copper substrate. The etching solution comes into contact with the copper foil exposed in the target blind hole area and dissolves it, removing the copper foil in the target blind hole area to obtain multiple first blind holes.

[0013] Preferably, step S30 specifically includes: A single-sided copper substrate with multiple first blind holes formed on the surface of the upper copper foil is placed on the worktable of a carbon dioxide laser drilling machine. The laser beam is controlled to be aligned with each of the first blind hole positions in sequence. At each first blind hole position, multiple laser pulses are continuously emitted by the same laser beam until the insulating substrate layer at the first blind hole position is completely ablated and removed, forming a second blind hole. Alternatively, a multi-beam laser head can be used to simultaneously align with the corresponding first blind hole positions. At each aligned first blind hole position, multiple laser pulses are continuously emitted by the corresponding laser beam until the insulating substrate layer at the first blind hole position is completely ablated and removed, forming a second blind hole.

[0014] Preferably, the following steps are included before step S10: S101. Remove oxides and foreign matter from the surface of the upper copper foil of the single-sided copper substrate.

[0015] Preferably, step S30 specifically includes: A single-sided copper substrate with a first blind hole formed by etching the surface of the upper copper foil is placed in a spray decoction device. Sodium hydroxide solution was used as a stripping solution to spray a single-sided copper substrate, causing the anti-etching mask layer covering the single-sided copper substrate to swell, peel off and dissolve. The single-sided copper substrate is subjected to hot water spray washing, room temperature pure water spray washing, and then hot air drying treatment.

[0016] Furthermore, the present invention also provides the application of the above-described blind hole electroplating filling process on a single-sided copper substrate, wherein the thickness of the upper copper foil of the single-sided copper substrate is 18μm~70μm and the thickness of the intermediate insulating substrate is 80μm~100μm.

[0017] The beneficial effects of this invention are as follows: The blind via electroplating filling process provided by this invention involves chemically etching the copper foil in the target blind via region on the surface of the upper copper foil to obtain multiple first blind vias. Then, laser drilling is performed at the location of the first blind vias to penetrate the insulating substrate layer and form second blind vias. After copper plating, pulse electroplating is performed on the single-sided copper substrate, and finally, copper plating is performed on the entire board. Without adding copper reduction and browning treatment processes, blind via opening processing can be achieved on single-sided copper substrates with upper copper foil thickness in the range of 18μm to 70μm. At the same time, it can reduce the blind via diameter error, reduce the surface depression defect rate of the upper copper foil after blind via electroplating filling, and effectively ensure the heat dissipation performance of the single-sided copper substrate. In addition, since the single-sided copper substrate does not need to undergo copper reduction and browning treatment, the process production cost can be reduced compared with the existing traditional process. Attached Figure Description

[0018] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a cross-sectional view of the recessed blind hole location on a single-sided copper substrate after using the traditional blind hole electroplating filling process.

[0019] Figure 2 This is a schematic diagram of the process for electroplating and filling blind holes according to the present invention.

[0020] Figure 3 yes Figure 2 A detailed flowchart of step S10.

[0021] Figure 4 This is another schematic diagram of the process for filling blind holes by electroplating according to the present invention.

[0022] Figure 5 This is a plan view of the single-sided copper substrate corresponding to Example 1 after the target blind hole pattern transfer is completed.

[0023] Figure 6 This is a plan view of the single-sided copper substrate corresponding to Example 1 after the target blind hole etching is completed.

[0024] Figure 7 This is a slice image of a single-sided copper substrate corresponding to Example 1 after laser drilling of the target blind hole. Detailed Implementation

[0025] The following drawings disclose several embodiments of the present invention. For clarity, many practical details will be described in the following description. However, it should be understood that these practical details are not intended to limit the invention. That is, in some embodiments of the invention, these practical details are not essential. Furthermore, for the sake of simplicity, some conventional structures and components will be shown in the drawings in a simple schematic manner.

[0026] It should be noted that all directional indications in the embodiments of the present invention, such as up, down, left, right, front, back, etc., are only used to explain the relative positional relationship and movement of the components in a specific posture as shown in the attached figure. If the specific posture changes, the directional indication will also change accordingly.

[0027] Furthermore, in this invention, the use of terms such as "first," "second," etc., is for descriptive purposes only and does not specifically refer to any order or sequence, nor is it intended to limit the invention. They are merely used to distinguish items or operations described using the same technical terms and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but only if they are feasible for those skilled in the art. If a combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0028] To further understand the invention's content, features, and effects, the following embodiments are provided, and detailed descriptions are given below in conjunction with the accompanying drawings: Reference Figure 2 , Figure 2 This is a flow chart of the process method for electroplating and filling blind holes according to the present invention. The process method for electroplating and filling blind holes provided by the present invention includes the following steps: S10. Determine the target blind hole area and other areas on the surface of the upper copper foil of the single-sided copper substrate, and form an etch-resistant mask layer in the other areas.

[0029] See Figure 3 , Figure 3 yes Figure 2 A detailed flowchart illustrating step S10. Step S10 specifically includes: S11. Coat the surface of the upper copper foil of the single-sided copper substrate with photoresist ink to form a wet film layer.

[0030] This step specifically employs the conventional roller coating method, applying a photoresist ink with a thickness of 10μm~30μm to the surface of the upper copper foil on a single-sided copper substrate.

[0031] S12. The wet film layer is pre-cured to form a semi-solid film layer.

[0032] Specifically, step S12 includes the following process: a single-sided copper substrate with a wet film layer coated on the surface of the upper copper foil is fed into a tunnel furnace, and the conveying speed of the single-sided copper substrate in the tunnel furnace is controlled to be 7 m / min to 8 m / min. The single-sided copper substrate passes through multiple temperature-controlled zones in the tunnel furnace in sequence to achieve pre-curing of the wet film layer, forming a semi-solid film layer on the surface of the upper copper foil.

[0033] The multiple temperature control zones include: a first temperature control zone, a second temperature control zone, a third temperature control zone, a fourth temperature control zone, a fifth temperature control zone, and a sixth temperature control zone. Specifically, the temperature range of the first temperature control zone is 95℃~105℃; the temperature range of the second temperature control zone is 105℃~115℃; the temperature range of the third temperature control zone is 115℃~125℃; the temperature range of the fourth temperature control zone is 105℃~115℃; the temperature range of the fifth temperature control zone is 115℃~125℃; and the temperature range of the sixth temperature control zone is 115℃~125℃.

[0034] S13. Based on the target blind hole area pattern preset on the surface of the upper copper foil, expose and develop the semi-solid film layer to remove the semi-solid film layer in the target blind hole area, retain the semi-solid film layer in other areas, and form an anti-etching mask layer in other areas.

[0035] In this invention, the diameter of the target blind via is 80μm to 170μm; the ratio of the diameter to the depth of the target blind via is between 1.0 and 1.2. That is, this invention requires ensuring that the ratio of the diameter to the depth of the target blind via is between 1.0 and 1.2. The blind via diameter corresponding to the preset target blind via region pattern ranges from 80μm to 170μm, with the specific value depending on the thickness of the upper copper foil layer and the thickness of the intermediate insulating substrate layer. Furthermore, the ratio of the via opening diameter to the bottom diameter ranges from 1.2 to 1.4, and the via has an inverted isosceles trapezoidal shape.

[0036] S20. Perform chemical etching on the target blind hole region to remove the copper foil in the target blind hole region and obtain multiple first blind holes.

[0037] The present invention requires a protective film pre-formed on the bottom surface of the bottom copper substrate of a single-sided copper substrate for blind hole electroplating filling, which is used to protect the bottom surface of the copper substrate from etching. Step S20 specifically includes the following processing: spray etching is used, with a copper chloride solution of concentration of 150 g / L~200 g / L as the etching solution, at 45℃~50℃, etching the target blind hole area on the surface of the upper copper foil of the single-sided copper substrate for 60 seconds~120 seconds, so that the etching solution contacts and dissolves the copper foil exposed in the target blind hole area, removing the copper foil in the target blind hole area, and obtaining multiple first blind holes.

[0038] S30, Remove the anti-etching mask layer from the other areas.

[0039] Specifically, step S30 includes the following processing: A single-sided copper substrate with a first blind hole formed after etching the surface of the upper copper foil is placed in a spray stripping device. A sodium hydroxide solution with a concentration of 3wt% to 5wt% and a temperature range of 50℃ to 60℃ is used as the stripping solution. The single-sided copper substrate is sprayed for 1 to 3 minutes to cause the etch-resistant mask layer covering the single-sided copper substrate to swell, peel off, and dissolve. The single-sided copper substrate is then rinsed with warm water at 40℃ to 50℃, rinsed with pure water at room temperature, and then dried with hot air.

[0040] S40. Laser drilling is performed at the location of the first blind hole to penetrate the insulating substrate layer and form the second blind hole.

[0041] Specifically, step S30 includes the following processing: placing a single-sided copper substrate with multiple first blind holes formed on the surface of the upper copper foil on the worktable of a CO2 laser drilling machine. The laser beam is controlled to sequentially align with each of the first blind hole positions, and multiple laser pulses are continuously emitted from the same laser beam at each first blind hole position until the insulating substrate layer at the first blind hole position is completely ablated and removed, forming a second blind hole. Alternatively, a multi-beam laser head is used to simultaneously align with the corresponding first blind hole positions, and multiple laser pulses are continuously emitted from the corresponding laser beam at each aligned first blind hole position until the insulating substrate layer at the first blind hole position is completely ablated and removed, forming a second blind hole.

[0042] In this specific operation, within each first blind via location, multiple laser pulses sequentially act on the same position, causing the insulating substrate layer to be ablated and removed layer by layer, gradually increasing the hole depth. When the last pulse touches the copper foil of the underlying copper substrate, the ablation automatically stops due to the high reflectivity of the copper foil, and each first blind via location forms a second blind via exposing the bottom of the copper substrate.

[0043] After laser drilling of blind holes, the hole walls of the second blind hole need to be treated to remove adhesive residue generated during drilling. The specific adhesive residue treatment process includes: using an alkaline potassium permanganate method, first immersing the single-sided copper substrate in a swelling agent to soften the adhesive residue, then immersing it in a potassium permanganate solution with a concentration of 50g / L~70g / L at a temperature of 70℃~80℃ for 10~15 minutes to oxidize and decompose the adhesive residue, and finally immersing it in a neutralization solution to remove the residue. After adhesive residue removal, a thorough water rinse is performed to ensure the hole wall surface is clean and free of residue.

[0044] S50. A copper plating process is performed on a single-sided copper substrate, and a first copper layer is deposited in the second blind via to form a third blind via.

[0045] Before performing copper plating on a single-sided copper substrate, the protective film layer on the bottom surface of the single-sided copper substrate needs to be removed. The copper plating process after removing the protective film layer is as follows: Using a chemical copper plating method, the single-sided copper substrate is first immersed in a palladium activation solution with a palladium concentration of 30ppm~50ppm, causing the walls of the second blind via to adsorb a palladium catalyst layer. Then, the single-sided copper substrate is immersed in a chemical copper plating solution for 15 minutes~25 minutes, depositing a thin copper layer with a thickness of 0.5μm~1.5μm on the walls of the second blind via, forming a third blind via, which serves as the conductive substrate for subsequent electroplating. The chemical copper plating solution contains copper salts, a reducing agent, and a complexing agent; the temperature of the chemical copper plating solution is 30℃~35℃, and the pH value is 12.0~13.0.

[0046] S60. Perform pulse electroplating on a single-sided copper substrate to deposit a second copper layer in the first copper layer of the third blind hole until the third blind hole is fully plated with copper.

[0047] Specifically, step S50 includes the following process: placing the copper-plated single-sided copper substrate in an electroplating solution at a temperature of 30°C to 45°C, and applying alternating forward and reverse pulse currents to the electroplating solution for 20 to 60 minutes, so that copper preferentially deposits at the bottom of the third blind hole and fills it from bottom to top, forming a dense second copper layer within the first copper layer of the third blind hole. Specifically, the copper-plated single-sided copper substrate is placed in an electroplating solution at a temperature of 30°C to 45°C, and pulse currents are applied. The pulsed current includes alternating positive and negative pulses; the positive pulse current density is 1–10 A / dm², and the pulse width is 10–800 ms; the negative pulse current density is 3–100 A / dm², and the pulse width is 0.5–100 ms; the ratio of the positive pulse width to the negative pulse width is (5–30):1; the electroplating solution temperature is 30–45℃, and the electroplating time is 20–60 minutes, so that copper is preferentially deposited at the bottom of the blind hole and filled from bottom to top, finally forming a dense second copper layer in the third blind hole.

[0048] S70. Thicken the copper plating layer on the entire single-sided copper substrate.

[0049] Specifically, step S60 includes the following processing: immersing the single-sided copper substrate after electroplating and filling into an electroplating solution containing copper sulfate and sulfuric acid, wherein the concentration of copper sulfate is 60g / L~80g / L, the concentration of sulfuric acid is 180g / L~240g / L, and the concentration of chloride ions is 30ppm~90ppm; adding a brightener, and electroplating for 20 minutes~40 minutes at a current density of 1.5A / dm²~2.5A / dm² and a temperature of 22℃~30℃, depositing a dense second copper layer of 5μm~8μm on the entire surface of the single-sided copper substrate, including the top of the filled blind holes.

[0050] Further, see Figure 4 , Figure 4 This is another schematic diagram of the process for electroplating and filling blind holes according to the present invention. S101. Remove oxides and foreign matter from the surface of the upper copper foil of the single-sided copper substrate.

[0051] In step S101, a 3%~5% sulfuric acid solution is used for cleaning, followed by mechanical polishing with a needle brush, water washing, and drying. This creates a clean surface with a microscopic roughness on the upper copper foil, thereby enhancing the mechanical adhesion between the photoresist ink and the upper copper foil surface.

[0052] The blind via electroplating filling process provided by this invention involves chemically etching the copper foil in the target blind via area on the surface of the upper copper foil to obtain multiple first blind vias. Then, laser drilling is performed at the location of the first blind vias to penetrate the insulating substrate layer and form second blind vias. After copper plating, pulse electroplating is performed on the single-sided copper substrate, and finally, copper plating is performed on the entire board. Without adding copper reduction and browning treatment processes, blind via opening processing can be achieved on single-sided copper substrates with upper copper foil thickness in the range of 18μm to 70μm. At the same time, it can reduce the blind via diameter error, reduce the surface depression defect rate of the upper copper foil after blind via electroplating filling, and effectively ensure the heat dissipation performance of the single-sided copper substrate.

[0053] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention. Equivalent adjustments or optimizations made by those skilled in the art based on the core concept of the present invention should still fall within the scope of protection of the present invention.

[0054] Example 1 S01. Prepare a single-sided copper substrate with an upper copper foil thickness of 25μm, an intermediate insulating substrate layer thickness of 90μm, and a total board thickness of 1.2mm. A protective film is attached to the bottom surface of the single-sided copper substrate to protect it from etching during the chemical etching process of creating blind vias.

[0055] S101. Remove oxides and foreign matter from the surface of the upper copper foil of the single-sided copper substrate: clean with 4% sulfuric acid, mechanically polish with a needle brush, wash with water and dry to form a clean surface with micro-roughness on the surface of the upper copper foil, thereby enhancing the mechanical adhesion between the photoresist ink and the surface of the upper copper foil.

[0056] S11. Coating the surface of the upper copper foil of the single-sided copper substrate with photoresist ink to form a wet film layer: using a roller coating method, coating the surface of the upper copper foil of the single-sided copper substrate with photoresist ink with a thickness of 15μm.

[0057] S12. Pre-curing the wet film layer to form a semi-solid film layer: A single-sided copper substrate with a wet film layer coated on the surface of the upper copper foil is fed into a tunnel furnace, and the conveying speed of the single-sided copper substrate in the tunnel furnace is controlled at 7.5 m / min. The single-sided copper substrate passes through the following six temperature control zones in the tunnel furnace in sequence: first temperature control zone 100℃; second temperature control zone 110℃; third temperature control zone 120℃; fourth temperature control zone 110℃; fifth temperature control zone 120℃; sixth temperature control zone 120℃. This achieves pre-curing of the wet film layer, forming a semi-solid film layer on the surface of the upper copper foil.

[0058] S13. Design the target blind hole area pattern on the surface of the upper copper foil. In this embodiment 1, the standard aperture of the target blind hole in the target blind hole area pattern on the surface of the upper copper foil is 90 μm. According to the target blind hole area pattern preset on the surface of the upper copper foil, expose and develop the semi-solid film layer to remove the semi-solid film layer in the target blind hole area, retain the semi-solid film layer in other areas, and form an anti-etching mask layer in other areas: Use an ultraviolet exposure machine with an exposure energy of 200 mJ / cm² to selectively expose the target blind hole area pattern on the surface of the upper copper foil of the single-sided copper substrate. After exposure, use a sodium carbonate developer with a mass fraction of 1.0% to spray and develop at a temperature of 30°C for 50 seconds to remove the unexposed semi-solid film layer above the target blind hole area, thereby retaining the semi-solid film layer formed in other areas on the surface of the upper copper foil; then rinse with deionized water to complete the transfer of the target blind hole pattern.

[0059] S20. Chemical etching is performed on the target blind via region to remove the copper foil in the target blind via region, resulting in multiple first blind vias. Spray etching is used with a copper chloride solution of 180 g / L as the etchant. The target blind via region on the upper copper foil surface of the single-sided copper substrate is etched for 90 seconds at 48°C, allowing the etchant to contact and dissolve the exposed copper foil in the target blind via region, removing the copper foil in the target blind via region, and obtaining multiple first blind vias. In this Example 1, the standard diameter of the etched target blind via is 120 μm. See [link to example]. Figure 6 In this embodiment 1, the diameter of the etched target blind hole is 121.10 μm, and the ratio of the hole diameter to the hole depth is 121.10:111.81, ranging from 1.0 to 1.2. The ratio of the hole opening diameter to the hole bottom diameter is 121.10:100.01, ranging from 1.2 to 1.4, and the shape is an inverted isosceles trapezoid, which is beneficial for subsequent electroplating filling.

[0060] S30. Removing the etch-resistant mask layer from the other areas: The single-sided copper substrate with the first blind hole formed after etching the surface of the upper copper foil is placed in a spray stripping device. A 4wt% sodium hydroxide solution at a temperature within the range of 55°C is used as the stripping solution to spray the single-sided copper substrate for 2 minutes, causing the etch-resistant mask layer covering the single-sided copper substrate to swell, peel off, and dissolve. The single-sided copper substrate is then rinsed with 45°C warm water, rinsed with room temperature pure water, and dried with hot air.

[0061] S40. Laser drilling is performed at the location of the first blind hole to penetrate the insulating substrate layer and form the second blind hole: A single-sided copper substrate with multiple first blind holes formed on the surface of the upper copper foil is placed on the worktable of a CO2 laser drilling machine. The laser beam is controlled to be aligned sequentially with each first blind hole position, and multiple laser pulses are continuously emitted from the same laser beam at each first blind hole position until the insulating substrate layer at the first blind hole position is completely ablated and removed, forming the second blind hole. The laser pulse energy is 10 mJ, the pulse width is 18 μs, the number of pulses is 6, and the frequency is 2.5 kHz.

[0062] S401. The wall of the second blind via is treated to remove adhesive residue: Using an alkaline potassium permanganate method, the single-sided copper substrate is first immersed in a swelling agent to soften the adhesive residue, then immersed in a 60g / L potassium permanganate solution at 75℃ for 12 minutes to oxidize and decompose the adhesive residue. Finally, it is immersed in a neutralization solution to remove any residue. After removing the adhesive residue, the substrate is thoroughly rinsed with water to ensure the via wall surface is clean and free of residue.

[0063] S50. A copper plating process is performed on the single-sided copper substrate to deposit a first copper layer within the second blind via, forming a third blind via. The protective film layer on the bottom surface of the single-sided copper substrate is removed. Using a chemical copper plating method, the single-sided copper substrate is first immersed in a palladium activation solution with a palladium concentration of 40 ppm, causing the walls of the second blind via to adsorb a palladium catalyst layer. Then, the single-sided copper substrate is immersed in a chemical copper plating solution for 20 minutes to deposit a thin copper layer with a thickness of 1.0 μm on the walls of the second blind via, forming a third blind via, which serves as the conductive substrate for subsequent electroplating. The chemical copper plating solution contains copper salts, a reducing agent, and a complexing agent. The temperature of the chemical copper plating solution is 32°C, and the pH value is 12.5.

[0064] S60. Perform pulse electroplating on a single-sided copper substrate to deposit a second copper layer within the first copper layer of the third blind hole until the third blind hole is fully plated with copper: Place the copper-plated single-sided copper substrate in an electroplating solution at a temperature of 38°C, and apply alternating forward and reverse pulse currents to the electroplating solution for 40 minutes, so that copper preferentially deposits at the bottom of the third blind hole and fills it from bottom to top, forming a dense second copper layer within the first copper layer of the third blind hole. Specifically, place the copper-plated single-sided copper substrate in an electroplating solution at a temperature of 38°C and apply pulse current. The pulsed current includes alternating positive and negative pulses; the positive pulse current density is 5 A / dm², and the pulse width is 400 ms; the negative pulse current density is 50 A / dm², and the pulse width is 50 ms; the ratio of the positive pulse width to the negative pulse width is 8:1; the electroplating solution temperature is 38℃, and the electroplating time is 40 minutes, so that copper is preferentially deposited at the bottom of the blind hole and filled from bottom to top, and finally a dense second copper layer is formed in the third blind hole.

[0065] S70. Thickening the copper layer on the entire single-sided copper substrate: Immerse the single-sided copper substrate after electroplating and filling the holes in an electroplating solution containing copper sulfate and sulfuric acid, wherein the concentration of copper sulfate is 70 g / L, the concentration of sulfuric acid is 210 g / L, and the concentration of chloride ions is 600 ppm; add a brightener, and electroplat for 30 minutes at a current density of 2.0 A / dm² and a temperature of 26°C to deposit a dense second copper layer on the entire surface of the single-sided copper substrate, including the top of the filled blind holes.

[0066] The following performance indicators were tested on the single-sided copper substrate after the blind hole electroplating filling process provided in Example 1. The test results are shown in Table 1.

[0067] Table 1:

[0068] See Figure 5 , Figure 5 This is a plan view of the single-sided copper substrate corresponding to Example 1 after the target blind hole etching is completed. Figure 5 The width of the red box represents the target blind hole diameter, and the red numbers represent the size of the target blind hole diameter. The target hole diameter R1 in the upper red box is 0.122mm, which is equivalent to 122μm. The target hole diameter R2 in the lower red box is 0.124mm, which is equivalent to 124μm.

[0069] See Figure 6 , Figure 6 This is a slice image of a single-sided copper substrate corresponding to Example 1 after laser drilling of the target blind hole. Figure 6The red horizontal dimension line in the upper right corner represents the aperture R3 of the blind via on the upper copper foil layer; the red horizontal dimension line in the lower right corner represents the aperture R4 of the blind via at the bottom of the intermediate insulating substrate layer; the red vertical dimension line in the upper left corner represents the copper foil thickness D1 on the substrate surface; and the red vertical dimension line in the lower left corner represents the thickness D2 of the intermediate insulating substrate layer. Specifically, R3 is 121.1 μm, R4 is 100.01 μm, D1 is 21.56 μm, and D2 is 90.25 μm. The aperture-to-depth ratio is 121.1:111.81, which is between 1.0 and 1.2. The error in R3 compared to the standard diameter of the etched target blind via (120 μm) is 1.1 μm, and the aperture error is less than 5 μm.

[0070] See Figure 7 , Figure 7 This is a cross-sectional view of the single-sided copper substrate corresponding to Example 1 after the target blind via electroplating and filling. The yellow horizontal dimension line in the figure represents the depression D3 of the copper and blind via after electroplating, with a depression value of 6.88 μm.

[0071] Based on the test results in Table 1, and Figures 5 to 7 The results show that the single-sided copper substrate treated in Example 1 has the following excellent technical effects.

[0072] First, the via filling quality is excellent. The void ratio of blind vias is 1%, far below the ≤5% limit requirement specified in the IPC-6012 standard, and the maximum size of a single void is only 8μm, with no through-cracks inside the blind vias. This indicates that the electroplating filling process used in this invention can achieve dense filling of the copper layer inside the blind vias, effectively avoiding defects such as voids and cracks, and ensuring the reliability and stability of the blind via conductivity.

[0073] Secondly, the drilling accuracy is high. The hole diameter deviation is controlled within 5μm, meeting the stringent requirements of high-density interconnect boards for the consistency of blind via diameters. This demonstrates that the laser drilling process parameters of this invention are precisely controlled, enabling stable processing accuracy to be maintained in mass production.

[0074] Third, it exhibits excellent surface flatness. The indentation value after blind via filling is only 6.88μm, meeting the surface flatness requirements of the in-disk via structure. This smaller indentation value facilitates subsequent BGA device soldering, effectively reducing the risk of solder voids and improving assembly yield and product reliability.

[0075] In summary, this invention achieves excellent technical results in terms of blind hole filling quality, blind hole drilling accuracy, and surface flatness through an optimized blind hole electroplating filling manufacturing process, which can meet the stringent requirements of high-reliability electronic products for the performance of blind holes on single-sided copper substrates.

[0076] The specific testing methods for the relevant properties of the single-sided copper substrate processed by the process method provided in Example 1 are as follows: I. Blind Hole Void Rate Test According to IPC-TM-650 2.1.1 "General Test Methods for Printed Circuit Boards", metallographic sectioning was used for testing. The specific operation steps are as follows: A sample containing blind vias was cut from the single-sided copper substrate processed in Example 1, avoiding the edge of the board, and a representative blind via area was selected; the sample was vacuum-mounted with epoxy resin and cured under vacuum conditions to prevent air bubble interference; the sample was ground along the direction perpendicular to the blind via axis to the center section of the blind via, and then ground stepwise with 240 grit, 800 grit, and 1200 grit sandpaper; then polished to a mirror finish with a diamond suspension with a particle size of 1μm to 0.05μm; finally, the sample was observed and photographed under a metallographic microscope at 500x magnification.

[0077] Image analysis software was used to precisely delineate the filling area of ​​the electroplated copper layer along the edge of the blind hole wall, which was taken as the total filling area of ​​the blind hole; the total area of ​​all voids in this area was then calculated.

[0078] The formula for calculating the void ratio is: Void ratio (%) = (Total void area in blind holes / Total filling area of ​​blind holes) × 100%.

[0079] Among them, the total area of ​​voids inside blind holes refers to the sum of the areas of all void regions inside the copper-filled blind hole in metallographic section observation; the total filling area of ​​blind holes refers to the total area actually filled by the electroplated copper layer along the edge of the blind hole wall.

[0080] II. Blind Hole Diameter Error Test According to IPC-6012 "Rigid Printed Circuit Board Qualification and Performance Specification", optical measurement methods were used for testing.

[0081] The specific operating steps are as follows: Use a high-magnification optical microscope or image measuring instrument with a measurement accuracy of ±0.1μm; fix the single-sided copper substrate sample processed in Example 1 on the measuring stage and ensure that it is placed horizontally; randomly select no less than 30 blind holes and measure the actual hole diameter of each blind hole (measure the maximum diameter of the hole opening); take the arithmetic mean of the measured values ​​as the actual hole diameter value.

[0082] The formula for calculating aperture deviation is: Aperture deviation (mm) = |Actual aperture value - Design aperture value|.

[0083] III. Depression Value Test After Blind Hole Filling According to the IPC-TM-650 standard, the inspection is carried out using a laser confocal microscope or a surface profilometer.

[0084] The specific operating steps are as follows: Use a laser confocal microscope or surface profilometer with a vertical resolution of 0.1 μm; place the single-sided copper substrate sample processed in Example 1 on the measurement platform to ensure that the surface is clean and level; randomly select no less than 30 blind holes, and measure the depression depth of each blind hole, that is, the height difference between the surface copper layer directly above the center of the blind hole and the surface copper layer at the edge of the hole; take the arithmetic mean of the depression depth of each blind hole as the final depression value.

[0085] The formula for calculating the indentation value is: Indentation value (μm) = Height of copper layer surface at the edge of the hole - Height of copper layer surface directly above the center of the blind hole.

[0086] The improved blind via electroplating process provided by this invention achieves a blind via void rate as low as 1%, a blind via diameter error as low as 5μm, and a post-filling depression value as low as 6.88μm. Compared with existing traditional processes, this significantly reduces the blind via void rate, blind via diameter error, and post-filling depression value after blind via electroplating on single-sided copper substrates. It solves the problems of excessive depression and high void rate in single-sided copper substrates due to electroplating filling, improves yield, and reduces production costs for enterprises compared to existing traditional processes because single-sided copper substrates do not require copper reduction and browning treatments.

[0087] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A process for electroplating and filling blind holes, characterized in that, Includes the following steps: S10. Determine the target blind hole area and other areas on the surface of the upper copper foil of the single-sided copper substrate, and form an etch-resistant mask layer in the other areas. S20. Perform chemical etching on the target blind hole region to remove the copper foil in the target blind hole region and obtain a plurality of first blind holes; S30. Remove the etch-resistant mask layer from the other areas; S40. Laser drilling is performed at the location of the first blind hole to penetrate the insulating substrate layer and form a second blind hole; S50. A copper plating process is performed on a single-sided copper substrate, and a first copper layer is deposited in the second blind via to form a third blind via. S60. Perform pulse electroplating on a single-sided copper substrate, depositing a second copper layer in the first copper layer of the third blind hole until the third blind hole is fully plated with copper layer. S70. Thicken the copper plating layer on the entire single-sided copper substrate.

2. The process for electroplating and filling blind holes according to claim 1, characterized in that, The diameter of the target blind hole is 80μm~170μm; the ratio of the diameter to the depth of the target blind hole is between 1.0 and 1.

2.

3. The process for electroplating and filling blind holes according to claim 1, characterized in that, Step S50 specifically includes: The single-sided copper substrate after copper plating is placed in the electroplating solution, and alternating positive and reverse pulse currents are applied to the electroplating solution to cause copper to be preferentially deposited at the bottom of the third blind hole and filled from bottom to top, forming a dense second copper layer within the first copper layer of the third blind hole.

4. The process for electroplating and filling blind holes according to claim 1, characterized in that, Step S10 specifically includes: S11. Coat the surface of the upper copper foil of the single-sided copper substrate with photoresist ink to form a wet film layer; S12. Pre-curing the wet film layer to form a semi-solid film layer; S13. Based on the target blind hole area pattern preset on the surface of the upper copper foil, expose and develop the semi-solid film layer to remove the semi-solid film layer in the target blind hole area, retain the semi-solid film layer in other areas, and form an anti-etching mask layer in other areas.

5. The process for electroplating and filling blind holes according to claim 4, characterized in that, Step S12 specifically includes: A single-sided copper substrate with a wet film layer coated on the surface of the upper copper foil is fed into a tunnel furnace. The single-sided copper substrate is controlled to pass through multiple temperature control zones in the tunnel furnace in sequence to achieve pre-curing of the wet film layer and form a semi-solid film layer on the surface of the upper copper foil.

6. The process method for electroplating and filling blind holes according to claim 1, characterized in that, Step S20 specifically includes: Spray etching is used, with copper chloride solution as the etching solution, to etch the target blind hole area on the surface of the upper copper foil of the single-sided copper substrate. The etching solution comes into contact with the copper foil exposed in the target blind hole area and dissolves it, removing the copper foil in the target blind hole area to obtain multiple first blind holes.

7. The process for electroplating and filling blind holes according to claim 1, characterized in that, Step S30 specifically includes: A single-sided copper substrate with multiple first blind holes formed on the surface of the upper copper foil is placed on the worktable of a carbon dioxide laser drilling machine. The laser beam is controlled to be aligned with each of the first blind hole positions in sequence. At each first blind hole position, multiple laser pulses are continuously emitted by the same laser beam until the insulating substrate layer at the first blind hole position is completely ablated and removed, forming a second blind hole. Alternatively, a multi-beam laser head can be used to simultaneously align with the corresponding first blind hole positions. At each aligned first blind hole position, multiple laser pulses are continuously emitted by the corresponding laser beam until the insulating substrate layer at the first blind hole position is completely ablated and removed, forming a second blind hole.

8. The process method for electroplating and filling blind holes according to claim 1, characterized in that, The following steps are included before step S10: S101. Remove oxides and foreign matter from the surface of the upper copper foil of the single-sided copper substrate.

9. The process for electroplating and filling blind holes according to claim 1, characterized in that, Step S30 specifically includes: A single-sided copper substrate with a first blind hole formed by etching the surface of the upper copper foil is placed in a spray decoction device. Sodium hydroxide solution was used as a stripping solution to spray a single-sided copper substrate, causing the anti-etching mask layer covering the single-sided copper substrate to swell, peel off and dissolve. The single-sided copper substrate is subjected to hot water spray washing, room temperature pure water spray washing, and then hot air drying treatment.

10. The application of the blind-hole electroplating filling process according to any one of claims 1 to 9 on a single-sided copper substrate, characterized in that, The thickness of the upper copper foil on the single-sided copper substrate is 18μm~70μm, and the thickness of the middle insulating substrate is 80μm~100μm.

Images