Chemical copper plating solution for improving blind via bottom void and copper plating method thereof

Abstract

The embodiment of the present application discloses a chemical copper plating solution for improving blind hole bottom cavity and a copper plating method thereof, the copper plating solution comprises the following mass concentration components: copper sulfate: 8-15 g / L; complexing agent: 20-40 g / L; dispersing agent: 10-80 mg / L; stabilizer: 20-50 mg / L; accelerator: 0.2-0.8 g / L; reducing agent: 4-10 g / L; the complexing agent is a carboxyl amino pyridine compound; the dispersing agent is a diol alkyl sulfonate compound; the stabilizer is a heterocyclic indole carboxylic acid compound; and the accelerator is an amino pyrazine compound. The present application can realize the phenomenon of no cavity in the blind hole filling hole bottom, ensure the subsequent chemical dense plating in the hole, and the plating solution is stable and reliable, and the plating layer is uniform.

Description

Technical Field

[0001] This invention relates to the field of chemical copper plating technology, and in particular to a chemical copper plating solution and method for improving the voids at the bottom of blind holes. Background Technology

[0002] As high-end HDI circuit boards and chip substrates develop towards micro-aperture, high aspect ratio laser blind via structures, the quality of blind via metallization has become a key factor restricting PCB conductivity reliability and mass production yield. Chemical copper plating, as the core process for preparing the conductive substrate of the blind via insulating wall, requires the formation of a continuous and dense thin copper layer on the inner wall of the closed blind via.

[0003] Existing traditional alkaline chemical copper plating processes have poor compatibility. Blind vias have a closed microporous structure, resulting in low efficiency of chemical convection and mass transfer. Concentration polarization problems, such as insufficient copper ion concentration, easily occur at the bottom of the via. At the same time, the formaldehyde copper plating reaction continuously releases hydrogen gas, making it difficult to vent the gas inside the micro-blind via. Bubbles easily become trapped at the bottom of the via, forming a shielding layer that blocks copper deposition and easily produces defects such as copper voids, insufficient copper, and discontinuous copper layers at the bottom of the via.

[0004] In addition, the traditional colloidal palladium activation process has weak penetration ability for high aspect ratio blind holes, and the catalytic nucleation sites at the bottom of the hole are sparse. In addition, the reaction rate of conventional copper plating solution is uneven, with too fast deposition at the hole opening and slow deposition at the bottom of the hole, which further aggravates the void defects.

[0005] Currently, the industry improves defects by optimizing stirring, extending copper plating time, and adding conventional additives. However, this only slightly alleviates shallow blind via defects and cannot solve the core problems of poor mass transfer, hydrogen evolution retention, and uneven nucleation. Furthermore, it can easily lead to issues such as copper floating on the board surface and decreased chemical stability. Therefore, there is an urgent need to develop a new chemical copper plating process to effectively eliminate copper voids at the bottom of blind vias and improve the uniformity of blind via metallization and product reliability. Summary of the Invention

[0006] The technical problem to be solved by the embodiments of the present invention is to provide a chemical copper plating solution and a copper plating method for improving the voids at the bottom of blind holes, so as to achieve the phenomenon of no voids at the bottom of blind holes, ensure the subsequent chemical deposition inside the hole is dense, and at the same time the plating solution is stable and reliable and the plating layer is uniform.

[0007] To address the aforementioned technical problems, embodiments of the present invention propose a chemical copper plating solution for improving the voids at the bottom of blind vias, comprising the following components by mass concentration: Copper sulfate: 8–15 g / L; Complexing agent: 20–40 g / L; Dispersant: 10–80 mg / L; Stabilizer: 20–50 mg / L; Accelerator: 0.2–0.8 g / L; Reducing agent: 4–10 g / L; The complexing agent is a carboxyaminopyridine compound; the dispersant is a diol alkyl sulfonate compound; the stabilizer is a heterocyclic indole carboxylic acid compound; and the accelerator is an aminopyrazine compound.

[0008] Furthermore, the carboxyaminopyridine compound is 5-carboxy-2,3-diaminopyridine.

[0009] Furthermore, the reducing agent is formaldehyde.

[0010] Furthermore, the plating temperature of the chemical copper plating solution is 35–45°C, and the pH of the chemical copper plating solution is 11–12.

[0011] Furthermore, the diol alkyl sulfonate compound is diethylene glycol dimethyl sulfonate.

[0012] Furthermore, the heterocyclic indole carboxylic acid compound is 7-azaindole-3-carboxylic acid.

[0013] Furthermore, the aminopyrazine compound is 5-amino-2-pyrazinic acid.

[0014] Accordingly, embodiments of the present invention also provide a method for copper plating using a chemical copper plating solution to improve the voids at the bottom of blind vias, comprising: Step 1: Perform alkaline swelling on the copper plating circuit board; Step 2: Remove adhesive with alkaline potassium permanganate; Step 3: Reduction and neutralization to remove manganese salts; Step 4: Perform alkaline low-foaming precision degreasing using an alkaline degreasing plating solution; Step 5: First-level silent immersion water wash, room temperature, 2 independent tank washes; Step 6: Perform acidic ionic palladium activation using an acidic ionic palladium activation solution; Step 7: Perform copper plating using the aforementioned chemical copper plating solution; Step 8: Multi-stage silent water wash.

[0015] Further, in step 4, the alkaline degreasing plating solution comprises the following components by mass concentration: anhydrous sodium carbonate 28 g / L, trisodium phosphate 15 g / L, flake sodium hydroxide 12 g / L, fatty alcohol polyoxyethylene ether (AEO-9) 4.0 g / L, imidazo[1,2-a]pyridine-7-carboxylic acid 1.2 g / L, with the balance being pure water.

[0016] Further, in step 6, the acidic ionic palladium activation solution comprises the following components by mass concentration: 60 mL / L sulfuric acid (98%), 0.35 g / L palladium chloride, 1.0 g / L fatty alcohol polyoxyethylene ether (AEO-9), 0.1 g / L 2-ethylhexanol EO / PO copolymer (9EO), 0.5 g / L aminoethylated acrylic polymer, with the remainder being pure water.

[0017] The beneficial effects of this invention are as follows: 1) The present invention employs an alkaline degreasing process (composite alkaline salt combined with a high-efficiency penetrating surfactant and a special organic corrosion inhibitor) and an acidic ionic palladium activation process. This process provides strong degreasing capabilities, operates at low temperatures without damaging the board surface or hole walls, and the low-foaming plating solution quickly wets micro-blind holes, preventing foam buildup and clogging, resulting in high pretreatment cleanliness. The acidic ionic palladium activation solution exhibits excellent compatibility, combining penetrating aids and functional polymers. Its strong penetrating power allows it to reach deep into the bottom of blind holes for uniform catalytic activation, compensating for insufficient activation sites at the bottom of the holes and ensuring uniform and continuous copper plating.

[0018] 2) This invention uses 5-carboxy-2,3-diaminopyridine as a complexing agent, which can achieve a wider pH operating range, and the resulting coating has finer and more uniform grains than the traditional EDTA system. The stable range of the traditional EDTA copper plating system is only pH 12.0 to 12.3, which is extremely difficult to control in on-site production. pH fluctuations can easily induce a large number of voids. Trace ions and oil impurities introduced in the pretreatment will preferentially occupy EDTA complexing sites, and the EDTA system coating has coarser grains, insufficient density, and poor initial nucleation uniformity.

[0019] 3) The dispersant of this invention, diethylene glycol dimethyl sulfonate, has excellent water solubility, is stable in alkaline copper plating solutions, exhibits strong compatibility, and does not disrupt the balance of the complexation system. It can efficiently disperse copper powder and reactive impurities in the plating solution, preventing particles from adhering to the bottom of blind holes and causing voids; it can reduce the surface tension of the solution, enhance micropore permeability, accelerate the removal of bubbles from the holes, and improve insufficient solution exchange at the bottom of the holes; it uniformly transports copper complex ions to the depths of blind holes, balancing the deposition rate on the plate surface and at the bottom of the holes, refining copper crystals, and reducing intergranular micropores; it does not poison activation sites, effectively improving the uniformity and density of the copper plating layer, and steadily reducing the defect rate of voids in blind hole copper plating.

[0020] 4) The promoter 5-amino-2-pyrazine carboxylic acid of the present invention can effectively reduce the activation energy of copper deposition, accelerate the generation of crystal nuclei at the bottom of blind holes, and solve the problem of lag in deep copper deposition; it can also enhance the catalytic effect of palladium activation sites, promote the rapid formation of a continuous copper layer at the bottom of the hole, reduce copper voids, and significantly improve the overall quality of copper deposition in blind holes. Detailed Implementation

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will be further described in detail below with reference to specific embodiments.

[0022] The chemical copper plating solution for improving the bottom voids of blind vias according to embodiments of the present invention comprises the following components by mass concentration: Copper sulfate: 8–15 g / L; Complexing agent: 20–40 g / L; Dispersant: 10–80 mg / L; Stabilizer: 20–50 mg / L; Accelerator: 0.2–0.8 g / L; Reducing agent: 4–10 g / L; The complexing agent is a carboxyaminopyridine compound; the dispersant is a diol alkyl sulfonate compound; the stabilizer is a heterocyclic indole carboxylic acid compound; and the accelerator is an aminopyrazine compound.

[0023] The carboxyaminopyridine compound is 5-carboxy-2,3-diaminopyridine.

[0024] The reducing agent is formaldehyde. The plating temperature of the chemical copper plating solution is 35–45°C, and the pH of the chemical copper plating solution is 11–12.

[0025] The diol alkyl sulfonate compound is diethylene glycol dimethyl sulfonate. The heterocyclic indole carboxylic acid compound is 7-azaindole-3-carboxylic acid. The aminopyrazine compound is 5-amino-2-pyrazine carboxylic acid.

[0026] The copper plating method of the chemical copper plating solution for improving the voids at the bottom of blind holes in the present invention includes steps 1 to 8.

[0027] Step 1: Perform alkaline swelling on the circuit board to be coated with copper, so that the epoxy resin polymer material on the blind hole wall of the circuit board to be coated with copper expands and softens.

[0028] Plating solution formula: 60 mL / L ethylene glycol ethyl ether, 35 g / L sodium hydroxide, and the balance is water.

[0029] Process parameters: temperature 70±2℃, time 6 min, slight up-and-down shaking, aeration prohibited, pH 13.0~13.5.

[0030] Step 2: Alkaline potassium permanganate descaling. Using the strong oxidizing properties of potassium permanganate (KMnO4), the swollen and softened resin drilling debris is oxidized and decomposed, thereby cleaning the hole wall.

[0031] Plating solution formula: potassium permanganate 40-60 g / L, sodium hydroxide 30-50 g / L.

[0032] Process parameters: temperature 80±2℃, time 8 min, operation mode is gentle oscillation, no strong stirring.

[0033] Step 3: Reduction and neutralization to remove manganese salts. The walls of the reduction pores will be cleaned of residual permanganate ions, which have strong oxidizing properties.

[0034] Plating solution formulation: sulfuric acid 30-50 mL / L, hydroxylamine salt 20-30 g / L.

[0035] Process parameters: temperature 45±2℃, time 5 min, pH 2.0~3.0, mainly static soaking with slight shaking.

[0036] Step 4: Perform alkaline low-foaming precision degreasing using an alkaline degreasing plating solution.

[0037] Alkaline degreasing plating solution formula: anhydrous sodium carbonate 28 g / L, trisodium phosphate 15 g / L, flake sodium hydroxide 12 g / L, AEO-9 (fatty alcohol polyoxyethylene ether) 4.0 g / L, imidazo[1,2-a]pyridine-7-carboxylic acid 1.2 g / L, with the balance being pure water.

[0038] Process parameters: temperature 50±1℃, soaking time 300±10 s, pH of the solution 11.5±0.3, specific gravity of the solution 1.035±0.005, movement mode is vertical up and down swing, swing stroke 30~40 mm, swing frequency 4~6 times / minute.

[0039] Step 5: First-level silent immersion water wash.

[0040] Water temperature: 25±3℃; Water flow state: static soaking, no overflow impact, no high-pressure water spray.

[0041] Operating parameters: Two independent water washes, each wash lasting 60±5 seconds; the plate must be completely submerged 20 mm below the liquid surface; the movement method is static immersion, and shaking or swaying is prohibited.

[0042] Step 6: Perform acidic ionic palladium activation using an acidic ionic palladium activation solution.

[0043] The formulation of the acidic palladium ionic activation solution is as follows: sulfuric acid (98%) 60 mL / L, palladium chloride 0.35 g / L, AEO-9 1.0 g / L, 2-ethylhexanol EO / PO copolymer (9EO) 0.1 g / L, aminoethylated acrylic polymer 0.5 g / L, and the balance is made up with pure water.

[0044] Process parameters: Temperature 30℃, time 2 min. Rinse with water after activation.

[0045] Step 7: Chemical copper plating.

[0046] The chemical copper plating solution described in this invention is used (see examples for specific formulation).

[0047] Operating conditions: The plate oscillation method is vertical small-amplitude oscillation, with an oscillation stroke of 25-35 mm and an oscillation frequency of 3-5 times / min; aeration, bubbling, and strong airflow disturbance in the tank are strictly prohibited; the tank solution circulation is slow bottom side flow circulation, with a filtration accuracy of 1 μm; the tank solution stirring state is a slight horizontal flow on the liquid surface, without rolling or vortex; the spacing between the plates is ≥15 mm. The plating temperature is 35-45℃, the pH is 11-12, and the time is 20 min.

[0048] Step 8: Multi-stage silent water wash.

[0049] Three-stage overflow water rinsing thoroughly removes any residual chemicals from the surface before proceeding to the next step.

[0050] Example 1:

[0051] The chemical copper plating solution formulation of this invention is as follows: copper sulfate 11 g / L, 5-carboxy-2,3-diaminopyridine 30 g / L, diethylene glycol dimethanesulfonate 45 mg / L, 7-azaindole-3-carboxylic acid 35 mg / L, 5-amino-2-pyrazinic acid 0.5 g / L, formaldehyde 7 g / L, and pure water balance.

[0052] Process parameters: temperature 40℃, pH 11.5, time 20 min.

[0053] Performance test results: The chemical copper plating coverage is excellent (full coverage), there are no voids at the bottom of the holes, and the service life of the plating solution is excellent (more than 6 months).

[0054] Example 2:

[0055] The chemical copper plating solution formulation of this invention is as follows: copper sulfate 15 g / L, 5-carboxy-2,3-diaminopyridine 40 g / L, diethylene glycol dimethanesulfonate 80 mg / L, 7-azaindole-3-carboxylic acid 20 mg / L, 5-amino-2-pyrazinic acid 0.2 g / L, formaldehyde 5 g / L, and pure water balance.

[0056] Process parameters: temperature 45℃, pH 12, time 20 min.

[0057] Performance test results: Same as Example 1, all are excellent.

[0058] Example 3:

[0059] The chemical copper plating solution formulation of this invention is as follows: copper sulfate 8 g / L, 5-carboxy-2,3-diaminopyridine 20 g / L, diethylene glycol dimethanesulfonate 10 mg / L, 7-azaindole-3-carboxylic acid 50 mg / L, 5-amino-2-pyrazinic acid 0.8 g / L, formaldehyde 10 g / L, and pure water balance.

[0060] Process parameters: temperature 45℃, pH 12, time 20 min.

[0061] Performance test results: Same as Example 1, all are excellent.

[0062] Comparative Example 1 (lacking complexing agent): Plating solution formulation: Same as in Example 1, but without 5-carboxy-2,3-diaminopyridine.

[0063] Test results: The coverage of the chemical copper plating was poor (below 64%), the void area at the bottom of the hole was greater than 25%, and the service life of the plating solution was poor (below 1 month).

[0064] Comparative Example 2 (lacking dispersant): Plating solution formulation: Same as in Example 1, but without diethylene glycol dimethyl sulfonate.

[0065] Test results: The coverage of the chemical copper plating was good (85% to 99%), the void area at the bottom of the hole was less than 10%, and the service life of the plating solution was excellent (more than 6 months).

[0066] Comparative Example 3 (lacking stabilizer): Plating solution formulation: Same as in Example 1, but without 7-azaindole-3-carboxylic acid.

[0067] Test results: The coverage of the chemical copper plating was good (85% to 99%), the void area at the bottom of the hole was less than 10%, and the service life of the plating solution was good (more than 5 months).

[0068] Comparative Example 4 (lacking accelerator): Plating solution formulation: Same as in Example 1, but without 5-amino-2-pyrazine carboxylic acid.

[0069] Test results: The coverage of the chemical copper plating was good (85% to 99%), the void area at the bottom of the hole was less than 10%, and the service life of the plating solution was excellent (more than 6 months).

[0070] The judgment criteria are shown in Table 1:

[0071] The results of the above embodiments and comparative examples show that the components of the chemical copper plating solution of the present invention work synergistically, and exhibit excellent performance in terms of copper plating coverage, elimination of voids at the bottom of holes, and stability of the plating solution. Each link and step of the present invention is interconnected, and the absence of any key component or step will lead to a decrease in performance.

[0072] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A chemical copper plating solution for improving voids at the bottom of blind vias, characterized in that, Includes the following components by mass concentration: Copper sulfate: 8–15 g / L; Complexing agent: 20–40 g / L; Dispersant: 10–80 mg / L; Stabilizer: 20–50 mg / L; Accelerator: 0.2–0.8 g / L; Reducing agent: 4–10 g / L; The complexing agent is a carboxyaminopyridine compound; the dispersant is a diol alkyl sulfonate compound; the stabilizer is a heterocyclic indole carboxylic acid compound; the accelerator is an aminopyrazine compound; and the carboxyaminopyridine compound is 5-carboxy-2,3-diaminopyridine. The diol alkyl sulfonate compound is diethylene glycol dimethyl sulfonate; the heterocyclic indole carboxylic acid compound is 7-azaindole-3-carboxylic acid; and the aminopyrazine compound is 5-amino-2-pyrazine carboxylic acid.

2. The chemical copper plating solution for improving the voids at the bottom of blind holes as described in claim 1, characterized in that, The reducing agent is formaldehyde.

3. The chemical copper plating solution for improving the voids at the bottom of blind holes as described in claim 1, characterized in that, The plating temperature of the chemical copper plating solution is 35-45℃, and the pH of the chemical copper plating solution is 11-12.

4. A copper plating method using a chemical copper plating solution as described in any one of claims 1 to 3 to improve the voids at the bottom of blind vias, characterized in that, include: Step 1: Perform alkaline swelling on the copper plating circuit board; Step 2: Remove adhesive with alkaline potassium permanganate; Step 3: Reduction and neutralization to remove manganese salts; Step 4: Perform alkaline low-foaming precision degreasing using an alkaline degreasing plating solution; Step 5: First-level silent immersion water wash, room temperature, 2 independent tank washes; Step 6: Perform acidic ionic palladium activation using an acidic ionic palladium activation solution; Step 7: Perform copper plating using the aforementioned chemical copper plating solution; Step 8: Multi-stage silent water wash.

5. The copper plating method for improving the voids at the bottom of blind holes using a chemical copper plating solution as described in claim 4, characterized in that... In step 4, the alkaline degreasing plating solution comprises the following components by mass concentration: 28 g / L anhydrous sodium carbonate, 15 g / L trisodium phosphate, 12 g / L flake sodium hydroxide, 4.0 g / L fatty alcohol polyoxyethylene ether, 1.2 g / L imidazo[1,2-a]pyridine-7-carboxylic acid, with the balance being pure water.

6. The copper plating method for improving the voids at the bottom of blind holes using a chemical copper plating solution as described in claim 4, characterized in that, In step 6, the acidic ionic palladium activation solution comprises the following components by mass concentration: 60 mL / L sulfuric acid, 0.35 g / L palladium chloride, 1.0 g / L fatty alcohol polyoxyethylene ether, 0.1 g / L 2-ethylhexanol EO / PO copolymer, 0.5 g / L aminoethylated acrylic polymer, with the remainder being pure water.

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