A nickel-free type electroless copper plating solution and a preparation method thereof

Abstract

The present application relates to the technical field of electroless copper plating, in particular to H05K3 / 18, more particularly to a nickel-free electroless copper plating solution and a preparation method thereof.The nickel-free electroless copper plating solution comprises a copper ion source, a stabilizer, a reducing agent, a complexing agent and an accelerator.The nickel-free electroless copper plating solution provided by the present application does not contain nickel element, is non-toxic and environmentally friendly, solves the problem of environmental pollution caused by nickel-containing copper waste liquid, and reduces the wastewater treatment cost.Meanwhile, the electroless copper plating can be continuously carried out in high stability, the appearance of the plating layer is bright, the performance of the plating layer is good, the peel strength reaches the industry standard, the back light level reaches more than 9 levels, and the copper deposition rate reaches the industry standard.

Description

Technical Field

[0001] This invention relates to the field of electroless copper plating technology, specifically to H05K3 / 18, and more specifically, to a nickel-free electroless copper plating solution and its preparation method. Background Technology

[0002] Electroless copper plating involves a catalytic chemical reduction reaction that continuously reduces copper ions to copper, forming a dense and continuous conductive copper layer on the substrate. However, current electroless copper plating solutions typically add a certain amount of nickel to increase the plating rate. Nickel is not only harmful to health but also environmentally unfriendly. Furthermore, omitting nickel from the plating solution significantly reduces the copper deposition rate and presents technical challenges for high-frequency, high-speed, and high-aspect-ratio copper deposition processes on substrates.

[0003] Chinese patent CN 107460461 A provides a chemical copper plating solution. However, its stabilizer is composed of thiouracil, bipyridine, and potassium tetracyanonitrile(II) hydrate, which still contains nickel, thus having a certain negative impact on environmental protection. Its copper plating rate, backlight level, and copper solution stability also need to be further improved. Moreover, if potassium tetracyanonitrile(II) hydrate is not added in this patent, the stability of the plating solution will be poor, making it impossible to achieve a good balance between the stability of the plating solution and the copper plating rate. Summary of the Invention

[0004] To address some problems existing in the prior art, the first aspect of the present invention provides a nickel-free electroless copper plating solution, the components of which include a copper ion source, a stabilizer, a reducing agent, a complexing agent, and an accelerator.

[0005] In one embodiment, the stabilizer is a nitrogen-containing five-membered ring and / or a nitrogen-containing six-membered ring having a bipyridine structure.

[0006] Preferably, the nitrogen-containing six-membered ring with a bipyridine structure is a viologen compound with the structure shown in (I).

[0007]

[0008] Among them, R1 and R2 are groups composed of at least one atomic group from C, O, N, and S.

[0009] Preferably, R1 and R2 are independently selected from C1-5 alkyl groups. Any one of them, of which R8, R9 and R 10 Oxygen- and / or nitrogen-containing groups that are independently alkyl-substituted or unsubstituted.

[0010] Preferably, R8, R9 and R 10 It can be categorized as either a carboxyl group or a nitro group.

[0011] The alkyl groups in C1-5 of this invention can be listed as methyl, ethyl, propyl, butyl, pentyl, isopropyl, etc.

[0012] Preferably, the nitrogen-containing five-membered ring is a hydantoin compound with the structure shown in (II).

[0013]

[0014] Among them, R3, R4, R5 and R6 are groups composed of at least one atomic group from C, H, N, S and O, and R7 is a group composed of at least one atomic group from S, N and O.

[0015] Preferably, R5 and R6 are independently any one of C1-5 alkyl, H, and C1-3 carboxyl groups.

[0016] Preferably, R3 is any one of H, C1-5 hydroxyl, C1-5 alkyl, and phenyl.

[0017] In one embodiment, the nitrogen-containing five-membered ring is selected from 5,5-dimethylhydantoin. 1,3-Dihydroxymethyl-5,5-dimethylhydantoin 1-N-Butylhydantoin 2-Thiohydantoin Phenylacetin-alanine Hydantoin-5-acetic acid One or more of them.

[0018] Preferably, the nitrogen-containing six-membered ring having a bipyridine structure is selected from dichloride-1,1,1,di(4-carboxy-benzylmethyl)-4,4'-bipyridine. Ethyl viologen dibromide 1,1,1-Di(3,4-dicarboxy-benzyl)-4,4-bipyridine dibromide

[0019]

[0020] 1,1'-Bis(2,4-dinitrophenyl)-4,4'-bipyridine dichloride One or more of them.

[0021] In one embodiment, the stabilizer is 1,1'-bis(2,4-dinitrophenyl)-4,4'-bipyridine dichloride and 2-thiohydantoin in a weight ratio of 1:(1-3), preferably 1:2.

[0022] In one embodiment, the stabilizer is 1,1'-bis(2,4-dinitrophenyl)-4,4'-bipyridine dichloride and phenylthiohydantoin-alanine in a weight ratio of (0.5-2.5):(1.5-3.5), such as 1:2, 0.5:2, 1.5:2, 2.5:2, 1.5:1.5, 1.5:2.5, 1.5:3.5, etc.

[0023] In one embodiment, the stabilizer is 1,1'-bis(2,4-dinitrophenyl)-4,4'-dichlorinated bipyridine, 2-thiohydantoin, and phenylthiohydantoin-alanine in a weight ratio of (1-1.5):(0.5-3):(1-3), such as 1:2:2 or 1.5:0.5:2.5.

[0024] In one embodiment, the stabilizer is 1,1'-bis(2,4-dinitrophenyl)-4,4'-bipyridine dichloride and 2-thiohydantoin in a weight ratio of 1:(1-3), preferably 1:2.

[0025] The stability and copper deposition rate of electroless copper plating solutions are key indicators for evaluating these solutions, affecting not only the plating effect but also the lifespan of the plating bath. The industry utilizes specialized stabilizers combined with nickel-containing phases to improve the stability and rate of electroless copper plating solutions, thereby enhancing plating performance. However, nickel poses certain health risks; skin contact with nickel can cause dermatitis, allergies, and long-term exposure may lead to cancer. Furthermore, nickel is environmentally damaging; the EU has already completed legislation to completely ban its use. The presence of nickel in the plating solution also significantly complicates the treatment of copper deposition wastewater, increasing wastewater treatment costs. Therefore, nickel-free electroless copper plating technology has attracted considerable attention and research. However, nickel-free electroless copper plating often suffers from problems such as low copper deposition rates and technical difficulties in high-frequency, high-speed, and high-aspect-ratio plate copper deposition processes.

[0026] In existing technologies, the copper deposition rate of nickel-free copper plating solutions is only about 0.3 μm / 15 min. However, this invention, by controlling the addition of stabilizers, including specific violane compounds and / or hydantoin compounds, combined with other components such as surfactants, not only achieves a copper decomposition time of over 550 min, but also a copper deposition rate of over 0.7 μm / 15 min. The possible reason is that the nitrogen-containing heterocycles in violane compounds and hydantoin compounds, as well as the double-electron layer structure of the activator surface modified with suitable groups, make it easier for reducing agents such as formaldehyde to be activated during the copper plating process. In contrast, the activation of formaldehyde and other reducing agents is hindered in the bulk system of the plating solution before copper plating.

[0027] In one embodiment, the concentration of the stabilizer in the nickel-free electroless copper plating solution is 1-50 ppm.

[0028] In one embodiment, the accelerator is present at a concentration of 1-100 ppm in a nickel-free electroless copper plating solution.

[0029] Furthermore, the electroless copper plating solution of this invention does not contain nickel, thus avoiding the gelation phenomenon caused by the participation of nickel.

[0030] The copper ion source described in this invention is not particularly limited, and those skilled in the art can make conventional choices, such as copper sulfate pentahydrate, copper chloride dihydrate, copper acetate, copper nitrate, copper hydroxide, basic copper carbonate, copper aminosulfonate, etc.

[0031] The complexing agent described in this invention is not particularly limited, and those skilled in the art can make conventional selections, such as potassium sodium tartrate, sodium tartrate, sodium salicylate, citrate, disodium ethylenediaminetetraacetate (EDTA·2Na), pentiacic acid (DTPA), hyponitroacetic acid (NTA) and its alkali metal salts, gluconic acid, gluconate, triethanolamine, modified ethylenediamine, etc.

[0032] The reducing agent described in this invention is not particularly limited, and those skilled in the art can make conventional choices. Examples include formaldehyde, formaldehyde derivatives such as paraformaldehyde, borohydrides, etc.; borohydrides such as sodium borohydride derivatives, etc.; boranes such as dimethylamine borane (DMAB), etc.; hypophosphite and its salts, such as sodium hypophosphite, etc.; hydroquinone, catechol, resorcinol, and gallic acid, etc.

[0033] The accelerators described in this invention are not particularly limited, and those skilled in the art can make conventional choices. Examples include potassium ferrocyanide, thiourea, thiourea pyrimidine, tetrahydroxypropyl ethylenediamine, triethanolamine, glucose, sorbitol, cellulose, sucrose, mannitol and gluconic acid lactone, D-malic acid, salicylic acid, hydroquinone, catechol, etc.

[0034] In one embodiment, the accelerator is thiourea, tetrahydroxypropylethylenediamine and potassium ferrocyanide in a weight ratio of 1:(2-4):(5-8), preferably 1:3:6.

[0035] The pH value described in this invention is not particularly limited, and those skilled in the art can make conventional choices, such as inorganic bases, organic bases, inorganic acids, organic acids, etc.

[0036] The inorganic bases mentioned in this invention can include sodium hydroxide, sodium carbonate, potassium hydroxide, etc.; the organic bases can include sodium methoxide, potassium ethoxide, potassium tert-butoxide, etc.; the inorganic acids can include sulfuric acid, hydrochloric acid, etc.; and the organic acids can include acetic acid, citric acid, benzoic acid, etc.

[0037] In one embodiment, the nickel-free electroless copper plating solution further includes polymers of linear alkylbenzene sulfonates and / or ethylene oxide hydrolysis products.

[0038] Preferably, the linear alkylbenzene sulfonate has more than 15 carbon atoms.

[0039] Preferably, the linear alkylbenzene sulfonate is sodium dodecylbenzene sulfonate.

[0040] Preferably, the weight-average molecular weight of the polymer of the ethylene oxide hydrolysis product is greater than or equal to 1000.

[0041] Preferably, the polymer of the ethylene oxide hydrolysis product is polyethylene glycol.

[0042] Preferably, the nickel-free electroless copper plating solution has a pH range of 11-13 at 30-35°C, and more preferably a pH range of 12-13.

[0043] The second aspect of the present invention provides a method for preparing the nickel-free electroless copper plating solution, which is obtained by mixing the components.

[0044] The third aspect of this invention provides a copper plating process using the aforementioned nickel-free electroless copper plating solution, including the following process flow: brushing and cleaning of the plated parts, expansion, desmearing, pre-neutralization, neutralization, hole shaping, micro-etching, pre-immersion, activation, reduction, and copper plating.

[0045] Compared with the prior art, the present invention has the following advantages:

[0046] The nickel-free electroless copper plating solution provided by this invention contains no nickel, is non-toxic, and environmentally friendly, solving the problem of environmental pollution caused by nickel-containing copper wastewater and reducing wastewater treatment costs. It also allows for highly stable and continuous electroless copper plating, producing a bright, powdery coating with good performance, peel strength meeting industry standards, a backlight rating of 9 or higher, and copper deposition rates that all meet industry standards. Attached Figure Description

[0047] Figure 1-14 The images shown are backlit images of the nickel-free electroless copper plating solution (substrate is S1000-2M) described in Examples 1-14.

[0048] Figure 15-28 The image shows the backlight of the chemical copper plating solution (substrate is KB-6160 board) described in Examples 1-14. Detailed Implementation

[0049] The present invention will be described below through specific embodiments, but is not limited to the specific embodiments given below.

[0050] Examples 1-14

[0051] Examples 1-14 of the present invention provide a nickel-free chemical copper plating solution, and the specific composition of copper plating baths 1-14 is shown in Table 1.

[0052] Table 1

[0053]

[0054]

[0055]

[0056]

[0057] The preparation methods of nickel-free electroless copper plating solutions in Examples 1-14 are as follows:

[0058] In a beaker, add the corresponding amounts of potassium sodium tartrate and NaOH sequentially, and then add 500 mL of distilled water to dissolve, obtaining solution A. In another beaker, add the corresponding amounts of copper sulfate pentahydrate sequentially, add 200 mL of distilled water to dissolve and mix, and then add 11 mL of 37% formaldehyde to obtain solution B. In yet another beaker, add the corresponding amounts of thiourea, tetrahydroxypropyl ethylenediamine, potassium ferrocyanide, PEG-1000, sodium dodecylbenzenesulfonate, 1,1'-bis(2,4-dinitrophenyl)-4,4'-dichlorinated bipyridine, 2-thiohydantoin, and phenylthiohydantoin-alanine sequentially, and add 200 mL of distilled water to dissolve, obtaining solution C. Mix solutions A, B, and C sequentially, and then dilute to 1 L with distilled water. Adjust the copper plating solution to pH 13 using a pH meter.

[0059] In the preparation of nickel-free electroless copper plating solution, the components in Table 1 should be added strictly according to the requirements. If the content of a certain substance is 0, then the substance does not need to be added.

[0060] Copper plating rate performance evaluation:

[0061] Copper plating was performed using the electroless copper plating solutions from Examples 1-14. After the electroless copper plating process was completed, the copper deposition rate of the resin board was calculated using the following formula:

[0062]

[0063] V represents the copper plating thickness in μm; M1 and M2 represent the masses before and after copper plating, respectively, in g; ρ represents the density of copper, 8.9 g / cm³. 3 S represents the surface area of ​​the board, in cm². 2 .

[0064] The electroless copper plating process is as follows:

[0065] (1) Treat the workpiece to be plated at 80°C with 240L of a bulking agent (SCC-A01H, Guangdong Shuocheng Technology Co., Ltd.) for 6 minutes, and then rinse with tap water at room temperature for 1 minute.

[0066] (2) Place the part to be plated in 80℃, 550L of adhesive remover (SCC-A02, Guangdong Shuocheng Technology Co., Ltd.) for 12 minutes, and then rinse it in tap water at room temperature for 1 minute.

[0067] (3) Place the workpiece to be plated in a pre-neutralizing agent (sulfuric acid / hydrogen peroxide system, Guangdong Shuocheng Technology Co., Ltd.) at 30°C for 1 minute, and then rinse it in tap water at room temperature for 1 minute.

[0068] (4) Place the workpiece to be plated in a 50℃ neutralizing agent (SCC-A03H, Guangdong Shuocheng Technology Co., Ltd.) for 1 min, and then rinse it in tap water at room temperature for 1 min;

[0069] (5) Weigh the part to be plated at room temperature and record it as m1. Then place the part to be plated in a 50℃ conditioning agent (SCC-A04H, Guangdong Shuocheng Technology Co., Ltd.) for 1 min and then rinse it in tap water at room temperature for 1 min.

[0070] (6) Place the workpiece to be plated in an activation solution (SCC-A06H, Guangdong Shuocheng Technology Co., Ltd.) at 50℃ for 45 seconds, and then soak it in tap water at room temperature for 1 minute.

[0071] (7) Place the part to be plated in 180L of reducing agent (SCC-A07H, Guangdong Shuocheng Technology Co., Ltd.) at 35℃ for 35s;

[0072] (8) Place the parts to be plated in a copper plating solution at a temperature of 33°C for chemical copper plating for 30 minutes. Then rinse the copper plating board with running tap water for 4 minutes. Then dry each copper plating board with a blower. Weigh the substrates after copper plating at room temperature and record the weight as m2.

[0073] The test results of Examples 1-14 are shown in Table 2: (Using the S1000-2M and KB6160 substrates as copper plating rate substrates)

[0074]

[0075]

[0076] As shown in Table 2, the test results indicate that adding the stabilizer described in this invention can significantly improve the copper plating rate. Backlight performance evaluation:

[0077] Multiple 1mm thick side sections were selected from the hole walls of each board. Each substrate section was observed under a metallographic optical microscope at 50X magnification. The quality of the deposited copper film was measured under a microscope using illumination, and the via wall coating thickness was determined using a European backlight grading table. Backlight values ​​show the effect of the reducing composition of this invention on backlighting.

[0078] The backlight level classification standards are as follows: Level 1: Transmittance, transmittance area greater than 90%; Level 2: Transmittance, 80% < transmittance area ≤ 90%; Level 3: Transmittance, 70% < transmittance area ≤ 80%; Level 4: Transmittance, 60% < transmittance area ≤ 70%; Level 5: Transmittance, 50% < transmittance area ≤ 60%; Level 6: Dark light, 40% < visible light area ≤ 50%, with clear fibrous texture; Level 7: Dark light, 30% < visible light area ≤ 40%. Level 8: Dark light, 20% < visible light area ≤ 30%, some dark light initially appears fibrous; Level 8.5: Dark light, 10% < visible light area ≤ 20%, first to see <10 scattered dark light spots; Level 9: Dark light, 5% < visible light area ≤ 10%, first to see <5 scattered dark light spots; Level 9.5: Dark light, 1% < visible light area ≤ 5%, first to see <2 scattered dark light spots; Level 10: Completely black.

[0079] The test results of Examples 1-14 are shown in Table 3:

[0080] Table 3

[0081]

[0082]

[0083] in, Figure 1-14 The images shown are backlit images of the nickel-free electroless copper plating solution (substrate is S1000-2M) described in Examples 1-14. Figure 15-28 The image shows the backlight of the chemical copper plating solution (substrate is KB-6160 board) described in Examples 1-14.

[0084] As can be seen from the test results in Table 3, adding the stabilizer of this invention can achieve a backlight level of 9 or higher.

[0085] Stability assessment of chemical copper plating solution

[0086] The electroless copper plating solutions obtained in Examples 1-14 were placed in beakers respectively. 20 mL of 0.18 g / L palladium chloride solution was added to every 100 mL of electroless copper plating solution to carry out the catalytic decomposition reaction, and the start time of decomposition was recorded. The test results are shown in Table 4.

[0087] Table 4

[0088]

[0089] As can be seen from the test results in Table 4, the addition of the stabilizer in this invention significantly improves the stability of the copper liquid.

[0090] Peel strength assessment

[0091] After completing the pre-process of chemical copper plating according to the copper plating method in the copper plating rate test, the S1000-2M board surface is subjected to the following steps: (1) Wash with clean water;

[0092] (2) Degreasing: Remove surface grease;

[0093] (3) Use a Harlin tank to electroplate copper to a thickness of 25um, and then blow dry and clean it.

[0094] (4) Bake in a 120℃ oven for 2 hours;

[0095] (5) After baking, use a scriber to cut a 2cm*10cm strip of copper foil on the board and tear a small opening; (6) Place it in a Shimadzu Auto Graph AGS-X series testing machine and test it at a speed of 20mm / min. The test results are shown in Table 5.

[0096] Table 5

[0097]

[0098] As can be seen from the test results in Table 5, the peel strength reaches the industry standard when the stabilizer of this invention is added.

Claims

1. A nickel-free electroless copper plating solution, characterized in that, Its components include a copper ion source, stabilizer, reducing agent, complexing agent, and accelerator, wherein the stabilizer is a nitrogen-containing five-membered ring and a nitrogen-containing six-membered ring with a bipyridine structure; The stabilizer is 1,1'-bis(2,4-dinitrophenyl)-4,4'-dichlorinated bipyridine and phenylthiohydantoin-alanine in a weight ratio of (0.5-2.5):(1.5-3.5). Alternatively, the stabilizer may be 1,1'-bis(2,4-dinitrophenyl)-4,4'-dichloride bipyridine, 2-thiohydantoin and phenylthiohydantoin-alanine, in a weight ratio of (1-1.5):(0.5-3):(1-3).

2. The nickel-free electroless copper plating solution according to claim 1, characterized in that, The nickel-free electroless copper plating solution also includes polymers of linear alkylbenzene sulfonates and / or ethylene oxide hydrolysis products.

3. The nickel-free electroless copper plating solution according to claim 2, characterized in that, The nickel-free electroless copper plating solution has a pH range of 11-13 at 30-35℃.

4. The nickel-free electroless copper plating solution according to any one of claims 1-3, characterized in that, The concentration of the stabilizer in the nickel-free electroless copper plating solution is 1-30 ppm.

5. A method for preparing a nickel-free electroless copper plating solution according to any one of claims 1-4, characterized in that, include: Simply mix the ingredients together to obtain the final product.

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