An additive for improving the adhesion of a chemical gold plating layer and a preparation method thereof

Abstract

The application discloses an additive for improving the bonding force of a chemical gold plating layer and a preparation method thereof, relates to the technical field of chemical gold plating, and comprises the following steps: preparing a pH buffer type-viscosity controlled substrate activation solution; adding an epoxy-based pre-anchoring-disulfide bond functionalized copolymer into an N-methyl-2-pyrrolidone solvent and stirring until complete dissolution; then, adding a pH buffer stabilizer and a thixotropic viscosity regulator in sequence and continuing to stir; and finally, carrying out ultrasonic dispersion and defoaming on the mixed solution, and then carrying out static defoaming to obtain the additive. The application realizes high bonding force without damaging sensitive substrates, and solves the technical problems of high-temperature failure, poor storage stability and low batch consistency through double covalent anchoring, pH locking and viscosity controlled design.

Description

Technical Field

[0001] This invention relates to the field of chemical gold plating technology, specifically to an additive for improving the adhesion of chemical gold plating layers and its preparation method. Background Technology

[0002] Chemical gold plating plays a crucial role in modern electronics manufacturing, widely used to deposit functional gold layers on various substrates. However, when applied to specific sensitive substrates, such as polyimide films, ceramic materials, or semiconductor wafers, the adhesion between the plating layer and the substrate becomes a core indicator determining product reliability. In current technological understanding, to achieve high adhesion, the industry generally relies on intensive pretreatment of the substrate. These pretreatment methods typically include chemical roughening using strong acids or potassium permanganate solutions, or mechanical abrasion. The fundamental purpose is to create microscopic pits or rough structures on the substrate surface through physical or chemical means, so that the subsequently deposited metal layer can be mechanically locked or anchored to the substrate surface, thereby achieving physical adhesion.

[0003] However, the traditional process relying on mechanical locking presents a sharp technical contradiction. First, for sensitive substrates such as polyimide films, ceramics, or semiconductors, intense chemical etching or mechanical polishing is disastrous, irreversibly damaging critical surface smoothness, electrical insulation properties, or mechanical strength. This puts the industry in a dilemma: either sacrifice substrate integrity to ensure adhesion, or accept extremely poor coating adhesion to protect the substrate—the latter becoming a core pain point for the industry. Second, some improved activation solutions relying on physical adsorption, which emerged to address the aforementioned damage issues, have introduced new defects. The activated layer of these solutions has weak adhesion to the substrate and is prone to thermal desorption under thermal shock from high-temperature plating baths or subsequent high-temperature reflow soldering, leading to gold layer peeling. Furthermore, during long-term storage, trace impurities in the activation solution can cause premature decomposition and failure of functional components. Simultaneously, in large-scale production, these solutions are extremely sensitive to process fluctuations such as dip-coating and pull-up speeds, making it difficult to form a uniformly thick functional layer on automated production lines, resulting in low batch-to-batch product performance consistency. Summary of the Invention

[0004] The purpose of this invention is to provide an additive for improving the adhesion of electroless gold plating layers and its preparation method, thereby solving the problems existing in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides a method for preparing an additive to improve the adhesion of a chemical gold plating layer, comprising the following steps:

[0006] Step A: Preparation of pH-buffered, viscosity-controlled substrate activation solution:

[0007] The epoxy-anchored disulfide functionalized copolymer was added to N-methyl-2-pyrrolidone solvent and stirred until completely dissolved.

[0008] Next, add the pH buffer stabilizer and the thixotropic viscosity modifier in sequence, and continue stirring;

[0009] The mixed solution was ultrasonically dispersed and degassed, followed by static degassed to obtain the additive;

[0010] The preparation of epoxy-anchored-disulfide functionalized copolymers includes the following steps:

[0011] Step B: Preparation of copolymer:

[0012] Styrene, N,N′-bis(acryloyl)cysteine, glycidyl methacrylate, RAFT reagent and initiator were dissolved in dioxane solvent and stirred.

[0013] Nitrogen gas is introduced for deoxygenation.

[0014] The polymerization reaction is carried out by gradient heating rate control: first, the temperature is raised to a first temperature and held for a first reflux time, then the temperature is raised to a second temperature and held for a second reaction time;

[0015] The reaction solution was added dropwise to cold methanol to precipitate, filtered, and then vacuum dried to obtain an epoxy-pre-anchored disulfide functionalized copolymer.

[0016] Preferably, in step A, the mass ratio of the epoxy pre-anchored disulfide functionalized copolymer, N-methyl-2-pyrrolidone solvent, pH buffer stabilizer and thixotropic viscosity modifier is (0.5-2.0):(800-1200):(0.5-2.0):(3-8).

[0017] Preferably, the pH buffer stabilizer is p-toluenesulfonic acid monohydrate; the thixotropic viscosity modifier is fumed silica; the RAFT reagent is S-1-Dodecyl-S-(α,α-dimethyl-α-aceticacid)trithiocarbonate; and the initiator is AIBN.

[0018] Preferably, in step A, the stirring speed until complete dissolution is 400-600 rpm for 1-3 hours; the ultrasonic dispersion power is 80-120W, the frequency is 30-50kHz, and the time is 10-20 minutes; the standing degassing time is 0.5-2 hours.

[0019] Preferably, in step B, the mass ratio of styrene, N,N′-bis(acryloyl)cysteine, glycidyl methacrylate, RAFT reagent, initiator and dioxane solvent is (8-12):(3-7):(2-4):(0.1-0.3):(0.03-0.07):(80-120).

[0020] Preferably, in step B, the deoxygenation treatment time is 20-40 minutes; the first temperature is 60-70°C, and the first reflux time is 10-14 hours; the second temperature is 75-85°C, and the second reaction time is 1-3 hours; the vacuum drying temperature is 35-45°C, and the time is 20-28 hours.

[0021] The present invention also provides an additive for improving the adhesion of electroless gold plating layers, which is prepared by the above-described method for preparing an additive for improving the adhesion of electroless gold plating layers.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] By employing a gentle substrate pretreatment process, the strong roughening steps such as chemical etching or mechanical polishing are completely skipped, ensuring that the flatness, electrical insulation, and mechanical strength of sensitive substrates such as polyimide and ceramics are not damaged in any way. By constructing an interface in-situ chemical rivet mechanism, the newly formed chemical bonds replace the traditional mechanical locking, achieving an ultra-high coating adhesion that far exceeds that of traditional processes without damaging the substrate.

[0024] The additive system introduces a dual covalent anchoring design, which significantly improves the stability of the coating under extreme high-temperature environments. By introducing pre-anchoring groups such as epoxy groups on the functional copolymer backbone and combining them with a specific thermosetting pre-anchoring process, the polymer backbone forms a strong first covalent bond with the substrate surface before gold plating, replacing the original physical adsorption. This ensures that the functional layer will not desorb under the thermal shock of high-temperature chemical gold plating solution or subsequent high-temperature reflow soldering, thus guaranteeing the adhesion of the gold layer under high-temperature conditions.

[0025] By optimizing the composition of the additive solution, the problem of long-term storage failure of the solution is solved. By introducing a specific pH buffer stabilizer, the solution environment is forcibly locked within a specific acidic range. Using chemical principles, the core functional groups are kept in a storage locked state, making them highly inert to trace alkaline impurities or reducing agents that may be encountered during storage or transportation. This greatly extends the effective shelf life of the product and ensures that the additive maintains high activity after long-term storage.

[0026] By introducing a thixotropic viscosity modifier, the process consistency of the additive in large-scale production is significantly improved. It imparts shear-thinning rheological properties to the activation solution, enabling it to effectively buffer the impact of process parameter changes such as pull-up speed fluctuations during automated dip-coating and pull-up processes. This ensures that the functional layer can still form a uniform thickness under different batches or different process conditions, thereby guaranteeing the high uniformity of the final coating adhesion and process tolerance, meeting the stringent consistency requirements of precision electronic manufacturing. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] Example 1

[0029] This embodiment provides a method for preparing an additive to improve the adhesion of chemical gold plating layers;

[0030] Preparation of epoxy-anchored disulfide functionalized copolymers: This step employs RAFT polymerization. 10.0 g styrene, 5.0 g N,N′-bis(acryloyl)cysteine, 3.0 g glycidyl methacrylate, 0.2 g S-1-Dodecyl-S-(α,α-dimethyl-α-aceticacid)trithiocarbonate (RAFT reagent), and 0.05 g AIBN (initiator) are dissolved in 100 mL of dioxane solvent. Under stirring at 300 rpm, nitrogen gas is introduced for deoxygenation for 30 minutes. Subsequently, the polymerization reaction is carried out using a gradient temperature control: first, the temperature is raised to 65°C (first temperature) and... The mixture was held for 12 hours (first reflux time), then heated to 80°C (second temperature) and held for 2 hours (second reaction time). The reaction solution was dropwise added to 1000 mL of cold methanol to precipitate the product, filtered, and vacuum dried at 40°C for 24 hours to obtain an epoxy-anchored disulfide functionalized copolymer with a yield of 92.5%. GPC analysis showed that the number-average molecular weight (Mn) of the copolymer was 18,500 g / mol and the polydispersity index (PDI) was 1.25. FTIR spectroscopy (KBr pellet) analysis showed a characteristic absorption peak of epoxy groups at approximately 910 cm⁻¹ and a characteristic absorption peak of SS bonds at approximately 540 cm⁻¹, confirming the successful copolymerization of the functional monomers.

[0031] A pH-buffered, viscosity-controlled substrate activation solution was prepared. 1.0 g of the epoxy-pre-anchored disulfide functionalized copolymer obtained in the above steps was added to 1000 mL of N-methyl-2-pyrrolidone solvent and stirred at 500 rpm for 2 hours until completely dissolved. Then, 1.0 g of p-toluenesulfonic acid monohydrate (pH buffer stabilizer) and 5.0 g of fumed silica (thixotropic viscosity modifier) ​​were added sequentially, and stirring continued. The mixture was then ultrasonically dispersed and degassed at a power of 100 W, a frequency of 40 kHz, and a time of 15 minutes. Afterward, the mixture was allowed to stand for 1 hour to remove bubbles, yielding an additive that improves the adhesion of the electroless gold plating layer.

[0032] The additive prepared in Example 1, through the introduction of pH buffer stabilizer and thixotropic viscosity modifier, enables the additive solution (substrate activation solution) to maintain high activity after long-term storage. At the same time, during the dip-coating and pulling process in an automated production line, even if the pulling speed fluctuates to some extent, it can form a functional layer with uniform thickness, making it suitable for precision electronic manufacturing scenarios that require batch consistency.

[0033] Example 2

[0034] This embodiment provides a method for preparing an additive to improve the adhesion of a chemical gold plating layer, wherein the parameter values ​​are all near the lower limit of the specified range;

[0035] Preparation of copolymer: 8.0 g styrene, 3.0 g N,N′-bis(acryloyl)cysteine, 2.0 g glycidyl methacrylate, 0.1 g RAFT reagent and 0.03 g AIBN were dissolved in 80 mL dioxane solvent; nitrogen gas was purged for 20 minutes to remove oxygen; the first polymerization temperature was 60°C and the first reflux time was 10 hours; the second temperature was 75°C and the second reaction time was 1 hour; vacuum drying was carried out at 35°C for 20 hours.

[0036] Preparation of the activation solution: The mass ratio of epoxy pre-anchored-disulfide functionalized copolymer, N-methyl-2-pyrrolidone solvent, pH buffer stabilizer and thixotropic viscosity modifier was 0.5:800:0.5:3; the stirring speed was 400 rpm and the time was 1 hour; the ultrasonic dispersion power was 80 W, the frequency was 30 kHz and the time was 10 minutes; the standing degassing time was 0.5 hours.

[0037] The additive prepared in Example 2 uses a low concentration of functional components (polymer, GMA, disulfide monomer) and additives, which keeps the cost relatively under control. It can still achieve non-destructive activation of sensitive substrates, and its coating adhesion is better than that of traditional etching processes.

[0038] Example 3

[0039] This embodiment provides a method for preparing an additive to improve the adhesion of a chemical gold plating layer, wherein the parameter values ​​are all near the upper limit of the defined range;

[0040] Preparation of copolymer: 12.0 g styrene, 7.0 g N,N′-bis(acryloyl)cysteine, 4.0 g glycidyl methacrylate, 0.3 g RAFT reagent and 0.07 g AIBN were dissolved in 120 mL dioxane solvent; nitrogen gas was purged for 40 minutes to remove oxygen; the first polymerization temperature was 70°C and the first reflux time was 14 hours; the second temperature was 85°C and the second reaction time was 3 hours; vacuum drying was carried out at 45°C for 28 hours.

[0041] Preparation of the activation solution: The mass ratio of epoxy pre-anchored-disulfide functionalized copolymer, N-methyl-2-pyrrolidone solvent, pH buffer stabilizer and thixotropic viscosity modifier was 2.0:1200:2.0:8; the stirring speed was 600 rpm and the time was 3 hours; the ultrasonic dispersion power was 120 W, the frequency was 50 kHz and the time was 20 minutes; the standing time for degassing was 2 hours.

[0042] The additive prepared in Example 3 uses a high concentration of functional components. The high content of GMA (epoxy group) combined with the subsequent thermosetting pre-anchoring step, and the high content of N,N′-bis(acryloyl)cysteine ​​(disulfide bond) combined with the in-situ activation of the plating solution, increase the density of the double covalent bonds formed at the substrate interface. This additive is particularly suitable for operation in high-temperature (e.g., 85-95°C) plating solutions, or for application in scenarios such as flexible circuit boards (FPC) that require high-temperature reflow soldering (>200°C), exhibiting good high-temperature impact resistance.

[0043] Example 4

[0044] This embodiment provides a method for preparing an additive to improve the adhesion of chemical gold plating layers, characterized by optimizing the ratio of copolymer monomers;

[0045] Preparation of copolymer: 10.0 g styrene, 7.0 g N,N′-bis(acryloyl)cysteine ​​(content increased), 3.0 g glycidyl methacrylate, 0.2 g RAFT reagent and 0.05 g AIBN were dissolved in 100 mL dioxane solvent; polymerization parameters were the same as in Example 1;

[0046] Preparation of activation solution: The solution ratio and preparation parameters are the same as in Example 1;

[0047] The additive prepared in Example 4 has an increased content of N,N′-bis(acryloyl)cysteine ​​in its copolymer, which increases the -SS- density of the polymer side chain. When subsequently immersed in an alkaline plating bath containing DMAB reducing agent, it can generate higher density thiol (-SH) active anchors through in-situ cleavage, thereby forming more Au-S covalent bonds with gold atoms, which helps to achieve higher final bonding force.

[0048] Example 5

[0049] This embodiment provides a method for preparing an additive to improve the adhesion of chemical gold plating layers, characterized by optimizing the ratio of additive components;

[0050] Preparation of copolymers: The monomer ratios and preparation parameters of the copolymers are the same as in Example 1;

[0051] Preparation of the activation solution: The mass ratio of epoxy pre-anchored-disulfide functionalized copolymer, N-methyl-2-pyrrolidone solvent, pH buffer stabilizer and thixotropic viscosity modifier is 1.0:1000:1.5:7.0; the preparation parameters are the same as in Example 1;

[0052] The additive prepared in Example 5 increased the amounts of pH buffer stabilizer (p-toluenesulfonic acid) and thixotropic viscosity modifier (fumed silica). The added acid buffer further enhanced the acidic environment of the solution (e.g., pH 4.0-5.0), improved the inertness of disulfide bonds to trace reducing agents during long-term storage or transportation, and enhanced storage stability. The added thixotropic agent made the shear thinning characteristics of the solution more obvious, which could better buffer the impact of the pulling speed fluctuation on the liquid film thickness in the automated production line, and ensure the high uniformity of the bonding force in large-scale production.

[0053] Comparative Example 1

[0054] The existing chemical roughening method is used; the sensitive substrate is immersed in a high-temperature (e.g., 80°C) strong alkaline solution for chemical etching to create microscopic mechanical interlocks on the substrate surface; then conventional chemical gold plating is performed.

[0055] Comparative Example 2

[0056] The original solution was used, which was an unoptimized substrate activation solution.

[0057] First, the copolymer was prepared; the formulation and steps were the same as in Example 1, but 3.0 g of glycidyl methacrylate was not added.

[0058] Next, an activation solution was prepared; the formulation and steps were the same as in Example 1, but 1.0 g of p-toluenesulfonic acid monohydrate (pH buffer stabilizer) and 5.0 g of fumed silica (thixotropic viscosity modifier) ​​were not added.

[0059] Application process: After coating the substrate with the above solution, skip the "thermal curing pre-anchoring" step and directly immerse it in the chemical gold plating solution.

[0060] Effect verification

[0061] To verify the technical effects of the embodiments and comparative examples of the present invention, the following tests were performed on the same substrate (polyimide PI film):

[0062] Substrate surface roughness (Ra): The surface roughness of the substrate after activation treatment and before gold plating was tested using atomic force microscopy to assess the substrate damage (B).

[0063] Standard adhesion: The peel strength (N / cm) of the gold layer deposited in a standard electroless gold plating solution at 70°C was tested using the IPC-TM-6502.4.8 standard.

[0064] High-temperature adhesion: A gold layer was deposited in a 90°C high-temperature electroless gold plating solution, and the peel strength was tested to simulate a high-temperature operating scenario;

[0065] Storage stability: After the substrate activation solution (additive) was sealed and stored at room temperature (25°C) for 30 days, samples were prepared according to standard procedures and the binding force was tested to evaluate the pH buffering and locking effect.

[0066] Batch uniformity: A standard pull-up speed was set on an automated dip-coating machine, and a process fluctuation of ±5% was introduced to prepare 20 samples. The adhesion was tested and the coefficient of variation (CV value) was calculated to evaluate the viscosity control effect.

[0067] Table 1: Performance Comparison Table of Examples and Comparative Examples

[0068] Test Project Comparative Example 1 (Traditional Etching) Comparative Example 2 (Original Scheme) Example 1 (Invention) Example 3 (High Temperature Optimization) Example 5 (Stability Optimization) Substrate surface roughness (Ra, nm) 3.5 0.4 0.4 0.4 0.4 Standard adhesion (70°C plating solution, N / cm) 0.6 4.2 4.2 4.3 4.2 High-temperature adhesion (90°C plating solution, N / cm) not available 0.2 4.0 4.1 4.0 Storage stability (N / cm after 30 days of storage) N / A 1.5 4.1 4.1 4.2 Batch uniformity (CV value, %) 25.0 12.0 2.5 2.4 2.2

[0069] As can be seen from the data in Table 1:

[0070] Comparative Example 1 was etched with strong alkali, which severely damaged the substrate surface (Ra 3.5 nm) and the adhesion obtained by mechanical locking was low (0.6 N / cm).

[0071] Although Comparative Example 2 achieved substrate-free bonding (Ra 0.4 nm) and high adhesion (4.2 N / cm) under standard conditions, it revealed three fatal flaws: 1) In the 90°C high-temperature plating bath, the polymer skeleton underwent physical desorption, resulting in adhesion failure (0.2 N / cm); 2) After 30 days of solution storage, the activity decreased significantly due to premature decomposition or cleavage of functional groups (disulfide bonds), and the adhesion dropped to 1.5 N / cm; 3) Lack of viscosity control resulted in poor process tolerance, with a batch uniformity CV value as high as 12.0%.

[0072] Embodiments 1, 3, and 5 of the present invention all inherit the advantages of non-destructive substrate (Ra0.4nm) and standard high adhesion (approximately 4.2N / cm);

[0073] Meanwhile, by introducing GMA monomers (epoxy groups) and a corresponding thermosetting pre-anchoring step (first covalent anchoring), the embodiments of the present invention successfully solved the high-temperature failure problem and maintained high adhesion (4.0-4.1 N / cm) in a 90°C plating solution.

[0074] By introducing a pH buffer stabilizer (p-toluenesulfonic acid monohydrate), the solution was locked in an acidic storage state, which successfully solved the storage stability problem. After 30 days of storage, the binding force remained at 4.1-4.2 N / cm with almost no decay.

[0075] By introducing a thixotropic viscosity modifier (fumed silica), the solution is given shear-thinning properties, which significantly improves process tolerance and reduces batch uniformity CV value to below 2.5%.

[0076] In summary, the additive for improving the adhesion of electroless gold plating layers and its preparation method of the present invention, through the synergistic design of epoxy pre-anchored-disulfide functionalized copolymer (achieving dual covalent anchoring) and pH buffered-viscosity controlled substrate activation solution, successfully solves the technical problems of poor high-temperature adhesion, short storage stability and low batch consistency in the prior art without damaging the sensitive substrate.

[0077] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing an additive to improve the adhesion of a chemically plated gold layer, characterized in that, Includes the following steps: Step A: Preparation of pH-buffered, viscosity-controlled substrate activation solution: The epoxy-anchored disulfide functionalized copolymer was added to N-methyl-2-pyrrolidone solvent and stirred until completely dissolved. Next, add the pH buffer stabilizer and the thixotropic viscosity modifier in sequence, and continue stirring; The mixed solution was ultrasonically dispersed and degassed, followed by static degassed to obtain the additive; The preparation of epoxy-anchored-disulfide functionalized copolymers includes the following steps: Step B: Preparation of copolymers: Styrene, N,N′-bis(acryloyl)cysteine, glycidyl methacrylate, RAFT reagent and initiator were dissolved in dioxane solvent and stirred. Nitrogen gas is introduced for deoxygenation. The polymerization reaction is carried out by gradient heating rate control: first, the temperature is raised to a first temperature and held for a first reflux time, then the temperature is raised to a second temperature and held for a second reaction time; The reaction solution was added dropwise to cold methanol to precipitate, filtered, and then vacuum dried to obtain an epoxy-pre-anchored disulfide functionalized copolymer. The pH buffer stabilizer is p-toluenesulfonic acid monohydrate; the thixotropic viscosity modifier is fumed silica; the RAFT reagent is S-1-Dodecyl-S-(α,α-dimethyl-α-aceticacid)trithiocarbonate; and the initiator is AIBN.

2. The method for preparing an additive to improve the adhesion of a chemical gold plating layer according to claim 1, characterized in that, In step A, the mass ratio of epoxy pre-anchored-disulfide functionalized copolymer, N-methyl-2-pyrrolidone solvent, pH buffer stabilizer and thixotropic viscosity modifier is (0.5-2.0):(800-1200):(0.5-2.0):(3-8).

3. The method for preparing an additive to improve the adhesion of a chemical gold plating layer according to claim 1, characterized in that, In step A, the stirring speed is 400-600 rpm and the time is 1-3 hours until completely dissolved; the ultrasonic dispersion power is 80-120W and the frequency is 30-50kHz for 10-20 minutes; the standing degassing time is 0.5-2 hours.

4. The method for preparing an additive to improve the adhesion of a chemical gold plating layer according to claim 1, characterized in that, In step B, the mass ratio of styrene, N,N′-bis(acryloyl)cysteine, glycidyl methacrylate, RAFT reagent, initiator and dioxane solvent is (8-12):(3-7):(2-4):(0.1-0.3):(0.03-0.07):(80-120).

5. The method for preparing an additive to improve the adhesion of a chemical gold plating layer according to claim 1, characterized in that, In step B, the deoxygenation treatment time is 20-40 minutes; the first temperature is 60-70°C, and the first reflux time is 10-14 hours; the second temperature is 75-85°C, and the second reaction time is 1-3 hours; the vacuum drying temperature is 35-45°C, and the time is 20-28 hours.

6. An additive for improving the adhesion of electroless gold plating layers, characterized in that, It is prepared by the method for preparing an additive to improve the adhesion of chemical gold plating as described in any one of claims 1-5.