Method for inhibiting the penetration and leakage of electroless nickel plating on ultra-fine circuit of flexible substrate of integrated circuit package and application

Abstract

The present application relates to the advanced material technology field of integrated circuit packaging COF technology, and in particular to a method for inhibiting the chemical nickel plating and plating leakage of ultra-fine lines of a flexible substrate of an integrated circuit package and application. The method, through the systematic synergistic effect of pre-activation pre-dipping treatment, activation treatment and post-dipping treatment, can promote the uniformity of line activation, can control the deposition rate of nickel plating around the line, can improve the plating and plating leakage phenomenon caused by the uneven palladium adsorption amount on both sides of the line, can reduce the nickel plating deposition between fine lines, and can avoid the nickel bridging problem of fine lines caused by the excessive activity of palladium or the palladium residue between fine lines. The method has the characteristics of simple process, simple operation, low production cost and being suitable for large-scale production, and can be well applied to the chemical nickel plating process of the ultra-fine lines of the flexible substrate containing line width and line spacing below 12 microns and line width greater than 50 microns.

Description

Technical Field

[0001] This invention relates to the field of advanced materials technology for COF (Coefficient of Form) packaging of integrated circuits, and particularly to electroless nickel plating technology for ultra-fine lines (line width and spacing of 12 μm) on flexible substrates. Specifically, it relates to a method and application for suppressing nickel plating penetration and leakage in electroless nickel plating of ultra-fine lines on flexible substrates for integrated circuit packaging. Background Technology

[0002] With the widespread adoption of mobile electronic devices and large-screen displays, the market has placed higher demands on low-cost, high-density, and mass-production electronic manufacturing technologies. To adapt to this trend, the design philosophy of electronic products is moving towards thinner and smaller designs. For example, liquid crystal displays (LCDs), LCD TVs, plasma TVs, and 3C products such as mobile phones, digital cameras, and digital camcorders are all pursuing more compact forms and lighter weights. To meet these demands, packaging technology must evolve towards high density, miniaturization, and flexibility. COF technology (Chip on Flex or Chip on Film) emerged in response to these market demands. It achieves higher assembly density, reduces product weight and size by directly packaging integrated circuits (ICs) onto flexible printed circuit boards, while providing a flexible and bendable installation method. However, as the display density of displays increases, the requirements for driver chip I / O also increase accordingly. The pitch between lead pads is already below 30μm, and the interconnect spacing has reached 15μm and continues to decrease, which places higher precision demands on the fine circuit fabrication of flexible substrates.

[0003] Chemical nickel-gold (ENIG) plating is a commonly used surface treatment process for circuit boards, primarily used to prevent the copper traces from oxidizing or corroding. However, in the ENIG process for fine circuitry in flexible printed circuits (FPCs), the existing nickel plating process in ENIG plating presents several challenges. Firstly, for traces with linewidths and spacings of 50 micrometers or less, it suffers from severe nickel bridging and nickel plating infiltration. Secondly, for traces with linewidths greater than 50 micrometers, it is prone to incomplete plating, leading to a decrease in product yield. Therefore, surface treatment of fine circuitry in FPCs has become a research hotspot and a challenge in the precision machining of high-end circuit boards in recent years. The main reasons for nickel bridging and nickel diffusion are as follows: Traditional electroless nickel plating processes require palladium activation treatment. On the one hand, after palladium activation treatment, the residual palladium ion activator will produce suspended palladium nuclei or palladium hydroxide, which will adhere to the non-copper surface and cause excess nickel deposition. On the other hand, due to the fine spacing of the lines, too much palladium is adsorbed in the areas on both sides of the line spacing, so the nickel deposition rate on both sides of the line is faster than on the surface. In mild cases, sparse spots or burrs appear on the edge of the line. In severe cases, thickening or diffusion of nickel may occur around the line, or even more serious bridging between lines may occur. These defects are more serious, especially for printed circuit boards with high density fine lines, which will greatly increase the product defect rate.

[0004] To reduce plating bleeding during electroless nickel-gold plating, the industry has proposed various solutions. These solutions mainly suppress plating bleeding by improving activation processes, adding post-dip processes, and modifying plating solution formulations. Below are some specific patent application disclosures demonstrating different methods to address this challenge:

[0005] 1) Improved Activation Process: Patent application US20010040047 discloses a palladium-free activation method using a composition of alkaline permanganate, chromate, or chlorite as the activator. Although the palladium-free activation method is not as effective as the palladium-based method, it provides an alternative to reduce plating penetration. Additionally, patent application US20130003332A discloses a method to reduce nickel bridging that may occur during nickel plating. This method includes the following steps: first, a short-time (1 minute) impregnation of electroless nickel deposition to obtain a 0.1 μm nickel layer, followed by electroless palladium / displacement gold. This method avoids excess nickel deposition or nickel bridging by reducing the thickness of the electroless nickel, but its drawbacks include poor stability of electroless palladium, high cost, and a long process flow. Furthermore, patent application EP0707093 discloses an activation additive containing imidazole or imidazole derivatives, which can be used to reduce plating penetration problems, but its application effect on 12 μm narrow-pitch fine-line substrates has not been reported.

[0006] 2) Post-dip process: Patent application CN113737159A describes a method using polyethyleneimine as a post-dip additive, which can effectively shield monovalent copper ions at the edges of the plating surface and reduce plating penetration problems. Additionally, patent application CN102405306A discloses a chemical nickel plating method that can suppress excess nickel deposition. This method includes steps i) activating the copper surface with palladium ions; ii) removing excess palladium ions or precipitates formed therefrom with a pretreatment composition containing at least two different types of acids, one of which is an organic aminocarboxylic acid; iii) chemical nickel plating. This method, because it subsequently uses acid to treat excess palladium ions, is prone to incomplete plating.

[0007] 3) Improved plating solution formulation: Patent application CN109280907A discloses an additive for nickel plating solution of ultra-fine lines. The additive contains phenylthiourea as a stabilizer and 2-thiourea pyrimidine as a special additive, which is used to suppress plating penetration, plating omission and color difference on lines with line width and line spacing not greater than 50μm.

[0008] The aforementioned existing technologies address the nickel plating penetration problem during ENIG by improving the activation process, post-dip process, and plating solution formulation. However, they still present some technical and process challenges, including: 1) The double-edged sword effect of additives: One approach to solving the penetration problem is to add additives with complexing properties to the activation process or nickel plating solution system to suppress palladium activity in non-plating areas. However, these sulfur-containing additives, while inhibiting penetration, may also poison palladium particles on the surface of fine lines, especially in fine lines containing both linewidths and spacings of 12 μm and below and linewidths greater than 50 μm. This can lead to incomplete plating or failure to initiate plating on some lines. 2) Limitations of the post-dip process: While additives in the post-dip process can appropriately suppress penetration, solving both penetration and incomplete plating problems solely through the post-dip process for narrow-spacing fine lines like 12 μm remains a significant challenge. In addition, existing technologies, which use sulfuric acid solutions for pre-dip and post-dip processes, do not inhibit plating penetration for fine lines with a line spacing of 12μm. The use of sulfuric acid solutions in both the pre-dip and post-dip processes is only to remove surface oxides and has little impact on the activation effect of fine lines.

[0009] In summary, although existing methods provide possible solutions to the nickel plating penetration problem, current nickel plating processes still cannot avoid nickel bridging and nickel penetration issues for high-density ultrafine FPC boards with interconnect spacing of 12μm or less. At the same time, they also cannot avoid the problem of missing plating for lines with linewidth greater than 50μm on flexible substrates. Summary of the Invention

[0010] To overcome the shortcomings of the prior art, the first objective of this invention is to provide a method for suppressing nickel plating penetration and missed plating in electroless nickel plating of ultra-fine lines on flexible substrates for integrated circuit packaging. This method can effectively avoid nickel bridging and nickel plating penetration problems for lines with line width and line spacing of 12μm and below in the nickel plating process, and can also effectively avoid missed plating problems for lines with line width greater than 50μm, thereby greatly improving product yield.

[0011] To overcome the shortcomings of the prior art, the second objective of this invention is to provide a method for suppressing electroless nickel plating penetration and missing plating of ultra-fine lines on flexible substrates in integrated circuit packaging, and its application in the nickel plating process.

[0012] To achieve the first objective of the invention, the technical solution adopted by the present invention is as follows:

[0013] This invention provides a method for suppressing nickel plating penetration and plating omission in the electroless plating of ultra-fine lines on flexible substrates for integrated circuit packaging, comprising the following steps:

[0014] S1. Pre-impregnation treatment before activation: The flexible substrate is pre-impregnated using a pre-impregnation solution; the pre-impregnation solution includes water and pre-impregnation additives, the pre-impregnation additives including cationic surfactants and / or nonionic surfactants; and / or

[0015] The cationic surfactant includes hexadecyltrimethylammonium bromide and / or benzyldimethylphenylammonium chloride; and / or, the nonionic surfactant includes emulsifier OP-10;

[0016] S2. Activation: After completing the pre-immersion treatment before activation, the flexible substrate is activated using palladium activation solution;

[0017] S3. Post-immersion treatment: After activation, the flexible substrate is subjected to post-immersion treatment using a post-immersion solution; the post-immersion solution includes water and a post-immersion additive, and the post-immersion additive is a thiourea compound.

[0018] The pre-impregnation solution is prepared by adding pre-impregnation additives to ultrapure water and mixing them evenly, without adjusting the pH value. Similarly, the post-impregnation solution is prepared by adding post-impregnation additives to ultrapure water and mixing them evenly, without adjusting the pH value.

[0019] The activated flexible substrate can be rinsed directly with ultrapure water for 30 seconds without ultrasonic cleaning.

[0020] The cationic or nonionic surfactants in the pre-immersion solution before activation can form a uniform adsorption layer on the circuit surface, increasing the wetting ability of the fine circuit and promoting the adsorption and adhesion of palladium ions. This makes it easier for palladium ions to be evenly distributed across the entire surface, reducing the possibility of local activation differences or over-activation. It ensures that the adsorption amount on both sides and the top surface of the circuit is uniform. At the same time, the charge of the cationic surfactant or the hydrophobic group of the nonionic surfactant creates a certain repulsion effect with the palladium ions in the activation solution, preventing the accumulation of a large number of palladium ions and avoiding nickel bridging caused by excessive palladium adsorption on both sides. Under the synergistic effect of the cationic or nonionic surfactants, the uniformity and efficiency of activation are improved, while ensuring that the nickel deposition rate around the circuit is consistent, making the subsequent electroless nickel plating more uniform and reducing the possibility of missed plating of fine circuits.

[0021] In this post-immersion solution, the sulfur atoms in the thiourea compounds can react with palladium ions to form palladium-thiourea compounds. This can, to some extent, inhibit the catalytic activity of palladium particles on non-plating substrates, reduce nickel deposition between fine lines, and thus avoid nickel bridging issues, thereby preventing short circuits between lines and improving product yield. Simultaneously, this post-immersion solution can be adsorbed onto the surface of the circuit, inhibiting the formation rate of the autocatalytic layer in the fine lines to some extent, reducing nickel bridging caused by excessively fast nickel plating.

[0022] In addition, the present invention combines pre-dip treatment before activation and post-dip treatment after activation. The pre-dip treatment before activation has the effect of electrostatic repulsion and promotes uniform adsorption, while the post-dip treatment plays a role in poisoning palladium particles. Through the synergistic effect of the two, it can effectively prevent nickel bridging during nickel plating of lines with interconnect spacing of 12μm and below, and ensure the initial plating of lines with line width greater than 50μm and avoid the phenomenon of missed plating.

[0023] Furthermore, in step S1, the pre-impregnation solution before activation comprises the following components: water, hexadecyltrimethylammonium bromide 0.05 g / L to 1 g / L and / or benzyldimethylphenylammonium chloride 0.05 g / L to 1 g / L; and / or

[0024] In step S2, the palladium activation solution is a palladium sulfate solution; and / or, the concentration of the palladium sulfate solution is 0.01 g / L to 0.05 g / L.

[0025] Furthermore, in step S3, the thiourea compound is a compound with the structure shown in Formula I;

[0026]

[0027] R1 and R2 are respectively one of hydrogen atom, alkyl, amino or phenyl, and only one of R1 and R2 can be phenyl.

[0028] Furthermore, the thiourea compound is at least one of thiourea, N-methylthiourea, phenylthiourea, and thioaminourea.

[0029] Furthermore, in step S1, the concentration of the pre-impregnation additive in the pre-impregnation solution before activation is 0.05 g / L-2 g / L; and / or

[0030] In step S3, the concentration of the post-immersion additive in the post-immersion solution is 0.01 g / L to 1 g / L.

[0031] Furthermore, before the pre-immersion treatment before activation in step S1, the flexible substrate is micro-etched with a micro-etching solution for 1 to 2 minutes; wherein the flexible substrate after micro-etching is rinsed with ultrapure water.

[0032] The micro-etching solution comprises the following components: water, sodium persulfate 25g / L-100g / L and sulfuric acid 30g / L-50g / L.

[0033] Among them, the oxidizing substances in the micro-etching solution can roughen the circuit surface, forming a tiny uneven structure on the circuit surface, increasing the surface roughness. This increases the surface area, provides more activation sites, which is beneficial for subsequent palladium activation, promotes the adhesion and wettability of surfactants in the subsequent pre-dip process, further enhances the activation effect, and can improve the adhesion of the plating layer. At the same time, the acidic substances can remove surface oxides or deposits on the flexible substrate, avoiding plating problems caused by impurities on the circuit surface.

[0034] Furthermore, before the micro-etching process, the flexible substrate is degreased; after the micro-etching process and before the pre-immersion process before activation, the flexible substrate is acid-washed with sulfuric acid.

[0035] Furthermore, in step S1, the temperature of the pre-soaking treatment is 25℃~30℃, and the time of the pre-soaking treatment is 1min~5min; the temperature of the post-soaking treatment is 25℃~30℃, and the time of the post-soaking treatment is 10s~60s.

[0036] To achieve the second objective of the invention, the technical solution adopted by the present invention is as follows:

[0037] This invention provides a process for electroless nickel plating of ultra-fine lines on a flexible substrate for integrated circuit packaging, including a pretreatment step for nickel plating and an electroless nickel plating step; the pretreatment step for nickel plating employs the aforementioned method for suppressing nickel plating over-plating and under-plating of ultra-fine lines on a flexible substrate.

[0038] Furthermore, in the electroless nickel plating process, the flexible substrate that has completed the pretreatment process is placed in the nickel plating solution, and the temperature of the nickel plating solution is controlled at 70℃-90℃, the pH value is controlled at 4.0-6.0, and the electroless nickel plating time is 10min-50min; and / or

[0039] After completing the electroless nickel plating, electroless gold plating is then performed.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] (1) The present invention provides a method for suppressing nickel plating diffusion and missing plating in ultra-fine lines of integrated circuit packaging flexible substrates. Through the systematic synergistic effect of pre-dip treatment before activation, activation treatment, and post-dip treatment, it can avoid nickel plating bridging in fine lines with line width and line spacing of 12μm and below, and also avoid the problems of skipping and missing plating in lines with line width greater than 50μm. In addition, the pre-dip process before activation can form a uniform palladium adsorption layer on the surface of the line during activation, increasing the wetting ability of the fine lines and helping to improve the subsequent palladium adsorption effect on the surface, thereby improving the uniformity of activation. This effectively solves the problem of skipping and missing plating in lines with line width greater than 50μm due to low or uneven palladium adsorption. At the same time, the pre-dip treatment before activation can reduce the palladium activation adsorption amount in lines with line width and line spacing of 12μm and below without affecting the palladium activation effect in lines with line width greater than 50μm, thereby suppressing nickel bridging. In addition, the post-immersion treatment can effectively suppress the catalytic activity of palladium particles in non-plated substrates for fine lines with interconnect spacing of 12μm or less, reduce nickel deposition between fine lines, and avoid nickel bridging problems in fine lines caused by excessive palladium activity or palladium residue between fine lines.

[0042] (2) The method of the present invention for suppressing electroless nickel plating penetration and leakage in ultra-fine lines of flexible substrates for integrated circuit packaging eliminates the need for ultrapure water rinsing after pre-immersion treatment before activation, allowing direct activation; after activation, the flexible substrate can be directly rinsed with ultrapure water without ultrasonic cleaning; and after post-immersion treatment, the flexible substrate can be directly plated with nickel without ultrapure water rinsing. Therefore, this method is characterized by simple process, convenient operation, low production cost, and applicability to large-scale production.

[0043] (3) The process of electroless nickel plating of ultra-fine lines on flexible substrate of integrated circuit packaging according to the present invention can avoid the problems of plating penetration and plating leakage of fine lines. It is especially suitable for electroless nickel plating of fine lines with line width and line spacing of 12μm, and the nickel plating uniformity is good, with the thickness difference of the nickel plating layer on the copper surface of the flexible substrate line being less than 10%. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 The image shows a metallographic image of a flexible substrate with a line width and spacing of 12 μm, obtained by electroless nickel plating using the method described in Example 1.

[0046] Figure 2 The image shows a metallographic image of a flexible substrate with a line width and spacing of 250 μm, obtained by electroless nickel plating using the method described in Example 1.

[0047] Figure 3 This is a metallographic image showing the morphology and line spacing measurement of the flexible substrate circuit with a line width and line spacing of 12 μm in Example 1 before electroless nickel plating.

[0048] Figure 4 This is a metallographic image showing the morphology and line width / spacing measurements of the flexible substrate circuit with a line width and spacing of 250 μm in Example 1 before electroless nickel plating.

[0049] Figure 5 The image shows a metallographic image of a flexible substrate with a line width and spacing of 12 μm, obtained by electroless nickel plating using the method described in Comparative Example 1.

[0050] Figure 6 The image shows a metallographic image of a flexible substrate with a line width and spacing of 250 μm, obtained by electroless nickel plating using the method described in Comparative Example 3.

[0051] Figure 7 The image shows a metallographic image of a flexible substrate with a line width and spacing of 12 μm, obtained by electroless nickel plating using the method described in Comparative Example 3.

[0052] Figure 8 The image shows a metallographic image of a flexible substrate with a line width and spacing of 12 μm, obtained by electroless nickel plating using the method described in Comparative Example 4.

[0053] Figure 9 The image shows a metallographic image of a 250μm line on a flexible substrate after electroless nickel plating using the method described in Comparative Example 6.

[0054] Figure 10 This is a SEM image of a flexible substrate with a line width and spacing of 12 μm, obtained by electroless nickel plating using the method described in Example 1.

[0055] Figure 11 This is an EDS analysis image of a flexible substrate sample that has undergone the chemical nickel plating process in Example 1 of this invention.

[0056] Figure 12 This is a schematic diagram illustrating the principle of the pre-soaking treatment before activation in this invention.

[0057] Figure 13 This is a schematic diagram illustrating the principle of the post-immersion treatment of the present invention. Detailed Implementation

[0058] To make the technical problem to be solved, the technical solution, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0059] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. In this invention, the singular forms “a,” “the,” and “the” as used in the embodiments and appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0060] In this embodiment of the invention, the "fine lines" or "ultra-fine lines" are pure copper, and the "flexible substrate" is made of polyimide.

[0061] In this embodiment of the invention, the narrowest line width and line spacing used is 12μm, and the widest line width and line spacing used is 250μm.

[0062] In this embodiment of the invention, a method for suppressing nickel plating penetration and plating omission in the electroless plating of ultra-fine lines on a flexible substrate for integrated circuit packaging includes the following steps:

[0063] S1. Pre-impregnation treatment before activation: The flexible substrate after micro-etching is pre-impregnated using a pre-impregnation solution; the pre-impregnation solution includes water and pre-impregnation additives, the pre-impregnation additives include cationic surfactants and / or nonionic surfactants; and / or

[0064] The cationic surfactant includes hexadecyltrimethylammonium bromide and / or benzyldimethylphenylammonium chloride; and / or, the nonionic surfactant includes emulsifier OP-10;

[0065] S2. Activation: After completing the pre-immersion treatment before activation, the flexible substrate is activated using palladium activation solution;

[0066] S3. Post-immersion treatment: After activation, the flexible substrate is subjected to post-immersion treatment using a post-immersion solution; the post-immersion solution includes water and a post-immersion additive, and the post-immersion additive is a thiourea compound.

[0067] In some embodiments, in step S1, the pre-impregnation solution before activation comprises the following components: water, hexadecyltrimethylammonium bromide 0.05 g / L to 1 g / L and / or benzyldimethylphenylammonium chloride 0.05 g / L to 1 g / L.

[0068] In some embodiments, in step S3, the thiourea compound is a compound with the structure shown in Formula I;

[0069]

[0070] R1 and R2 are respectively one of hydrogen atom, alkyl, amino or phenyl, and only one of R1 and R2 can be phenyl.

[0071] In some embodiments, the thiourea compound is at least one of thiourea, N-methylthiourea, phenylthiourea, and thioaminourea.

[0072] In some embodiments, in step S1, the concentration of the pre-impregnation additive in the pre-impregnation solution before activation is 0.05 g / L-2 g / L; and / or

[0073] In step S3, the concentration of the post-immersion additive in the post-immersion solution is 0.01 g / L to 1 g / L.

[0074] In some embodiments, before the pre-immersion treatment before activation in step S1, the flexible substrate is further subjected to micro-etching treatment with micro-etching solution for 1 min to 2 min.

[0075] The micro-etching solution comprises the following components: water, sodium persulfate 25g / L-100g / L and sulfuric acid 30g / L-50g / L.

[0076] In some embodiments, before the micro-etching process, the flexible substrate is further subjected to an oil removal process; after the micro-etching process and before the pre-immersion process before activation, the flexible substrate is further subjected to an acid pickling process using sulfuric acid.

[0077] In some embodiments, in step S1, the temperature of the pre-immersion treatment is 25°C to 30°C, and the time of the pre-immersion treatment is 1 min to 5 min; the temperature of the post-immersion treatment is 25°C to 30°C, and the time of the post-immersion treatment is 10 s to 60 s.

[0078] In this embodiment of the invention, a process for electroless nickel plating of ultra-fine lines on a flexible substrate includes a pretreatment step and an electroless nickel plating step; the pretreatment step employs the method described above for suppressing nickel plating penetration and incomplete plating of ultra-fine lines on a flexible substrate.

[0079] In some embodiments, during the electroless nickel plating process, the flexible substrate that has completed the pretreatment process is placed in a nickel plating solution, and the temperature of the nickel plating solution is controlled at 70℃-90℃, the pH value is controlled at 4.0-6.0, and the electroless nickel plating time is controlled at 10min-50min; and / or

[0080] After completing the electroless nickel plating, electroless gold plating is then performed.

[0081] The following description is based on specific embodiments.

[0082] Example 1

[0083] A method for suppressing nickel plating penetration and plating omission in electroless nickel plating of ultra-fine lines on flexible substrates for integrated circuit packaging includes the following steps:

[0084] A1. Degreasing: The flexible substrate is degreased with a degreasing solution for 2 minutes. In this embodiment, the degreasing solution includes the following components: water, sodium phosphate 20g / L, sodium hydroxide 10g / L, sodium silicate 10g / L, and sodium carbonate 20g / L.

[0085] A2. Micro-etching: The flexible substrate is micro-etched with a micro-etching solution for 1.5 min; In this embodiment, the micro-etching solution includes the following components: water, sodium persulfate 80 g / L and sulfuric acid 40 g / L;

[0086] A3. Pickling; The flexible substrate is micro-etched with pickling solution for 2 minutes; In this embodiment, the pickling solution includes the following components: water and sulfuric acid 30g / L;

[0087] S1. Pre-impregnation treatment before activation: The flexible substrate is pre-impregnated at 28°C for 1 min using a pre-impregnation solution before activation. In this embodiment, the pre-impregnation solution before activation includes the following components by mass concentration: water and cetyltrimethylammonium bromide 0.1 g / L.

[0088] S2. Activation: After the pre-immersion treatment before activation is completed, the flexible substrate is activated using a palladium sulfate solution with a concentration of 0.04 g / L.

[0089] S3. Post-immersion treatment: After activation, the flexible substrate is subjected to a post-immersion treatment at 28°C for 30 seconds using a post-immersion solution. The post-immersion solution includes water and a post-immersion additive with a concentration of 0.01 g / L. In this embodiment, the post-immersion additive is N-methylthiourea.

[0090] A process for electroless nickel plating of ultra-fine lines on a flexible substrate for integrated circuit packaging includes the above-mentioned pretreatment process and electroless nickel plating process.

[0091] In the electroless nickel plating process, the flexible substrate that has completed the pretreatment process is placed into the nickel plating solution, and the temperature of the nickel plating solution is controlled at 80℃, the pH value is 5.0, and the electroless nickel plating time is 25 minutes.

[0092] The nickel plating solution includes the following components: water, nickel sulfate hexahydrate 20g / L, sodium hypophosphite 20g / L, sodium succinate 5g / L, lactic acid 5g / L, malic acid 4g / L, sodium acetate 9.7g / L, and stabilizer 4mg / L.

[0093] The thickness of the nickel plating layer is in the range of 0.9μm-1.0μm.

[0094] In this embodiment, the line width and line spacing of the flexible substrate include two types of lines: 12μm and 250μm.

[0095] Example 2

[0096] A method for suppressing nickel plating penetration and incomplete plating in electroless nickel plating of ultra-fine lines on flexible substrates for integrated circuit packaging is disclosed. The difference between this embodiment and Embodiment 1 is that benzyl dimethylphenyl ammonium chloride is used instead of hexadecyl trimethylammonium bromide in the pre-immersion solution before activation. All other components and methods are the same as in Embodiment 1.

[0097] Example 3

[0098] A method for suppressing nickel plating penetration and incomplete plating of ultra-fine lines on flexible substrates for integrated circuit packaging is disclosed. This embodiment differs from Embodiment 1 in that thiourea is used instead of N-methylthiourea in the post-immersion solution. All other components and methods are the same as in Embodiment 1.

[0099] Example 4

[0100] A method for suppressing nickel plating penetration and plating leakage in electroless plating of ultra-fine lines on flexible substrates for integrated circuit packaging is disclosed. This embodiment differs from Embodiment 1 in that phenylthiourea is used instead of N-methylthiourea in the post-immersion solution. All other components and methods are the same as in Embodiment 1.

[0101] Example 5

[0102] A method for suppressing nickel plating penetration and incomplete plating of ultra-fine lines on flexible substrates for integrated circuit packaging is disclosed. This embodiment differs from Embodiment 1 in that thioaminourea is used instead of N-methylthiourea in the post-immersion solution. All other components and methods are the same as in Embodiment 1.

[0103] Example 6

[0104] A method for suppressing nickel plating penetration and incomplete plating of ultra-fine lines on flexible substrates for integrated circuit packaging is disclosed. This embodiment differs from Embodiment 1 in that the emulsifier OP-10 from the nonionic surfactant is used instead of hexadecyltrimethylammonium bromide in the pre-immersion solution before activation. All other components and methods are the same as in Embodiment 1.

[0105] Among them, the use of OP-10 emulsifier in nonionic surfactants as a pre-impregnation additive has the effect of increasing interfacial wettability, promoting the uniformity of palladium ion adsorption, and reducing the occurrence of incomplete plating.

[0106] Example 7

[0107] A method for suppressing nickel plating penetration and incomplete plating in electroless nickel plating of ultra-fine lines on flexible substrates for integrated circuit packaging is disclosed. This embodiment differs from Embodiment 1 in that the pre-impregnation solution before activation uses a combination of nonionic surfactant OP-10 and cationic surfactant hexadecyltrimethylammonium bromide as pre-impregnation additives, with both OP-10 and hexadecyltrimethylammonium bromide having a concentration of 0.05 g / L. All other components and methods are the same as in Embodiment 1.

[0108] Example 8

[0109] A method for suppressing nickel plating penetration and incomplete plating in electroless nickel plating of ultra-fine lines on flexible substrates for integrated circuit packaging is disclosed. This embodiment differs from Embodiment 1 in that, after electroless nickel plating, electroless gold plating is performed. All other components and methods are the same as in Embodiment 1.

[0110] Comparative Example 1

[0111] A method for suppressing nickel plating penetration and plating omission in electroless plating of ultra-fine lines on flexible substrates for integrated circuit packaging is disclosed. This comparative example differs from Example 1 in that the pre-impregnation additive in this comparative example uses anionic surfactants. Specifically, sodium dodecyl sulfate (SDS) is used instead of hexadecyltrimethylammonium bromide (CTAB) in the pre-impregnation solution before activation. All other components and methods are the same as in Example 1.

[0112] Tests on the sample prepared in Comparative Example 1 showed that the line with a spacing of 12 μm had slight plating penetration.

[0113] Comparative Example 2

[0114] A method for suppressing nickel plating penetration and incomplete plating of ultra-fine lines on flexible substrates for integrated circuit packaging is disclosed. This comparative example differs from Example 1 in that the pre-impregnation additive in this comparative example uses anionic surfactants. Specifically, sodium dodecylbenzenesulfonate (SDBS) is used instead of hexadecyltrimethylammonium bromide (CTAB) in the pre-impregnation solution before activation. All other components and methods are the same as in Example 1.

[0115] Tests on the sample prepared in Comparative Example 2 showed that the line with a spacing of 12 μm had slight plating penetration.

[0116] Comparative Example 3

[0117] A method for suppressing nickel plating penetration and incomplete plating in electroless nickel plating of ultra-fine lines on flexible substrates for integrated circuit packaging is disclosed. This comparative example differs from Example 1 in that no pre-dip treatment is performed before activation in this comparative example. The linewidth and line spacing of the flexible substrate in this comparative example are 250 μm. All other components and methods are the same as in Example 1.

[0118] The sample prepared in Comparative Example 3 was tested: the line with a spacing of 250 μm showed a "skipping plating" phenomenon, meaning that plating could not be performed at all.

[0119] Comparative Example 4

[0120] A method for suppressing nickel plating penetration and plating omission in electroless plating of ultra-fine lines on flexible substrates for integrated circuit packaging is disclosed. This comparative example differs from Example 1 in that no post-immersion treatment is performed. All other components and methods are the same as in Example 1.

[0121] Tests on the sample prepared in Comparative Example 4 showed that nickel bridging was observed in the line with a spacing of 12 μm.

[0122] Comparative Example 5

[0123] A method for suppressing nickel plating penetration and incomplete plating in electroless nickel plating of ultra-fine lines on flexible substrates for integrated circuit packaging is disclosed. This embodiment differs from Embodiment 1 in that, in the activation step, palladium chloride solution is used instead of palladium sulfate solution. All other components and methods are the same as in Embodiment 1.

[0124] Using palladium chloride solution as the palladium activating solution makes it more prone to diffusion plating. A possible reason for this is that in palladium sulfate solution, palladium exists as [Pd(H₂O)₄]. 2+ Palladium exists primarily as [PdCl4], forming hydrated ions. Palladium ions form complexes with water molecules and carry a positive charge. In palladium chloride solutions, palladium mainly exists as [PdCl4]. 2- Palladium ions exist in the form of chloride ions, which more readily form complexes with chloride ions and possess a negative charge. The surfactant CTAB carries a positively charged hydrophilic group, which is beneficial for [Pd(H₂O)₄]. 2+ It has a certain inhibitory effect, which can inhibit plating penetration, especially for negatively charged [PdCl4]. 2- However, it has a promoting effect, which leads to the adsorption of a large number of palladium ions between the circuits, resulting in severe plating penetration.

[0125] Comparative Example 6

[0126] A method for suppressing nickel plating diffusion and incomplete plating of ultra-fine lines on flexible substrates for integrated circuit packaging is disclosed. This comparative example differs from Example 1 in that it does not involve pre-dip immersion before activation or post-dip immersion treatment. All other components and methods are the same as in Example 1.

[0127] The samples prepared in Comparative Example 6 were tested: the lines with a line width and line spacing of 12 μm showed severe nickel bridging, and the lines with a line width of 250 μm showed obvious plating defects.

[0128] Comparative Example 7

[0129] A method for suppressing nickel plating penetration and plating omission in electroless plating of ultra-fine lines on flexible substrates for integrated circuit packaging is disclosed. This comparative example differs from Example 1 in that the activated pre-immersion solution consists of hexadecyltrimethylammonium bromide and N-methylthiourea, with the concentration of hexadecyltrimethylammonium bromide at 0.1 g / L and the concentration of N-methylthiourea at 0.01 g / L. No post-immersion treatment is performed. All other components and methods are the same as in Example 1.

[0130] Tests on samples prepared in Comparative Example 7 showed that lines with a spacing of 12 μm exhibited slight plating penetration, while lines with a spacing of 250 μm showed plating skipping.

[0131] Comparative Example 8

[0132] A method for suppressing nickel plating penetration and plating omission in electroless plating of ultra-fine lines on flexible substrates for integrated circuit packaging is disclosed. This comparative example differs from Example 1 in that no pre-immersion treatment is performed, and the immersion solution after activation is changed to consist of hexadecyltrimethylammonium bromide and N-methylthiourea, wherein the concentration of hexadecyltrimethylammonium bromide is 0.1 g / L and the concentration of N-methylthiourea is 0.01 g / L. All other components and methods are the same as in Example 1.

[0133] Test of the sample prepared in Comparative Example 8: The line with a spacing of 250 μm showed obvious plating defects.

[0134] Experimental testing:

[0135] (I) Morphological characterization using metallographic microscopes

[0136] The flexible substrate sample that underwent the electroless nickel plating process in Example 1 was characterized in morphology using a metallographic microscope, such as... Figure 1 and Figure 2 As shown. By Figure 1 As can be seen, after electroless nickel plating of the flexible substrate with a linewidth and spacing of 12 μm using the method of Example 1, no nickel plating bridging phenomenon was observed in the fine line area (12 μm). Figure 2 As can be seen, after electroless nickel plating of the flexible circuit with a line width and spacing of 250 μm using the method of Example 1, no plating bridging or under-plating was observed in the wide line area (250 μm). For the metallographic morphology and line spacing measurements of the flexible substrate circuit with a line width and spacing of 12 μm before electroless nickel plating, please refer to [link to relevant documentation]. Figure 3 As shown. The metallographic morphology and linewidth / spacing measurements of a flexible substrate circuit with a linewidth and spacing of 250 μm before electroless nickel plating are shown in the image. Figure 4 As shown.

[0137] The flexible substrate sample from Comparative Example 1, after undergoing the chemical nickel plating process, was characterized in morphology using a metallographic microscope, such as... Figure 5 As shown. By Figure 5 As can be seen, after electroless nickel plating was performed on a flexible substrate with a line width and spacing of 12 μm using the method in Comparative Example 1, slight plating penetration occurred in the fine line (12 μm) area.

[0138] The flexible substrate sample from Comparative Example 3, after undergoing the chemical nickel plating process, was characterized in morphology using a metallographic microscope, such as... Figure 6 and Figure 7 As shown. By Figure 6 As can be seen, after electroless nickel plating was performed on a flexible substrate with a linewidth and spacing of 250 μm using the method in Comparative Example 3, a significant skipping phenomenon occurred in the wide line area (250 μm), indicating that plating was difficult to perform. Figure 7 As can be seen, after electroless nickel plating was performed on the flexible substrate with a line width and spacing of 12μm using the method in Comparative Example 3, obvious skipping plating phenomenon appeared in the fine line (12μm) area.

[0139] The flexible substrate sample from Comparative Example 4, after undergoing the electroless nickel plating process, was characterized in morphology using a metallographic microscope, such as... Figure 8 As shown. By Figure 8 As can be seen, after the flexible substrate with a line width and spacing of 12μm was electroless nickel plating using the method in Comparative Example 4, obvious nickel plating bridging phenomenon appeared in the fine line (12μm) area.

[0140] The flexible substrate sample from Comparative Example 6, after undergoing the chemical nickel plating process, was characterized in morphology using a metallographic microscope, such as... Figure 9 As shown. By Figure 9 As can be seen, after electroless nickel plating was performed on the flexible substrate with a line width of 250μm using the method of Comparative Example 6, obvious plating defects appeared in the wide line area (250μm).

[0141] (II) Morphological characterization by scanning electron microscopy

[0142] The flexible substrate sample that underwent the electroless nickel plating process in Example 1 was characterized by morphology using a scanning electron microscope, such as... Figure 10 As shown. By Figure 10 As can be seen, after the flexible substrate circuit with a line width and line spacing of 12μm was electroless nickel plating using the method in Example 1, no nickel plating bridging phenomenon was observed in the fine line (12μm) area.

[0143] (III) EDS Energy Dispersive Spectroscopy Analysis of Nickel Plating Layer on Circuit Boards

[0144] The flexible substrate sample that underwent the chemical nickel plating process in Example 1 was analyzed using energy dispersive spectroscopy (EDS). Figure 11 As shown. By Figure 11 It can be seen that there are obvious nickel and phosphorus peaks, indicating that the copper layer of the flexible substrate sample circuit in Example 1 is the expected nickel-phosphorus layer after the completion of the chemical nickel plating process.

[0145] (IV) Principle Analysis of Pre-soaking Treatment Before Activation

[0146] like Figure 12 As shown, surfactants generally have both hydrophilic and hydrophobic groups. This invention utilizes cationic or nonionic surfactants in the pre-immersion solution to form a uniform adsorption layer on the circuit surface, increasing the wetting ability of the fine circuit and promoting the adsorption and adhesion of palladium ions. This allows palladium ions to be easily and uniformly distributed across the entire surface, reducing the possibility of localized activation differences or over-activation. This ensures uniform adsorption on both sides and the top surface of the circuit. Simultaneously, the charge of the cationic surfactant or the hydrophobic group of the nonionic surfactant creates a certain repulsion effect with the palladium ions in the activation solution, preventing the accumulation of large amounts of palladium ions and avoiding nickel bridging caused by excessive palladium adsorption on both sides. Under the synergistic effect of cationic or nonionic surfactants, the uniformity and efficiency of activation are improved, ensuring a consistent nickel deposition rate around the circuit. This makes subsequent electroless nickel plating more uniform and reduces the possibility of missed plating on fine circuits.

[0147] (V) Principle Analysis of Post-Immersion Treatment

[0148] like Figure 13 As shown, the sulfur in the thiourea compounds in the post-immersion solution of this invention can combine with palladium ions to form palladium-thiourea compounds, which can inhibit the catalytic activity of palladium particles on non-plating substrates to a certain extent and reduce nickel deposition between fine lines. At the same time, the post-immersion solution can also be adsorbed on the surface of the lines, which can inhibit the formation rate of the autocatalytic layer of the fine lines to a certain extent and reduce nickel bridging caused by excessively fast nickel plating.

[0149] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for suppressing nickel plating penetration and plating leakage in chemical plating of ultra-fine lines on flexible substrates for integrated circuit packaging, characterized in that, Includes the following steps: S1. Pre-impregnation treatment before activation: The flexible substrate is pre-impregnated using a pre-impregnation solution; the pre-impregnation solution includes water and pre-impregnation additives, the pre-impregnation additives including cationic surfactants and / or nonionic surfactants; and / or The cationic surfactant includes hexadecyltrimethylammonium bromide and / or benzyldimethylphenylammonium chloride; and / or, the nonionic surfactant includes emulsifier OP-10; S2. Activation: After completing the pre-immersion treatment before activation, the flexible substrate is activated using palladium activation solution; S3. Post-immersion treatment: After activation, the flexible substrate is subjected to post-immersion treatment using a post-immersion solution; the post-immersion solution includes water and a post-immersion additive, and the post-immersion additive is a thiourea compound; In step S1, the concentration of hexadecyltrimethylammonium bromide is 0.05 g / L to 1 g / L, and / or the concentration of benzyldimethylphenylammonium chloride is 0.05 g / L to 1 g / L; In step S2, the palladium activation solution is a palladium sulfate solution; In step S3, the concentration of the post-immersion additive in the post-immersion solution is 0.01 g / L to 1 g / L.

2. The method for suppressing nickel plating penetration and plating leakage in the electroless plating of ultra-fine lines on a flexible substrate for integrated circuit packaging as described in claim 1, characterized in that, In step S1, the pre-impregnation solution before activation comprises the following components: water, hexadecyltrimethylammonium bromide 0.05 g / L to 1 g / L and / or benzyldimethylphenylammonium chloride 0.05 g / L to 1 g / L; and / or In step S2, the concentration of the palladium sulfate solution is 0.01 g / L to 0.05 g / L.

3. The method for suppressing nickel plating penetration and plating leakage in the electroless plating of ultra-fine lines on a flexible substrate for integrated circuit packaging as described in claim 1, characterized in that, In step S3, the thiourea compound is a compound with the structure shown in Formula I; ， R1 and R2 are respectively one of hydrogen atom, alkyl, amino or phenyl, and only one of R1 and R2 can be phenyl.

4. The method for suppressing nickel plating penetration and plating leakage in the electroless plating of ultra-fine lines on a flexible substrate for integrated circuit packaging as described in claim 3, characterized in that, The thiourea compound is at least one of thiourea, N-methylthiourea, phenylthiourea, and thioaminourea.

5. The method for suppressing nickel plating penetration and plating leakage in the electroless plating of ultra-fine lines on a flexible substrate for integrated circuit packaging as described in claim 1, characterized in that, In step S1, the concentration of the pre-impregnation additive in the pre-impregnation solution before activation is 0.05 g / L-2 g / L.

6. The method for suppressing nickel plating penetration and plating leakage in the electroless plating of ultra-fine lines on a flexible substrate for integrated circuit packaging as described in claim 1, characterized in that, Before the pre-immersion treatment before activation in step S1, the flexible substrate is further subjected to micro-etching treatment with micro-etching solution for 1 min to 2 min. The micro-etching solution comprises the following components: water, sodium persulfate 25g / L-100g / L and sulfuric acid 30g / L-50g / L.

7. The method for suppressing nickel plating penetration and plating leakage in the electroless plating of ultra-fine lines on a flexible substrate for integrated circuit packaging as described in claim 6, characterized in that, Before the micro-etching process, the flexible substrate is further subjected to degreasing treatment; after the micro-etching process and before the pre-immersion treatment before activation, the flexible substrate is further subjected to acid washing treatment with sulfuric acid.

8. The method for suppressing nickel plating penetration and plating leakage in the electroless plating of ultra-fine lines on a flexible substrate for integrated circuit packaging as described in claim 1, characterized in that, In step S1, the temperature of the pre-soaking treatment is 25℃~30℃, and the time of the pre-soaking treatment is 1min~5min; the temperature of the post-soaking treatment is 25℃~30℃, and the time of the post-soaking treatment is 10s~60s.

9. A process for electroless nickel plating of ultra-fine lines on a flexible substrate for integrated circuit packaging, characterized in that, It includes a pretreatment process and a chemical nickel plating process; the pretreatment process adopts the method described in any one of claims 1 to 8 for suppressing the diffusion and missing plating of chemical nickel plating on ultra-fine lines of integrated circuit packaging flexible substrates.

10. The process for electroless nickel plating of ultra-fine lines on a flexible substrate for integrated circuit packaging as described in claim 9, characterized in that, In the electroless nickel plating process, the flexible substrate that has completed the pretreatment process is placed in the nickel plating solution, and the temperature of the nickel plating solution is controlled at 70℃-90℃, the pH value is controlled at 4.0-6.0, and the electroless nickel plating time is 10min-50min; and / or After completing the electroless nickel plating, electroless gold plating is then performed.

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