Method for inhibiting diffusion plating and skip plating of chemical nickel plating of superfine circuit of integrated circuit packaging flexible substrate and application

Abstract

The invention relates to the technical field of advanced materials of an integrated circuit packaging COF technology, in particular to a method for inhibiting diffusion plating and skip plating of chemical nickel plating of a superfine circuit of an integrated circuit packaging flexible substrate and application. According to the method, through the systematic synergistic effect of pre-dipping treatment before activation, activation treatment and post-dipping treatment, the uniformity of line activation can be promoted, the deposition rate of nickel plating around the line can be regulated and controlled, diffusion plating and skip plating phenomena caused by non-uniform adsorption amount of palladium on the two sides of the line are improved, nickel plating deposition between fine lines is reduced, and the service life of the line is prolonged. And the problem of nickel bridging of the fine line caused by over-strong palladium activity or palladium residues at intervals of the fine line is avoided. The method has the advantages of being simple in process, easy and convenient to operate, low in production cost and capable of being suitable for large-scale production, and can be well applied to the chemical nickel plating process of the superfine circuit of the flexible substrate with the line width smaller than 12 micrometers and the line width larger than 50 micrometers at the same time.

Description

Technical Field

[0001] The present invention relates to the field of advanced materials technology for integrated circuit packaging COF technology, and in particular to a chemical nickel plating technology for ultrafine circuits (line width and line spacing of 12 μm) on flexible substrates. Specifically, it relates to a method and application for suppressing permeation and leakage plating of chemical nickel plating on ultrafine circuits on flexible substrates for integrated circuit packaging. Background Art

[0002] With the widespread adoption of mobile electronic devices and large-screen displays, the market is placing higher demands on electronic manufacturing technologies that combine low cost, high density, and large-scale production. To adapt to this trend, electronic product design concepts are evolving towards thinner, lighter, and smaller designs. For example, liquid crystal displays (LCDs), LCD TVs, plasma TVs, as well as 3C products such as mobile phones, digital cameras, and digital video cameras, are all striving for more compact designs and lighter weight. To meet these demands, packaging technology must evolve towards higher density, miniaturization, and flexibility. Chip on Flex (COF) technology (or Chip on Film) emerged precisely to meet these market demands. By directly packaging integrated circuits (ICs) onto flexible printed circuit boards (PCBs), it achieves higher assembly density, reduces product weight and size, and offers flexible and bendable mounting options. However, as display density increases, so too do the requirements for driver chip I / O. The pitch between lead pads has already fallen below 30μm, and the interconnect pitch has reached 15μm and continues to decrease. This places even higher demands on the precision of fine circuitry fabricated on flexible substrates.

[0003] The electroless nickel-gold (ENIG) process is a commonly used surface treatment for circuit boards. Its primary function is to prevent copper circuit oxidation and corrosion. However, in the ENIG process for fine lines on flexible printed circuits (FPCs), the nickel plating process in the existing electroless nickel-gold process, on the one hand, suffers from serious nickel bridging and nickel seepage issues for lines with line widths and spacings of 50 microns or less; on the other hand, for lines with line widths greater than 50 microns, plating leakage issues are more likely to occur, leading to reduced product yield. Therefore, the surface treatment of fine FPC lines has become a research hotspot and difficulty in the precision machining of high-end circuit boards in recent years. The main reasons for nickel bridging and nickel infiltration are: the traditional chemical nickel plating process requires metal palladium activation treatment. On the one hand, after the metal palladium activation treatment, the residual palladium ion activator will produce suspended palladium nuclei or palladium hydroxides, which adhere to the non-copper surface and cause excess nickel deposition; on the other hand, due to the fine circuit spacing, excessive palladium adsorption occurs in the areas on both sides of the circuit spacing, so that the nickel deposition rate on both sides of the circuit is faster than that on the surface. In mild cases, there will be sparse burrs or burrs on the edge of the circuit. In severe cases, the area around the circuit will grow fat or infiltrate, and even more serious bridging between circuits will occur. Especially for printed circuit boards with high-density and fine lines, these defects will be more serious, resulting in a greatly increased product defect rate.

[0004] To reduce the permeation phenomenon during electroless nickel-gold plating, the industry has proposed a variety of solutions. These solutions primarily address this problem by improving the activation process, adding a post-immersion process, and refining the plating solution formula. The following are some specific patent applications that demonstrate different approaches to addressing this challenge:

[0005] 1) Improved Activation Process: Patent application US20010040047 proposes a palladium-free activation method using a combination of alkaline permanganate, chromate, or chlorite as an activator. Although this palladium-free activation method is not as effective as palladium-based methods, it provides an alternative solution for reducing permeation. Additionally, patent application US20130003332A discloses a method for reducing nickel bridging that can occur during nickel plating. This method includes the following steps: first, a short-term (1 minute) alluvial electroless nickel deposition to obtain a 0.1-micron nickel layer, followed by electroless palladium / displacement gold. This method reduces the thickness of the electroless nickel to avoid excess nickel deposition or nickel bridging, but drawbacks include poor stability of electroless palladium, high cost, and a lengthy process. Furthermore, patent application EP0707093 discloses an activation additive containing imidazole or an imidazole derivative that can be used to reduce permeation, but its effectiveness on substrates with narrow 12μm fine lines has not yet been reported.

[0006] 2) Post-dip process: Patent application CN113737159A describes a method using polyethyleneimine as a post-dip additive, which effectively shields monovalent copper ions at the edge of the plated surface, reducing plating leakage. Additionally, patent application CN102405306A discloses an electroless nickel plating method that suppresses excess nickel deposition. This method comprises the steps of i) activating the copper surface with palladium ions; ii) removing excess palladium ions or resulting precipitates using a pretreatment composition comprising at least two different acids, one of which is an organic aminocarboxylic acid; and iii) electroless nickel plating. However, this method is susceptible to skip plating due to the subsequent acid treatment of excess palladium ions.

[0007] 3) Improved plating solution formula: Patent application CN109280907A discloses an additive for nickel plating solution for ultrafine circuits. The additive contains phenylthiourea as a stabilizer and 2-thiouracil as a special additive. It is used to suppress seepage, leakage plating and color difference on circuits with a line width and line spacing of no more than 50μm.

[0008] The above-mentioned existing technologies solve the nickel permeation problem in the ENIG process by improving the activation process, post-immersion process and plating solution formulation respectively. However, there are still some technical and process challenges, including 1) the double-edged sword effect of additives: One of the ideas to solve the permeation problem is to add additives with chelating effects in the activation process or nickel plating solution system to suppress the palladium activity in the non-plated area. However, these sulfur-containing additives, although they can suppress permeation, may also have a poisonous effect on the palladium particles on the surface of fine lines, especially in fine lines with line widths and spacings of 12μm and below and line widths greater than 50μm. This may cause some lines to miss plating or be unable to be plated. 2) Limitations of the post-immersion process: Although the additives in the post-immersion process can appropriately suppress the permeation phenomenon, it is still very challenging to solve the permeation and miss plating problems for narrow-pitch fine lines such as 12μm by simply using the post-immersion process. In addition, the existing technology uses sulfuric acid solution for pre-immersion and post-immersion processes respectively, which has no inhibitory effect on the plating of fine lines with a line spacing of 12μm. The sulfuric acid solution is used in both the pre-immersion solution and the post-immersion solution only to remove surface oxides, which has little effect on the activation effect of the fine lines.

[0009] In summary, although the existing methods provide a possible way to solve the nickel plating seepage problem, the current nickel plating process still cannot avoid the nickel bridging and nickel seepage problems for high-density ultra-fine FPC boards with interconnection spacing of the nickel plating layer of 12μm or less, and the nickel plating seepage problem for lines with a width greater than 50μm on the flexible substrate cannot be avoided. Summary of the Invention

[0010] In order to overcome the shortcomings of the prior art, the first object of the present invention is to provide a method for suppressing electroless nickel plating and nickel leakage in ultra-fine circuits of integrated circuit packaging flexible substrates. This method can effectively avoid the problems of nickel bridging and nickel leakage in the nickel plating process for circuits with line widths and line spacings of 12μm or less, and can also effectively avoid the problem of nickel leakage for circuits with line widths greater than 50μm, thereby greatly improving product yield.

[0011] In order to overcome the deficiencies of the prior art, a second object of the present invention is to provide an integrated circuit package method for suppressing electroless nickel plating penetration and leakage plating of ultra-fine circuits on flexible substrates and its application in a nickel plating process.

[0012] In order to achieve the first object of the above invention, the technical solution adopted by the present invention is as follows:

[0013] The present invention provides a method for suppressing electroless nickel plating penetration and leakage plating of ultra-fine circuits on flexible substrates for integrated circuit packaging, comprising the following steps:

[0014] S1. Pre-impregnation treatment before activation: pre-impregnation treatment of the flexible substrate with a pre-impregnation liquid before activation; the pre-impregnation liquid before activation comprises water and a pre-impregnation additive, and the pre-impregnation additive comprises a cationic surfactant and / or a non-ionic surfactant; and / or

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

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

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

[0018] The pre-dip solution before activation is prepared by adding the pre-dip additive to ultrapure water and mixing them evenly, and no pH adjustment is required. The post-dip solution is prepared by adding the post-dip additive to ultrapure water and mixing them evenly, and no pH adjustment is required.

[0019] Among them, the flexible substrate after activation treatment can be directly rinsed with ultrapure water for 30 seconds without ultrasonic cleaning.

[0020] Among them, the cationic or non-ionic surfactant in the pre-dip solution before activation can form a uniform adsorption layer on the surface of the circuit, increase the wetting ability of the fine circuit, promote the adsorption and adhesion of palladium ions, and make the palladium ions easily and evenly distributed on the entire surface, reducing the possibility of local activation differences or excessive activation, and can make the adsorption amount on both sides and the upper surface of the circuit consistent. At the same time, the charge of the cationic surfactant or the hydrophobic group of the non-ionic surfactant produces a certain repulsive effect with the palladium ions in the activation solution, which will not lead to the enrichment of a large amount of palladium ions and avoid the nickel bridging phenomenon caused by excessive palladium adsorption on both sides; under the synergistic effect of the cationic or non-ionic surfactant, the uniformity and efficiency of the activation are improved at the same time, while ensuring the uniform nickel deposition rate around the circuit, making the subsequent chemical nickel plating more uniform and reducing the possibility of plating leakage in the fine circuit.

[0021] The sulfur atoms in the thiourea compounds in the post-dip solution react with palladium ions to form palladium-thiourea compounds, which can inhibit the catalytic activity of the non-plated palladium particles, reduce nickel deposition between fine lines, and thus avoid nickel bridging, thereby preventing short circuits between lines and improving product yield. The post-dip solution can also adsorb onto the surface of the circuit, inhibiting the formation of the autocatalytic layer on the fine lines to a certain extent, reducing nickel bridging caused by excessive nickel plating speeds.

[0022] In addition, the present invention cooperates with the pre-impregnation treatment before activation and the post-impregnation treatment after activation. The pre-impregnation treatment before activation plays the role of electrostatic repulsion and promotion of uniform adsorption, and the post-impregnation treatment plays the role of poisoning palladium particles. Through the synergistic effect of the two, the circuits with interconnection spacing of 12 μm and below can avoid the problem of nickel bridging during the nickel plating process, and can also ensure the plating of circuits with a line width greater than 50 μm and avoid the phenomenon of plating leakage.

[0023] Furthermore, in step S1, the pre-activation pre-dip solution comprises the following components: water, 0.05 g / L to 1 g / L of cetyltrimethylammonium bromide and / or 0.05 g / L to 1 g / L of benzyldimethylphenylammonium chloride; 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 having a structure shown in formula I;

[0026]

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

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

[0029] Furthermore, in step S1, the concentration of the pre-soak additive in the pre-soak 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 liquid is 0.01 g / L to 1 g / L.

[0031] Furthermore, before the pre-pre-preg treatment before activation in step S1, the flexible substrate is further subjected to micro-etching treatment using 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, 25 g / L-100 g / L of sodium persulfate, and 30 g / L-50 g / L of sulfuric acid.

[0033] Among them, the oxidizing substances in the micro-etching solution can coarsen the surface of the circuit, forming tiny concave and convex structures on the circuit surface and increasing the surface roughness. This can increase the surface area and provide more activation sites, which is beneficial to the subsequent palladium activation and promotes the adhesion and wettability of the surfactant in the subsequent pre-dip process, further improving the activation effect and improving the bonding strength of the coating; at the same time, the acidic substance can remove the surface oxides or attachments of the flexible substrate, avoiding plating problems caused by impurities on the circuit surface.

[0034] Furthermore, before the micro-etching treatment, the flexible substrate is subjected to degreasing treatment; after the micro-etching treatment and before the activation pre-dip treatment, the flexible substrate is subjected to pickling treatment using sulfuric acid.

[0035] Furthermore, in step S1, the temperature of the pre-impregnation treatment is 25°C to 30°C, and the time of the pre-impregnation treatment is 1 minute to 5 minutes; the temperature of the post-impregnation treatment is 25°C to 30°C, and the time of the post-impregnation treatment is 10 seconds to 60 seconds.

[0036] In order to achieve the second purpose of the above invention, the technical solution adopted by the present invention is as follows:

[0037] The present invention provides a process for chemical nickel plating of ultra-fine circuits on flexible substrates for integrated circuit packaging, comprising a nickel plating pretreatment process and a chemical nickel plating process; the nickel plating pretreatment process adopts the above-mentioned method for inhibiting chemical nickel plating permeation and leakage plating of ultra-fine circuits on flexible substrates.

[0038] Furthermore, in the chemical 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 to be 70° C.-90° C., the pH value is 4.0-6.0, and the chemical nickel plating time is 10 min-50 min; and / or

[0039] After the electroless nickel plating is completed, the electroless gold plating is continued.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) The present invention provides a method for suppressing electroless nickel plating and leak plating of ultra-fine circuits on flexible substrates for integrated circuit packaging. Through the systematic synergistic effect of pre-pre-impregnation treatment before activation, activation treatment, and post-impregnation treatment, it can avoid the nickel bridging phenomenon of thin circuits with a line width and line spacing of 12μm and below, and can also avoid the problems of skip plating and leak plating of circuits with a line width greater than 50μm. In addition, through the pre-impregnation process before activation, a uniform palladium adsorption layer can be formed on the surface of the circuit during activation, which increases the wetting ability of the fine circuit and helps to improve the subsequent adsorption effect of palladium on the surface, thereby improving the uniformity of activation, and effectively solves the problems of skip plating and leak plating caused by low or uneven palladium adsorption on circuits with a line width greater than 50μm. At the same time, the pre-impregnation treatment before activation can reduce the palladium activation adsorption amount of circuits with a line width and line spacing of 12μm and below without affecting the palladium activation effect of circuits with a line width greater than 50μm, thereby suppressing the nickel bridging phenomenon. In addition, through post-immersion treatment, the catalytic activity of non-plated substrate palladium particles can be effectively suppressed for fine lines with interconnection spacing of 12μm and below, reducing nickel plating deposition between fine lines and avoiding the problem of nickel bridging in fine lines caused by excessive palladium activity or palladium residue in fine line spacing.

[0042] (2) The present invention provides a method for suppressing electroless nickel plating and leakage plating on ultrafine circuits of flexible substrates for integrated circuit packaging. The flexible substrate after pre-impregnation treatment before activation does not need to be cleaned with ultrapure water and can be directly activated. The flexible substrate after activation treatment can be directly rinsed with ultrapure water without ultrasonic cleaning. The flexible substrate after post-impregnation treatment does not need to be cleaned with ultrapure water and can be directly nickel-plated. Therefore, the method has the characteristics of simple process, simple and convenient operation, low production cost, and applicability to large-scale production.

[0043] (3) The process of chemical nickel plating of ultra-fine circuits on flexible substrates for integrated circuit packaging of the present invention can avoid the problems of seepage and leakage plating of fine circuits, and is particularly suitable for chemical nickel plating of fine circuits with a line width and line spacing of 12 μm. The nickel plating has good uniformity, and the thickness difference of the nickel plating layer on the copper surface of the flexible substrate circuit is less than 10%. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0045] Figure 1 This is a metallographic image of a circuit with a line width and line spacing of 12 μm on a flexible substrate subjected to chemical nickel plating using the method of Example 1.

[0046] Figure 2 This is a metallographic image of a circuit with a line width and line spacing of 250 μm on a flexible substrate subjected to chemical nickel plating using the method of Example 1.

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

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

[0049] Figure 5 This is a metallographic image of a circuit with a line width and line spacing of 12 μm on a flexible substrate subjected to chemical nickel plating using the method of Comparative Example 1.

[0050] Figure 6 This is a metallographic image of a circuit with a line width and line spacing of 250 μm on a flexible substrate subjected to chemical nickel plating using the method of Comparative Example 3.

[0051] Figure 7 This is a metallographic image of a circuit with a line width and line spacing of 12 μm on a flexible substrate subjected to chemical nickel plating using the method of Comparative Example 3.

[0052] Figure 8 This is a metallographic image of a circuit with a line width and line spacing of 12 μm on a flexible substrate subjected to chemical nickel plating using the method of Comparative Example 4.

[0053] Figure 9 This is a metallographic image of a circuit with a line width of 250 μm on a flexible substrate subjected to chemical nickel plating using the method of Comparative Example 6.

[0054] Figure 10 This is a SEM image of a circuit with a line width and line spacing of 12 μm on a flexible substrate subjected to chemical nickel plating using the method of Example 1.

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

[0056] Figure 12 It is a schematic diagram of the principle of prepreg treatment before activation of the present invention.

[0057] Figure 13 It is a schematic diagram of the principle of post-immersion treatment of the present invention. DETAILED DESCRIPTION

[0058] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0059] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. In the present invention, the singular forms "a", "an", "the" and "the" used in the embodiments and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0060] The “fine circuit” or “ultra-fine circuit” mentioned in the embodiment of the present invention is pure copper, and the material of the “flexible substrate” is polyimide.

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

[0062] In an embodiment of the present invention, a method for suppressing electroless nickel plating and leakage plating of ultra-fine circuits on a flexible substrate for integrated circuit packaging includes the following steps:

[0063] S1. Pre-impregnation treatment before activation: pre-impregnation treatment is performed on the micro-etched flexible substrate using a pre-impregnation liquid before activation; the pre-impregnation liquid before activation includes water and a pre-impregnation additive, and the pre-impregnation additive includes a cationic surfactant and / or a non-ionic surfactant; and / or

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

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

[0066] S3. Post-immersion treatment: After activation is completed, the flexible substrate is subjected to post-immersion treatment using a post-immersion liquid; the post-immersion liquid 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-activation pre-dip solution comprises the following components: water, 0.05 g / L to 1 g / L of cetyltrimethylammonium bromide and / or 0.05 g / L to 1 g / L of benzyldimethylphenylammonium chloride.

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

[0069]

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

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

[0072] In some embodiments, in step S1, the concentration of the pre-soak additive in the pre-soak 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 liquid is 0.01 g / L to 1 g / L.

[0074] In some embodiments, before the pre-pre-preg treatment before activation, step S1 further includes micro-etching the flexible substrate with a micro-etching solution for 1 minute to 2 minutes;

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

[0076] In some embodiments, before the micro-etching treatment, the flexible substrate is further subjected to degreasing treatment; after the micro-etching treatment and before the pre-activation pre-dip treatment, the flexible substrate is further subjected to pickling treatment using sulfuric acid.

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

[0078] In an embodiment of the present invention, a process for chemical nickel plating of ultrafine circuits on a flexible substrate includes a pretreatment step and a chemical nickel plating step; the pretreatment step adopts the above-mentioned method for inhibiting permeation and leakage plating of chemical nickel plating of ultrafine circuits on a flexible substrate.

[0079] In some embodiments, in the chemical nickel plating process, the flexible substrate that has completed the pre-treatment process is placed in a nickel plating solution, and the temperature of the nickel plating solution is controlled to be 70° C.-90° C., the pH value is 4.0-6.0, and the chemical nickel plating time is 10 min-50 min; and / or

[0080] After the electroless nickel plating is completed, the electroless gold plating is continued.

[0081] The following describes the details in conjunction with specific embodiments.

[0082] Example 1

[0083] A method for suppressing electroless nickel plating and leakage plating of ultra-fine circuits on flexible substrates for integrated circuit packaging, comprising the following steps:

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

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

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

[0087] S1. Pre-activation pre-dip treatment: The flexible substrate is pre-dip treated with a pre-activation pre-dip solution at 28° C. for 1 minute. In this embodiment, the pre-activation pre-dip solution includes the following components in the following mass concentrations: water and 0.1 g / L cetyltrimethylammonium bromide.

[0088] S2. Activation: After completing the pre-impregnation treatment before activation, 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 post-immersed in a post-immersion liquid at 28° C. for 30 seconds. The post-immersion liquid 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 chemical nickel plating of ultra-fine circuits on a flexible substrate for integrated circuit packaging comprises the above-mentioned pre-treatment process and chemical nickel plating process.

[0091] In the chemical nickel plating process, the flexible substrate that has completed the pre-treatment process is placed in the nickel plating solution, and the temperature of the nickel plating solution is controlled to be 80°C, the pH value is 5.0, and the chemical nickel plating time is 25 minutes;

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

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

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

[0095] Example 2

[0096] A method for suppressing electroless nickel permeation and leakage plating on ultrafine circuits on flexible substrates for integrated circuit packaging. This embodiment differs from Example 1 in that benzyldimethylphenylammonium chloride is used in place of cetyltrimethylammonium bromide in the pre-activation pre-dip solution. The remaining components and method are the same as those in Example 1.

[0097] Example 3

[0098] A method for suppressing electroless nickel permeation and leakage plating on ultrafine circuits on flexible substrates for integrated circuit packaging. This embodiment differs from Example 1 in that thiourea is used in the post-dip solution instead of N-methylthiourea. The remaining components and method are the same as those in Example 1.

[0099] Example 4

[0100] A method for suppressing electroless nickel permeation and leakage plating on ultrafine circuits on flexible substrates for integrated circuit packaging. This embodiment differs from Example 1 in that phenylthiourea is used in the post-dip solution instead of N-methylthiourea. The remaining components and method are the same as those in Example 1.

[0101] Example 5

[0102] A method for suppressing electroless nickel permeation and leakage plating on ultrafine circuits on flexible substrates for integrated circuit packaging. This embodiment differs from Example 1 in that thiosemicarbazide is used in the post-dip solution instead of N-methylthiourea. The remaining components and method are the same as those in Example 1.

[0103] Example 6

[0104] A method for suppressing electroless nickel permeation and skipping on ultrafine circuits on flexible substrates for integrated circuit packaging is disclosed. This embodiment differs from Example 1 in that the nonionic surfactant emulsifier OP-10 is used in place of cetyltrimethylammonium bromide in the pre-activation pre-dip solution. The remaining components and method are the same as those in Example 1.

[0105] Among them, the emulsifier OP-10 in the non-ionic surfactant is used as a pre-dip additive, which has the effect of increasing the interface wettability, promoting the uniformity of palladium ion adsorption, and reducing the occurrence of plating leakage.

[0106] Example 7

[0107] A method for suppressing electroless nickel permeation and leakage plating on ultrafine circuits on flexible substrates for integrated circuit packaging is disclosed. This embodiment differs from Example 1 in that a nonionic surfactant, OP-10, and a cationic surfactant, cetyltrimethylammonium bromide, are used as pre-dip additives in the pre-activation pre-dip solution. The concentrations of both OP-10 and cetyltrimethylammonium bromide are 0.05 g / L. The remaining components and method are the same as those in Example 1.

[0108] Example 8

[0109] A method for suppressing electroless nickel plating and leakage plating on ultrafine circuits on flexible substrates for integrated circuit packaging. This embodiment differs from Example 1 in that, after completing the electroless nickel plating, electroless gold plating is performed. The remaining components and methods are the same as those in Example 1.

[0110] Comparative Example 1

[0111] A method for inhibiting electroless nickel permeation and leakage plating in ultrafine circuits on flexible substrates for integrated circuit packaging is disclosed. This comparative example differs from Example 1 in that an anionic surfactant is used as a predip additive. Specifically, sodium dodecyl sulfate (SDS) replaces cetyltrimethylammonium bromide (CTAB) in the predip solution before activation. The remaining components and methods are the same as those in Example 1.

[0112] The sample obtained in Comparative Example 1 was tested: the circuit with a line spacing of 12 μm had a slight plating phenomenon.

[0113] Comparative Example 2

[0114] A method for inhibiting electroless nickel plating and leakage during ultrafine circuitry on flexible substrates for integrated circuit packaging is disclosed. This comparative example differs from Example 1 in that an anionic surfactant is used as a predip additive. Specifically, sodium dodecylbenzenesulfonate (SDBS) replaces cetyltrimethylammonium bromide (CTAB) in the predip solution prior to activation. The remaining components and methods are the same as those in Example 1.

[0115] The sample obtained in Comparative Example 2 was tested: the circuit with a line spacing of 12 μm had a slight plating phenomenon.

[0116] Comparative Example 3

[0117] A method for suppressing electroless nickel permeation and leakage plating on ultrafine circuits on flexible substrates for integrated circuit packaging. This comparative example differs from Example 1 in that no pre-activation pre-dip treatment is performed. The flexible substrate in this comparative example has a line width and line spacing of 250 μm. The remaining components and methods are the same as in Example 1.

[0118] The sample obtained in Comparative Example 3 was tested: the circuit with a line spacing of 250 μm had a "skip plating" phenomenon, that is, plating could not be performed at all.

[0119] Comparative Example 4

[0120] A method for suppressing electroless nickel plating and leakage plating of ultrafine circuits on flexible substrates for integrated circuit packaging is provided. This comparative example differs from Example 1 in that no post-immersion treatment is performed. The remaining components and methods are the same as those in Example 1.

[0121] The sample obtained in Comparative Example 4 was tested: nickel bridging occurred in the circuit with a line spacing of 12 μm.

[0122] Comparative Example 5

[0123] A method for suppressing electroless nickel permeation and leakage plating on ultrafine circuits on flexible substrates for integrated circuit packaging. This embodiment differs from Example 1 in that a palladium chloride solution is used in place of a palladium sulfate solution in the activation step. The remaining components and methods are the same as those in Example 1.

[0124] The use of palladium chloride solution as palladium activation solution is more likely to cause plating. The possible reason is that in palladium sulfate solution, palladium is converted to [Pd(H2O)4] 2+ exists in the form of hydrated ions, palladium ions form complexes with water molecules and carry positive charges; in palladium chloride solution, palladium is mainly present in the form of [PdCl4] 2- The palladium ion is more likely to form a complex with the chloride ion and has a negative charge. The surfactant CTAB has a positively charged hydrophilic group. For [Pd(H2O)4] 2+ It has a certain inhibitory effect and can inhibit the plating. For the negatively charged [PdCl4] 2- However, it has a promoting effect, which leads to the adsorption of a large amount of palladium ions between the circuits and serious circuit plating phenomenon.

[0125] Comparative Example 6

[0126] A method for suppressing electroless nickel permeation and leakage plating on ultrafine circuits on flexible substrates for integrated circuit packaging. This comparative example differs from Example 1 in that neither pre-activation pre-dip nor post-dip treatment is performed. The remaining components and methods are the same as those in Example 1.

[0127] The samples prepared in Comparative Example 6 were tested: the circuits with a line width and line spacing of 12 μm had serious nickel bridging phenomenon, and the circuits with a line width of 250 μm had obvious plating leakage phenomenon.

[0128] Comparative Example 7

[0129] A method for inhibiting electroless nickel permeation and skipping during electroless nickel plating of ultrafine circuits on flexible substrates for integrated circuit packaging is disclosed. This comparative example differs from Example 1 in that the activation pre-dip solution comprises cetyltrimethylammonium bromide and N-methylthiourea, with the concentration of cetyltrimethylammonium bromide being 0.1 g / L and the concentration of N-methylthiourea being 0.01 g / L, and no post-dip treatment is performed. The remaining components and method are the same as those in Example 1.

[0130] The sample prepared in Comparative Example 7 was tested: the circuit with a line spacing of 12 μm had slight plating penetration, and the circuit with a line spacing of 250 μm had skipping plating.

[0131] Comparative Example 8

[0132] A method for suppressing electroless nickel permeation and leakage plating on ultrafine circuits on flexible substrates for integrated circuit packaging is disclosed. This comparative example differs from Example 1 in that no pre-dip treatment is performed, and the post-activation dip solution is modified to contain cetyltrimethylammonium bromide and N-methylthiourea, with the concentration of cetyltrimethylammonium bromide being 0.1 g / L and the concentration of N-methylthiourea being 0.01 g / L. The remaining components and method are the same as those in Example 1.

[0133] The sample prepared in Comparative Example 8 was tested: the circuit with a line spacing of 250 μm showed obvious plating leakage.

[0134] Experimental testing:

[0135] (1) Morphological characterization by metallographic microscope

[0136] The flexible substrate sample that has been subjected to the chemical nickel plating process in Example 1 was characterized by metallographic microscopy. Figure 1 and Figure 2 As shown. Figure 1 As can be seen from the figure, after the flexible substrate circuit with a line width and line spacing of 12 μm is subjected to chemical nickel plating by the method of Example 1, there is no nickel plating bridging phenomenon in the thin circuit area (12 μm). Figure 2 As can be seen in the figure, after the flexible circuit with a line width and line spacing of 250μm was electrolessly nickel-plated using the method of Example 1, there was no plating bridging phenomenon in the wide line (250μm) area. In addition, the metallographic morphology and line spacing measurement of the flexible substrate circuit with a line width and line spacing of 12μm before electroless nickel plating can be seen in the figure. Figure 3 For the metallographic morphology and line width and line spacing measurement of a flexible substrate circuit with a line width and line spacing of 250μm before chemical nickel plating, please refer to Figure 4 shown.

[0137] The morphology of the flexible substrate sample after the chemical nickel plating process in Comparative Example 1 was characterized by metallographic microscope. Figure 5 As shown. Figure 5 As can be seen, after the flexible substrate with a line width and line spacing of 12 μm is subjected to chemical nickel plating using the method of Comparative Example 1, a slight plating penetration problem occurs in the thin line (12 μm) area.

[0138] The morphology of the flexible substrate sample after the chemical nickel plating process in Comparative Example 3 was characterized by metallographic microscope. Figure 6 and Figure 7 As shown. Figure 6 As can be seen from the figure, after the flexible substrate with a line width and line spacing of 250 μm was electrolessly nickel-plated by the method of Comparative Example 3, obvious skipping plating occurred in the wide line (250 μm) area, that is, it was difficult to perform plating. Figure 7 As can be seen, after the flexible substrate with a line width and line spacing of 12 μm was subjected to chemical nickel plating using the method of Comparative Example 3, obvious skipping plating occurred in the thin line (12 μm) area.

[0139] The flexible substrate sample that completed the chemical nickel plating process in Comparative Example 4 was characterized by metallographic microscopy. Figure 8 As shown. Figure 8 As can be seen, after the flexible substrate with a line width and line spacing of 12 μm is subjected to chemical nickel plating using the method of Comparative Example 4, obvious nickel bridging phenomenon occurs in the thin line (12 μm) area.

[0140] The flexible substrate sample that completed the chemical nickel plating process in Comparative Example 6 was characterized by metallographic microscopy. Figure 9 As shown. Figure 9 As can be seen, after the flexible substrate with a line width of 250 μm is subjected to chemical nickel plating using the method of Comparative Example 6, obvious plating leakage occurs in the wide line (250 μm) area.

[0141] (2) Morphological characterization by scanning electron microscopy

[0142] The flexible substrate sample that has been subjected to the chemical nickel plating process in Example 1 was characterized by scanning electron microscopy. Figure 10 As shown. Figure 10 As can be seen, after the flexible substrate circuit with a line width and line spacing of 12 μm is subjected to chemical nickel plating using the method of Example 1, no nickel bridging phenomenon occurs in the thin circuit area (12 μm).

[0143] (3) EDS spectrum analysis of nickel plating layer

[0144] The flexible substrate sample that has been subjected to the chemical nickel plating process in Example 1 was analyzed using an energy dispersive spectrometer (EDS). Figure 11 As shown. Figure 11 It can be seen that there are obvious nickel peaks 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 chemical nickel plating process is completed.

[0145] (IV) Analysis of the principle of pre-preg treatment before activation

[0146] like Figure 12 As shown, surfactants generally have hydrophilic groups and hydrophobic groups. The present invention uses cationic or nonionic surfactants in the pre-dip solution to form a uniform adsorption layer on the circuit surface, thereby increasing the wetting ability of fine circuits and promoting the adsorption and adhesion of palladium ions. This allows the palladium ions to be easily and evenly distributed over the entire surface, reducing the possibility of local activation differences or excessive activation, and ensuring that the adsorption amount on both sides and the upper surface of the circuit is uniform. At the same time, the charge of the cationic surfactant or the hydrophobic group of the nonionic surfactant repel the palladium ions in the activation solution to a certain extent, preventing the enrichment of a large amount of palladium ions and avoiding the nickel bridging phenomenon 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 a uniform nickel deposition rate around the circuit, making the subsequent chemical nickel plating more uniform and reducing the possibility of plating leakage on fine circuits.

[0147] (V) Analysis of the principle of post-immersion treatment

[0148] like Figure 13 As shown, the sulfur in the thiourea compound in the post-dip solution of the present invention can combine with palladium ions to form a palladium-thiourea compound, which can inhibit the catalytic activity of the non-plated substrate palladium particles to a certain extent, reducing nickel plating deposition between fine lines. Simultaneously, the post-dip solution can also be adsorbed on the surface of the circuit, to a certain extent inhibiting the formation of the self-catalytic layer on the fine lines and reducing nickel bridging caused by excessive nickel plating speed.

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

Claims

1. A method for inhibiting electroless nickel plating and leakage plating of ultra-fine circuits on flexible substrates for integrated circuit packaging, characterized in that: The following steps are involved: S1. Pre-impregnation treatment before activation: pre-impregnation treatment of the flexible substrate with a pre-impregnation liquid before activation; the pre-impregnation liquid before activation comprises water and a pre-impregnation additive, and the pre-impregnation additive comprises a cationic surfactant and / or a non-ionic surfactant; and / or The cationic surfactant includes cetyltrimethylammonium bromide and / or benzyldimethylphenylammonium chloride; and / or the nonionic surfactant includes emulsifier OP-10; S2. Activation: After completing the pre-impregnation treatment before activation, the flexible substrate is activated using a palladium activation solution; S3. Post-immersion treatment: After activation is completed, the flexible substrate is subjected to post-immersion treatment using a post-immersion liquid; the post-immersion liquid includes water and a post-immersion additive, and the post-immersion additive is a thiourea compound.

2. The method for suppressing electroless nickel plating and leakage plating of ultra-fine circuits on flexible substrates for integrated circuit packaging according to claim 1, characterized in that: In step S1, the pre-activation pre-dip solution comprises the following components: water, 0.05 g / L to 1 g / L of cetyltrimethylammonium bromide and / or 0.05 g / L to 1 g / L of benzyldimethylphenylammonium chloride; and / or 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.

3. The method for suppressing electroless nickel plating and leakage plating of ultra-fine circuits on flexible substrates for integrated circuit packaging according to claim 1, characterized in that: In step S3, the thiourea compound is a compound having a structure shown in formula I; Wherein, R1 and R2 are respectively one of a hydrogen atom, an alkyl group, an amino group or a phenyl group, and only one of R1 and R2 can be a phenyl group.

4. The method for suppressing electroless nickel plating and leakage plating of ultra-fine circuits on flexible substrates for integrated circuit packaging according to claim 3, characterized in that: The thiourea compound is at least one of thiourea, N-methylthiourea, phenylthiourea and thiosemicarbazide.

5. The method for suppressing electroless nickel plating and leakage plating of ultra-fine circuits on flexible substrates for integrated circuit packaging according to claim 1, wherein: In step S1, the concentration of the pre-soak additive in the pre-soak solution before activation is 0.05 g / L-2 g / L; and / or In step S3, the concentration of the post-immersion additive in the post-immersion liquid is 0.01 g / L to 1 g / L.

6. The method for suppressing electroless nickel plating and leakage plating of ultra-fine circuits on flexible substrates for integrated circuit packaging according to claim 1, characterized in that: The step S1 includes performing a micro-etching treatment on the flexible substrate for 1 to 2 minutes before the pre-preg treatment before activation; The micro-etching solution comprises the following components: water, 25 g / L-100 g / L of sodium persulfate, and 30 g / L-50 g / L of sulfuric acid.

7. A method for suppressing electroless nickel plating and leakage plating of ultra-fine circuits on flexible substrates for integrated circuit packaging according to claim 6, characterized in that: Before the micro-etching treatment, the flexible substrate is further subjected to degreasing treatment; after the micro-etching treatment and before the pre-activation pre-dip treatment, the flexible substrate is further subjected to pickling treatment using sulfuric acid.

8. The method for suppressing electroless nickel plating and leakage plating of ultra-fine circuits on flexible substrates for integrated circuit packaging according to claim 1, characterized in that: In the step S1, the temperature of the pre-impregnation treatment is 25°C to 30°C, and the time of the pre-impregnation treatment is 1 minute to 5 minutes; the temperature of the post-impregnation treatment is 25°C to 30°C, and the time of the post-impregnation treatment is 10 seconds to 60 seconds.

9. A process for chemical nickel plating of ultra-fine circuits on flexible substrates for integrated circuit packaging, characterized in that: The method comprises a pre-treatment process and a chemical nickel plating process; the pre-treatment process adopts the method of suppressing chemical nickel plating penetration and leakage plating of ultra-fine circuits on flexible substrates according to any one of claims 1 to 8.

10. The process for chemical nickel plating of ultra-fine circuits on flexible substrates for integrated circuit packaging according to claim 9, characterized in that: In the chemical nickel plating process, the flexible substrate that has completed the pre-treatment process is placed in a nickel plating solution, and the temperature of the nickel plating solution is controlled to be 70° C.-90° C., the pH value is 4.0-6.0, and the chemical nickel plating time is 10 min-50 min; and / or After the electroless nickel plating is completed, the electroless gold plating is continued.

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