Chemical gold plating anti-corrosion process for gold-silver alloy or pure silver bump

Abstract

The invention discloses a chemical gold plating anti-corrosion process for a gold-silver alloy or pure silver bump. The chemical gold plating anti-corrosion process comprises the following steps: forming a metal bump structure on the surface of a substrate; performing patterning processing on the metal bump structure to form a metal bump with a required pattern; carrying out pretreatment on the metal bump, wherein the pretreatment comprises acid washing and deionized water rinsing; immersing the pretreated metal bump into a chemical gold plating solution to form a continuous metal gold layer on the surface of the metal bump; and rinsing and drying the gold-plated structure to obtain the metal bump structure with the anti-corrosion performance.

Description

Technical Field

[0001] The invention relates to a chemical gold plating anti-corrosion process for gold-silver alloy or pure silver bumps. Background Art

[0002] In the fields of microelectronics packaging, MEMS device manufacturing, and precision connection, metal bump structures are widely used for electrical interconnection and mechanical support between chips and substrates. Gold-silver alloy and pure silver bumps are important materials in the current electronic packaging industry due to their excellent conductivity and good solderability. However, silver and its alloys are susceptible to oxidation and sulfidation in air, resulting in the formation of electrically insulating silver oxide or silver sulfide on the surface, which reduces connection reliability and affects the overall performance stability of the device.

[0003] To improve the corrosion resistance of metal bumps, surface coating technology is often used to protect them. Common methods for forming protective layers include gold electroplating, nickel / gold electroplating stacks, vapor deposition, and chemical plating. While gold electroplating is widely used on the surfaces of integrated circuit lead frames and connectors, it places high demands on the dimensional consistency of the bump structure, requires an external power supply, and ensures uniform electrode contact surfaces. Otherwise, uneven edge coating or localized stress concentration can occur, impacting the packaging yield.

[0004] In contrast, electroless gold plating is an autocatalytic process that deposits gold layers without the need for an applied current, relying on the reaction of a reducing agent with gold ions. It can produce uniform, dense coatings on complex surfaces and is particularly suitable for metal treatment of three-dimensional structures and irregular surfaces. However, existing electroless gold plating techniques are primarily targeted at metal substrates such as copper and nickel. Research on gold plating processes for silver-based materials, particularly for microstructured bumps, is still immature, facing technical bottlenecks such as poor adhesion, discontinuous coatings, and difficulty in thickness control.

[0005] Therefore, developing a high-stability chemical gold plating anti-corrosion process suitable for gold-silver alloy or pure silver bumps, which has good adhesion control ability, stable gold layer growth characteristics and a simple process flow, is an important technical demand facing the current electronic packaging and interconnection fields. Summary of the Invention

[0006] The purpose of the present invention is to solve the above deficiencies in the prior art and to provide a chemical gold plating anti-corrosion process for gold-silver alloy or pure silver bumps.

[0007] A chemical gold plating anti-corrosion process for gold-silver alloy or pure silver bumps, comprising the following steps:

[0008] forming a metal bump structure on a surface of the substrate;

[0009] Performing patterning on the metal bump structure to form a metal bump of a desired pattern;

[0010] Pre-treating the metal bumps, wherein the pre-treatment includes pickling and rinsing with deionized water;

[0011] Immersing the pre-treated metal bumps in a chemical gold plating solution to form a continuous metal gold layer on their surfaces;

[0012] The gold-plated structure is rinsed and dried to obtain a metal bump structure with corrosion resistance.

[0013] Furthermore, the metal bump is a gold-silver alloy or a pure silver bump, wherein the mass ratio of gold to silver in the gold-silver alloy is 1–3:9–7.

[0014] Furthermore, the step of forming the metal bump includes electroplating under the condition of a current density of 0.5 ASD, an electroplating time of 1800 seconds, and an electroplating thickness of 7-11 μm.

[0015] Furthermore, during the electroplating process, the flow rate of the plating solution is maintained at 10–15 L / min, and the shaking frequency is applied at 10–30 Hz.

[0016] Furthermore, the patterning process includes removing the photoresist, performing alloy etching, and etching the titanium-tungsten metal layer.

[0017] Furthermore, the pickling uses a 5% citric acid solution, and the treatment time is 1-5 minutes.

[0018] Furthermore, the chemical gold plating solution is a non-electrolytic gold salt solution, the reaction temperature of the chemical gold plating step is 50-65° C., and the reaction time is 5-60 minutes.

[0019] Furthermore, the thickness of the metal gold layer is 0.05-0.5 μm.

[0020] Furthermore, the rinsing step is a rapid deionized water rinsing, and the drying step is a hot air drying or nitrogen drying, and the drying temperature is 80-120°C.

[0021] Beneficial Effects: Compared with existing technologies, the chemical gold plating anti-corrosion process provided by this invention significantly improves the corrosion resistance of gold-silver alloy or pure silver bumps in microelectronic devices and high-density packaging applications. By depositing a dense and continuous gold layer on the metal bump surface, it effectively isolates the intrusion of corrosive media such as oxygen, water vapor, and sulfides, preventing metal oxidation, discoloration, and performance degradation, extending the device's service life and ensuring the stability of its electrical performance.

[0022] This process uses a non-electrolytic method for metal deposition, eliminating the need for an external power source and avoiding plating defects caused by uneven current distribution. It is particularly suitable for treating metal surfaces with complex structures or high-density patterns. Compared to traditional electroplating processes, it offers significant advantages in consistency control, deposition uniformity, and adaptability to structural diversity, making it particularly well-suited for gold plating on small, irregular bump surfaces.

[0023] By introducing electroplating flow rate control and shaking frequency adjustment, the quality stability of the metal bump formation stage is further improved. The patterning process ensures pattern accuracy and interface integrity, providing a high-quality substrate for subsequent gold plating. A mild citric acid solution is used in the pretreatment stage. This solution is not only environmentally friendly and non-toxic, but also effectively cleans the metal surface and improves the adhesion strength and density of the gold layer.

[0024] In addition, the process flow of the present invention is simple, the process conditions are easy to control, and it is suitable for large-scale industrial production, which helps to reduce overall manufacturing costs. At the same time, the chemical gold plating solution formula used can be customized according to environmental protection and functional requirements, which is conducive to meeting the technical specifications and regulatory requirements of different scenarios, and enhancing the flexibility of the technical route and the breadth of commercial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the process flow chart of this example. DETAILED DESCRIPTION

[0026] In order to deepen the understanding of the present invention, the present invention will be further described in detail below with reference to embodiments and drawings. The embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0027] A chemical gold plating anti-corrosion process for gold-silver alloy or pure silver bumps, comprising the following steps:

[0028] First, a metal bump structure is formed on the substrate surface. The metal bumps are made of a gold-silver alloy or pure silver, with a mass ratio of gold to silver of 1–3:9–7. The metal bumps are formed by electroplating at a current density of 0.5 ASD for 1800 seconds to a thickness of 7–11 μm. During this process, the plating solution flow rate is controlled at 10–15 L / min, and a shaking frequency of 10–30 Hz is applied to ensure uniformity and adhesion of the coating.

[0029] Subsequently, the metal bump structure is patterned, which includes removing the photoresist, etching the alloy, and etching the titanium-tungsten metal layer to accurately form the desired metal pattern structure.

[0030] The next step is pretreatment. First, a 5% citric acid solution is used for pickling for 1–5 minutes to remove surface oxides and impurities. This is followed by a quick rinse with deionized water to remove residual acid and prevent secondary contamination.

[0031] The pretreated metal bumps are immersed in a non-electrolytic gold plating solution. A chemical reduction reaction is performed at a temperature of 50–65°C for 5–60 minutes, forming a continuous, dense gold layer on the surface of the metal bumps. This layer, with a thickness of 0.05–0.5 μm, exhibits excellent corrosion resistance and electrical properties.

[0032] Finally, the gold-plated structure is post-processed, i.e., quickly rinsed with deionized water to remove residual reactants, and dried by hot air drying or nitrogen blowing at a temperature of 80–120°C to obtain a stable, reliable metal bump structure with corrosion resistance.

[0033] Working Principle: This process relies on the principle of electroless reduction deposition, depositing a dense, continuous layer of gold on the surface of gold-silver alloy or pure silver bumps to effectively protect the metal structures in microelectronic devices. The basic principle is to use a chemical reduction reaction to reduce gold ions in the plating solution and deposit them on the pretreated metal surface, forming a uniform metal coating that effectively blocks corrosion from external corrosive media.

[0034] In the initial stage of the process, electroplating is used to form the metal bump structure on the substrate surface. The electroplating process ensures that the metal layer thickness and structural properties meet the preset standards by controlling the current density, plating time, and liquid flow disturbance parameters. To achieve precise structural layout, the process continues with patterning steps, including photoresist stripping, alloy etching, and titanium-tungsten layer etching. This effectively defines the metal deposition area and improves the selectivity and precision of subsequent processing.

[0035] For surface treatment, pickling with 5% citric acid removes the metal surface oxide layer and organic residues, improving the adhesion of the coating. Rinsing with deionized water then removes residual acid, prevents contamination of the plating solution, and maintains the active state of the substrate surface.

[0036] The core electroless gold plating process, without the need for an applied current, involves immersing pretreated metal bumps in a non-electrolytic gold salt solution at a controlled temperature between 50–65°C for 5–60 minutes. This allows gold ions to be stably deposited under the action of a reducing agent, forming a metallic gold layer with excellent density and coverage. This layer effectively encapsulates the base metal and enhances its electrochemical stability.

[0037] The final step includes a quick rinse and hot air or nitrogen drying to ensure the integrity of the coating and remove surface moisture. The various steps of the entire process work together to not only simplify the process but also take into account the reliability and controllability of the process.

[0038] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A chemical gold plating anti-corrosion process for gold-silver alloy or pure silver bumps, characterized in that: The steps include: forming a metal bump structure on a surface of the substrate; Performing patterning on the metal bump structure to form a metal bump of a desired pattern; Pre-treating the metal bumps, wherein the pre-treatment includes pickling and rinsing with deionized water; Immersing the pre-treated metal bumps in a chemical gold plating solution to form a continuous metal gold layer on their surfaces; The gold-plated structure is rinsed and dried to obtain a metal bump structure with corrosion resistance.

2. The method according to claim 1, characterized in that The metal bump is a gold-silver alloy or a pure silver bump, wherein the mass ratio of gold to silver in the gold-silver alloy is 1-3:9-7.

3. The chemical gold plating anti-corrosion process according to claim 2, wherein: The step of forming the metal bump includes electroplating under the condition of a current density of 0.5 ASD, an electroplating time of 1800 seconds, and an electroplating thickness of 7-11 μm.

4. The chemical gold plating anti-corrosion process according to claim 3, wherein: During the electroplating process, the flow rate of the plating solution was maintained at 10–15 L / min, and the shaking frequency was applied at 10–30 Hz.

5. The chemical gold plating anticorrosion process according to claim 1, wherein: The patterning process includes removing the photoresist, performing alloy etching, and etching the titanium tungsten metal layer.

6. The chemical gold plating anti-corrosion process according to claim 1, characterized in that: The pickling process uses a 5% citric acid solution and the treatment time is 1-5 minutes.

7. The chemical gold plating anticorrosion process according to claim 1, characterized in that: The chemical gold plating solution is a non-electrolytic gold salt solution. The reaction temperature of the chemical gold plating step is 50-65° C., and the reaction time is 5-60 minutes.

8. The chemical gold plating anti-corrosion process according to claim 7, characterized in that: The thickness of the metal gold layer is 0.05-0.5 μm.

9. The chemical gold plating anticorrosion process according to claim 1, characterized in that: The rinsing step is a quick deionized water rinse, and the drying step is a hot air drying or nitrogen drying, and the drying temperature is 80-120°C.

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