Electroplating method for forming Au / Ag alloy bump

Abstract

The invention discloses an electroplating method for forming an Au / Ag alloy bump. The electroplating method comprises the following steps: carrying out electroplating treatment on a base material in an Au / Ag alloy plating solution containing gold salt and silver salt; the electroplating process comprises two stages, and different current densities are set; in the first stage, alloy electro-deposition is carried out by adopting the first current density; in the second stage, electroplating is continued by adopting second current density in the later period of alloy layer formation; the current densities of the two stages are different, so that component gradient distribution from bottom to top is formed in the alloy layer.

Description

Technical Field

[0001] The present invention is an electroplating method for forming Au / Ag alloy bumps. Background Art

[0002] In the processes of modern microelectronic packaging and integrated circuit manufacturing, metal bumps play a crucial role as important structures for realizing electrical connection and mechanical support between chips and substrates or circuits. Common bump materials include pure gold, pure silver, tin alloys, copper, etc. Among them, gold is widely used in high-end packaging fields due to its excellent electrical conductivity, chemical stability, and good bonding properties. However, the high cost of pure gold materials restricts their application in a wider range.

[0003] To reduce costs while maintaining some key properties, Au / Ag alloy has become an ideal alternative material. Silver has good electrical and thermal conductivities and low cost. After forming an alloy with gold, it can inherit the stability and bonding characteristics of gold to a certain extent. However, in traditional Au / Ag alloy electroplating processes, it is often difficult to accurately control the gold-silver ratio in the alloy, and the alloy composition usually shows a uniform distribution in the thickness direction, making it difficult to achieve optimized interface design.

[0004] In practical applications, the chip soldering and bonding processes often require a relatively high gold content at the top of the bumps to ensure interface reaction activity and reliability, while the gold content at the bottom can be appropriately reduced to cut costs. Therefore, how to form Au / Ag alloy bumps with a composition gradient distribution from the bottom to the top during electroplating has become a key technical problem concerned in the industry. In addition, to achieve process stability and industrial scalability, systematic optimization is also needed in the setting of electroplating parameters (such as current density, time, liquid flow rate, etc.).

[0005] Therefore, there is an urgent need for a new electroplating method for Au / Ag alloy bumps that can effectively control the alloy composition distribution and balance cost and performance to meet the multiple technical requirements for bump structures in high-performance integrated packaging. Summary of the Invention

[0006] The purpose of the present invention is to solve the above-mentioned deficiencies of the prior art and provide an electroplating method for forming Au / Ag alloy bumps.

[0007] An electroplating method for forming Au / Ag alloy bumps includes the following steps:

[0008] Performing electroplating treatment on a substrate in an Au / Ag alloy plating solution containing a gold salt and a silver salt, where the concentration ratio of the gold salt to the silver salt in the plating solution is 1:9;

[0009] The electroplating process includes two stages, with different current densities set respectively:

[0010] In the first stage, alloy electroplating is carried out at the first current density;

[0011] In the second stage, electroplating is continued at the second current density in the later stage of the formation of the alloy layer;

[0012] The current densities in the two stages are different to form a compositional gradient distribution from the bottom to the top in the alloy layer.

[0013] Furthermore, the first current density is 0.2 - 0.8 A / dm 2 , and the second current density is 1 - 5 A / dm 2 .

[0014] Furthermore, the duration of electroplating in the second stage is 30 - 120 seconds.

[0015] Furthermore, the duration of electroplating in the first stage is 1000 - 2400 seconds.

[0016] Furthermore, the thickness of the alloy bump is 5 - 11 μm, and the gold content purity within the thickness range of 1 - 2 μm at the top is above 80%.

[0017] Furthermore, the electroplating solution maintains a flow rate of 10 - 15 L / min and a shaking frequency of 10 - 30 Hz throughout the electroplating process.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0019] The compositional gradient structure improves the interface performance: By introducing two-stage current density control during electroplating, an Au / Ag alloy bump with a gold content gradient structure from the bottom to the top is formed. The top region is rich in gold (purity above 80%), significantly improving the interface wettability, conductivity, and connection reliability of subsequent soldering or bonding.

[0020] Cost optimization: The bottom is mainly composed of silver with lower cost, and a higher proportion of gold elements is used only in the top region, effectively controlling the usage of precious metals and significantly reducing the material cost on the premise of ensuring functional performance.

[0021] Structural stability and precise thickness control: The electroplating time is controlled at 1000 - 2400 seconds in the first stage and 30 - 120 seconds in the second stage respectively, and the overall thickness is controlled within the range of 5 - 11 μm, achieving the stability and repeatability of the electro-deposited structure, which is beneficial to the consistency control of subsequent packaging processes.

[0022] High-quality electro-deposited surface: The electroplating solution maintains a flow rate of 10 - 15 L / min and a shaking frequency of 10 - 30 Hz throughout the process, effectively suppressing the electrode polarization phenomenon, promoting the rapid exchange of metal ions and the uniformity of deposition, and reducing surface defects such as holes and cracks.

[0023] Enhance process adaptability: By adopting electroplating parameters with strong generality (such as conventional current density range and liquid flow rate), it is convenient for industrial promotion and compatibility with existing PCB / IC packaging lines, and has good manufacturing adaptability and technical extensibility.

[0024] Improve antioxidant capacity and corrosion resistance: The top gold-rich layer significantly enhances the antioxidant and corrosion resistance of the alloy bumps, and enhances the long-term stability of the product in harsh usage environments. Brief Description of the Drawings

[0025] Figure 1 is a flowchart of an electroplating method for forming Au / Ag alloy bumps. Detailed Embodiments

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

[0027] An electroplating method for forming Au / Ag alloy bumps includes the following steps: electroplating a substrate in an Au / Ag alloy plating solution containing gold salt and silver salt, and the concentration ratio of gold salt to silver salt in the plating solution is 1:9; the electroplating process includes two stages, and different current densities are set respectively: in the first stage, alloy electro-deposition is carried out using a first current density; in the second stage, electroplating is continued using a second current density in the later stage of the formation of the alloy layer; the current densities of the two stages are different to form a composition gradient distribution from the bottom to the top in the alloy layer.

[0028] This embodiment is based on the principle of the reduction of metal ions on the electrode surface during the electro-deposition process. By regulating the ratio of gold salt to silver salt in the electroplating solution and setting the current density in stages, the deposition rate and ratio of gold and silver in the Au / Ag alloy can be controlled. Adopting a lower current density in the first stage helps to promote the uniform initial deposition of the alloy components; increasing the current density in the second stage makes the deposition rate faster and enhances the priority of gold ion reduction, so as to obtain a structure with a higher gold content at the top of the alloy layer. This staged control strategy promotes the formation of an obvious composition gradient from the bottom to the top of the entire alloy layer, that is, the silver content is higher at the bottom and the gold content is higher at the top, thereby optimizing the physical and electrical properties of the alloy layer.

[0029] This method realizes the gradient regulation of the composition of the Au / Ag alloy layer through simple two-stage current control, effectively improving the functionality of the electroplated layer structure. For example, in microelectronic packaging, the high-gold-content area at the top is beneficial to subsequent welding and bonding performance, while the area with a higher silver content at the bottom takes into account cost control and conductivity. In addition, since no complex process control links are introduced, this method has good industrial feasibility and replicability.

[0030] In a possible implementation, the first current density is 0.2 - 0.8 A / dm 2 , and the second current density is 1 - 5 A / dm 2 .

[0031] By setting different current densities in two stages, the composition regulation during the alloy electro - deposition process is achieved. In the first stage, a lower current density (0.2 - 0.8 A / dm 2 ) is used, which can reduce the reduction rate of gold ions, making the silver content in the initial stage of the alloy layer relatively high. In the second stage, a higher current density (1 - 5 A / dm 2 ) is adopted. Since the standard electrode potential of gold ions is relatively high, they are more easily reduced at high current densities, thus promoting the increase of gold content in the later stage of deposition, forming the required composition gradient distribution.

[0032] This current density configuration makes the electro - deposition process have good controllability and repeatability, ensuring the formation of a gradient structure with an increasing gold content from bottom to top, effectively improving the welding adaptability and surface corrosion resistance of the alloy layer, while maintaining the rationality of the overall cost.

[0033] In a possible implementation, the duration of electroplating in the second stage is 30 - 120 seconds.

[0034] Controlling the duration of the second stage helps to regulate the thickness of the gold content at the top of the alloy. In the time range of 30 - 120 seconds, the high current density enables the rapid reduction of gold ions, making gold mainly deposited on the surface layer, thus forming a high - purity gold coating in the top region of the finally formed alloy layer, effectively achieving the required composition gradient.

[0035] By reasonably setting the electroplating time in the second stage, it can ensure the formation of a gold - enriched layer with a moderate thickness, enabling the top region to maintain good electrical conductivity and oxidation resistance while avoiding material waste, and improving the overall structural performance and process economy.

[0036] In a possible implementation, the duration of electroplating in the first stage is 1000 - 2400 seconds.

[0037] The first stage is the main deposition stage of the alloy layer. By controlling the electroplating time between 1000 and 2400 seconds, it can ensure the formation of a base layer structure with an appropriate thickness and a relatively high silver content. The low - current - density deposition within this time range is conducive to uniform deposition and avoiding excessive internal stress, thereby improving the stability of the overall structure.

[0038] This duration setting achieves good electroplating uniformity and structural integrity, providing a solid foundation for the subsequent second-stage gold enrichment, while reducing the risk of silver oxidation, helping to improve the underlying electrical conductivity and overall corrosion resistance.

[0039] In a possible implementation, the thickness of the alloy bump is 5 - 11 μm, and the gold content purity within the top 1 - 2 μm thickness range is above 80%.

[0040] Combined with multi-stage current density control and deposition time adjustment, during the entire electroplating process, the alloy that grows layer by layer forms a structure with an overall thickness of 5 - 11 μm, where the top forms a high-purity region with a gold content ≥ 80% under the conditions of high current density and rapid deposition in a short period, effectively meeting the requirements of high-performance package connection.

[0041] This structure realizes the top function optimization on the basis of ensuring overall cost control, enhancing the welding reliability and the stability of electrical connection. The high-purity gold surface layer also effectively improves the antioxidant and corrosion resistance properties, making the alloy bump more adaptable to the high-density interconnect environment.

[0042] In a possible implementation, the electroplating solution maintains a flow rate of 10 - 15 L / min and a shaking frequency of 10 - 30 Hz during the entire electroplating process.

[0043] Maintaining a stable flow rate and an appropriate shaking frequency helps the uniform distribution of metal ions in the electroplating solution, avoiding ion concentration gradients and polarization phenomena, and improving the stability of the electrodeposition process. A flow rate of 10 - 15 L / min can effectively carry away the reaction products and supplement fresh ions, while a shaking frequency of 10 - 30 Hz enhances the solution perturbation, which is beneficial to improving the deposition rate and uniformity.

[0044] This dynamic control method of the electroplating solution significantly improves the quality of the alloy layer, reduces surface defects and compositional non-uniformity, while optimizing the electroplating efficiency and equipment utilization rate, and enhancing the repeatability and industrial adaptability of the process.

[0045] In summary, this process method involves electroplating a substrate in an Au / Ag alloy plating solution containing gold salt and silver salt, where the concentration ratio of gold salt to silver salt in the plating solution is 1:9. The electroplating process includes two stages, with different current densities set respectively to form a compositional gradient distribution from the bottom to the top, specifically including:

[0046] In the first stage, a first current density of 0.2 - 0.8 A / dm 2 is used for alloy electrodeposition, and the electroplating duration is 1000 - 2400 seconds;

[0047] In the second stage, a second current density of 1 - 5 A / dm 2Continue electroplating for 30 - 120 seconds;

[0048] The overall thickness of the alloy bump formed under the action of the above two stages is 5 - 11 μm, and the gold content purity within the thickness range of 1 - 2 μm at the top is above 80%;

[0049] During electroplating, the flow rate of the electroplating solution is maintained at 10 - 15 L / min, and a shaking operation is performed at a frequency of 10 - 30 Hz to enhance the uniformity of ion distribution and the electro-deposition effect.

[0050] Working principle: The electroplating method of the Au / Ag alloy bump described in the present invention effectively realizes the gradient regulation of the alloy composition along the thickness direction by setting precise process parameters, combining multi-stage current density control, electroplating time management, and dynamic adjustment of the electroplating solution. Its technical basis is the principle of electrochemical deposition, that is, metal ions are reduced and deposited on the surface of the conductive substrate under the action of an electric field to form a metal layer.

[0051] In the electroplating solution, the concentration ratio of gold salt to silver salt is 1:9, and the silver ion concentration is relatively high, which is beneficial to preferentially deposit to form a silver-rich bottom layer structure under low current density conditions. In the first stage, a current density of 0.2 - 0.8 A / dm 2 is adopted and maintained for 1000 - 2400 seconds to obtain an initial alloy layer with uniform thickness and stable composition. Subsequently, in the second stage, by increasing the current density to 1 - 5 A / dm 2 and controlling the electroplating duration to 30 - 120 seconds, the reduction rate of gold ions is accelerated using the high current density, and a gold-rich surface layer is rapidly deposited on the surface of the alloy layer.

[0052] The entire electroplating process is carried out under the conditions of maintaining the electroplating solution flow rate of 10 - 15 L / min and the shaking frequency of 10 - 30 Hz, ensuring the continuous renewal of metal ions in the solution, reducing electrode polarization and component gradient deviation, and thus improving the stability and consistency of electroplating quality.

[0053] This technical solution makes the formed Au / Ag alloy bump have an obvious gold content gradient structure from bottom to top by controlling the current density and time in stages and combining the dynamic condition adjustment of the electroplating solution. The gold content purity in the top 1 - 2 μm region can reach above 80%, and the overall thickness is controlled within the range of 5 - 11 μm, thereby effectively controlling costs while meeting functional requirements.

[0054] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An electroplating method for forming Au / Ag alloy bumps, characterized in that, Including the following steps: Electroplating a substrate in an Au / Ag alloy plating solution containing a gold salt and a silver salt; The electroplating process includes two stages with different current densities set respectively: In the first stage, alloy electro-deposition is carried out using a first current density; In the second stage, electroplating is continued using a second current density in the later stage of the formation of the alloy layer; The current densities of the two stages are different to form a compositional gradient distribution from the bottom to the top in the alloy layer.

2. The electroplating method according to claim 1, wherein The first current density is 0.2 - 0.8 A / dm 2 , and the second current density is 1 - 5 A / dm 2 .

3. The electroplating method according to claim 2, characterized in that, The duration of the electroplating in the second stage is 30 - 120 seconds.

4. The electroplating method according to claim 3, characterized in that The duration of the electroplating in the first stage is 1000 - 2400 seconds.

5. The electroplating method according to claim 4, wherein The thickness of the alloy bump is 5 - 11 μm, and the gold content purity within the thickness range of 1 - 2 μm at the top is above 80%.

6. The electroplating method according to claim 5, characterized in that, The flow rate of the plating solution is maintained at 10 - 15 L / min and the shaking frequency is 10 - 30 Hz during the whole electroplating process.

7. The electroplating method according to claim 1, characterized in that, The concentration ratio of the gold salt to the silver salt in the plating solution is 1:9.

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