Electroplating solution and electroplating method of nickel-gold alloy coating for MEMS (Micro Electro Mechanical System) technology

Abstract

The invention discloses an electroplating solution and an electroplating method of a nickel-gold alloy coating for an MEMS technology, the electroplating solution does not contain cyanide, and each liter of the electroplating solution comprises 22-31 g of sodium gold sulfite, 65-87 g of nickel sulfate, 5.5-6.5 g of nickel chloride, 65-75 g of sodium dihydrogen phosphate, 76-81 g of disodium hydrogen phosphate, 2.0-3.0 g of saccharin sodium salt, 0.5-0.8 g of potassium sodium tartrate, 1.9-3.4 g of ethylenediamine tetraacetic acid (EDTA), 5.5-6.2 g of sulfophenolimine benzoate, 0.1-0.2 g of thiosalicylic acid, 0.05-0.1 g of 2-ethylhexyl sodium sulfate, 0.10-0.20 g of 3, 4, 5-trimethyl-1, 3, 4-trimethyl-1, 3, 4-trimethyl-1, 3, 4-trimethyl-1, 3, 4- the component A is 1, 3, 5-trihydroxy sodium benzoate, and the balance of deionized water; the electroplating method comprises the following steps: sputtering a seed layer on the surface of a substrate; etching the required coating morphology on the surface of the seed layer; carrying out pretreatment on the etched substrate; preparing an electroplating solution so as to immerse the pretreated substrate into the electroplating solution; electrifying the substrate and the electroplating liquid to form a nickel-gold plating layer on the surface of the substrate; the MEMS device is cleaned and dried; the process is simple and convenient to operate, and the appearance, performance and quality of the plating layer are improved.

Description

Technical Field

[0001] The present application relates to the field of electroplating technology, and in particular to an electroplating solution and an electroplating method for a nickel-gold alloy plating layer used in MEMS technology. Background Art

[0002] Electroplating gold can be divided into soft gold plating and hard gold plating. Soft gold generally refers to pure gold, while hard gold is the product of co-deposition of gold ions and other metal / non-metallic element ion groups. The doped elements can promote the grain refinement of the gold plating layer, thereby increasing the hardness of the gold plating layer. In the actual production of MEMS technology, hard gold plays an important role. Hard gold electroplating can provide extremely strong conductivity and excellent corrosion resistance, which can prevent oxidation and corrosion on the surface of MEMS devices. In addition, hard gold electroplating can also provide good welding and mechanical properties, and is suitable for enhanced electroplating at the connection between MEMS devices and PCB substrates. Among the many soft gold plating solution hardeners, nickel salt hardeners are the first choice because they will bring relatively low internal stress in the plating and relatively easy concentration control methods.

[0003] Most of the existing electroplating gold plating solution systems used for MEMS technology are cyanide-containing systems. Although the traditional cyanide gold plating solution has the characteristics of stability and reliability, fine crystallization of the coating, and good bonding strength, the coating obtained by using the cyanide plating solution has high residual internal stress, the plating solution corrodes the photoresist, the hydrogen evolution reaction is serious, and it is extremely harmful to the environment and the human body of the operator. With the continuous improvement of green production requirements, it is an inevitable trend for the cyanide-free gold plating process to replace the cyanide-containing process.

[0004] The existing MEMS structure hard gold plating process generally adopts the process route of "first doping elements to lay the base - then depositing soft gold". Although this process simplifies the configuration of the plating solution and the difficulty of operation, the resulting coating is prone to stress concentration, delamination, warping and shedding at the connection, and non-isotropic mechanical properties. These unfavorable conditions will be magnified in MEMS devices with micron- or even nano-scale structures, and thus appear more frequently in actual production, causing unnecessary losses. Summary of the invention

[0005] In order to solve the above technical problems, the purpose of this application is to provide an electroplating solution and an electroplating method for nickel-gold alloy plating for MEMS technology.

[0006] To achieve the above-mentioned purpose, in a first aspect, the present application provides an electroplating solution for nickel-gold alloy plating for MEMS technology, which does not contain cyanide, and each liter of the electroplating solution includes: 22-31g sodium gold sulfite, 65-87g nickel sulfate, 5.5-6.5g nickel chloride, 65-75g sodium dihydrogen phosphate, 76-81g disodium hydrogen phosphate, 2.0-3.0g sodium saccharin, 0.5-0.8g potassium sodium tartrate, 1.9-3.4g ethylenediaminetetraacetic acid (EDTA), 5.5-6.2g benzoic acid sulfonyl imine, 0.1-0.2g thiosalicylic acid, 0.05-0.1g 2-ethylhexyl sodium sulfate, 0.10-0.20g sodium 3,4,5-trihydroxybenzoate, and the balance is deionized water.

[0007] In the above technical solution, it is further preferred that the pH value of the electroplating solution is 4-6.

[0008] In the above technical solution, it is further preferred that the temperature of the electroplating solution is 50°C to 55°C.

[0009] By changing the content and proportion of the main salt in the electroplating solution, the type and content of additives and the electroplating parameters, the electrodeposition rate in the electroplating process can be accelerated, the production cycle can be shortened, and the economic effect can be improved; the electroplating solution has low toxicity, is stable and reliable, and has improved cathode polarization and dispersion capabilities, while meeting the requirements of safe production and green production.

[0010] In a second aspect, the present application provides an electroplating method for a nickel-gold alloy coating for MEMS technology, the electroplating method comprising: Step 1, sputtering a seed layer on the surface of the substrate; Step 2, etching the desired coating morphology on the surface of the seed layer by applying photoresist, developing, flooding, hardening and photolithography; Step 3, pre-treating the etched substrate; Step 4, preparing an electroplating solution according to the ratio of the electroplating solution provided in this application, and immersing the pre-treated substrate in the prepared electroplating solution; Step 5, the substrate and the electroplating solution are energized to form a nickel-gold plating layer on the surface of the substrate; Step six, taking out the MEMS device with the nickel-gold plating layer formed on the surface from the electroplating solution, and cleaning and drying it.

[0011] In the above technical solution, it is further preferred that in the step 1, the material of the seed layer is an inactive metal.

[0012] In the above technical solution, it is further preferred that in the step three, the pre-treatment includes substrate roughening, activation and cleaning.

[0013] In the above technical solution, it is further preferred that in the step 4, the pH value of the electroplating solution is 4.3 to 4.8.

[0014] In the above technical solution, it is further preferred that in the step five, the electroplating solution is contained in an electroplating tank, the substrate is immersed in the electroplating solution and electrically connected to a DC power supply, and the electroplating solution is stirred in the electroplating tank at a stirring rate of 150 to 300 r / min.

[0015] In the above technical solution, it is further preferred that the current density of the DC power supply is 1 to 1.7 A / dm 2 The electroplating time is 10 to 400 seconds, and the stirring rate is 200 to 280 r / min.

[0016] In the above technical solution, it is further preferred that in the step six, the MEMS device is sequentially dried by cold nitrogen protection blowing, hot nitrogen protection drying, and cold nitrogen protection blowing.

[0017] The electroplating method has a simple process and is easy to operate; the electroplating solution prepared based on the ratio of the electroplating solution provided above makes the coating surface of the MEMS device produced by the electroplating method dense and smooth, with high gloss, low porosity, and excellent appearance and morphology, and the strength, hardness and wear resistance of the nickel-gold alloy coating are greatly improved, the coating stress is greatly reduced, and the service life is long, ensuring that all performances of the manufactured MEMS device can meet the relevant performance indicators required by the MEMS industry. DETAILED DESCRIPTION

[0019] To describe the technical content, structural features, achieved purpose and effect of the application in detail, the technical solutions in the embodiments of the application will be described below in conjunction with the embodiments of the application. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all of the embodiments. In the following description, for the purpose of explanation, many specific details are set forth to provide a detailed description of various exemplary embodiments or implementations of the invention. However, various exemplary embodiments may also be implemented without these specific details or in the case of one or more equivalent arrangements. In addition, various exemplary embodiments may be different, but not necessarily exclusive. For example, without departing from the inventive concept, the specific shape, structure and characteristics of the exemplary embodiment may be used or implemented in another exemplary embodiment.

[0020] The present application provides an electroplating solution for nickel-gold alloy plating for MEMS technology, which does not contain cyanide, reduces the toxicity of the electroplating solution, improves the performance of the nickel-gold alloy plating, and meets the requirements of green production. Each liter of the electroplating solution includes: 22-31g sodium gold sulfite, 65-87g nickel sulfate, 5.5-6.5g nickel chloride, 65-75g sodium dihydrogen phosphate, 76-81g disodium hydrogen phosphate, 2.0-3.0g sodium saccharin, 0.5-0.8g potassium sodium tartrate, 1.9-3.4g ethylenediaminetetraacetic acid (EDTA), 5.5-6.2g benzoic acid sulfonyl imine, 0.1-0.2g thiosalicylic acid, 0.05-0.1g 2-ethylhexyl sodium sulfate, 0.10-0.20g 3,4,5-trihydroxy benzoic acid sodium, and the balance is deionized water. In the present application, the pH value of the electroplating solution is 4-6, and the temperature of the electroplating solution is 50°C-55°C.

[0021] The gold ions in the electroplating solution are mainly derived from sodium gold sulfite, and the nickel ions are mainly derived from nickel sulfate. The content of sodium gold sulfite is 22 to 31 g, such as 22.0 g, 22.1 g, 22.2 g...30.8 g, 30.9 g, 31.0 g. The content of nickel sulfate is 65 to 87 g, such as 65.1 g, 65.2 g, 65.3 g...86.8 g, 86.9 g, 87.0 g. Too high a main salt content will inhibit the polarization effect of the cathode, which is not conducive to the growth of the coating, and at the same time make the electroplating solution have poor dispersibility; too low a content will lead to too low a plating speed, affecting production efficiency.

[0022] The content of nickel chloride is 5.5-6.5g, for example, 5.50g, 5.51g, 5.52g...6.48g, 6.49g, 6.50g. Nickel chloride can significantly improve the conductivity of the electroplating solution, reduce the maximum voltage required for the electroplating solution, and thus effectively reduce the working load, achieving the purpose of safe production and clean production. Too high a nickel chloride content will cause excessive corrosion of the anode, resulting in problems such as nodules on the coating and uneven edges. Too low a content will cause passivation on the anode surface, affecting the electroplating rate.

[0023] The content of sodium dihydrogen phosphate is 65-75g, such as 65.1g, 65.2g, 65.3g...74.8g, 74.9g, 75.0g. The content of disodium hydrogen phosphate is 76-81g, such as 76.1g, 76.2g, 76.3g...80.8g, 80.9g, 81.0g. Sodium dihydrogen phosphate / disodium hydrogen phosphate are a pair of buffers. The pH of the former is acidic and the pH of the latter is alkaline. The two can cooperate with each other to control the pH value of the electroplating solution. As the electroplating process proceeds, some hydrogen ions (H +) will discharge to form hydrogen gas that escapes from the plating solution, causing the pH of the plating solution to tend to rise. Adding sodium dihydrogen phosphate / disodium hydrogen phosphate can stabilize the pH during the electroplating process and simplify the pH adjustment operation method. If the pH is too low, the coating stress is large and the current efficiency is low; if the pH is too high, the discharge efficiency of the coating ions on the cathode workpiece to be plated decreases, and severe hydrogen evolution will occur. The coating will experience "hydrogen embrittlement" and cause the coating to peel or even crack.

[0024] The content of sodium saccharin is 2.0-3.0g, such as 2.01g, 2.02g, 2.03g...2.98g, 2.99g, 3.00g. Sodium saccharin is a common brightener in the electroplating industry, which can optimize the grain structure morphology, thereby improving the glossiness of the coating and reducing the stress of the coating. However, if its content is too high, the coating will contain too much sulfur and carbon, thereby reducing the strength of the coating.

[0025] The content of potassium sodium tartrate is 0.5-0.8g, such as 0.51g, 0.52g, 0.53g, 0.78g, 0.79g, 0.80g; the content of ethylenediaminetetraacetic acid is 1.9-3.4g, such as 1.91g, 1.92g, 1.93g, 3.38g, 3.39g, 3.40g; the content of benzoic acid sulfonyl imine is 5.5-6.2g, such as 5.50g, 5.51g, 5.52g, 6.18g, 6.19g, 6.20g. Potassium sodium tartrate, ethylenediaminetetraacetic acid, and benzoic acid sulfonyl imine are complexing agents that can reduce trivalent gold ions that may exist in the electroplating solution to stable monovalent gold ions, thereby improving the current efficiency and making the reaction proceed stably.

[0026] The content of thiosalicylic acid is 0.1-0.2g, for example, 0.10g, 0.11g, 0.12g...0.18g, 0.19g, 0.20g. Thiosalicylic acid is used to improve the metal distribution force and ductility, making the coating brighter and more uniform.

[0027] Sodium saccharin, potassium sodium tartrate, and thiosalicylic acid are also used as fillers / brighteners. During the electroplating process, fillers / brighteners are generally present in the plating solution at a relatively low concentration and are consumed as the electroplating process proceeds, so they need to be added on time as needed.

[0028] The content of 2-ethylhexyl sodium sulfate is 0.05 to 0.1 g, such as 0.05 g, 0.06 g, ... 0.09 g, 0.10 g. As a surfactant, 2-ethylhexyl sodium sulfate can effectively reduce the surface tension of the electroplating solution, thereby significantly reducing the solid-liquid contact angle, and then enhancing the wetting effect of the electroplating solution on the surface of the workpiece to be plated, and finally increasing the wettability between the electroplating solution and the workpiece, and by wrapping the microscopic sharp protrusions on the surface of the workpiece to be plated, the disordered growth of grains is inhibited, and the flatness of the surface of the electroplated layer is improved.

[0029] The content of sodium 3,4,5-trihydroxybenzoate is 0.10-0.20 g, such as 0.10 g, 0.11 g, ... 0.19 g, 0.20 g. Sodium 3,4,5-trihydroxybenzoate has the characteristics of multiple hydroxy groups and can be used as an electroplating stabilizer and reducing agent. It can enhance the polarization of the cathode workpiece to be plated, increase the alloy nucleation rate, and make the alloy nucleation tend to the continuous nucleation mechanism, so that the metal precipitation reaction can be carried out stably.

[0030] The present application also provides an electroplating method for a nickel-gold alloy coating for MEMS technology, the electroplating method is used to electroplate a uniform nickel-gold alloy coating on the surface of a substrate of a MEMS structure, the electroplating method comprises the following steps: Step 1, sputtering a seed layer on the surface of the substrate; Step 2, etching the desired coating morphology on the surface of the seed layer by applying photoresist, developing, flooding, hardening and photolithography; Step 3, pre-treating the etched substrate; Step 4, preparing an electroplating solution according to the above-mentioned electroplating solution ratio, and immersing the pre-treated substrate in the prepared electroplating solution; Step 5, the substrate and the electroplating solution are energized, and a nickel-gold coating is formed on the surface of the substrate according to the coating morphology; Step six, taking out the MEMS device with the nickel-gold plating layer formed on the surface from the electroplating solution, and cleaning and drying it.

[0031] In step 1, the material of the seed layer is an inactive metal, which is one or more of copper, titanium, and gold. When the substrate is immersed in the electroplating solution for electroplating, the inactive metal does not react with the electroplating solution, thereby ensuring the electroplating effect of the substrate.

[0032] In step 2, a photoresist is applied, developed, exposed, hardened and photolithographically processed to etch a photolithographic pattern of the desired coating morphology on the surface of the substrate according to production requirements. In step 5, a nickel-gold alloy coating is electroplated according to the photolithographic pattern.

[0033] In step three, the pretreatment includes substrate roughening, activation and cleaning. First, the substrate with the photolithographic pattern is placed in an ozone generator, 100mL of pure oxygen is introduced into the ozone generator, and 100-150W power is used to discharge for 10 minutes to continuously generate ozone to treat the substrate surface; after the substrate surface is treated with ozone, the oxidized substrate is washed with deionized water; then a 5%-10% volume ratio of sulfuric acid aqueous solution is used to remove the oxidation on the substrate surface and activate it; finally, the surface activated substrate is washed with deionized water. After the pretreatment of the substrate with the photolithographic pattern, the surface becomes rough, thereby enhancing the adhesion of the coating on the substrate surface, so that the coating formed on the substrate surface is not easy to fall off.

[0034] In step 4, the pH value of the electroplating solution is stabilized at 4.3 to 4.8, and the electroplating solution is maintained at a suitable pH value to effectively ensure electroplating efficiency and electroplating quality.

[0035] In step 5, the electroplating solution is placed in an electroplating tank after preparation, the substrate is immersed in the electroplating solution in the electroplating tank as a cathode, a platinum-titanium mesh is immersed in the electroplating solution as an anode, and the substrate and the platinum-titanium mesh are connected to a DC power supply, and the DC power supply applies voltage to the substrate and the platinum-titanium mesh, so that the electroplating solution and the platinum-titanium mesh are electrolyzed to form a nickel-gold alloy coating on the substrate. The current density of the DC power supply is 1 to 1.7A / dm 2 , the electroplating time is 10 to 400s.

[0036] During the electroplating process, with long-term consumption, the concentration of nickel ions and gold ions in the electroplating solution around the substrate decreases, which will affect the thickness and uniformity of the coating on the substrate. In order to electroplate a nickel-gold alloy coating with uniform thickness and in accordance with production requirements on the surface of the substrate, the ion concentration in the electroplating solution around the substrate needs to remain stable. The present application uses a stirring device to stir the electroplating solution in the electroplating tank, and the stirring rate of the stirring device is 150 to 300 r / min. The stirring rate will affect the distribution of nickel ions and gold ions in the plating solution on the surface of the workpiece to be plated. If the stirring rate is too slow, the nickel ions and gold ions to be deposited cannot be updated to the vicinity of the workpiece in time. The concentrations of nickel ions and gold ions near the workpiece continue to be low, and the concentration polarization phenomenon is serious, which ultimately causes the coating to be thin. At the same time, the hydrogen bubbles generated near the cathode cannot be away from the workpiece to be plated in time, causing nodules on the surface of the coating. If the stirring rate is too fast, a large number of tiny air bubbles will appear in the plating solution, and the bubbles will attach to the surface of the coating to form defects such as wrinkles, pinholes, and nodules. In addition, the surface of the coating will also appear water-like patterns due to the fast stirring rate, affecting the gloss and smoothness of the coating.

[0037] Preferably, the stirring rate is 200-280 r / min, which can ensure that the concentration of nickel ions and gold ions near the workpiece is appropriate, and the electroplating solution does not generate air bubbles that affect the molding quality of the coating.

[0038] In step six, after the electroplating is completed, the MEMS device is taken out from the electroplating solution, washed with deionized water, and then subjected to cold nitrogen protection blow drying, hot nitrogen protection drying, and cold nitrogen protection blow drying in sequence.

[0039] The present application is further described below through a number of embodiments and comparative examples. Example 1

[0040] Each liter of the plating solution contains 22g of sodium gold sulfite, 65g of nickel sulfate, 5.5g of nickel chloride, 65g of sodium dihydrogen phosphate, 76g of disodium hydrogen phosphate, 2g of sodium saccharin, 0.5g of potassium sodium tartrate, 1.9g of ethylenediaminetetraacetic acid, 5.5g of benzoic acid sulfonimide, 0.1g of thiosalicylic acid, 0.05g of 2-ethylhexyl sodium sulfate and 0.1g of sodium 3,4,5-trihydroxybenzoate, and the balance is deionized water. The pH value of the plating solution is adjusted to 4.3 with sodium dihydrogen phosphate / disodium hydrogen phosphate, and the plating solution is heated to 50°C. The current density of the DC power supply is 1A / dm 2 , stirring rate 200r / min, maintain the plating solution temperature at 50℃ for electroplating, and the electroplating time is 20s. Example 2

[0041] Each liter of the plating solution contains 22g of sodium gold sulfite, 65g of nickel sulfate, 5.5g of nickel chloride, 65g of sodium dihydrogen phosphate, 76g of disodium hydrogen phosphate, 2g of sodium saccharin, 0.5g of potassium sodium tartrate, 1.9g of ethylenediaminetetraacetic acid, 5.5g of benzoic acid sulfonimide, 0.1g of thiosalicylic acid, 0.05g of 2-ethylhexyl sodium sulfate and 0.1g of sodium 3,4,5-trihydroxybenzoate, and the balance is deionized water. The pH value of the plating solution is adjusted to 4.3 with sodium dihydrogen phosphate / disodium hydrogen phosphate, and the plating solution is heated to 50°C. The current density of the DC power supply is 1A / dm 2 , stirring rate 200r / min, maintaining the plating solution temperature at 50℃ for electroplating, and the electroplating time is 60s. Example 3

[0042] Each liter of the plating solution contains 31g of sodium gold sulfite, 87g of nickel sulfate, 6.5g of nickel chloride, 65g of sodium dihydrogen phosphate, 76g of disodium hydrogen phosphate, 2g of sodium saccharin, 0.5g of potassium sodium tartrate, 1.9g of ethylenediaminetetraacetic acid, 5.5g of benzoic acid sulfonyl imine, 0.1g of thiosalicylic acid, 0.05g of 2-ethylhexyl sodium sulfate and 0.1g of sodium 3,4,5-trihydroxybenzoate, and the balance is deionized water. The pH value of the plating solution is adjusted to 4.3 with sodium dihydrogen phosphate / disodium hydrogen phosphate, the plating solution is heated to 50°C, and the current density of the DC power supply is 1A / dm 2 , stirring rate 200r / min, maintain the plating solution temperature at 50℃ for electroplating, and the electroplating time is 20s. Example 4

[0043] Each liter of the plating solution contains 22g of sodium gold sulfite, 87g of nickel sulfate, 6.5g of nickel chloride, 65g of sodium dihydrogen phosphate, 76g of disodium hydrogen phosphate, 2g of sodium saccharin, 0.5g of potassium sodium tartrate, 1.9g of ethylenediaminetetraacetic acid, 5.5g of benzoic acid sulfonyl imine, 0.1g of thiosalicylic acid, 0.05g of 2-ethylhexyl sodium sulfate and 0.1g of sodium 3,4,5-trihydroxybenzoate, and the balance is deionized water. The pH value of the plating solution is adjusted to 4.3 with sodium dihydrogen phosphate / disodium hydrogen phosphate, and the plating solution is heated to 50°C. The current density of the DC power supply is 1A / dm 2 , stirring rate 200r / min, maintain the plating solution temperature at 50℃ for electroplating, and the electroplating time is 20s. Example 5

[0044] Each liter of the plating solution contains 22g of sodium gold sulfite, 65g of nickel sulfate, 5.5g of nickel chloride, 65g of sodium dihydrogen phosphate, 76g of disodium hydrogen phosphate, 2g of sodium saccharin, 0.5g of potassium sodium tartrate, 1.9g of ethylenediaminetetraacetic acid, 5.5g of benzoic acid sulfonyl imine, 0.1g of thiosalicylic acid, 0.05g of 2-ethylhexyl sodium sulfate and 0.1g of sodium 3,4,5-trihydroxybenzoate, and the balance is deionized water. The pH value of the plating solution is adjusted to 5.5 with sodium dihydrogen phosphate / disodium hydrogen phosphate, and the plating solution is heated to 50°C. The current density of the DC power supply is 1A / dm 2 , stirring rate 200r / min, maintain the plating solution temperature at 50℃ for electroplating, and the electroplating time is 20s. Example 6

[0045] Each liter of the plating solution contains 22g of sodium gold sulfite, 65g of nickel sulfate, 5.5g of nickel chloride, 65g of sodium dihydrogen phosphate, 76g of disodium hydrogen phosphate, 2g of sodium saccharin, 0.5g of potassium sodium tartrate, 1.9g of ethylenediaminetetraacetic acid, 5.5g of benzoic acid sulfonyl imine, 0.1g of thiosalicylic acid, 0.05g of 2-ethylhexyl sodium sulfate and 0.1g of sodium 3,4,5-trihydroxybenzoate, and the balance is deionized water. The pH value of the plating solution is adjusted to 4.3 with sodium dihydrogen phosphate / disodium hydrogen phosphate, and the plating solution is heated to 55°C. The current density of the DC power supply is 1A / dm 2 , stirring rate 200r / min, maintain the plating solution temperature at 55℃ for electroplating, and the electroplating time is 20s. Example 7

[0046] Each liter of the plating solution contains 22g of sodium gold sulfite, 65g of nickel sulfate, 5.5g of nickel chloride, 65g of sodium dihydrogen phosphate, 76g of disodium hydrogen phosphate, 2g of sodium saccharin, 0.5g of potassium sodium tartrate, 1.9g of ethylenediaminetetraacetic acid, 5.5g of benzoic acid sulfonimide, 0.1g of thiosalicylic acid, 0.05g of 2-ethylhexyl sodium sulfate and 0.1g of sodium 3,4,5-trihydroxybenzoate, and the balance is deionized water. The pH value of the plating solution is adjusted to 4.3 with sodium dihydrogen phosphate / disodium hydrogen phosphate, the plating solution is heated to 50°C, and the current density of the DC power supply is 1.5A / dm 2 , stirring rate 200r / min, maintain the plating solution temperature at 50℃ for electroplating, and the electroplating time is 20s. Example 8

[0047] Each liter of the plating solution contains 22g of sodium gold sulfite, 65g of nickel sulfate, 5.5g of nickel chloride, 65g of sodium dihydrogen phosphate, 76g of disodium hydrogen phosphate, 2g of sodium saccharin, 0.5g of potassium sodium tartrate, 1.9g of ethylenediaminetetraacetic acid, 5.5g of benzoic acid sulfonimide, 0.1g of thiosalicylic acid, 0.05g of 2-ethylhexyl sodium sulfate and 0.1g of sodium 3,4,5-trihydroxybenzoate, and the balance is deionized water. The pH value of the plating solution is adjusted to 4.3 with sodium dihydrogen phosphate / disodium hydrogen phosphate, and the plating solution is heated to 50°C. The current density of the DC power supply is 1A / dm 2 , stirring rate 300r / min, maintain the plating solution temperature at 50℃ for electroplating, and the electroplating time is 20s. Example 9

[0048] Each liter of the plating solution contains 22g of sodium gold sulfite, 65g of nickel sulfate, 5.5g of nickel chloride, 65g of sodium dihydrogen phosphate, 76g of disodium hydrogen phosphate, 3g of sodium saccharin, 0.8g of potassium sodium tartrate, 3.4g of ethylenediaminetetraacetic acid, 6.2g of benzoic acid sulfonyl imine, 0.2g of thiosalicylic acid, 0.1g of 2-ethylhexyl sodium sulfate and 0.2g of sodium 3,4,5-trihydroxybenzoate, and the balance is deionized water. The pH value of the plating solution is adjusted to 4.3 with sodium dihydrogen phosphate / disodium hydrogen phosphate, the plating solution is heated to 50°C, and the current density of the DC power supply is 1A / dm 2 , stirring rate 200r / min, maintain the plating solution temperature at 50℃ for electroplating, and the electroplating time is 20s.

[0049] Comparative Example 1 Use commercially available soft gold plating solution, adjust the pH value of the plating solution to 4.3 with sodium dihydrogen phosphate / disodium hydrogen phosphate, raise the temperature of the plating solution to 50°C, and set the current density of the DC power supply to 1A / dm 2 , stirring rate 200r / min, maintain the plating solution temperature at 50℃ for electroplating, and the electroplating time is 20s.

[0050] Comparative Example 2 First, the plating solution is prepared with 65g nickel sulfate, 5.5g nickel chloride, 65g sodium dihydrogen phosphate, 76g sodium dihydrogen phosphate, 2g sodium saccharin, 0.5g potassium sodium tartrate, 1.9g ethylenediaminetetraacetic acid, 5.5g benzoic acid sulfonyl imine, 0.1g thiosalicylic acid, 0.05g 2-ethylhexyl sodium sulfate, 0.10g sodium 3,4,5-trihydroxybenzoate, and the balance is deionized water, wherein the pH value of the plating solution is adjusted to 4.3 with sodium dihydrogen phosphate / sodium dihydrogen phosphate. The plating solution is heated to 50°C and the DC power supply current density is set to 3A / dm 2 , stirring rate 200r / min, maintain the plating solution temperature at 50℃ for electroplating, the plating time is 10s, and a layer of pure nickel plating is plated on the outer layer of the substrate. Subsequently, a commercially available soft gold plating solution is used, and the pH value of the plating solution is adjusted to 4.3 with sodium dihydrogen phosphate / disodium hydrogen phosphate. The current density of the DC power supply is 1A / dm 2 , stirring rate 200r / min, keeping the plating solution temperature at 50°C, electroplating again on the obtained pure nickel coating, the electroplating time is 20s.

[0051] After the substrates were electroplated with the plating solutions of the above 9 embodiments and 2 comparative examples, the electroplated MEMS devices were tested respectively, mainly for the thickness, hardness, stress value and mass percentage of gold of the nickel-gold alloy coating of each MEMS device.

[0052] The following is a table showing the main performance test results of the nickel-gold alloy coatings of the MEMS devices obtained in the above 9 embodiments and 2 comparative examples after testing:

[0053] As shown in the above-mentioned main performance test result table, compared with the commercially available electroplating solution, the electroplating solution of the present application changes the type, content and ratio of the main salt, the type and content of the additives and the electroplating parameters in the sulfite system nickel-gold alloy electroplating solution. The electroplating solution of the present application ensures that the formed coating has a smooth, dense and bright appearance, and the strength, hardness and wear resistance are greatly improved, the stress of the coating is greatly reduced, and the service life is long; while the coating formed by electroplating with the commercially available electroplating solution has excessive internal stress in the coating, such as roughness, edge warping and even cracking; the appearance, performance and quality of the coating formed by electroplating with the electroplating solution of the present application are higher than those of the coating formed by electroplating with the commercially available electroplating solution.

[0054] The electroplating method of the present application has a simple process and is easy to operate. By changing the content and proportion of the main salt in the electroplating solution, the type and content of the additives, and the electroplating parameters, the electrodeposition rate in the electroplating process is accelerated, the production cycle is shortened, and the economic effect is improved. The surface of the coating of the MEMS device produced by the electroplating method is dense and smooth, with high gloss, low porosity, and excellent appearance. The strength, hardness, and wear resistance of the nickel-gold alloy coating are greatly improved, the coating stress is greatly reduced, and the service life is long, ensuring that all performances of the prepared MEMS device can meet the relevant performance indicators required by the MEMS industry. The additives in the electroplating solution of the present application improve the cathode polarization and dispersion ability of the nickel-gold alloy plating solution, while meeting the requirements of safe production and green production.

[0055] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited by the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present application. Without departing from the spirit and scope of the present application, the present application may have various changes and improvements, and the scope of protection required by the present application is defined by the attached claims, description and their equivalents.

Claims

1. A plating solution for nickel-gold alloy plating for MEMS technology, which does not contain cyanide, characterized in that: The electroplating solution comprises per liter: 22-31 g of sodium gold sulfite, 65-87 g of nickel sulfate, 5.5-6.5 g of nickel chloride, 65-75 g of sodium dihydrogen phosphate, 76-81 g of disodium hydrogen phosphate, 2.0-3.0 g of sodium saccharin, 0.5-0.8 g of potassium sodium tartrate, 1.9-3.4 g of ethylenediaminetetraacetic acid (EDTA), 5.5-6.2 g of benzoic acid sulfonyl imine, 0.1-0.2 g of thiosalicylic acid, 0.05-0.1 g of 2-ethylhexyl sodium sulfate, 0.10-0.20 g of 3,4,5-trihydroxy sodium benzoate, and the balance is deionized water.

2. The electroplating solution according to claim 1, characterized in that The pH value of the electroplating solution is 4-6.

3. The electroplating solution according to claim 1, characterized in that The temperature of the electroplating solution is 50°C to 55°C.

4. A method for electroplating a nickel-gold alloy coating for MEMS technology, characterized in that: The electroplating method comprises: Step 1, sputtering a seed layer on the surface of the substrate; Step 2, etching the desired coating morphology on the surface of the seed layer by applying photoresist, developing, flooding, hardening and photolithography; Step 3, pre-treating the etched substrate; Step 4, preparing the electroplating solution according to any one of claims 1 to 3, and immersing the pre-treated substrate in the prepared electroplating solution; Step 5, the substrate and the electroplating solution are energized to form a nickel-gold plating layer on the surface of the substrate; Step six, taking out the MEMS device with the nickel-gold plating layer formed on the surface from the electroplating solution, and cleaning and drying it.

5. The electroplating method according to claim 4, characterized in that: In the step 1, the material of the seed layer is an inactive metal.

6. The electroplating method according to claim 4, characterized in that: In the step three, the pre-treatment includes substrate roughening, activation and cleaning.

7. The electroplating method according to claim 4, characterized in that: In the step 4, the pH value of the electroplating solution is 4.3-4.

8.

8. The electroplating method according to claim 4, characterized in that: In the step five, the electroplating solution is contained in an electroplating tank, the substrate is immersed in the electroplating solution and electrically connected to a DC power supply, and the electroplating solution is stirred in the electroplating tank at a stirring rate of 150 to 300 r / min.

9. The electroplating method according to claim 8, characterized in that: The current density of the DC power supply is 1-1.7A / dm 2 The electroplating time is 10 to 400 seconds, and the stirring rate is 200 to 280 r / min.

10. The electroplating method according to claim 4, characterized in that: In step six, the MEMS device is sequentially dried by cold nitrogen protection blowing, hot nitrogen protection drying, and cold nitrogen protection blowing.

Images