Silver plating process for lead frame of integrated circuit

Abstract

The invention discloses a silver plating process for a lead frame of an integrated circuit, and relates to the technical field of electroplating processes. The invention discloses a silver plating process for an integrated circuit lead frame. The silver plating process sequentially comprises the steps of surface oil removal and degreasing, acid pickling, activation, copper plating, silver pre-plating, silver electroplating, annealing passivation and the like. In the step of silver electroplating, used silver electroplating liquid comprises a water-soluble silver salt compound with the mass concentration being 15-25 g / L, sodium thiosulfate with the mass concentration being 200-230 g / L, potassium metabisulfite with the mass concentration being 40-45 g / L, potassium oxalate with the mass concentration being 20-35 g / L, a stabilizer with the mass concentration being 0.35-1.2 g / L, a reducing agent with the mass concentration being 4-12 g / L, a brightening agent with the mass concentration being 0.5-0.8 g / L and a pH buffering agent with the mass concentration being 10-20 g / L according to silver ions. Specifically, the stabilizer is one or a mixture of two of a thiourea derivative or methylaminothiazole, and silver ions can be uniformly deposited on the surface of the lead frame at a stable speed in a silver electroplating liquid system taking sodium thiosulfate as a main complexing agent, so that the surface of a silver plating layer is smooth and flat and has good brightness; and meanwhile, good adhesiveness and thickness uniformity are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of electroplating technology, and in particular to a silver plating technology for an integrated circuit lead frame. Background Art

[0002] The integrated circuit lead frame is a basic component for manufacturing integrated circuit semiconductor components. As a chip carrier, it is a key structural component that uses bonding wires to achieve electrical connection between the internal circuit lead end of the chip and the external lead and form an electrical circuit, and plays a bridge role in connecting with external wires. At present, the general integrated circuit lead frame uses a special alloy as a collecting plate, which is etched through by stamping or chemical etching. After the shape of the lead frame is initially formed, the surface treatment of the chip loading area and bonding area on the lead frame surface is required to make the lead frame have good chip loading performance and bonding performance in the packaging process, thereby ensuring good welding between the chip and the wire and the lead frame.

[0003] The surface treatment process of integrated circuit lead frame generally includes multiple steps such as degreasing, pickling, activation, surface plating, plating protection treatment and subsequent cleaning and drying. In the surface plating step, a layer of copper is generally plated on the surface of the lead frame, and then a silver plating layer is formed on the copper plating layer by electroplating or chemical plating.

[0004] At present, the thickness uniformity of the silver coating formed by the general electroplating process is poor, and the difference between the minimum thickness value and the maximum thickness value is large. However, if the silver plating time is kept unchanged in order to meet the minimum thickness requirement of the silver coating, the maximum thickness of the silver coating will exceed the standard, which will not only cause the finished product to have various problems such as excessively thick and uneven coating and poor surface quality, but also directly affect the chip mounting performance and bonding performance of the lead frame, so that the chip and the welding wire cannot form a good connection relationship with the lead frame, affecting product quality. Summary of the invention

[0005] In order to improve the surface silver plating process of integrated circuit lead frames, increase the thickness uniformity of the silver plating layer, and ensure the quality of the surface silver plating layer of the integrated circuit lead frames, the present application provides a silver plating process for integrated circuit lead frames.

[0006] The present application provides an integrated circuit lead frame silver plating process using the following technical solutions: A silver plating process for an integrated circuit lead frame, wherein the process treatment steps sequentially include surface degreasing, pickling, activation, copper plating, pre-silver plating, silver electroplating and annealing passivation; in the silver electroplating step, the lead frame is immersed in a silver electroplating solution for electroplating, wherein the silver electroplating solution includes a water-soluble silver salt compound II, a complexing agent II, a stabilizer, a reducing agent, a brightener and a pH buffer; The water-soluble silver salt compound II is calculated as silver ions, and the mass concentration of silver ions in the silver electroplating solution is 15-25 g / L; The complexing agent II includes a mixture of sodium thiosulfate, potassium pyrosulfite and potassium oxalate, wherein the mass concentration of the sodium thiosulfate in the silver electroplating solution is 200-230 g / L, the mass concentration of the potassium pyrosulfite in the silver electroplating solution is 40-45 g / L, and the mass concentration of the potassium oxalate in the silver electroplating solution is 20-35 g / L; The stabilizer is one or a mixture of thiourea derivatives or methylaminothiazole, and the mass concentration of the stabilizer is 0.35-1.2 g / L; The mass concentration of the reducing agent is 4-12 g / L; The mass concentration of the brightener is 0.5-0.8 g / L; The mass concentration of the pH buffer is 10-20 g / L.

[0007] By adopting the above technical scheme, the complexing agent is a mixture of sodium thiosulfate, potassium pyrosulfite and potassium oxalate, and is combined with one or more mixed stabilizers of thiourea derivatives or aminothiazoles, so that the deposition rate and crystal fineness of silver ions in the electroplating process can be adjusted, which is conducive to the silver ions being uniformly deposited on the surface of the lead frame at a stable rate, so that the surface of the electroplated silver coating is smooth and flat, has good brightness, and also has good adhesion and thickness uniformity.

[0008] Optionally, the stabilizer is a mixture of the thiourea derivative and methylaminothiazole, and the mixing weight ratio of the two is (1-4):1.

[0009] By adopting the above technical scheme, both thiourea derivatives and methylaminothiazole have a certain stabilizing effect on the electroplating deposition of silver ions, and the thiourea derivative has a certain degree of brightening effect on the surface of the coating. When the stabilizer is a thiourea derivative and methylaminothiazole mixed in a weight ratio of (1-4):1, it is not only beneficial for the silver ions to be uniformly deposited on the surface of the lead frame at a stable speed, improving the uniformity and coverage of the silver coating, but also beneficial for improving the surface brightness of the silver coating, and the surface performance of the silver coating is better.

[0010] Optionally, the thiourea derivative is one of isothioureapropanesulfonic acid inner salt or isothioureapropionic acid hydrochloride.

[0011] By adopting the above technical solution, both isothioureapropanesulfonic acid inner salt and isothioureapropionic acid hydrochloride can regulate and control the electroplating deposition rate of silver ions in a silver electroplating solution system with sodium thiosulfate as a complexing agent, which is conducive to making silver ions uniformly deposited on the surface of the lead frame at a stable speed and improving the uniformity and coverage of the silver plating layer to a certain extent. Moreover, both isothioureapropanesulfonic acid inner salt and isothioureapropionic acid hydrochloride have a certain brightener effect, and the use of a brightener together can further improve the brightness of the silver plating layer.

[0012] Optionally, the stabilizer is selected from isothiourea propionate hydrochloride and methylaminothiazole mixed in a weight ratio of (2.5-3):1, and the mass concentration of the stabilizer in the silver plating solution is less than or equal to 0.6 g / L.

[0013] By adopting the above technical scheme, when the stabilizer is selected to be isothiourea propionate hydrochloride and methylaminothiazole mixed in a weight ratio of (2.5-3):1, and the mass concentration of the stabilizer in the silver electroplating solution is less than or equal to 0.6g / L, the electroplating solution has a certain amount of chloride ions, which is beneficial to further improve the conductivity and brightness of the silver plating layer, and can prevent excessive chloride ions, which is beneficial to prevent excessive chloride ions from hindering the normal electroplating deposition of silver ions, and can effectively ensure the brightness of the silver plating layer.

[0014] Optionally, the reducing agent is at least one of sodium hypophosphite and sodium phosphite, and the pH buffer is at least one of potassium dihydrogen phosphate or potassium citrate.

[0015] By adopting the above technical scheme, sodium hypophosphite or sodium phosphite can promote the reduction of silver ions during the electroplating process and adjust the electroplating deposition rate of silver ions, which is beneficial to further refine the deposition crystallization of the silver plating layer and form a uniform, dense and highly adhesive silver plating layer.

[0016] Optionally, the pH value of the silver electroplating solution is controlled at 4.8-5.5.

[0017] By adopting the above technical solution, in a weakly acidic environment, the electroplating deposition rate of silver ions is stable, and the generation of oxides and other impurities in the silver plating layer can be reduced, which is conducive to forming a uniform and delicate silver plating layer.

[0018] Optionally, in the silver electroplating step, the anode is connected to the metal silver, the cathode is connected to the lead frame that has undergone the pre-silver plating step, and the current density of the electroplating is 0.1-0.3A / dm 2 , the area ratio of cathode to anode is 1:(2-3), the electroplating time is 15-25s, and the electroplating temperature is maintained at 35-40℃.

[0019] By adopting the above technical scheme, it is beneficial to slowly and evenly electroplating and depositing silver ions, so that the crystallization of the silver coating can be further refined, which is not only beneficial to improving the surface brightness of the silver coating and the surface quality of the overall coating, but also beneficial to improving the thickness uniformity and surface flatness of the silver coating.

[0020] Optionally, in the pre-silver plating step, the lead frame is immersed in the silver pre-dip solution for pre-dip plating, wherein the silver pre-dip solution comprises a water-soluble silver salt compound I and a complexing agent I; The water-soluble silver salt compound I is calculated as silver ions, and the mass concentration of silver ions in the silver pre-dip solution is 1-1.5 g / L; The complexing agent I includes sodium thiosulfate, sodium dodecyl sulfate and thiourea, wherein the mass concentration of the sodium thiosulfate in the silver pre-dip solution is 25-35 g / L, the mass concentration of the sodium dodecyl sulfate in the silver pre-dip solution is 1.2-1.5 g / L, and the mass concentration of the thiourea in the silver pre-dip solution is 30-40 g / L.

[0021] By adopting the above technical scheme, sodium dodecyl sulfate can be used as a surfactant to reduce the surface tension of the silver pre-dip solution, which is beneficial to improving the wettability of the silver pre-dip solution to the surface of the lead frame, promoting the uniform deposition of silver ions in the silver pre-plating step to form a uniform pre-plating layer, and is also beneficial to reducing the adhesion of bubbles on the surface of the pre-plating layer, preventing defects such as pinholes or pitting on the pre-plating layer, and is beneficial to making the subsequently formed silver plating layer smoother.

[0022] Optionally, before the pre-silver plating step, the surface of the lead frame is further treated with dopamine to form a polydopamine coating, wherein the dopamine treatment comprises the following steps: The lead frame after the copper plating step is immersed in a dopamine solution for 8-12 hours under light-proof conditions, and then the surface of the lead frame is ultrasonically cleaned with deionized water, and then air-dried at room temperature and placed in a vacuum drying oven for drying to obtain a lead frame with a polydopamine coating on the surface.

[0023] By adopting the above technical solution, a layer of polydopamine coating is first formed on the surface that needs pre-plating. Since the dopamine coating is rich in functional groups such as catechol and amino groups, these functional groups have high affinity for metal ions and can promote the enrichment and adsorption of silver ions on the coating surface, and make the silver ions more effectively reduced and deposited on the lead frame, forming a silver pre-plating layer with more uniform distribution and finer particle size, which is beneficial to improve the thickness uniformity of the final silver plating layer and improve the adhesion of the overall silver plating layer.

[0024] Optionally, the dopamine solution comprises the following preparation steps: Dopamine hydrochloride is added to a mixed solution of 10 mM Tris-HCL buffer and anhydrous ethanol at a mass concentration of 2-3 mg / ml, and after dispersion treatment using ultrasound, the pH value is adjusted to 8-8.5 to obtain a dopamine solution.

[0025] By adopting the above technical solution, since dopamine can self-polymerize into a colloidal substance through an oxidative polymerization reaction in an alkaline environment, and the pH value of the dopamine solution is controlled within the range of 8-8.5, the polymerization rate of dopamine can be effectively slowed down. Combined with a long-term immersion treatment, it is beneficial to form a dopamine coating with a suitable polymerization degree on the surface of the lead frame, thereby preventing the excessive polymerization of the dopamine coating from affecting the pre-silver plating or electroplating silver.

[0026] In summary, the technical solution of this application has at least one of the following beneficial effects: 1. By using a mixed complexing agent of sodium thiosulfate, potassium pyrosulfite and potassium oxalate, and coordinating one or more mixed stabilizers of thiourea derivatives or aminothiazole, the deposition rate and crystal fineness of silver ions in the electroplating process can be adjusted, which is conducive to making the silver ions be uniformly deposited on the surface of the lead frame at a stable speed, so that the surface of the electroplated silver coating is smooth and flat, with good brightness, good adhesion and thickness uniformity. DETAILED DESCRIPTION

[0027] The present application is further described in detail below in combination with preparation examples, embodiments and comparative examples.

[0028] Preparation Example [Preparation Example 1-1] A silver pre-dip solution comprises silver nitrate and a complexing agent I.

[0029] Wherein, the complexing agent I includes sodium thiosulfate, sodium dodecyl sulfate and thiourea.

[0030] Specifically, the mass concentration of each component in the silver pre-dip solution is as follows: The mass concentration of silver nitrate is calculated as silver ion, silver ion 1g / L; Sodium thiosulfate 25g / L; Sodium dodecyl sulfate 1.5 g / L; Thiourea 40g / L.

[0031] In this preparation example, the pH value of the silver pre-dip solution was adjusted to 8.5 using dilute sulfuric acid.

[0032] [Preparation Example 1-2] A silver pre-dip solution comprises silver nitrate and a complexing agent I.

[0033] Wherein, the complexing agent I includes sodium thiosulfate, sodium dodecyl sulfate and thiourea.

[0034] Specifically, the mass concentration of each component in the silver pre-dip solution is as follows: The mass concentration of silver nitrate is calculated as silver ion, silver ion is 1.5g / L; Sodium thiosulfate 35g / L; Sodium dodecyl sulfate 1.2 g / L; Thiourea 30g / L.

[0035] In this preparation example, the pH value of the silver pre-dip solution was adjusted to 8.5 using dilute sulfuric acid.

[0036] [Preparation Example 1-3] A silver pre-dip solution, which differs from [Preparation Example 1-1] in that sodium dodecyl sulfate is not added.

[0037] [Preparation Example 2-1] A silver electroplating solution comprises silver nitrate, a complexing agent II, a stabilizer, a reducing agent, a brightener and a pH buffer.

[0038] Among them, the complexing agent II includes sodium thiosulfate, potassium metabisulfite and potassium oxalate, the stabilizer is isothioureapropanesulfonic acid salt, the reducing agent is sodium hypophosphite, the brightener is Ag-935 silver plating brightener A and Ag-935 silver plating brightener B of Cu Yu New Materials Co., Ltd., which are mixed in a weight ratio of 5:1, and the pH buffer is potassium dihydrogen phosphate.

[0039] Specifically, the mass concentration of each component in the silver electroplating solution is as follows: The mass concentration of silver nitrate is calculated as silver ion, silver ion is 20g / L; Sodium thiosulfate 220g / L; Potassium metabisulfite 40g / L; Potassium oxalate 28g / L; Isothiourea propanesulfonic acid inner salt 0.6g / L; Sodium hypophosphite 6g / L; Brightener 0.72g / L; Potassium dihydrogen phosphate 15g / L.

[0040] In this embodiment, the pH value of the silver plating solution is 5.

[0041] [Preparation Example 2-2] A silver electroplating solution comprises silver nitrate, a complexing agent II, a stabilizer, a reducing agent, a brightener and a pH buffer.

[0042] Among them, the complexing agent II includes sodium thiosulfate, potassium metabisulfite and potassium oxalate, the stabilizer is methylaminothiazole, the reducing agent is sodium phosphite, the brightener is Ag-935 silver plating brightener A and Ag-935 silver plating brightener B of Cu Yu New Materials Co., Ltd., which are mixed in a weight ratio of 5:1, and the pH buffer is potassium citrate.

[0043] Specifically, the mass concentration of each component in the silver electroplating solution is as follows: The mass concentration of silver nitrate is calculated as silver ion, silver ion is 15g / L; Sodium thiosulfate 200g / L; Potassium metabisulfite 45g / L; Potassium oxalate 15g / L; Methylaminothiazole 0.35 g / L; Sodium phosphite 12g / L; Brightener 0.96g / L; Potassium citrate 20g / L.

[0044] In this embodiment, the pH value of the silver plating solution is 4.8.

[0045] [Preparation Example 2-3] A silver electroplating solution comprises silver nitrate, a complexing agent II, a stabilizer, a reducing agent, a brightener and a pH buffer.

[0046] Among them, the complexing agent II includes sodium thiosulfate, potassium metabisulfite and potassium oxalate, the stabilizer is isothiourea propionate hydrochloride and methylaminothiazole mixed in a weight ratio of 2.5:1, the reducing agent is sodium hypophosphite, the brightener is Ag-935 silver plating brightener A and Ag-935 silver plating brightener B of Cu Yu New Materials Co., Ltd. mixed in a weight ratio of 5:1, and the pH buffer is potassium dihydrogen phosphate and potassium citrate mixed in a weight ratio of 1:1.

[0047] Specifically, the mass concentration of each component in the silver electroplating solution is as follows: The mass concentration of silver nitrate is calculated as silver ion, silver ion is 25g / L; Sodium thiosulfate 230g / L; Potassium metabisulfite 40g / L; Potassium oxalate 35g / L; Stabilizer 1g / L; Sodium hypophosphite 4g / L; Brightener 0.6g / L; pH buffer 16g / L.

[0048] In this embodiment, the pH value of the silver plating solution is 5.5.

[0049] [Preparation Example 2-4] A silver electroplating solution, which differs from [Preparation Example 2-1] in that: the stabilizer is replaced by isothioureapropanesulfonic acid inner salt and methylaminothiazole mixed in a weight ratio of 4:1, and the mass concentration of the stabilizer added remains unchanged.

[0050] [Preparation Example 2-5] A silver electroplating solution, which differs from [Preparation Example 2-1] in that: the stabilizer is replaced by isothiourea propionic acid hydrochloride and methylaminothiazole mixed in a weight ratio of 4:1, and the mass concentration of the stabilizer added remains unchanged.

[0051] [Preparation Example 2-6] A silver electroplating solution, which differs from [Preparation Example 2-1] in that: the stabilizer is replaced by isothiourea propionic acid hydrochloride and methylaminothiazole mixed in a weight ratio of 3:1, and the mass concentration of the stabilizer added remains unchanged.

[0052] [Preparation Example 2-7] A silver electroplating solution, which differs from [Preparation Example 2-1] in that no stabilizer is added. Example

[0053] [Example 1] A silver plating process for an integrated circuit lead frame comprises the following steps: S1. Surface degreasing: Use alkaline cleaning solution and ultrasonic cleaning to remove residual grease on the surface of the lead frame, and then wash with water.

[0054] S2, pickling: immerse the lead frame treated in step S1 in a 15% sulfuric acid solution for soaking and cleaning, grind and scrub the surface of the lead frame until the surface of the lead frame is uniform and flat, and then wash with water.

[0055] S3, activation: soak the lead frame treated in step S2 in the S-32 activator solution provided by SMIT for 2 minutes, and then wash with water.

[0056] S4, copper plating: the lead frame processed in step S3 is connected to the electroplating circuit as a cathode, and the phosphor copper alloy is connected to the electroplating circuit as an anode, and they are immersed in a copper electroplating solution for electroplating, and then washed with water after the electroplating is completed.

[0057] The copper plating solution includes 15g / L copper sulfate, 20g / L copper chloride, 220g / L potassium citrate, 2g / L sodium phosphite, and 0.6g / L copper plating brightener. The specific copper plating brightener is CU-320A and CU-320B of Dongguan Cuyu New Materials Co., Ltd. mixed in a weight ratio of 2:1. The electroplating current density is 4.8A / dm2, the electroplating time is 15s, and the electroplating temperature is maintained at 40°C.

[0058] S5, pre-silver plating: soak the lead frame treated in step S4 in a silver pre-dip solution at room temperature for 2 minutes, and then wash with water.

[0059] Among them, the silver pre-dip solution selected is the silver pre-dip solution prepared in [Preparation Example 1-1].

[0060] S6, silver electroplating: the lead frame processed in step S5 is connected to the electroplating circuit as a cathode, and the metal silver is connected to the electroplating circuit as an anode, and they are immersed in a silver electroplating solution for electroplating, and then washed with water after the electroplating is completed.

[0061] The silver electroplating solution used was the silver electroplating solution prepared in [Preparation Example 2-1]. The electroplating current density was 0.15 A / dm 2 , the area ratio of cathode to anode is 1:2, the electroplating time is 20s, and the electroplating temperature is maintained at 35℃.

[0062] S7, annealing and passivation: slowly heat the lead frame processed in step S5 to 350°C for annealing within 3 hours, soak it in passivation solution when it naturally cools to 60°C, and continue soaking for 60 minutes, then take it out, wash it with water and dry it, to obtain a finished integrated circuit lead frame.

[0063] [Example 2] A silver plating process for an integrated circuit lead frame, which differs from [Example 1] in that the S5 pre-silver plating step and the S6 electro-silver plating step are different.

[0064] In this embodiment, the silver pre-immersion solution used in the S5 pre-silver plating step is the silver pre-immersion solution prepared in [Preparation Example 1-2]. The silver electroplating solution used in the S6 electro-silver plating step is the silver electroplating solution prepared in [Preparation Example 2-2], and the electroplating current density is 0.3A / dm 2 , the area ratio of cathode to anode is 1:2, the electroplating time is 15s, and the electroplating temperature is maintained at 35℃.

[0065] [Example 3] A silver plating process for an integrated circuit lead frame, which differs from [Example 1] in that the S6 electro-silver plating step is different.

[0066] In this embodiment, the silver electroplating solution used in the S6 silver electroplating step is the silver electroplating solution prepared in [Preparation Example 2-3], and the electroplating current density is 0.1A / dm 2 , the area ratio of cathode to anode is 1:3, the electroplating time is 25s, and the electroplating temperature is maintained at 40℃.

[0067] [Example 4] A silver plating process for an integrated circuit lead frame, which differs from [Example 1] in that a different silver plating solution is used in the S6 silver plating step.

[0068] In this embodiment, the silver electroplating solution is the silver electroplating solution prepared in [Preparation Example 2-4].

[0069] [Example 5] A silver plating process for an integrated circuit lead frame, which differs from [Example 1] in that a different silver plating solution is used in the S6 silver plating step.

[0070] In this embodiment, the silver electroplating solution is the silver electroplating solution prepared in [Preparation Example 2-5].

[0071] [Example 6] A silver plating process for an integrated circuit lead frame, which differs from [Example 1] in that a different silver plating solution is used in the S6 silver plating step.

[0072] In this embodiment, the silver electroplating solution is the silver electroplating solution prepared in [Preparation Example 2-6].

[0073] [Example 7] A silver plating process for an integrated circuit lead frame, which differs from [Example 6] in that the silver pre-dip solution used in the S5 pre-silver plating step is different.

[0074] In this embodiment, the silver pre-dip solution is the silver pre-dip solution prepared in [Preparation Example 1-3].

[0075] [Example 8] A silver plating process for an integrated circuit lead frame, which differs from [Example 6] in that before the S5 pre-silver plating step, the lead frame is also treated with dopamine and a polydopamine coating is formed on the surface. Specifically, the dopamine treatment includes the following steps: The lead frame after the S4 copper plating step is immersed in a dopamine solution for 12 hours under light-proof conditions, and then the surface of the lead frame is ultrasonically cleaned with deionized water, and then air-dried at room temperature and placed in a vacuum drying oven for drying to obtain a lead frame with a polydopamine coating.

[0076] Wherein, the dopamine solution comprises the following preparation steps: Dopamine hydrochloride is added to a mixed solution of 10mM Tris-HCL buffer and anhydrous ethanol at a concentration of 2mg / ml, and after dispersion and stirring using ultrasound, the pH value is adjusted to 8-8.5 using a 5% sodium hydroxide solution to obtain a dopamine solution.

[0077] Comparative Example [Comparative Example 1] A silver plating process for an integrated circuit lead frame, which differs from [Example 1] in that the silver plating solution used in the S6 silver plating step is different.

[0078] In this embodiment, the silver electroplating solution is the silver electroplating solution prepared in [Preparation Example 2-7].

[0079] [Comparative Example 2] A silver plating process for an integrated circuit lead frame, which differs from [Example 1] in that the S5 pre-silver plating step is not performed.

[0080] Performance test data Preparation of samples to be tested: According to the silver plating process disclosed in the above embodiments and comparative examples, corresponding integrated circuit lead frames with silver plating are prepared as samples to be tested.

[0081] 1. Surface state of electroplated layer: observe the surface of the coating of the sample to be tested according to the requirements of Section 3.1 of Chapter 3 of "SJ / T 11774-2021 Technical Specification for Electroplated Silver Layer of Integrated Circuit Lead Frame", and record the surface state of the sample to be tested prepared in each embodiment and comparative example. Reflective observation is to align the electroplated plane with the light source and judge the surface state of the electroplated plane by the reflection of the light source, while direct observation is to judge directly without aligning the light source.

[0082] 2. Brightness of the coating: According to the method in Chapter 3, Section 3.2 of "SJ / T 11774-2021 Technical Specification for Electroplated Silver Layer of Integrated Circuit Lead Frame", the surface brightness of the silver coating was tested, and the surface brightness (GAM) of the samples to be tested prepared in each embodiment and comparative example was recorded.

[0083] 3. Overall coating bonding strength: According to Chapter 3, Section 3.1 of "SJ / T 11774-2021 Technical Specification for Electroplated Silver Layer of Integrated Circuit Lead Frame", the silver stripping test of the electroplated silver layer was carried out, and the glass phenomenon of the silver plating layer in each embodiment and comparative example was recorded. Among them, the baking temperature was set to 250°C and the time was set to 60min. And the stripping was carried out with a tape with a viscosity of 250N / 100mm.

[0084] 4. Coating uniformity coefficient: First, measure the silver coating thickness values ​​of 10 different areas of each sample according to Section 3.3 of Chapter 3 of "SJ / T 11774-2021 Technical Specification for Electroplated Silver Layer of Integrated Circuit Lead Frame", and then calculate the average thickness μ of the silver coating of a single sample, and calculate the standard deviation α of the silver coating thickness in different areas of the sample, and finally calculate and record the uniformity coefficient CV of the overall coating in the samples prepared in each embodiment and comparative example. Among them, the uniformity coefficient of the coating CV = (α / μ) * 100%. Among them, the lower the uniformity coefficient, the smaller the fluctuation of the silver coating thickness in different areas of the sample, and the better the uniformity of the silver coating thickness of the sample.

[0085] Table 1 Coating performance test data Combining Example 1, Example 4 and Comparative Example 1 and the data in Table 1, it can be seen that when one or more of thiourea derivatives or aminothiazole are added to the silver electroplating solution as a stabilizer, the silver coating of the prepared lead frame not only has a smooth surface and good brightness, but also has good adhesion and thickness uniformity, and the uniformity coefficient is less than 8. This may be because in the silver electroplating solution system with sodium thiosulfate as a complexing agent, isothiourea propanesulfonic acid inner salt and aminothiazole can both adjust the deposition rate and crystal fineness of silver ions, so that silver ions can be uniformly deposited on the surface of the lead frame at a stable speed, and the formed crystal grain size is finer, thereby improving the uniformity and coverage of the silver coating. Secondly, isothiourea propanesulfonic acid inner salt may also have a certain brightener effect, and the use of a brightener can further improve the brightness of the coating. As the concentration of isothiourea propanesulfonic acid inner salt in the electroplating solution decreases and the concentration of aminothiazole increases, the brightness of the coating decreases slightly, and the appearance and thickness uniformity of the coating do not change much.

[0086] Combined with Examples 4-6 and the data in Table 1, it can be seen that when the stabilizer in the silver electroplating solution is selected from isothiourea propionic acid hydrochloride and aminothiazole in a weight ratio of 4:1, compared with the mixture of isothiourea propanesulfonic acid inner salt and aminothiazole, the thickness uniformity of the electroplated silver coating surface will decrease slightly, but the effect is not great, and the brightness of the silver coating surface is significantly improved, and the overall performance of the silver coating is better. This may be because the stability of isothiourea propionic acid hydrochloride for silver ion deposition is not as good as that of isothiourea propanesulfonic acid inner salt, but the isothiourea propionic acid hydrochloride introduces chloride ions into the electroplating solution, and the chloride ions can be adsorbed on the surface of the lead frame and form a thin film, which helps to smooth the surface of the silver coating, thereby helping to improve the conductivity and brightness of the silver coating. Secondly, when the isothiourea propionic acid hydrochloride in the stabilizer is mixed with aminothiazole in a weight ratio of 3:1, compared with the mixture in a weight ratio of 4:1, it is equivalent to a decrease in the concentration of chloride ions, and the brightness of the coating can be further improved. This may be because as the concentration of chloride ions increases, excessive chloride ion adsorption may form a thicker film layer, hindering the normal deposition of silver ions, which may directly affect the brightness of the silver coating.

[0087] Combining Example 1 and Comparative Example 2, Example 6-7 and the data in Table 1, it can be seen that by pre-silvering before the silver electroplating step, the surface of the silver coating can be made smoother and flatter, without pinholes or pits, and has good brightness, coating adhesion and thickness uniformity. By adding a certain amount of sodium dodecyl sulfate to the silver pre-dip used in the pre-silvering step, not only can the pinholes on the surface of the silver coating be reduced, but also the brightness and thickness uniformity of the silver coating can be improved. This may be because sodium dodecyl sulfate has a certain wetting effect, which can be used as a surfactant to reduce the surface tension of the silver pre-dip, thereby not only improving the wettability of the silver pre-dip on the lead frame surface, but also promoting the silver ions to be uniformly deposited on the lead frame surface in the silver pre-plating step and forming a pre-plating layer, and the gas generated during the pre-plating process also has a decreased adhesion due to the adsorption of sodium dodecyl sulfate, and is easier to detach from the lead frame surface, which is conducive to reducing the defects such as pinholes or pitting on the pre-plating layer, so that the subsequent silver coating formed is smoother.

[0088] Combining Example 6 and Example 8 with the data in Table 1, it can be seen that by treating the lead frame with dopamine before pre-silver plating, a layer of polydopamine coating is formed on the surface to be pre-plated, which can make the thickness uniformity of the final electroplated silver coating better.

[0089] This specific implementation manner is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the specific implementation manner as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A silver plating process for an integrated circuit lead frame, characterized in that: The process steps include surface degreasing, pickling, activation, copper plating, pre-silver plating, silver electroplating and annealing passivation in sequence; in the silver electroplating step, the lead frame is immersed in a silver electroplating solution for electroplating, wherein the silver electroplating solution includes a water-soluble silver salt compound II, a complexing agent II, a stabilizer, a reducing agent, a brightener and a pH buffer; The water-soluble silver salt compound II is calculated as silver ions, and the mass concentration of silver ions in the silver electroplating solution is 15-25 g / L; The complexing agent II includes a mixture of sodium thiosulfate, potassium pyrosulfite and potassium oxalate, wherein the mass concentration of the sodium thiosulfate in the silver electroplating solution is 200-230 g / L, the mass concentration of the potassium pyrosulfite in the silver electroplating solution is 40-45 g / L, and the mass concentration of the potassium oxalate in the silver electroplating solution is 20-35 g / L; The stabilizer is one or a mixture of thiourea derivatives or methylaminothiazole, and the mass concentration of the stabilizer is 0.35-1.2 g / L; The mass concentration of the reducing agent is 4-12 g / L; The mass concentration of the brightener is 0.5-0.8 g / L; The mass concentration of the pH buffer is 10-20 g / L.

2. The integrated circuit lead frame silver plating process according to claim 1, characterized in that: The stabilizer is a mixture of the thiourea derivative and methylaminothiazole, and the mixing weight ratio of the two is (1-4):

1.

3. The integrated circuit lead frame silver plating process according to claim 2, characterized in that: The thiourea derivative is one of isothiourea propanesulfonic acid inner salt and isothiourea propionic acid hydrochloride.

4. The integrated circuit lead frame silver plating process according to claim 3, characterized in that: The stabilizer is selected from isothiourea propionate hydrochloride and methylaminothiazole mixed in a weight ratio of (2.5-3):1, and the mass concentration of the stabilizer in the silver electroplating solution is less than or equal to 0.6 g / L.

5. The integrated circuit lead frame silver plating process according to claim 1, characterized in that: The reducing agent is selected from at least one of sodium hypophosphite and sodium phosphite, and the pH buffer is selected from at least one of potassium dihydrogen phosphate or potassium citrate.

6. The integrated circuit lead frame silver plating process according to claim 1, characterized in that: The pH value of the silver electroplating solution is controlled at 4.8-5.

5.

7. The integrated circuit lead frame silver plating process according to any one of claims 1 to 6, characterized in that: In the silver electroplating step, the anode is connected to the metal silver, and the cathode is connected to the lead frame after the pre-silver plating step. The current density of the electroplating is 0.1-0.3A / dm 2 , the area ratio of cathode to anode is 1: (2-3), the electroplating time is 15-25s, and the electroplating temperature is maintained at 35-40℃.

8. The integrated circuit lead frame silver plating process according to claim 1, characterized in that: In the pre-silver plating step, the lead frame is immersed in a silver pre-dip solution for pre-dip plating, wherein the silver pre-dip solution comprises a water-soluble silver salt compound I and a complexing agent I; The water-soluble silver salt compound I is calculated as silver ions, and the mass concentration of silver ions in the silver pre-dip solution is 1-1.5 g / L; The complexing agent I includes sodium thiosulfate, sodium dodecyl sulfate and thiourea, wherein the mass concentration of the sodium thiosulfate in the silver pre-dip solution is 25-35 g / L, the mass concentration of the sodium dodecyl sulfate in the silver pre-dip solution is 1.2-1.5 g / L, and the mass concentration of the thiourea in the silver pre-dip solution is 30-40 g / L.

9. The integrated circuit lead frame silver plating process according to claim 1, characterized in that: Before the pre-silvering step, the surface of the lead frame is also treated with dopamine to form a polydopamine coating, wherein the dopamine treatment includes the following steps: The lead frame after the copper plating step is immersed in a dopamine solution for 8-12 hours under light-proof conditions, and then the surface of the lead frame is ultrasonically cleaned with deionized water, and then air-dried at room temperature and placed in a vacuum drying oven for drying to obtain a lead frame with a polydopamine coating on the surface.

10. The integrated circuit lead frame silver plating process according to claim 9, characterized in that: The dopamine solution comprises the following preparation steps: Dopamine hydrochloride is added to a mixed solution of 10mM Tris-HCL buffer and anhydrous ethanol at a mass concentration of 2-3mg / ml, and after dispersion treatment using ultrasound, the pH value is adjusted to 8.5-9 to obtain a dopamine solution.

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