A silver-plated lead frame for semiconductor and a method for manufacturing the same

Abstract

The application discloses a silver-plated lead frame for semiconductor, and particularly relates to the technical field of lead frames, which comprises a copper-based alloy base, a stress buffer layer, a barrier transition layer and a composite silver plating layer. The copper-based alloy base is externally electroplated with the stress buffer layer, the barrier transition layer and the composite silver plating layer. The three plating layers are complementary in function, the Ni-W layer matches the thermal expansion coefficient of the copper base to relieve thermal stress, the Pd-Co layer blocks the diffusion of copper atoms to the silver layer due to its ultra-fine grain and dense structure, and the Ag functional layer forms mechanical anchoring with EMC through acicular grain structure, thereby forming a complete stress release-diffusion barrier-function coupling system, and realizing the comprehensive reliability level that cannot be achieved by the existing single or double silver plating scheme.

Description

Technical Field

[0001] This invention relates to the field of lead frame technology, and more specifically, to a silver-plated lead frame for semiconductors and its preparation method. Background Technology

[0002] The leadframe is a crucial component in semiconductor packaging, connecting the internal and external circuitry of a chip. It plays a vital role in supporting the chip, transmitting signals, distributing power, and dissipating heat. To ensure reliable connections between the leadframe, the chip, and the bonding wires, while maintaining the electrical performance of the component, the functional areas of the leadframe are typically silver-plated.

[0003] Currently, silver plating of leadframes mostly uses copper or copper alloys as the base material, with silver being electroplated directly onto the surface. Silver plating possesses excellent electrical and thermal conductivity, weldability, and contact strength, and has been widely used in high-density integrated circuits, power devices, and automotive electronics.

[0004] However, existing silver plating technology for lead frames still has the following technical defects that urgently need to be addressed: 1. Insufficient adhesion between the silver plating and the sealing resin (EMC, i.e., epoxy molding compound). Silver or silver-containing alloys have poor adhesion to EMC, and in high-temperature and high-humidity environments, the packaged components are prone to delamination or even a "popcorn" effect, leading to device failure. With the increasing demands for MSL-1 level (i.e., moisture sensitivity level 1—no delamination within 168 hours at 85℃ and 85% relative humidity) in automotive electronics and 5G communications, existing silver-plated lead frames are insufficient to meet higher reliability requirements. 2. The interface between the silver plating and the copper substrate is prone to diffusion and corrosion failure. Due to the lack of an effective diffusion barrier layer between copper and silver, copper atoms easily diffuse into the silver plating under high-temperature operating conditions. Simultaneously, the microporosity of the silver plating allows corrosive media to easily penetrate the substrate interface, leading to plating blistering, peeling, and increased contact resistance, severely impacting the long-term reliability of the device. Existing technologies employ a method of first plating nickel and then silver, but this multi-layer electroplating process is complex, costly, and results in high interfacial stress and low overall strength of the plating layer.

[0005] For example, Chinese Patent Publication No. CN 116516335 B discloses a high-strength lead frame and its preparation method. In this invention, a mixture of composite carbon nanotubes, tungsten oxide, and aluminum is used as the cladding material. By controlling their mass ratio, an in-situ self-generated network structure of tungsten carbide ceramic reinforcement phase is achieved. The composite carbon nanotubes are silver-lanthanum-based organic framework composite carbon nanotubes with mercaptoporphyrin as ligand. While acting as a light absorber to improve laser efficiency, the in-situ synthesis of porous carbon in the bimetallic organic framework and the welding of tungsten carbide achieve a synergistic effect, thereby increasing the complexity of the conductive network of the cladding layer and significantly improving the wear resistance of the generated lead frame. After laser cladding, silver plating is performed to improve the welding quality of the lead frame. The composite carbon nanotubes are introduced into the silver plating solution to improve the bonding force between silver and the cladding layer.

[0006] However, the above-mentioned solutions are complex and costly, and the thermal compatibility between the laser cladding layer and the copper substrate is difficult to solve. Summary of the Invention

[0007] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide a silver-plated lead frame for semiconductors and a method for preparing the same. The problem to be solved by the present invention is: how to improve the yellowing resistance of polyurethane glass film and improve the mechanical properties of glass film.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a silver-plated lead frame for semiconductors, comprising a copper-based alloy substrate, a stress buffer layer, a barrier transition layer, and a composite silver plating layer, wherein the copper-based alloy substrate comprises the following raw materials by weight percentage: iron 0.25-0.65%, chromium 0.5-1.5%, tin 0.3-1.0%, zinc 0.1-0.5%, cerium 0.05-0.15%, silicon 0.05-0.2%, with the balance being copper and unavoidable impurities; The stress buffer layer is applied to a copper-based alloy substrate by electroplating a stress buffer layer plating solution. Each liter of the stress buffer layer plating solution contains the following raw materials: nickel sulfamate 250-350 g / L, sodium tungstate 20-50 g / L, boric acid 30-40 g / L, sodium citrate 15-25 g / L, saccharin 1-3 g / L, and sodium dodecyl sulfate 0.05-0.15 g / L. The barrier transition layer is formed by electroplating a barrier transition layer plating solution onto the stress buffer layer. Each liter of the barrier transition layer plating solution comprises the following raw materials: palladium chloride 10-20 g / L, cobalt sulfate 1-5 g / L, ammonium chloride 30-50 g / L, 25% ammonia water 100-150 ml / L, butynediol 0.2-0.5 g / L, and o-sulfonylbenzeneimide 0.5-1.0 g / L. The composite silver plating layer is applied to the barrier transition layer by electroplating. Each liter of the composite silver plating solution comprises the following raw materials: silver nitrate 30-50 g / L, butyrylimide 60-100 g / L, potassium hydroxide 15-30 g / L, potassium carbonate 20-40 g / L, nano-cerium oxide 0.5-2.0 g / L, nano-graphene oxide 0.05-0.2 g / L, polyethyleneimine 0.02-0.08 g / L, and sodium polydisulfide dipropane sulfonate 0.5-2.0 g / L.

[0009] In a preferred embodiment, the material comprises a copper-based alloy substrate, a stress-reducing layer, a barrier transition layer, and a composite silver plating layer. The copper-based alloy substrate comprises the following raw materials by weight percentage: iron 0.35-0.55%, chromium 0.8-1.2%, tin 0.5-0.7%, zinc 0.2-0.4%, cerium 0.08-0.12%, silicon 0.12-0.16%, with the balance being copper and unavoidable impurities. The stress buffer layer is applied to a copper-based alloy substrate by electroplating a stress buffer layer plating solution. Each liter of the stress buffer layer plating solution contains the following raw materials: nickel sulfamate 280-320 g / L, sodium tungstate 30-40 g / L, boric acid 32-38 g / L, sodium citrate 18-22 g / L, saccharin 1.5-2.5 g / L, and sodium dodecyl sulfate 0.08-0.12 g / L. The barrier transition layer is formed by electroplating a barrier transition layer plating solution onto the stress buffer layer. Each liter of the barrier transition layer plating solution comprises the following raw materials: palladium chloride 12-18 g / L, cobalt sulfate 2-4 g / L, ammonium chloride 35-45 g / L, 25% ammonia water 120-140 ml / L, butynediol 0.3-0.4 g / L, and o-sulfonylbenzeneimide 0.6-0.8 g / L. The composite silver plating layer is applied to the barrier transition layer by electroplating. Each liter of the composite silver plating solution comprises the following raw materials: silver nitrate 35-45 g / L, butyrylimide 70-90 g / L, potassium hydroxide 18-25 g / L, potassium carbonate 25-35 g / L, nano-cerium oxide 0.8-1.5 g / L, nano-graphene oxide 0.08-0.15 g / L, polyethyleneimine 0.03-0.06 g / L, and sodium polydisulfide dipropane sulfonate 1.0-1.5 g / L.

[0010] In a preferred embodiment, the material includes a copper-based alloy substrate, a stress-reducing layer, a barrier transition layer, and a composite silver plating layer. The copper-based alloy substrate comprises the following raw materials by weight percentage: 0.45% iron, 1.0% chromium, 0.6% tin, 0.3% zinc, 0.1% cerium, and 0.14% silicon, with the balance being copper and unavoidable impurities. The stress buffer layer is applied to a copper-based alloy substrate by electroplating a stress buffer layer plating solution. Each liter of the stress buffer layer plating solution contains the following raw materials: nickel aminosulfonate 300g / L, sodium tungstate 35g / L, boric acid 35g / L, sodium citrate 20g / L, saccharin 2g / L, and sodium dodecyl sulfate 0.1g / L. The barrier transition layer is formed by electroplating a barrier transition layer plating solution onto the stress buffer layer. Each liter of the barrier transition layer plating solution contains the following raw materials: 15 g / L palladium chloride, 3 g / L cobalt sulfate, 40 g / L ammonium chloride, 130 ml / L 25% ammonia water, 0.35 g / L butynediol, and 0.7 g / L o-sulfonylbenzeneimide. The composite silver plating layer is applied to the barrier transition layer by electroplating. Each liter of the composite silver plating solution contains the following raw materials: silver nitrate 40 g / L, butyrylimide 80 g / L, potassium hydroxide 2 g / L, potassium carbonate 230 g / L, nano-cerium oxide 0.12 g / L, nano-graphene oxide 0.012 g / L, polyethyleneimine 0.0045 g / L, and sodium polydisulfide dipropane sulfonate 1.2 g / L.

[0011] This invention also provides a method for preparing a silver-plated lead frame for semiconductors, the specific preparation steps of which are as follows: Step 1: Weigh the raw materials according to the weight percentage of the copper-based alloy matrix mentioned above, and put the weighed raw materials into a melting furnace for melting. The argon pressure in the melting furnace is 40-45 kPa, and the temperature inside the melting furnace is raised to 1380-1420℃ to obtain a liquid alloy liquid. Pour the liquid alloy liquid into a mold, and then cool it to obtain an alloy ingot. The alloy ingot is subjected to homogenization treatment, hot rolling, quenching, cold rolling, and aging treatment to obtain the copper-based alloy matrix. Step 2: After pretreatment of the copper-based alloy substrate, the copper-based alloy substrate is placed in the stress buffer layer plating solution, and a Ni-W alloy coating is deposited using a segmented current pulse electroplating process to obtain the stress buffer layer. Step 3: Place the copper-based alloy substrate obtained in Step 2 into the barrier transition layer plating solution, and deposit a Pd-Co alloy coating using a DC electroplating process to obtain the barrier transition layer; Step 4: Place the copper-based alloy substrate obtained in Step 3 into a composite silver plating solution, deposit a functional composite silver plating layer using a pulse reverse electroplating process, and then perform sealing and anti-oxidation treatment to obtain a silver-plated lead frame for semiconductors.

[0012] In a preferred embodiment, the homogenization treatment in step one is carried out at a temperature of 750-780℃ for 2-4 hours, the hot rolling time is 15-20 minutes, the rolling rate is controlled at 0.1-1 s⁻¹, and the hot rolling deformation is 50-65%. The cold rolling rate is controlled at 0.1-1 s⁻¹, and the cold rolling deformation is 62-68%. The aging treatment is carried out at a temperature of 550-600℃ for 4-5 hours.

[0013] In a preferred embodiment, the pretreatment of the copper-based alloy substrate in step two includes electrolytic degreasing, pickling, and plasma cleaning. The degreasing solution used in the electrolytic degreasing includes 140-145 g / L sodium chloride, 35-40 g / L sodium hydroxide, 4-6 g / L sodium silicate, and 2-3 g / L sodium thiosulfate, with a current density of 0.5-1 A / dm², a temperature of 60-70°C, and a time of 20-30 minutes. The pickling process first uses an 8-12 wt% sulfuric acid solution, followed by a 4-6 wt% sulfuric acid mixed solution containing 2-4 wt% ascorbic acid, with each pickling time being 15-25 seconds. The plasma cleaning process involves plasma bombardment in an Ar-H2 mixed atmosphere for 100-150 seconds.

[0014] In a preferred embodiment, the segmented current pulse electroplating process in step two includes the following parameters: first pulse segment: current density 2.0-3.0 A / dm², pulse frequency 500-1000 Hz, duty cycle 20-40%, temperature 50-60℃, electroplating time 30-60 seconds; second pulse segment: current density 1.0-2.0 A / dm², pulse frequency 100-500 Hz, duty cycle 40-60%, temperature 55-65℃, electroplating time 60-120 seconds.

[0015] In a preferred embodiment, the current density of the DC electroplating process in step three is 0.5-1.5 A / dm², the temperature is 45-55℃, the pH value is 9.0-9.5, and the electroplating time is 2-5 minutes.

[0016] In a preferred embodiment, the forward pulse current density of the pulse reverse electroplating process in step four is 1.5-2.5 A / dm², the pulse width is 1-3 ms, the reverse pulse current density is 0.3-0.8 A / dm², the pulse width is 0.2-0.5 ms, the pulse frequency is 50-200 Hz, the temperature is 25-35℃, and the time is 4-8 minutes.

[0017] In a preferred embodiment, during the sealing and anti-oxidation treatment in step four, the copper-based alloy substrate is immersed in the sealing solution for 5-15 minutes, then dried at 80-120°C for 20-40 minutes in a nitrogen atmosphere, and then placed in a plasma deposition chamber for low-temperature plasma chemical vapor deposition in an Ar-CH4 mixed atmosphere to grow a graphene thin film coating with a thickness of 1-5 nm on the surface of the silver plating layer in situ.

[0018] The technical effects and advantages of this invention are as follows: The silver-plated leadframe for semiconductors prepared using the raw material formulation of this invention introduces the synergistic effect of tin and zinc into the copper-chromium system: chromium and silicon form a dispersed reinforcing phase, significantly improving the matrix strength; tin dissolves in the copper matrix, enhancing its resistance to high-temperature softening and corrosion resistance; and zinc lowers the alloy melting temperature and improves the wettability at the interface with subsequent plating layers. The synergistic effect of these three components allows the matrix to maintain good conductivity (≥80% IACS) while achieving a tensile strength of 450-550 MPa. This invention incorporates a stress-relief layer on a copper substrate. The coefficients of thermal expansion (CTE) of Ni and Cu in this layer are similar, effectively reducing interfacial thermal stress during thermal cycling. The introduction of W significantly improves the coating hardness (≥600 HV) and corrosion resistance. Furthermore, the amorphous structure of the Ni-W alloy avoids the penetrating micropores caused by columnar crystal growth. The Pd-Co alloy coating in the barrier transition layer exhibits a dense, pinhole-free structure, and the introduction of Co refines the palladium grains (grain size ≤20). The nanometer-sized nanoparticles significantly reduce the porosity of the coating (≤1 porosity / cm²), acting as an effective barrier layer against copper diffusion. Simultaneously, their noble metal properties provide a favorable deposition substrate for subsequent silver plating. Nano-CeO2 and nano-GO are introduced into the barrier transition layer. Nano-CeO2, with its unique high oxygen storage / release capacity, endows the coating with self-passivation capabilities—in humid and hot environments, CeO2 preferentially reacts with infiltrating sulfides to form stable cerium sulfide, thus protecting the silver substrate from corrosion. The high specific surface area and two-dimensional lamellar structure of nano-GO form a physical barrier network within the coating, further preventing the penetration channels of corrosive media. Under the dispersion and stabilization effect of PEI, the two nanomaterials are uniformly co-deposited in the silver coating, forming a dense composite protective network. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention. Example 1

[0020] This invention provides a silver-plated lead frame for semiconductors, comprising a copper-based alloy substrate, a stress buffer layer, a barrier transition layer, and a composite silver plating layer. The copper-based alloy substrate comprises the following raw materials by weight percentage: 0.25% iron, 0.5% chromium, 0.3% tin, 0.1% zinc, 0.05% cerium, and 0.05% silicon, with the balance being copper and unavoidable impurities. The stress buffer layer is applied to a copper-based alloy substrate by electroplating a stress buffer layer plating solution. Each liter of the stress buffer layer plating solution contains the following raw materials: nickel aminosulfonate 250g / L, sodium tungstate 20g / L, boric acid 30g / L, sodium citrate 15g / L, saccharin 1g / L, and sodium dodecyl sulfate 0.05g / L. The barrier transition layer is formed by electroplating a barrier transition layer plating solution onto the stress buffer layer. Each liter of the barrier transition layer plating solution contains the following raw materials: 10 g / L palladium chloride, 1 g / L cobalt sulfate, 30 g / L ammonium chloride, 100 ml / L 25% ammonia water, 0.2 g / L butynediol, and 0.5 g / L o-sulfonylbenzeneimide. The composite silver plating layer is applied to the barrier transition layer by electroplating. Each liter of the composite silver plating solution comprises the following raw materials: 30 g / L silver nitrate, 60 g / L butyrylimide, 15 g / L potassium hydroxide, 20 g / L potassium carbonate, 0.5 g / L nano cerium oxide, 0.05 g / L nano graphene oxide, 0.02 g / L polyethyleneimine, and 0.5 g / L sodium didithiopropane sulfonate.

[0021] This invention also provides a method for preparing a silver-plated lead frame for semiconductors, the specific preparation steps of which are as follows: Step 1: Weigh the raw materials according to the weight percentage of the copper-based alloy matrix mentioned above, and put the weighed raw materials into a melting furnace for melting. The argon pressure in the melting furnace is 42 kPa, and the temperature inside the melting furnace is raised to 1400°C to obtain a liquid alloy liquid. Pour the liquid alloy liquid into a mold, and then cool it to obtain an alloy ingot. The alloy ingot is subjected to homogenization treatment, hot rolling, quenching, cold rolling, and aging treatment to obtain the copper-based alloy matrix. Step 2: After pretreatment of the copper-based alloy substrate, the copper-based alloy substrate is placed in the stress buffer layer plating solution, and a Ni-W alloy coating is deposited using a segmented current pulse electroplating process to obtain a stress buffer layer. The specific thickness of the stress buffer layer is 1.0 μm. Step 3: Place the copper-based alloy substrate obtained in Step 2 into the barrier transition layer plating solution, and deposit a Pd-Co alloy coating using a DC electroplating process to obtain the barrier transition layer. The specific thickness of the barrier transition layer is 0.2 μm. Step 4: Place the copper-based alloy substrate obtained in Step 3 into the composite silver plating solution, and deposit the functional composite silver plating layer using a pulse reverse electroplating process. Then, perform sealing and anti-oxidation treatment to obtain a silver-plated lead frame for semiconductors. The specific thickness of the composite silver plating layer is 2.5 μm.

[0022] In a preferred embodiment, the homogenization treatment in step one is carried out at a temperature of 760°C for 3 hours, the hot rolling time is 18 minutes, and the rolling rate is controlled at 0.6 seconds. -1 The hot rolling deformation is 50-65%, and the cold rolling rate is controlled at 0.6s. -1 The cold rolling deformation is 62-68%, the aging treatment temperature is 580℃, and the treatment time is 4.5h.

[0023] In a preferred embodiment, the pretreatment of the copper-based alloy substrate in step two includes electrolytic degreasing, pickling, and plasma cleaning. The degreasing solution used in the electrolytic degreasing process comprises 142 g / L sodium chloride, 38 g / L sodium hydroxide, 5 g / L sodium silicate, and 2.5 g / L sodium thiosulfate, with a current density of 0.8 A / dm², a temperature of 65°C, and a time of 25 minutes. The pickling process first uses a 10 wt% sulfuric acid solution, followed by a 5 wt% sulfuric acid mixed solution containing 3 wt% ascorbic acid, with each pickling time being 20 seconds. The plasma cleaning process involves plasma bombardment in an Ar-H2 mixed atmosphere for 130 seconds.

[0024] In a preferred embodiment, the segmented current pulse electroplating process in step two has the following characteristics: first pulse segment: current density 2.5 A / dm², pulse frequency 800 Hz, duty cycle 30%, temperature 55℃, electroplating time 45 seconds; second pulse segment: current density 1.5 A / dm², pulse frequency 300 Hz, duty cycle 50%, temperature 60℃, electroplating time 90 seconds.

[0025] In a preferred embodiment, the DC electroplating process in step three has a current density of 1.0 A / dm², a temperature of 50°C, a pH value of 9.2, and an electroplating time of 4 minutes.

[0026] In a preferred embodiment, the forward pulse current density of the pulse reverse electroplating process in step four is 2.0 A / dm², the pulse width is 2 ms, the reverse pulse current density is 0.5 A / dm², the pulse width is 0.3 ms, the pulse frequency is 130 Hz, the temperature is 30℃, and the time is 6 minutes.

[0027] In a preferred embodiment, during the sealing and anti-oxidation treatment in step four, the copper-based alloy substrate is immersed in the sealing solution for 10 minutes, then dried at 100°C for 30 minutes in a nitrogen atmosphere, and then placed in a plasma deposition chamber for low-temperature plasma chemical vapor deposition in an Ar-CH4 mixed atmosphere to grow a 3nm thick graphene film coating in situ on the surface of the silver plating layer. Example 2

[0028] Unlike Example 1, the present invention provides a silver-plated lead frame for semiconductors, comprising a copper-based alloy substrate, a stress buffer layer, a barrier transition layer, and a composite silver plating layer. The copper-based alloy substrate comprises the following raw materials by weight percentage: 0.45% iron, 1.0% chromium, 0.6% tin, 0.3% zinc, 0.1% cerium, and 0.14% silicon, with the balance being copper and unavoidable impurities. The stress buffer layer is applied to a copper-based alloy substrate by electroplating a stress buffer layer plating solution. Each liter of the stress buffer layer plating solution contains the following raw materials: nickel aminosulfonate 300g / L, sodium tungstate 35g / L, boric acid 35g / L, sodium citrate 20g / L, saccharin 2g / L, and sodium dodecyl sulfate 0.1g / L. The barrier transition layer is formed by electroplating a barrier transition layer plating solution onto the stress buffer layer. Each liter of the barrier transition layer plating solution contains the following raw materials: 15 g / L palladium chloride, 3 g / L cobalt sulfate, 40 g / L ammonium chloride, 130 ml / L 25% ammonia water, 0.35 g / L butynediol, and 0.7 g / L o-sulfonylbenzeneimide. The composite silver plating layer is applied to the barrier transition layer by electroplating. Each liter of the composite silver plating solution contains the following raw materials: silver nitrate 40 g / L, butyrylimide 80 g / L, potassium hydroxide 2 g / L, potassium carbonate 230 g / L, nano-cerium oxide 0.12 g / L, nano-graphene oxide 0.012 g / L, polyethyleneimine 0.0045 g / L, and sodium polydisulfide dipropane sulfonate 1.2 g / L. Example 3

[0029] Unlike Examples 1-2, the present invention provides a silver-plated lead frame for semiconductors, comprising a copper-based alloy substrate, a stress buffer layer, a barrier transition layer, and a composite silver plating layer. The copper-based alloy substrate comprises the following raw materials by weight percentage: 0.65% iron, 1.5% chromium, 1.0% tin, 0.5% zinc, 0.15% cerium, and 0.2% silicon, with the balance being copper and unavoidable impurities. The stress buffer layer is applied to a copper-based alloy substrate by electroplating a stress buffer layer plating solution. Each liter of the stress buffer layer plating solution contains the following raw materials: nickel aminosulfonate 350g / L, sodium tungstate 50g / L, boric acid 40g / L, sodium citrate 25g / L, saccharin 3g / L, and sodium dodecyl sulfate 0.15g / L. The barrier transition layer is formed by electroplating a barrier transition layer plating solution onto the stress buffer layer. Each liter of the barrier transition layer plating solution contains the following raw materials: 20 g / L palladium chloride, 5 g / L cobalt sulfate, 50 g / L ammonium chloride, 150 ml / L 25% ammonia water, 0.5 g / L butynediol, and 1.0 g / L o-sulfonylbenzeneimide. The composite silver plating layer is applied to the barrier transition layer by electroplating. Each liter of the composite silver plating solution comprises the following raw materials: 50 g / L silver nitrate, 100 g / L butyrylimide, 30 g / L potassium hydroxide, 40 g / L potassium carbonate, 2.0 g / L nano cerium oxide, 0.2 g / L nano graphene oxide, 0.08 g / L polyethyleneimine, and 2.0 g / L sodium didithiopropane sulfonate.

[0030] Comparative Example 1: The present invention provides a silver-plated lead frame for semiconductors, comprising a copper-based alloy matrix, wherein the copper-based alloy matrix comprises the following raw materials in weight percentages: 0.25% iron, 0.5% chromium, 0.3% tin, 0.1% zinc, 0.05% cerium, 0.05% silicon, with the balance being copper and unavoidable impurities.

[0031] This invention also provides a method for preparing a silver-plated lead frame for semiconductors, the specific preparation steps of which are as follows: Step 1: Weigh the raw materials according to the weight percentage of the copper-based alloy matrix mentioned above, and put the weighed raw materials into the melting furnace for melting. The argon pressure in the melting furnace is 42 kPa, and the temperature inside the melting furnace is raised to 1400°C to obtain liquid alloy liquid. Pour the liquid alloy liquid into a mold and then cool it to obtain an alloy ingot. The alloy ingot is subjected to homogenization treatment, hot rolling, quenching, cold rolling, and aging treatment to obtain the copper-based alloy matrix. A cyanide silver plating process is directly applied to the copper-based alloy matrix, and the silver plating layer thickness is about 3.0 μm.

[0032] In a preferred embodiment, the homogenization treatment in step one is carried out at a temperature of 760°C for 3 hours, the hot rolling time is 18 minutes, and the rolling rate is controlled at 0.6 seconds. -1 The hot rolling deformation is 50-65%, and the cold rolling rate is controlled at 0.6s. -1 The cold rolling deformation is 62-68%, the aging treatment temperature is 580℃, and the treatment time is 4.5h.

[0033] Comparative Example 2: This invention provides a silver-plated lead frame for semiconductors, comprising a copper-based alloy substrate, a stress buffer layer, and a barrier transition layer. The copper-based alloy substrate comprises the following raw materials by weight percentage: 0.25% iron, 0.5% chromium, 0.3% tin, 0.1% zinc, 0.05% cerium, and 0.05% silicon, with the balance being copper and unavoidable impurities. The stress buffer layer is applied to a copper-based alloy substrate by electroplating a stress buffer layer plating solution. Each liter of the stress buffer layer plating solution contains the following raw materials: nickel aminosulfonate 250g / L, sodium tungstate 20g / L, boric acid 30g / L, sodium citrate 15g / L, saccharin 1g / L, and sodium dodecyl sulfate 0.05g / L. The barrier transition layer is formed by electroplating a barrier transition layer plating solution onto the stress buffer layer. Each liter of the barrier transition layer plating solution contains the following raw materials: 10 g / L palladium chloride, 1 g / L cobalt sulfate, 30 g / L ammonium chloride, 100 ml / L 25% ammonia water, 0.2 g / L butynediol, and 0.5 g / L o-sulfonylbenzeneimide.

[0034] This invention also provides a method for preparing a silver-plated lead frame for semiconductors, the specific preparation steps of which are as follows: Step 1: Weigh the raw materials according to the weight percentage of the copper-based alloy matrix mentioned above, and put the weighed raw materials into a melting furnace for melting. The argon pressure in the melting furnace is 42 kPa, and the temperature inside the melting furnace is raised to 1400°C to obtain a liquid alloy liquid. Pour the liquid alloy liquid into a mold, and then cool it to obtain an alloy ingot. The alloy ingot is subjected to homogenization treatment, hot rolling, quenching, cold rolling, and aging treatment to obtain the copper-based alloy matrix. Step 2: After pretreatment of the copper-based alloy substrate, the copper-based alloy substrate is placed in the stress buffer layer plating solution, and a Ni-W alloy coating is deposited using a segmented current pulse electroplating process to obtain a stress buffer layer. The specific thickness of the stress buffer layer is 1.0 μm. Step 3: Place the copper-based alloy substrate obtained in Step 2 into the barrier transition layer plating solution, and deposit a Pd-Co alloy coating using a DC electroplating process to obtain the barrier transition layer. The specific thickness of the barrier transition layer is 0.2 μm. Step 4: The copper-based alloy substrate obtained in Step 3 is sealed and subjected to anti-oxidation treatment to obtain a silver-plated lead frame for semiconductors. The specific thickness of the composite silver plating is 2.5 μm.

[0035] In a preferred embodiment, the homogenization treatment in step one is carried out at a temperature of 760°C for 3 hours, the hot rolling time is 18 minutes, and the rolling rate is controlled at 0.6 seconds. -1 The hot rolling deformation is 50-65%, and the cold rolling rate is controlled at 0.6s. -1The cold rolling deformation is 62-68%, the aging treatment temperature is 580℃, and the treatment time is 4.5h.

[0036] In a preferred embodiment, the pretreatment of the copper-based alloy substrate in step two includes electrolytic degreasing, pickling, and plasma cleaning. The degreasing solution used in the electrolytic degreasing process comprises 142 g / L sodium chloride, 38 g / L sodium hydroxide, 5 g / L sodium silicate, and 2.5 g / L sodium thiosulfate, with a current density of 0.8 A / dm², a temperature of 65°C, and a time of 25 minutes. The pickling process first uses a 10 wt% sulfuric acid solution, followed by a 5 wt% sulfuric acid mixed solution containing 3 wt% ascorbic acid, with each pickling time being 20 seconds. The plasma cleaning process involves plasma bombardment in an Ar-H2 mixed atmosphere for 130 seconds.

[0037] In a preferred embodiment, the segmented current pulse electroplating process in step two has the following characteristics: first pulse segment: current density 2.5 A / dm², pulse frequency 800 Hz, duty cycle 30%, temperature 55℃, electroplating time 45 seconds; second pulse segment: current density 1.5 A / dm², pulse frequency 300 Hz, duty cycle 50%, temperature 60℃, electroplating time 90 seconds.

[0038] In a preferred embodiment, the DC electroplating process in step three has a current density of 1.0 A / dm², a temperature of 50°C, a pH value of 9.2, and an electroplating time of 4 minutes.

[0039] In a preferred embodiment, during the sealing and anti-oxidation treatment in step four, the copper-based alloy substrate is immersed in the sealing solution for 10 minutes, then dried at 100°C for 30 minutes in a nitrogen atmosphere, and then placed in a plasma deposition chamber for low-temperature plasma chemical vapor deposition in an Ar-CH4 mixed atmosphere to grow a 3nm thick graphene film coating in situ on the surface of the silver plating layer.

[0040] Comparative Example 3: This invention provides a silver-plated lead frame for semiconductors, comprising a copper-based alloy substrate, a stress buffer layer, a barrier transition layer, and a composite silver plating layer. The copper-based alloy substrate comprises the following raw materials by weight percentage: 0.25% iron, 0.5% chromium, 0.3% tin, 0.1% zinc, 0.05% cerium, and 0.05% silicon, with the balance being copper and unavoidable impurities. The stress buffer layer is applied to a copper-based alloy substrate by electroplating a stress buffer layer plating solution. Each liter of the stress buffer layer plating solution contains the following raw materials: nickel aminosulfonate 250g / L, sodium tungstate 20g / L, boric acid 30g / L, sodium citrate 15g / L, saccharin 1g / L, and sodium dodecyl sulfate 0.05g / L. The barrier transition layer is formed by electroplating a barrier transition layer plating solution onto the stress buffer layer. Each liter of the barrier transition layer plating solution contains the following raw materials: 10 g / L palladium chloride, 1 g / L cobalt sulfate, 30 g / L ammonium chloride, 100 ml / L 25% ammonia water, 0.2 g / L butynediol, and 0.5 g / L o-sulfonylbenzeneimide. The composite silver plating layer is applied to the barrier transition layer by electroplating. Each liter of the composite silver plating solution comprises the following raw materials: 30 g / L silver nitrate, 60 g / L butyrylimide, 15 g / L potassium hydroxide, 20 g / L potassium carbonate, 0.5 g / L nano cerium oxide, 0.05 g / L nano graphene oxide, 0.02 g / L polyethyleneimine, and 0.5 g / L sodium didithiopropane sulfonate.

[0041] This invention also provides a method for preparing a silver-plated lead frame for semiconductors, the specific preparation steps of which are as follows: Step 1: Weigh the raw materials according to the weight percentage of the copper-based alloy matrix mentioned above, and put the weighed raw materials into a melting furnace for melting. The argon pressure in the melting furnace is 42 kPa, and the temperature inside the melting furnace is raised to 1400°C to obtain a liquid alloy liquid. Pour the liquid alloy liquid into a mold, and then cool it to obtain an alloy ingot. The alloy ingot is subjected to homogenization treatment, hot rolling, quenching, cold rolling, and aging treatment to obtain the copper-based alloy matrix. Step 2: After pretreatment of the copper-based alloy substrate, the copper-based alloy substrate is placed in the stress buffer layer plating solution, and a Ni-W alloy coating is deposited using a segmented current pulse electroplating process to obtain a stress buffer layer. The specific thickness of the stress buffer layer is 1.0 μm. Step 3: Place the copper-based alloy substrate obtained in Step 2 into the barrier transition layer plating solution, and deposit a Pd-Co alloy coating using a DC electroplating process to obtain the barrier transition layer. The specific thickness of the barrier transition layer is 0.2 μm. Step 4: Place the copper-based alloy substrate obtained in Step 3 into the composite silver plating solution, and use a pulse reverse electroplating process to deposit a functional composite silver plating layer to obtain a silver-plated lead frame for semiconductors. The specific thickness of the composite silver plating layer is 2.5 μm.

[0042] In a preferred embodiment, the homogenization treatment in step one is carried out at a temperature of 760°C for 3 hours, the hot rolling time is 18 minutes, and the rolling rate is controlled at 0.6 seconds. -1 The hot rolling deformation is 50-65%, and the cold rolling rate is controlled at 0.6s. -1 The cold rolling deformation is 62-68%, the aging treatment temperature is 580℃, and the treatment time is 4.5h.

[0043] In a preferred embodiment, the pretreatment of the copper-based alloy substrate in step two includes electrolytic degreasing, pickling, and plasma cleaning. The degreasing solution used in the electrolytic degreasing process comprises 142 g / L sodium chloride, 38 g / L sodium hydroxide, 5 g / L sodium silicate, and 2.5 g / L sodium thiosulfate, with a current density of 0.8 A / dm², a temperature of 65°C, and a time of 25 minutes. The pickling process first uses a 10 wt% sulfuric acid solution, followed by a 5 wt% sulfuric acid mixed solution containing 3 wt% ascorbic acid, with each pickling time being 20 seconds. The plasma cleaning process involves plasma bombardment in an Ar-H2 mixed atmosphere for 130 seconds.

[0044] In a preferred embodiment, the segmented current pulse electroplating process in step two has the following characteristics: first pulse segment: current density 2.5 A / dm², pulse frequency 800 Hz, duty cycle 30%, temperature 55℃, electroplating time 45 seconds; second pulse segment: current density 1.5 A / dm², pulse frequency 300 Hz, duty cycle 50%, temperature 60℃, electroplating time 90 seconds.

[0045] In a preferred embodiment, the DC electroplating process in step three has a current density of 1.0 A / dm², a temperature of 50°C, a pH value of 9.2, and an electroplating time of 4 minutes.

[0046] In a preferred embodiment, the forward pulse current density of the pulse reverse electroplating process in step four is 2.0 A / dm², the pulse width is 2 ms, the reverse pulse current density is 0.5 A / dm², the pulse width is 0.3 ms, the pulse frequency is 130 Hz, the temperature is 30℃, and the time is 6 minutes.

[0047] In a preferred embodiment, during the sealing and anti-oxidation treatment in step four, the copper-based alloy substrate is immersed in the sealing solution for 10 minutes, then dried at 100°C for 30 minutes in a nitrogen atmosphere, and then placed in a plasma deposition chamber for low-temperature plasma chemical vapor deposition in an Ar-CH4 mixed atmosphere to grow a 3nm thick graphene film coating in situ on the surface of the silver plating layer.

[0048] The silver-plated lead frames for semiconductors produced in Examples 1-3 were selected as Experimental Group 1, Experimental Group 2 and Experimental Group 3, respectively. The lead frames produced in Comparative Examples 1-3 were selected as Comparative Examples 1, Comparative Examples 2 and Comparative Examples 3, respectively. The selected lead frames were subjected to microscopic analysis, coating adhesion and porosity tests.

[0049] Microscopic inspection: The surface and cross-sectional morphology of the coating are observed using a scanning electron microscope (SEM) to check for defects such as bubbles, pinholes, pores, and peeling. Coating adhesion: Evaluation was conducted according to SJ / T 11112-1996 standard, using the cross-cut adhesion test (ISO 2819 / GB 5270) and thermal shock test (200℃ / 30min, quenching in room temperature water). The cross-cut adhesion test was rated from 0 to 5 according to ASTM B571 (0 for complete no peeling, 5 for severe peeling). Porosity detection: Porosity was determined using the potassium ferricyanide test paper method and expressed as the number of pores per unit area (pores / cm²). The minimum detectable pore diameter was 0.05μm.

[0050] The test results are shown in Table 1:

[0051] Table 1 As shown in Table 1, the semiconductor silver-plated lead frames produced using Examples 1-3 of this invention have smooth surfaces, good coating adhesion, and low porosity. In contrast, Comparative Example 1, which directly employs a cyanide silver plating process, exhibits obvious pinholes and crystalline roughness on the plating surface, with a porosity exceeding 50 pinholes / cm². Comparative Example 2, compared to Example 1, reduces the composite silver plating layer, resulting in a small number of pinholes on the surface and a porosity of 15 pinholes / cm². Although Example 3 has the same three-layer plating structure as Example 1, it lacks pore sealing treatment and graphene coating deposition, resulting in a porosity of 3 pinholes / cm², higher than the 1 pinhole / cm² of Example 1. This indicates that pore sealing treatment and graphene coating further fill and seal the micropores on the plating surface. Therefore, this invention incorporates a stress buffer layer on a copper substrate. The coefficients of thermal expansion (CTE) of Ni and Cu in this layer are similar, effectively reducing interfacial thermal stress during thermal cycling. The introduction of W significantly improves the coating hardness (≥600 HV) and corrosion resistance. Furthermore, the Ni-W alloy's amorphous structure avoids the penetrating micropores caused by columnar crystal growth, ensuring a dense, pinhole-free Pd-Co alloy coating in the transition layer. The introduction of Co refines the palladium grains (grain size ≤20). The nanometer-sized nanoparticles significantly reduce the porosity of the coating (≤1 porosity / cm²), acting as an effective barrier layer against copper diffusion. Simultaneously, their noble metal properties provide a favorable deposition substrate for subsequent silver plating. Nano-CeO2 and nano-GO are introduced into the barrier transition layer. Nano-CeO2, with its unique high oxygen storage / release capacity, endows the coating with self-passivation capabilities—in humid and hot environments, CeO2 preferentially reacts with infiltrating sulfides to form stable cerium sulfide, thus protecting the silver substrate from corrosion. The high specific surface area and two-dimensional lamellar structure of nano-GO form a physical barrier network within the coating, further preventing the penetration channels of corrosive media. Under the dispersion and stabilization effect of PEI, the two nanomaterials are uniformly co-deposited in the silver coating, forming a dense composite protective network.

[0052] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A silver-plated lead frame for semiconductors, characterized in that: It includes a copper-based alloy substrate, a stress buffer layer, a barrier transition layer, and a composite silver plating layer. The copper-based alloy substrate comprises the following raw materials by weight percentage: iron 0.25-0.65%, chromium 0.5-1.5%, tin 0.3-1.0%, zinc 0.1-0.5%, cerium 0.05-0.15%, silicon 0.05-0.2%, with the balance being copper and unavoidable impurities. The stress buffer layer is applied to a copper-based alloy substrate by electroplating a stress buffer layer plating solution. Each liter of the stress buffer layer plating solution contains the following raw materials: nickel sulfamate 250-350 g / L, sodium tungstate 20-50 g / L, boric acid 30-40 g / L, sodium citrate 15-25 g / L, saccharin 1-3 g / L, and sodium dodecyl sulfate 0.05-0.15 g / L. The barrier transition layer is formed by electroplating a barrier transition layer plating solution onto the stress buffer layer. Each liter of the barrier transition layer plating solution comprises the following raw materials: palladium chloride 10-20 g / L, cobalt sulfate 1-5 g / L, ammonium chloride 30-50 g / L, 25% ammonia water 100-150 ml / L, butynediol 0.2-0.5 g / L, and o-sulfonylbenzeneimide 0.5-1.0 g / L. The composite silver plating layer is applied to the barrier transition layer by electroplating. Each liter of the composite silver plating solution comprises the following raw materials: silver nitrate 30-50 g / L, butyrylimide 60-100 g / L, potassium hydroxide 15-30 g / L, potassium carbonate 20-40 g / L, nano-cerium oxide 0.5-2.0 g / L, nano-graphene oxide 0.05-0.2 g / L, polyethyleneimine 0.02-0.08 g / L, and sodium polydisulfide dipropane sulfonate 0.5-2.0 g / L.

2. The silver-plated lead frame for semiconductors according to claim 1, characterized in that: It includes a copper-based alloy substrate, a stress buffer layer, a barrier transition layer, and a composite silver plating layer. The copper-based alloy substrate comprises the following raw materials by weight percentage: iron 0.35-0.55%, chromium 0.8-1.2%, tin 0.5-0.7%, zinc 0.2-0.4%, cerium 0.08-0.12%, silicon 0.12-0.16%, with the balance being copper and unavoidable impurities. The stress buffer layer is applied to a copper-based alloy substrate by electroplating a stress buffer layer plating solution. Each liter of the stress buffer layer plating solution contains the following raw materials: nickel sulfamate 280-320 g / L, sodium tungstate 30-40 g / L, boric acid 32-38 g / L, sodium citrate 18-22 g / L, saccharin 1.5-2.5 g / L, and sodium dodecyl sulfate 0.08-0.12 g / L. The barrier transition layer is formed by electroplating a barrier transition layer plating solution onto the stress buffer layer. Each liter of the barrier transition layer plating solution comprises the following raw materials: palladium chloride 12-18 g / L, cobalt sulfate 2-4 g / L, ammonium chloride 35-45 g / L, 25% ammonia water 120-140 ml / L, butynediol 0.3-0.4 g / L, and o-sulfonylbenzeneimide 0.6-0.8 g / L. The composite silver plating layer is applied to the barrier transition layer by electroplating. Each liter of the composite silver plating solution comprises the following raw materials: silver nitrate 35-45 g / L, butyrylimide 70-90 g / L, potassium hydroxide 18-25 g / L, potassium carbonate 25-35 g / L, nano-cerium oxide 0.8-1.5 g / L, nano-graphene oxide 0.08-0.15 g / L, polyethyleneimine 0.03-0.06 g / L, and sodium polydisulfide dipropane sulfonate 1.0-1.5 g / L.

3. The silver-plated lead frame for semiconductors according to claim 1, characterized in that: It includes a copper-based alloy substrate, a stress buffer layer, a barrier transition layer, and a composite silver plating layer. The copper-based alloy substrate comprises the following raw materials by weight percentage: 0.45% iron, 1.0% chromium, 0.6% tin, 0.3% zinc, 0.1% cerium, and 0.14% silicon, with the balance being copper and unavoidable impurities. The stress buffer layer is applied to a copper-based alloy substrate by electroplating a stress buffer layer plating solution. Each liter of the stress buffer layer plating solution comprises the following raw materials: Nickel sulfamate 300 g / L, sodium tungstate 35 g / L, boric acid 35 g / L, sodium citrate 20 g / L, saccharin 2 g / L, sodium dodecyl sulfate 0.1 g / L; The barrier transition layer is formed by electroplating a barrier transition layer plating solution onto the stress buffer layer. Each liter of the barrier transition layer plating solution contains the following raw materials: 15 g / L palladium chloride, 3 g / L cobalt sulfate, 40 g / L ammonium chloride, 130 ml / L 25% ammonia water, 0.35 g / L butynediol, and 0.7 g / L o-sulfonylbenzeneimide. The composite silver plating layer is applied to the barrier transition layer by electroplating. Each liter of the composite silver plating solution contains the following raw materials: silver nitrate 40 g / L, butyrylimide 80 g / L, potassium hydroxide 2 g / L, potassium carbonate 230 g / L, nano-cerium oxide 0.12 g / L, nano-graphene oxide 0.012 g / L, polyethyleneimine 0.0045 g / L, and sodium polydisulfide dipropane sulfonate 1.2 g / L.

4. A method for preparing a silver-plated lead frame for semiconductors according to any one of claims 1-3, characterized in that: The specific preparation steps are as follows: Step 1: Weigh the raw materials according to the weight percentage of the copper-based alloy matrix mentioned above, and put the weighed raw materials into a melting furnace for melting. The argon pressure in the melting furnace is 40-45 kPa, and the temperature inside the melting furnace is raised to 1380-1420℃ to obtain a liquid alloy liquid. Pour the liquid alloy liquid into a mold, and then cool it to obtain an alloy ingot. The alloy ingot is subjected to homogenization treatment, hot rolling, quenching, cold rolling, and aging treatment to obtain the copper-based alloy matrix. Step 2: After pretreatment of the copper-based alloy substrate, the copper-based alloy substrate is placed in the stress buffer layer plating solution, and a Ni-W alloy coating is deposited using a segmented current pulse electroplating process to obtain the stress buffer layer. Step 3: Place the copper-based alloy substrate obtained in Step 2 into the barrier transition layer plating solution, and deposit a Pd-Co alloy coating using a DC electroplating process to obtain the barrier transition layer; Step 4: Place the copper-based alloy substrate obtained in Step 3 into a composite silver plating solution, deposit a functional composite silver plating layer using a pulse reverse electroplating process, and then perform sealing and anti-oxidation treatment to obtain a silver-plated lead frame for semiconductors.

5. The method for preparing a silver-plated lead frame for semiconductors according to claim 4, characterized in that: In step one, the homogenization treatment is carried out at a temperature of 750-780℃ for 2-4 hours, the hot rolling time is 15-20 minutes, and the rolling rate is controlled between 0.1 and 1 second. -1 The hot rolling deformation is 50-65%, and the cold rolling speed is controlled between 0.1 and 1 second. -1 The cold rolling deformation is 62-68%, the aging treatment temperature is 550-600℃, and the treatment time is 4-5h.

6. The method for fabricating a silver-plated lead frame for semiconductors according to claim 4, characterized in that: Step two, the pretreatment of the copper-based alloy substrate, includes electrolytic degreasing, pickling, and plasma cleaning. The degreasing solution used in the electrolytic degreasing process consists of 140-145 g / L sodium chloride, 35-40 g / L sodium hydroxide, 4-6 g / L sodium silicate, and 2-3 g / L sodium thiosulfate, with a current density of 0.5-1 A / dm², a temperature of 60-70°C, and a time of 20-30 minutes. The pickling process first uses an 8-12 wt% sulfuric acid solution, followed by a 4-6 wt% sulfuric acid mixed solution containing 2-4 wt% ascorbic acid, with each pickling lasting 15-25 seconds. The plasma cleaning process involves plasma bombardment in an Ar-H2 mixed atmosphere for 100-150 seconds.

7. The method for preparing a silver-plated lead frame for semiconductors according to claim 4, characterized in that: In step two, the segmented current pulse electroplating process has the following characteristics: first pulse segment: current density 2.0-3.0 A / dm², pulse frequency 500-1000 Hz, duty cycle 20-40%, temperature 50-60℃, electroplating time 30-60 seconds; second pulse segment: current density 1.0-2.0 A / dm², pulse frequency 100-500 Hz, duty cycle 40-60%, temperature 55-65℃, electroplating time 60-120 seconds.

8. The method for fabricating a silver-plated lead frame for semiconductors according to claim 4, characterized in that: In step three, the DC electroplating process has a current density of 0.5-1.5 A / dm², a temperature of 45-55℃, a pH value of 9.0-9.5, and an electroplating time of 2-5 minutes.

9. The method for preparing a silver-plated lead frame for semiconductors according to claim 4, characterized in that: In step four, the forward pulse current density of the pulse reverse electroplating process is 1.5-2.5 A / dm², the pulse width is 1-3 ms, the reverse pulse current density is 0.3-0.8 A / dm², the pulse width is 0.2-0.5 ms, the pulse frequency is 50-200 Hz, the temperature is 25-35℃, and the time is 4-8 minutes.

10. The method for preparing a silver-plated lead frame for semiconductors according to claim 4, characterized in that: In step four, during the sealing and anti-oxidation treatment, the copper-based alloy substrate is immersed in the sealing solution for 5-15 minutes, then dried in a nitrogen atmosphere at 80-120°C for 20-40 minutes, and then placed in a plasma deposition chamber for low-temperature plasma chemical vapor deposition in an Ar-CH4 mixed atmosphere to grow a graphene thin film coating with a thickness of 1-5 nm on the surface of the silver plating layer in situ.

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