High-reliability SOP lead frame and manufacturing method thereof

Abstract

The invention belongs to the technical field of semiconductor packaging, and discloses a high-reliability SOP (Small Outline Package) lead frame and a manufacturing method of the high-reliability SOP lead frame. The method comprises the following steps: S1, pretreatment; s2, depositing a bottom layer; s3, depositing a stress adjusting layer; s4, depositing a functional top layer; preferably, the method further comprises the step S5 of chemical vapor deposition. According to the invention, through the doping of the indium element, the composite nano additive and the coordinated regulation and control of the process, the interlayer adhesion and conductivity are enhanced, the problems of falling off of the SOP packaging bent plating layer and layering of plastic packaging are solved, the humidity sensitivity level reaches the MSL-1 level, and the cyanide-free plating solution is adopted, so that the green manufacturing trend is met.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor packaging technology, specifically relating to a high-reliability SOP lead frame and its manufacturing method. Background Technology

[0002] The leadframe is the core chip carrier of integrated circuits. It enables the electrical connection between the internal and external circuits of the chip through bonding materials, and also plays a crucial role in supporting the chip and bonding with the molding compound to form the package shell. As semiconductor technology develops towards miniaturization and high integration, SOP (Small Outline Package) packaging is widely used in various integrated circuits due to its high assembly density and wide applicability.

[0003] In existing technologies, leadframes are typically fabricated using multi-layer electroplating processes, such as sequentially depositing metal layers like tin, nickel, palladium, and silver on a copper substrate to improve performance. For example, invention patent CN 116479485 A discloses a high-reliability leadframe that improves the density and oxidation resistance of the plating by introducing composite additives into the nickel and palladium-nickel layers. However, in specific application scenarios of SOP packaging, this type of existing technology still has significant drawbacks: 1. Insufficient resistance to bending failure of plating: SOP package requires the pins to be bent into a 90° "wing" or "J" shape. Existing technology uses single-pulse deposition of tin layer. The tin layer and copper substrate are only physically bonded. The difference in modulus between the layers is large and the internal stress accumulation is obvious. When bending, the plating is very easy to crack, peel or even peel off, which seriously affects solderability and service reliability. 2. High risk of delamination at the molding interface: During the SMT reflow soldering process, the lead frame experiences drastic temperature fluctuations. In the existing technology, the metal frame and epoxy molding compound lack effective chemical bonding. The mismatch in thermal expansion coefficients leads to easy delamination at the interface, causing moisture intrusion and the "popcorn effect". 3. Insufficient synergistic effect of additives: Existing inorganic additives only focus on sealing nanopores and have not achieved synergistic doping with metal elements, making it difficult to simultaneously optimize contact resistance and coating toughness. 4. The environmental friendliness of the process needs to be improved: Some silver plating solutions use cyanide-containing systems, which have high environmental treatment costs and do not conform to the trend of green manufacturing.

[0004] Therefore, developing a SOP lead frame that can withstand high-ratio bending, has strong bonding with molding compound, low internal stress, and high conductivity is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0005] This invention provides a method for fabricating a high-reliability SOP lead frame, characterized by the following steps: S1, pretreatment: a copper substrate is sequentially subjected to electrolytic degreasing, acid pickling, and plasma cleaning to obtain a pretreated copper-based lead frame; S2, underlayer deposition: the pretreated copper-based lead frame is placed in a nickel-based plating solution, and a nickel-indium alloy underlayer is formed by electrodeposition using a dual-pulse commutated current to obtain lead frame A; wherein, the nickel-indium alloy underlayer is formed by controlling the reverse pulse current parameters, and the anodic dissolution characteristics of the reverse pulse current are used to eliminate interfacial concentration polarization and refine grains, forming a high-density barrier layer; S3, stress-adjusting layer deposition: lead frame A is placed in a nickel-palladium plating solution, and a nickel-palladium alloy layer is formed by gradient DC electrodeposition to obtain lead frame B; the current density and plating solution temperature are simultaneously controlled during the gradient DC electrodeposition process; S4, functional top layer deposition: lead frame B is placed in a silver plating solution, and a silver layer is pulsedly electrodeposited to obtain the high-reliability SOP lead frame.

[0006] Furthermore, in step S1, the degreasing solution for electrolytic degreasing includes 40-60 g / L sodium carbonate, 35-40 g / L sodium hydroxide, 4-6 g / L sodium silicate, and 2-3 g / L sodium thiosulfate; the process parameters are a current density of 0.5-1 A / dm², a temperature of 60-70°C, and a time of 20-30 minutes.

[0007] Furthermore, in step S2, the parameters of the dual-pulse commutation current are: forward pulse frequency 80-150Hz, duty cycle 50-60%; reverse pulse current density is 10-15% of the forward current density, used to eliminate growth stress caused by lattice mismatch in the early stage of deposition.

[0008] Furthermore, in step S2, the nickel-based plating solution contains 20-35 g / L nickel chloride, 4-7 g / L indium chloride, 15-20 g / L methylene diphosphonic acid and 0.5-1 g / L 6-amidinyl-2-naphthol methanesulfonic acid, and the mass fraction of indium in the nickel-indium alloy underlayer is 3%-8%.

[0009] Furthermore, in step S3, during gradient DC deposition of the nickel-palladium alloy layer, the current density is gradually reduced from 2-2.5 A / dm² to 1 A / dm², with a step value of 0.5 A / dm² / 5 min; the temperature is gradually reduced from 55-60℃ to 45℃, with a step value of 5℃ / 5 min. Preferably, an additional 2 g / L of crystallization modifier (selected from disodium ethylenediaminetetraacetate) is added, and deposition is carried out at a DC current of 2 A / dm² for 2 minutes. The modifier inhibits the growth of Ni crystal planes, forming a nickel layer with a needle-cone array structure on the surface.

[0010] Furthermore, in step S4, the silver plating solution includes 28-32 g / L silver nitrate, 110-125 g / L 3-hydroxymethyl-5,5-dimethylhydantoin and 1.5-3 g / L sodium 3-mercapto-1-propanesulfonate.

[0011] Furthermore, the nickel-based plating solution in step S2 and the silver plating solution in step S4 each contain a composite additive, which is a mixture of indium selenide-reduced graphene oxide support prepared by ionic liquid microwave method and an organic dispersant.

[0012] Furthermore, in the composite additive, the mass ratio of indium selenide-reduced graphene oxide to β-naphthol polyoxyethylene ether is 1:(0.4-0.5).

[0013] Furthermore, after step S4 is completed, step S5 is also included: chemical vapor deposition: using a mask to cover the functional area of ​​the lead frame, a silane coupling agent film with a thickness of 10-30 nm is deposited in the non-functional area by chemical vapor deposition to enhance the peel strength between the SOP lead frame and the molding compound; the functional area includes a silver layer surface for bonding or soldering.

[0014] A high-reliability SOP lead frame prepared by the above manufacturing method.

[0015] The present invention has the following beneficial effects: Completely solve the problem of high-temperature stratification.

[0016] This invention uses a high-melting-point nickel-indium alloy instead of the traditional easily fusible tin as the base coat. Even at a reflow soldering temperature of 260°C, the base coat remains a stable solid, completely eliminating plating "floating" and delamination failure caused by base coat melting, significantly improving the thermal stability of the device.

[0017] Mechanical interlocking enhances the bonding force.

[0018] By controlling the process, a "needle-cone array structure" is constructed on the coating surface. Combined with the "gradient deposition" nickel-palladium alloy layer, it not only relieves internal stress, but also forms a strong mechanical interlock with the molding compound like countless tiny "rivets", which greatly improves the peel strength between the lead frame and the molding compound.

[0019] Micro-nano composites enhance weather resistance.

[0020] An indium selenide-graphene composite additive was introduced into the plating bath. The shielding effect of graphene was used to fill microscopic defects in the coating and construct a labyrinthine anti-corrosion path, which significantly enhanced the coating's resistance to salt spray corrosion and anti-aging performance (excellent performance in PCT test).

[0021] Balancing bonding and airtightness.

[0022] An innovative "mask-assisted chemical vapor deposition process" is employed to deposit silane films only in non-functional areas to enhance hermeticity, while ensuring a clean and contamination-free surface in the functional areas (silver layer). This solves the problem of moisture infiltration and guarantees extremely high tensile strength and yield for the "first solder joint" of gold wire bonding. Detailed Implementation

[0023] To enable those skilled in the art to better understand the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and experimental data. It must be noted that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0024] Preparation method of composite additives: The composite additive used in Examples 1-2 and the comparative examples of this invention is an aqueous dispersion of reduced graphene oxide (rGO) loaded with indium selenide (InSe) nanoparticles. Its preparation process aims to solve the problem of easy agglomeration of nanomaterials in strong electrolyte electroplating solutions. The specific steps are as follows: Step 1: Microwave synthesis of precursors for ionic liquids.

[0025] 1.0 g of indium powder (In) and 1.5 g of selenium powder (Se) (molar ratio approximately 1:2, with a slight excess of selenium to compensate for volatilization) were added to 10 mL of ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM]BF4). The mixture was placed in a microwave reactor, and the microwave power was set to 500 W. The reaction was carried out at 140 °C for 10 minutes. The ionic liquid, as an excellent microwave absorbing medium, induced rapid in-situ nucleation of indium selenide atoms, forming a uniform dispersion of InSe nanocrystal precursor.

[0026] Step 2: Liquid-phase assembly and hydrothermal reduction.

[0027] The precursor dispersion was slowly added dropwise to 100 mL of a 5 mg / mL graphene oxide (GO) aqueous suspension and ultrasonically dispersed for 30 minutes. The mixture was then transferred to a polytetrafluoroethylene-lined high-pressure reactor and subjected to a hydrothermal reaction at 160-180 °C for 6 hours. During this process, the high temperature and pressure reduced GO to conductive rGO, while InSe nanocrystals underwent epitaxial growth and solidification on the rGO sheets. After the reaction, the solid was separated by centrifugation and washed three times with ethanol to remove residual ionic liquid.

[0028] Step 3: Surface modification and slurry preparation.

[0029] The washed wet InSe-rGO composite material was mixed with the organic dispersant β-naphthol polyoxyethylene ether at a mass ratio of 1:0.4, and an appropriate amount of deionized water was added. The mixture was then subjected to high-speed shear dispersion at 5000 rpm for 15 minutes to finally prepare a composite additive dispersion with a solid content of 10 mg / mL.

[0030] Example 1 A method for manufacturing a high-reliability SOP lead frame, the specific steps of which are as follows: S1, Pretreatment: A 0.2mm thick copper sheet substrate is placed in an electrolytic degreasing solution composed of 50g / L sodium carbonate, 40g / L sodium hydroxide, 5g / L sodium silicate, and 2g / L sodium thiosulfate. Process parameters: current density 1 A / dm², temperature 65℃, time 25 minutes. This is followed by pickling with 8wt% sulfuric acid and 2wt% ascorbic acid for 15 seconds, and finally plasma cleaning for 120 seconds under an Ar-H2 atmosphere.

[0031] S2, Underlayer Deposition (NiIn Alloy Underlayer): The pretreated copper-based lead frame is placed in a nickel-based plating solution.

[0032] Plating solution formulation: 30 g / L nickel chloride, 5 g / L indium chloride, 18 g / L methylene diphosphonic acid, 0.8 g / L 6-amidinyl-2-naphthol methanesulfonic acid, 0.3 g / L composite additive, i.e., adding 30 mL / L of composite additive dispersion (indium selenide-reduced graphene oxide to β-naphthol polyoxyethylene ether mass ratio 1:0.4).

[0033] Dual-pulse parameters: forward current density 2.5 A / dm², frequency 100 Hz, duty cycle 50%; reverse current density 0.375 A / dm² (15% of the forward), frequency 100 Hz, duty cycle 50%.

[0034] Process conditions: Temperature 50℃, deposition time 30 seconds. A dense nickel-indium alloy underlayer with a thickness of approximately 0.1 μm is formed.

[0035] S3, Deposition of stress-regulating layer: Step 1 (Pure Nickel Transition): Add an additional 2 g / L of crystallization modifier (selected from disodium ethylenediaminetetraacetate) to the nickel sulfamate plating bath, and deposit for 2 minutes under a DC current of 2 A / dm². Utilize the inhibitory effect of the modifier on the growth of Ni crystal planes to form a nickel layer with a needle-cone array structure on the surface.

[0036] Step 2 (gradient nickel-palladium): Transfer to nickel-palladium plating bath (50 g / L dichlorodiaminopalladium, 20 g / L nickel chloride). Gradient DC electrodeposition is used: initial current density 2.5 A / dm², initial temperature 60℃; within 15 minutes, the current density linearly decreases to 1 A / dm², and the temperature linearly decreases to 45℃.

[0037] S4, Functional Top Layer Deposition: The lead frame is placed in a silver plating solution (30 g / L silver nitrate, 120 g / L 3-hydroxymethyl-5,5-dimethylhydantoin, 2 g / L sodium 3-mercapto-1-propanesulfonate, 0.2 g / L composite additive, i.e., 20 mL / L composite additive dispersion is added).

[0038] Pulsed electrodeposition was used: average current density 1.5 A / dm², frequency 500 Hz, duty cycle 40%, deposition time 1 minute to obtain a silver functional layer.

[0039] S5, Chemical Vapor Deposition (with Mask): The functional areas of the lead frame (i.e., the surface of the bonding silver layer) are completely masked using a precision physical mask. The frame is placed in a vacuum chamber, and gaseous silane coupling agent (KH-560) is introduced to deposit a 20 nm thick silane film in the non-functional areas (base sidewalls and pin gaps).

[0040] Example 2 The only difference from Example 1 is the parameter adjustment: in S1, the sodium carbonate content in the degreasing solution is 40 g / L. In S2, the nickel-based plating solution contains 20 g / L nickel chloride and 7 g / L indium chloride; the reverse pulse current density is 10% of the forward current. In S5, the silane film thickness is 10 nm. The remaining steps are the same as in Example 1.

[0041] Comparative Example 1 The difference from Example 1 is that step S2 is replaced with a bottom tin plating process.

[0042] S2 specific operation: Place the pretreated copper-based lead frame in tin plating solution (165mL / L tin methanesulfonate), and electrodeposit a pure tin layer as the bottom layer with a thickness of 0.5μm.

[0043] Comparative Example 2 The difference from Example 1 is that no mask is used in step S5.

[0044] S5 specific operation: The silver-plated lead frame is directly placed in the chemical vapor deposition chamber to deposit silane coupling agent, resulting in the surface of the silver functional layer also being covered with a 20nm insulating silane film.

[0045] Comparative Example 3 The difference from Example 1 is as follows: S2 nickel-based plating solution does not contain indium chloride (i.e., pure nickel base plating). All plating solutions S2, S3, and S4 do not contain composite additives.

[0046] Performance Tests and Results: The SOP lead frames prepared in Examples 1-2 and Comparative Examples 1-3 were subjected to reliability and functional tests using the following methods: Reflow soldering reliability.

[0047] Testing standards: Refer to IPC / JEDEC J-STD-020 standard.

[0048] Test process: 1. Pretreatment: The packaged SOP device is subjected to moisture absorption at 85℃ / 85% relative humidity (high temperature and high humidity) for 168 hours (corresponding to MSL-1 level moisture absorption conditions).

[0049] 2. Reflow soldering: Pass the moisture-absorbing sample through a lead-free reflow oven with a peak temperature set at 260℃ (+0 / -5℃) and a transfer speed ensuring that the time above 255℃ exceeds 30 seconds.

[0050] 3. Number of cycles: Perform 3 consecutive reflow soldering cycles to simulate the thermal shock during the actual assembly process.

[0051] 4. Judgment Method: After reflow soldering, use an ultrasonic scanning microscope to check whether there is delamination or blistering at the interface between the lead frame and the molding compound, and at the interface between the plating and the substrate. No delamination or blistering is recorded as "pass".

[0052] II. Bond tensile test.

[0053] 1. Testing instrument: DAGE 4000 push-pull force testing machine.

[0054] 2. Test conditions: Ball soldering was performed on the functional area (silver-plated surface) of the lead frame using gold wire with a diameter of 25μm (1mil).

[0055] 3. Bonding parameters: ultrasonic power 60mW, time 15ms, pressure 30g.

[0056] 4. Test method: After bonding is completed, apply a pulling force to the gold wire in a direction perpendicular to the chip surface until the gold wire breaks or the solder joint falls off, and record the maximum pulling force value (g).

[0057] 5. Judgment criteria: A tensile strength > 5g and a fracture mode of gold wire neck fracture (rather than solder joint detachment) are considered qualified; "non-stick" or extremely low tensile strength are considered as failure.

[0058] III. Shear force test after aging.

[0059] 1. Aging conditions: Place the bonded sample in a high-pressure cooker (PCT) at 121°C, 100% relative humidity, and 2 atm for 96 hours.

[0060] 2. Test method: After aging, the shearing module of the push-pull force tester was used. The push blade height was set to 3μm and the shearing speed was 100μm / s. The shearing test was performed on the gold ball solder joint, and the shearing force value (g) was recorded. If the shearing force was extremely low, it was determined to be a failure.

[0061] 3. Objective: To evaluate the stability of intermetallic compounds in the coating and the degradation of interfacial adhesion after high temperature and high humidity aging.

[0062] IV. Salt spray test.

[0063] Test standard: Refer to GB / T 10125 standard.

[0064] Test conditions: 1. Solution: 5wt% NaCl neutral salt solution.

[0065] 2. Internal temperature: 35±2℃.

[0066] 3. Spraying time: Continuous spraying for 48 hours.

[0067] Judgment method: After the test, clean with deionized water and dry, then observe the surface of the lead frame under a 10x microscope. If green copper rust or black corrosion spots appear on the surface, it is judged as corrosion; if the surface is shiny and unchanged, it is judged as "no corrosion".

[0068] V. MSL Level Test.

[0069] Test standard: IPC / JEDEC J-STD-020.

[0070] Decision logic: 1. Level 1 (highest level): After the sample absorbs moisture at 85℃ / 85% relative humidity for 168 hours, it undergoes three reflow soldering cycles at 260℃ without delamination or cracking.

[0071] 2. Level 3: After the sample absorbed moisture for 192 hours at 30℃ / 60% relative humidity, it underwent three reflow soldering cycles at 260℃ without delamination.

[0072] 3. Failure: If the above standards are not met, stratification or failure will occur.

[0073] The results are shown in the table below: Table 1. Reliability and Functional Test Data Results for Examples and Comparative Examples Conclusion Analysis: Comparative Example 1 demonstrates that tin plating of the bottom layer is not feasible, which in turn proves that the use of nickel-indium alloy as the bottom layer (S2) in this application is the key to achieving high-temperature reliability.

[0074] Comparative Example 2 demonstrates the necessity of the chemical vapor deposition masking process (S5) for ensuring bonding functionality.

[0075] The comparison between Example 1 and Comparative Example 3 demonstrates the significant effect of indium doping and composite additives on improving aging resistance.

[0076] The specific embodiments of the present invention have been described in detail above, but they are merely examples, and the present invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications and substitutions to the present invention are also within the scope of the present invention. Therefore, all equivalent transformations and modifications made without departing from the spirit and scope of the present invention should be covered within the scope of the present invention.

Claims

1. A method for manufacturing a high-reliability SOP lead frame, characterized in that, Includes the following steps: S1, Pretreatment: The copper substrate is sequentially subjected to electrolytic degreasing, pickling, and plasma cleaning to obtain a pretreated copper-based lead frame; S2, Underlayer Deposition: The pretreated copper-based lead frame is placed in a nickel-based plating solution, and a nickel-indium alloy underlayer is formed by electrodeposition using a dual-pulse commutated current to obtain lead frame A; wherein, the nickel-indium alloy underlayer is formed by controlling the reverse pulse current parameters; S3, Stress Adjustment Layer Deposition: Lead frame A is placed in a nickel-palladium plating solution, and a nickel-palladium alloy layer is formed by gradient DC electrodeposition to obtain lead frame B; the current density and plating solution temperature are simultaneously controlled during the gradient DC electrodeposition process; S4, Functional Top Layer Deposition: Lead frame B is placed in a silver plating solution, and a silver layer is pulsedly electrodeposited to obtain the high-reliability SOP lead frame.

2. The manufacturing method according to claim 1, characterized in that: In step S1, the degreasing solution for electrolytic degreasing includes 40-60 g / L sodium carbonate, 35-40 g / L sodium hydroxide, 4-6 g / L sodium silicate, and 2-3 g / L sodium thiosulfate; the process parameters are current density 0.5-1 A / dm², temperature 60-70℃, and time 20-30 minutes.

3. The manufacturing method according to claim 1, characterized in that: In step S2, the parameters of the dual-pulse commutation current are: forward pulse frequency 80-150Hz, duty cycle 50-60%; reverse pulse current density is 10-15% of the forward current density, used to eliminate growth stress caused by lattice mismatch in the early stage of deposition.

4. The manufacturing method according to claim 1, characterized in that: In step S2, the nickel-based plating solution contains 20-35 g / L nickel chloride, 4-7 g / L indium chloride, 15-20 g / L methylene diphosphonic acid and 0.5-1 g / L 6-amidinyl-2-naphthol methanesulfonic acid, and the mass fraction of indium in the nickel-indium alloy underlayer is 3%-8%.

5. The manufacturing method according to claim 1, characterized in that: In step S3, during gradient DC deposition of the nickel-palladium alloy layer, the current density is gradually reduced from 2-2.5 A / dm² to 1 A / dm², with a step value of 0.5 A / dm² / 5 min; the temperature is gradually reduced from 55-60℃ to 45℃, with a step value of 5℃ / 5 min.

6. The manufacturing method according to claim 1, characterized in that: In step S4, the silver plating solution includes 28-32 g / L silver nitrate, 110-125 g / L 3-hydroxymethyl-5,5-dimethylhydantoin and 1.5-3 g / L sodium 3-mercapto-1-propanesulfonate.

7. The manufacturing method according to claim 1, characterized in that: The nickel-based plating solution in step S2 and the silver plating solution in step S4 each contain a composite additive, which is a mixture of indium selenide-reduced graphene oxide support prepared by ionic liquid microwave method and an organic dispersant.

8. The manufacturing method according to claim 7, characterized in that: In the composite additive, the mass ratio of indium selenide-reduced graphene oxide to β-naphthol polyoxyethylene ether is 1:(0.4-0.5).

9. The manufacturing method according to any one of claims 1-8, characterized in that: After step S4 is completed, step S5 is also included: chemical vapor deposition: using a mask to cover the functional area of ​​the lead frame, a silane coupling agent film with a thickness of 10-30 nm is deposited in the non-functional area by chemical vapor deposition to enhance the peel strength between the SOP lead frame and the molding compound; the functional area includes a silver layer surface for bonding or soldering.

10. A high-reliability SOP lead frame prepared by the manufacturing method as described in claim 1.

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