Process for preparing single-sided coarsened pre-electroplated lead frame

Abstract

The invention discloses a process for preparing a single-sided coarsened pre-electroplated lead frame, and belongs to the field of semiconductor devices. The invention discloses a process for preparing a single-sided coarsened pre-electroplated lead frame. The process comprises the following steps of: attaching a heat release adhesive tape on a lead bonding surface of the lead frame; deoiling, washing and activating the tin soldering surface of the lead frame; performing common nickel electro-deposition, palladium electro-deposition and gold electro-deposition on the lead frame in sequence; washing and drying the lead frame, and removing the heat release adhesive tape attached to the lead bonding surface of the lead frame; a heat release adhesive tape is attached to the tin soldering face of the lead frame; carrying out oil removal, water washing and activation on the lead bonding surface of the lead frame; performing rough nickel electro-deposition, palladium electro-deposition and gold electro-deposition on the lead frame in sequence; and washing and drying the lead frame, and removing the heat release adhesive tape attached to the tin soldering surface of the lead frame. By adopting the heat release adhesive tape, the single-side coarsening process of the lead frame is realized, and the binding force between the lead bonding surface and the plastic package epoxy resin can be increased.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor devices, and more particularly, to a process for preparing a single-sided roughened pre-plated lead frame. Background Art

[0002] The lead frame is the main structural material for integrated circuit packaging, playing an important role in connecting external circuits, transmitting electrical signals, dissipating heat to the outside, supporting and fixing chips in the circuit, and is a key component for forming electrical circuits in integrated circuits. Most semiconductor integrated blocks require the use of lead frames, which are key basic materials in the electronic information industry. In 1989, Texas Instruments introduced the pre-plated lead frame (Pre-Plating frame Finish, PPF). The pre-plated lead frame refers to plating nickel, palladium, and gold layers on the surface of the lead frame. Since the pre-plated lead frame can ensure the quality of soldering, the post-packaging plating process can be omitted, thus greatly saving costs and time, and has been widely studied.

[0003] After retrieval, the existing Chinese patent CN112133640A discloses a method for preparing a lead frame with rough sidewalls. First, single-sided brown oxidation is performed on the upper surface of the lead frame, and then after electroplating and etching, the semi-etched area and the sidewalls are super-roughened. By controlling the super-roughening process conditions, a rough surface with good roughness is formed on the sidewalls and the semi-etched area, increasing the bonding force of the lead frame in the area in contact with the plastic encapsulation resin. The lower surface of the lead frame is not roughened, and only a pre-plated layer with a smooth surface is formed in the exposed pad area, reducing the area of surface roughening. At the same time, the lower surface is not easily adhered to the overflow material generated during the plastic encapsulation process, reducing the cleaning difficulty, which is beneficial to simplifying the process and saving roughening and electroplating costs.

[0004] The above patent uses brown oxidation to increase the roughness of the lead bonding surface, and the copper material surface after brown oxidation treatment needs to be laminated twice. Since the copper material surface after brown oxidation is very rough, when laminating twice and then stripping the film, there will be a problem of incomplete film stripping. Secondly, the rough structure formed after brown oxidation is relatively fragile, and pressure is required for film pressing during the second lamination process, resulting in the destruction of the rough structure. In view of this, we propose a process for preparing a single-sided roughened pre-plated lead frame. Summary of the Invention

[0005] 1. Technical Problems to be Solved The purpose of the present invention is to provide a process for preparing a single-sided roughened pre-plated lead frame to solve the problems raised in the above background art.

[0006] 2. Technical Solutions The present invention is realized through the following technical solutions: A process for preparing a single-sided roughened pre-plated lead frame, comprising the following steps: S1. Attach a thermal release tape to the wire bonding surface of the lead frame; S2. Degrease, wash with water, and activate the soldering surface of the lead frame; S3. Electro-deposit ordinary nickel, electro-deposit palladium, and electro-deposit gold on the lead frame in sequence; S4. Wash and dry the lead frame, and remove the thermal release tape attached to the wire bonding surface of the lead frame; S5. Attach a thermal release tape to the soldering surface of the lead frame; S6. Degrease, wash with water, and activate the wire bonding surface of the lead frame; S7. Electro-deposit rough nickel, electro-deposit palladium, and electro-deposit gold on the lead frame in sequence; S8. Wash and dry the lead frame, and remove the thermal release tape attached to the soldering surface of the lead frame.

[0007] As an alternative to the technical solution of this application document, in S7, the current density during electro-deposition of rough nickel is calculated using the following formula:

[0008] Where J is the current density, I is the set current value during electroplating, A is the initial area of the lead frame, and Y is the covered area of the thermal release tape.

[0009] As an alternative to the technical solution of this application document, the thermal release temperature of the thermal release tape is higher than the temperatures of degreasing, electro-deposition of ordinary nickel, electro-deposition of rough nickel, electro-deposition of palladium, and electro-deposition of gold, and the thermal release temperature of the thermal release tape is lower than the drying temperature.

[0010] As an alternative to the technical solution of this application document, in S1 and S5, the attachment pressure of the thermal release tape is 0.5 Mpa, and the thermal release temperature of the thermal release tape is 80 - 100 °C.

[0011] As an alternative to the technical solution of this application document, in S3 and S7, the temperature of electro-depositing ordinary nickel is 60 °C, the temperature of electro-depositing rough nickel is 60 °C, the temperature of electro-depositing palladium is 45 °C, and the temperature of electro-depositing gold is 45 °C.

[0012] As an alternative to the technical solution of this application document, in S4 and S8, the drying temperature is 110 °C.

[0013] As an alternative solution to the technical solution of this application document, in S3, the electroplating solution for electrodepositing ordinary nickel contains: nickel sulfamate 50 - 100 g / L, nickel chloride 3 - 5 g / L, and boric acid 35 - 45 g / L.

[0014] As an alternative solution to the technical solution of this application document, in S7, the electroplating solution for electrodepositing rough nickel contains: starter agent 200 - 450 g / L, stabilizer 20 - 45 g / L, microstructure agent 50 - 200 g / L, and dispersant 1 - 10 g / L.

[0015] As an alternative solution to the technical solution of this application document, in S2 and S6, the degreasing temperature is 55 - 65 °C.

[0016] 3. Beneficial effects Compared with the prior art, the beneficial effects of the present invention are as follows: 1) By using a thermal release tape in this application, a single-sided roughening process for the lead frame is achieved. The roughened nickel-palladium-gold on the lead bonding surface of the lead frame can improve the bonding strength between the encapsulating epoxy resin and the pre-plated lead frame, enabling the moisture sensitivity level to meet the requirements of MSL-1 and automotive grade. The solder surface is ordinary nickel-palladium-gold, which can ensure a tight fit between the polyimide tape and the pre-plated lead frame, preventing the molten epoxy resin from seeping into the space between the polyimide tape and the pre-plated lead frame during the encapsulation process, ensuring the solder quality, and thus enabling the pre-plated lead frame after encapsulation to be well combined with the circuit board.

[0017] 2) By controlling the current density during electroplating of the lead frame with the thermal release tape attached, the electroplating uniformity of the lead bonding surface of the lead frame can be effectively increased, avoiding color differences between the base island and the pins on the lead bonding surface and affecting the product quality.

[0018] 3) By first electrodepositing ordinary nickel and then electrodepositing rough nickel in this application, the residue of the thermal release tape on the surface of the lead frame can be avoided. Specific embodiments

[0019] The present invention provides a technical solution: Example 1: A process for preparing a single-sided roughened pre-plated lead frame includes the following steps: S1. Attach a thermal release tape to the lead bonding surface of the lead frame; S2. Degrease, wash with water, and activate the solder surface of the lead frame; S3. Electrodeposit ordinary nickel, electrodeposit palladium, and electrodeposit gold on the lead frame in sequence; S4. Wash and dry the lead frame, and remove the thermal release tape attached to the lead bonding surface of the lead frame; S5. Attach a heat-release tape to the soldering surface of the lead frame; S6. Degrease, wash with water, and activate the wire bonding surface of the lead frame; S7. Electro-deposit rough nickel, electro-deposit palladium, and electro-deposit gold on the lead frame in sequence; S8. Wash and dry the lead frame, and remove the heat-release tape attached to the soldering surface of the lead frame.

[0020] In S1 and S5, the heat-release temperature of the heat-release tape is higher than the temperatures of degreasing, electro-depositing ordinary nickel, electro-depositing rough nickel, electro-depositing palladium, and electro-depositing gold, and the heat-release temperature of the heat-release tape is lower than the drying temperature. This can prevent the heat-release tape from falling off during the electroplating and degreasing steps; at the same time, it can lose its adhesiveness during drying to avoid residues on the surface of the lead frame during removal.

[0021] Preferably, in S1 and S5, the attachment pressure of the heat-release tape is 0.5 Mpa, and the heat-release temperature of the heat-release tape is 80 - 100 °C; in S3 and S7, the temperature of electro-depositing ordinary nickel is 60 °C, the temperature of electro-depositing rough nickel is 60 °C, the temperature of electro-depositing palladium is 45 °C, and the temperature of electro-depositing gold is 45 °C; in S4 and S8, the drying temperature is 110 °C; in S2 and S6, the degreasing temperature is 55 - 65 °C.

[0022] In S2, activation is to neutralize the alkaline degreasing solution remaining on the soldering surface of the lead frame.

[0023] Preferably, in S3, the electro-chemical deposition solution for electro-depositing ordinary nickel contains: nickel sulfamate 50 - 100 g / L, nickel chloride 3 - 5 g / L, boric acid 35 - 45 g / L. In S7, the electro-chemical deposition solution for electro-depositing rough nickel contains: bath conditioner 200 - 450 g / L, stabilizer 20 - 45 g / L, microstructure agent 50 - 200 g / L, dispersant 1 - 10 g / L. By forming a rough electroplated layer on the wire bonding surface of the lead frame, the bonding force between the wire bonding surface and the encapsulating epoxy resin can be increased, improving the sealing effect; at the same time, it can also avoid the problem of completely cured epoxy resin residues on the soldering surface of the electroplated lead frame.

[0024] When the size of the adopted lead frame is 300 mm * 90 mm, the initial area A of the lead frame is 5.4 dm 2 , the area covered by the heat-release tape is 2.4225 dm 2 , and the current density is 3 A / dm 2 , the specific experimental data are shown in Table 1: Table 1: Experimental data table for post-electroplated rough nickel

[0025] When adopting the process of first electroplating rough nickel and then electroplating ordinary nickel, the achieved data is shown in Table 2 as follows: Table 2: Experimental data table of electroplating rough nickel first

[0026] When adopting the electroplating process in S7 to simultaneously electroplate ordinary nickel, electroplate palladium, and electroplate gold on the wire bonding surface and the soldering surface of the lead frame, the achieved data is shown in Table 3 as follows: Table 3: Experimental data table of one-time electroplating

[0027] From the above achieved data, it can be known that the thermal release tape will remain on the wire bonding surface with a relatively high roughness, and it is necessary to electroplate the soldering surface first; when adopting the one-time electroplating process, it is impossible to obtain significantly different roughness on the wire bonding surface and the soldering surface, and it will increase the electroplating non-uniformity of the wire bonding surface; by adopting the electroplating process described in this embodiment, different roughness can be obtained on the wire bonding surface and the soldering surface, and the residual of the thermal release tape on the wire bonding surface or the soldering surface can be avoided; the purpose of improving the bonding force between the encapsulating epoxy resin and the pre-electroplated lead frame and avoiding the molten epoxy resin from infiltrating between the polyimide tape and the pre-electroplated lead frame during the encapsulation process and ensuring the soldering quality can be achieved.

[0028] Example 2: When adopting the process of preparing a single-sided roughened pre-electroplated lead frame described in Example 1, it is necessary to control the current density during electroplating, and the current density will affect the electroplating uniformity of the soldering surface and the wire bonding surface; since the required electroplating roughness of the wire bonding surface is greater than that of the soldering surface, during electroplating the wire bonding surface, it is necessary to further control the electroplating uniformity of the wire bonding surface.

[0029] The size of the adopted lead frame is 300mm * 90mm, the initial area A of the lead frame is 5.4dm 2 , and the area covered by the thermal release tape is 2.4225dm 2 ; by adjusting the set current value during the electroplating process of the wire bonding surface, the roughness of the wire bonding surface under different current densities is obtained, as shown in Table 4: Table 4: Comparison table of experimental data of electroplating under different current densities

[0030] In this embodiment, the current density is calculated using the following formula:

[0031] Among them, J is the current density, I is the set current value during electroplating, that is, the magnitude of the current passing through the lead frame, A is the initial area of the lead frame, and Y is the covering area of the thermal release tape.

[0032] From the above experimental data, it can be seen that when the current density is 3 - 6 A / dm 2 no color difference will appear between the base island and the pins of the lead bonding surface, meeting the quality requirements.

Claims

1. A process for preparing a single-sided roughened pre-plated lead frame, characterized in that: Including: S1. Attach a thermal release tape to the wire bonding surface of the lead frame; S2. Degrease, wash with water, and activate the soldering surface of the lead frame; S3. Electro-deposit ordinary nickel, electro-deposit palladium, and electro-deposit gold on the lead frame in sequence; S4. Wash and dry the lead frame, and remove the thermal release tape attached to the wire bonding surface of the lead frame; S5. Attach a thermal release tape to the soldering surface of the lead frame; S6. Degrease, wash with water, and activate the wire bonding surface of the lead frame; S7. Electro-deposit rough nickel, electro-deposit palladium, and electro-deposit gold on the lead frame in sequence; S8. Wash and dry the lead frame, and remove the thermal release tape attached to the soldering surface of the lead frame.

2. The process for preparing a single-sided roughened pre-plated lead frame according to claim 1, wherein: In S7, the current density during electro-deposition of rough nickel is calculated using the following formula: Where, J is the current density, I is the set current value during electroplating, A is the initial area of the lead frame, and Y is the covered area of the thermal release tape.

3. A process for preparing a single-sided roughened pre-plated lead frame according to claim 1, characterized in that: The thermal release temperature of the thermal release tape is higher than the temperatures of degreasing, electro-depositing ordinary nickel, electro-depositing rough nickel, electro-depositing palladium, and electro-depositing gold, and the thermal release temperature of the thermal release tape is lower than the drying temperature.

4. A process for preparing a single-sided roughened pre-plated lead frame according to claim 1, characterized in that: In S1 and S5, the attachment pressure of the thermal release tape is 0.5 Mpa, and the thermal release temperature of the thermal release tape is 80 - 100 °C.

5. A process for preparing a single-sided roughened pre-plated lead frame according to claim 1, characterized in that: In S3 and S7, the temperature for electro-depositing ordinary nickel is 60 °C, the temperature for electro-depositing rough nickel is 60 °C, the temperature for electro-depositing palladium is 45 °C, and the temperature for electro-depositing gold is 45 °C.

6. The process for preparing a single-sided roughened pre-plated lead frame according to claim 1, characterized in that: In S4 and S8, the drying temperature is 110 °C.

7. A process for preparing a single-sided roughened pre-plated lead frame according to claim 1, characterized in that: In S3, the electro-chemical deposition solution for electro-depositing ordinary nickel contains: nickel sulfamate 50 - 100 g / L, nickel chloride 3 - 5 g / L, and boric acid 35 - 45 g / L.

8. A process for preparing a single-sided roughened pre-plated lead frame according to claim 1, characterized in that: In S7, the electro-chemical deposition solution for electro-depositing rough nickel contains: starting agent 200 - 450 g / L, stabilizer 20 - 45 g / L, microstructure agent 50 - 200 g / L, and dispersant 1 - 10 g / L.

9. A process for preparing a single-sided roughened pre-plated lead frame according to claim 1, characterized in that: In S2 and S6, the degreasing temperature is 55 - 65 °C.

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