Nickel plating process and pre-electroplating lead frame

Abstract

The invention discloses a nickel layer plating process and a pre-electroplated lead frame, a nickel layer is formed on a metal layer in an electroplating mode, and electroplating liquid adopted when the nickel layer is electroplated at least comprises an anode with nickel ions, tannic acid and 3, 5-diamino-1, 2, 4 triazole; wherein the tannic acid and the 3, 5-diamino-1, 2, 4 triazole cooperate to increase the grain size in the nickel layer, thereby coarsening the nickel layer. The two additives of tannic acid and 3, 5-diamino-1, 2, 4 triazole play a role of a surfactant, and the number of crystal nucleuses formed on the surface of a metal layer can be effectively reduced in the nickel layer electroplating process, so that crystal grains with larger sizes are formed, namely the average crystal grain size in the nickel electroplating layer is increased, and the purpose of coarsening the nickel layer is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated circuit packaging technology, in particular to a nickel plating process and a pre-electroplating lead frame. Background Art

[0002] The lead frame is a primary component of integrated circuit packaging, serving as a vital component for connecting to external circuits, transmitting electrical signals, and supporting and securing the chip. It is a key component in forming the electrical circuit within an integrated circuit and is required in most semiconductor integrated circuits. Pre-plating lead frame finish (PPF) involves electroplating nickel, palladium, and gold layers onto the lead frame surface. Because pre-plating ensures solder quality, it eliminates the need for post-chip packaging tin or lead plating.

[0003] However, the bonding strength between the pre-plated lead frame and the epoxy molding compound is poor. As a result, after the chip, pre-plated lead frame, and epoxy molding compound are encapsulated, their moisture sensitivity level reaches up to MSL-3, failing to meet higher requirements such as MSL-2, MSL-1, and automotive grades. Therefore, increasing the surface roughness of the pre-plated lead frame—that is, increasing the surface area of ​​the pre-plated lead frame, and thereby increasing the contact area between the pre-plated lead frame and the epoxy molding compound—is one of the key methods for improving the bonding strength between the pre-plated lead frame and the epoxy molding compound. Summary of the Invention

[0004] The purpose of the present invention is to provide a nickel plating process and a pre-plated lead frame, which improve the surface roughness of the nickel layer and thus improve the bonding force between the pre-plated lead frame with the nickel layer and the epoxy resin molding compound.

[0005] The purpose of the present invention is achieved by the following technical solutions:

[0006] The present invention provides a nickel plating process, wherein the nickel layer is formed on a metal layer by electroplating, and the electroplating solution used when electroplating the nickel layer at least comprises an anode containing nickel ions, succinic acid and 3,5-diamino-1,2,4-triazole;

[0007] The ruthenium chloride and 3,5-diamino-1,2,4-triazole are combined to increase the grain size of the nickel layer, thereby roughening the nickel layer.

[0008] As a further improvement of one embodiment of the present invention, the mass ratio of the ruthenic acid to the 3,5-diamino-1,2,4-triazole is (0.5-1.5):(0.4-0.8).

[0009] As a further improvement of one embodiment of the present invention, the average grain size of the nickel layer is greater than 0.3 μm, and the average surface roughness of the nickel layer is greater than 0.15 μm.

[0010] As a further improvement of one embodiment of the present invention, the mass ratio of the ruthenic acid to the 3,5-diamino-1,2,4-triazole is 1:0.6.

[0011] As a further improvement of one embodiment of the present invention, the average grain size of the nickel layer is 1.4 μm, and the average surface roughness of the nickel layer is 0.18 μm.

[0012] As a further improvement of one embodiment of the present invention, the nickel grains in the nickel layer are of a cocklebur-like structure.

[0013] As a further improvement of one embodiment of the present invention, the electroplating solution further includes lactic acid and formic acid, and the mass ratio of the lactic acid to formic acid is 2:4.

[0014] As a further improvement of one embodiment of the present invention, the anode having nickel ions is nickel sulfamate, and the nickel sulfamate content in the electroplating solution is (60±7) g / L;

[0015] The electroplating solution also includes boric acid, and the boric acid content in the electroplating solution is (40±5) g / L.

[0016] As a further improvement of one embodiment of the present invention, the process conditions for electroplating the nickel layer are: a current density of 7A / dm 2 ~16A / dm 2 , the electroplating temperature is (60±5)℃, the pH is 2.0~3.0, and the electroplating time is 60s~90s.

[0017] The present invention also provides a pre-electroplated lead frame, comprising a copper substrate, and a nickel layer, a palladium layer and a gold layer sequentially formed on the surface of the copper substrate, wherein the nickel layer is prepared using the nickel plating process described above.

[0018] Compared with the prior art, the beneficial effects of the present invention include at least: the present invention provides a nickel plating process, which forms a nickel layer on a metal layer by electroplating. It only requires adding two additives, succinic acid and 3,5-diamino-1,2,4-triazole, to the plating solution required for the electroplating of the nickel layer in the commonly used technology. The two additives, succinic acid and 3,5-diamino-1,2,4-triazole, act as surfactants. During the process of electroplating the nickel layer, the number of crystal nuclei formed on the surface of the metal layer can be effectively reduced, thereby forming larger grains, that is, increasing the average grain size in the electroplated nickel layer, thereby achieving the purpose of roughening the nickel layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1This is an electron microscope image of the nickel layer of the present invention magnified 20,000 times;

[0020] Figure 2 1 is a schematic structural diagram of a pre-plated lead frame according to one embodiment of the present invention;

[0021] Figure 3 These are electron microscope images of sample A and sample B of the present invention magnified 500 times and 20,000 times, respectively;

[0022] Figure 4 This is the tinning test of sample B of the present invention.

[0023] In the figure: 1. Copper substrate; 2. Nickel layer; 3. Palladium layer; 4. Gold layer. DETAILED DESCRIPTION

[0024] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concepts of the example embodiments to those skilled in the art. Identical reference numerals in the drawings represent identical or similar structures, and thus repeated descriptions thereof will be omitted.

[0025] The words expressing positions and directions described in the present invention are all explained with reference to the accompanying drawings as examples, but can be modified as needed, and all such modifications are within the scope of protection of the present invention.

[0026] The present invention provides a nickel plating process, wherein the nickel layer is formed on a metal layer by electroplating. The electroplating solution used for the nickel plating comprises at least an anode containing nickel ions, succinic acid, and 3,5-diamino-1,2,4-triazole. The succinic acid and 3,5-diamino-1,2,4-triazole are combined to increase the grain size of the electroplated nickel layer, thereby roughening the nickel layer.

[0027] When a nickel layer is prepared on a metal layer by using the nickel plating process provided by the present invention, the metal layer sample to be formed into a nickel layer is placed in an electroplating solution. During the electroplating process, the metal layer sample serves as a cathode, and the nickel ions (Ni 2+ ) obtains electrons on the surface of the metal layer and is reduced to nickel atoms (Ni 0When the nickel atom concentration exceeds a critical value, crystal nuclei will first form on the surface of the metal layer. Since the plating solution in this embodiment also includes two additives, succinic acid and 3,5-diamino-1,2,4-triazole, these two additives act as surfactants, reducing the number of crystal nuclei formed per unit area. When the number of crystal nuclei formed on the metal layer surface decreases, the limited nickel atoms will preferentially deposit on the surface of the already formed crystal nuclei. At this time, individual crystal nuclei can obtain more nickel atoms, resulting in a faster growth rate, and ultimately forming larger grains on the metal layer surface, thereby increasing the surface roughness of the electroplated nickel layer.

[0028] In this embodiment, the metal layer is a copper layer. For example, a nickel layer is electroplated on the surface of the copper substrate of the lead frame using the nickel plating process provided by the present invention to improve the surface roughness of the prepared pre-plated lead frame, thereby improving the bonding strength between the pre-plated lead frame and the plastic packaging material in the subsequent packaging process, and enhancing the structural strength of the plastic packaging body.

[0029] Specifically, the anode with nickel ions is nickel sulfamate solution, which provides the cations (Ni 2+ The plating solution also includes boric acid to maintain a stable pH value.

[0030] More specifically, the content (mass concentration) of nickel sulfamate in the electroplating solution is (60±7) g / L, and the content of boric acid in the electroplating solution is (40±5) g / L.

[0031] Furthermore, the electroplating solution also includes lactic acid and formic acid, which cooperate with boric acid to further adjust the pH value of the electroplating solution. At the same time, lactic acid and formic acid also play a role in adjusting the liquid density in the electroplating solution and reducing the chemical polarization of the electroplating solution.

[0032] The aqueous solution composed of nickel sulfamate and boric acid is the electroplating solution for the electroplating nickel layer used in conventional technology. The present invention adds succinic acid, 3,5-diamino-1,2,4-triazole, lactic acid and formic acid to the electroplating solution used in conventional technology, so as to increase the surface roughness of the nickel layer formed by electroplating. Specifically, succinic acid and 3,5-diamino-1,2,4-triazole can be added to the aqueous solution composed of nickel sulfamate and boric acid in a mass ratio of (0.5-1.5): (0.4-0.8), and lactic acid and formic acid are added to the aqueous solution composed of nickel sulfamate and boric acid in a mass ratio of 2:4 to form the electroplating solution required for the roughening of the nickel layer in the present invention. The metal layer sample is placed in the electroplating solution, and the electroplating process conditions can be set to: the current density is 7A / dm 2 ~16A / dm 2 , the electroplating temperature is (60±5)℃, the pH is 2.0~3.0, and the electroplating time is 60s~90s.

[0033] like Figure 1 It can be seen from the figure that the nickel grains obtained by the nickel plating process of the present invention are of a cocklebur-like structure, that is, the surface of the nickel layer is composed of a plurality of conical protrusion structures, which increases the surface area of ​​the nickel layer and thus increases the surface roughness of the nickel layer.

[0034] Specifically, the average grain size of the nickel layer formed by electroplating is greater than 0.3 μm.

[0035] Specifically, the average surface roughness Sa of the nickel layer formed by electroplating is greater than 0.15 μm.

[0036] The present invention provides Examples 1 to 9, wherein different mass proportions of ruthenic acid and 3,5-diamino-1,2,4-triazole are added to an aqueous solution of nickel sulfamate and boric acid to prepare nickel layers with different surface roughnesses.

[0037] Example 1

[0038] Add succinic acid, 3,5-diamino-1,2,4-triazole, lactic acid, and formic acid to an aqueous solution of nickel sulfamate and boric acid to form electroplating solution a. In electroplating solution a, the content of nickel sulfamate is (60±7) g / L, the content of boric acid is (40±5) g / L, and succinic acid, 3,5-diamino-1,2,4-triazole, lactic acid, and formic acid are added to the aqueous solution of nickel sulfamate and boric acid in a mass ratio of 0.5:0.4:2:4. The metal layer sample is placed in electroplating solution a, and the electroplating process conditions are set as follows: current density 11A / dm 2 , the electroplating temperature is 60℃, the pH is 2.5, and the electroplating time is 75s.

[0039] Example 2

[0040] Add succinic acid, 3,5-diamino-1,2,4-triazole, lactic acid, and formic acid to an aqueous solution of nickel sulfamate and boric acid to form electroplating solution b. In electroplating solution b, the content of nickel sulfamate is (60±7) g / L, the content of boric acid is (40±5) g / L, and succinic acid, 3,5-diamino-1,2,4-triazole, lactic acid, and formic acid are added to the aqueous solution of nickel sulfamate and boric acid in a mass ratio of 1:0.4:2:4. Place the metal layer sample in electroplating solution b, and the electroplating process conditions are set as follows: current density 11A / dm 2 , the electroplating temperature is 60℃, the pH is 2.5, and the electroplating time is 75s.

[0041] Example 3

[0042] Add succinic acid, 3,5-diamino-1,2,4-triazole, lactic acid, and formic acid to an aqueous solution of nickel sulfamate and boric acid to form electroplating solution C. In electroplating solution C, the nickel sulfamate content is (60±7) g / L, and the boric acid content is (40±5) g / L. Succinic acid, 3,5-diamino-1,2,4-triazole, lactic acid, and formic acid are added to the aqueous solution of nickel sulfamate and boric acid in a mass ratio of 1.5:0.4:2:4. The metal layer sample is placed in electroplating solution C, and the electroplating process conditions are set as follows: a current density of 11 A / dm 2 , the electroplating temperature is 60℃, the pH is 2.5, and the electroplating time is 75s.

[0043] Example 4

[0044] Add succinic acid, 3,5-diamino-1,2,4-triazole, lactic acid, and formic acid to an aqueous solution of nickel sulfamate and boric acid to form electroplating solution d. In electroplating solution d, the nickel sulfamate content is (60±7) g / L, and the boric acid content is (40±5) g / L. Succinic acid, 3,5-diamino-1,2,4-triazole, lactic acid, and formic acid are added to the aqueous solution of nickel sulfamate and boric acid in a mass ratio of 0.5:0.6:2:4. The metal layer sample is placed in electroplating solution d, and the electroplating process conditions are set as follows: a current density of 11 A / dm 2 , the electroplating temperature is 60℃, the pH is 2.5, and the electroplating time is 75s.

[0045] Example 5

[0046] Add succinic acid, 3,5-diamino-1,2,4-triazole, lactic acid, and formic acid to an aqueous solution of nickel sulfamate and boric acid to form electroplating solution e. In electroplating solution e, the nickel sulfamate content is (60±7) g / L, and the boric acid content is (40±5) g / L. Succinic acid, 3,5-diamino-1,2,4-triazole, lactic acid, and formic acid are added to the aqueous solution of nickel sulfamate and boric acid in a mass ratio of 1:0.6:2:4. A metal layer sample is placed in electroplating solution e, and the electroplating process conditions are set as follows: a current density of 11 A / dm 2 , the electroplating temperature is 60℃, the pH is 2.5, and the electroplating time is 75s.

[0047] Example 6

[0048] Add succinic acid, 3,5-diamino-1,2,4-triazole, lactic acid, and formic acid to an aqueous solution of nickel sulfamate and boric acid to form electroplating solution f. In electroplating solution f, the nickel sulfamate content is (60±7) g / L, and the boric acid content is (40±5) g / L. Succinic acid, 3,5-diamino-1,2,4-triazole, lactic acid, and formic acid are added to the aqueous solution of nickel sulfamate and boric acid in a mass ratio of 1.5:0.6:2:4. A metal layer sample is placed in electroplating solution f, and the electroplating process conditions are set as follows: a current density of 11 A / dm 2 , the electroplating temperature is 60℃, the pH is 2.5, and the electroplating time is 75s.

[0049] Example 7

[0050] Add succinic acid, 3,5-diamino-1,2,4-triazole, lactic acid, and formic acid to an aqueous solution of nickel sulfamate and boric acid to form electroplating solution g. In electroplating solution g, the content of nickel sulfamate is (60±7) g / L, the content of boric acid is (40±5) g / L, and succinic acid, 3,5-diamino-1,2,4-triazole, lactic acid, and formic acid are added to the aqueous solution of nickel sulfamate and boric acid in a mass ratio of 0.5:0.8:2:4. Place the metal layer sample in electroplating solution g, and the electroplating process conditions are set as follows: current density 11A / dm 2 , the electroplating temperature is 60℃, the pH is 2.5, and the electroplating time is 75s.

[0051] Example 8

[0052] Add succinic acid, 3,5-diamino-1,2,4-triazole, lactic acid, and formic acid to an aqueous solution of nickel sulfamate and boric acid to form electroplating solution h. In electroplating solution h, the nickel sulfamate content is (60±7) g / L, and the boric acid content is (40±5) g / L. Succinic acid, 3,5-diamino-1,2,4-triazole, lactic acid, and formic acid are added to the aqueous solution of nickel sulfamate and boric acid in a mass ratio of 1:0.8:2:4. A metal layer sample is placed in electroplating solution h, and the electroplating process conditions are set as follows: a current density of 11 A / dm 2 , the electroplating temperature is 60℃, the pH is 2.5, and the electroplating time is 75s.

[0053] Example 9

[0054] Add succinic acid, 3,5-diamino-1,2,4-triazole, lactic acid, and formic acid to an aqueous solution of nickel sulfamate and boric acid to form electroplating solution i. In electroplating solution i, the content of nickel sulfamate is (60±7) g / L, the content of boric acid is (40±5) g / L, and succinic acid, 3,5-diamino-1,2,4-triazole, lactic acid, and formic acid are added to the aqueous solution of nickel sulfamate and boric acid in a mass ratio of 1.5:0.8:2:4. The metal layer sample is placed in electroplating solution i, and the electroplating process conditions are set as follows: current density 11A / dm 2 , the electroplating temperature is 60℃, the pH is 2.5, and the electroplating time is 75s.

[0055] The performance of the nickel layers prepared in Examples 1 to 9 was characterized, and the data are shown in Table 1.

[0056] Specifically, the average grain size of the nickel layer can be measured by obtaining a three-dimensional topography image of the nickel layer using instruments such as an atomic force microscope or a scanning electron microscope to measure the size of the grains.

[0057] Specifically, the average surface roughness Sa of the nickel layer can be measured and obtained by using instruments such as an atomic force microscope or a white light interferometer.

[0058] Table 1 Performance characterization results of the electroplated nickel layer of Examples 1 to 9

[0059]

[0060]

[0061] Example 5 is a preferred embodiment of the present invention. To an aqueous solution consisting of nickel sulfamate and boric acid, ruthenic acid, 3,5-diamino-1,2,4-triazole, lactic acid, and formic acid are added in a mass ratio of 1:0.6:2:4 to form an electroplating solution e. The metal layer sample is placed in the electroplating solution e and electroplated. The average grain size of the prepared nickel layer is 1.4 μm, and the average surface roughness Sa of the nickel layer is 0.18 μm. Compared with the average grain size of the nickel layer prepared by the traditional nickel plating process (about 200 nm), it is about 6 times larger, and compared with the average surface roughness Sa (0.09 μm) of the nickel layer prepared by the traditional nickel plating process, it is 1 times larger.

[0062] The present invention also provides a pre-plated lead frame, such as Figure 2, comprising a copper substrate 1, and a nickel layer 2, a palladium layer 3, and a gold layer 4 sequentially formed on the surface of the copper substrate 1, wherein the nickel layer 2 is prepared using the nickel plating process described in any of the above embodiments. Since the palladium layer 3 and the gold layer 4 of the pre-plated lead frame are relatively thin, generally, the palladium layer 3 has a thickness of 0.01μm to 0.15μm, and the gold layer 4 has a thickness of 0.003μm to 0.015μm, increasing the surface roughness of the nickel layer 2 can effectively increase the surface roughness of the pre-plated lead frame, improve the bonding strength between the pre-plated lead frame and the epoxy resin molding compound, and improve the delamination problem of the packaged product.

[0063] like Figure 3 The left side shows electron micrographs of the surface of a conventional pre-plated lead frame (Sample A) at 500x and 20,000x magnifications, while the right side shows electron micrographs of the surface of a pre-plated lead frame according to the present invention (Sample B, where the nickel layer 2 is prepared using the nickel plating process of Example 5 of the present invention) at 500x and 20,000x magnifications. The nickel layer prepared using the nickel plating process of the present invention has a significantly increased surface roughness.

[0064] The present invention also tested and compared the surface roughness Sa at different points on the surface of sample A and sample B prepared using the nickel plating process of the present invention, as shown in Table 2.

[0065] Table 2 Comparison of surface roughness at various points on sample A and sample B

[0066]

[0067]

[0068] From this, it can be calculated that the average surface roughness Sa of sample A is 0.09 μm, and the average surface roughness Sa of sample B is 0.18 μm. Compared with sample A, the average surface roughness of sample B is doubled.

[0069] In other words, the surface roughness of the nickel layer formed by conventional electroplating is relatively low, resulting in a relatively low surface roughness of the final pre-plated lead frame (sample A). The bonding area between the pre-plated lead frame (sample A) and the epoxy resin molding compound is relatively small, thereby affecting the bonding strength between the pre-plated lead frame (sample A) and the epoxy resin molding compound and the moisture sensitivity level. Conventionally, if the nickel layer is to be roughened, it is necessary to use a roughening process such as etching to roughen the surface of the nickel layer formed by electroplating after the nickel layer is electroplated. This method increases the number of steps in the preparation of the pre-plated lead frame, resulting in reduced preparation efficiency and increased costs for the pre-plated lead frame.

[0070] In the present application, a novel electroplating solution is provided to enable the nickel layer formed by electroplating to have a higher roughness, thereby improving the surface roughness of the final pre-plated lead frame (sample B). The bonding area between the pre-plated lead frame (sample B) and the epoxy resin molding compound is increased, thereby improving the bonding strength and moisture sensitivity level of the pre-plated lead frame (sample B) and the epoxy resin molding compound. The present application does not require an additional roughening process for the nickel layer, simplifies the process flow, improves the preparation efficiency of the pre-plated lead frame with a higher surface roughness, and reduces the cost.

[0071] like Figure 4 The present invention also conducted a tinning test on sample B. It can be seen that most areas of the pins of the pre-electroplated lead frame can be effectively tinned, and the tinned area is greater than 95% of the pin area. All pins passed the test, that is, the nickel plating process provided by the present invention will not affect the welding performance of the pre-electroplated lead frame.

[0072] In summary, the present invention provides a nickel plating process and a pre-electroplating lead frame, which form a nickel layer on a metal layer by electroplating. It only requires adding two additives, succinic acid and 3,5-diamino-1,2,4-triazole, to the plating solution required for the nickel plating layer in the commonly used technology. The two additives, succinic acid and 3,5-diamino-1,2,4-triazole, act as surfactants. During the nickel plating process, the number of crystal nuclei formed on the surface of the metal layer can be effectively reduced, thereby forming larger grains, that is, increasing the average grain size in the electroplated nickel layer, thereby achieving the purpose of roughening the nickel layer, improving the bonding strength between the pre-electroplated lead frame and the plastic packaging material, and increasing the structural strength of the packaged product.

[0073] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limiting the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the invention without departing from the principles and purpose of the present invention. All such changes shall fall within the scope of protection of the claims of the present invention.

Claims

1. A nickel plating process, wherein the nickel layer is formed on a metal layer by electroplating, characterized in that: The electroplating solution used when electroplating the nickel layer at least includes an anode having nickel ions, succinic acid and 3,5-diamino-1,2,4-triazole; The ruthenium chloride and 3,5-diamino-1,2,4-triazole are combined to increase the grain size of the nickel layer, thereby roughening the nickel layer.

2. The nickel plating process according to claim 1, wherein: The mass ratio of the rutile acid to the 3,5-diamino-1,2,4-triazole is (0.5-1.5):(0.4-0.8).

3. The nickel plating process according to claim 2, wherein: The average grain size of the nickel layer is greater than 0.3 μm, and the average surface roughness of the nickel layer is greater than 0.15 μm.

4. The nickel plating process according to claim 2, wherein: The mass ratio of the rutile acid to the 3,5-diamino-1,2,4-triazole is 1:0.

6.

5. The nickel plating process according to claim 4, characterized in that: The average grain size of the nickel layer was 1.4 μm, and the average surface roughness of the nickel layer was 0.18 μm.

6. The nickel plating process according to claim 1, wherein: The nickel grains in the nickel layer are of a cocklebur-like structure.

7. The nickel plating process according to claim 1, wherein: The electroplating solution also includes lactic acid and formic acid, and the mass ratio of the lactic acid to formic acid is 2:

4.

8. The nickel plating process according to claim 1, wherein: The anode having nickel ions is nickel sulfamate, and the nickel sulfamate content in the electroplating solution is (60±7) g / L; The electroplating solution also includes boric acid, and the boric acid content in the electroplating solution is (40±5) g / L.

9. The nickel plating process according to claim 1, wherein: The process conditions for electroplating the nickel layer are: current density of 7A / dm 2 ~16A / dm 2 , the electroplating temperature is (60±5)℃, the pH is 2.0~3.0, and the electroplating time is 60s~90s.

10. A pre-plated lead frame, characterized in that: The invention comprises a copper substrate, and a nickel layer, a palladium layer and a gold layer sequentially formed on the surface of the copper substrate, wherein the nickel layer is prepared by the nickel plating process according to any one of claims 1 to 9.

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