A gold plating solution for an integrated circuit chip package lead frame and a gold plating method thereof

Abstract

The application discloses a kind of integrated circuit chip package lead frame's electroless gold plating solution and its gold plating method, it is related to integrated circuit chip packaging field.Therein, electroless gold plating solution is following concentration component aqueous solution: water-soluble gold compound, with Au, concentration is 1-1.5g / L;Sodium hypophosphite 10~20g / L;Malic acid 15~20g / L;Citric acid 15~20g / L;N,N'-bis (2-hydroxyethyl) ethylenediamine 10~15g / L;Triammonium citrate 15~20g / L;EDTA-2Na 5~10g / L;5,5'-dimethyl hydantoin 5~10g / L;Metal ion catalyst, with metal ion, concentration is 2~3ppm;Mercaptoimidazole 0.01~0.015g / L;Hexamethylenetetramine 5~10g / L.The electroless gold plating solution in the application can consider stability, high deposition rate and plating layer deposition uniformity.

Description

Technical Field

[0001] This application relates to the field of integrated circuit chip packaging, and in particular to a chemical gold plating solution and a gold plating method for lead frames used in integrated circuit chip packaging. Background Technology

[0002] As a key component of integrated circuit chip packaging, the leadframe plays a crucial role in supporting the chip, connecting the internal circuitry to external circuit pins, and dissipating heat generated during operation. Its performance directly affects the reliability, stability, and lifespan of the integrated circuit. To ensure excellent conductivity, oxidation resistance, solderability, and adhesion to the encapsulation resin, the leadframe typically requires gold plating on its surface (especially the bonding and soldering areas).

[0003] The core components of electroless gold plating solutions include a gold source, a reducing agent, and various complexing agents, stabilizers, and accelerators. Among them, electroless gold plating systems using sodium hypophosphite as a reducing agent have attracted widespread attention due to their relatively low cost and environmental friendliness. However, existing sodium hypophosphite-based electroless gold plating solutions still face several serious challenges in practical industrial applications. These include: poor stability of the plating solution, with a production cycle typically of 2-3 MTOs; slow gold deposition efficiency, below 0.1 μm / 15 min; and poor gold deposition uniformity, with a coating uniformity coefficient greater than 8%.

[0004] Therefore, there is an urgent need in the field to develop a new type of chemical gold plating solution that must simultaneously possess: (1) excellent long-term stability to support large-scale, long-cycle production; (2) a gold plating rate greater than 0.1 μm / 15 min to improve production efficiency; and (3) excellent plating uniformity to ensure the reliability of the final packaged product. Summary of the Invention

[0005] To address the issue that chemical gold plating solutions in related technologies struggle to simultaneously achieve stability, high deposition rate, and uniform coating uniformity, this application provides a chemical gold plating solution and a gold plating method for lead frames used in integrated circuit chip packaging.

[0006] A chemical gold plating solution for lead frames used in integrated circuit chip packaging, wherein the chemical gold plating solution is an aqueous solution with the following concentrations: Water-soluble gold compounds, calculated as Au, with a concentration of 1-1.5 g / L; Sodium hypophosphite 10-20 g / L; Malic acid 15-20 g / L; Citric acid 15-20 g / L; N,N'-bis(2-hydroxyethyl)ethylenediamine 10-15 g / L; Triammonium citrate 15-20 g / L; EDTA-2Na 5~10g / L; 5,5'-Dimethylhydantoin 5-10 g / L; Metal ion catalyst, with a concentration of 2-3 ppm based on metal ions; Mercaptoimidazole 0.01–0.015 g / L; Hexamethylenetetramine 5-10 g / L.

[0007] In this application, the electroless gold plating solution for lead frames used in integrated circuit chip packaging improves the stability of the electroless gold plating solution through the combined action of a specific concentration of water-soluble gold compound, sodium hypophosphite, malic acid, citric acid, N,N'-bis(2-hydroxyethyl)ethylenediamine, triammonium citrate, EDTA-2Na, 5,5'-dimethylhydantoin, metal ion catalyst, mercaptoimidazole, and hexamethylenetetramine. This allows the production cycle of the electroless gold plating solution to reach more than 8 MTO, while accelerating the gold deposition rate and ensuring good deposition uniformity.

[0008] In some specific embodiments, the metal ion catalyst is a combination of thallium ion catalyst and cobalt ion catalyst, wherein the mass concentration ratio of thallium ion catalyst to cobalt ion catalyst is 1:(1-1.5).

[0009] In some specific embodiments, the thallium ion catalyst is at least one of thallium sulfate, thallium nitrate, and thallium acetate.

[0010] In some specific embodiments, the cobalt ion catalyst is at least one of cobalt nitrate, cobalt sulfate, and cobalt acetate.

[0011] In some specific embodiments, the mercaptoimidazole includes 2-mercaptobenzimidazole and 2-mercapto-5-methylbenzimidazole, and the mass concentration ratio of 2-mercaptobenzimidazole to 2-mercapto-5-methylbenzimidazole is (1-1.5):1.

[0012] In this application, the metal ion catalyst is preferably a combination of thallium ion catalyst and cobalt ion catalyst. When the mass concentration ratio of thallium ion catalyst to cobalt ion catalyst is 1:(1-1.5), it is beneficial to further improve the gold deposition efficiency of the electroless gold plating solution. At the same time, the combination with specific concentrations of 2-mercaptobenzimidazole, 2-mercapto-5-methylbenzimidazole and 5,5'-dimethylhydantoin can improve the gold deposition efficiency of the electroless gold plating solution while further improving the density and uniformity of the plated gold layer.

[0013] In some specific embodiments, the water-soluble gold compound is potassium gold citrate.

[0014] A method for gold plating a lead frame for integrated circuit chip packaging involves chemically plating a lead frame, which has been sequentially plated with a nickel layer and a palladium layer, in the chemical gold plating solution described in any one of the above claims.

[0015] In some specific embodiments, the pH of the electroless gold plating solution is controlled to be 6.8 to 7.2, and the electroless gold plating temperature is 75 to 85°C.

[0016] In this application, during the gold plating process, the pH of the electroless gold plating solution is controlled within the range of 6.8 to 7.2, and the temperature of the electroless gold plating is preferably controlled within the range of 75 to 85°C, which can further optimize the gold deposition process and make the gold plating layer more uniform and dense.

[0017] A lead frame for integrated circuit chip packaging is prepared by the gold plating method described above.

[0018] In this application, the gold plating layer of the lead frame for integrated circuit chip packaging is smooth and bright, with no plating defects. At the same time, the gold plating layer has good adhesion, ensuring the reliability and durability of the lead frame.

[0019] In summary, this application includes at least the following beneficial effects: (1) In this application, the chemical gold plating solution for the lead frame of integrated circuit chip packaging improves the stability of the chemical gold plating solution through the combined action of a specific concentration of water-soluble gold compound, sodium hypophosphite, malic acid, citric acid, N,N'-bis(2-hydroxyethyl)ethylenediamine, triammonium citrate, EDTA-2Na, 5,5'-dimethylhydantoin, metal ion catalyst, mercaptoimidazole and hexamethylenetetramine, so that the production cycle of the chemical gold plating solution can reach more than 8MTO, while accelerating the gold deposition rate and taking into account good deposition uniformity.

[0020] (2) In this application, the metal ion catalyst is preferably a combination of thallium ion catalyst and cobalt ion catalyst. When the mass concentration ratio of thallium ion catalyst to cobalt ion catalyst is 1:(1-1.5), it is beneficial to further improve the gold deposition efficiency of the electroless gold plating solution. At the same time, the combination with specific concentrations of 2-mercaptobenzimidazole, 2-mercapto-5-methylbenzimidazole and 5,5'-dimethylhydantoin can improve the gold deposition efficiency of the electroless gold plating solution and further improve the density and uniformity of the gold plating layer. Detailed Implementation

[0021] The following detailed experiments further illustrate this application. In this application, the lead frames plated with nickel and palladium are qualified products obtained through the same manufacturing process. Example

[0022]

Example 1

[0023]

Example 2

[0024]

Example 3

[0025]

Example 4

[0026]

Example 5

[0027]

Example 6

[0028]

Example 7

[0029]

Example 8

[0030]

Example 9

[0031] Comparative Example Comparative Example 1 A chemical gold plating solution for lead frames used in integrated circuit chip packaging is specifically an aqueous solution with the following concentration components: Potassium gold citrate, calculated as Au, has a concentration of 1 g / L; Sodium hypophosphite 10g / L; Malic acid 5g / L; Citric acid 25g / L; N,N'-Bis(2-hydroxyethyl)ethylenediamine 20g / L; Triammonium citrate 5g / L; EDTA-2Na 10g / L; 5,5'-Dimethylhydantoin 3 g / L; Thallium nitrate, calculated as thallium, has a concentration of 3 ppm; 2-Mercaptobenzimidazole 0.02 g / L; Hexamethylenetetramine 10 g / L.

[0032] Comparative Example 2 The chemical gold plating solution for a lead frame used in integrated circuit chip packaging differs from that in [Example 7] in that: 5,5'-Dimethylhydantoin was replaced with potassium cyanide at a concentration of 5 g / L.

[0033] Application examples

Application Example 1

[0034]

Application Example 2

[0035]

Application Example 3

[0036]

Application Example 4

[0037]

Application Example 5

[0038]

Application Example 6

[0039]

Application Example 7

[0040]

Application Example 8

[0041]

Application Example 9

[0042] Comparative Application Examples

Comparative Application Example 1

[0043]

Comparative Application Example 2

[0044] Performance testing 1. MTO Test: Based on the gold salt calculation, each additional gold salt added to the initial tank volume is considered 1 MTO. In this test, gold salt was added once for every 10% decrease in gold ions. When the deposition rate of the electroless gold plating solution was below 0.05 μm / 15 min, no more gold salt was added, and the number of MTOs was counted.

[0045] 2. Immersion Gold Rate: Gold plating was performed according to the conditions in each application example and the comparative application example. The immersion gold rate of the chemical gold plating solution was tested during the first tank opening. Ten samples were randomly selected from each group of samples to test the uniformity coefficient of the gold plating layer. The uniformity coefficient was calculated as follows: the average thickness μ of the gold plating layer of the same group of samples was calculated, and the standard deviation α of the gold plating layer thickness of the same group of samples was calculated. The uniformity coefficient CV of the gold plating layer in each group of samples was calculated according to the uniformity coefficient of the gold plating layer = (α / μ)*100%. The smaller the uniformity coefficient, the better the uniformity of the gold plating layer. In the actual production process, a uniformity coefficient CV of less than 8% is considered qualified.

[0046] Table 1

[0047] By comparing Application Example 1 and Application Example 1-2 and the test data in Table 1, it can be seen that when the mass concentration of each raw material is not within the range of this application, the production cycle of the electroless gold plating solution is shortened and cannot meet the requirement of 8MTO or more. In addition, under the same conditions, the uniformity of the gold plating layer is poor and cannot meet the usage requirements.

[0048] Combining Application Examples 1 and 3-5 with the detection data in Table 1, it can be seen that when the metal ion catalyst is a combination of thallium ion catalyst and cobalt ion catalyst, and the mass concentration ratio of thallium ion catalyst to cobalt ion catalyst is 1:(1-1.5), it is beneficial to improve the gold deposition efficiency of the electroless gold plating solution.

[0049] Combining Application Examples 5-9, Comparative Application Example 2, and the detection data in Table 1, it can be seen that when the metal ion catalyst is a combination of thallium ion catalyst and cobalt ion catalyst, and the mass concentration ratio of thallium ion catalyst to cobalt ion catalyst is 1:(1-1.5), combined with specific concentrations of 2-mercaptobenzimidazole, 2-mercapto-5-methylbenzimidazole, and 5,5'-dimethylhydantoin, the gold deposition efficiency of the electroless gold plating solution can be improved while ensuring the density and uniformity of the gold plating layer.

[0050] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A chemical gold plating solution for lead frames used in integrated circuit chip packaging, characterized in that, The electroless gold plating solution is an aqueous solution with the following concentrations: Water-soluble gold compounds, calculated as Au, with a concentration of 1-1.5 g / L; Sodium hypophosphite 10-20 g / L; Malic acid 15-20 g / L; Citric acid 15-20 g / L; N,N'-bis(2-hydroxyethyl)ethylenediamine 10-15 g / L; Triammonium citrate 15-20 g / L; EDTA-2Na 5~10g / L; 5,5'-Dimethylhydantoin 5-10 g / L; Metal ion catalyst, with a concentration of 2-3 ppm based on metal ions; Mercaptoimidazole 0.01–0.015 g / L; Hexamethylenetetramine 5-10 g / L.

2. The chemical gold plating solution for a lead frame for integrated circuit chip packaging according to claim 1, characterized in that: The metal ion catalyst is a combination of thallium ion catalyst and cobalt ion catalyst, wherein the mass concentration ratio of thallium ion catalyst to cobalt ion catalyst is 1:(1-1.5).

3. The chemical gold plating solution for a lead frame for integrated circuit chip packaging according to claim 2, characterized in that: The thallium ion catalyst is at least one of thallium sulfate, thallium nitrate, and thallium acetate.

4. The chemical gold plating solution for a lead frame for integrated circuit chip packaging according to claim 2, characterized in that: The cobalt ion catalyst is at least one of cobalt nitrate, cobalt sulfate, and cobalt acetate.

5. The chemical gold plating solution for a lead frame for integrated circuit chip packaging according to claim 1, characterized in that: The mercaptoimidazole includes 2-mercaptobenzimidazole and 2-mercapto-5-methylbenzimidazole, with a mass concentration ratio of (1-1.5):1 for 2-mercaptobenzimidazole and 2-mercapto-5-methylbenzimidazole.

6. The chemical gold plating solution for a lead frame for integrated circuit chip packaging according to claim 1, characterized in that: The water-soluble gold compound used is potassium gold citrate.

7. A method for gold plating a lead frame for integrated circuit chip packaging, characterized in that: The lead frame, which is sequentially plated with nickel and palladium layers, is chemically plated with gold in the electroless gold plating solution described in any one of claims 1 to 6.

8. The gold plating method for a lead frame for integrated circuit chip packaging according to claim 7, characterized in that: The pH of the electroless gold plating solution is controlled to be 6.8–7.2, and the electroless gold plating temperature is 75–85°C.

9. A lead frame for packaging an integrated circuit chip, characterized in that: It is prepared by the gold plating method of the lead frame for integrated circuit chip packaging as described in claim 8.

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