TW202315981A - Plating solution for electroplating gold on nickel plating, method for electroplating gold on nickel plating, and gold-plated item - Google Patents

Abstract

The present invention relates to the field of electroplating gold on nickel plating, and disclosed are a plating solution for electroplating gold on nickel plating, a method for electroplating gold on nickel plating, and a gold-plated article. The plating solution comprises a gold source, an electrically conductive salt and an organic phosphonic acid. When electroplating gold on a nickel plating, the organic phosphonic acid can selectively adsorb on the nickel surface to form a barrier layer, effectively inhibiting substitution between nickel and gold, and thereby achieving the preparation of a gold-plated layer having a uniform appearance and excellent bonding force by means of cyanide-free electroplating.

Description

Plating solution for electroplating gold on nickel plating, method and gold-plated article for electroplating gold on nickel plating

The invention relates to the technical field of electroplating gold on nickel plating, in particular to a plating solution for electroplating gold on nickel plating, a method for electroplating gold on nickel plating, and a gold-plated piece prepared by the method.

Gold is the metal second only to silver and copper in terms of electrical and thermal conductivity. Gold has excellent chemical stability. It will not be oxidized under normal temperature or heating conditions, and it does not react with most chemical substances. It has good solderability and can be hot pressed. Bonding, low contact resistance, so gold plating is widely used in PCB, electronic connectors, semiconductor wafer manufacturing, etc. In wafer manufacturing, the interconnection between the wafer and the substrate is realized through gold bump flip-chip technologies such as TAB (Tape Automated Bonding), COG (Chip on glass), COF (Chip on Film), COP (Chip on Plastics), etc. , can be applied to LCD driver chips, CMOS image sensors, fingerprint sensors, etc.

Compared with conductive metals such as copper, nickel and tin commonly used in other applications, gold is expensive as a precious metal. In order to reduce the cost of gold bumps, an alternative is to first make a passivation layer, UBM layer and photoresist on the aluminum electrode on the wafer surface Define the pattern area, then electroplate about 10μm copper bump, then electrodeposit 2-3μm electrodeposited nickel on the copper bump, and finally electrodeposit 0.2-0.5 μm electrodeposited gold on the nickel, which can ensure the bump The hardness can ensure the good welding performance of the bump.

The reason for nickel-gold substitution is that the equilibrium potential of nickel is more negative than that of gold, so nickel easily loses electrons and enters the solution, while free gold ions in the solution get electrons and deposit on the surface of the nickel electrode. Compared with the cyanide-deposited gold system, sulfurous acid electroplating gold is more likely to replace nickel and gold on the nickel surface, resulting in a decrease in the binding force of the deposited layer, because the complexation stability constant of [Au(SO ₃ ) ₂ ] ^3- is 10 ¹⁰ , Much lower than the complex stability constant of Au(CN) ₂ ^- 10 ³⁸ . That is to say, in the basic plating solution containing [Au(SO ₃ ) ₂ ] ^3- , there are more free monovalent Au ions, resulting in the substitution of nickel and gold.

Electroplating gold is widely used in connectors. First, 2-3μm electroplating nickel is electroplated on copper as a barrier layer, and then tens of nanometers of gold is electroplated. Because the outermost gold needs to meet the plug-in function, it needs to be used Hard electroplating gold-cobalt or gold-nickel alloy, the production of cemented carbide should use cyanide gold plating system.

In order to solve the nickel-gold replacement problem in the cyanide gold plating system, JP62218594A discloses the addition of dithiocarbamic acid, CN102154667B discloses the addition of mercaptotetrazole compounds, CN106661751B discloses the addition of mercaptotriazole compounds, and CN107709628B discloses the addition of triazole compounds with mercapto groups. At least one compound among the azole compound and the aliphatic compound having a sulfonic acid group and a mercapto group can effectively suppress the degree of substitution of nickel and gold, and obtain a cemented carbide layer with uniform appearance and good bonding force.

However, compounds containing mercapto groups usually adsorb too strongly on gold surfaces, which may lead to missed plating. In addition, as mentioned above, the complexation stability constant of [Au(SO ₃ ) ₂ ] ^3- is much lower than that of Au(CN) ₂ ^- , and the concentration of free monovalent Au in the plating solution is higher, so compared with cyanide gold plating system, the reaction degree of nickel-gold substitution in the cyanide-free electroplating system will be higher.

Therefore, for the application of cyanide-free electroplating gold plating solution in the manufacture of related electronic components and semiconductors, it is necessary to be able to overcome the adverse effects of nickel-gold substitution, which is more challenging than cyanide gold plating technology.

The purpose of the present invention is to solve the electroplating gold used for connectors and wafers. When the electroplated nickel surface is immersed in the cyanide-free electroplating gold plating solution for electroplating, the appearance uniformity and bonding force of the gold plating are affected by the substitution of nickel and gold. The problem is to provide a plating solution for electroplating gold on a nickel coating and a method and a gold-plated article for electroplating gold on a nickel coating.

In order to achieve the above object, the first aspect of the present invention provides a plating solution for electroplating gold on nickel plating, wherein the plating solution comprises: a gold source, a conductive salt and an organic phosphonic acid.

Preferably, the organic phosphonic acid is selected from at least one of methylene phosphonic acid, homocarbon diphosphonic acid, and carboxylic acid phosphonic acid, preferably selected from hydroxyethylidene diphosphonic acid, ammonia trimethylene phosphonic acid, ethylenediamine At least one of tetramethylene phosphonic acid; more preferably hydroxyethylidene diphosphonic acid and/or amino trimethylene phosphonic acid.

Preferably, in the plating solution, the concentration of the organic phosphonic acid is 1-50 g/L, preferably 4-30 g/L.

The second aspect of the present invention provides a method for electroplating gold on a nickel coating, wherein the method includes: placing a component with a nickel coating into a gold plating solution for electroplating; wherein the gold plating solution is the plating solution provided by the present invention liquid.

The third aspect of the present invention provides a gold-plated article produced by the method of the present invention.

Through the above technical scheme, the gold plating solution provided by the present invention contains organic phosphonic acid, and when gold is electroplated on the nickel coating, the organic phosphonic acid can be selectively adsorbed on the nickel surface to form a barrier layer, effectively inhibiting the replacement of nickel and gold, thereby realizing A gold-plated layer with uniform appearance and good adhesion is prepared by cyanide-free electroplating.

Neither the endpoints of the ranges nor any values disclosed herein are limited to such precise ranges or values, and these ranges or values are understood to include values approaching these ranges or values. For numerical ranges, between the endpoints of each range, between the endpoints of each range and individual point values, and between individual point values may be combined with each other to obtain one or more new numerical ranges, These numerical ranges are to be considered as specifically disclosed herein.

The first aspect of the present invention provides a plating solution for electroplating gold on nickel plating, wherein the plating solution comprises: a gold source, a conductive salt and an organic phosphonic acid.

In the present invention, the plating solution provided contains organic phosphonic acid as an auxiliary complexing agent for cyanide-free electroplating gold, and when it is used for electroplating gold on the surface of nickel plating, it suppresses the replacement of nickel and gold by selectively adsorbing on the surface of electroplated nickel. When nickel After the surface is completely covered by gold, it does not affect the deposition process of electroplating gold, so it will not cause problems such as missing plating or poor thickness uniformity.

The plating solution provided by the present invention also contains a solvent, which may be water.

In some embodiments of the present invention, preferably, the organic phosphonic acid is selected from at least one of methylene phosphonic acid, homocarbon diphosphonic acid, and carboxylic acid phosphonic acid, preferably selected from hydroxyethylidene diphosphonic acid (HEDP) , at least one of aminotrimethylenephosphonic acid (ATMP) and ethylenediaminetetramethylenephosphonic acid (EDTMP); more preferably hydroxyethylidene diphosphonic acid and/or aminotrimethylenephosphonic acid.

In some embodiments of the present invention, preferably, the concentration of the organic phosphonic acid in the plating solution is 1-50 g/L. In the present invention, when the concentration of the organic phosphonic acid is greater than 50 g/L, the ability to complex with monovalent gold becomes stronger, resulting in too dense electroplating film, which may cause poor welding. When the concentration of the organic phosphonic acid is less than 1 g/L, the plating solution becomes unstable and the plating layer becomes rough. Preferably, the concentration of the organic phosphonic acid is, for example, 1 g/L, 2 g/L, 3 g/L, 4 g/L, 5 g/L, 6 g/L, 7 g/L, 8 g/L L, 9 g/L, 10 g/L, 11 g/L, 12 g/L, 13 g/L, 14 g/L, 15 g/L, 16 g/L, 17 g/L, 18 g/L, 19 g/L L, 20g/L, 21g/L, 22g/L, 23g/L, 24g/L, 25g/L, 26g/L, 27g/L, 28g/L, 29g/L, 30g/L, 31g/L , 32 g/L, 33 g/L, 34 g/L, 35 g/L, 36 g/L, 37 g/L, 38 g/L, 39 g/L, 40 g/L, 41 g/L , 42 g/L, 43 g/L, 44 g/L, 45 g/L, 46 g/L, 47 g/L, 48 g/L, 49 g/L, 50 g/L, and any two of the above Any value in the range of three numerical values, preferably 4-30 g/L.

In some embodiments of the present invention, preferably, the gold source is selected from gold sulfate and/or sulfite, preferably at least one of sodium gold sulfite, potassium gold sulfite, and ammonium gold sulfite.

In some embodiments of the present invention, preferably, the amount of the gold source is such that the concentration of gold ions in the plating solution is 1-20 g/L. In the present invention, when the concentration of gold ions is less than 1 g/L, the cathode precipitation efficiency is too low, and the electroplating solution becomes unstable at the same time, and gold is easy to precipitate in the plating solution instead of the surface of the cathode. When the concentration of gold ions is greater than 20g/L, although the stability of the electroplating solution and the appearance and physical properties of the coating have no effect, the gold is wasted due to the stripping of the plating solution after the plated sheet is completed, and the cost rises. The concentration of gold ions is, for example, 1 g/L, 2 g/L, 3 g/L, 4 g/L, 5 g/L, 6 g/L, 7 g/L, 8 g/L, 9 g/L, 10g/L, 11g/L, 12g/L, 13g/L, 14g/L, 15g/L, 16g/L, 17g/L, 18g/L, 19g/L, 20g/L L, and any value in the range consisting of any two values above, is preferably 1-12 g/L.

In some embodiments of the present invention, preferably, the conductive salt is selected from sulfite and/or sulfate, preferably selected from sodium sulfite, potassium sulfite, ammonium sulfite, sodium bisulfite, sodium sulfate, potassium sulfate, At least one of ammonium sulfate and sodium bisulfate, preferably sodium sulfite and sodium sulfate.

In some embodiments of the present invention, preferably, the concentration of sodium sulfite in the plating solution is 10-120 g/L. When it is less than 10 g/L, the uniformity of electroplating will decrease, the hardness of the coating will be high, and even the electroplating solution may decompose. When it is greater than 120 g/L, the current density range in the high zone becomes narrow and the coating becomes rough. The preferred concentration of sodium sulfite is for example 10 g/L, 15 g/L, 20 g/L, 25 g/L, 30 g/L, 35 g/L, 40 g/L, 45 g/L, 50 g/L , 55 g/L, 60 g/L, 65 g/L, 70 g/L, 75 g/L, 80 g/L, 85 g/L, 90 g/L, 95 g/L, 100 g/L , 105 g/L, 110 g/L, 115 g/L, 120 g/L, and any value in the range consisting of any two of the above values, preferably 30-80 g/L. The concentration of sodium sulfate is 1-120 g/L. When the concentration of sodium sulfate is greater than 120 g/L, the high current density range may be narrowed and the coating may become rough. The concentration of sodium sulfate is preferably 1 g/L, 5 g/L, 10 g/L, 15 g/L, 20 g/L, 25 g/L, 30 g/L, 35 g/L, 40 g/L L, 45 g/L, 50 g/L, 55 g/L, 60 g/L, 65 g/L, 70 g/L, 75 g/L, 80 g/L, 85 g/L, 90 g/L L, 95 g/L, 100 g/L, 105 g/L, 110 g/L, 115 g/L, 120 g/L, and any value in the range composed of any two of the above values, preferably 10- 60g/L.

In some embodiments of the present invention, preferably, the plating solution further includes a pH additive; preferably, the pH of the plating solution is 7-9. When the pH of the plating solution is lower than 7.0, the long-term stability of the plating solution deteriorates. When the pH of the plating solution is higher than 9.0, the photoresist dissolves or seepage occurs, and at the same time, the appearance of the plating layer is uneven because gold is difficult to restore. The pH of the preferred plating solution is, for example, 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7., 7.8, 7.9, 8, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 9, And any value in the range composed of any two of the above values, preferably 7.4-9. As the pH adjuster, sulfurous acid, sulfuric acid, etc. can be used as the acid, and sodium hydroxide, potassium hydroxide, ammonia water, etc. can be used as the base.

In the present invention, the plating solution may be prepared by putting the above-mentioned components into water and dissolving them completely. Wherein, the conductive salt and the organic phosphonic acid can be completely dissolved by directly putting the corresponding compound into water. The gold source can be added in the form of an aqueous solution, but the actual amount is calculated as the gold element, and finally each component is completely dissolved. Preferably, the conductive salt, organic phosphonic acid and water can be mixed first to obtain a completely dissolved solution, and then the gold source is added in the form of a solution to completely dissolve. The dissolution process can be carried out at room temperature with stirring. The pH value of the solution obtained by dissolving is also adjusted to meet the pH requirement of 7-9, preferably 7.4-9. The requirements for pH adjustment are as described above and will not be repeated here. Further, volume adjustment of the obtained solution is also performed to obtain the final plating solution and meet the concentration requirements for each component.

The second aspect of the present invention provides a method for electroplating gold on a nickel coating, wherein the method includes: placing a component with a nickel coating into a gold plating solution for electroplating; wherein the gold plating solution is the plating solution provided by the present invention liquid.

In some embodiments of the present invention, preferably, the electroplating temperature is 40-70°C. When the temperature of electroplating is higher than 70°C, sometimes the plating solution will decompose, and at the same time, it will be difficult to manage the plating solution because the plating solution will be too fast. When the plating temperature is lower than 40° C., the deposition efficiency decreases, and the appearance of the plating layer may be uneven. Preferably 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, 70°C, and any two of the above Any value within the range of numerical composition, preferably 50-60°C.

In some embodiments of the present invention, preferably, the current density of the electroplating is 0.1-2 A/dm ² (ASD). Preferably, for example, 0.1 ASD, 0.2 ASD, 0.3 ASD, 0.4 ASD, 0.5 ASD, 0.6 ASD, .07 ASD, 0.8 ASD, 0.9 ASD, 1 ASD, 1.1 ASD, 1.2 ASD, 1.3 ASD, 1.4 ASD, 1.5 ASD, 1.6 ASD, 1.7 ASD, 1.8 ASD, 1.9 ASD, 2.0 ASD, and any value in the range composed of any two values above, preferably 0.2-1.2 ASD. When the current density exceeds the above-mentioned range, the decomposition of the plating solution or the uneven appearance of the plating layer may sometimes occur.

The third aspect of the present invention provides a gold-plated article produced by the method of the present invention.

The prepared gold-plated piece forms a gold-plated layer with good bonding force on the nickel-plated layer.

The present invention will be described in detail below by way of examples. Test Methods

Nickel-gold replacement gold thickness: Use freshly prepared bright nickel-plated copper substrates as substrates, immerse them in the cyanide-free electroplating solution without power, stay under magnetic stirring for two minutes, and then use XRF to measure the thickness of gold replacement.

Bonding force test: stay under magnetic stirring for 30s, then energize, conduct electroplating at a current density of 0.5 A/dm ² for 2 minutes, use a beta test, use 3M adhesive tape to bond the coating, check the peeling of the coating and the area of gold on the tape, A shedding area of less than 10% was evaluated as good binding force, and a shedding area greater than 10% was evaluated as poor binding force. Example 1

In a 2 L beaker, add 60 g of sodium sulfite, 30 g of sodium sulfate, 10 g of amino trimethylene phosphonic acid, add 600 mL of deionized water, stir to dissolve completely, then add sulfurous acid with a gold content of 8 g Gold sodium aqueous solution, after being completely dissolved, adjust the liquid level of the plating solution to 1 L and adjust the pH value of the plating solution to 8.0.

Heating the temperature of the plating solution to 55°C for nickel-gold displacement electroplating. The results show that the gold thickness of the fresh nickel-plated sheet is 1.3 nm after soaking for 2 minutes without electricity, and the plating layer after soaking for 30 seconds and then electrified for 2 minutes is bright and uniform, and the bonding force is good. Example 2

According to the method of Example 1, the difference is that "10 g hydroxyethylidene diphosphoric acid" is added to replace "10 g aminotrimethylene phosphonic acid", and "gold sodium sulfite with a gold element content of 12 g" is added to replace "gold Sodium gold sulfite with an element content of 8 g", adjust "the pH of the plating solution is 7.4" to replace "the pH of the plating solution is 8.0".

Heat the temperature of the plating solution to 40 °C for nickel-gold displacement plating. The results show that the gold thickness of the fresh nickel-plated sheet is 2.0 nm after soaking for 2 minutes without electricity, and the plating layer after soaking for 30 seconds and then energized for 2 minutes is bright and uniform, and the bonding force is good. Example 3

According to the method of Example 1, the difference is that "5 g of hydroxyethylidene diphosphoric acid, 5 g of ammonia trimethylene phosphonic acid" is added to replace "10 g of ammonia trimethylene phosphonic acid", and "the content of gold element is 1 g Gold sodium sulfite" replaces "gold sodium sulfite with a gold element content of 8 g", and adjusts the pH of the plating solution to 9.0 to replace "the pH of the plating solution is 8.0".

Heating the temperature of the plating solution to 60°C for nickel-gold displacement electroplating. The results show that the thickness of gold is 2.5 nm after the fresh nickel-plated sheet is soaked for 2 minutes without power on, and the coating is bright and uniform after the fresh nickel-plated sheet is soaked for 30 seconds and then energized for 2 minutes, and the bonding force is good. Comparative example 1

According to the method of Example 1, the difference is that an aqueous sodium arsenite solution with an arsenic content of 15 mg was additionally added.

Heat the temperature of the plating solution to 55 °C for nickel-gold displacement plating. The results showed that the thickness of gold was 12.0 nm after the fresh nickel-plated sheet was soaked for 2 minutes without electricity, and the coating was bright and uniform after the fresh nickel-plated sheet was soaked for 30 seconds and then energized for 2 minutes, but the bonding strength was poor. Comparative example 2

According to the method of Example 1, the difference is that an aqueous solution of thallium sulfate with a thallium content of 30 mg was additionally added.

Heating the temperature of the plating solution to 55°C for nickel-gold displacement electroplating. The results show that the gold thickness of the fresh nickel-plated sheet is 47.8 nm after soaking for 2 minutes without power on, and the coating brightness is not uniform after the fresh nickel-plated sheet is soaked for 30 seconds and then energized and electroplated for 2 minutes, and the bonding force test is poor. Comparative example 3

According to the method of Example 1, the difference is that "10 g ethylenediamine" is used instead of "10 g aminotrimethylene phosphonic acid".

Heating the temperature of the plating solution to 55°C for nickel-gold displacement electroplating. The results show that the thickness of gold is 31.3 nm after the fresh nickel-plated sheet is soaked for 2 minutes without power on, and the plating layer with the fresh nickel-plated sheet soaked for 30 seconds and then energized for 2 minutes has uneven brightness and poor bonding force.

The results of electroplating gold in the above examples and comparative examples are shown in Table 1. Table 1 serial number Example comparative example 1 2 3 1 2 3 Plating conditions Plating temperature (°C) 55 40 60 55 55 55 Current Density (ASD) 0.5 0.5 0.5 0.5 0.5 0.5 Plating time (min) 2 2 2 2 2 2 Plating solution composition (g/L) Gold (sodium gold sulfite) 8 12 1 8 8 8 Sulfite 60 60 60 60 60 60 sodium sulfate 30 30 30 30 30 30 Ethylenediamine (ethylenediamine sulfate) 10 Amino trimethylene phosphonic acid 10 5 10 10 hydroxyethylidene diphosphate 10 5 Arsenic (sodium arsenite) 15 Thallium (thallous sulfate) 30 pH 8.0 7.4 9.0 8 8 8.0 Plating result 2min gold replacement thickness (nm) 1.3 2.0 2.5 12.0 47.8 31.3 Appearance after 2min electroplating uniform uniform uniform uniform uneven uneven Binding force good good good Difference Difference Difference

As can be seen from the foregoing examples and Table 1, in Examples 1-3, ammonia trimethylene phosphonic acid and/or hydroxyethylidene diphosphoric acid are added separately, and in the case of no electrification, the gold plated after soaking for 2 min The thickness is less than 2.5 nm. After electroplating, the appearance of the coating is uniform and bright, and the bonding force is good. The addition of arsenic or thallium is used to improve the precipitation efficiency of the plating solution and improve the crystal structure of the coating. In Comparative Example 1, it was found that the degree of nickel-gold substitution increased slightly after the addition of arsenic, and the coating was uniform but the bonding force was poor. In Comparative Example 2, it was found that the nickel-gold substitution after the addition of thallium The degree is greatly increased, the coating is uneven and the bonding force is poor. In addition, in Comparative Example 7, ethylenediamine was used instead of organic phosphonic acid in the cyanide-free gold plating system. Under the same conditions, the thickness of substituted gold was 31.3 nm, and the appearance of the plating layer after electroplating was uneven and not bright.

From the results in Table 1, it can be seen that the use of gold sulfite, organic polyphosphonic acid and conductive salt in cyanide-free gold plating, while not containing thallium or arsenic as a crystallization regulator, can significantly and effectively inhibit the degree of nickel-gold substitution, and obtain Gold-plated parts with a uniform appearance and good bonding force on the nickel-plated layer.

The preferred embodiments of the present invention have been described in detail above, however, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the content disclosed in the present invention, Belong to the protection scope of the present invention.

Claims (11)

A plating solution for electroplating gold on nickel plating, characterized in that the plating solution comprises: gold source, conductive salt and organic phosphonic acid. The plating solution according to claim 1, wherein the organic phosphonic acid is selected from at least one of methylene phosphonic acid, homocarbon diphosphonic acid, and carboxylic acid phosphonic acid. The plating solution according to claim 2, wherein the organic phosphonic acid is selected from at least one of hydroxyethylidene diphosphonic acid, ammonia trimethylene phosphonic acid, and ethylenediamine tetramethylene phosphonic acid. The plating solution according to claim 3, wherein the organic phosphonic acid is hydroxyethylidene diphosphonic acid and/or aminotrimethylene phosphonic acid. The plating solution according to any one of claims 1-4, wherein, in the plating solution, the concentration of the organic phosphonic acid is 1-50 g/L. The plating solution as described in any one of claim items 1-5, wherein, the gold source is selected from gold sulfate and/or sulfite; and/or, the amount of the gold source makes the plating solution The concentration of gold ions in the medium is 1-20 g/L. The plating solution according to any one of claim items 1-6, wherein, the conductive salt is selected from at least one of sulfite, bisulfite, sulfate, bisulfate; and/or, the In the plating solution, the concentration of sodium sulfite is 10-120 g/L; the concentration of sodium sulfate is 1-120 g/L. The plating solution according to any one of claims 1-7, wherein the plating solution further includes a pH additive; and/or, the pH of the plating solution is 7-9. A method for electroplating gold on a nickel coating, characterized in that the method comprises: placing parts with a nickel coating into a gold plating solution for electroplating; wherein the gold plating solution is any one of Claims 1-8 The plating solution. The method according to claim 9, wherein the temperature of the electroplating is 40-70°C; and/or the current density of the electroplating is 0.1-2 A/dm ² . A gold-plated piece prepared by the method described in Claim 9 or 10.