Cyanide-free chemical gold plating solution and method based on amino acid-furan carboxylic acid double complexing system

Abstract

The invention relates to a cyanide-free chemical displacement gold plating solution and a gold plating method, which are particularly suitable for deposition of an ultrathin gold layer (less than or equal to 0.1 mu m) on the surface of a nickel base material. The gold plating solution comprises a buffering agent, gold salt and a double-complexing-agent system composed of L-glutamine and 2-furancarboxylic acid. Amido and amino of L-glutamine synergistically act on the surface of nickel, so that mild activation is realized; furan epoxy atoms in 2-furancarboxylic acid and carboxyl form a steric-hindrance effect, so that gold ion release kinetics is regulated and controlled, and excessive substitution reaction is inhibited. The two synergistically solve the problems of unstable gold plating liquid, uneven coverage and the like in replacement gold plating on the nickel layer, and the obtained gold layer is compact and non-porous, and the gold plating liquid is stable. The process is environment-friendly and is suitable for high-reliability gold plating of the microelectronic packaging nickel substrate.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high-reliability gold plating of microelectronic packaging nickel substrates, and is particularly suitable for replacing thin gold on a nickel layer or a nickel-phosphorus alloy layer. BACKGROUND

[0002] Although cyanide gold plating has advantages such as stable plating solution and excellent plating layer performance, the cyanide plating solution contains highly toxic cyanide, which can pollute the environment and affect the safety of operators. Moreover, such a gold plating solution is strongly alkaline and can easily erode circuit board solder resist films. Non-cyanide chemical gold plating has become a trend, but there is a problem of poor plating solution stability. The mainstream sulfite-thiosulfate system has a rapid deposition rate, but the soldering reliability is reduced due to sulfur inclusions. Some formulations excessively pursue the deposition rate by adding thiourea as an accelerator, and ignore the requirement for the thin gold layer to be dense.

[0003] In non-cyanide chemical gold plating, complexing agents play an important role. Current complexing agent design is trapped in a homogenization dilemma: single complexing agent systems such as phosphonate or malic acid cannot balance substrate activation and deposition control, and are prone to form rough plating layers; traditional primary and secondary complexing agents (such as EDTA / citric acid combination) only stack coordination ability, and do not solve the timing contradiction between activation and deposition, resulting in poor interface bonding, and the secondary complexing agent can be replaced.

[0004] The present application proposes a division of labor mechanism for double primary complexing agents, and the functions of the two are not interchangeable. The absence of either complexing agent will cause the plating solution to fail: amino acid complexing agents can mildly activate the substrate surface to avoid corrosion of the substrate; furan carboxylic acid complexing agents can regulate gold ion release kinetics and inhibit local over-deposition. The two achieve synergistic effect through functional decoupling, significantly improve the uniformity and adhesion of the plating layer compared to single complexing agent systems, and provide a new solution for ultra-thin non-cyanide gold plating. SUMMARY

[0005] In view of the deficiencies mentioned in the above background art, the present application provides a non-cyanide chemical gold plating solution and method based on an amino acid-furan carboxylic acid double complexing system. The gold plating technology can replace thin gold on a nickel substrate, has good stability, and the gold plating layer is uniform and dense without color difference.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: The non-cyanide chemical gold plating solution and method based on the amino acid-furan carboxylic acid double complexing system comprise the following components: a buffer agent concentration of 20-60 g / L, and a gold salt content of 0.5-2 g / L.

[0007] The concentration of the amino acid is 10-50 g / L; and the concentration of the furan is 5-100 g / L.

[0008] Preferably, the concentration of the amino acid is 20-40 g / L; and the concentration of the furan is 10-50 g / L.

[0009] The gold salt is sodium sulfite, and the buffer is disodium hydrogen phosphate. The amino acid in the double complexing agent is any one of L-glutamine, glycine, aspartic acid, alanine, L-glutamic acid, L-cysteine, histidine, lysine, and arginine.

[0010] The furan carboxylic acid is any one of 2-furan carboxylic acid, 3-furan carboxylic acid, 2,5-furan dicarboxylic acid, 2,4-furan dicarboxylic acid, 3,4-furan dicarboxylic acid, 2,3,4-furan tricarboxylic acid, 2,3,5-furan tricarboxylic acid, furan carboxylic anhydride, 5-methyl-2-furan carboxylic acid, 3-methyl-2-furan carboxylic acid, 5-bromo-2-furan carboxylic acid, 5-chloro-2-furan carboxylic acid, 5-nitro-2-furan carboxylic acid, 5-amino-2-furan carboxylic acid, 5-hydroxymethyl furfural, and 5-hydroxy-2-furan carboxylic acid.

[0011] In some preferred embodiments, the molar ratio of the amino acid to the furan carboxylic acid is A:B = 1:0.5 to 1:2. The working temperature is 55-70°C, and the pH is 5.0-7.0.

[0012] A method for replacing gold plating on the surface of a nickel substrate, comprising: immersing the nickel substrate in the gold plating solution, and the replacement time is 5-10 min, and the thickness of the obtained gold layer is ≤0.1 μm.

[0013] The nickel substrate is a chemical nickel plating layer or a nickel alloy layer.

[0014] The cyanide-free chemical gold plating solution and method based on the amino acid-furan carboxylic acid double complexing system of the present application have the following advantages compared with the prior art: (1) The double complexing agent A (taking L-glutamine as an example) in the present application is a biologically derived amino acid with a unique zwitterion structure, which is not used for metal replacement activation in the prior art; the furan ring structure of the complexing agent B (taking 2-furan carboxylic acid as an example) is used as a complexing agent for the first time in the field of gold plating, and its weak aromaticity and controllable metal coordination ability are unique.

[0015] (2) The L-glutamine plus 2-furan carboxylic acid double complexing agent system, through the synergistic effect of the molecular structure, does not corrode the substrate during the chemical gold plating process, the replaced gold layer is dense and uniform, and the bonding force is good. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a scanning electron microscope plan view after chemical nickel gold plating in Example 1.

[0017] Figure 2 is a focused ion beam cross-sectional view after chemical nickel gold plating in Example 1.

[0018] Figure 3 This is a cross-sectional view of the focused ion beam after nickel-gold plating in Example 2.

[0019] Figure 4 This is a scanning electron microscope planar view of the nickel-gold plating after Example 4.

[0020] Figure 5 This is a scanning electron microscope planar view of the nickel-gold plating process in Example 6.

[0021] Figure 6 This is a scanning electron microscope planar view of the nickel-gold plating process in Example 7.

[0022] Figure 7 This is a cross-sectional view of the focused ion beam after nickel-gold plating in Example 8.

[0023] Figure 8 This is the scanning electron microscope plane after nickel-gold plating in Example 12. Detailed Implementation

[0024] The technical solution of the present invention will now be clearly and completely described with reference to specific embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] Example 1 Disodium hydrogen phosphate: 30 g / L; Gold content: 2g / L; L-Glutamine: 30g / L; 2-Furfuric acid: 46 g / L; pH=6.0.

[0026] A 2μm thick electroless nickel-plated sheet was immersed in a plating bath at 60℃ for 8 minutes, resulting in uniform gold layer coverage. Figure 1 ), without pores, with a gold layer thickness of 78nm ( Figure 2 The 3M tape showed no peeling during testing.

[0027] Example 2 Disodium hydrogen phosphate: 30 g / L; Gold content: 2g / L; L-Glutamine: 30g / L; 2-Furfuric acid: 11.5 g / L; pH=6.0.

[0028] In this embodiment, the molar ratio of L-glutamine to 2-furan carboxylic acid in the gold plating formulation is 1:0.5. A 2μm thick electroless nickel plating sheet is immersed in a plating bath at 60°C for 8 minutes. The result is a uniform gold layer with no pores, and a gold layer thickness of approximately 0.14μm. Figure 3 The 3M tape showed no peeling during testing.

[0029] Example 3 Disodium hydrogen phosphate: 30 g / L; Gold content: 2g / L; L-Glutamine: 30g / L; 2-Furfuric acid: 23 g / L; pH=6.0.

[0030] In this embodiment, the molar ratio of L-glutamine to 2-furan carboxylic acid in the gold plating formulation is 1:1. A 2μm thick electroless nickel plating sheet is immersed in a plating solution at 60°C for 8 minutes, resulting in a gold layer thickness of 58nm. The gold plating is dense, pore-free, and has good adhesion.

[0031] Example 4 Disodium hydrogen phosphate: 30 g / L; Gold content: 2g / L; L-Glutamine: 30g / L; 2-Furfuric acid: 46 g / L; pH=4.0.

[0032] In this embodiment, the molar ratio of L-glutamine to 2-furanoic acid in the gold plating formulation is 1:2. A 2μm thick electroless nickel plating sheet is immersed in a plating bath at 60°C for 8 minutes. The result is incomplete gold layer coverage, with some areas remaining unplated. Figure 4 The gold layer thickness was 0.05 μm. The 3M tape test showed no peeling. The solution changed color and gold precipitated after continuous heating. This was mainly due to the failure of L-glutamine hydrolysis at too low pH.

[0033] Example 5 Disodium hydrogen phosphate: 30 g / L; Gold content: 2g / L; L-Glutamine: 30g / L; 2-Furfuric acid: 46 g / L; pH=5.0.

[0034] In this embodiment, the molar ratio of L-glutamine to 2-furan carboxylic acid in the gold plating formulation is 1:2. The electroless nickel plating sheet with a nickel layer thickness of 2μm is immersed in the plating solution at 60°C and replaced for 8 minutes. The plating layer is uniformly covered, the gold layer thickness is 48nm, the adhesion is good, and there is no peeling.

[0035] Example 6 Disodium hydrogen phosphate: 30 g / L; Gold content: 2g / L; L-Glutamine: 30g / L; 2-Furfuric acid: 46 g / L; pH=6.0.

[0036] In this embodiment, the molar ratio of L-glutamine to 2-furan carboxylic acid in the gold plating formulation is 1:2. A 2μm thick electroless nickel plating sheet is immersed in a plating bath at 40°C for 8 minutes. The result is incomplete gold layer coverage. Figure 5 There are some unreplaced gold layers, with a gold layer thickness of 0.06 μm. 3M tape tests show localized detachment, and the activation ability of glutamine decreases at low temperatures.

[0037] Example 7 Disodium hydrogen phosphate: 30 g / L; Gold content: 2g / L; L-Glutamine: 30g / L; 2-Furfuric acid: 46 g / L; pH=6.0.

[0038] In this embodiment, the molar ratio of L-glutamine to 2-furanoic acid in the gold plating formulation is 1:2. A 2μm thick electroless nickel plating sheet is immersed in an 80°C plating bath for 8 minutes. The result is incomplete gold layer coverage, with some areas remaining unplated. Figure 6 The gold layer thickness is 0.11μm, and the 3M tape test showed no peeling. High temperature will accelerate the hydrolysis of furanylformic acid.

[0039] Example 8 Disodium hydrogen phosphate: 30 g / L; Gold content: 2g / L; Serine: 30g / L; 2-Furfuric acid: 46 g / L; pH=6.0.

[0040] A 2μm thick electroless nickel-plated sheet was immersed in a 60℃ plating solution for 8 minutes. The result was a thick gold layer but a poorly corroded nickel layer with numerous pores. Figure 3 ).

[0041] Example 9 Disodium hydrogen phosphate: 30 g / L; Gold content: 2g / L; L-Glutamine: 30g / L; 5-Sulfo-2-furanoic acid: 81.9 g / L; pH=6.0.

[0042] When a 2μm thick electroless nickel plating sheet is immersed in a plating solution at 60℃, the plating solution begins to turn red after 5 minutes of displacement, and gold is completely precipitated in the plating solution after 10 minutes. This is mainly because the complexing agent has weak complexing ability, which leads to instability of the plating solution and gold precipitation during plating.

[0043] Example 10 Disodium hydrogen phosphate: 30 g / L; Gold content: 2g / L; L-Glutamine: 30g / L; 5-Bromo-2-furanic acid: 76.7 g / L; pH=6.0.

[0044] A 2μm thick electroless nickel plated sheet was immersed in a plating solution at 60℃. After 8 minutes of displacement, the gold layer was uniform with a thickness of 50nm, and no peeling was observed in the 3M test.

[0045] Example 11 Disodium hydrogen phosphate: 30 g / L; Gold content: 2g / L; L-Glutamine: 30g / L; pH=6.0.

[0046] A 2μm thick electroless nickel plated sheet was immersed in a plating solution at 60℃ for 8 minutes. The result was that the gold layer thickness was uneven and the deviation was large. The 3M tape test showed local peeling. This was mainly due to the lack of displacement inhibition and the local deposition being too fast.

[0047] Example 12 Disodium hydrogen phosphate: 30 g / L; Gold content: 2g / L; 2-Furfuric acid: 46 g / L; pH=6.0.

[0048] A 2μm thick electroless nickel plated sheet was immersed in a plating bath at 60℃ for 8 minutes, and the result was that the gold layer did not completely cover the plate. Figure 8 The 3M tape tested detached from the test area.

[0049] Based on the above examples and comparative examples, the conclusion that can be drawn is that the present invention utilizes an L-glutamine plus 2-furanoic acid dual complexing agent system to rapidly displace a thin gold layer (≤0.1μm) on a nickel layer under the conditions of 60℃ and pH=6.0. The gold layer is dense and defect-free, with good adhesion and no gold layer peeling off.

Claims

1. A cyanide-free electroless gold plating solution based on an amino acid-furan carboxylic acid dual-main complexation system, characterized in that, It contains the following components: buffer, gold salt, amino acid, furan.

2. The cyanide-free electroless gold plating solution according to claim 1, characterized in that, The gold salt is sodium gold sulfite; the buffer is disodium hydrogen phosphate.

3. The cyanide-free electroless gold plating solution according to claim 1, characterized in that, The buffer concentration is 20-60 g / L, and the gold salt content is 0.5-2 g / L.

4. The cyanide-free electroless gold plating solution according to claim 1, characterized in that, In the dual complexing agent, complexing agent A is any one of L-glutamine, glycine, aspartic acid, alanine, L-glutamic acid, L-cysteine, histidine, lysine, and arginine.

5. The cyanide-free electroless gold plating solution according to claim 1, characterized in that, The furan is selected from any one of 2-furancarboxylic acid, 3-furancarboxylic acid, 2,5-furandicarboxylic acid, 2,4-furandicarboxylic acid, 3,4-furandicarboxylic acid, 2,3,4-furantricarboxylic acid, 2,3,5-furantricarboxylic acid, furancarboxylic anhydride, 5-methyl-2-furancarboxylic acid, 3-methyl-2-furancarboxylic acid, 5-bromo-2-furancarboxylic acid, 5-chloro-2-furancarboxylic acid, 5-nitro-2-furancarboxylic acid, 5-amino-2-furancarboxylic acid, 5-hydroxymethylfurfural, and 5-hydroxy-2-furancarboxylic acid.

6. The cyanide-free electroless gold plating solution according to claim 1, characterized in that, The concentration of amino acids is 10-50 g / L; the concentration of furans is 5-100 g / L.

7. The cyanide-free electroless gold plating solution according to claim 6, characterized in that, The concentration of amino acids is 20-40 g / L; the concentration of furans is 10-50 g / L.

8. A method for displacement gold plating on a nickel substrate, comprising: The nickel substrate is immersed in the gold plating solution according to any one of claims 1-7, and the replacement time is 5-10 min, resulting in a gold layer thickness ≤0.1μm.

9. The method for displacement gold plating on a nickel substrate surface according to claim 8, characterized in that, During the replacement gold plating process, the working temperature is 55-70℃ and the pH is 5.0-7.

0.

10. The method for displacement gold plating on a nickel substrate surface according to claim 8, characterized in that, The nickel substrate is a chemically plated nickel layer or a nickel alloy layer, wherein the nickel alloy layer includes a nickel-phosphorus alloy layer.

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