Nickel-free electroless gold process for printed circuit board

Abstract

The invention discloses a nickel-free electroless gold process for a printed circuit board. The nickel-free electroless gold process comprises the following steps: S1, micro-etching; s2, washing with water; s3, copper barrier layer deposition: a copper barrier layer protection copper surface is formed by deposition of corrosion inhibition liquid medicine, a chemical nickel layer is replaced, potential migration of gold ions to copper ions during gold melting is blocked, and anti-aging protection of a substrate copper layer is achieved; s4, washing with water; s5, nickel-free gold plating is carried out; s6, gold recovery; and S7, washing. According to the nickel-free chemical gold technology, interference of a nickel layer on signals is avoided, the nickel-free chemical gold technology is particularly outstanding in high-frequency and high-speed signal transmission, pure signal transmission can be ensured, and the equipment requirement can be effectively improved in the fields such as 5G communication and radar which have extremely high signal transmission requirements; moreover, the nickel-free substitute is an environment-friendly surface treatment solution, is lead-free, cyanide-free, nickel-pollution-free and non-toxic, and is more in line with RoHS and REACH standards; in addition, compared with an ENIG technology, the nickel-free chemical gold production process is effectively shortened, and the production efficiency can be greatly improved.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board technology, and in particular to a nickel-free gold plating process for printed circuit boards. Background Technology

[0002] ENIG is short for Electroless Nickel Immersion Gold, a process commonly used for surface treatment of printed circuit boards (PCBs). The process flow and plating layer stack-up are as follows: Figure 1 and Figure 2 As shown, the process involves several steps: Electroless Nickel Plating: This step involves depositing a uniform nickel layer on the surface of copper or other substrates through a chemical reaction. This nickel layer not only provides good conductivity and corrosion resistance but also enhances the adhesion between the gold layer and the substrate. Immersion Gold Plating: After electroless nickel plating, the circuit board is immersed in a solution containing gold ions. Through a displacement reaction, a very thin gold layer is deposited on the surface of the nickel layer, primarily to prevent oxidation of the nickel layer and to provide good solderability and appearance.

[0003] ENIG technology offers several advantages, including good solderability, long-term reliability, a smooth surface, and suitability for lead-free soldering. However, in existing ENIG processes, the electron migration process during nickel-to-gold replacement inevitably attacks the nickel layer. Poor nickel layer quality or excessive gold replacement can lead to nickel corrosion. Severe corrosion results in black nickel oxide on the surface during subsequent packaging processes, causing insufficient bonding strength between components, component detachment, and functional defects. Furthermore, FPCs, due to their thinness and flexibility requirements, exhibit porous characteristics in their chemically treated soft nickel columnar crystals, leading to weak resistance to salt spray corrosion. In addition, the existing ENIG process involves 17 steps, resulting in low production efficiency and significant waste of water resources, which is detrimental to energy conservation and environmental protection. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention provides a nickel-free gold plating process for printed circuit boards, comprising the following steps: S1. Micro-etching: Micro-etching treatment is performed on the surface of the copper layer; S2. Water washing: The copper layer surface after micro-etching is washed with water to remove impurities and chemicals; S3. Copper barrier layer deposition: A copper barrier layer is formed by depositing an anti-corrosion solution to protect the copper surface, replacing the chemical nickel layer. This prevents the potential migration of gold ions to copper ions during chemical gold treatment, thus achieving anti-aging protection for the base copper layer. S4. Water washing: The surface of the deposited copper barrier layer is washed with water to remove the slow-release drug; S5. Nickel-free gold: A thin gold layer is deposited on the surface of the deposited copper barrier layer through a substitution reaction; S6. Gold Recycling: Using strong or weak base anion exchange resin, metal cations contained in the water tank liquid are adsorbed. The saturated resin is periodically removed and handed over to a professional solid waste treatment company for combustion and gold extraction. S7. Water washing: Remove surface chemicals by water washing.

[0005] In step S2, two consecutive water washing processes are performed.

[0006] In step S4, two consecutive water washing processes are performed.

[0007] In step S7, two consecutive water washing processes are performed.

[0008] Through the above technical solutions, the nickel-free gold plating process adopted in this invention avoids interference from the nickel layer on the signal, especially in high-frequency and high-speed signal transmission, ensuring pure signal transmission. In fields with extremely high requirements for signal transmission, such as 5G communication and radar, it can effectively improve equipment performance. Moreover, the nickel-free alternative is an environmentally friendly surface treatment solution: lead-free, cyanide-free, nickel-free pollution-free, and non-toxic, and it is more compliant with RoHS and REACH standards. In addition, the nickel-free gold plating production process of this invention is effectively shortened compared to the ENIG process, which can greatly improve production efficiency. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0010] Figure 1 This is a schematic diagram of the existing ENIG process flow; Figure 2 This is a schematic diagram of the nickel-free gold plating process disclosed in the embodiments of the present invention; Figure 3 This is a schematic diagram of the post-coating stack structure of the existing ENIG process; Figure 4 This is a schematic diagram of the post-plating stack structure of the nickel-free gold plating process disclosed in the embodiments of the present invention.

[0011] In the diagram: 10. Copper layer; 20. Nickel layer; 30. Gold layer; 40. Copper barrier layer. Detailed Implementation

[0012] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0013] refer to Figure 2The present invention provides a nickel-free gold plating process for printed circuit boards, comprising the following steps: S1. Micro-etching: Micro-etching treatment is performed on the surface of copper layer 10; S2. Two water rinses: The surface of the micro-etched copper layer 10 is rinsed with water to remove impurities and chemicals; S3. Copper barrier layer deposition: A copper barrier layer 40 is formed by deposition using an anti-corrosion solution to protect the copper surface, replacing the electroless nickel layer 20. This prevents the potential migration of gold ions to copper ions during electroless gold deposition, thus achieving anti-aging protection for the base copper layer 10. S4. Two water washes: The surface of the deposited copper barrier layer 40 is washed with water to remove the slow-release drug; S5. Nickel-free gold: A very thin gold layer 30 is deposited on the surface of the deposited copper barrier layer 40 by a substitution reaction; S6. Gold Recycling: Using strong or weak base anion exchange resin, metal cations contained in the water tank liquid are adsorbed. The saturated resin is periodically removed and handed over to a professional solid waste treatment company for combustion and gold extraction. S7. Two water washes: Remove surface chemicals by water washing.

[0014] Example parameters for each step in the process described in this embodiment are as follows: process Preprocessing Water wash Cu Barrier layer Water wash Imm Au Water wash Water wash temperature normal temperature normal temperature 50-60 degrees normal temperature 80-90 degrees normal temperature normal temperature time 10s 15s 20-25 mins 15s 3-5 minutes (adjusted according to customer requirements) 15s 15s Control of drug concentration pH 11~13, specific gravity 0.97~1.03 pH 2~3, specific gravity 1~1.1, gold concentration >0.4783g / L Actual concentration of the medicine Actual value 12.01 Actual value 0.988 Actual 2.06 Actual 1.031 Actual 0.536 refer to Figure 4 Based on the above process flow and parameter settings, the thickness of each layer in the plating stack obtained by the process of this invention is as follows: the thickness of copper layer 10 is 14~16μm, the thickness of copper barrier layer 40 is 0.05~0.08μm, and the thickness of gold layer 30 is 0.05~0.13μm. Figure 3 The thickness of the nickel layer 20 in the ENIG post-plating stack shown is 2~6μm.

[0015] Therefore, the nickel-free gold plating process adopted in this invention avoids interference with signals caused by the nickel layer 20, especially in high-frequency and high-speed signal transmission, ensuring pure signal transmission. In fields with extremely high signal transmission requirements, such as 5G communication and radar, it can effectively improve equipment performance. Moreover, the nickel-free alternative is an environmentally friendly surface treatment solution: lead-free, cyanide-free, nickel-free pollution-free, and non-toxic, and it is more compliant with RoHS and REACH standards. In addition, the nickel-free gold plating production process of this invention is effectively shortened compared to the ENIG process, which can greatly improve production efficiency. Furthermore, the thickness of the copper barrier layer 40 obtained by the nickel-free gold plating process of this invention is significantly reduced compared to the thickness of the nickel layer 20, thereby further reducing the thickness of the circuit board.

[0016] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to the above embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A nickel-free gold plating process for printed circuit boards, characterized in that, Includes the following steps: S1. Micro-etching: Micro-etching treatment is performed on the surface of the copper layer (10); S2. Water washing: The surface of the copper layer (10) after micro-etching is washed with water to remove impurities and chemicals; S3. Copper barrier layer deposition: A copper barrier layer (40) is formed by deposition using an anti-corrosion solution to protect the copper surface, replacing the electroless nickel layer (20), blocking the potential migration of gold ions to copper ions during electroless gold deposition, and achieving anti-aging protection for the base copper layer (10). S4. Water washing: The surface of the deposited copper barrier layer (40) is washed with water to remove the slow-release drug; S5. Nickel-free gold: A thin gold layer (30) is deposited on the surface of the deposited copper barrier layer (40) by a displacement reaction. S6. Gold Recovery: Adsorbs metal cations contained in the water tank liquid through strong or weak base anion exchange resin; S7. Water washing: Remove surface chemicals by water washing.

2. The nickel-free gold plating process for printed circuit boards according to claim 1, characterized in that, In step S2, two consecutive water washing processes are performed.

3. The nickel-free gold plating process for printed circuit boards according to claim 1, characterized in that, In step S4, two consecutive water washing processes are performed.

4. The nickel-free gold plating process for printed circuit boards according to claim 1, characterized in that, In step S7, two consecutive water washing processes are performed.

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