Anti-corrosion weldable surface treatment method for electronic circuit

Abstract

The invention belongs to the field of surface final coating of PCBs (printed circuit boards) and packaging substrates, and particularly provides an anti-corrosion weldable surface treatment method of an electronic circuit, which is used for improving the manufacturing reliability of final decoration mounting of the PCBs and the packaging substrates and controlling the manufacturing cost at the same time. The method comprises the following steps: firstly, carrying out chemical nickel plating treatment on the exposed copper foil surfaces of the PCB and the packaging carrier, carrying out activation sensitization treatment on the nickel-plated layer, then, carrying out chemical tin plating on the treated nickel layer surface, and finally, carrying out reflow soldering treatment to finish the surface finishing. According to the method, the nickel layer is introduced through chemical nickel plating (Ni) before the copper layer is subjected to tin surface treatment, a Cu / Ni / Sn three-layer structure is formed, alloying between Cu and Sn is blocked through the Ni layer, tin whiskers with electrical conductivity are prevented from spontaneously growing on the surface, and the electromigration resistance of an interface is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of PCB and package board surface finishing, and specifically provides an anti-corrosion solderable surface treatment method for electronic circuits. BACKGROUND

[0002] In order to ensure that the PCB and package board can normally run and play a role in various applications, surface treatment is a crucial link. By using appropriate surface treatment methods, a coating or plating layer of a specific material can be formed on the surface of the PCB to improve its performance and function. According to the oxidation resistance of the metal and organic matter after surface treatment, the oxidation and corrosion of the copper circuit and pad can be prevented, and these surface treatment methods directly affect the reliability of the soldered connection, the quality of signal transmission, the stability of the circuit, and the durability of the PCB.

[0003] Currently, common surface finishing techniques mainly include organic solderability preservatives (OSP), tin immersion film, and hot air solder leveling (HASL), but still have some defects. For example, the OSP surface treatment reflow times are limited, and the solderability is insufficient. The tin immersion film and HASL can cause tin whisker growth due to stress, which can affect the reliability of the substrate. The chemical nickel plating and gold immersion have good oxidation resistance, high solderability, good wetting ability, and other performance advantages, and are suitable for wire bonding. However, the gold plating solution and palladium activator are expensive, and the commonly used cyanide gold salt has certain pollution. Therefore, the application continuously explores new surface treatment methods to overcome the drawbacks of traditional methods. SUMMARY

[0004] The purpose of the application is to provide an anti-corrosion solderable surface treatment method for electronic circuits to improve the manufacturing reliability of PCB and package board finishing and assembly, while controlling the manufacturing cost. Before tin surface treatment of the copper layer, the application introduces a nickel layer by chemical nickel plating (Ni) to form a Cu / Ni / Sn three-layer structure. The Ni layer blocks the alloying between Cu-Sn, inhibits the growth of tin whiskers with conductivity on the surface, and improves the anti-electromigration performance of the interface.

[0005] To achieve the above purpose, the technical solution adopted by the application is as follows:

[0006] An anti-corrosion solderable surface treatment method for electronic circuits, characterized by the following steps:

[0007] Step 1: Perform chemical nickel plating treatment on the surface of the copper layer to be treated to form a nickel layer on the surface of the copper layer.

[0008] Step 2: Perform activation and sensitization treatment on the plated nickel layer.

[0009] Step 3, tin layer is formed on the surface of the nickel layer after the surface of the nickel layer is treated by chemical plating tin treatment;

[0010] Step 4, the tin layer is treated by reflow soldering.

[0011] Further, in step 1, the copper layer (PCB board) to be treated is pre-cleaned before the chemical nickel plating treatment, and the pre-cleaning process includes alkaline washing, etching, acid washing, activation, and post-immersion acid washing in sequence.

[0012] Further, in step 1, the plating solution used in the chemical nickel plating treatment includes 30-35 g / L of main salt, 40-50 g / L of complexing agent, 24-36 g / L of reducing agent, and 25-30 g / L of stabilizer, wherein the main salt is NiSO4, the complexing agent is citric acid, the reducing agent is NaH2PO2, the pH adjuster is NaOH (pH adjustment: 4.4-4.8), and the stabilizer is lactic acid.

[0013] Further, in step 1, the process parameters of the chemical nickel plating treatment are: plating temperature is 80℃, plating time is 40min, and the thickness of the nickel layer obtained is 2-3μm.

[0014] Further, in step 2, the etching process is used for activation and sensitization treatment, and the etching treatment time is 2-3min. Further, the etching solution includes 30-35 g / L of sodium m-nitrobenzenesulfonate, 30.5-32.5 g / L of sodium sulfate, 1.8-2.1 g / L of nickel sulfate hexahydrate, 1.8-2.1 g / L of ammonium sulfhydrate, 0.35 g / L of benzene propyl triazene, and 75 ml / L of sulfuric acid.

[0015] Further, in step 3, the plating solution used in the chemical tin plating treatment includes 25-50 g / L of tin salt, 50-150 g / L of acid, 70-80 g / L of complexing agent, 50-150 g / L of reducing agent, 1-10 g / L of surfactant, and 0.5-1.0 g / L of brightener, wherein the complexing agent is citric acid, the reducing agent is sodium hypophosphite, the surfactant is ethylene glycol polymer, and the brightener is benzyl ketone and its derivatives.

[0016] Further, in step 3, the process parameters of the chemical tin plating treatment are: plating temperature is 40℃, plating time is 15min, and the thickness of the tin layer obtained is 0.5-2μm.

[0017] Further, in step 4, the process of reflow soldering is: the sample after chemical tin plating is placed on the conveyor belt of the reflow soldering furnace for continuous flow type furnace heat treatment. Further, the peak temperature of the reflow zone of the soldering furnace is 231℃-244℃, and the cycle is 5 times.

[0018] Based on the above technical scheme, the anti-corrosion solderable surface treatment method of the electronic circuit has the following advantages:

[0019] 1. A layer of uniform and well-adhesive nickel is formed on the copper substrate by chemical nickel plating, and then a layer of tin is chemically plated on the nickel layer to form a Cu / Ni / Sn three-layer structure, effectively blocking the alloying reaction between Cu and Sn and reducing the adverse effects of tin whisker growth on reliability.

[0020] 2. The tin layer plated on the nickel layer maintains good wetting properties and does not form a brittle intermetallic compound (IMC) layer when soldered with the widely used SAC solder.

[0021] 3. Compared with organic solderability preservatives (OSP), the method has better solderability; compared with traditional tin plating and hot air leveling (HASL), the method has better reliability; compared with electroless nickel immersion gold (ENIG), electroplated gold, and electroplated silver, the method has lower cost of noble metal electrolyte and relatively simple process.

[0022] 4. The surface of the PCB and carrier board is treated with chemical nickel plating and chemical tin plating, which does not require circuit pattern wiring connection, avoiding unnecessary complex wiring. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The figure is a flowchart of the traditional tin surface treatment process.

[0024] Figure 2 The figure is a flowchart of the new anti-corrosion solderable surface treatment method of the application.

[0025] Figure 3 The figure is a surface SEM and EDS graph of the plating layer obtained by the new anti-corrosion solderable surface treatment method of the application. DETAILED DESCRIPTION

[0026] To make the purpose, technical scheme, and beneficial effects of the application clearer and more apparent, the application is further described in detail below with reference to the drawings and examples.

[0027] In the field of surface finishing of PCB and packaging carrier boards, the solder pad surface after surface finishing needs to be soldered with components and leads. Currently, the commonly used solder is SAC solder with different proportions of tin, silver, and copper, and the tin content usually accounts for more than 60%. Due to the differences in metal structure, thermal stress and pressure stress exist after soldering with SAC solder, which produces adverse factors such as intermetallic compounds, affecting soldering reliability. Therefore, it is necessary to perform tin surface treatment on the copper substrate before soldering. However, since copper is easy to move to the surface in diffusion defects, direct tin surface treatment on the copper layer will produce single-crystal tin whiskers of different lengths, resulting in reduced soldering reliability. For example, the tin whiskers will grow in the direction of the diffusion defects, and the tin whiskers will grow in the direction of the diffusion defects.Figure 1 As shown, both electroless tin plating and hot air leveling (HASL) as commonly used tin surface treatment methods have such a risk of reliability deficiency.

[0028] To solve the above problems, the embodiment provides a nickel plating-tin plating surface finishing method, as shown in the formula. Figure 2 As shown, for the surface copper layer of the PCB and the packaging board, after chemical nickel plating (Ni) on the surface of the copper layer and depositing a 2 μm nickel layer, a Cu / Ni / Sn three-layer structure is formed by chemical tin plating (Sn) to block the alloying between Cu and Sn by the Ni layer, inhibit the surface from growing tin whiskers with conductivity, and improve the anti-electromigration performance of the interface.

[0029] Specifically, the following steps are included:

[0030] Step 1, taking a demonstration PCB copper-clad plate as an example, the PCB copper-clad plate is cleaned: sequentially performing alkali washing, micro-etching, acid washing, activation, and post-immersion acid washing, which are all known technologies in the art and will not be described in detail here; the cleaned PCB copper-clad plate is subjected to chemical nickel plating treatment, and the formula of the chemical nickel plating is: 32 g / L NiS04, 45 g / L citric acid, 32 g / L NaH2PO2, and 28 g / L lactic acid, and the plating temperature is set to 80°C and the plating time is set to 40 min, so that a nickel plating layer with a thickness of 2-3 μm is obtained.

[0031] Step 2, the nickel layer is subjected to etching treatment, and the formula of the nickel etching solution is: 32 g / L of m-nitrobenzenesulfonic acid sodium, 31.5 g / L of sodium sulfate, 2 g / L of nickel sulfate hexahydrate, 1.9 g / L of ammonium hydrosulfide, 0.35 g / L of benzene propyl triazene, and 75 ml / L of sulfuric acid, and the etching treatment time is 2 min; in this embodiment, the nickel layer is subjected to activation and sensitization treatment to ensure that there are more active sites on the surface of the nickel layer.

[0032] Step 3, the activated nickel layer is subjected to acid washing and then subjected to displacement tin plating, and the formula of the chemical tin plating is: 35 g / L SnSO4, 75 g / L H2SO4, 75 g / L citric acid, 50-150 g / L NaH2PO2, 2 g / L MPEG 500, and 1.0 g / L benzyl ketone, and the plating temperature is set to 40°C and the plating time is set to 15 min, so that a tin plating layer with a thickness of 0.5-2 μm is obtained; in this embodiment, the Ni layer blocks the alloying between Cu and Sn, improves the anti-electromigration performance of the interface, inhibits the growth of tin whiskers, and retains the good wetting and soldering properties of the chemical tin plating layer.

[0033] Step 4, reflow soldering, the copper clad plate after the electroless tin plating is placed on the conveying belt of the reflow soldering furnace for continuous flow type furnace heat treatment, the peak temperature of the reflow zone of the soldering furnace is 231-244℃, and the cycle is 5 times; in this embodiment, the tin layer after the surface treatment is reflow soldered, so that the integrity of the plating layer surface can be ensured.

[0034] The morphology of the prepared plating layer is observed by SEM and EDS, as shown in FIGS. Figure 3 It can be confirmed from the figures that there is no tin whisker growth on the plating layer surface, that is, the Cu / Ni / Sn three-layer structure is formed by introducing the Ni layer to block the alloying between Cu and Sn, to inhibit the surface self-growth of tin whiskers with conductivity, and to improve the anti-electromigration performance of the interface.

[0035] The above is only a specific embodiment of the present application, any feature disclosed in the specification can be replaced by other equivalent or similar purpose alternative features unless specifically described, and all features disclosed or steps in all methods or processes can be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A corrosion resistant solderable surface treatment method for electronic circuits, characterized in that, The method comprises the following steps: Step 1, performing chemical nickel plating treatment on the surface of the copper layer to be treated to form a nickel layer on the surface of the copper layer; Step 2, performing activation and sensitization treatment on the nickel layer plated; Step 3, performing chemical tin plating treatment on the surface of the nickel layer after the activation and sensitization treatment to form a tin layer on the surface of the nickel layer; Step 4, performing reflow soldering treatment on the tin layer plated.

2. The corrosion-resistant solderable surface treatment method for electronic circuits according to claim 1, characterized in that: In step 1, the copper layer (PCB board) to be treated is pre-cleaned before the chemical nickel plating treatment, and the pre-cleaning process comprises alkaline cleaning, etching, acid cleaning, activation and post-dipping acid cleaning in sequence.

3. The method of claim 1, wherein the electronic circuit is a printed circuit board. In step 1, the plating solution used in the chemical nickel plating treatment comprises 30-35 g / L of main salt, 40-50 g / L of complexing agent, 24-36 g / L of reducing agent, and 25-30 g / L of stabilizer, wherein the main salt is NiSO4, the complexing agent is citric acid, the reducing agent is NaH2PO2, the pH adjusting agent is NaOH (pH adjustment: 4.4-4.8), and the stabilizer is lactic acid.

4. The method of claim 1, wherein the electronic circuit is a printed circuit board. In step 1, the process parameters of the chemical nickel plating treatment are as follows: plating temperature is 80°C, and plating time is 40 min, so as to obtain a nickel layer with a thickness of 2-3 μm.

5. The method of claim 1, wherein the electronic circuit is a printed circuit board. In step 2, the activation and sensitization treatment adopts etching process, and the etching treatment time is 2-5 min.

6. The method of claim 5, wherein the surface treatment is applied to the electronic circuit by a soldering process. Furthermore, the etching solution comprises 30-35 g / L of sodium m-nitrobenzenesulfonate, 30.5-32.5 g / L of sodium sulfate, 1.8-2.1 g / L of nickel sulfate hexahydrate, 1.8-2.1 g / L of ammonium sulfhydrate, 0.35 g / L of benzene propyl triazene, and 75 ml / L of sulfuric acid.

7. The method of claim 1, wherein the electronic circuit is a printed circuit board. In step 3, the plating solution used in the chemical tin plating treatment comprises 25-50 g / L of tin salt, 50-150 g / L of acid, 70-80 g / L of complexing agent, 50-150 g / L of auxiliary reducing agent, 1-10 g / L of surfactant, and 0.5-1.0 g / L of brightener, wherein the complexing agent is citric acid, the auxiliary reducing agent is sodium hypophosphite, the surfactant is ethylene glycol polymer, and the brightener is benzyl ketone and its derivatives.

8. The method of claim 1, wherein the electronic circuit is a printed circuit board. In step 3, the process parameters of the chemical tin plating treatment are as follows: plating temperature is 40°C, and plating time is 15 min, so as to obtain a tin layer with a thickness of 0.5-2 μm.

9. The method of claim 1, wherein the electronic circuit is a printed circuit board. In step 4, the process of the reflow soldering treatment is that the sample after the chemical tin plating is placed on the conveying belt of the reflow soldering furnace for continuous flow type furnace heat treatment.

10. The method of claim 1, wherein the electronic circuit is a printed circuit board. The peak temperature of the reflow area of the soldering furnace is 231-244°C, and the cycle is 5 times.

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