CN110468394A - A kind of silver-based wiring board of chemical nickel plating porpezite and preparation method thereof - Google Patents

Abstract

The invention discloses a silver-based circuit board with electroless nickel-palladium-gold plating and a preparation method thereof. The silver-based circuit board includes a silver-based substrate, and the surface of the silver-based substrate is sequentially plated with a nickel layer, Palladium layer, gold layer. The preparation method includes the following steps: performing micro-etching, pickling, pre-dipping, palladium activation, and post-dipping pre-treatment on the cleaned silver-based substrate in sequence, and then performing pre-treatment on the pre-treated silver-based substrate in sequence. Electroless nickel plating, electroless palladium plating, and electroless gold plating are silver-based circuit boards containing nickel-palladium-gold coating. Compared with traditional copper-based electroless nickel-palladium-gold plating, the thickness of nickel-palladium-gold electroless plating can be greatly reduced, thereby saving The use content of metals, while avoiding the problem of pollution to the environment. Furthermore, with the silver base as the base, the entire product has stronger electrical and thermal conductivity, higher sensitivity, longer life, and better overall performance.

Description

A silver-based circuit board with electroless nickel-palladium-gold plating and preparation method thereof

technical field

The invention relates to a silver-based circuit board with electroless nickel-palladium-gold plating and a preparation method thereof, belonging to the technical field of surface treatment technology.

Background technique

With the rapid development of the electronics industry, the demand for circuit boards is increasing day by day. However, today's electronic products have gradually developed towards the direction of multi-function, high performance, portability, reliability and low cost. In order to meet the needs of the market and technology, it is not only required that the electronic packaging process must move towards high-density packaging such as system packaging or IC packaging. There is a need for a coating that can meet a variety of packaging processes, so the "universal" reputation of the electroless nickel-palladium-gold surface treatment process is born from this.

The main processes of electroless nickel palladium plating are electroless nickel plating, electroless palladium plating and chemical immersion gold. The treatment of each step of the process has a great impact on the performance of the product. The quality of the coating determines the performance of the entire product. good or bad.

At present, the commonly used electroless plating substrate is copper base, but the copper base after microetching treatment is easily polluted and oxidized by the environment. At the same time, the use of copper-based substrates generally requires thicker nickel and palladium layers to prevent the oxidation of the copper-based substrate and prevent the diffusion of copper ions to the gold layer and migration to the surface of the circuit board, resulting in poor solderability of the product. Furthermore, considering factors such as its performance and production cost, many people choose the electroless nickel plating process instead of the electroless gold plating process. However, the electroless nickel plating process has poor bonding ability with gold wires, and it is difficult to form a competitive advantage and be promoted. However, the pure chemical gold plating process causes a large amount of use of precious metals, which not only wastes costs, but also easily pollutes the environment.

Compared with copper-based, silver-based has much better electrical conductivity, thermal conductivity, and sensitivity. It is expected to produce high-quality circuit boards with good electrical conductivity, thermal conductivity, high sensitivity, corrosion resistance, and strong oxidation resistance. However, currently Also do not adopt the process method of the electroless nickel-palladium-gold plating with silver base as the substrate in the prior art.

Contents of the invention

Aiming at the deficiencies of the prior art, the present invention provides a silver-based circuit board with electroless nickel-palladium-gold plating with good thermal conductivity, high sensitivity, corrosion resistance and strong oxidation resistance and a preparation method thereof

In order to achieve the above object, the present invention provides the following technical solutions:

The invention relates to a silver-based circuit board with electroless nickel-palladium-gold plating. The silver-based circuit board includes a silver-based substrate, and the surface of the silver-based substrate is sequentially plated with a nickel layer, a palladium layer, and a gold layer from the inside to the outside.

A method for preparing a silver-based circuit board with electroless nickel-palladium-gold plating of the present invention comprises the following steps: performing microetching, pickling, pre-dipping acid, palladium activation, post-dipping and pre-pickling on the silver-based circuit board after cleaning. treatment, and then the pretreated silver-based substrate is sequentially subjected to electroless nickel plating, electroless palladium plating, and electroless gold plating to obtain a silver-based circuit board containing nickel-palladium-gold plating.

In a preferred scheme, the cleaning treatment process is as follows: the silver-based substrate is first cleaned with ultrapure water for 10-15 minutes, and then degreasing treatment and deoxidation treatment are performed; the degreasing treatment uses a mass fraction of 3% to 5% A mixed solution of sodium dodecylsulfonate and 20-30g/L sodium hydroxide, the deoxidation treatment uses at least one of 30mL/L methanesulfonic acid, chloric acid, perchloric acid, and nitric acid Mixture with 50~80g/L dodecyl ammonium chloride.

During the cleaning process, ultra-pure water is used to clean the dust and other impurities on the silver-based substrate. After cleaning, the products are put into the cleaning agent for degreasing and deoxidizing in turn, and ultrasonic vibration is added to completely remove the fingerprints, oil and other pollution on the board surface. Material sources and oxides existing on the silver-based surface, and then perform hot water washing and double water washing operations in sequence. When washing with hot water, the treatment temperature is 55-65°C, and the treatment time is 1-3 minutes. Double water washing means placing the product in a secondary water tank with continuous and uniform water flow for 2-3 minutes to wash off the residual acidic substances on the board surface. , the acid cleaner.

In a preferred scheme, the micro-etching process is as follows: placing the cleaned silver-based substrate in a mixed solution of oxide and micro-etching acid, and treating it at 20-30° C. for 2-3 minutes; the oxide The concentration of the microetching acid is 60 to 120g/L, and the concentration of the microetching acid is 15 to 40mL/L; the oxide is selected from any one of potassium permanganate and hydrogen peroxide, and the microetching acid is selected from nitric acid, Any one of chloric acid and methanesulfonic acid.

The present invention initiates electroless nickel-palladium-gold plating with a silver base as a substrate. The inventors have found that, in order to successfully obtain a uniform coating with excellent electrical and thermal conductivity in the electroless plating process, the pretreatment in the early stage is very important. In the hydrochloric acid system or sulfuric acid system in the technology, due to the chloride ion contained in the hydrochloric acid, the sulfate ion contained in the sulfuric acid all can precipitate or form insoluble matter on the silver-based surface, which will not only increase the subsequent electroless nickel-palladium-gold process. Difficulty, unevenness, and even the problem that it cannot be plated, and it will seriously affect its electrical and thermal properties. The present invention modifies the various pretreatment processes through a large number of experiments, in order to form a uniform and strong nickel-palladium-gold Coating provides foundation, as in the microetching pretreatment process of the present invention, adopts hydrogen peroxide to make oxygenant, with nitric acid, chloric acid, perchloric acid, the acidic environment that at least one in methanesulfonic acid provides effect, to The surface of the board is micro-etched to form a slight bite layer on the surface to obtain a fresh silver surface and provide better adhesion for subsequent plating.

The inventors found that the micro-etching treatment has a great influence on the subsequent nickel-palladium-gold plating. First, the combination of the above-mentioned specific oxidant and acid needs to be used, and secondly, the concentration of the oxidant and acid needs to be effectively controlled. Insufficient concentration of oxidant or too low concentration of acid will cause insufficient depth of micro-etched holes and poor size uniformity of micro-etched holes, which will increase the difficulty of subsequent electroless nickel plating layer, resulting in uneven nickel plating layer , Poor binding force. If the concentration of the oxidizing agent is too high or the concentration of the acid is too high, it will cause the problem that the depth of the micro-etched hole is too deep and the diameter of the micro-etched hole is too large, which will destroy the silver layer substrate of the circuit board, making the product reduce the excellent performance of the silver layer substrate, and Waste reagents, increase cost input, and cause losses.

As a further preference, the oxide and microetching acid are selected from any one of the following combinations: hydrogen peroxide and chloric acid; hydrogen peroxide and methanesulfonic acid, potassium permanganate and methanesulfonic acid.

In the above further preferred combination, after the microetching treatment, the surface of the silver layer is flat and smooth; the uniformity of the microetching aperture is good, and the surface roughness is small; the microetching liquid system is stable and the rate is controllable; after the microetching, nickel plating, nickel Layer bonding is strong.

In a preferred scheme, the pickling process is as follows: the silver-based substrate treated by microetching is placed in a pickling solution with a concentration of 80-120mL/L, and treated for 1-3 minutes; the pickling solution is selected from nitric acid solution , at least one of chloric acid solution, perchloric acid solution, and methanesulfonic acid solution.

Pickling process Pre-dipping pickling process, put the product into the pickling solution for pickling, remove the residual micro-etching agent, and then perform double washing operation, the treatment time is 2 to 3 minutes, remove the residual pre-etching agent on the board surface liquid medicine.

The preferred solution, the pre-soaking process is as follows: the pickled silver-based substrate is placed in a pre-soaking solution with a concentration of 6-12mL/L, and treated for 1-3 minutes; the pre-soaking solution is selected At least one of nitric acid solution, chloric acid solution, perchloric acid solution and methanesulfonic acid solution.

During the pre-dipping process, put the pickled silver-based substrate into the pre-dipping acid solution to provide an acidic environment for the activation of the silver layer, so that the surface of the circuit board is in an oxygen-free state, and ensure that the subsequent activation solution will not be damaged. Diluted by bringing in too much water.

In a preferred scheme, the palladium activation process is as follows: the silver-based substrate that has been pre-soaked with acid is placed in a palladium activation solution, and treated at 20-30°C for 2-3 minutes, and the palladium activation solution is composed of acid and corresponding acid radicals. The palladium salt of ion is composed of, and the acid is selected from any one of nitric acid, chloric acid, perchloric acid or methyl acid; the concentration of the acid is 60～100mL/L; the concentration of the palladium salt corresponding to the acid radical is 60～120mL/L.

After the palladium is activated, a layer of activated palladium is deposited on the surface of the silver layer to provide catalysis for the subsequent nickel plating. After palladium activation, the circuit board needs to be washed with double water for 2 to 3 minutes to remove the residual pre-medication solution on the board surface.

The preferred solution, the post pickling process is: place the silver-based substrate activated by palladium in a post pickling solution with a concentration of 15-40mL/L, and treat it for 1-3min. At least one of nitric acid solution, chloric acid solution, perchloric acid solution and methanesulfonic acid solution.

During the post pickling process, the cleaned product is put into the post pickling solution to remove the residual palladium activation compound on the circuit board surface. After pickling, the circuit board needs to be washed with double water for 2 to 3 minutes to remove the residual pre-chemical solution on the board surface.

The preferred scheme, the process of electroless nickel plating is as follows: the silver-based substrate treated with post pickling is placed in an electroless nickel plating solution for electroless nickel plating treatment, the pH of the electroless nickel plating solution is controlled to be 3.0 to 4.5, and the temperature is 85 ~ 90 ℃, the time of electroless nickel plating treatment is 25 ~ 40min.

As a further preference, the electroless nickel plating solution comprises the following components: nickel sulfonate 25-35g/L, sodium hypophosphite 20-40g/L, sodium citrate 10-15g/L, lactic acid 15-25g/L, Propionic acid 5-15g/L; Potassium iodate 35-50mg/L, PPS (propane sulfonate pyridinium salt) 5-10mg/L, DEP (N,N-diethylpropynylamine) 5-10mg/L .

The electroless nickel plating layer is the direct contact layer with the silver baseline plate. Through a large number of experiments, the inventor has optimized nickel sulfonate as the main nickel salt, sodium hypophosphite as the reducing agent, and sodium citrate, lactic acid, and propionic acid as the main salt. Complexing agent, accelerator and solution buffer, potassium iodate as stabilizer, PPS and DEP as surfactant, utilize the formula provided by the present invention to carry out nickel plating on the silver-based substrate, the gained electroless nickel layer is smooth; the pores Low rate, strong corrosion resistance of the coating; excellent stability of the plating solution; moderate plating speed; good bonding force; good brightness.

In the electroless nickel plating formula of the present invention, all medicaments are indispensable, mutual synergy just can obtain the best effect, for example propionic acid acts as accelerator in electroless nickel plating, simultaneously through synergy, can make up for the addition of lactic acid As a result of rough board surface, proper addition of propionic acid can improve the leveling effect of the board surface and obtain a smoother and smoother coating.

At the same time, the content of any chemical agent is also very important. If too much is added, it may cause the instability of the plating solution or the phenomenon of poisoning of the plating solution. For example, if the content of propionic acid is adjusted to 30g/L or more, it is obvious that the plating speed of the plating solution is accelerated, the stability of the plating solution is deteriorated, and the phosphorus content in the deposited nickel layer can be increased, reducing the high temperature resistance and corrosion resistance of the product. and other performance.

As a further preference, the electroless nickel plating solution comprises the following components: nickel sulfonate 30g/L, sodium hypophosphite 30g/L, lactic acid 20g/L, propionic acid 10g/L, sodium citrate 12g/L, iodic acid Potassium 45mg/L, PPS 8mg/L, DEP 8mg/L.

Through electroless nickel plating, a dense metal nickel layer with good adhesion is formed on the silver-based surface; then the residual nickel plating reagent is removed by double water washing.

The preferred scheme, the process of electroless palladium plating is: the silver-based substrate processed by electroless nickel plating is placed in the electroless palladium plating solution to carry out the electroless palladium plating treatment, the pH of the control electroless palladium plating solution is 4.5～6.5, and the temperature is 48 ~ 52 ° C, the time of electroless palladium plating treatment is 25 ~ 40 minutes.

In the present invention, after nickel plating is carried out, when carrying out the plating of other coatings again, its environment is basically identical with the environment after nickel plating of circuit boards such as prior art copper base, and the acid radical ion of other effects has no effect on the substrate silver layer. Obvious impact, so the conventional electroless palladium plating solution in the prior art can be applicable to the technical scheme of the present invention.

As a further preference, the electroless palladium plating solution comprises the following components: palladium nitrate 1.2-1.5g/L, sodium hypophosphite 8-12g/L, ethylenediamine 25-40g/L, triethanolamine 20g-30g/L, Citric acid 15-25g/L, ammonium citrate 6-12g/L, alkylthiourea 20-30mg/L, sodium thiosulfate 15-25mg/L.

The electroless palladium plating is carried out by the above-mentioned preferred electroless palladium plating solution, and the obtained palladium coating is bright and uniform; the binding force is strong; the corrosion resistance is good; the stability of the plating solution is good, and the MTO is greater than 6.

By electroless palladium plating, a metal palladium layer is formed on the surface of the nickel layer; then the residual palladium plating reagent is removed by double water washing. The processing time is 2-3 minutes.

In a preferred scheme, the chemical gold plating process is as follows: placing the silver-based substrate treated with chemical palladium plating in the chemical gold plating solution for chemical gold plating treatment, controlling the pH of the chemical gold plating solution to be 5.8 to 6.2, and the temperature to be 82 to 85°C , The time for electroless gold plating treatment is 8-12 minutes.

As a further preference, the electroless gold plating solution comprises the following components: 2.0-4.0 g/L potassium gold cyanide, and 100-120 mL/L potassium hydroxide.

Through electroless gold plating, a thin layer of gold is formed on the surface of the palladium layer, and the electroless nickel-palladium-gold plating process on the silver-based surface of the circuit board is completed.

In a preferred solution, the silver-based substrate treated with electroless gold plating is first placed in normal temperature water, and then placed in water at 55-65°C for 1-3 minutes to obtain a silver-based circuit board containing nickel-palladium-gold coating.

Immerse the product in a sink filled with clear water to fully recover the remaining gold-containing solution on the board surface, avoid wasting gold salt and reduce environmental pollution, and then wash it with hot water to completely remove the residual pre-medication solution on the board surface. A silver-based circuit board containing nickel-palladium-gold plating is obtained.

Beneficial effect

The present invention is the first to carry out electroless nickel-palladium plating on the silver-based substrate, and has formed the most suitable silver-based process from the pretreatment process to the chemical nickel-plating process. For the traditional copper-based electroless nickel-palladium-gold plating, the thickness of the nickel-palladium-gold electroless plating layer can be greatly reduced, thereby saving the content of metal used and avoiding the problem of environmental pollution. Furthermore, with the silver base as the base, the entire product has stronger electrical and thermal conductivity, higher sensitivity, longer life, and better overall performance.

Detailed ways

In order to make the object, advantage and technical solution of the present invention clearer, the present invention will be studied in more detail next. Combined with specific examples to illustrate.

The following specific examples are only preferred embodiments provided by the present invention.

Example 1

Cleaning: Put the silver-based substrate into a super water tank filled with ultra-pure water, immerse the silver-based substrate, apply slight vibration at room temperature, and treat for 10 minutes to remove dust and other impurities on the surface of the silver-based substrate. Then put the product into a mixed solution of 3% sodium dodecylsulfonate and 20g/L sodium hydroxide for ultrasonic vibration degreasing treatment; use 50g/L dodecyl ammonium chloride and 30mL/L The chloric acid mixture is ultrasonically oscillated for deoxidation treatment.

Micro-etching treatment: place the above-mentioned cleaned silver-based substrate in a mixed solution containing 30mL/L of chloric acid and 100g/L of hydrogen peroxide for micro-etching treatment. The treatment temperature is 25°C, and the time is 2min. After treatment, the surface of the silver layer is relatively flat and smooth; the micro-etching pore size is relatively uniform, and the surface roughness is small; the micro-etching rate is relatively large, the micro-etching system is relatively stable, and the rate is controllable.

Pickling: Place the microetched silver-based substrate in a nitric acid solution with a concentration of 100mL/L for 2 minutes.

Pre-dipping pickling: place the pickling treated product in a nitric acid solution with a concentration of 10mL/L for 2 minutes.

For palladium activation, place the pre-dipped silver-based substrate in a palladium activation solution containing 90mL/L nitric acid and 80mL/L palladium nitrate, and treat it at 25°C for 2min.

Post-acid dipping: place the silver-based substrate activated by palladium in a nitric acid solution with a concentration of 20mL/L, and treat it for 2min.

Electroless nickel plating: place the silver-based substrate treated with post pickling in the electroless nickel plating bath for electroless nickel plating, control the pH of the electroless nickel plating bath to be 3.0, the temperature is 85°C, and the time for electroless nickel plating treatment is 25min, the composition of electroless nickel plating solution is nickel sulfonate 30g/L, sodium hypophosphite 30g/L, lactic acid 20g/L, propionic acid 10g/L, sodium citrate 12g/L, potassium iodate 45mg/L, PPS8mg/ L. DEP 8mg/L. The electroless nickel plating layer is smooth; the porosity is low, the detected value is 0.11 pieces/cm ² , the coating has strong corrosion resistance; the stability of the plating solution is excellent; the plating speed is 34.5μm/h; the bonding force is good; the brightness is good.

Electroless palladium plating: place the substrate containing nickel plating in the electroless palladium plating solution for electroless palladium plating treatment, control the pH of the electroless palladium plating solution to 4.5 and the temperature at 48°C, the time of electroless palladium plating treatment is 25min, and the electroless palladium plating The formula of the solution is: palladium nitrate 1.2g/L, sodium hypophosphite 8g/L, ethylenediamine 25g/L, triethanolamine 20g/L, citric acid 15g/L, ammonium citrate 6g/L, alkylthiourea 20mg /L, sodium thiosulfate 15mg/L.

Electroless gold plating: place the substrate containing nickel and palladium plating in the chemical gold plating solution for chemical gold plating treatment, control the pH of the chemical gold plating solution to 5.8 and the temperature at 82°C, the time of chemical gold plating treatment is 10min, the formula of the chemical gold plating solution is : Potassium gold cyanide 3.0g/L, potassium hydroxide 100mL/L.

Put the product into a sink filled with clear water to fully recover the gold-containing solution remaining on the surface of the board, and then place the product in hot water at a temperature of 55°C for 1 minute to completely remove the residual liquid on the board and obtain silver Base - nickel palladium gold circuit.

Performance evaluation: the product obtained in Example 1 has strong weldability and good weldability; the bonding force is better, and the bonding strength is 2892gf measured by the heating stretching method; the corrosion resistance is strong; compared with the traditional copper-based PCB board (the thermal conductivity is 16.5W/mK), the thermal conductivity of the product is increased to 20.8W/mK, an increase of 26%, the thermal conductivity is high, and the heat dissipation is uniform. It can be well used in fields that require higher performances such as heat resistance and corrosion resistance of products.

Example 2

Cleaning: Put the silver-based substrate into a super water tank filled with ultra-pure water, immerse the silver-based substrate, apply slight vibration at room temperature, and treat for 10 minutes to remove dust and other impurities on the surface of the silver-based substrate. Then put the product into a mixed solution of sodium dodecylsulfonate with a mass fraction of 4% and 25g/L sodium hydroxide for ultrasonic vibration degreasing treatment; use 60g/L lauryl ammonium chloride and 30mL/L The methanesulfonic acid mixture is ultrasonically oscillated for deoxidation treatment.

Microetching treatment: place the above-mentioned cleaned silver-based substrate in a mixed solution containing 30mL/L of methanesulfonic acid and 100g/L of hydrogen peroxide for microetching treatment at a temperature of 25°C for 2 minutes. After micro-etching treatment, the surface of the silver layer is relatively flat and smooth; the micro-etching pore size is relatively uniform, and the surface roughness is small; the micro-etching rate is relatively large, the micro-etching system is relatively stable, and the rate is controllable.

Pickling: Place the microetched silver-based substrate in a methanesulfonic acid solution with a concentration of 100mL/L for 2 minutes.

Pre-dipping pickling: place the pickling treated product in a methanesulfonic acid solution with a concentration of 10mL/L, and treat it for 2 minutes.

For palladium activation, place the pre-dipped silver-based substrate in a palladium activation solution containing 90mL/L methanesulfonic acid and 80mL/L palladium methanesulfonate, and treat it at 25°C for 2min.

Post-acid dipping: place the silver-based substrate activated by palladium in a methanesulfonic acid solution with a concentration of 20mL/L, and treat it for 2min.

Electroless nickel plating: place the silver-based substrate treated with post pickling in an electroless nickel plating solution for electroless nickel plating, control the pH of the electroless nickel plating solution to be 4.0 and the temperature to be 85°C, and the time for the electroless nickel plating treatment to be 30min , The composition of electroless nickel plating solution is nickel sulfonate 30g/L, sodium hypophosphite 30g/L, lactic acid 10g/L, propionic acid 5g/L, sodium citrate 5g/L, potassium iodate 45mg/L, PPS8mg/L , DEP 8mg/L. After testing, the electroless nickel plating layer is relatively smooth; the porosity is low, and the detected value is 2.2 pieces/cm ² , the coating has strong corrosion resistance; the stability of the plating solution is good; the plating speed is 18.7μm/h; the binding force is good ; Good brightness.

Electroless palladium plating: place the substrate containing nickel plating in the electroless palladium plating solution for electroless palladium plating treatment, control the pH of the electroless palladium plating solution to 5.5 and the temperature at 50°C, the time of electroless palladium plating treatment is 30min, and the electroless palladium plating The formula of the solution is: palladium nitrate 1.5g/L, sodium hypophosphite 10g/L, ethylenediamine 30g/L, triethanolamine 25g/L, citric acid 20g/L, ammonium citrate 8g/L, alkylthiourea 25mg /L, sodium thiosulfate 20mg/L.

Electroless gold plating: place the substrate containing nickel and palladium plating in the chemical gold plating solution for chemical gold plating treatment, control the pH of the chemical gold plating solution to 6.0 and the temperature at 85°C, and the time for chemical gold plating treatment is 10 minutes. The formula of the chemical gold plating solution is : Potassium gold cyanide 3.0g/L, potassium hydroxide 100mL/L.

Put the product into a sink filled with clean water to fully recover the gold-containing solution remaining on the surface of the board, and then place the product in hot water at a temperature of 60°C for 2 minutes to completely remove the remaining liquid on the board and obtain silver Base - nickel palladium gold circuit.

Performance evaluation: The product obtained in Example 2 has strong weldability and good weldability; good bonding force, and the bonding strength measured by heating and stretching method is 2978gf; strong corrosion resistance; compared with traditional copper-based PCB board (thermal conductivity is 16.5W /mK), the thermal conductivity of the product is increased to 21.5W/mK, an increase of 30%, with high thermal conductivity and uniform heat dissipation. It can be well used in fields that require higher performances such as heat resistance and corrosion resistance of products.

Example 3

Cleaning: Put the silver-based substrate into a super water tank filled with ultra-pure water, immerse the silver-based substrate, apply slight vibration at room temperature, and treat for 10 minutes to remove dust and other impurities on the surface of the silver-based substrate. Then put the product into a mixed solution of sodium dodecylsulfonate and 30g/L sodium hydroxide with a mass fraction of 5% to carry out ultrasonic vibration degreasing treatment; make 80g/L lauryl ammonium chloride and 30mL/L The nitric acid mixture is ultrasonically oscillated for deoxidation treatment.

Microetching treatment: place the above-mentioned cleaned silver-based substrate in a mixed solution containing 30mL/L of methanesulfonic acid and 100g/L of potassium permanganate for microetching treatment at a temperature of 25°C for 2 minutes , after micro-etching treatment, the surface of the silver layer is flat and smooth; micro-etching pore size uniformity is good, surface roughness is small; micro-etching rate is 1.25 μm/min, which meets the requirements; micro-etching solution system is stable and the rate is controllable.

Pickling: Place the micro-etched silver-based substrate in a perchloric acid solution with a concentration of 100mL/L for 2 minutes.

Pre-dipping pickling: place the pickling treated product in a perchloric acid solution with a concentration of 10mL/L for 2 minutes.

For palladium activation, place the pre-dipping acid-treated silver-based substrate in a palladium activation solution containing 90mL/L perchloric acid and 80mL/L palladium perchlorate, and treat it at 25°C for 2min.

Post-acid dipping: Put the silver-based substrate activated by palladium in a perchloric acid solution with a concentration of 20mL/L, and treat it for 2min.

Electroless nickel plating: place the silver-based substrate treated with post pickling in the electroless nickel plating bath for electroless nickel plating, control the pH of the electroless nickel plating bath to be 3.0, the temperature is 85°C, and the time for electroless nickel plating treatment is 25min, the composition of electroless nickel plating solution is nickel sulfonate 30g/L, sodium hypophosphite 30g/L, lactic acid 20g/L, propionic acid 10g/L, sodium citrate 12g/L, potassium iodate 45mg/L, PPS8mg/ L. DEP 8mg/L. The electroless nickel plating layer is smooth; the porosity is low, the detected value is 0.11 pieces/cm ² , the coating has strong corrosion resistance; the stability of the plating solution is excellent; the plating speed is 34.5μm/h; the bonding force is good; the brightness is good.

Electroless palladium plating: place the substrate containing nickel plating in the electroless palladium plating solution for electroless palladium plating treatment, control the pH of the electroless palladium plating solution to 6.5 and the temperature at 52°C, the time of electroless palladium plating treatment is 40min, and the electroless palladium plating The formula of the liquid is: palladium nitrate 1.5g/L, sodium hypophosphite 12g/L, ethylenediamine 40g/L, triethanolamine 30g/L, citric acid 25g/L, ammonium citrate 12g/L, alkylthiourea 30mg /L, sodium thiosulfate 25mg/L.

Electroless gold plating: place the substrate containing nickel and palladium plating in the chemical gold plating solution for chemical gold plating treatment, control the pH of the chemical gold plating solution to 6.2 and the temperature at 85°C, and the time for chemical gold plating treatment is 10 minutes. The formula of the chemical gold plating solution is : Potassium gold cyanide 3.0g/L, potassium hydroxide 100mL/L.

Put the product into a sink filled with clear water to fully recover the gold-containing solution remaining on the surface of the board, and then place the product in hot water at a temperature of 65°C for 3 minutes to completely remove the residual liquid on the board and obtain silver Base - nickel palladium gold circuit.

Performance evaluation: The product obtained in Example 3 has strong weldability and good weldability; good bonding force, and the bonding strength measured by heating and stretching method is 2954gf; strong corrosion resistance; compared with traditional copper-based PCB board (thermal conductivity is 16.5W /mK), the thermal conductivity of the product is increased to 22.1W/mK, an increase of 34%, with high thermal conductivity and uniform heat dissipation. It can be well used in fields that require higher performances such as heat resistance and corrosion resistance of products.

Example 4

Other conditions are identical with embodiment 3, only microetching agent is the solution that contains methanesulfonic acid 10mL/L and potassium permanganate 60g/L, after microetching process, silver layer surface is flat, smooth; Good, but the hole depth is shallow and the surface roughness is small; the microetch rate is 0.50μm/min, and the rate is low.

In the above embodiments: before the circuit board is subjected to micro-etching treatment, hot water washing and double water washing operations need to be performed sequentially. When washing with hot water, the treatment temperature is 55-65°C, and the treatment time is 1-3 minutes. Double water washing means placing the product in a secondary water tank with continuous and uniform water flow for 2-3 minutes to wash off the residual acidic substances on the board surface. , the acid cleaner. Before the pre-dipping treatment of the circuit board, the circuit board needs to be washed with double water for 2 to 3 minutes to remove the residual pre-dipping solution on the board surface.

Before the post pickling treatment of the circuit board, the circuit board needs to be washed with double water for 2 to 3 minutes to remove the residual pre-chemical solution on the board surface.

Before the circuit board is treated with electroless nickel-palladium-gold plating, the circuit board needs to be washed with double water for 2 to 3 minutes to remove the residual pre-chemical solution on the board surface.

When the circuit board is treated with electroless nickel-palladium-gold process, two double washings are required, which are respectively after electroless nickel plating, to remove the remaining chemical nickel plating solution on the board surface, and after electroless palladium plating, to remove the residual chemical plating solution on the board surface. Palladium plating solution. The processing time is 2 to 3 minutes.

Comparative example 1

Other conditions are identical with embodiment 1, and only microetching agent is the solution that contains nitric acid 30mL/L and sodium persulfate 100g/L; After the result microetching process, white precipitation appears on the surface immediately; First, the roughness is large, and some micro-etch holes are still covered by precipitation; the micro-etch rate is high, but the micro-etch system is unstable and the rate is uncontrollable.

Comparative example 2

Other conditions are identical with embodiment 2, and only microetching agent is the solution of chloric acid 30mL/L and ferric chloride 100g/L, after the result microetching process, silver layer surface is smoother, smoother; Microetching aperture is comparatively uniform, The surface roughness is small; the micro-etch rate is small, the micro-etch system is unstable, and the rate is uncontrollable.

Comparative example 3

Other conditions are identical with embodiment 3, only microetching agent is the solution that contains perchloric acid 30mL/L and sodium ferrate 100g/L, after microetching treatment, silver layer surface is smoother, smoother; Microetching pore size is comparatively uniform, The surface roughness is small; the micro-etching rate is high, the micro-etching system is unstable, and the rate is uncontrollable; after treatment, it is not dried and placed in the air, and the micro-etched surface will appear discoloration and oxidation within 30s.

Comparative example 5

Other conditions are identical with embodiment 1, only nickel-plating liquid is different with, can't obtain the nickel-plating effect on silver-based substrate in the embodiment, concrete nickel-plating liquid composition and performance result are as shown in table 1:

Table 1 Nickel plating solution and performance results

The above descriptions are only ideal examples of the present invention, and are not intended to limit the present invention. The technical scope of the present invention is not limited to the contents of this specification, and any modification, modification or improvement made within the technical thought and principle of the present invention shall be protected by the present invention.

Claims (10)

1. a silver-based circuit board of electroless nickel-palladium-gold plating, it is characterized in that: described silver-based circuit board comprises silver-based substrate, and the surface of described silver-based substrate is plated with nickel layer, palladium layer sequentially from inside to outside , gold layer. 2. prepare the method for the silver-based circuit board of a kind of electroless nickel-palladium-gold plating as claimed in claim 1, it is characterized in that, comprise the steps: the silver-based substrate after the cleaning treatment is carried out micro-etching, pickling, Pre-dipping, palladium activation, post-dipping pretreatment, and then sequentially performing electroless nickel plating, electroless palladium plating, and electroless gold plating on the pretreated silver-based substrate to obtain a silver-based circuit board containing nickel-palladium-gold coating. 3. the preparation method of the silver-based circuit board of a kind of electroless nickel-palladium-gold plating according to claim 2, it is characterized in that: described cleaning treatment process is, the silver-based substrate is first cleaned with ultrapure water for 10～15min, Then carry out degreasing treatment, deoxidation treatment; described deoiling treatment uses the mixed solution of the sodium dodecylsulfonate of mass fraction 3%～5% and 20～30g/L sodium hydroxide, described deoxidation The mixture of at least one of 30mL/L methanesulfonic acid, chloric acid, perchloric acid and nitric acid and 50-80g/L dodecyl ammonium chloride was used for the treatment of the substance. 4. the preparation method of the silver-based circuit board of a kind of electroless nickel-palladium-gold plating according to claim 2, is characterized in that: described micro-etching process is, the silver-based substrate after cleaning is placed in by oxidation In the mixed solution of the compound and microetching acid, treat at 20～30°C for 2～3 minutes; the concentration of the oxide is 60～120g/L, and the concentration of the microetching acid is 15～40mL/L; the concentration of the oxide Any one selected from potassium permanganate and hydrogen peroxide, the microetching acid selected from any one of nitric acid, chloric acid, and methanesulfonic acid. 5. the preparation method of the silver-based circuit board of a kind of electroless nickel-palladium-gold plating according to claim 2, is characterized in that: described pickling process is: the silver-based substrate that will be processed through microetching, is placed in concentration 80-120mL/L pickling solution, treatment for 1-3min; said pickling solution is selected from at least one of nitric acid solution, chloric acid solution, perchloric acid solution, and methanesulfonic acid solution; The pre-soaking process is as follows: the pickled silver-based substrate is placed in a pre-soaking solution with a concentration of 6-12mL/L, and treated for 1-3 minutes; the pre-soaking solution is selected from nitric acid solution, At least one of chloric acid solution, perchloric acid solution, and methanesulfonic acid solution. 6. the preparation method of the silver-based circuit board of a kind of electroless nickel-palladium-gold plating according to claim 2, is characterized in that: described palladium activation process is: the silver-based substrate processed through pre-soaking acid is placed in palladium In the activation solution, treat at 20-30°C for 2-3 minutes. The palladium activation solution is composed of an acid and a palladium salt corresponding to the acid radical ion, and the acid is selected from nitric acid, chloric acid, perchloric acid or methyl acid. Any one; the concentration of the acid is 60-100mL/L; the concentration of the palladium salt corresponding to the acid radical is 60-120mL/L. The post pickling process is as follows: place the silver-based substrate activated by palladium in a post pickling solution with a concentration of 15-40mL/L, and treat it for 1-3 minutes. The post pickling solution is selected from nitric acid solution, At least one of chloric acid solution, perchloric acid solution, and methanesulfonic acid solution. 7. the preparation method of the silver-based circuit board of a kind of electroless nickel-palladium-gold according to claim 2, is characterized in that: described electroless nickel-plating process is: the silver-based substrate that will be processed after acid dipping is placed in The electroless nickel plating treatment is carried out in the electroless nickel plating solution, the pH of the electroless nickel plating solution is controlled to be 3.0 to 4.5, the temperature is 85 to 90°C, and the time of the electroless nickel plating treatment is 25 to 40 minutes. The electroless nickel plating solution contains the following components: nickel sulfonate 25-35g/L, sodium hypophosphite 20-40g/L, sodium citrate 10-15g/L, lactic acid 15-25g/L, propionic acid 5-15g /L; Potassium iodate 35-50mg/L, PPS 5-10mg/L, DEP 5-10mg/L. 8. the preparation method of the silver-based circuit board of a kind of electroless nickel-palladium-gold according to claim 2, is characterized in that: described electroless palladium plating process is: the silver-based substrate processed through electroless nickel plating is placed in The electroless palladium plating treatment is carried out in the electroless palladium plating solution, the pH of the electroless palladium plating solution is controlled to be 4.5-6.5, the temperature is 48-52° C., and the time for the electroless palladium plating treatment is 25-40 minutes. 9. The preparation method of a silver-based circuit board with electroless nickel-palladium-gold plating according to claim 8, characterized in that: said electroless palladium plating solution comprises the following components: palladium nitrate 1.2～1.5g/L, hypophosphorous acid Sodium 8-12g/L, ethylenediamine 25-40g/L, triethanolamine 20g-30g/L, citric acid 15-25g/L, ammonium citrate 6-12g/L, alkylthiourea 20-30mg/L , Sodium thiosulfate 15-25mg/L. 10. the preparation method of the silver-based circuit board of a kind of electroless nickel-palladium-gold according to claim 2, is characterized in that, described chemical gold-plating process is: the silver-based substrate that is processed through electroless palladium plating is placed in chemical Carry out chemical gold plating treatment in the gold plating solution, control the pH of the chemical gold plating solution to be 5.8～6.2, the temperature is 82～85 ℃, the time of chemical gold plating treatment is 8～12min; The chemical gold plating solution contains the following components: 2.0～4.0g /L potassium gold cyanide, 100~120mL/L potassium hydroxide.