CN110724943A - Palladium-free activating solution before chemical nickel plating on copper surface, preparation method and nickel plating method - Google Patents
Palladium-free activating solution before chemical nickel plating on copper surface, preparation method and nickel plating method Download PDFInfo
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- CN110724943A CN110724943A CN201911199185.2A CN201911199185A CN110724943A CN 110724943 A CN110724943 A CN 110724943A CN 201911199185 A CN201911199185 A CN 201911199185A CN 110724943 A CN110724943 A CN 110724943A
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
- C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
- C23C18/18—Pretreatment of the material to be coated
- C23C18/1803—Pretreatment of the material to be coated of metallic material surfaces or of a non-specific material surfaces
- C23C18/1824—Pretreatment of the material to be coated of metallic material surfaces or of a non-specific material surfaces by chemical pretreatment
- C23C18/1837—Multistep pretreatment
- C23C18/1844—Multistep pretreatment with use of organic or inorganic compounds other than metals, first
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
- C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
- C23C18/31—Coating with metals
- C23C18/32—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron
- C23C18/34—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron using reducing agents
- C23C18/36—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron using reducing agents using hypophosphites
Abstract
The invention provides a palladium-free activating solution before chemical nickel plating on the surface of copper, a preparation method and a nickel plating method, wherein the palladium-free activating solution comprises the following components: nickel salt, reducing agent, complexing agent, stabilizing agent and pH regulator; the invention relates to a method for pre-plating a nickel plating layer with catalytic activity on the copper surface of a printed circuit board by using a non-palladium activation plating solution, which enables the subsequent chemical nickel plating link to continue, and the chemical nickel plating layer obtained by non-palladium activation has better corrosion resistance than the chemical nickel plating layer obtained by palladium activation.
Description
Technical Field
The invention relates to a process for activating a copper surface before chemical nickel plating, in particular to a palladium-free activating solution before chemical nickel plating on a Printed Circuit Board (PCB), a preparation method and a nickel plating method.
Background
A Printed Circuit Board (PCB) is a functional substrate for connecting components by forming a pre-designed Circuit on the surface of an insulating substrate using electronic printing. The surface finishing technology of the printed circuit board is to perform a final surface treatment process on the surface of the circuit in order to ensure the weldability, corrosion resistance, oxidation resistance and the like of the printed circuit board in the subsequent assembly and use. The electroless nickel/displacement gold (ENIG) process is widely used as one of the surface finishing techniques for its good electrical conductivity and compatibility with high density packaging. In the chemical nickel plating process, sodium hypophosphite is mostly used as a reducing agent, a nickel phosphorus layer is continuously deposited on the surface with catalytic activity, the copper-based surface of the printed circuit board does not have self-catalytic activity, and metal with catalytic activity is deposited on the surface of the copper-based surface of the printed circuit board to initiate chemical nickel plating. The prunin and the like immerse a PCB copper circuit into a nickel activation solution prepared from sulfur-containing organic matters, nickel sulfate, organic acid and the like, and a compound containing C-S groups is added into the nickel immersion solution, so that the replacement reaction of metal nickel can be realized on the surfaces of copper and copper alloy, and a catalytic layer is obtained. Wangjianhua et al uses active metal to contact with copper in plating solution to form primary cell, electrons flow to matrix, and nickel ions are reduced to deposit on the surface of copper and copper alloy. Zhangchaoyang et al have demonstrated the electrochemical properties of copper and copper alloys in the induction process of electroless Ni-P alloys by using two methods, cathodic current induction and induction of active metals contacting the substrate in the bath. The electrochemical activation method is to utilize the electrochemical action of a couple to immerse a metal or alloy with catalytic activity in a solution and contact with a matrix metal, or immerse the metal or alloy in the solution simultaneously with the matrix metal and connect with a lead to transfer electrons. The electrode potential of the base metal is negatively shifted, so that the nickel ions adsorbed on the surface of the base metal are reduced and deposited on the surface of the base. Linjianghui etc. firstly uses hydrogen atom produced by decomposition of formaldehyde to adsorb on the surface of copper, then uses the catalytic action of hydrogen atom to make chemical nickel-plating, but formaldehyde is toxic and hydrogen atom can only be existed in air for a very short time. Yaojun et al use diamine borane compound dimethylamino borane (DMAB) as the reducing agent of chemical pre-nickel plating, form a layer of thin nickel on the surface of red copper as the activation substrate of the subsequent chemical nickel plating to carry out nickel autocatalytic deposition, realize the replacement nickel plating on the surface of copper and get the nickel layer with autocatalysis, but carry on the chemical nickel plating with this method, dimethylamino borane decomposes fast under the high temperature alkaline, therefore need to add DMAB constantly to keep the reaction going on, increase the cost of production indirectly. Therefore, the development of a low-cost and high-stability electroless nickel plating activation solution has become a focus of research in the field. Chinese patent CN 107868947 discloses a palladium-free activation method, which uses single or multiple boron-containing substances as reducing agents to achieve the effect of pre-plating active nickel on copper, but as can be seen from the SEM picture in the attached drawings, the electroless nickel plating layer obtained by the palladium-free activation pre-plating method has very uneven surface and many cracks and small black holes are likely to cause the phenomenon of "black nickel".
Therefore, the research of the palladium-free activated nickel plating method which has high stability, low cost, smooth chemical nickel plating and simple process and is suitable for large-scale production becomes the key point of the research in the field.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, it is an object of the present invention to provide a palladium-free activated electroless nickel plating process on copper surfaces using sodium hypophosphite (NaH)2PO2·H2O) and dimethylamino borane (DMAB) double reducing agents enable nickel to be rapidly deposited on the copper surface, simultaneously, the solution is kept stable, the problems of high cost and pollution caused by waste liquid discharge in the prior art that noble metal palladium is adopted as an activation raw material are solved, and a layer of compact and continuous chemical nickel plating layer with high catalytic activity and good corrosion resistance is successfully plated on the copper surface.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a palladium-free activating solution used before chemical nickel plating on a copper surface comprises: nickel salt, reducing agent, complexing agent, stabilizing agent and pH regulator;
the nickel salt is one or more of nickel sulfate, nickel chloride, nickel hypophosphite and nickel nitrate; the concentration of the nickel salt is 25-35 g/L;
the reducing agent is a double reducing agent comprising sodium hypophosphite NaH2PO2And dimethylaminoborane DMAB, in which NaH2PO2The concentration is 1-5 g/L; the concentration of the dimethyl amino borane in the activating solution is 2-4 g/L;
the complexing agent is one or more of lactic acid, citric acid, sodium salt of citric acid and ammonium chloride, and the concentration is 10-30 g/L;
the stabilizer is one or more of thiourea, pyrimidine and 2-aminobenzothiazole, and the concentration is 0.01 g/L;
the pH value of the palladium-free activating solution is 8.5-9.5.
Preferably, the pH regulator is one or more of ammonia water, sodium hydroxide and sulfuric acid;
preferably, the pyrimidine is 4, 6-dimethyl-2-mercaptopyrimidine DLMP.
Preferably, the formula and the concentration of the palladium-free activating solution are as follows: 30g/L of nickel sulfate, 25g/L of sodium citrate, 4g/L of sodium hypophosphite, 2g/L of dimethylamino borane, 20g/L of ammonium chloride and 0.01g/L of stabilizer, and the pH value is adjusted to 9-9.2.
Preferably, the formula and the concentration of the palladium-free activating solution are as follows: 30g/L of nickel sulfate, 25g/L of sodium citrate, 8g/L of sodium hypophosphite, 2g/L of dimethylamino borane, 15g/L of ammonium chloride and 0.01g/L of stabilizer, and the pH value is adjusted to 9-9.2.
Preferably, the formula and the concentration of the palladium-free activating solution are as follows: 30g/l of nickel sulfate, 25g/l of sodium citrate, 12g/l of sodium hypophosphite, 2g/l of dimethylaminoborane, 10g/l of ammonium chloride and 0.1mg/l of stabilizer, and the PH is adjusted to 9-9.2.
In order to achieve the above object, the present invention further provides a method for preparing the palladium-free activating solution before electroless nickel plating on the surface of copper, comprising the following steps: dissolving nickel salt in water to obtain a solution A; dissolving sodium hypophosphite and dimethylamino borane in water to obtain a solution B; dissolving a complexing agent and a stabilizing agent in water to obtain a solution C; mixing the solution A and the solution C to obtain a solution E; and mixing the solution B and the solution E to obtain the activation solution.
Preferably, the temperature of the activation treatment is 50-70 ℃; the activation treatment time is 3-5 min.
In order to achieve the above object, the present invention also provides a method for palladium-free activation chemical nickel plating on a copper surface, comprising the steps of: the method comprises the steps of removing oil on the copper surface of the printed circuit board, degreasing, acid washing, micro-etching, palladium-free activation and electroless nickel plating, wherein the palladium-free activation step adopts the palladium-free activation solution before the chemical nickel plating on the copper surface as claimed in any one of claims 1 to 5.
Preferably, the method for palladium-free activation electroless nickel plating on the copper surface comprises the following steps:
(1) oil removal: soaking the printed circuit board by adopting an acidic degreasing liquid, wherein the acidic degreasing liquid is prepared by mixing sulfuric acid, an OP emulsifier and deionized water, wherein the volume percentage concentration of the sulfuric acid is 3-10%, and the volume percentage concentration of the OP emulsifier is 3-10%; the conditions of degreasing and deoiling treatment are as follows: the operation temperature is 40-60 ℃, and the oil removing time is 3-5 min;
(2) acid washing: after the treatment of the step (1), carrying out acid washing on the copper-clad plate, wherein the acid washing temperature is normal temperature, the time is 60 seconds, and the copper-clad plate is washed by deionized water to obtain a pretreated copper-clad plate, and the acid washing solution is sulfuric acid with the mass percentage of 5%;
(3) micro-etching: after the treatment of the step (2), soaking the copper-clad plate by adopting a microetching solution, wherein the microetching solution has two formulas: the first one is prepared by mixing sodium persulfate, sulfuric acid and deionized water, wherein the content of the sodium persulfate is 10-80 g/L, and the content of the sulfuric acid is 20-100 g/L; the second one is prepared by mixing hydrogen peroxide, ammonia water and deionized water, wherein the volume ratio of the deionized water to the ammonia water to the hydrogen peroxide is 1:1 (0.1-0.2); the conditions of the microetching treatment are as follows: the operation temperature is 25-30 ℃, and the micro-etching time is 1-5 min;
(4) no palladium activation: after the treatment of the step (3), carrying out palladium-free activation treatment on the copper-clad plate by using a palladium-free activation solution, wherein the activation temperature is 50-70 ℃, the activation time is 3-5 min, and washing with deionized water to obtain the palladium-free activated copper-clad plate;
(5) the formula of the chemical nickel plating solution adopted in the chemical nickel plating step is as follows: the method comprises the following steps: nickel salt, reducing agent, complexing agent, accelerator, buffering agent, stabilizing agent and pH regulator; the nickel salt is NiSO4The concentration is 20-30 g/L; the reducing agent is NaH2PO2The concentration is 20-30 g/L; the complexing agent is lactic acid, and the concentration of the complexing agent is 20-30 g/L; the accelerator is propionic acid, and the concentration of the accelerator is 3-5 g/L; the buffering agent is sodium acetate, and the concentration of the buffering agent is 10-15 g/L; the stabilizer is thiourea, potassium iodide and pyridine substances, and the concentration is 0.01 g/L; the pH regulator is more than one of ammonia water, sodium hydroxide and sulfuric acid; the pH value of the chemical nickel plating solution is 5-5.5. This makes it possible to obtain a uniform and fine amorphous nickel-phosphorus alloy.
The non-palladium activation formula can only react on the metal copper surface of the printed circuit board, so that the probability of the plating leakage and the plating overflow of the printed circuit board with the double-sided window under the activation of the non-palladium activation solution is greatly reduced.
The invention has the beneficial effects that:
(1) the invention uses the method of pre-plating a nickel plating layer with catalytic activity on the copper surface of the printed circuit board by using the non-palladium activation plating solution, so that the subsequent chemical nickel plating link can be continued, and the chemical nickel plating layer obtained by non-palladium activation has better corrosion resistance than the chemical nickel plating layer obtained by palladium activation.
(2) The non-palladium activating solution involved in the method contains two reducing agents of boron and phosphorus and a certain amount of stabilizing agent, so that the stability of the solution can be ensured while the high reduction rate is ensured.
(3) The printed circuit board with double-sided windows is treated by the method, and the probability of plating leakage of the printed circuit board treated by non-palladium activation is found to be greatly reduced.
(4) The method is simple, low in cost and easy to operate.
Drawings
FIG. 1 is a process flow diagram of palladium-free activated electroless nickel plating provided in an embodiment of the present invention;
FIGS. 2 (1) - (4) are scanning electron microscope photographs of the surface of the electroless nickel-plated nickel layer after palladium activation of the printed circuit board of comparative example 1 and non-palladium activation of examples 5-7, respectively, according to the present invention;
FIG. 3 is a Tafel plot of the electroless nickel coatings obtained in examples 5-7 of the present invention and the electroless nickel coating obtained in comparative example 1. In the figure, legends 1-3 are curves for examples 5-7, respectively, and legend 4 is a curve for comparative example 1.
FIG. 4 is a graph showing the cathodic hydrogen evolution of the electroless nickel plated layer obtained in example 7 of the present invention and the electroless nickel plated layer obtained in comparative example 1.
Fig. 5 is a diagram of a printed circuit board with double-sided windows processed by chemical nickel plating after being acted by an activating solution in example 7 of the present invention, wherein (a) is an optical diagram of the surface of the printed circuit board with chemical nickel plating after palladium activation, which shows an obvious phenomenon of over plating, and (b) is an optical diagram of the surface of the printed circuit board processed by non-palladium activation in the present invention, which does not show the phenomenon of over plating and under plating.
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Example 1
A palladium-free activating solution used before chemical nickel plating on a copper surface comprises: nickel salt, reducing agent, complexing agent, stabilizing agent and pH regulator;
the nickel salt is one or more of nickel sulfate, nickel chloride, nickel hypophosphite and nickel nitrate; the concentration of the nickel salt is 25-35 g/L;
the reducing agent is a double reducing agent comprising sodium hypophosphite NaH2PO2And dimethylaminoborane DMAB, in which NaH2PO2The concentration is 1-5 g/L; the concentration of the dimethyl amino borane in the activating solution is 2-4 g/L;
the complexing agent is one or more of lactic acid, citric acid, sodium salt of citric acid and ammonium chloride, and the concentration is 10-30 g/L;
the stabilizer is one or more of thiourea, pyrimidine and 2-aminobenzothiazole, and the concentration is 0.01 g/L;
the pH value of the palladium-free activating solution is 8.5-9.5.
The pH regulator is more than one of ammonia water, sodium hydroxide and sulfuric acid;
the pyrimidine is preferably 4, 6-dimethyl-2-mercaptopyrimidine DLMP.
The embodiment also provides a preparation method of the palladium-free activating solution before electroless nickel plating on the surface of copper, which comprises the following steps: dissolving nickel salt in water to obtain a solution A; dissolving sodium hypophosphite and dimethylamino borane in water to obtain a solution B; dissolving a complexing agent and a stabilizing agent in water to obtain a solution C; mixing the solution A and the solution C to obtain a solution E; and mixing the solution B and the solution E to obtain the activation solution.
The temperature of the activation treatment is 50-70 ℃; the activation treatment time is 3-5 min.
Example 2
This example differs from example 1 in that: the formula and the concentration of the palladium-free activating solution are as follows: 30g/L of nickel sulfate, 25g/L of sodium citrate, 4g/L of sodium hypophosphite, 2g/L of dimethylamino borane, 20g/L of ammonium chloride and 0.01g/L of stabilizer, and the pH value is adjusted to 9-9.2.
Example 3
This example differs from example 1 in that: the formula and the concentration of the palladium-free activating solution are as follows: 30g/L of nickel sulfate, 25g/L of sodium citrate, 8g/L of sodium hypophosphite, 2g/L of dimethylamino borane, 15g/L of ammonium chloride and 0.01g/L of stabilizer, and the pH value is adjusted to 9-9.2.
Example 4
A method for palladium-free activation chemical nickel plating on a copper surface comprises the following steps: the method comprises the steps of removing oil on the copper surface of the printed circuit board, degreasing, acid washing, micro-etching, palladium-free activation and chemical nickel plating, wherein the palladium-free activation step adopts any one of the palladium-free activation solutions before chemical nickel plating on the copper surface in the embodiment 1 to 3.
Example 5
A method for palladium-free activation chemical nickel plating on a copper surface comprises the following steps:
(1) oil removal: soaking the printed circuit board by adopting an acidic degreasing liquid, wherein the acidic degreasing liquid is prepared by mixing sulfuric acid, an OP emulsifier and deionized water, wherein the volume percentage concentration of the sulfuric acid is 3-10%, and the volume percentage concentration of the OP emulsifier is 3-10%; the conditions of degreasing and deoiling treatment are as follows: the operation temperature is 40-60 ℃, and the oil removing time is 3-5 min;
(2) acid washing: after the treatment of the step (1), carrying out acid washing on the copper-clad plate, wherein the acid washing temperature is normal temperature, the time is 60 seconds, and the copper-clad plate is washed by deionized water to obtain a pretreated copper-clad plate, and the acid washing solution is sulfuric acid with the mass percentage of 5%;
(3) micro-etching: after the treatment of the step (2), soaking the copper-clad plate by adopting a microetching solution, wherein the microetching solution has two formulas: the first one is prepared by mixing sodium persulfate, sulfuric acid and deionized water, wherein the content of the sodium persulfate is 10-80 g/L, and the content of the sulfuric acid is 20-100 g/L; the second one is prepared by mixing hydrogen peroxide, ammonia water and deionized water, wherein the volume ratio of the deionized water to the ammonia water to the hydrogen peroxide is 1:1 (0.1-0.2); the conditions of the microetching treatment are as follows: the operation temperature is 25-30 ℃, and the micro-etching time is 1-5 min;
(4) no palladium activation: after the treatment of the step (3), carrying out palladium-free activation treatment on the copper-clad plate by using a palladium-free activation solution, wherein the activation temperature is 60 ℃, the activation time is 4min, and washing with deionized water to obtain the palladium-free activated copper-clad plate;
the palladium-free activating solution used before electroless nickel plating on the surface of copper adopted in the embodiment comprises: nickel salt, reducing agent, complexing agent, stabilizing agent and pH regulator; the nickel salt is nickel sulfate, and the reducing agent is a dual reducing agent comprising sodium hypophosphite NaH2PO2And dimethylamino borane DMAB, the complexing agent is sodium citrate and ammonium chloride, the stabilizer is one or more of thiourea, pyrimidine and 2-aminobenzothiazole, and the pyrimidine is preferably 4, 6-dimethyl-2-mercaptopyrimidine DLMP.
The formula and the concentration of the palladium-free activating solution are as follows: 30g/L of nickel sulfate, 25g/L of sodium citrate, 4g/L of sodium hypophosphite, 2g/L of dimethylamino borane, 20g/L of ammonium chloride and 0.01g/L of stabilizer, and the pH value is adjusted to 9-9.2.
(5) The formula of the chemical nickel plating solution adopted in the chemical nickel plating step is as follows:
the method comprises the following steps: nickel salt, reducing agent, complexing agent, accelerator, buffering agent, stabilizing agent and pH regulator; the nickel salt is NiSO4The concentration is 20-30 g/L; the reducing agent is NaH2PO2The concentration is 20-30 g/L; the complexing agent is lactic acid, and the concentration of the complexing agent is 20-30 g/L; the accelerator is propionic acid, and the concentration of the accelerator is 3-5 g/L; the buffering agent is sodium acetate, and the concentration of the buffering agent is 10-15 g/L; the stabilizer is thiourea, potassium iodide and pyridine substances, and the concentration is 0.01 g/L; the pH regulator is more than one of ammonia water, sodium hydroxide and sulfuric acid; the pH value of the chemical nickel plating solution is 5-5.5.
The scanning electron microscope observation is carried out on the nickel coating on the surface of the printed circuit board of the embodiment of the invention, the test result is shown in fig. 2- (2), and as can be seen from fig. 2- (2), the arrangement of nickel particles on the surface of the circuit board is more uniform and compact. The electrochemical test was performed using an electrochemical workstation model CHI600E, manufactured by shanghai huachen corporation, and the tafel curve of the nickel-plated layer obtained in this example was tested, and the test results are shown in the curve indicated by legend 1 in fig. 3.
Example 6
This example provides a palladium-free activated electroless nickel plating method on copper surface, and the difference between this example and example 5 is: the formula and the concentration of the palladium-free activating solution are as follows: 30g/L of nickel sulfate, 25g/L of sodium citrate, 8g/L of sodium hypophosphite, 2g/L of dimethylaminoborane, 15g/L of ammonium chloride and 0.01g/L of stabilizer, wherein the pH value is adjusted to 9-9.2, the activation temperature is 55 ℃, and the deposition time is 4 min.
The scanning electron microscope observation of the nickel plating layer on the surface of the printed circuit board of this example shows the test result as shown in fig. 2- (3), and it can be seen from fig. 2- (3) that the electroless nickel plating layer obtained in example 6 has a tighter surface arrangement than the electroless nickel plating layer obtained by palladium activation. The electrochemical test was conducted using an electrochemical workstation model CHI600E, manufactured by shanghai huachen corporation, and the tafel curve of the nickel-plated layer obtained in example 1 of the present invention was tested, and the test results are shown in the curve indicated by legend 2 in fig. 3, and it can be seen from the corrosion current values that the electroless nickel-plated layer obtained by the palladium-free activation formulation has more excellent corrosion resistance.
Example 7
This example provides a palladium-free activated electroless nickel plating method on copper surface, and the difference between this example and example 5 is: the formula and the concentration of the palladium-free activating solution are as follows: 30g/l of nickel sulfate, 25g/l of sodium citrate, 12g/l of sodium hypophosphite, 2g/l of dimethylaminoborane, 10g/l of ammonium chloride and 0.1mg/l of stabilizer, wherein the PH is adjusted to 9-9.2, the activation temperature is 65 ℃, and the activation time is 4 min.
The scanning electron microscope observation of the nickel plating layer on the surface of the printed circuit board of this example shows the test results as shown in fig. 2- (4), and it can be seen from fig. 2- (4) that the electroless nickel plating layer obtained in example 7 has a tighter surface arrangement than the electroless nickel plating layer obtained by palladium activation. The electrochemical test was conducted using an electrochemical workstation model CHI600E, manufactured by shanghai huachen corporation, and the tafel curve of the nickel-plated layer obtained in example 7 of the present invention was tested, and the test results are shown in the curve indicated by legend 3 in fig. 3. The cathodic hydrogen evolution curve of the nickel-plated layer obtained in example 7 of the present invention was measured, and as shown in the non-palladium activation curve of fig. 4, the curve was used to characterize the catalytic activity of the plating layer. The activation solution of the embodiment 7 of the invention acts on the printed circuit board with double-sided windows and then carries out chemical nickel plating, and the phenomenon of plating leakage does not occur, as shown in figure 5.
Comparative example 1
(1) Oil removal: and (3) deoiling the copper-clad plate at the deoiling temperature of 55 ℃ for 5 minutes. The deoiling liquid is an acidic deoiling liquid and contains sulfuric acid with the volume percentage concentration of 5%, OP emulsifier with the volume percentage concentration of 3% -10% and deionized water.
(2) Acid washing: and (2) after the treatment of the step (1), carrying out acid washing on the copper-clad plate at normal temperature for 60 seconds, and washing with deionized water to obtain the pretreated copper-clad plate. The pickling solution is sulfuric acid with the mass percentage of 5%.
(3) Micro-etching: and (3) after the treatment of the step (2), carrying out acid microetching on the copper-clad plate, wherein the microetching temperature is 25 ℃, the microetching time is 1min, and washing with deionized water to obtain the microetched copper-clad plate. The microetching solution is a mixed solution of 50g/L sulfuric acid solution and 50g/L sodium persulfate.
(4) Activating palladium: and (4) after the treatment of the step (3), carrying out palladium activation treatment on the copper-clad plate, wherein the activation temperature is 40-50 ℃, the activation time is 4min, and washing with deionized water to obtain the palladium-activated copper-clad plate. The palladium activating solution is an activating solution which comprises the following components: 0.1g/L of palladium chloride and 5mL/L of 36.5 percent concentrated hydrochloric acid.
(5) Chemical nickel plating: after the treatment of the step (4), carrying out chemical nickel plating on the copper-clad plate, wherein the chemical nickel-phosphorus plating solution comprises the following steps: NiSO4：20g/L，NaH2PO2：25g/L，C3H6O3：24g/L，CH3CH2COOH：4g/L，CH3COONa：10g/L，CH4N2S: 0.01g/L, pH 5.5 and temperature 85 ℃.
Scanning electron microscope observation is carried out on the nickel coating on the surface of the printed circuit of the comparative example 1, the test result is shown in figure 2- (1), and as can be seen from figure 2- (1), the nickel particles on the surface of the circuit board are distributed uniformly and compactly. The nickel-plated layer obtained in comparative example 1 of the present invention was tested for the Tafel curve by performing an electrochemical test using an electrochemical workstation model CHI600E manufactured by Shanghai Huachen corporation, and the test results are shown in the curve indicated by legend 4 in FIG. 3. The nickel-plated layer obtained in comparative example 1 of the present invention was tested for the cathodic hydrogen evolution curve, and the palladium activation corresponding curve in fig. 4 was used to characterize the catalytic activity of the palladium activated plating.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (10)
1. A palladium-free activating solution used before chemical nickel plating on a copper surface is characterized by comprising: nickel salt, reducing agent, complexing agent, stabilizing agent and pH regulator;
the nickel salt is one or more of nickel sulfate, nickel chloride, nickel hypophosphite and nickel nitrate; the concentration of the nickel salt is 25-35 g/L;
the reducing agent is a double reducing agent comprising sodium hypophosphite NaH2PO2And dimethylaminoborane DMAB, in which NaH2PO2The concentration is 1-5 g/L; the concentration of the dimethyl amino borane in the activating solution is 2-4 g/L;
the complexing agent is one or more of lactic acid, citric acid, sodium salt of citric acid and ammonium chloride, and the concentration is 10-30 g/L;
the stabilizer is one or more of thiourea, pyrimidine and 2-aminobenzothiazole, and the concentration is 0.01 g/L;
the pH value of the palladium-free activating solution is 8.5-9.5.
2. The palladium-free activating solution before electroless nickel plating on the surface of copper according to claim 1, characterized in that: the pH regulator is more than one of ammonia water, sodium hydroxide and sulfuric acid.
3. The palladium-free activating solution before electroless nickel plating on the surface of copper according to claim 1, characterized in that: the pyrimidine is preferably 4, 6-dimethyl-2-mercaptopyrimidine DLMP.
4. The palladium-free activating solution before electroless nickel plating on the surface of copper according to claim 1, characterized in that: the formula and the concentration of the palladium-free activating solution are as follows: 30g/L of nickel sulfate, 25g/L of sodium citrate, 4g/L of sodium hypophosphite, 2g/L of dimethylamino borane, 20g/L of ammonium chloride and 0.01g/L of stabilizer, and the pH value is adjusted to 9-9.2.
5. The palladium-free activating solution before electroless nickel plating on the surface of copper according to claim 1, characterized in that: the formula and the concentration of the palladium-free activating solution are as follows: 30g/L of nickel sulfate, 25g/L of sodium citrate, 8g/L of sodium hypophosphite, 2g/L of dimethylamino borane, 15g/L of ammonium chloride and 0.01g/L of stabilizer, and the pH value is adjusted to 9-9.2.
6. The palladium-free activating solution before electroless nickel plating on the surface of copper according to claim 1, characterized in that: the formula and the concentration of the palladium-free activating solution are as follows: 30g/l of nickel sulfate, 25g/l of sodium citrate, 12g/l of sodium hypophosphite, 2g/l of dimethylaminoborane, 10g/l of ammonium chloride and 0.1mg/l of stabilizer, and the PH is adjusted to 9-9.2.
7. The method for preparing palladium-free activating solution before electroless nickel plating on the surface of copper according to any one of claims 1 to 6, characterized by comprising the steps of: dissolving nickel salt in water to obtain a solution A; dissolving sodium hypophosphite and dimethylamino borane in water to obtain a solution B; dissolving a complexing agent and a stabilizing agent in water to obtain a solution C; mixing the solution A and the solution C to obtain a solution E; and mixing the solution B and the solution E to obtain the activation solution.
8. The method for preparing the palladium-free activating solution before electroless nickel plating on the surface of copper according to claim 7, wherein the method comprises the following steps: the temperature of the activation treatment is 50-70 ℃; the activation treatment time is 3-5 min.
9. A method for palladium-free activation chemical nickel plating on a copper surface is characterized by comprising the following steps: the method comprises the steps of removing oil on the copper surface of the printed circuit board, degreasing, acid washing, micro-etching, palladium-free activation and electroless nickel plating, wherein the palladium-free activation step adopts the palladium-free activation solution before the chemical nickel plating on the copper surface as claimed in any one of claims 1 to 5.
10. The palladium-free activated electroless nickel plating process on copper surfaces as claimed in claim 9, characterized by comprising the steps of:
(1) oil removal: soaking the printed circuit board by adopting an acidic degreasing liquid, wherein the acidic degreasing liquid is prepared by mixing sulfuric acid, an OP emulsifier and deionized water, wherein the volume percentage concentration of the sulfuric acid is 3-10%, and the volume percentage concentration of the OP emulsifier is 3-10%; the conditions of degreasing and deoiling treatment are as follows: the operation temperature is 40-60 ℃, and the oil removing time is 3-5 min;
(2) acid washing: after the treatment of the step (1), carrying out acid washing on the copper-clad plate, wherein the acid washing temperature is normal temperature, the time is 60 seconds, and the copper-clad plate is washed by deionized water to obtain a pretreated copper-clad plate, and the acid washing solution is sulfuric acid with the mass percentage of 5%;
(3) micro-etching: after the treatment of the step (2), soaking the copper-clad plate by adopting a microetching solution, wherein the microetching solution has two formulas: the first one is prepared by mixing sodium persulfate, sulfuric acid and deionized water, wherein the content of the sodium persulfate is 10-80 g/L, and the content of the sulfuric acid is 20-100 g/L; the second one is prepared by mixing hydrogen peroxide, ammonia water and deionized water, wherein the volume ratio of the deionized water to the ammonia water to the hydrogen peroxide is 1:1 (0.1-0.2); the conditions of the microetching treatment are as follows: the operation temperature is 25-30 ℃, and the micro-etching time is 1-5 min;
(4) no palladium activation: after the treatment of the step (3), carrying out palladium-free activation treatment on the copper-clad plate by using a palladium-free activation solution, wherein the activation temperature is 50-70 ℃, the activation time is 3-5 min, and washing with deionized water to obtain the palladium-free activated copper-clad plate;
(5) the formula of the chemical nickel plating solution adopted in the chemical nickel plating step is as follows:
the method comprises the following steps: nickel salt, reducing agent, complexing agent, accelerator, buffering agent, stabilizing agent and pH regulator; the nickel salt is NiSO4The concentration is 20-30 g/L; the reducing agent is NaH2PO2The concentration is 20-30 g/L; the complexing agent is lactic acid, and the concentration of the complexing agent is 20-30 g/L; the accelerator is propionic acid, and the concentration of the accelerator is 3-5 g/L; the buffering agent is sodium acetate, and the concentration of the buffering agent is 10-15 g/L; the stabilizer is thiourea, potassium iodide and pyridine substances, and the concentration is 0.01 g/L; the pH regulator is more than one of ammonia water, sodium hydroxide and sulfuric acid; the pH value of the chemical nickel plating solution is 5-5.5.
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