CN112301334B - Chemical palladium plating solution, application thereof and chemical palladium plating method - Google Patents
Chemical palladium plating solution, application thereof and chemical palladium plating method Download PDFInfo
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- CN112301334B CN112301334B CN202011187103.5A CN202011187103A CN112301334B CN 112301334 B CN112301334 B CN 112301334B CN 202011187103 A CN202011187103 A CN 202011187103A CN 112301334 B CN112301334 B CN 112301334B
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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
- C23C18/42—Coating with noble metals
- C23C18/44—Coating with noble metals using reducing agents
Abstract
The invention belongs to the technical field of circuit board surface treatment, and particularly relates to a chemical palladium plating solution, application thereof and a chemical palladium plating method. The invention provides a chemical palladium plating solution, which takes water as a solvent and comprises the following solutes in mass concentration: 1-10 g/L tetraammine palladium sulfate, 1-20 g/L sodium hypophosphite, 10-30 g/L composite complexing agent and 10-30 g/L composite stabilizer; the composite complexing agent comprises ethylenediamine, 2-amino n-butyl alcohol and isobutanolamine, and the composite stabilizer comprises methacrylic acid, crotonic acid and polyethyleneimine. The chemical palladium plating solution provided by the invention has stronger activity, and a palladium plating layer with excellent performance can be obtained without activating a dragging cylinder. The results of the examples show that the electroless palladium plating solution provided by the invention has good stability and longer service life; the palladium plating layer obtained by using the chemical palladium plating solution to carry out chemical palladium plating has good corrosion resistance and bonding performance.
Description
Technical Field
The invention belongs to the technical field of circuit board surface treatment, and particularly relates to a chemical palladium plating solution, application thereof and a chemical palladium plating method.
Background
A Printed Circuit Board (PCB) is a substrate for assembling electronic parts, and is a printed Board on which inter-dot connections and printed elements are formed on a general-purpose substrate in a predetermined design. In order to ensure the weldability and other properties of the circuit board in later assembly and use, the surface of the circuit board needs to be treated.
The currently common surface technology is a chemical nickel-plating and gold-dipping process, i.e. a nickel layer is deposited on the copper surface of the circuit board, and then a gold layer is plated on the nickel layer through a displacement reaction. Although the chemical nickel plating and gold dipping process has smooth plating layer and good welding performance, the nickel layer is easily attacked by the gold plating solution in the gold plating process to form local corrosion, namely a 'black disc' phenomenon. The corrosion area is covered by the gold plating layer and is difficult to be perceived from the appearance, the strength of a welding point is reduced after welding, and the welding point is easy to be brittle and cracked under the impact of external force, so that the part fails. Research shows that the palladium layer added between the nickel layer and the gold layer can play a role of a barrier layer, prevent diffusion and migration between nickel and gold layers in the subsequent heat treatment process, effectively avoid excessive corrosion of displacement gold plating on nickel, and prevent the black disc phenomenon.
Therefore, the heat tide of the chemical palladium plating solution is researched. Electroless palladium plating solutions such as disclosed in patent CN 103290399 a include tetraamminepalladium dichloride, sodium nitrite (complexing agent), sodium hypophosphite (reducing agent), indium trichloride, and thiosemicarbazide (stabilizer); although the formula can ensure the stability in the plating process and inhibit the decomposition of the plating solution, the stabilizer contains indium ions which are toxic and are not friendly to the environment. For another example, patent CN 102449192B discloses an electroless palladium plating solution comprising a palladium-containing compound, an amine compound, a sulfide compound, and a reducing agent; the plating solution formula contains sulfide, and sulfur is eutectoid in the palladium layer in the plating process, so that the corrosion resistance of the palladium layer is reduced. Patents CN 103857826B, CN 101228293B and CN 103774127B both disclose formulations of electroless palladium plating solutions, which do not contain indium ions and sulfides, but these electroless palladium plating solutions require a large-area cylinder pulling plate to perform cylinder pulling operation on the plating solution before plating to activate the activity of the plating solution. This results in a waste of precious metal palladium, which greatly increases the cost of the process.
How to prepare an environment-friendly high-activity chemical palladium plating solution is a technical problem which needs to be solved urgently.
Disclosure of Invention
In view of the above, the invention provides a chemical palladium plating solution, which does not contain toxic ions such as lead ions and indium ions, has good environmental protection property, high activity and stability, and can obtain a palladium plating layer with excellent performance without cylinder dragging activation.
The invention provides a chemical palladium plating solution, which takes water as a solvent and comprises the following solutes in mass concentration: 1-10 g/L tetraammine palladium sulfate, 1-20 g/L sodium hypophosphite, 10-30 g/L composite complexing agent and 10-30 g/L composite stabilizer;
the composite complexing agent comprises ethylenediamine, 2-amino-n-butanol and isobutanolamine;
the composite stabilizer comprises methacrylic acid, crotonic acid and polyethyleneimine.
Preferably, the mass ratio of the ethylenediamine to the 2-amino-n-butanol to the isobutanolamine is (1-3) to (2-4) to (3-5).
Preferably, the mass ratio of the methacrylic acid to the crotonic acid to the polyethyleneimine is 1 (0.5-2) to 0.0001-0.001.
Preferably, the number average molecular weight of the polyethyleneimine is 3000-3500.
Preferably, the pH value of the chemical palladium plating solution is 6-8.
Preferably, the pH regulator for regulating the pH value of the electroless palladium plating solution comprises a sulfuric acid solution and/or a sodium hydroxide solution.
The invention also provides the application of the chemical palladium plating solution in the technical scheme in chemical palladium plating.
The invention also provides a method for chemically plating palladium, which comprises the following steps:
performing chemical palladium plating on the surface of the substrate to obtain a palladium plating layer;
the chemical palladium plating solution for chemical palladium plating is the chemical palladium plating solution in the technical scheme;
the temperature of the chemical palladium plating is 40-60 ℃.
Preferably, the time for the chemical palladium plating is 8-12 min.
Preferably, the thickness of the palladium plating layer is 0.1-1 μm.
The invention provides a chemical palladium plating solution, which takes water as a solvent and comprises solutes with the following mass concentration, 1-10 g/L tetraamminepalladium sulfate, 1-20 g/L sodium hypophosphite, 10-30 g/L composite complexing agent and 10-30 g/L composite stabilizer; the composite complexing agent comprises ethylenediamine, 2-amino n-butyl alcohol and isobutanolamine, and the composite stabilizer comprises methacrylic acid, crotonic acid and polyethyleneimine. The chemical palladium plating solution provided by the invention does not contain indium ions and sulfides, and has better environmental protection property. The method takes ethylenediamine, 2-amino-n-butanol and isobutanolamine as a composite complexing agent, so that the chemical palladium plating solution has stronger complexing ability, the stability of the chemical palladium plating solution is improved, and the activity of the chemical palladium plating solution is not reduced; methacrylic acid, crotonic acid and polyethyleneimine are taken as composite stabilizers, so that the stability of the chemical palladium plating solution is effectively improved; the chemical palladium plating solution has better stability and higher activity under the combined action of the components with the specific content, and a palladium plating layer with excellent performance can be obtained without cylinder dragging activation. The results of the examples show that the electroless palladium plating solution provided by the invention has good stability and longer service life; the palladium plating layer obtained by directly carrying out chemical palladium plating by using the chemical palladium plating solution provided by the invention has good corrosion resistance and bonding performance, and the palladium plating layer with good performance can be obtained without carrying out cylinder dragging activity by using the chemical palladium plating solution provided by the invention to carry out chemical palladium plating.
The invention also provides a chemical palladium plating method, wherein the chemical palladium plating adopts the chemical palladium plating solution of the technical scheme to carry out chemical palladium plating directly at 40-60 ℃ to obtain a palladium plating layer. When the chemical palladium plating solution provided by the invention is used for chemical palladium plating, the chemical palladium plating solution does not need to be subjected to cylinder dragging activation treatment, and can be directly subjected to chemical palladium plating. The results of the examples show that the palladium plating layer obtained by the invention has good micro-morphology, corrosion resistance and bonding performance.
Drawings
FIG. 1 is a scanning electron microscope image of a cross section of a plating layer prepared in examples 1 to 5 and comparative examples 1 to 2, wherein a1 is a scanning electron microscope image of a cross section of a plating layer prepared in example 1; b1 is a scanning electron microscope image of the cross section of the plating layer prepared in example 2; c1 is a scanning electron microscope image of the cross section of the plating prepared in example 3; d1 is a scanning electron micrograph of a cross section of the plating prepared in example 4; e1 is a scanning electron micrograph of a cross section of the plating prepared in example 5; f1 is a scanning electron microscope image of the cross section of the plating layer prepared in comparative example 1; g1 is a scanning electron microscope image of the cross section of the plating layer prepared in comparative example 2;
FIG. 2 is a scanning electron microscope image of the surface of the plating layer with the gold-plating removed prepared in examples 1 to 5 and comparative examples 1 to 2, wherein a2 is the scanning electron microscope image of the surface of the plating layer with the gold-plating removed prepared in example 1; b2 is a scanning electron microscope image of the surface of the plating layer prepared in example 2 after the gold plating layer is removed; c2 is a scanning electron microscope image of the surface of the plating layer prepared in example 3 after the gold plating layer is removed; d2 is a scanning electron microscope image of the surface of the plating layer prepared in example 4 after the gold plating layer is removed; e2 is a scanning electron microscope image of the surface of the plating layer prepared in example 5 after gold plating is removed; f2 is a scanning electron microscope image of the surface of the plating layer prepared in the comparative example 1 after the gold plating layer is removed; g2 is a scanning electron microscope image of the surface of the plated layer prepared in comparative example 2 from which the gold plating layer was removed.
Detailed Description
The invention provides a chemical palladium plating solution, which takes water as a solvent and comprises the following solutes in mass concentration: 1-10 g/L tetraammine palladium sulfate, 1-20 g/L sodium hypophosphite, 10-30 g/L composite complexing agent and 10-30 g/L composite stabilizer;
the composite complexing agent comprises ethylenediamine, 2-amino-n-butanol and isobutanolamine;
the composite stabilizer comprises methacrylic acid, crotonic acid and polyethyleneimine.
In the present invention, all the raw materials are commercially available products well known to those skilled in the art unless otherwise specified.
The chemical palladium plating solution provided by the invention takes water as a solvent, and the water is preferably deionized water.
The chemical palladium plating solution provided by the invention comprises 1-10 g/L tetraamminepalladium sulfate by mass concentration, and preferably 3-5 g/L. In the invention, the mass concentration of the tetraamminepalladium sulfate is less than 1g/L, which can reduce the deposition rate in the chemical palladium plating and influence the performance of a palladium plating layer; when the mass concentration of the tetraamminepalladium sulfate is more than 10g/L, palladium ions ionized by the tetraamminepalladium sulfate in the chemical palladium plating solution are easy to reduce and separate out, the stability of the chemical palladium plating solution can be reduced, and the tetraamminepalladium sulfate is wasted.
The chemical palladium plating solution provided by the invention comprises 1-20 g/L of sodium hypophosphite, preferably 5-15 g/L, and more preferably 10-12 g/L by mass concentration. In the invention, the sodium hypophosphite can be used as a reducing agent to reduce palladium ions in the tetraamminepalladium sulfate. When the content of sodium hypophosphite is limited within the range, the concentration of hypophosphite in the chemical palladium plating solution is proper, the metal palladium deposition rate of palladium ions reduced by hypophosphite is moderate, and the stability of the chemical palladium plating solution is favorably improved.
The chemical palladium plating solution provided by the invention comprises 10-30 g/L of composite complexing agent by mass concentration, and preferably 20-25 g/L. In the invention, the composite complexing agent comprises ethylenediamine, 2-amino-n-butyl alcohol and isobutanolamine, and the mass ratio of the ethylenediamine to the 2-amino-n-butyl alcohol to the isobutanolamine is preferably (1-3) to (2-4) to (3-5), more preferably (1.5-2.5) to (3.5-3.75).
In the invention, the ethylenediamine has stronger complexing ability to palladium ions and can form a stable five-membered ring chelate with the palladium ions; the 2-amino n-butanol and the isobutanolamine can improve the compactness of the coating. According to the invention, the composite complexing agent enables the chemical palladium plating solution to have stronger complexing capability, and when the content of the composite complexing agent is limited within the range, a stable chelate can be formed with palladium ions in the chemical palladium plating solution, so that the electrochemical polarization degree of the chemical palladium plating solution is increased, a compact palladium plating layer is promoted to be obtained, and the corrosion resistance of the palladium plating layer is improved.
The chemical palladium plating solution provided by the invention comprises 10-30 g/L of composite stabilizer by mass concentration, preferably 20.001-20.005 g/L. In the invention, the composite stabilizer comprises methacrylic acid, crotonic acid and polyethyleneimine, and the molecular weight of the polyethyleneimine is preferably 3000-3500. In the present invention, the mass ratio of the methacrylic acid, the crotonic acid and the polyethyleneimine is preferably 1 (0.5-2) to 0.0001-0.001, and specifically 1:1:0.0001, 1:1.5:0.000375, and 1:1.5:0.000625 in the embodiments of the present invention.
In the invention, the composite stabilizer effectively improves the stability of the chemical palladium plating solution. In the invention, the polyethyleneimine has strong stabilizing effect, but the excessive consumption can cause poisoning of the plating solution; although the stabilizing effect of the methacrylic acid and the crotonic acid is relatively weak, the addition of a proper amount of the methacrylic acid and the crotonic acid can improve the stability of the plating solution and avoid the poisoning of the plating solution; the invention limits the proportion of each component in the composite stabilizer, can improve the stability of the chemical palladium plating solution, and is beneficial to the implementation of chemical palladium plating. In the invention, the poor stability of the composite stabilizer with the concentration lower than 10g/L of the chemical palladium plating solution is not beneficial to the implementation of the chemical palladium plating, and if the concentration of the composite stabilizer with the concentration higher than 30g/L of the chemical palladium plating solution is poor in activity, the palladium deposition rate is slow or even the palladium deposition cannot be carried out.
In the invention, the pH value of the chemical palladium plating solution is preferably 6-8, and more preferably 7. In the invention, the pH regulator for regulating the pH value of the chemical palladium plating solution comprises a sulfuric acid solution and/or a sodium hydroxide solution, wherein the concentration of the sulfuric acid solution is preferably 50-90%, and more preferably 60-70%; the concentration of the sodium hydroxide solution is preferably 4-8 g/L, and more preferably 5-6 g/L. The invention has no special requirement on the dosage of the sulfuric acid solution and/or the sodium hydroxide solution as long as the required pH value can be achieved.
The invention limits the content of each raw material component of the chemical palladium plating solution within the range, improves the stability of the chemical palladium plating solution, ensures that the chemical palladium plating solution has higher activity, and can obtain a palladium plating layer with excellent performance without dragging a cylinder to activate the activity of the chemical palladium plating solution.
According to the invention, the raw material components are mixed according to the proportion to obtain the chemical palladium plating solution. In the present invention, the mixing preferably comprises the steps of:
dissolving polyethyleneimine in first part of water to obtain a polyethyleneimine concentrated solution;
sequentially carrying out first mixing on tetraammine palladium sulfate, ethylenediamine, 2-amino n-butanol, isobutanolamine, methacrylic acid, crotonic acid, a polyethyleneimine concentrated solution, sodium hypophosphite and second part of water to obtain a primary mixed solution;
and carrying out second mixing on the primary mixed solution and the residual water to obtain the chemical palladium plating solution.
According to the invention, polyethyleneimine is dissolved in first part of water to obtain a polyethyleneimine concentrated solution. In the present invention, the concentration of the concentrated polyethyleneimine solution is preferably 50mg/L to 100mg/L, and more preferably 80mg/L to 100 mg/L. The present invention is not particularly limited as long as the dissolution can be completed. According to the method, the polyethyleneimine is dissolved in the first part of water, so that the content of the polyethyleneimine in the chemical palladium plating solution can be accurately controlled.
The method comprises the steps of sequentially mixing tetraammine palladium sulfate, ethylenediamine, 2-amino n-butanol, isobutanolamine, methacrylic acid, crotonic acid, a polyethyleneimine concentrated solution, sodium hypophosphite and second part of water for the first time to obtain a primary mixed solution. In the invention, the mass percentage content of the second part of water in the total water is preferably 30-50%, and more preferably 40-50%.
After the primary mixed solution is obtained, the primary mixed solution and the residual water are subjected to second mixing to obtain the chemical palladium plating solution. In the invention, the concentration of polyethyleneimine in the electroless palladium plating solution is preferably 1-10 mg/L, and more preferably 3-5 mg/L. In the present invention, the first mixing and the second mixing are preferably carried out independently under stirring, and the stirring is not particularly limited as long as the dissolution is complete. In the present invention, the stirring rotation speed in the first mixing and the second mixing is preferably the same.
The invention also provides the application of the chemical palladium plating solution in the technical scheme in chemical palladium plating. In the invention, the method is applied to preparing the chemical coating on the surface of the printed circuit board.
The invention also provides a method for chemically plating palladium, which comprises the following steps:
performing chemical palladium plating on the surface of the substrate to obtain a palladium plating layer;
the chemical palladium plating solution for chemical palladium plating is the chemical palladium plating solution in the technical scheme;
the temperature of the chemical palladium plating is 40-60 ℃.
In the present invention, the substrate preferably comprises a copper substrate printed wiring board plated with a nickel layer. In the invention, the temperature of the chemical palladium plating is 40-60 ℃, preferably 45-55 ℃, and most preferably 50 ℃; the time for the chemical palladium plating is preferably 8-12 min, and more preferably 10 min. In the invention, the thickness of the palladium plating layer prepared by the chemical palladium plating is preferably 0.1-1 μm. In the invention, the temperature of the chemical palladium plating is lower than 40 ℃, so that the deposition rate of the palladium plating solution is reduced, a loose palladium plating layer is obtained, the compactness of the palladium plating layer is reduced, and the nickel corrosion is easily generated during gold plating; the chemical palladium plating temperature higher than 60 ℃ can reduce the stability of the palladium plating solution and easily cause the decomposition of the palladium plating solution; the invention limits the chemical palladium plating temperature in the range, is beneficial to obtaining a compact palladium plating layer and improves the corrosion resistance of the palladium plating layer.
The chemical palladium plating solution provided by the invention can be used for chemical palladium plating without cylinder dragging activation treatment, and can be used for directly performing chemical palladium plating to obtain a palladium plating layer with excellent performance.
In the embodiment of the invention, in order to verify the feasibility of the scheme of performing chemical palladium plating by using the chemical palladium plating solution, palladium plating is specifically performed on a printed circuit board plated with a nickel layer; the specific process preferably comprises the following steps:
and sequentially carrying out chemical nickel plating, chemical palladium plating and chemical gold plating on the printed circuit board to obtain the chemical plating layer.
The invention preferably pre-treats the printed wiring board before electroless nickel plating, and the pre-treatment is preferably carried out according to the following steps: first acid washing → first water washing → micro etching → second water washing → second acid washing → third water washing → pre-soaking → activation → fourth water washing → post-soaking.
In the invention, the first pickling washing liquor is preferably a solution of an acidic cleaning agent, and the acidic cleaning agent is preferably an acidic cleaning agent purchased from Shenzhen Hongdahu technology Limited with model number HDQ-201; the volume concentration of the acidic cleaning agent in the acidic cleaning agent solution is preferably 90-110 ml/L, more preferably 100ml/L, the first acid washing is preferably soaking, and the time of the first acid washing is preferably 3-7 min, more preferably 5 min.
In the invention, the first water washing, the second water washing, the third water washing and the fourth water washing are preferably independent deionized water, the first water washing, the second water washing, the third water washing and the fourth water washing are preferably independent soaking washing, and the time is preferably independent for 30-60 s.
In the present invention, the microetching solution preferably includes a mixed solution of sodium persulfate and concentrated sulfuric acid, and the concentrated sulfuric acid is preferably concentrated sulfuric acid with a mass fraction of 98%. In the invention, the concentration of sodium persulfate in the mixed solution is preferably 98-102 g/L, more preferably 100g/L, and the volume concentration of concentrated sulfuric acid is preferably 18-22 mL/L, more preferably 20 mL/L; the microetching time is preferably 80-100 s, and more preferably 90 s.
In the invention, the second acid washing lotion is preferably an aqueous solution of concentrated sulfuric acid, and the concentrated sulfuric acid is preferably concentrated sulfuric acid with the mass fraction of 98%; the volume concentration of concentrated sulfuric acid in the concentrated sulfuric acid aqueous solution is preferably 18-22 mL/L, and more preferably 20 mL/L; the second acid washing is preferably bubble washing, and the time of the second acid washing is preferably 50-70 s, and more preferably 60 s.
In the invention, the solution for pre-soaking is preferably concentrated sulfuric acid water solution, and the concentrated sulfuric acid is preferably concentrated sulfuric acid with the mass fraction of 98%; the volume concentration of concentrated sulfuric acid in the concentrated sulfuric acid aqueous solution is preferably 18-22 mL/L, and more preferably 20 mL/L; the presoaking time is preferably 50-70 s, and more preferably 60 s.
In the invention, the activator for activation is preferably a palladium sulfate type catalyst activator, the model of the palladium sulfate type catalyst activator is preferably an activator purchased from Shenzhen Hongdahu technology Limited with model number HDQ-205P, the activation is preferably that the quoted circuit board after third washing is soaked in an activator solution, and the concentration of the activator in the activator solution is preferably 75-85 mL/L, and more preferably 80 mL/L; the activation time is preferably 2.5-3.5 min, and more preferably 3 min.
In the invention, the post-leaching solution is preferably a concentrated sulfuric acid solution, and the volume concentration of concentrated sulfuric acid in the concentrated sulfuric acid solution is preferably 18-22 mL/L, and more preferably 20 mL/L; the post-soaking time is preferably 50-70 s, and more preferably 60 s.
In the invention, the chemical nickel plating solution for chemical nickel plating preferably comprises a mixed nickel plating solution of HDQ-209M chemical nickel plating solution, HDQ-209A chemical nickel plating solution and HDQ-209D chemical nickel plating solution, and the volume concentration of the HDQ-209M chemical nickel plating solution in the mixed nickel plating solution is preferably 110-130 mL/L, and more preferably 120 mL/L; the volume concentration of the HDQ-209A chemical nickel plating solution in the mixed nickel plating solution is preferably 40-50 mL/L, and more preferably 45 mL/L; the volume concentration of the HDQ-209D chemical nickel plating solution in the mixed nickel plating solution is preferably 2-4 mL/L, and more preferably 3 mL/L. In the invention, the HDQ-209M chemical nickel plating solution, the HDQ-209A chemical nickel plating solution and the HDQ-209D chemical nickel plating solution are independently and preferably purchased from Shenzhen Hongdahu technology Limited. In the invention, the pH value of the mixed nickel plating solution is preferably 4.5-4.9, and more preferably 4.7. The temperature of the chemical nickel plating is preferably 80-90 ℃, more preferably 84-87 ℃, and the time is preferably 20-30 min, more preferably 25 min. In the invention, the thickness of the nickel plating layer prepared by the chemical nickel plating is preferably 3-5 μm.
In the invention, the chemical nickel plating further preferably comprises water washing, the water for water washing is preferably deionized water, the water washing is preferably soaking washing, and the soaking washing time is preferably 30-60 s, and more preferably 40-50 s.
In the invention, the electroless palladium plating solution for electroless palladium plating is the electroless palladium plating solution in the technical scheme, the pH value of the electroless palladium plating solution is preferably 6-8, and more preferably 7, and the method for adjusting the pH value of the electroless palladium plating solution is not particularly limited as long as the required range can be adjusted. In the invention, the temperature of the chemical palladium plating is preferably 40-60 ℃, more preferably 45-55 ℃, and most preferably 50 ℃; the time is preferably 8-12 min, and more preferably 10 min. In the invention, the thickness of the palladium plating layer prepared by the chemical palladium plating is preferably 0.1-1 μm.
In the invention, the electroless palladium plating further preferably comprises water washing, the water for water washing is preferably deionized water, the water washing is preferably bubble washing, and the bubble washing time is preferably 30-60 s, and more preferably 30-40 s.
In the present invention, the electroless gold plating solution for electroless gold plating is preferably HDQ-71 electroless gold plating solution and KAu (CN)2The volume concentration of the HDQ-71 chemical gold plating solution in the mixed solution is preferably 90-110 mL/L, and more preferably 100 mL/L; KAu (CN) in the mixed solution2The concentration of (b) is preferably 1.2 to 1.7g/L, more preferably 1.5 g/L. In the invention, the HDQ-71 chemical gold plating solution is preferably purchased from Shenzhen Hongdahu technology Limited.
In the invention, the pH value of the electroless gold plating solution is preferably 4.6-5, and more preferably 4.8; the temperature of the electroless gold plating is preferably 80-90 ℃, more preferably 84-87 ℃, and the time is preferably 15-25 min, more preferably 20 min. In the invention, the thickness of the gold plating layer prepared by electroless gold plating is preferably 0.1-1 μm.
In order to further illustrate the present invention, the following embodiments are described in detail, but they should not be construed as limiting the scope of the present invention.
Example 1
Dissolving polyethyleneimine in deionized water to obtain a polyethyleneimine concentrated solution with the concentration of 100 mg/L;
1g of tetraamminepalladium sulfate, 5g of ethylenediamine, 7.5g of 2-amino n-butanol, 7.5g of isobutanolamine, 10g of methacrylic acid, 10g of crotonic acid, 10mL of polyethyleneimine concentrated solution with the mass concentration of 100mg/L, 5g of sodium hypophosphite and 0.5L of deionized water are mixed, stirred and dissolved to obtain a primary mixed solution;
mixing, stirring and dissolving the primary mixed solution and 0.5L of deionized water to obtain chemical palladium plating solution; adjusting the pH value of the chemical palladium plating solution to 7;
the printed circuit board is pretreated according to the following steps: first acid washing (100mL/LHDQ-201 acidic cleaner solution, 5min) → first water washing (deionized water, bubble washing 30s) → microetching (sodium persulfate 100g/L, concentrated sulfuric acid 20mL/L, 90s) → second water washing (deionized water, bubble washing 30s) → second acid washing (20mL/L concentrated sulfuric acid solution, 60s) → third water washing (deionized water, bubble washing 30s) → pre-soaking (20mL/L concentrated sulfuric acid solution, 60s) → activation (80mL/L HDQ-205P activator solution, 3min) → fourth water washing (deionized water, 30s) → post-soaking (20mL/L concentrated sulfuric acid solution, 60 s);
carrying out chemical nickel plating on the surface of the pretreated printed circuit board to obtain a nickel plating layer with the thickness of about 3 mu m; the volume concentration of the HDQ-209M chemical nickel plating solution in the chemical nickel plating solution is 120mL/L, the volume concentration of the HDQ-209A chemical nickel plating solution is 45mL/L, and the volume concentration of the HDQ-209D chemical nickel plating solution is 3 mL/L; the pH value of the chemical nickel plating solution is 4.7, the temperature is 84 ℃, and the chemical nickel plating time is 25 min;
performing chemical palladium plating on the surface of the nickel plating layer to obtain a palladium plating layer with the thickness of 0.1 mu m; the temperature of the chemical palladium plating is 50 ℃, and the time is 10 min;
carrying out chemical gold plating on the surface of the palladium plating layer to obtain a gold plating layer with the thickness of 0.1 mu m; the volume concentration of the chemical gold plating solution HDQ-71 is 100mL/L, KAu (CN)2The concentration of (A) is 1.5g/L, the temperature of electroless gold plating is 84 ℃, and the time is 20 min.
Example 2
Dissolving polyethyleneimine in deionized water to obtain a polyethyleneimine concentrated solution with the concentration of 100 mg/L;
1g of tetraamminepalladium sulfate, 3g of ethylenediamine, 75g of 2-aminon-butanol, 10g of isobutanolamine, 8g of methacrylic acid, 12g of butenoic acid, 50mL of 100mg/L polyethyleneimine concentrated solution, 5g of sodium hypophosphite and 0.5L of deionized water are mixed, stirred and dissolved to obtain a primary mixed solution;
mixing, stirring and dissolving the primary mixed solution and 0.5L of deionized water to obtain chemical palladium plating solution; the pH value of the chemical palladium plating solution is adjusted to 7.
An electroless palladium plating solution was prepared according to the method of example 1, except that the electroless palladium plating solution prepared in example 2 was used.
Example 3
Dissolving polyethyleneimine in deionized water to obtain a polyethyleneimine concentrated solution with the concentration of 100 mg/L;
1g of tetraamminepalladium sulfate, 6g of ethylenediamine, 7g of 2-aminon-butanol, 7g of isobutanolamine, 8g of methacrylic acid, 12g of butenoic acid, 50mL of 100mg/L polyethyleneimine concentrated solution, 5g of sodium hypophosphite and 0.5L of deionized water are mixed, stirred and dissolved to obtain a primary mixed solution;
mixing, stirring and dissolving the primary mixed solution and 0.5L of deionized water to obtain chemical palladium plating solution; the pH value of the chemical palladium plating solution is adjusted to 7.
An electroless palladium plating solution was prepared according to the method of example 1, except that the electroless palladium plating solution prepared in example 3 was used.
Example 4
Dissolving polyethyleneimine in deionized water to obtain a polyethyleneimine concentrated solution with the concentration of 100 mg/L;
mixing, stirring and dissolving 2g of tetraamminepalladium sulfate, 5g of ethylenediamine, 7.5g of 2-aminon-butanol, 7.5g of isobutanolamine, 10g of methacrylic acid, 10g of crotonic acid, 10mL of 100mg/L concentrated polyethyleneimine solution, 5g of sodium hypophosphite and 0.5L of deionized water to obtain a primary mixed solution;
mixing, stirring and dissolving the primary mixed solution and 0.5L of deionized water to obtain chemical palladium plating solution; the pH value of the chemical palladium plating solution is adjusted to 7.
An electroless palladium plating solution was prepared according to the method of example 1, except that the electroless palladium plating solution prepared in example 4 was used.
Example 5
Dissolving polyethyleneimine in deionized water to obtain a polyethyleneimine concentrated solution with the concentration of 100 mg/L;
1g of tetraamminepalladium sulfate, 5g of ethylenediamine, 7.5g of 2-amino n-butanol, 7.5g of isobutanolamine, 10g of methacrylic acid, 10g of crotonic acid, 10mL of 100mg/L polyethyleneimine concentrated solution, 10g of sodium hypophosphite and 0.5L of deionized water are mixed, stirred and dissolved to obtain a primary mixed solution;
mixing, stirring and dissolving the primary mixed solution and 0.5L of deionized water to obtain chemical palladium plating solution; the pH value of the chemical palladium plating solution is adjusted to 7.
An electroless palladium plating solution was prepared according to the method of example 1, except that the electroless palladium plating solution prepared in example 5 was used.
Comparative example 1
1g of tetraamminepalladium sulfate, 10g of ethylenediamine, 20g of methacrylic acid, 5g of sodium hypophosphite and 0.5L of deionized water are mixed, stirred and dissolved to obtain a primary mixed solution;
mixing, stirring and dissolving the primary mixed solution and 0.5L of deionized water to obtain chemical palladium plating solution; the pH value of the chemical palladium plating solution is adjusted to 7.
An electroless palladium plating solution was prepared according to the method of example 1, except that the electroless palladium plating solution prepared in comparative example 1 was used.
Comparative example 2
An electroless plating layer was prepared as in example 3, except that the electroless palladium plating solution was subjected to cylinder pulling activation for 40min before electroless palladium plating.
Test example
The stability of the electroless palladium plating solution was tested as follows:
heating chemical palladium plating solution to 50 ℃, putting the solution into a cylinder dragging plate for plating for 1h (for low load of 0.4 dm)2L) was removed, the electroless palladium plating solution was maintained at 50 ℃, and the time during which the electroless palladium plating solution was precipitated was recorded, and the results are shown in table 1.
The service life of the electroless palladium plating solution is detected according to the following method:
continuously plating in chemical palladium plating solution, continuously supplementing palladium tetraammine sulfate and sodium hypophosphite in the plating process to ensure the concentration of the palladium tetraammine sulfate and the sodium hypophosphite, and limiting the loading amount to be 0.4dm2L, recording the working period of the chemical palladium plating solution; the working period (MTO) is the time for consuming the initial palladium content of the chemical palladium plating solution, for example, the concentration of tetraamminepalladium sulfate in the chemical palladium plating solution is 1g/L, and the time for consuming 1g of palladium sulfate by using 1L of the chemical palladium plating solution to carry out continuous chemical palladium plating is one working period. The results of the electroless palladium plating bath duty cycle are listed in table 1.
And (3) detecting the appearance of the plating layer:
and (4) visually observing the surface of the plating layer, if the surface is flat and smooth, the color is consistent and glossy, and the plating leakage and the diffusion are avoided, evaluating that the plating is good, and otherwise, evaluating that the plating is bad.
And (3) detecting the microscopic morphology of the plating layer:
detecting the microscopic morphology of the cross section of the plating layer by using a Scanning Electron Microscope (SEM) of Hitachi SU1510 to obtain a scanning electron microscope image, as shown in FIG. 1, wherein a1 is the scanning electron microscope image of the cross section of the plating layer prepared in example 1; b1 is a scanning electron microscope image of the cross section of the plating layer prepared in example 2; c1 is a scanning electron microscope image of the cross section of the plating prepared in example 3; d1 is a scanning electron micrograph of a cross section of the plating prepared in example 4; e1 is a scanning electron micrograph of a cross section of the plating prepared in example 5; f1 is a scanning electron microscope image of the cross section of the plating layer prepared in comparative example 1; g1 is a scanning electron micrograph of a cross section of the coating prepared in comparative example 2. In the figure, Ni represents a nickel plating layer, a printed wiring board copper layer is arranged below the nickel plating layer, and a palladium plating layer is arranged above the nickel plating layer. The microstructure was evaluated as "good" if it was completely dense and free from corrosion, and "bad" if the microstructure had defects, crystal grain malformations, nickel corrosion, and the like, and the results are shown in table 1.
The rectangular marked part in f1 in FIG. 1 is the part which is subjected to strong corrosion of nickel layer by electroless palladium plating, and as can be seen from f1 in FIG. 1, strong corrosion of nickel layer by electroless palladium plating carried out by the electroless palladium plating solution of comparative example 1 is generated; as can be seen from a1, b1, c1, d1 and e1 in FIG. 1, the nickel layer was not corroded by the electroless palladium plating solution prepared in examples 1 to 5, and a complete and dense plating layer was obtained. Comparing c1 and g1, the performance of the plating layer obtained by directly plating palladium by using the chemical palladium plating solution provided by the invention is consistent with the performance of the plating layer obtained by plating palladium after cylinder pulling activation, and the chemical palladium plating solution provided by the invention is proved to have higher activity and can obtain a plating layer with excellent performance without cylinder pulling activation.
Observing the micro-morphology of the surface after the gold plating is removed by using a Scanning Electron Microscope (SEM) of Hitachi SU1510 (because a nickel corrosion area generated during gold plating is possibly covered by a subsequent gold plating and cannot be observed from the surface micro-morphology, the micro-morphology of the surface after the gold plating is removed needs to be observed). in the invention, the method for removing the gold plating is preferably to put a sample into a gold stripping solution to be soaked for 1-3 min to obtain a scanning electron microscope image, as shown in FIG. 2, wherein a2 is the scanning electron microscope image of the surface after the gold plating is removed, which is prepared in example 1; b2 is a scanning electron microscope image of the surface of the plating layer prepared in the strong example 2 after the gold plating layer is removed; c2 is a scanning electron microscope image of the surface of the plating layer prepared in example 3 after the gold plating layer is removed; d2 is a scanning electron microscope image of the surface of the plating layer prepared in example 4 after the gold plating layer is removed; f2 is a scanning electron microscope image of the surface of the plating layer prepared in example 5 after the gold plating layer is removed; f2 is a scanning electron microscope image of the surface of the plating layer prepared in the comparative example 1 after the gold plating layer is removed; g2 is a scanning electron microscope image of the surface of the plated layer prepared in comparative example 2 from which the gold plating layer was removed.
The microstructure was evaluated as "good" if it was completely dense and free from corrosion, and "bad" if the microstructure had defects, crystal grain malformations, nickel corrosion, and the like, and the results are shown in table 1.
It is understood from f2 in fig. 2 that the palladium plating layer obtained by palladium plating using the electroless palladium plating solution prepared in comparative example 1 is corroded during gold plating, and it is understood from a2, b2, c2, d2 and e2 in fig. 2 that the palladium plating layer obtained by palladium plating using the electroless palladium plating solution prepared in examples 1 to 5 of the present invention can effectively prevent corrosion of the palladium plating layer during gold plating. Comparing c2 and g2, the performance of the palladium plating layer obtained by directly plating palladium by using the chemical palladium plating solution provided by the invention is consistent with the performance of the palladium plating layer obtained by plating palladium after cylinder pulling activation, and the chemical palladium plating solution provided by the invention is proved to have higher activity and can obtain a plating layer with excellent performance without cylinder pulling activation.
And (3) bonding performance test:
the method comprises the steps of cleaning the surface of a nickel-palladium-gold plating layer, bonding a gold wire by adopting an ASM-EG60 full-automatic welding machine, performing tension test on a circuit board which is bonded by adopting a DAGE4000 push-pull tester, recording the maximum tension when the circuit board is broken, judging a failure mode, evaluating the bonding performance of the plating layer, wherein the bonding temperature is 170 ℃, the diameter of the gold wire is 0.6mil, the wire pulling speed is 20mil/s, and the wire pulling stroke is 40 mil. If the tensile force is more than or equal to 1.5g when the gold wire is broken, the gold wire neck part, the wire and the welding spot shoulder part are broken in the breaking mode, the gold wire is evaluated to be qualified, and the other cases are evaluated to be unqualified. The results are shown in Table 1.
TABLE 1 Properties of electroless Palladium plating solutions and coatings prepared in examples 1 to 5 and Performance parameters of electroless Palladium plating solutions and coatings prepared in comparative examples 1 to 2
The chemical palladium plating solution of the comparative example 1 is used for chemical palladium plating to obtain the appearance of a plating layer, the micro morphology is unqualified, the corrosion condition is serious after gold plating, the qualified requirement cannot be met, and the production requirement cannot be met, so the binding performance of the plating layer obtained by chemical palladium plating of the chemical palladium plating solution of the comparative example 1 is not detected.
The results in table 1 show that the chemical palladium plating solution provided by the invention has strong stability and stable deposition rate, and meanwhile, the chemical palladium plating solution provided by the invention has strong activity, a cylinder dragging before plating is not needed, and the performance of the obtained plating layer is as excellent as that of the plating layer obtained by cylinder dragging treatment.
Although the present invention has been described in detail with reference to the above embodiments, it is only a part of the embodiments of the present invention, not all of the embodiments, and other embodiments can be obtained without inventive step according to the embodiments, and the embodiments are within the scope of the present invention.
Claims (8)
1. An electroless palladium plating solution takes water as a solvent and comprises the following solutes in mass concentration: 1-10 g/L tetraammine palladium sulfate, 1-20 g/L sodium hypophosphite, 10-30 g/L composite complexing agent and 10-30 g/L composite stabilizer;
the composite complexing agent is ethylenediamine, 2-amino-n-butanol and isobutanolamine; the mass ratio of the ethylenediamine to the 2-amino-n-butyl alcohol to the isobutanolamine is (1-3) to (2-4) to (3-5);
the composite stabilizer is methacrylic acid, crotonic acid and polyethyleneimine; the mass ratio of the methacrylic acid to the crotonic acid to the polyethyleneimine is 1 (0.5-2) to 0.0001-0.001.
2. The electroless palladium plating solution according to claim 1, wherein the polyethyleneimine has a number average molecular weight of 3000 to 3500.
3. The electroless palladium plating solution according to claim 1, wherein the electroless palladium plating solution has a pH value of 6 to 8.
4. The electroless palladium plating solution according to claim 3, wherein the pH adjusting agent for adjusting the pH of the electroless palladium plating solution comprises a sulfuric acid solution and/or a sodium hydroxide solution.
5. Use of the electroless palladium plating solution according to any one of claims 1 to 4 for electroless palladium plating.
6. A method for electroless palladium plating comprises the following steps:
performing chemical palladium plating on the surface of the substrate to obtain a palladium plating layer;
the electroless palladium plating solution for electroless palladium plating is the electroless palladium plating solution as defined in any one of claims 1 to 4;
the temperature of the chemical palladium plating is 40-60 ℃.
7. The method for electroless palladium plating according to claim 6, wherein the time for electroless palladium plating is 8-12 min.
8. The method of claim 6 or 7, wherein the palladium plating layer has a thickness of 0.1 to 1 μm.
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