CN112609172B - Chemical palladium plating solution for wafer packaging field and preparation method thereof - Google Patents

Abstract

The invention discloses a chemical palladium plating solution used in the field of wafer packaging and a preparation method thereof, wherein the chemical palladium plating solution comprises the following components in concentration by mass: 25-30g/L of palladium tetraammine sulfate; 30-60g/L of complexing agent; malic acid 5-10 g/L; 5-15g/L of polyamino polyether methylene phosphonic acid; 5-9g/L saccharin; 2-55-9g/L of reducing agent; 0.1-10g/L of complexing agent; 0.2-0.4g/L stabilizer; 0.05-0.2 g/L of surfactant. Mixing the tetraammine palladium sulfate, the citric acid, the malic acid, the polyamino polyether methylene phosphonic acid, the saccharin, the coordination agent, the stabilizing agent and the surfactant according to the proportion, adjusting the pH value to be 6.5-8.5 by adopting a buffering agent to form a palladium plating solution, wherein the modulation temperature is 50-60 ℃, and the palladium plating time is 5-15 min. The plating layer obtained by using the palladium plating solution of the invention has compact structure and fine and uniform crystallization.

Description

Chemical palladium plating solution for wafer packaging field and preparation method thereof

Technical Field

The invention relates to the technical field of packaging and materials, in particular to a chemical palladium plating solution used in the field of wafer packaging and a preparation method thereof.

Background

Wafer level packaging, which is generally oriented to perform most or all of the packaging test procedures directly on the wafer and then cut into individual components, has the advantages of smaller package size and better electrical performance, and is mainly used for various semiconductor products, and the requirements mainly come from the characteristic requirements of portable products for being light, thin, short and small.

The wafer level package has a very important surface treatment process, which is directly related to the use of subsequent electronic products. The existing surface treatment processes (nickel-gold, nickel-palladium-gold, silver-plating, tin-plating, OSP and tin spraying) can not simultaneously meet the performances of gold wire bonding, fine circuit (1.5mil/1.5mil and below line width/line distance), bending resistance (bending for 3 times at 180 degrees), and the like.

The palladium-plated layer is widely used in the field of wafer level packaging due to its excellent corrosion resistance, wear resistance, electrical conductivity, chemical inertness, white appearance, etc., and the palladium film serves as an excellent barrier layer for preventing other metals in the substrate from migrating to the contact surface where oxidation of other metals may occur. First, the surface is activated and then the plated part with the surface to be coated is immersed in an acidic palladium solution, causing it to form extremely fine palladium particles on which nickel deposition is initiated. The palladium coating is not hermetic, but is very finely distributed.

However, the current palladium plating solution has the following defects:

1) if the plating part is exposed in water or air for a long time, the phenomenon of color change and oxidation can occur; thus, the use of the plated part in the later period is easily influenced; and the palladium tank can be separated out due to the occurrence of homogeneous catalysis in use, thereby causing the instability of the electroless palladium plating.

2) In the chemical palladium plating layer, the deposition rate of palladium plating and the compactness of the palladium layer cannot be controlled due to the difference of temperature and electroplating time, and finally, the corrosion performance, the ductility and the bending performance of the palladium plating layer are poor. In addition, water-soluble compounds are mainly used as palladium salts in the market at present, and the storage and transportation of the palladium salts are liquid, so that the production operation is not facilitated.

Disclosure of Invention

Aiming at the defects in the technology, the invention discloses a chemical palladium plating solution used in the field of wafer packaging and a preparation method thereof, which can well control the deposition rate of palladium and the compactness of a palladium layer and can obtain the palladium layer with excellent ductility.

In order to achieve the above purpose, the invention provides an electroless palladium plating solution for the field of wafer packaging, which comprises the following components in concentration by mass:

the complexing agent consists of citric acid and malic acid, and the mass concentration ratio of the citric acid to the malic acid is 6: 1;

mixing the tetraammine palladium sulfate, the citric acid, the malic acid, the polyamino polyether methylene phosphonic acid, the saccharin, the reducing agent, the coordination agent, the stabilizing agent and the surfactant according to the proportion, adjusting the pH value to be 6.5-8.5 by adopting a buffering agent to form a palladium plating solution, wherein the modulation temperature is 50-60 ℃, and the palladium plating time is 5-15 min.

Wherein the stabilizer consists of antimony potassium tartrate and cerium sulfate, and the concentration ratio of the cerium sulfate to the antimony potassium tartrate is 3: 1.

Wherein the surfactant is any one of polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene amine ether and polyoxypropylene glycerol ether.

Wherein the complexing agent is: one or more of ethylenediamine, benzylamine, N-benzylmethylamine, 4-fluorobenzylamine and N-methyl-1-naphthylmethylamine.

In order to achieve the above object, the present invention further provides a method for preparing an electroless palladium plating solution for use in the field of wafer packaging, comprising the following specific steps:

1) preparing a palladium tank, wherein a stirring pump is carried in the palladium tank;

2) pouring tetraamminepalladium sulfate into a palladium tank, adding deionized water, continuously stirring until the tetraamminepalladium sulfate is completely dissolved, and preparing the tetraamminepalladium sulfate into a solution A with the mass concentration of 25-30 g/L;

3) sequentially adding citric acid and malic acid with the concentration ratio of 6:1 into the solution A, and stirring to obtain a solution B;

4) continuously stirring the solution B, and adding 5-15g/L polyamino polyether methylene phosphonic acid, 5-9g/L saccharin, 2-5g/L reducing agent, 0.1-10g/L coordination agent, 0.2-0.4g/L stabilizer and 0.05-0.2 g/L surfactant to obtain a solution C;

5) and (3) adopting a buffering agent to adjust the pH value of the solution C to be between 6.5 and 8.5 to form a palladium solution.

The invention has the beneficial effects that: compared with the prior art, the chemical palladium plating solution for the field of wafer packaging and the preparation method thereof provided by the invention have the following advantages:

1) in the components, citric acid is used as a main complexing agent of the palladium plating solution, malic acid is used as an auxiliary complexing agent of the auxiliary plating solution, the concentration ratio of the citric acid to the malic acid is designed to be 6:1, the coordination of the citric acid and the malic acid in an accurate proportion can complex palladium ions of tetraamminepalladium sulfate more effectively, the combination of the two complexing agents can ensure that palladium is arranged more orderly in the deposition process, so that the obtained plating layer is relatively flat and compact; therefore, the deposition rate of palladium and the compactness of the palladium layer can be well controlled, and meanwhile, the palladium layer with excellent ductility can be obtained;

2) the palladium salt in the invention adopts tetraammine palladium sulfate which is solid soluble palladium salt, palladium exists in the form of tetraammine palladium complex, and the palladium is stably stored in the form of solid at normal temperature and is easy to store and transport; compared with other palladium salts such as palladium sulfate and the like, the tetraamminepalladium sulfate has stronger stability, and solves the problem that the palladium is easy to precipitate.

3) The polyamino polyether methylene phosphonic acid is used as a protective agent and can be attached to the surface of a plating layer to prevent the plating layer from discoloring and oxidizing in water or air;

4) the method has low cost, convenient operation, high stability and long-term use;

5) the plating layer obtained by using the palladium plating solution of the invention has a compact structure, and the crystallization of the plating layer is fine and uniform; not only meets the requirement of good corrosion resistance test, but also has better extension and bending performance.

Detailed Description

In order to express the present invention more clearly, the present invention is further described below with reference to examples.

The invention provides a chemical palladium plating solution for the field of wafer packaging, which comprises the following components in concentration by mass:

the complexing agent consists of citric acid and malic acid, and the mass concentration ratio of the citric acid to the malic acid is 6: 1;

mixing the tetraammine palladium sulfate, the citric acid, the malic acid, the polyamino polyether methylene phosphonic acid, the saccharin, the reducing agent, the coordination agent, the stabilizing agent and the surfactant according to the proportion, adjusting the pH value to be 6.5-8.5 by adopting a buffering agent to form a palladium plating solution, wherein the modulation temperature is 50-60 ℃, and the palladium plating time is 5-15 min.

In this example, the stabilizer consisted of potassium antimony tartrate and cerium sulfate, with a concentration ratio of cerium sulfate to potassium antimony tartrate of 3: 1. The mass concentration ratio of cerium sulfate to antimony potassium tartrate is designed to be 3:1, so that the occurrence of autocatalytic reaction in a palladium tank can be better controlled, the phenomenon that the palladium tank is separated out due to homogeneous catalysis in use is prevented, and the continuous and stable operation of the autocatalytic reaction of the heterogeneous surface in the tank liquor is better ensured.

In the invention, the tetraamminepalladium sulfate provides a source of palladium ions in the chemical palladium solution for the solution; citric acid is a main complexing agent in the chemical palladium plating solution; malic acid is an auxiliary complexing agent in the chemical palladium plating solution; cerium ions in the cerium sulfate are used as a main stabilizer of chemical palladium; antimony ions in the antimony potassium tartrate are an auxiliary stabilizer of chemical palladium; the surfactant reduces the surface tension of gas, so that hydrogen on the plating layer is released in time, the porosity of the plating layer is reduced, the density of a palladium layer is improved, and the corrosion risk of palladium is reduced; saccharin can reduce the stress of the plating layer, so that the plating layer has certain flexibility; the polyamino polyether methylene phosphonic acid is a chemical palladium surface protective agent, and can be attached to the surface after chemical palladium plating is finished, so that a chemical palladium plating layer is prevented from discoloring and oxidizing in water or air.

In this embodiment, the surfactant is any one of polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene amine ether, and polyoxypropylene glycerol ether. The existence of the surfactant can be the wetting of micropores, blind holes and step grooves in the PCB, and the plating leakage in the welding pads, the holes and the grooves is prevented.

In this embodiment, the complexing agent is: one or more of ethylenediamine, benzylamine, N-benzylmethylamine, 4-fluorobenzylamine and N-methyl-1-naphthylmethylamine. The proper content of the complexing agent can well control the deposition rate of palladium and the compactness of the palladium layer, and meanwhile, the palladium layer with excellent ductility can be obtained.

In order to achieve the above object, the present invention further provides a method for preparing an electroless palladium plating solution for use in the field of wafer packaging, comprising the following steps:

1) preparing a palladium tank, wherein a stirring pump is carried in the palladium tank;

2) pouring tetraamminepalladium sulfate into a palladium tank, adding deionized water, continuously stirring until the tetraamminepalladium sulfate is completely dissolved, and preparing the tetraamminepalladium sulfate into a solution A with the mass concentration of 25-30 g/L;

3) sequentially adding citric acid and malic acid with the concentration ratio of 6:1 into the solution A, and stirring to obtain a solution B;

4) continuously stirring the solution B, and adding 5-15g/L polyamino polyether methylene phosphonic acid, 5-9g/L saccharin, 2-5g/L reducing agent, 0.1-10g/L coordination agent, 0.2-0.4g/L stabilizer and 0.05-0.2 g/L surfactant to obtain a solution C;

5) and (3) adopting a buffering agent to adjust the pH value of the solution C to be between 6.5 and 8.5 to form a palladium solution.

Compared with the prior art, the chemical palladium plating solution for the wafer packaging field and the preparation method thereof provided by the invention have the following advantages:

1) in the components, citric acid is used as a main complexing agent of the palladium plating solution, malic acid is used as an auxiliary complexing agent of the auxiliary plating solution, the concentration ratio of the citric acid to the malic acid is designed to be 6:1, the coordination of the citric acid and the malic acid in an accurate proportion can complex palladium ions of tetraamminepalladium sulfate more effectively, the combination of the two complexing agents can ensure that palladium is arranged more orderly in the deposition process, so that the obtained plating layer is relatively flat and compact; therefore, the deposition rate of palladium and the compactness of the palladium layer can be well controlled, and meanwhile, the palladium layer with excellent ductility can be obtained;

2) the palladium salt in the invention adopts tetraammine palladium sulfate which is solid soluble palladium salt, palladium exists in the form of tetraammine palladium complex, and the palladium is stably stored in the form of solid at normal temperature and is easy to store and transport; compared with other palladium salts such as palladium sulfate and the like, the tetraamminepalladium sulfate has stronger stability, and solves the problem that the palladium is easy to precipitate.

3) The polyamino polyether methylene phosphonic acid is used as a protective agent and can be attached to the surface of a plating layer to prevent the plating layer from discoloring and oxidizing in water or air;

4) the method has low cost, convenient operation, high stability and long-term use;

5) the existence of the buffering agent can ensure that the pH value of the bath solution is maintained in a dynamic equilibrium range in the service cycle of the palladium bath, thereby ensuring the stability of the deposition rate, the quality of a plating layer and the service life of the bath solution;

7) the plating layer obtained by using the palladium plating solution of the invention has a compact structure, and the crystallization of the plating layer is fine and uniform; not only meets the requirement of good corrosion resistance test, but also has better extension and bending performance.

In this embodiment, the buffer is one or more of glycine, ammonium sulfate, ammonium chloride, and ammonium acetate.

The Au-Pd-Au plating layer is obtained on the copper substrate by the following method.

Oil removal cleaning (55-60 ℃, 5min) → hot water washing (55-60 ℃, 1-2 min) → pure water washing I (room temperature, 1.5 min) → microetching (potassium persulfate 70g/L, sulfuric acid 35mL/L, 2-3 min) → pure water washing II (room temperature, 2 min) → presoaking (sulfuric acid 20mL/L, room temperature, 1 min) → chemical immersion gold (gold bath solution matched with gold palladium gold process), post immersion solution matched with gold palladium gold process, pH 3.0-4.0, room temperature, 1 min) → pure water washing III (room temperature, 1.5 min) → pure water washing IV (room temperature, 1.5 min) → chemical plating palladium (adopting plating solution formula of embodiment of the invention, pH value 6.5-8.5, temperature of 50-60 ℃, temperature of 5-15min) → pure water washing I (room temperature, 1.5 min) → pure water washing II (room temperature, 2 min) → pre-immersion solution, 20mL/L, room temperature, 1 min) → chemical immersion solution of gold palladium (post immersion solution matched with gold palladium process, pH value of the formula of the invention, room temperature of the range of 6.0-4.0, 1 min → pure water washing III (room temperature, 1.5-8.5 min) → pure water washing III, 1.5 min) → pure water washing III (room temperature, 1.5 min) → pure water washing solution of the invention), and chemical plating solution of the order of the invention, and chemical plating solution of the order of, 1 minute) → pure water washing vi (room temperature, 1 minute) → pure water washing vii (room temperature, 1 minute) → chemical immersion gold → hot water washing (70-80 ℃, 1 minute) → pure water washing viii (room temperature, 1 minute) → baking.

The invention is illustrated by the following specific examples:

example 1:

wherein the temperature of the plating solution is 50 ℃; the time is 10 min.

By using the palladium plating solution in the embodiment, the palladium layer of the obtained plated part has a flat and silvery white appearance; the microscopic observation shows that the structure of the plating layer is very compact, the crystallization of the plating layer is fine and uniform, and no crack exists; the 180-degree bending test shows that the bonding force of the plating layer is good, and no obvious crack is observed when the plating layer is amplified by 100 times.

Example 2:

wherein the temperature of the plating solution is 55 ℃; the time is 12 min.

By using the palladium plating solution in the embodiment, the palladium layer of the obtained plated part has a flat and silvery white appearance; the microscopic observation shows that the structure of the plating layer is very compact, the crystallization of the plating layer is fine and uniform, and no crack exists; the 180-degree bending test shows that the bonding force of the plating layer is good, and no obvious crack is observed when the plating layer is amplified by 100 times.

Example 3:

wherein the temperature of the plating solution is 60 ℃; the time is 15 min.

By using the palladium plating solution in the embodiment, the palladium layer of the obtained plated part has a flat and silvery white appearance; the microscopic observation shows that the structure of the plating layer is very compact, the crystallization of the plating layer is fine and uniform, and no crack exists; the 180-degree bending test shows that the bonding force of the plating layer is good, and no obvious crack is observed when the plating layer is amplified by 100 times.

Comparative example 1:

palladium sulfate: 10g/L

Reducing agent: 10g/L of formic acid;

a stabilizer: 0.1g/L of bismuth nitrate;

pH buffer: 15g/L of borax;

surfactant: none;

plating conditions are as follows: temperature: 60 ℃; pH: 6.5;

the palladium plating solution in the palladium-gold plating process is used for preparing the palladium layer in the gold-palladium-gold process by using the parameters, although the circuit of the test board does not fall off and the like, the plating speed is slow, and the phenomenon of excessive plating is caused; and no significant cracking was observed at 100 x magnification as tested by the 180 ° bend test.

The test results for examples 1-3 and comparative example 1 are given in the following table:

1) coating appearance: visual inspection; 2) apparent morphology: tested by 180 degree bending test.

As can be seen from the experimental data in the table, the plating leakage phenomenon occurs because antimony potassium tartrate and cerium sulfate are not used as stabilizers in the invention. Moreover, the palladium layer of the plated part is smooth and silvery white in appearance by adopting the accurate mass concentration ratio; the microscopic observation shows that the structure of the plating layer is very compact, the crystallization of the plating layer is fine and uniform, and no crack exists; through 180-degree bending test, the bonding force of the plating layer is good, and no obvious crack is observed when the plating layer is amplified by 100 times; the method proves that the complexing agent adopts citric acid and malic acid, and the concentration ratio of the citric acid to the malic acid is designed to be 6:1, so that the compactness of the coating structure is perfectly ensured.

The above disclosure is only for a few specific embodiments of the present invention, but the present invention is not limited thereto, and any variations that can be made by those skilled in the art are intended to fall within the scope of the present invention.

Claims (4)

1. An electroless palladium plating solution for the field of wafer packaging is characterized by comprising the following components in concentration by mass:

25-30g/L of palladium tetraammine sulfate

Polyamino polyether methylene phosphonic acid 5-15g/L

Saccharin 5-9g/L

30-60g/L complexing agent

2-5g/L of reducing agent

0.1-10g/L complexing agent

0.2-0.4g/L stabilizer

0.05-0.2 g/L of surfactant

The complexing agent consists of citric acid and malic acid, and the mass concentration ratio of the citric acid to the malic acid is 6: 1;

the palladium plating solution is prepared by the following steps:

preparing a palladium tank, wherein a stirring pump is carried in the palladium tank;

pouring tetraamminepalladium sulfate into a palladium tank, adding deionized water, continuously stirring until the tetraamminepalladium sulfate is completely dissolved, and preparing the tetraamminepalladium sulfate into a solution A with the mass concentration of 25-30 g/L;

sequentially adding citric acid and malic acid with the concentration ratio of 6:1 into the solution A, and stirring to obtain a solution B;

continuously stirring the solution B, and adding 5-15g/L polyamino polyether methylene phosphonic acid, 5-9g/L saccharin, 2-5g/L reducing agent, 0.1-10g/L coordination agent, 0.2-0.4g/L stabilizer and 0.05-0.2 g/L surfactant to obtain a solution C;

regulating pH value of the solution C to 6.5-8.5 with buffer to obtain palladium solution at 50-60 deg.C for 5-15min;

the stabilizer consists of antimony potassium tartrate and cerium sulfate, and the concentration ratio of the cerium sulfate to the antimony potassium tartrate is 3: 1; the mass concentration ratio of the cerium sulfate to the antimony potassium tartrate is designed to be 3:1, so that the occurrence of autocatalytic reaction in the palladium tank can be better controlled, the phenomenon that the palladium tank is separated out due to homogeneous catalysis in use is prevented, and the continuous and stable operation of the autocatalytic reaction of the heterogeneous surface in the tank liquor is better ensured.

2. The electroless palladium plating solution for wafer packaging field as claimed in claim 1, wherein the surfactant is any one of polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene amine ether and polyoxypropylene glycerol ether.

3. The electroless palladium plating solution for the wafer packaging field as claimed in claim 1, wherein the complexing agent is: one or more of ethylenediamine, benzylamine, N-benzylmethylamine, 4-fluorobenzylamine and N-methyl-1-naphthylmethylamine.

4. A method for preparing an electroless palladium plating solution for the field of wafer packaging according to any one of claims 1 to 3, which is characterized by comprising the following specific steps:

1) preparing a palladium tank, wherein a stirring pump is carried in the palladium tank;

2) pouring tetraamminepalladium sulfate into a palladium tank, adding deionized water, continuously stirring until the tetraamminepalladium sulfate is completely dissolved, and preparing the tetraamminepalladium sulfate into a solution A with the mass concentration of 25-30 g/L;

3) sequentially adding citric acid and malic acid with the concentration ratio of 6:1 into the solution A, and stirring to obtain a solution B;

4) continuously stirring the solution B, and adding 5-15g/L polyamino polyether methylene phosphonic acid, 5-9g/L saccharin, 2-5g/L reducing agent, 0.1-10g/L coordination agent, 0.2-0.4g/L stabilizer and 0.05-0.2 g/L surfactant to obtain a solution C;

5) and (3) adopting a buffering agent to adjust the pH value of the solution C to be between 6.5 and 8.5 to form a palladium solution.