CN102220046A - Method for preparing nanometer tin coated copper conductive ink - Google Patents

Abstract

The invention relates to a preparation method of nano tin-clad copper conductive ink which can be used for ink-jet printing of printed circuit boards, and belongs to the technical field of preparation process of nano-metal materials and ink-jet printing ink. The characteristics of the present invention are: using NaH ₂ PO ₂ ·H ₂ O as the reducing agent, CuSO ₄ ·5H ₂ O as the precursor, CTAB and LomarD as the surfactant to prepare nano-copper conductive ink; adding tin salt, sulfur Urea (a special complexing agent for copper) is prepared by electroless plating, and the average particle size distribution is 60-200nm tin-clad copper nano-conductive ink; 90% (mass ratio) of impurities in the ink can be removed by electrodialysis. Particle size analysis, XRD and TEM prove that the present invention firstly tin-plates the surface of nano-copper to form a coating structure, and successfully prepares nano-tin tin-clad copper conductive ink, and its stability and dispersibility all reach the expected effect.

Description

Preparation method of nano tin-clad copper conductive ink

technical field

The present invention relates to a method applicable to the preparation of ink jet printing inks for printed circuit boards (PCBs).

Background technique

Printed circuit boards are processed by inkjet printing to replace the traditional methods used in metal wiring or electronic circuit manufacturing, which is an urgent need for the electronics industry and the information industry. At present, driven by developed countries such as the United States, Japan, Germany, and the United Kingdom, there is an international upsurge in research and development of metal conductive inks that can be applied to inkjet printing PCB circuit boards. The reason for this upsurge is that metal conductive ink can be applied to the high-speed and developing wireless intelligent identification (RFID) electronic tags, printed circuit boards (PCB), flexible printed circuit boards (FPCB), and can also be used for printing electromagnetic wave shielding materials, etc. . The key technology of inkjet printing is to prepare metal conductive ink that can be applied to printers. The current typical and low-cost metal conductive ink production method is: use chemical reduction to make metal nanoparticles and then ultrasonically disperse them in an organic solution to form ink. It is relatively easy to make conductive ink with precious metals such as gold and silver, but it is more difficult to use copper, because copper is easily oxidized and loses conductivity in the air. Tin plating on copper particles can solve these problems well. Tin-clad copper particles have good stability, electrical conductivity, wear resistance, corrosion resistance and electromagnetic shielding, and have semi-bright silvery white luster, decorative effect good. There are many reports about electroless tin plating, but there are not many literatures about electroless tin plating on copper particles. The invention studies the process and performance of the tin-clad copper conductive ink, expects to obtain tin-clad copper particles with high cost performance, and provides a basis for industrial application.

Contents of the invention

The purpose of the present invention is to apply a brand-new manufacturing method of printed circuit boards (PCBs)——inkjet printing to prepare full printed circuit boards, and propose a process for preparing nano-tin-coated copper conductive ink.

A kind of preparation method of nanometer tin-clad copper conductive ink of the present invention is characterized in that following technological process and steps are arranged:

Ink preparation method of the present invention is:

a. Preparation of copper sulfate solution:

Take copper sulfate pentahydrate and prepare a 0.1mol/l solution, add ammonia water to adjust the pH value to 4 for subsequent use;

b. Preparation of sodium hypophosphite solution:

Add 1g of Lomar D and 0.85g of CTAB double protective agent into 100ml of DEG, heat and stir to dissolve, then dissolve an appropriate amount of NaH ₂ PO ₂ ·H ₂ O in water to make a 0.1mol/l sodium hypophosphite solution, stir well and set aside;

c. Preparation of nano copper ink:

Measure 100ml of 0.1mol/l copper sulfate solution and add the copper sulfate solution dropwise to a three-necked flask filled with 100ml of 0.1mol/l sodium hypophosphite solution at a rate of 2ml/min. The molar ratio of sodium is 1:1. Heat to 120-160 ⁰ C and stir. After the dropwise addition, lower the temperature and continue stirring for 30 minutes to obtain a brownish-red solution.

d. Preparation process of nano tin-clad copper conductive ink

Add 25~70g of SnCl ₂ ·2H ₂ O to 1L of 36% hydrochloric acid by mass, and stir to dissolve it. Add 10~20g of complexing agent thiourea and 20~80g of stabilizer EDTA in turn under stirring, then add 10~25g of NaH ₂ PO ₂ ·H ₂ O, finally adjust the acidity of the bath to 1~2, filter at constant volume Slowly add nano-copper conductive ink with a constant current pump at 20~30°C;

e. Electrodialysis and impurity removal of nano tin-clad copper conductive ink

Cool the prepared nano tin-clad copper ink to room temperature, add it to the middle concentrated solution chamber of the electrodialysis device, add 5L of deionized water to the anode and cathode compartments on both sides, adjust the DC power supply to make the voltage reach 30V, every two The deionized water in the anode and cathode compartments is replaced every hour, and the impurities that basically reach 90% (mass percentage) are removed after 10 hours.

The inventive method is cooled to room temperature with the metal tin-clad copper conductive ink that makes, adopts the particle diameter of metal particle in the prepared ink of British Zetasizer3000HS particle size distribution analyzer detection, and Fig. 1 is the particle size distribution of tin-clad copper conductive ink after reaction picture. The results of the prepared nano-tin bimetal particles show that the particle size is between 60 and 200nm, and the particle size distribution is narrow.

In the method of the present invention, the prepared ink is sprayed on a copper grid with a carbon film, and the morphology of tin-clad copper particles is observed with a JEM-2010F transmission electron microscope (TEM) after drying. The results in Figure 2 show that when using DEG with a polarity weaker than water as the solvent, the diameter of the tiny nano-tin-coated copper grains is about 70nm-160nm, which is basically consistent with the particle size of most particles analyzed by particle size analysis.

The inventive method uniformly coats the tin-clad copper conductive ink prepared on the glass sheet to obtain a thin film of 1.00 × 1.00 × 0.01cm ³ , which is analyzed with a Japan Rigaku D/max-RD type X-ray diffractometer (XRD). Cu target, tube voltage 50kV, tube current 100mA, scan range 200-800, scan rate 49(°)/min. XRD analysis was carried out on the tin-clad copper conductive ink which was stable for a long time and did not settle. Figure 2 is the XRD spectrum of the prepared tin-clad copper ink. It can be seen from the figure that the powder contains three components of copper, tin and copper-tin alloy, which are respectively marked in the figure, and there is no copper or tin oxide component, which shows that the powder is a copper-tin bimetallic structure. It can be inferred that the prepared copper-tin bimetal has a core-shell structure. This is determined by the replacement reaction mechanism. Since the replacement reaction occurs on the surface of copper, the resulting copper-tin alloy or tin element also gathers on the surface of the copper powder to form a coating structure. Two facts can confirm this point. The color of the copper powder used as raw material is purple-red and the powder turns off-white after the tin is wrapped. Red, so it can be seen that the powder is a coated structure. The oxidation resistance of the nano-core-shell copper-tin bimetallic structure is better than that of the corresponding nano-copper. The purple-red nano-copper powder will be oxidized into earth-yellow cuprous oxide after being exposed to the air in a few minutes, while the nano-core-shell copper-tin bimetal has no oxidation in the XRD pattern after being stored for a few days under the same conditions. The peak of the substance shows that its antioxidant performance is greatly enhanced. This is because tin forms a coating structure on the surface of copper powder.

The present invention is the first time to form a coating structure by tin-plating the surface of nano-copper, and successfully prepares the nano-tin-coated copper conductive ink, and its stability and dispersibility both achieve expected effects. Its particle size is between 60-200nm, and it will not settle for 6 months under normal temperature and pressure.

Description of drawings

The particle size distribution test chart of the prepared nano tin-clad copper conductive ink of Fig. 1;

Fig. 2 The TEM test picture of the prepared nano-tin-clad copper conductive ink;

Figure 3 XRD test pattern of the prepared nano tin-clad copper conductive ink.

Detailed ways

Now the specific embodiment of the present invention is described in the following.

Example 1

Prepare recrystallized high-purity CuSO ₄ 5H ₂ O into 1000ml of 0.1mol/L standard solution, add ammonia water to adjust its pH value to 2, 3, 4, 4.5, and 5 five different solutions, 200ml each, for later use. Take 20ml of 0.1mol/L CuSO ₄ ·5H ₂ O solution with a pH value of 2 and add it to the constant flow pump; make NaH ₂ PO ₂ ·H ₂ O (analytical pure) into a 0.1mol/L standard solution for later use, take 35ml Put the solution into a 4-neck round bottom flask, put it on an intelligent constant temperature electromagnetic stirrer; take 100ml of diethylene glycol (DEG) and divide it into two parts, weigh 1g Lomar D dissolved in one part of DEG, weigh Dissolve 0.85g CTAB in another part of DEG, then mix the two parts of DEG solution into a 4-neck round bottom flask, heat to 120~1600C, then turn on the constant flow pump and inject CuSO ₄ 5H ₂ O solution at 2ml/min Add dropwise at a speed of 30 min after the reaction is completed, add 25 g of SnCl ₂ ·2H ₂ O to 1 L of 36% hydrochloric acid by mass, and stir to dissolve it. Under stirring, add 10g of complexing agent thiourea and 20g of stabilizer EDTA in turn, then add 10g of NaH ₂ PO ₂ ·H ₂ O, and finally adjust the acidity of the plating solution to 1, filter at a constant volume and slowly use a constant flow pump at 20°C Add nano-copper conductive ink dropwise; cool the prepared nano-tin-clad copper ink to room temperature, add it to the middle concentrated solution chamber of the electrodialysis device, add 5L of deionized water to the anode and cathode compartments on both sides, and adjust the DC power supply to make Its voltage reaches 30V, and the deionized water in the anode and cathode compartments is changed every two hours.

Experimental Formula and Process Conditions of Electroless Tin Plating Solution

Hydrochloric acid 36% (wt%)

SnCl ₂ 2H ₂ O 25~70 g/L

Reducing agent (sodium hypophosphite) 10~25 g/L

Accelerator (EDTA) 20~80 g/L

Complexing agent (thiourea) 10~20 g/L

Surfactant (CTAB+LD) 0.5~2 g/L

pH value 1~2

Temperature 20~30℃

time 30min

Claims (1)

1. the preparation method of nanometer tin copper-clad conductive ink is characterized in that having following processing step:

A. the preparation of copper-bath

Get the solution that cupric sulfate pentahydrate is mixed with 0.1mol/l, it is standby 4 to add ammoniacal liquor adjusting pH value;

B. the preparation of sodium hypophosphite solution

Heating and stirring among 1gLomar D and the two protective materials adding of the 0.85gCTAB 100mlDEG are made its dissolving, subsequently an amount of NaH ₂PO ₂H ₂O is dissolved in and is made into the 0.1mol/l sodium hypophosphite solution in the water, and it is standby to stir;

C. the preparation of nanometer copper ink

The copper-bath 100ml of measuring 0.1mol/l is added drop-wise to copper-bath in the three-necked flask that fills the 100ml0.1mol/l sodium hypophosphite solution with constant flow pump by the speed of 2ml/min, and copper sulfate and sodium hypophosphite amount mol ratio are 1:1, are heated to 120-160 ⁰C also stirs, and drips to finish the back cooling and continue stirring reaction 30min, finish the solution of maroon;

D. the preparation process of nanometer tin copper-clad conductive ink

In the 1L mass percent is to add 25 ~ 70gSnCl in 36% hydrochloric acid ₂2H ₂O stirs and makes it dissolving; Under agitation add complexing agent thiocarbamide 10 ~ 20g and stablizer EDTA20 ~ 80g successively, add the NaH of 10 ~ 25g again ₂PO ₂H ₂O, adjusting plating bath acidity at last is 1 ~ 2, constant volume filters the back and slowly drip nano-copper conductive ink with constant flow pump under 20 ~ 30 ℃;

E. the electrodialysis removal of impurities of nanometer tin copper-clad conductive ink

With the nanometer tin copper-clad ink cool to room temperature for preparing, join the middle strong solution chamber of electrodialysis unit, the deionized water that adds 5L in the anode on both sides and the cathodic compartment, adjusting direct supply makes its voltage reach 30V, every two hours change the deionized water in anode and the cathodic compartment, the impurity that reaches 90wt.% behind the 10h substantially is removed.

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