Conductive paste based on silver seed powder and its preparation process

Abstract

The present invention relates to a conductive paste based on seed silver powder and its preparation process, belonging to the technical field of photovoltaic cells. This conductive paste is composed of: 10-85% by weight of seed silver powder, 2-5% by weight of glass powder, and 8-12% by weight of organic support, the remainder being spherical silver powder; the seed silver powder uses a base metal powder, on which silver grows by reduction in the liquid phase at the surface with the help of a coating agent, forming numerous silver pores on the surface of the base metal powder after calcination.After photo-induced silver deposition, "silver feet" form and intertwine in the sintered layer, increasing the contact area between the sintered and electrodeposited layers, reducing the overall resistivity of the electrodes, improving the bond strength between the layers, slowing the increase in resistance between the layers, effectively improving the photoelectric conversion efficiency of the cells while reducing the cost of applying the conductive paste.

Description

Title of the invention: Conductive paste based on seed silver powder and its preparation process. Technical field of the invention

[0001] The present invention belongs to the technical field of photovoltaic cells, and relates more specifically to a conductive paste based on seed silver powder and its preparation process. Previous technique

[0002] Photovoltaic electricity production, as a means of directly converting solar energy into electricity, offers ecological and renewable advantages and constitutes one of the important directions in the development of clean and green energy. Conductive paste is a key material in the production of photovoltaic cells, primarily used to manufacture the front and rear electrodes of solar cells.

[0003] Traditional electrodes use screen printing to directly print and sinter the conductive paste, which limits the electrode height-to-width ratio. The use of a seed layer combined with a photo-induced electrolytic deposition technique can effectively improve the electrode height-to-width ratio, reduce their resistivity, increase the cell's light-receiving surface area, and decrease the amount of silver paste used for the electrodes, which has positive implications for cost reduction and improved photoelectric conversion efficiency of photovoltaic cells. However, the conductive paste of the seed layer is primarily based on ultrafine silver powder, resulting in high costs.Furthermore, there is a density difference between the seed layer and the electrodeposited layer, which can lead to the formation of microcracks between the layers during long-term use, particularly under conditions of large temperature variations. In addition, the electrochemical action of the current between the layers further deteriorates their adhesion, resulting in an increase in the cell's internal resistance and a decrease in photoelectric conversion efficiency. Therefore, this application aims to provide a conductive paste applicable to the seed layer. Description of the invention.

[0004] To solve the technical problems mentioned in the technical context, the objective of the present invention is to provide a conductive paste based on seed silver powder and its preparation process.

[0005] The objective of the present invention can be achieved by the following technical solutions:

[0006] A conductive paste based on seed silver powder, composed of the following elements: 10-85% by weight of seed silver powder, 2-5% by weight of glass powder and 8-12% by weight of organic support, the remainder being spherical silver powder.

[0007] Said silver seed powder is prepared according to the following method:

[0008] Step a1a: Mix tri-allylamine, mercaptoethanol and ethanol, heat to 55-65°C, stir at 120-160 rpm for activation for 20-30 min, then add the photoinitiator, mix and irradiate under UV at 200-300W / m2 for 2.5-311, at the end of the reaction, evaporate the ethanol by rotation to obtain the intermediate;

[0009] Furthermore, the proportions of tri-allylamine, mercaptoethanol, photoinitiator and ethanol are 0.1 mol : 0.3 mol : 0.25-0.3 mL : 3-4 mmol : 80-100 mL, the photoinitiator preferably being liquid photoinitiator 1173. Tri-allylamine and mercaptoethanol are activated by heating, then a click addition occurs under the effect of the photoinitiator, forming a thioether compound containing nitrogen at the center.

[0010] Step a2: Mix the intermediate, sodium methoxide and tetrahydrofuran, heat under reflux for 1-1.311, then add the trichloroethyl phosphate dispersion and triethylamine, control the temperature at 60-70°C, stir at 60-90 rpm for 5.5-711, at the end of the reaction, evaporate the low boiling point compounds by rotation to obtain the coating agent;

[0011] Furthermore, the proportions of intermediate, trichloroethyl phosphate, sodium methoxide, triethylamine, and tetrahydrofuran are 0.1 mol: 70-85 mmol: 25-30 mmol: 8-12 mL: 55-75 mL, with a volume fraction of the trichloroethyl phosphate dispersion of 30-40%. Under the action of sodium methoxide and triethylamine, the intermediate and trichloroethyl phosphate undergo etherification, forming a low molecular weight crosslinked compound.

[0012] Step a3: Pre-mix the base metal powder, coating agent, non-ionic surfactant and dimethylacetamide, then add the silver nitrate solution and stir for 30-40 min, introduce nitrogen for protection, slowly add the hydrated hydrazine solution under ultrasonic vibration and react for 1.5-211, at the end of the reaction, let stand for precipitation, remove the supernatant and dry to obtain the composite precursor;

[0013] Furthermore, the proportions of base metal powder, silver nitrate, hydrated hydrazine solution, coating agent, nonionic surfactant, and dimethylacetamide are 1 g: 3.8–14.2 g: 0.8–1.1 L: 0.4–0.6 g: 0.25–0.3 g: 35–50 mL, the mass fraction of the silver nitrate solution being 10%, the volume fraction of the hydrated hydrazine solution being 40%, the surfactant The preferred nonionic coating is Tween 80. The nitrogen-containing thioether structure in the coating agent molecule forms a strong, stable chelation, preferentially binding to active sites on the surface of the base metal powder. This allows the coating agent to adhere to the powder's surface. Conversely, the phosphate-oxygen structure in the coating agent molecule exhibits weaker chelation, accumulating on the base metal powder's surface to capture silver ions, thus forming a silver-rich initial layer. Subsequently, during the hydrazine reduction process, elemental silver grows on the surface, using the initial compound as its nucleus.

[0014] Furthermore, the common metal powder is one of the copper, nickel and iron powders, with an average particle diameter not exceeding Ipm.

[0015] Step a4: Calcine the composite precursor under a nitrogen atmosphere first at 550-620°C for 1.8-2.4 h, then continue heating at 880-920°C for 1-1.2 h, cool in the furnace to room temperature, grind and disperse to obtain the silver seed powder. The organic compounds in the composite precursor are thermally decomposed by the coating agent, forming an adherent silver layer with numerous pores on the surface of the base metal powder.

[0016] Preferably, the melting point of the glass powder is 600-700°C. At this melting temperature, the silver paste sinters easily in a dense manner.

[0017] Preferably, the average diameter of the particles of the spherical silver powder should not exceed 5qm, which promotes the improvement of the flatness of the electrodes after sintering.

[0018] A process for preparing conductive paste based on seed silver powder, the specific method consisting of:

[0019] a. First prepare the silver seed powder according to the method described above;

[0020] b. Pre-mix the silver seed powder, glass powder and powder spherical silver, then add the organic support, grind and prepare the paste to obtain the conductive paste.

[0021] The beneficial effects of the present invention:

[0022] The present invention discloses a method for preparing a silver-coated, base-metal seed powder, wherein a photo-initiated addition reaction between triallylamine and mercaptoethanol produces a nitrogen-containing thioether compound, namely the intermediate. Subsequently, under the action of sodium methoxide and triethylamine, the intermediate undergoes an etherification reaction with trichloroethyl phosphate to form a low molecular weight crosslinked compound, namely the coating agent. In a liquid-phase environment, it then combines with a fine metal powder. The nitrogen-containing thioether structure is present in the coating agent molecule. It forms a strong, stable chelation, preferentially binding to active sites on the surface of the base metal powder, allowing the coating agent to adhere to the powder's surface. The phosphate-oxygen structure in the coating agent molecule has a weaker chelation, capturing subsequently added silver ions to form an initial silver-rich layer on the base metal powder's surface. Elemental silver then grows on the surface through reduction to hydrazine, forming a composite precursor. Finally, calcination thermally decomposes the organic compounds in the composite precursor by the coating agent, forming an adherent silver layer with numerous pores on the base metal powder's surface.This method has few limitations regarding the type of base metal, allowing the selection of a suitable base metal as the core according to the application requirements of the conductive paste. This offers great flexibility in product design and significantly reduces the application cost of the conductive paste. Furthermore, the introduction of silver seed powder makes the conductive paste more suitable for the photo-induced electrolytic deposition technique. The surface of the silver seed powder contains numerous silver pores, which, after sintering, uniformly introduce micropores onto the surface of the sintered layer. These pores form areas of high local current density during the electrolytic deposition process, promoting the preferential deposition of silver to form interlocking "silver feet" within the sintered layer.On the one hand, this increases the contact area between the sintered layer and the electrodeposited layer, helping to reduce overall resistivity. On the other hand, it increases the bond strength between the sintered and electrodeposited layers, mitigating the problem of reduced photoelectric conversion efficiency caused by delamination of the contact interface, which is beneficial for improving the overall efficiency of photovoltaic modules over their lifetime. Description of the implementation methods

[0023] Examples of embodiments of the present invention will be clearly and fully described below. It is evident that the examples described are only a part of the examples of embodiments of the present invention, and not all of them. Based on the examples of embodiments of the present invention, all other examples of embodiments obtained by ordinary people in the field without creative effort are included within the scope of protection of the present invention.

[0024] The GT45 glass powder mentioned in the present invention refers to a composition comprising, in parts by weight: 10% to 30% aluminosilicate, 5% to 15% calcium carbonate, 1% to 5% sodium oxide, 30% to 45% borate, 1% to 5% alkaline earth metals.

[0025] The FD66A type glass powder mentioned in the present invention refers to a composition comprising, by mass percentage: 10% to 30% borate, 10% to 25% silicate, 50% to 70% bismuth oxide, 1% to 10% calcium carbonate. Implementation method 1

[0026] Preparation of a conductive paste based on seed silver powder, the specific implementation process is as follows:

[0027] (a) Preparation of silver seed powder

[0028] Step a1a: Mix tri-allylamine, mercaptoethanol, and ethanol, heat to 65°C, stir at 160 rpm for activation for 20 min, then add the photoinitiator, mix, and irradiate under UV at 300 W / m² for 2.5 h. The proportions of tri-allylamine, mercaptoethanol, photoinitiator, and ethanol are 0.1 mol: 0.3 mol: 0.3 mL: 4 mmol: 100 mL, the photoinitiator used being commercial photoinitiator 1173. At the end of the reaction, evaporate the ethanol by rotation to obtain the intermediate.

[0029] Step a2: Mix the intermediate, sodium methoxide, and tetrahydrofuran, heat under reflux for 1 h, then add the trichloroethyl phosphate dispersion and triethylamine, control the temperature at 70°C, and stir at 90 rpm for 5.5 h. The proportions of intermediate, trichloroethyl phosphate, sodium methoxide, triethylamine, and tetrahydrofuran are 0.1 mol: 85 mmol: 30 mmol: 12 mL: 75 mL. The trichloroethyl phosphate dispersion uses carbon tetrachloride as the dispersing solvent, with a volume fraction of 40% trichloroethyl phosphate. At the end of the reaction, evaporate the low-boiling compounds, mainly carbon tetrachloride and tetrahydrofuran, by swirling to obtain the coating agent.

[0030] Step a3: Pre-mix the base metal powder, coating agent, nonionic surfactant, and dimethylacetamide, then add the silver nitrate solution and stir for 30 minutes. Introduce nitrogen for protection, apply ultrasonic vibration at 20 kHz, slowly add the hydrated hydrazine solution, and react for 1.5 hours. The base metal powder chosen is Brofos-Fe-800 iron powder, with an average particle diameter of 800 nm. The nonionic surfactant chosen is commercial Tween 80. The silver nitrate solution is a 10% aqueous solution by mass. The hydrated hydrazine solution is an industrial raw material at 40% by volume. The proportions of base metal powder, silver nitrate, hydrated hydrazine solution, coating agent, non-ionic surfactant and dimethylacetamide are 1g : 3.8g : l,lmL : 0.6g : 0.3g : 50mL. At the end of the reaction, allow to stand for precipitation, remove the supernatant and dry to obtain the composite precursor.

[0031] Step a4: Place the composite precursor in a preheated nitrogen oven at 300°C, first heat at 620°C for 1.8h, then continue heating at 920°C for 12h, cool in the oven to room temperature, grind and disperse to obtain the silver seed powder.

[0032] (b) Preparation of the conductive paste

[0033] Formulation: Weigh the raw materials according to the percentages by weight, 10% by weight of seed silver powder, prepared in this example; 2% by weight of glass powder, using GT45 glass powder in the implementation process, with a melting point of about 635°C; 8% by weight of organic support, composed of dibutyl phthalate, ethylcellulose, xylene and terpineol in a mass ratio of 1:0.15:0.8:0.5; 80% by weight of spherical silver powder, using the raw material Brofos-Ag-W03, with an average particle diameter of 3qm.

[0034] Preparation of the paste: Mix the seed silver powder, glass powder and spherical silver powder at high speed in a high-speed mixer at 1000 rpm for 10 min, then add the organic support and grind in a grinder for 15 min, the product obtained is the conductive paste. Implementation method 2

[0035] Preparation of a conductive paste based on seed silver powder, the specific implementation process is as follows:

[0036] (a) Preparation of silver seed powder

[0037] Step a1a: Mix tri-allylamine, mercaptoethanol, and ethanol, heat to 55°C, stir at 120 rpm for activation for 30 min, then add the photoinitiator, mix, and irradiate under UV at 200 W / m² for 3 h. The proportions of tri-allylamine, mercaptoethanol, photoinitiator, and ethanol are 0.1 mol: 0.3 mol: 0.25 mL: 3 mmol: 80 mL, the photoinitiator used being commercial photoinitiator 1173. At the end of the reaction, evaporate the ethanol by rotation to obtain the intermediate.

[0038] Step a2: Mix the intermediate, sodium methoxide, and tetrahydrofuran, heat under reflux for 1.3 h, then add the trichloroethyl phosphate dispersion and triethylamine, control the temperature at 60°C, and stir at 60 rpm for 7 h. The proportions of intermediate, trichloroethyl phosphate, sodium methoxide, triethylamine, and tetrahydrofuran are 0.1 mol: 70 mmol: 25 mmol: 8 mL: 55 mL. The trichloroethyl phosphate dispersion uses carbon tetrachloride as the dispersion solvent, with a volume fraction of 30% trichloroethyl phosphate. At the end of the reaction, evaporate the low boiling point compounds, mainly carbon tetrachloride and tetrahydrofuran, by rotation to obtain the coating agent.

[0039] Step a3: Pre-mix the base metal powder, coating agent, nonionic surfactant, and dimethylacetamide, then add the silver nitrate solution and stir for 40 minutes. Introduce nitrogen for protection, apply ultrasonic vibration at 25 kHz, slowly add the hydrated hydrazine solution, and react for 2 hours. The base metal powder chosen is Brofos-Ni-800 nickel powder, with an average particle diameter of 800 nm. The nonionic surfactant chosen is commercial Tween 80. The silver nitrate solution is a 10% aqueous solution by mass. The hydrated hydrazine solution is an industrial raw material at 40% by volume. The proportions of base metal powder, silver nitrate, hydrated hydrazine solution, coating agent, nonionic surfactant and dimethylacetamide are 1g: 14.2g: 0.8mL: 0.4g: 0.253g: 35mL.At the end of the reaction, allow to stand for precipitation, remove the supernatant and dry to obtain the composite precursor.

[0040] Step a4: Place the composite precursor in a preheated nitrogen oven at 300°C, first heat at 550°C for 2.4h, then continue heating at 880°C for 1.2h, cool in the oven to room temperature, grind and disperse to obtain the silver seed powder.

[0041] (b) Preparation of the conductive paste

[0042] Formulation: Weigh the raw materials according to the percentages by weight, 55% by weight of seed silver powder, prepared in this example; 4% by weight of glass powder, using GT45 glass powder in the implementation process, with a melting point of about 635°C; 12% by weight of organic support, composed of dibutyl phthalate, ethylcellulose, xylene and terpineol in a mass ratio of 1:0.12:1.1:0.4; 29% by weight of spherical silver powder, using the raw material Brofos-Ag-W03.

[0043] Preparation of the paste: Mix the seed silver powder, glass powder and spherical silver powder at high speed in a high speed mixer at 1000 rpm for 10 min, then add the organic support and grind in a grinder for 15 min, the product obtained is the conductive paste. Implementation method 3

[0044] Preparation of a conductive paste based on seed silver powder, the specific implementation process is as follows:

[0045] (a) Preparation of silver seed powder

[0046] Step a1a: Mix the tri-allylamine, mercaptoethanol and ethanol, heat to 60°C, stir at 160 rpm for activation for 30 min, then add the photo Initiator, mix and irradiate under UV at 240W / m2 for 2.8h. The proportions of tri-allylamine, mercaptoethanol, photoinitiator and ethanol are 0.1 mol : 0.3 mol : 0.28 mL : 4 mmol : 90 mL, the photoinitiator used being the commercial photoinitiator 1173. At the end of the reaction, evaporate the ethanol by rotation to obtain the intermediate.

[0047] Step a2: Mix the intermediate, sodium methoxide, and tetrahydrofuran, heat under reflux for 1.2 h, then add the trichloroethyl phosphate dispersion and triethylamine, control the temperature at 70°C, and stir at 90 rpm for 6.5 h. The proportions of intermediate, trichloroethyl phosphate, sodium methoxide, triethylamine, and tetrahydrofuran are 0.1 mol: 75 mmol: 30 mmol: 10 mL: 70 mL. The trichloroethyl phosphate dispersion uses carbon tetrachloride as the dispersing solvent, with a volume fraction of 30% trichloroethyl phosphate. At the end of the reaction, evaporate the low-boiling compounds, mainly carbon tetrachloride and tetrahydrofuran, by swirling to obtain the coating agent.

[0048] Step a3: Pre-mix the base metal powder, coating agent, nonionic surfactant, and dimethylacetamide, then add the silver nitrate solution and stir for 40 min. Introduce nitrogen for protection, apply ultrasonic vibration at 25 kHz, slowly add the hydrated hydrazine solution, and react for 1.8 h. The base metal powder chosen is Brofos-Cu-800 copper powder, with an average particle diameter of 800 nm. The nonionic surfactant chosen is commercial Tween 80. The silver nitrate solution is a 10% aqueous solution by mass. The hydrated hydrazine solution is an industrial raw material at 40% by volume. The proportions of base metal powder, silver nitrate, hydrated hydrazine solution, coating agent, non-ionic surfactant and dimethylacetamide are 1g: 10.5g: 0.9mL: 0.5g: 0.28g: 45mL.At the end of the reaction, allow to stand for precipitation, remove the supernatant and dry to obtain the composite precursor.

[0049] Step a4: Place the composite precursor in a preheated nitrogen oven at 300°C, first heat at 600°C for 2.2h, then continue heating at 920°C for 1h, cool in the oven to room temperature, grind and disperse to obtain the silver seed powder.

[0050] (b) Preparation of the conductive paste

[0051] Formulation: Weigh the raw materials according to the percentages by weight, 85% by weight of seed silver powder, prepared in this example; 5% by weight of glass powder, using FD66A glass powder in the implementation process, with a melting point of approximately 700°C; 10% by weight of organic support, composed of dibutyl phthalate, ethylcellulose, xylene and terpineol in a mass ratio of 1:0.12:1:0.5.

[0052] Preparation of the paste: Mix the silver seed powder and glass powder at high speed in a high-speed mixer at 1000 rpm for 10 min, then add the organic support and grind in a grinder for 15 min, the resulting product is the conductive paste. Comparative example 1

[0053] This comparative example refers to embodiment 3, replacing the seed silver powder with spherical silver powder (selected from the raw material Brofos-Ag-W03, with an average particle diameter of 3qm), the rest of the implementation process being identical. Comparative example 2

[0054] This comparative example refers to embodiment 3, replacing the silver seed powder with the same weight proportion of silver-coated copper micropowder (selected from the raw material Brofos-CuAg30-W02, with a specific morphology: spherical, particle diameter of 2pm), the rest of the implementation process being identical.

[0055] Using a 156x156mm silicon wafer as a substrate, the conductive paste prepared as above is printed onto the surface, sintered, and subjected to photo-induced silver deposition to obtain a solar cell wafer. The initial resistivity p0 is measured using an SZT-B four-point tester. The solar cell wafer is placed in a variable-temperature chamber and subjected to a cyclic treatment from 0 to 70°C to simulate the actual operating temperature, with a single cycle time of 2h and a test period of 1000. Then, the resistivity after temperature variation pi is measured. A Berger tester is used to measure the initial conversion efficiency Eff0 and the conversion efficiency after temperature variation Effb. The specific test results are presented in Table 1: [Tables 1] Implementation Method 1 Implementation Method 2 Implementation Method 3 Comparative Example 1 Comparative Example 2 in / Q-cm1 3.35x106 3.82x106 3.69x106 3.07x106 4.12x106 ft / Q-cm1 3.61x106 4.19x106 3.88x106 3.91x106 5.39x106 Effo / % 26.61 26.54 26.57 26.69 26.24 Effj / % 26.29 26.14 26.30 26.14 25.59

[0056] According to the test results in Table 1, it can be seen that the initial resistivity of the solar cell wafers prepared with the conductive paste of the embodiment examples is slightly higher than that of comparative example 1, and the initial conversion efficiency is slightly lower than that of comparative example 1. However, compared to comparative example 2, the initial resistivity is significantly reduced, the photoelectric conversion efficiency is significantly improved, and the decrease in photoelectric conversion efficiency after the thermal cycle test is lower, which is favorable to maintaining the stability of the photovoltaic cells.

[0057] In the description in this document, references to "an embodiment," "example," "specific example," etc., indicate that the features, structures, materials, or specific characteristics described in relation to that embodiment or example are included in at least one embodiment or example of the present invention. In this document, the illustrative representations of the above terms do not necessarily refer to the same embodiments or examples. Furthermore, the features, structures, materials, or specific characteristics described may be appropriately combined in one or more embodiments or examples.

[0058] The above content is merely an example and illustration of the present invention. Technicians in the relevant technical field may make various modifications or additions to the specific embodiments described, or adopt similar replacement methods, provided they do not deviate from the invention or exceed the scope defined by the claims; all of this should fall within the scope of protection of the present invention.

Claims

Demands

1. Conductive paste based on seed silver powder, characterized in that it is composed of the following elements: 10-85% by weight of seed silver powder, 2-5% by weight of glass powder and 8-12% by weight of organic support, the remainder being spherical silver powder; said seed silver powder is prepared according to the following method: step a1: mix tri-allylamine, mercaptoethanol and ethanol, heat to 55-65°C and stir for activation for 20-30 min, then add the photoinitiator, mix and irradiate under UV at 200-300W / m2 for 2.5-311, at the end of the reaction, evaporate the ethanol by rotation to obtain the intermediate;step a2: mix the intermediate, sodium methoxide and tetrahydrofuran, heat under reflux for 1-1.311, then add the trichloroethyl phosphate dispersion and triethylamine, control the temperature at 60-70°C and stir for 5.5-711, at the end of the reaction, evaporate the low boiling point compounds by rotation to obtain the coating agent; step a3: premix the base metal powder, coating agent, nonionic surfactant and dimethylacetamide, then add the silver nitrate solution and stir for 30-40 min, introduce nitrogen for protection, slowly add the hydrated hydrazine solution under ultrasonic vibration and react for 1.5-211, at the end of the reaction, let stand for precipitation, remove the supernatant and dry to obtain the composite precursor;step a4: calcine the composite precursor under a nitrogen atmosphere first at 550-620°C for 1.8-2.4h, then continue heating at 880-920°C for 1-1.21h, cool in the oven to room temperature, grind and disperse to obtain the silver seed powder.

2. Conductive paste based on seed silver powder according to claim 1, characterized in that the proportions of intermediate, trichloroethyl phosphate, sodium methoxide, triethylamine and tetrahydrofuran are 0.1 mol: 70-85 mmol: 25-30 mmol: 8-12 mL: 55-75 mL.

3. Conductive paste based on seed silver powder according to claim 2, characterized in that the proportions of base metal powder, silver nitrate, hydrated hydrazine solution, coating agent, nonionic surfactant and dimethylacetamide are 1g: 3.8-14.2g: 0.8-1mL: 0.4-0.6g: 0.25-0.3g: 35-50mL, the volume fraction of the hydrated hydrazine solution being 40%.

4. Conductive paste based on seed silver powder according to claim 3, characterized in that the base metal powder is one of the powders of copper, nickel and iron, with an average particle diameter not exceeding Ipm.

5. Conductive paste based on seed silver powder according to claim 1, characterized in that the melting point of the glass powder is 600-700°C.

6. Conductive paste based on seed silver powder according to claim 1, characterized in that the average diameter of the spherical silver powder particles does not exceed 5qm.

7. A method for preparing conductive paste based on seed silver powder according to any one of claims 1 to 6, characterized in that the specific method consists of: premixing the seed silver powder, glass powder and spherical silver powder, then adding the organic support, grinding and preparing the paste to obtain the conductive paste.