Modification treatment method of glass powder for conductive paste

Abstract

The invention discloses a modification treatment method of glass powder for conductive paste. Glass powder with main components of PbO, SiO2 and ZnO is used as a raw material, a dielectric barrier discharge plasma auxiliary ball milling technology is used for carrying out ball milling treatment on the glass powder, then the treated glass powder is prepared into conductive paste, sintering is carried out, and a conductive silver film layer with good surface appearance is obtained. By adopting dielectric barrier discharge plasma to assist ball milling, the refining effect of the powder is greatly promoted, meanwhile, the surface activity of the powder is improved, a better silver film layer surface appearance is shown after sintering, the surface resistance of the sintered slurry is small, and the performance of the glass powder applied to the conductive slurry can be well improved.

Description

Technical Field

[0001] The invention belongs to the field of solar electricity technology, and in particular relates to a modification treatment method of glass powder for conductive paste. Background Art

[0002] As an inexhaustible renewable clean energy, solar energy has attracted more and more attention. Among the utilization of solar energy, crystalline silicon solar cells are currently the most widely used and most mature project. The conductive electrode of crystalline silicon solar cells is formed by printing and sintering conductive paste, in which the conductive paste is mainly composed of conductive phase, glass powder and organic carrier.

[0003] The conductive phase is mainly metal powders such as silver powder and copper powder, while glass powder is the bonding phase. The proportion of the bonding phase in the conductive paste is about 2%-5%. Although the content of glass powder is very small compared to the conductive phase silver powder, it plays a vital role. During the sintering process, the silver powder gradually softens due to heat, reacts with SiNx in the anti-reflection layer, opens the conductive channel, and enables the silver powder to contact the silicon substrate; secondly, it wets the silver powder and promotes the sintering of the silver powder, so that a dense conductive network is formed, and after cooling, the electrode will be tightly attached to the substrate.

[0004] In the application process of conductive slurry, the morphology, particle size distribution and thermal properties of glass powder will affect the quality of conductive electrode after sintering. The glass powder currently used is mainly prepared by melt-quenching method and sol-gel method, and then refined by ball milling. In the modification of glass powder, the main method is to change its performance by changing its original composition. Another method is to refine and modify it by simple mechanical ball milling. Mechanical ball milling has low efficiency and takes a long time to achieve the corresponding effect. It may also introduce certain impurities and other problems, and cannot meet the requirements of glass powder refinement and modification.

[0005] Existing literature (Sun Sheji, Influence of glass powder ball milling process on the performance of electronic slurry, Electronic Components and Materials, Issue 9, Volume 37) used different ball milling methods and ball milling process parameters to treat glass powder. The article adopted the method of rotary ball milling. According to the material-water ratio of 1:1 (mass ratio), the glass powder with suitable particle size and concentrated particle size distribution was obtained by ball milling at a rotation speed of 70r / min for 25h. This method uses rotary ball milling, which requires a long ball milling time. The average particle size of the powder after 60h of ball milling is 0.73μm, and the average particle size of the powder after 35h of ball milling is 1.165μm. The ball milling efficiency is relatively low, which is easy to cause powder contamination. In addition, the glass powder treated by this method has low activity, and the surface resistance of the slurry after sintering is large.

[0006] In order to solve this problem, the present invention provides a new method for ball milling and modifying glass powder for conductive slurry. The glass powder is modified by dielectric barrier discharge plasma assisted ball milling, which can greatly improve the efficiency of ball milling, thereby reducing the pollution generated during the ball milling process. In addition, the treatment of the powder surface by discharge plasma will also increase the surface activity of the powder, which helps the conductive slurry to form a dense conductive network after sintering. Summary of the invention

[0007] In view of the drawbacks of the prior art, the present invention provides a method for modifying glass powder for conductive paste. The present invention adopts a dielectric barrier plasma assisted ball milling method, which can greatly promote the refinement of glass powder and improve the surface activity, and further promote the sintering performance of the paste. The specific scheme of the present invention is as follows:

[0008] In a first aspect, the present invention provides a method for modifying glass powder for conductive paste, specifically a method for modifying glass powder by dielectric barrier discharge plasma assisted ball milling, comprising the following steps:

[0009] (1) Put grinding balls into a ball mill, weigh a certain amount of glass powder and put it into the ball mill, and then add a process control agent;

[0010] (2) The ball mill is sealed and evacuated to a vacuum state, and then filled with a certain discharge atmosphere, and discharge ball milling is performed using a dielectric barrier electrode made of polytetrafluoroethylene to obtain processed glass powder.

[0011] Preferably, the ball mill described in step (1) is made of stainless steel.

[0012] Preferably, the grinding balls in step (1) are stainless steel balls with a diameter of 3 to 7 mm.

[0013] Preferably, the main components of the glass powder in step (1) include PbO, SiO 2 、ZnO.

[0014] Preferably, the ratio of the mass of the grinding balls in the ball mill described in step (1) to the mass of the glass powder to be processed is 10:1 to 100:1.

[0015] Preferably, the process control agent in step (1) is one of anhydrous ethanol, liquid paraffin and deionized water, and the added amount is 2-5wt% of the glass powder.

[0016] Preferably, the discharge atmosphere in step (2) is argon, and the gas pressure in the ball mill is 0.01-0.1 MPa.

[0017] Preferably, the dielectric barrier layer of the electrode rod in step (2) is made of polytetrafluoroethylene and has a thickness of 3 to 5 mm.

[0018] Preferably, in the ball milling process described in step (2), a plasma ball mill is used, the ball mill is sealed and evacuated to a pressure of ≤10Pa, argon is filled to a pressure of 0.02MPa, and a polytetrafluoroethylene dielectric barrier electrode is used for discharge ball milling, wherein the thickness of the polytetrafluoroethylene electrode is 1-3mm, the speed of the ball mill is 960-1330rpm, the discharge voltage is 12-15KV, the pulse current frequency is 9.8-11.0KHz, the ball-to-material ratio is 10:1-100:1, the ball milling time is 2h-8h, the peak-to-peak amplitude of the grinding ball is 10mm-13mm, and the vibration gravity acceleration is 8g-15g, to obtain the modified glass powder.

[0019] In a second aspect, the present invention also provides a glass powder obtained by the above modification method. The glass powder has a D50 particle size of 0.5-2 μm and a specific surface area of ​​≥2.5 m 2 / g, and the surface resistance of the silver film layer after sintering at 750℃ is less than 3mΩ / sq.

[0020] In a third aspect, the present invention further provides an application of the glass powder obtained by the above-mentioned modification method in a conductive paste, wherein the application comprises the following steps:

[0021] The glass powder after dielectric barrier discharge plasma assisted ball milling is mixed with conductive metal powder and organic carrier in a mass ratio of 2-5:78-80:15-20 to prepare conductive metal slurry, which is then printed on a silicon wafer by screen printing technology and then sintered. The sintering process is as follows: heating from room temperature to 200-300°C at a heating rate of 5-10K / min, then keeping the temperature for 10-30min to remove the organic carrier; then heating to 650-800°C at a heating rate of 5-15K / min, keeping the temperature at this temperature for 10-30min, and then cooling to room temperature with the furnace to obtain a sintered conductive metal film layer.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0023] (1) The dielectric barrier discharge plasma assisted ball milling technology provided by the present invention is a new material processing method that combines cold field plasma technology and traditional ball milling technology. By introducing cold field plasma during the ball milling process, the plasma will generate high-frequency impact on the powder surface during the ball milling process, so that the surface activity of the powder is improved, and the particle bombardment of the plasma will cause the powder to produce greater internal stress, thereby promoting the refinement of the powder. Compared with ordinary ball milling, the dielectric barrier discharge plasma assisted ball milling technology, in addition to the input of mechanical force, also has the high-energy particle bombardment effect and temperature effect generated by the cold field plasma. The bombardment effect of high-energy particles will cause the powder surface to be frequently impacted, thereby promoting the refinement of the powder, improving the ball milling efficiency, reducing the ball milling time and reducing the pollution during the ball milling process; at the same time, the high-energy particles in the plasma will generate a large thermal effect when interacting with the powder, thereby improving the activity of the powder. Using this technology, a powder with extremely small particle size (average particle size of 0.424μm) can be obtained in about 6 hours of ball milling, which has great advantages over the ordinary ball milling that requires 12 hours or longer working time.

[0024] (2) The surface resistance of the modified glass powder obtained by the method provided by the present invention after sintering in conductive silver paste is 3.262mΩ / sq, while the surface resistance of the original powder and the glass powder after ordinary mechanical ball milling in conductive silver paste is 3.925mΩ / sq and 3.471mΩ / sq respectively, indicating that the glass powder treated by the method of the present invention has better application performance in conductive paste. For example, promoting powder refinement: mechanical crushing and plasma activation work together to reduce the D50 particle size of the glass powder from the original 4-5μm to 0.5-2μm, and the specific surface area is increased to ≥2.5m 2 / g (BET test), significantly improving the sintering activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention and the technical solutions in the prior art, the following briefly introduces the drawings required to be used in the embodiments or the description of the prior art.

[0026] Figure 1 This is a morphology diagram of the glass powder modified by dielectric barrier discharge plasma assisted ball milling in Example 1.

[0027] Figure 2 This is a morphology diagram of the glass powder modified by dielectric barrier discharge plasma assisted ball milling in Example 2.

[0028] Figure 3 This is a morphology diagram of the glass powder modified by dielectric barrier discharge plasma assisted ball milling in Example 3.

[0029] Figure 4This is a morphology diagram of the glass powder modified by dielectric barrier discharge plasma assisted ball milling in Example 4.

[0030] Figure 5 This is a morphology diagram of the glass powder modified by dielectric barrier discharge plasma assisted ball milling in Example 5.

[0031] Figure 6 This is a morphology diagram of the glass powder modified by dielectric barrier discharge plasma assisted ball milling in Example 6.

[0032] Figure 7 This is a morphology diagram of the glass powder modified by dielectric barrier discharge plasma assisted ball milling in Example 7.

[0033] Figure 8 This is a morphology diagram of the glass powder modified by dielectric barrier discharge plasma assisted ball milling in Example 8.

[0034] Fig. 9 This is a morphology diagram of the glass powder modified by dielectric barrier discharge plasma assisted ball milling in Example 9.

[0035] Fig.10 This is a morphology picture of the conductive paste obtained by using the glass powder of Example 7 after sintering in Example 10.

[0036] Fig.11 This is the morphology of the glass powder prepared by ordinary ball milling in Comparative Example 1.

[0037] Fig.12 This is the morphology of the original glass powder of Comparative Example 2.

[0038] Fig.13 This is the morphology of the conductive paste obtained by using the original glass powder after sintering in Comparative Example 3.

[0039] Fig.14 This is a morphology picture of the conductive paste obtained by comparative example 4 using the glass powder of comparative example 1 after sintering. DETAILED DESCRIPTION

[0040] The present invention will be further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

[0041] In the following examples, the plasma discharge atmosphere is argon, the grinding balls are stainless steel grinding balls with a diameter of 5 mm, the tank body is a stainless steel tank, the total volume of the grinding balls accounts for 30% to 50% of the volume of the ball mill tank, the ball-to-material ratio of the ball mill is 10:1 to 100:1, the discharge voltage is 15KV, the frequency of the pulse current is 10KHz, the peak-to-peak amplitude of the grinding balls is 10mm-13mm, and the gravity acceleration of the grinding ball vibration is 8g-15g.

[0042] In the following embodiments, the test method for the powder particle size parameters D10, D50, and D90 involved is: taking a certain amount of the glass powder to be tested and adding it to an alcohol solution, then ultrasonically dispersing it to completely dissolve the powder, and then testing it using a laser particle size analyzer; the specific surface area (BET) test method uses nitrogen for adsorption and desorption experiments.

[0043] Example 1

[0044] Use an electronic balance to weigh 50g of original glass powder, and then add it to a ball mill containing 500g of stainless steel grinding balls to make a ball-to-material ratio of 10:1, then add 5% (powder mass percentage) of anhydrous ethanol as a control agent and seal the ball mill; evacuate the sealed ball mill, and then fill it with 0.02MPa of argon for plasma ball milling (dielectric barrier discharge plasma-assisted ball milling). The electrode rod has a polytetrafluoroethylene dielectric barrier layer with a thickness of 3mm. The ball mill speed is 1330rpm and the ball milling time is 3h. The discharge voltage during the ball milling process is 15KV, and the frequency of the pulse current is 10KHz. The morphology of the glass powder after this process is as shown below. Figure 1 The particle size distribution data and BET test results of the powder are shown in Table 1.

[0045] Example 2

[0046] The steps of this embodiment are basically the same as those of embodiment 1, except that the mass of the grinding balls added in step (1) is 2.5 kg, and the ball-to-material ratio is 50:1. The morphology of the glass powder after the process is shown in FIG. Figure 2 The particle size distribution data and BET test results of the powder are shown in Table 1.

[0047] Example 3

[0048] The steps of this embodiment are basically the same as those of embodiment 1, except that the mass of the grinding balls added in step (1) is 5 kg, and the ball-to-material ratio is 100:1. The morphology of the glass powder after the process is shown in FIG. Figure 3 The particle size distribution data and BET test results of the powder are shown in Table 1.

[0049] Depend on Figure 1 to Figure 3 As you can see, Figure 1 The average particle size distribution of the powder is 0.978 μm. Figure 2 0.541μm, Figure 3 The average particle size of the powder is 0.425 μm. With the increase of the ball-to-material ratio, the average particle size of the powder gradually decreases. Figure 1 There are many large particles in Figure 2 and Figure 3 The number of medium and large particles decreases, and Figure 3 The particle size of medium and large particles also decreased significantly.

[0050] Example 4

[0051] The steps of this embodiment are basically the same as those of embodiment 2, except that the ball milling time in step (2) is 2 hours. The morphology of the glass powder after the process is as follows: Figure 4 The particle size distribution data and BET test results of the powder are shown in Table 1.

[0052] Example 5

[0053] The steps of this embodiment are basically the same as those of embodiment 2, except that the ball milling time in step (2) is 4 hours. The morphology of the glass powder after the process is shown in FIG. Figure 5 The particle size distribution data and BET test results of the powder are shown in Table 1.

[0054] Example 6

[0055] The steps of this embodiment are basically the same as those of embodiment 2, except that the ball milling time in step (2) is 5 hours. The morphology of the glass powder after the process is as follows: Figure 6 The particle size distribution data and BET test results of the powder are shown in Table 1.

[0056] Example 7

[0057] The steps of this embodiment are basically the same as those of embodiment 2, except that the ball milling time in step (2) is 6 hours. The morphology of the glass powder after the process is as follows: Figure 7 The particle size distribution data and BET test results of the powder are shown in Table 1.

[0058] Example 8

[0059] The steps of this embodiment are basically the same as those of embodiment 2, except that the ball milling time in step (2) is 7 hours. The morphology of the glass powder after the process is as follows: Figure 8 The particle size distribution data and BET test results of the powder are shown in Table 1.

[0060] Example 9

[0061] The steps of this embodiment are basically the same as those of embodiment 2, except that the ball milling time in step (2) is 8 hours. The morphology of the glass powder after the process is as follows: Fig. 9 The particle size distribution data and BET test results of the powder are shown in Table 1.

[0062] Depend on Figures 4 to 9It can be seen that the powder presents a distribution state of large and small particles. The average particle sizes of the glass powders of Examples 4 to 9 are 1.566μm, 1.182μm, 1.053μm, 0.484μm, 1.298μm, and 0.912μm, respectively. With the increase of ball milling time, the distribution of powder particle size changes dynamically, showing a trend of first decreasing and then increasing. In the early stage of ball milling, the powder particles are continuously impacted by mechanical energy and plasma with the increase of time, and the large particles are broken and refined significantly. However, after a certain time, the small-sized particles will be adsorbed and agglomerated together due to the increase of surface energy to form particles with larger particle size. Therefore, a suitable ball milling time is used to obtain a powder with a good particle size distribution.

[0063] Example 10

[0064] The glass powder obtained in Example 7 and silver powder, organic carrier (containing 60wt% pineol, 30wt% diethylene glycol butyl ether acetate, 5wt% silane coupling agent, 5wt% ethyl cellulose) were mixed in a mass ratio of 5:80:15 to prepare a conductive silver paste, and then the paste was printed on a silicon wafer by screen printing, and sintered according to the following process: the temperature was increased from room temperature to 200°C at a heating rate of 10K / min, and then the organic carrier was removed by keeping the temperature for 30 minutes; then the temperature was increased to 750°C at a heating rate of 10K / min, and the temperature was kept at this temperature for 10 minutes and then cooled to room temperature with the furnace. The morphology of the sintered silver film layer obtained by this process is as follows: Fig.10 As shown. Fig.10 It can be seen that the silver film layer after sintering has a very high density, the silver particles can form good contact with each other, and are evenly distributed without defects such as pores. The surface resistance of the conductive silver paste of Example 10 after sintering is 3.262 mΩ / sq.

[0065] Comparative Example 1

[0066] The steps of this comparative example are basically the same as those of Example 7, except that the ball milling method is ordinary ball milling, that is, no discharge treatment is performed during the ball milling process. The morphology of the glass powder after this process is shown in FIG. Fig.11 The particle size distribution data and BET test results of the powder are shown in Table 1. Figure 7 In comparison, this comparative example ( Fig.11 ) The particle size distribution of glass powder prepared by ordinary ball milling method is poor, with an average particle size distribution of 2.073μm. Fig.11 It can be seen that there are many unbroken particles with large particle sizes, and the powder agglomeration phenomenon is serious, which shows that the ordinary ball mill is obviously weaker in the powder refinement effect than the dielectric barrier discharge plasma ball mill.

[0067] Comparative Example 2

[0068] The comparative example uses the original glass powder without any treatment. The morphology of the original glass powder is as follows: Fig.12 The particle size distribution data and BET test results of the powder are shown in Table 1. Figure 7 In comparison, this comparative example ( Fig.12 ) The original glass powder particles are very unevenly distributed, and are basically large irregular particles with an average particle size of 4.023μm. This shows that the use of dielectric barrier discharge plasma ball milling can effectively promote the refinement of the powder, and large block particles can be significantly broken up in a relatively short time, reducing the particle size of the powder.

[0069] Comparative Example 3

[0070] The steps of this comparative example are basically the same as those of Example 10, except that the conductive paste is prepared using untreated raw powder. The morphology of the sintered silver film obtained by this process is as follows: Fig.13 As shown. Fig.13 It can be seen that the overall morphology of the silver film layer is well distributed, and the silver particles are in contact with each other, but there are many voids, which interrupts the connection between the silver particles. Fig.10 In contrast, Fig.13 The density of the silver film layer is reduced, and there are more defects such as voids, which is not conducive to forming a good conductive network. This shows that the sintering activity of the powder after plasma ball milling is greatly improved, which can effectively promote the sintering of silver powder and make the silver particles form a dense contact. The surface resistance of the conductive silver paste of Comparative Example 3 after sintering is 3.925mΩ / sq.

[0071] Comparative Example 4

[0072] The steps of this comparative example are basically the same as those of Example 10, except that the conductive paste is prepared using the glass powder processed in Comparative Example 1. The morphology of the sintered silver film obtained by this process is as follows: Fig.14 As shown. Fig.14 It can be seen that the silver particles are well sintered and can form contact with each other, but there are many defects such as voids and pores. Fig.10 In contrast, Fig.14 The density of the silver film layer is relatively low, and there are many sintering defects, which is not conducive to the formation of a complete conductive path between the silver particles. This is caused by the large powder particles and uneven particle size distribution. The surface resistance of the conductive silver paste of Comparative Example 4 after sintering is 3.471mΩ / sq.

[0073] The particle size distribution data of the glass powders after treatment in the above embodiments and comparative examples are shown in Table 1.

[0074] Table 1 Particle size distribution data of glass powder after treatment in different embodiments

[0075]

[0076] From the data in Table 1, it can be seen that the average particle size of the original powder is relatively large, and after plasma ball milling under different ball milling parameters, the particle size of the powder has been reduced to a certain extent. Although the particle size of the powder has also been reduced to a certain extent after ordinary ball milling, the refinement effect is not as good as plasma ball milling. Combined with the surface resistance data of the conductive silver paste, compared with the non-ball milling or ordinary ball milling method, the dielectric barrier discharge plasma assisted ball milling has a lower resistance, indicating that the glass powder after plasma ball milling is more active, which can promote the sintering of silver powder during the sintering process, so that the silver particles form a closer contact, which is conducive to the transmission of current.

[0077] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for modifying glass powder for conductive paste, characterized in that: The following steps are involved: (1) Put grinding balls into a ball mill, weigh glass powder and put it into the ball mill, and then add a process control agent; (2) The ball mill jar is sealed and evacuated to a vacuum state, filled with a discharge atmosphere, and discharge ball milling is performed using an electrode rod with a polytetrafluoroethylene material as a dielectric barrier layer to obtain a modified glass powder.

2. The method for modifying glass powder for conductive paste according to claim 1, characterized in that: The ball mill described in step (1) is made of stainless steel, and the grinding balls used are stainless steel balls with a diameter of 3 mm to 7 mm.

3. The method for modifying glass powder for conductive paste according to claim 1, characterized in that: The main components of the glass powder described in step (1) include PbO, SiO2, and ZnO.

4. The method for modifying glass powder for conductive paste according to claim 1, characterized in that: The process control agent in step (1) is one of anhydrous ethanol, liquid paraffin and deionized water, and the added amount is 2-5wt% of the glass powder.

5. The method for modifying glass powder for conductive paste according to claim 1, characterized in that: The discharge atmosphere in step (2) is argon, and the gas pressure in the ball mill is 0.01-0.1 MPa.

6. The method for modifying glass powder for conductive paste according to claim 1, characterized in that: The material of the dielectric barrier layer of the electrode rod described in step (2) is polytetrafluoroethylene and has a thickness of 3 to 5 mm.

7. The method for modifying glass powder for conductive paste according to claim 1, characterized in that: The ball milling process described in step (2) adopts a plasma ball mill, seals the ball mill jar and evacuates it to a pressure of ≤10Pa, fills it with argon gas to a pressure of 0.02MPa, and uses a polytetrafluoroethylene dielectric barrier electrode for discharge ball milling. The thickness of the polytetrafluoroethylene electrode is 1-3mm, the speed of the ball mill is 960-1330rpm, the discharge voltage is 12-15KV, the pulse current frequency is 9.8-11.0KHz, the ball-to-material ratio is 10:1-100:1, the ball milling time is 2h-8h, the peak-to-peak amplitude of the grinding ball is 10mm-13mm, and the vibration gravity acceleration is 8g-15g to obtain the modified glass powder.

8. The glass powder obtained by the modification treatment method of a glass powder for conductive paste according to any one of claims 1 to 7, characterized in that: The glass powder has a D50 particle size of 0.5-2 μm and a specific surface area of ​​≥2.5 m 2 / g, and the surface resistance of the silver film layer after sintering at 750℃ is less than 3mΩ / sq.

9. Use of the glass powder obtained by the modification treatment method of glass powder for conductive paste according to claim 8 in conductive paste.

10. The use according to claim 9, characterized in that: The following steps are involved: The glass powder, conductive metal powder and organic carrier are prepared into a conductive metal slurry in a mass ratio of 2-5:78-80:15-20, and then printed onto a silicon wafer by screen printing technology, and then sintered. The sintering process is: heating from room temperature to 200-300°C at a heating rate of 5-10K / min, and then keeping warm for 10-30min to remove the organic carrier; then heating to 650-800°C at a heating rate of 5-15K / min, keeping warm at this temperature for 10-30min, and then cooling to room temperature with the furnace to obtain a sintered conductive metal film layer.

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