Plate-adhesive-free crystal bonding method for silicon wafer cutting and application of plate-adhesive-free crystal bonding method

Abstract

The invention provides a plate-adhesive-free crystal bonding method for silicon wafer cutting and application, and relates to the technical field of solar cells. Specifically, the method comprises the following steps: preparing a steel crystal support and a plastic plate; wherein a plurality of groove structures are arranged on the single-side surface of the steel crystal support, and a plurality of tooth structures matched with the groove structures are arranged on the single-side surface of the plastic plate; the steel crystal support and the plastic plate are assembled, so that the groove structure and the tooth structure are connected in an embedded mode; and ultrasonic welding is conducted at the embedded position, the groove structure is completely filled with the molten tooth structure, and the steel crystal support-plastic plate composite part without plate glue is obtained. The invention provides a novel process method which does not contain an adhesive component aiming at a crystal bonding process before cutting a silicon wafer in a solar cell, can effectively solve the problems of adhesive during bonding, adhesive residue after cutting, environmental pollution, harm to human bodies and the like caused by a traditional adhesive, and has a good application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of solar cells, and in particular to a plate-free adhesive wafer bonding method for silicon wafer cutting and an application thereof. Background Art

[0002] The silicon wafer in the solar cell is the most important core component. Its quality is related to the power generation efficiency. Similarly, its price accounts for a large share of the photovoltaic module. The production process of silicon wafers in solar cells usually includes bonding, slicing, degumming, cleaning, sorting and packaging. Specifically, bonding refers to the process of bonding silicon materials (such as silicon ingots, silicon rods, silicon cubes, etc.) with the crystal tray for cutting; slicing is the process of cutting silicon materials into thin slices. Thinner silicon wafers can convert solar energy into electrical energy faster, thereby improving energy conversion efficiency; degumming is to separate the cut silicon wafers from the crystal tray, and then perform post-processing operations such as cleaning and sorting.

[0003] At present, the photovoltaic industry mainly uses adhesives and plastic plates as bonding media between steel crystal trays and silicon materials at the slicing / bonding end; the adhesive mainly uses an epoxy resin system, which is divided into two components A and B (usually an epoxy resin component and a curing agent component). After mixing these two components, they can be quickly cured. It has the advantages of rapid reaction, short curing time, high adhesion after complete curing, and very little plastic plate falling off during the cutting process, ensuring a firm connection between the steel crystal tray and the silicon material. The specific operation process includes: first, the plastic plate and the steel crystal tray are bonded with adhesive, and then the silicon material is bonded to the plastic plate; after the above two epoxy resin adhesives are completely cured, the high-quality silicon material can be firmly suspended on the crystal tray without falling off or shaking, and then transferred to the slicing machine for cutting to obtain thousands of micron-thick silicon wafers.

[0004] The existing epoxy resin adhesive system bonding method has an environmental problem. On the one hand, epoxy resin is not easy to decompose and lasts for a long time in the natural environment, which is easy to damage the environment. On the other hand, in order to meet the demand for rapid curing, the curing agent used in the epoxy resin system is generally a polythiol curing agent, which has a strong pungent odor, especially after heating. Operators are more sensitive to it. On the other hand, because the epoxy resin adhesive component is a fluid, it is easy to cause empty glue when the plastic plate is combined with the crystal tray, and there is a risk of falling off during the cutting process. Finally, when the plastic plate is separated from the crystal tray after slicing, there are many residues of the cured adhesive on the crystal tray, and the manual intervention and labor intensity are high.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The first object of the present invention is to provide a plate-free adhesive crystal bonding method for silicon wafer cutting, mainly used to solve the four major technical defects of traditional adhesives (mainly epoxy resin adhesive systems) when used for bonding between crystal carriers and plastic plates, including voids in bonding, residual glue after cutting, environmental unfriendliness, and harm to the human body.

[0007] The second object of the present invention is to provide a method for preparing silicon wafers for solar cells.

[0008] In order to achieve the above objects of the present invention, the following technical solutions are specifically adopted:

[0009] A plate-free adhesive crystal bonding method for silicon wafer cutting, comprising the following steps:

[0010] Prepare a steel crystal carrier and a plastic plate; wherein, a plurality of groove structures are arranged on one side surface of the steel crystal carrier, and a plurality of tooth structures matching with the groove structures are arranged on one side surface of the plastic plate;

[0011] Assemble the steel crystal carrier and the plastic plate, so that the groove structures and the tooth structures are fitted and connected; perform ultrasonic welding at the fitting part, so that the melted tooth structures completely fill into the groove structures, and obtain a plate-free adhesive steel crystal carrier - plastic plate composite.

[0012] A method for preparing a silicon wafer for a solar cell, comprising the plate-free adhesive crystal bonding method for silicon wafer cutting described above.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] The present invention provides a plate-free adhesive crystal bonding method for silicon wafer cutting. Since no adhesives are used, it effectively reduces environmental pollution and harm to the health of operators, and reduces the cost of adhesives. The crystal bonding method of the present invention can stably achieve the connection between the plastic plate and the crystal carrier, and will not have the defect of unstable connection caused by voids in the glue, thereby effectively avoiding the risk of rod dropping. Further, after the silicon wafer is obtained by subsequent cutting, the crystal carrier and the plastic plate can be separated more efficiently, improving the separation and turnover efficiency of the crystal carrier and avoiding the problem of difficult removal of residual glue. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0016] Figure 1Schematic diagram of a plastic plate - steel crystal carrier according to an embodiment of the present invention is provided. Detailed implementation manners

[0017] The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific implementation manners. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0018] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0019] The first aspect of the present invention lies in providing a plate - free adhesive crystal method for silicon wafer cutting.

[0020] Prepare a steel crystal carrier and a plastic plate; wherein, a plurality of groove structures are provided on one side surface of the steel crystal carrier, and a plurality of tooth structures matching the groove structures are provided on one side surface of the plastic plate; assemble the steel crystal carrier and the plastic plate so that the groove structures and the tooth structures are engaged and connected; perform ultrasonic welding at the engagement to make the melted tooth structures completely fill into the groove structures to obtain a steel crystal carrier - plastic plate composite with plate - free adhesive.

[0021] In a preferred implementation manner, there is a preferred shape design for the shapes of the groove structures and the tooth structures in the present invention to ensure that when bonding high - quality silicon materials on the other side of the plastic plate, the engaged structure has good load - bearing performance and stability.

[0022] As a preferred implementation manner, the cross - section of the groove structure in the thickness direction of the steel crystal carrier presents a trapezoid (more preferably an isosceles trapezoid); and it can be understood that the upper base of the trapezoid is located on the surface of the steel crystal carrier, and the lower base of the trapezoid is located inside the steel crystal carrier.

[0023] Further, as the tooth structure that cooperates with the groove structure: the tooth structure also presents a trapezoid (more preferably an isosceles trapezoid) in the cross-section in the thickness direction of the plastic plate; and it can be understood that the plastic plate can be understood as a cuboid plate, and a convex structure integrally formed based on the surface of the plate is used as the tooth structure; for the tooth structure, the upper base of the trapezoid is located on the surface of the cuboid plate, and the lower base of the trapezoid protrudes from the cuboid plate.

[0024] To ensure that the fitting structure has good load-bearing performance and stability, the structural parameters of the fitting structure are further designed as follows. It should be noted that for any one of the groove structure and the tooth structure, the cross-section in its thickness direction is the same.

[0025] As a more preferred embodiment, for the groove structure and / or the tooth structure, the difference in side lengths between the upper base and the lower base of the trapezoidal cross-section ≥ 20 mm. When further preferred, the difference in side lengths between the upper base and the lower base of the trapezoidal cross-section is 25 mm - 35 mm.

[0026] As a more preferred embodiment, for the groove structure and / or the tooth structure, the height of the trapezoidal cross-section > 3.5 mm. When further preferred, the height of the trapezoidal cross-section is 3.6 mm - 8 mm.

[0027] As a further preferred embodiment, for the groove structure and / or the tooth structure, the length of the upper base of the trapezoidal cross-section is 60 mm - 90 mm, and the length of the lower base of the trapezoidal cross-section is 90 mm - 120 mm.

[0028] As a further preferred embodiment, for the groove structure and / or the tooth structure, when the trapezoidal interface is an isosceles trapezoid, the waist length of the isosceles trapezoid is 10 mm - 25 mm.

[0029] Although it is defined in the present invention that the tooth structure on the plastic plate cooperates with the groove structure on the steel crystal holder, considering that the tooth structure of the plastic plate needs to be inserted into the groove structure in the lateral direction during the assembly process, if the shapes of the two structures are exactly the same, extremely high frictional force needs to be overcome, greatly increasing the difficulty of assembly; and any uneven configuration on the surface of the structure may lead to the failure of assembly. Therefore, the structural parameters of the fitting structure are further designed as follows in the present invention.

[0030] As a more preferred embodiment, taking the trapezoid presented by the cross-section of the groove structure in the thickness direction of the steel crystal holder as the first trapezoid, and taking the trapezoid presented by the cross-section of the tooth structure in the thickness direction of the plastic plate as the second trapezoid, the following relationship is satisfied between the two trapezoids:

[0031] (a) The difference in length between the lower base of the first trapezoid and the lower base of the second trapezoid is 0.5 mm to 3 mm;

[0032] (b) The difference in length between the upper base of the first trapezoid and the upper base of the second trapezoid is 0.5 mm to 3 mm;

[0033] (c) In a certain embodiment, the length differences involved in features (a) and (b) are the same;

[0034] (d) The difference in height between the first trapezoid and the second trapezoid is 0.3 mm to 1.5 mm.

[0035] It should be added that for the above features (a), (b), and (d), any difference is the corresponding parameter of the first trapezoid minus the second trapezoid, that is, the outer shape of the first trapezoid is larger than that of the second trapezoid. Since the weight of the steel crystal holder is much higher than that of the plastic plate, the above design can also facilitate the adaptive assembly between the two.

[0036] Based on the differential design between the above trapezoids, on the one hand, it can ensure that the plastic plate can be smoothly inserted into the steel crystal holder from the side before welding, and on the other hand, it can ensure that there is no gap between the two after ultrasonic welding, having excellent joint strength.

[0037] In addition, in a preferred embodiment, the present invention also designs the forming method, arrangement, and quantity of the groove structure and the tooth structure; mainly considering that the steel crystal holder - plastic plate composite without glue plays a role in fixing and suspending the silicon material in the subsequent silicon wafer slicing process, and the silicon material before cutting is usually very heavy. Taking the silicon rod used in a certain production line as an example, the weight is as high as 65 kg; therefore, as the fitting structure between the steel crystal holder and the plastic plate, it needs to have considerable reliability in terms of connection performance and layout.

[0038] As a preferred embodiment, the groove structure is integrally formed based on the steel crystal holder, and the tooth structure is also integrally formed based on the plastic plate.

[0039] As a preferred embodiment, the length and width of the steel crystal holder and the plastic plate are the same; and the groove structure on the surface of the steel crystal holder corresponds to the tooth structure on the surface of the plastic plate one by one.

[0040] As a preferred embodiment, the direction of the groove structure is parallel to the width direction of the steel crystal holder, and the length of the groove structure is the same as the width of the steel crystal holder; similarly, the direction of the tooth structure is parallel to the width direction of the plastic plate, and the length of the tooth structure is the same as the width of the plastic plate.

[0041] As a more preferred embodiment, the groove structures are evenly distributed in the length direction of the steel crystal holder; similarly, the tooth structures are evenly distributed in the length direction of the plastic plate.

[0042] As a further preferred embodiment, taking the center points of the groove structures and / or the tooth structures into account, the distance between any two adjacent groove structures and / or tooth structures ≤ 360 mm, and more preferably, the distance is 240 mm to 320 mm.

[0043] As a more preferred embodiment, taking the center points of the groove structures and / or the tooth structures into account, for the groove structures near the edge of the steel crystal holder, the distance between the groove structures and the edge is 65 mm to 85 mm; similarly, for the tooth structures near the edge of the plastic plate, the distance between the tooth structures and the edge is 65 mm to 85 mm.

[0044] Thus, the distance between the fitting part and the edges of the steel crystal holder and the plastic plate is relatively small, and the distance between adjacent structures should not be too large; on the one hand, it avoids the deformation of the plastic plate due to the quality of the silicon material in this margin, and on the other hand, it also avoids the warping of the edge parts of the two during the suspension of the silicon material, which has a negative impact on cutting.

[0045] As an alternative embodiment, those skilled in the art can adaptively adjust the number of the groove structures and the tooth structures based on the above-mentioned limitation of the distance parameters in combination with the length and width of the steel crystal holder and the plastic plate.

[0046] The ultrasonic welding is to convert the low-frequency (50 / 60 Hz) current into high-frequency (10 - 40 KHz) electrical energy by an ultrasonic generator. The converted high-frequency electrical energy is converted into mechanical motion of the same frequency again by a transducer; the mechanical motion is transmitted to the welding head through a horn that can change the amplitude, and then transmitted from the welding head to the joint part of the workpiece to be welded, and the vibrational mechanical energy is converted into heat energy by friction to melt the workpiece to be welded.

[0047] In the present invention, the increasingly mature ultrasonic welding method in the current welding field is cited to achieve the bonding between the plastic plate and the steel crystal holder, replacing the epoxy resin adhesive system used in the past. Generally speaking, the ultrasonic welding method utilizes high-frequency vibration waves to be transmitted to the surfaces of two welded objects. Under the condition of applying pressure, the surfaces of the two objects rub against each other, and the contact surfaces melt due to high temperature, thereby forming the fusion between the molecular layers of the materials. However, for the actual situation of the present invention, the plastic plate is a disposable item for the crystal bonding / cutting process, while the steel crystal holder can be reused multiple times, and the melting point of the steel crystal holder is much higher than that of the plastic plate. The method of melting and welding the two is impractical. Therefore, in the present invention, by designing a specific groove / tooth fitting structure, through the ultrasonic welding, a part of the plastic plate melts and fills into the groove structure. After cooling, the plastic solidifies again and forms a stable connection between the steel crystal holder and the plastic plate.

[0048] As a preferred embodiment, the "ultrasonic welding at the fitting part" includes the following steps: Place the steel crystal holder and the plastic plate with a fitting connection on the ultrasonic welding seat (the plastic plate is placed upward), and under the condition of applying external pressure to the fitting part, perform ultrasonic welding treatment on each fitting part with an ultrasonic welding head respectively; Further, the ultrasonic welding head can be fixed, and the steel crystal holder and the plastic plate with a fitting connection can be moved at a specific speed and time to achieve welding, or the steel crystal holder and the plastic plate with a fitting connection can be fixed, and the ultrasonic welding head can be moved at a specific speed and time to achieve welding. Those skilled in the art can make an adaptive selection according to the actual situation of the ultrasonic welding equipment.

[0049] It can be understood that after completing the ultrasonic welding and obtaining the steel crystal holder-plastic plate composite, those skilled in the art can transfer it to the sticking glue place to bond the silicon material and fix it on one side of the plastic plate; after completing the loading of the silicon material, transfer it to the cutting equipment again to officially cut the silicon material to obtain the silicon wafer for solar cells.

[0050] As a preferred embodiment, the ultrasonic welding includes the following parameters:

[0051] (1) The frequency is 15 kHz to 30 kHz, and the amplitude is 30 μm to 50 μm;

[0052] (2) The pressure is 0.8 MPa to 2 MPa, the pressure holding time is 0.3 s to 0.8 s, and the downward pressing speed is 1 mm / s to 4 mm / s;

[0053] (3) The welding time is 0.8 s to 2 s, and the delay time is 0.2 s to 0.5 s (the delay time is the time from starting the ultrasonic switch to emitting ultrasonic waves).

[0054] The second aspect of the present invention lies in providing a method for preparing a silicon wafer for a solar cell, including the plate-free adhesive crystal method for silicon wafer cutting as described in the first aspect. It can be understood that, in addition to covering the plate-free adhesive crystal method for silicon wafer cutting as described in the first aspect, the preparation method of the present invention should also include conventional or unconventional processes such as silicon material preparation, slicing, post-treatment, sorting and packaging, etc. And the above-mentioned processes involved can also be implemented in conventional or unconventional ways. In the present invention, no restrictions are imposed on the complete process of the preparation method. It can be understood that when including the plate-free adhesive crystal method for silicon wafer cutting, any feasible method for preparing a silicon wafer for a solar cell can be used as an implementation manner of the present invention.

[0055] Examples

[0056] As Figure 1 shown, a schematic structural diagram of the plastic plate - steel crystal carrier on the raw material side of this example is provided. It should be emphasized that, as Figure 1 shown, specific dimensions have been designed. For the sake of the intuitiveness and clarity of the drawing, Figure 1 the corresponding parameters of the structural dimensions represented are based on numbers, and the length of the line does not imply or guide the actual length of this example in any way.

[0057] In this example, the size of the plastic plate used is length * width * height = 850 mm * 181 mm * 10 mm; the size of the steel crystal carrier is length * width * height = 850 mm * 181 mm * 25 mm. The length and width dimensions of the plastic plate and the crystal carrier are the same, and the fitting parts of the two need to correspond one by one, and there are four fitting parts between the plastic plate and the steel crystal carrier respectively.

[0058] For the crystal carrier, the distance between the lower bottom edge of the trapezoidal cross-section corresponding to the two outermost depressions on both sides and the edge of the crystal carrier is 24 mm, and the same applies to the plastic plate.

[0059] For the crystal carrier, the central points of the four depressions are located at 75 mm, 308.3 mm, 541.6 mm, and 774.9 mm in the length direction of the crystal carrier respectively, and the same applies to the plastic plate.

[0060] For each depression structure of the crystal carrier and the tooth structure of the plastic plate, their dimensions are marked in Figure 1 . Among them, taking the trapezoid in the lateral cross-section, the lower bottom edge length of the depression structure is 102 mm, the upper bottom edge length is 72 mm, the waist lengths are both 16.2 mm, and the height is 6 mm; the lower bottom edge length of the tooth structure is 100 mm, the upper bottom edge length is 70 mm, the waist lengths are both 15.8 mm, and the height is 5 mm.

[0061] It can be seen that the recessed dimension of the steel crystal tray is slightly larger than the tooth structure of the plastic plate by 1-2 mm, which is to accommodate the deformation of the plastic plate during the welding process.

[0062] Insert the plastic plate into the crystal tray from the side, and then place it on the ultrasonic welding seat; start the ultrasonic welding head, and the welding conditions are as follows: frequency 20 kHz, amplitude 40 μm, pressure 1 MPa, holding pressure time 0.4 s, welding time 1 s, downward pressing speed 3 mm / s, delay time 0.4 s. Weld each fitting part in turn through the welding head to obtain the steel crystal tray-plastic plate composite part of the plate-free adhesive in this embodiment.

[0063] Although the present invention has been illustrated and described with specific embodiments, it should be realized that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; those of ordinary skill in the art should understand that: without departing from the spirit and scope of the present invention, the technical solutions recorded in the foregoing embodiments can be modified, or some or all of the technical features can be equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A board-free wafer bonding method for silicon wafer cutting, characterized in that: The steps include: A steel crystal tray and a plastic plate are prepared; wherein a single side surface of the steel crystal tray is provided with a plurality of groove structures, and a single side surface of the plastic plate is provided with a plurality of tooth structures matching with the groove structures; Assemble the steel crystal support and the plastic plate so that the groove structure and the tooth structure are engaged and connected; perform ultrasonic welding at the engagement point so that the melted tooth structure is completely filled into the groove structure, thereby obtaining a steel crystal support-plastic plate composite without plate glue.

2. The board-free wafer bonding method for silicon wafer cutting according to claim 1, characterized in that: The groove structure is trapezoidal in the cross section of the steel crystal tray in the thickness direction, preferably an isosceles trapezoid; and the upper base of the trapezoid is located on the surface of the steel crystal tray, and the lower base of the trapezoid is located inside the steel crystal tray; And / or, the tooth structure is trapezoidal in cross section in the thickness direction of the plastic plate, preferably an isosceles trapezoid; and the upper base of the trapezoid is located on the surface of the rectangular section of the plastic plate, and the lower base of the trapezoid is convex to the outside of the rectangular section of the plastic plate.

3. The board-free wafer bonding method for silicon wafer cutting according to claim 1, characterized in that: The trapezoidal cross-section of the groove structure in the thickness direction of the steel crystal support, and / or the trapezoidal cross-section of the tooth structure in the thickness direction of the plastic plate, meets the following requirements: The difference between the side lengths of the upper and lower bases of the trapezoidal cross section is ≥ 20 mm; The height of the trapezoidal cross section is >3.5 mm.

4. The board-free wafer bonding method for silicon wafer cutting according to claim 3, characterized in that: The length of the upper base of the trapezoidal cross section is 60 mm to 90 mm; The length of the lower base of the trapezoidal cross section is 90 mm to 120 mm; The height of the trapezoidal cross section is 3.6 mm to 8 mm.

5. The board-free wafer bonding method for silicon wafer cutting according to claim 1, characterized in that: The trapezoidal shape presented by the groove structure in the cross section of the steel crystal support in the thickness direction is a first trapezoidal shape, and the trapezoidal shape presented by the tooth structure in the cross section of the plastic plate in the thickness direction is a second trapezoidal shape, and the two trapezoids satisfy at least one of the following relationships (a) to (c): (a) the difference in length between the lower base of the first trapezoid and the lower base of the second trapezoid is 0.5 mm to 3 mm; (b) the difference in length between the upper base of the first trapezoid and the upper base of the second trapezoid is 0.5 mm to 3 mm; (c) A difference between a height of the first trapezoid and a height of the second trapezoid is 0.3 mm to 1.5 mm.

6. The board-free wafer bonding method for silicon wafer cutting according to claim 1, characterized in that: The length and width of the steel crystal tray and the plastic plate are the same; and the groove structure on the surface of the steel crystal tray corresponds to the tooth structure on the surface of the plastic plate one by one; And / or, the direction of the groove structure is parallel to the width direction of the steel crystal tray, and the length of the groove structure is the same as the width of the steel crystal tray; the direction of the tooth structure is parallel to the width direction of the plastic plate, and the length of the tooth structure is the same as the width of the plastic plate.

7. The board-free wafer bonding method for silicon wafer cutting according to claim 1, characterized in that: The groove structures are evenly distributed in the length direction of the steel crystal holder, and the tooth structures are evenly distributed in the length direction of the plastic plate; Preferably, one or both of the following characteristics (A) or (B) are met: (A) The distance between any two adjacent groove structures and / or tooth structures is ≤360 mm, measured from the center point of the groove structure and / or the tooth structure; (B) Taking the center point of the groove structure and / or the tooth structure as an example, for the groove structure close to the edge of the steel crystal tray, the distance between the groove structure and the edge of the steel crystal tray is 65 mm to 85 mm; for the tooth structure close to the edge of the plastic plate, the distance between the tooth structure and the edge of the plastic plate is 65 mm to 85 mm.

8. The board-free wafer bonding method for silicon wafer cutting according to claim 1, characterized in that: The ultrasonic welding at the joint comprises the following steps: Placing the steel crystal holder and the plastic plate that are connected in an embedded manner on an ultrasonic welding seat, with one side of the plastic plate facing upward; Under the condition of applying external pressure to the fitting parts, ultrasonic welding treatment is performed on each fitting part by using an ultrasonic horn.

9. The board-free wafer bonding method for silicon wafer cutting according to claim 8, characterized in that: The ultrasonic welding includes at least one of the following parameters (1) to (3): (1) The frequency is 15kHz to 30kHz, and the amplitude is 30μm to 50μm; (2) The pressure is 0.8 MPa to 2 MPa, the holding time is 0.3 s to 0.8 s, and the pressing speed is 1 mm / s to 4 mm / s; (3) The welding time is 0.8s~2s, and the delay time is 0.2s~0.5s.

10. A method for preparing a silicon wafer for a solar cell, characterized in that: The invention comprises a plate-free wafer bonding method for silicon wafer cutting as claimed in any one of claims 1 to 9.

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