A forward multi-wire sawing method for photovoltaic silicon wafers

Abstract

The application relates to a photovoltaic silicon wafer forward multi-wire cutting method, which comprises the following steps: S1. transferring old wires to a cutting main roller, and transferring the old wires of a wire transferring wheel to form a wire net; S2. starting cutting, setting an initial feeding position of a silicon rod at -0.1 mm, and starting to gradually increase a feeding speed, wherein when the cutting depth of the silicon rod reaches 110 mm, the feeding speed reaches a peak value, and when the cutting depth of the silicon rod reaches 165 mm, the feeding speed starts to gradually decrease; and the cutting tension is increased from 3.6 N to 3.8 N. Compared with the prior art, the step of transferring new wires is omitted, operation time is saved, production efficiency is improved, the abrasion of steel wires caused by transferring new wires is eliminated, the cutting force loss of the steel wires is avoided, the wire amount used in the process is reduced, no new wire is wasted after wire breakage, and the loss of the steel wires is reduced.

Description

Technical Field

[0001] This invention belongs to the field of silicon wafer manufacturing technology, and particularly relates to a method for forward multi-wire dicing of photovoltaic silicon wafers. Background Technology

[0002] Currently, in the existing photovoltaic silicon wafer cutting process, the cutting lines are distributed on the feed roller, wire mesh, and take-up roller of the cutting equipment. The cutting method includes the following steps:

[0003] S1. Turn the old line out of the reel, which takes 4 minutes.

[0004] S2. Transfer new line: Transfer the new line needed for this cutting process from the feed spool to the take-up spool, and then release the new line in the opposite direction from the take-up spool to form the cutting net. The process takes 7.5 minutes.

[0005] S3, Start cutting.

[0006] The existing cutting process has the following disadvantages:

[0007] ①Long changeover time and low production efficiency

[0008] Before each cut, the 16km of steel wire to be used in this cut needs to be transferred to the take-up reel. This process causes wear on the steel wire during the running process, resulting in a loss of cutting force. It also wastes time and reduces production efficiency.

[0009] ② High steel wire loss

[0010] The new steel wire used in this cutting is transferred to the take-up reel in advance. If the wire breaks during the cutting process on the side away from the take-up reel, then all the new wire from the break point onwards, as well as all the new wire stored in the take-up reel, cannot be used for cutting, and the brand-new, unused steel wire will be wasted. Summary of the Invention

[0011] To address the aforementioned problems in the prior art, this invention provides a method for forward multi-wire dicing of photovoltaic silicon wafers.

[0012] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0013] This invention provides a method for forward multi-wire dicing of photovoltaic silicon wafers, comprising:

[0014] S1. Transfer the old wire to the cutting main roller, and rotate the old wire from the feeding wheel to form a cutting wire mesh;

[0015] S2. Start cutting. Set the initial feed position of the silicon rod to -0.1mm and gradually increase the feed speed. The cutting tension is 3.6N. The feed speed reaches its peak when the cutting depth of the silicon rod is 110mm. When the cutting depth of the silicon rod reaches 175mm, the feed speed begins to gradually decrease. During the decrease, the cutting tension increases from 3.6N to 3.8N.

[0016] Furthermore, the peak value of the feed rate is 2600 μm / min.

[0017] Furthermore, the cutting frequency in step S2 is increased to 1.35–1.55 times / min.

[0018] Furthermore, the maximum linear velocity in step S2 is 2000 m / min.

[0019] Furthermore, the method also includes stabilizing the cutting mesh by increasing the angle of the mesh.

[0020] Furthermore, the number of misaligned grooves N in the oblique wire mesh is increased to greater than or equal to 4d+1, where N is the number of misaligned grooves in the oblique wire mesh and d is the single groove pitch on the main roller.

[0021] Furthermore, during the cutting process in step S2, if a jumper wire is not broken, the original wire mesh is lifted and then pressed down again, including:

[0022] S2-1. Record the amount of wire stored on the take-up reel (a) and the cutting depth (b), and lift the silicon rod away from the wire mesh;

[0023] S2-2. The amount of wire stored in the take-up reel is restored to the amount of wire stored in the take-up reel recorded in S2-1, a;

[0024] S2-3. At a linear speed of 100m / min, manually press the silicon rod down to the cutting depth b recorded in S2-1;

[0025] S2-4. Continue automatic cutting;

[0026] If a wire break occurs, weld the break point. The weld strength must be at least 3.5N. The cutting tension after the wire is pulled in is 3.0N, the wire speed is 800m / min, and the table speed is 500um / min. After the wire end is cut out, restore the original process parameters.

[0027] Furthermore, the length of the old wire that the wire feeding wheel rotates out in step S1 is estimated from the wire length used for cutting the wire mesh, and the wire length used for cutting the wire mesh is calculated according to the following formula;

[0028] S = (bar length / groove spacing + 1) * C;

[0029] C = L1 + L2 + L3 + πd;

[0030] In the formula, S is the length of the wire used for cutting the wire mesh, C is the circumference of one ring of the wire mesh, L1 is the distance between the main rollers, L2 and L3 are the distance between the main roller and the lower roller, and d is the diameter of the main roller.

[0031] Furthermore, the linear acceleration and deceleration time in step 2 is 5.2 seconds.

[0032] The beneficial effects of this invention are:

[0033] The above-mentioned forward multi-wire cutting method for photovoltaic silicon wafers eliminates the need to transfer new wires from the feed roller to the take-up roller, and then have the take-up roller release the new wires in reverse to form a cutting wire mesh for cutting monocrystalline silicon rods. This method allows the feed roller to release new wires to form a cutting wire mesh for forward cutting of monocrystalline silicon rods, thus solving the problems of long line transfer time, low production efficiency, and high steel wire loss in existing processes. Attached Figure Description

[0034] Figure 1 This is a schematic flowchart of the photovoltaic silicon wafer forward multi-wire cutting method described in this invention;

[0035] Figure 2 This is a schematic diagram illustrating the principle of calculating the wire length of the cutting mesh in the forward multi-wire cutting method for photovoltaic silicon wafers described in this invention.

[0036] Figure 3 These are photographs of actual silicon wafers used in a cutting experiment conducted using the photovoltaic silicon wafer forward multi-wire cutting method described in this invention.

[0037] Figure 4 These are photographs of actual silicon wafers used in cutting experiments employing existing processes. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0039] like Figure 1 As shown, the photovoltaic silicon wafer forward multi-wire dicing method of the present invention includes the following steps:

[0040] Step S1. Transfer the old wire to the cutting main roller, and rotate the old wire from the feed roller to form the cutting wire mesh. The length of the old wire rotated out by the feed roller in step S1 is estimated from the wire length needed for cutting the wire mesh; specifically, the length rotated out can be ±0.4 km of the wire length needed for cutting the wire mesh. The wire length S needed for cutting the wire mesh is calculated according to the following formula, the calculation principle of which is as follows: Figure 2 As shown in the figure, A1 is the main roller, A2 is the lower roller, and B is the cutting wire mesh;

[0041] S = (bar length / groove spacing + 1) * C;

[0042] C = L1 + L2 + L3 + πd;

[0043] In the formula, S is the length of the wire used for cutting the wire mesh, C is the circumference of one ring of the wire mesh, L1 is the distance between the main rollers, L2 and L3 are the distance between the main roller and the lower roller, and d is the diameter of the main roller.

[0044] For example, the wire consumption (length) for cutting the wire mesh for G10-150 monocrystalline silicon wafers is as follows:

[0045] C=415+390+390+π*180=1760.2mm=1.76m,

[0046] S=(830 / 0.200+1)*1.76=7.31KM,

[0047] Therefore, the estimated length of the old line that the wire reel rotates out is 7 km.

[0048] Step S2. Begin cutting. Set the initial feed position of the silicon ingot to -0.1mm and gradually increase the feed speed. The cutting tension is 3.6N. Since the wire mesh is old wire, the feed speed needs to be reduced before the depth reaches 110mm, controlled below the peak value. That is, the feed speed reaches its peak value when the silicon ingot is cut to a depth of 110mm. The feed speed gradually decreases until the silicon ingot is cut to a depth of 175mm, and during the decrease, the cutting tension increases from 3.6N to 3.8N. The peak feed speed is 2600um / min, the maximum wire speed is 2000m / min, and the cutting frequency increases to 1.35~1.55 times / min. For details, refer to the cutting parameter settings of the cutting machine in Table 1 below in the embodiment of the photovoltaic silicon wafer forward multi-wire cutting method of this invention.

[0049] Table 1

[0050]

[0051]

[0052] Compared with existing processes, the photovoltaic silicon wafer forward multi-wire cutting method of the present invention eliminates the step of switching to new wires. On the one hand, it can save operation time and improve production efficiency; on the other hand, it can eliminate the wear of steel wires caused by switching to new wires and avoid the loss of cutting force (experiments have verified that, under the same wire usage, the cutting capacity of the cutting method of the present invention is 1.05 to 1.15 times that of existing processes), reducing the amount of wire used in the process; and thirdly, there are no new wires on the take-up wheel side, and no new wires are wasted after a wire breaks, reducing steel wire loss.

[0053] Furthermore, the peak feed rate of existing dicing processes is only 2400 μm / min, with a maximum linear speed of 2100 m / min. In addition, the peak feed rate is reached before the silicon ingot is cut to a depth of 90 mm, resulting in low dicing efficiency. Therefore, this invention, by eliminating the two-step dicing method of converting to a new production line, achieves a peak feed rate of 2600 μm / min and a maximum linear speed of 2000 m / min, thereby improving dicing efficiency.

[0054] Furthermore, the photovoltaic silicon wafer forward multi-wire dicing method of the present invention, by adopting a high-frequency process design, increases the dicing frequency to 1.35-1.55 times / min, which can reduce the wear difference of steel wires at the same frequency, thereby avoiding the problem of poor wire marks. Furthermore, by adopting a gradient tension design that increases the dicing tension from 3.6N to 3.8N during the feed speed decrease, it can reduce steel wire vibration, further avoiding the problem of poor wire marks. Moreover, by extending the acceleration and deceleration times from the conventional 5S to 5.2S, and reducing the maximum wire speed to 2000m / min, it can also reduce steel wire vibration, further avoiding the problem of poor wire marks; thus improving the quality of the diced silicon wafers.

[0055] To further stabilize the cutting lines, avoid poor line marks, and improve the quality of cut silicon wafers, the photovoltaic silicon wafer forward multi-line cutting method of the present invention also includes increasing the oblique line mesh, specifically: increasing the number of misaligned grooves N of the oblique line mesh to greater than or equal to 4d+1, where N is the number of misaligned grooves of the oblique line mesh and d is the single groove spacing on the main roller.

[0056] In a preferred embodiment of the present invention, if a jumper wire is found to be unbroken during the cutting process in step S2, the original wire mesh is re-pressed, including:

[0057] S2-1. Record the amount of wire stored on the take-up reel (a) and the cutting depth (b), and lift the silicon rod away from the wire mesh;

[0058] S2-2. The amount of wire stored in the take-up reel is restored to the amount of wire stored in the take-up reel, a, recorded in S2-1;

[0059] S2-3. At a linear speed of 100m / min, manually press the silicon rod down to the cutting depth b recorded in S2-1;

[0060] S2-4. Continue automatic cutting;

[0061] If a wire break occurs, weld the broken section. The weld strength must be at least 3.5N. The cutting tension after the wire is pulled in is 3.0N, the wire speed is 800m / min, and the table speed is 500um / min. After the wire end is cut out, restore the original process parameters, that is, restore the process parameters before the wire break during the cutting process.

[0062] The photovoltaic silicon wafer forward multi-line dicing method of the present invention solves the problem of high proportion of color difference defects in the diced silicon wafers through the above-mentioned solution.

[0063] The following experiments verify the effectiveness of the photovoltaic silicon wafer forward multi-wire cutting method described in this invention in solving the high proportion of defects caused by wire marks and color differences.

[0064] This experiment involved cutting monocrystalline silicon rods using the forward multi-wire cutting method for photovoltaic silicon wafers described in this invention and the existing photovoltaic silicon wafer cutting process (reverse cutting method). Photos of the resulting silicon wafers are shown below. Figure 3 and Figure 4 As shown. The two silicon wafers were tested using a sorting machine according to the standard GB / T 30860-2014 "Test Method for Surface Roughness and Cutting Marks of Silicon Wafers for Solar Cells". The results are as follows:

[0065] 1. Line marks: Irregular marks in the shape of raised and recessed lines left on the surface of silicon wafers during the cutting of single-crystal silicon rods; the line marks in the table below refer to the surface roughness of silicon wafers.

[0066] Existing processes 7.5 0.85％ This application 6.5 0.55％

[0067] 2. Color difference issue: Uneven color patches on the silicon wafer surface are reflected by grayscale values.

[0068] Existing processes 40-80 1.20％ This application 65-95 0.90％

[0069] As can be seen, the forward multi-wire cutting method for photovoltaic silicon wafers described in this invention not only reduces steel wire loss and improves production efficiency as mentioned above, but also reduces the probability of severe steel wire vibration caused by the forward cutting method and increasing the probability of skipped wires and broken wires by adjusting the corresponding wire speed and tension and increasing the strength of the oblique wire mesh. It effectively reduces the color difference and wire marks caused by the forward cutting method, thereby achieving the goal of increasing production capacity, reducing energy consumption, and improving the yield of monocrystalline silicon wafers.

[0070] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for forward multi-wire dicing of photovoltaic silicon wafers, characterized in that, include: S1. Transfer the old wire to the cutting main roller, and rotate the old wire from the feeding wheel to form a cutting wire mesh; S2. Start cutting. Set the initial feed position of the silicon rod to -0.1mm and gradually increase the feed speed. The cutting tension is 3.6N. The feed speed reaches its peak when the cutting depth of the silicon rod is 110mm. When the cutting depth of the silicon rod reaches 165mm, the feed speed begins to gradually decrease. During the decrease, the cutting tension increases from 3.6N to 3.8N. The peak value of the feed rate is 2600 μm / min, and the maximum linear velocity in step S2 is 2000 m / min. The method also includes stabilizing the cutting wire mesh by increasing the oblique wire mesh size, increasing the number of misaligned grooves N of the oblique wire mesh to greater than or equal to 4d+1, where N is the number of misaligned grooves of the oblique wire mesh and d is the single groove spacing on the main roller.

2. The photovoltaic silicon wafer forward multi-wire dicing method according to claim 1, characterized in that, The cutting frequency in step S2 is increased to 1.35 to 1.55 times / min.

3. The method according to claim 1, characterized in that, If, during the cutting process in step S2, a jumper wire is not broken, the original wire mesh is lifted and then pressed down again, including: S2-1. Record the amount of wire stored on the take-up reel (a) and the cutting depth (b), and lift the silicon rod away from the wire mesh; S2-2. The amount of wire stored in the take-up reel is restored to the amount of wire stored in the take-up reel, a, recorded in S2-1; S2-3. At a linear speed of 100 m / min, manually press the silicon rod down to the cutting depth b recorded in S2-1; S2-4. Continue automatic cutting; If a wire break occurs, weld the break point. The weld strength must be at least 3.5N. The cutting tension after the wire is pulled in is 3.0N, the wire speed is 800m / min, and the table speed is 500µm / min. After the wire end is cut out, restore the original process parameters.

4. The method according to claim 1, characterized in that, The length of the old wire that the wire feeding wheel rotates out in step S1 is estimated from the length of the wire used for cutting the wire mesh. The length of the wire used for cutting the wire mesh is calculated according to the following formula. S = (bar length / groove spacing + 1) * C; C = L1 + L2 + L3 + πd; In the formula, S is the length of the wire used for cutting the wire mesh, C is the circumference of one ring of the wire mesh, L1 is the distance between the main rollers, L2=L3 are the distance between the main roller and the lower roller, and d is the diameter of the main roller.

5. The method according to claim 1, characterized in that, The linear acceleration and deceleration time in step 2 is 5.2 seconds.

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