Multi-wire cutting machine technology and application (1)

Wed Jun 08 17:10:14 CST 2022

Multi-wire cutting machine technology and application (1)

The multi-wire cutting machine is a new type of cutting equipment with a new concept. It has been more than 40 years since the concept of multi-wire cutting was put forward in the 1960s to the perfection today. Limited to the technological level and control concept at the time, it would be quite difficult to use multi-wire cutting to put it into practice. In the mid-1980s, the world's first usable multi-wire cutting machine came out. Among them, the main mechanical structure is mainly the magnetic powder clutch for the tension control of the pull wire. The tension adjustment uses an AC motor with a reducer. It is also equipped with a huge gear reducer and a chain gear transmission structure. The table is driven by a weight. Electric control is mainly relay and time relay. Regardless of the mechanism, it is a prototype multi-wire cutting machine that can be used after all. After that, it was experimental in 1986-1987; it was the second generation in 1988-1990. The next two or three years will be a new generation. Today, the ninth and tenth generation multi-wire cutting machines are already on the market.

The multi-wire machine cuts wafers with small bow, small warp and good parallelism (Tarp). The total thickness tolerance (TTV) is small, the cutting loss between slices is small, the surface damage layer of the processed wafer is shallow, the roughness is small, the slice processing rate is high, the production efficiency is high, and the return on investment is high.

Therefore, the application of multi-wire cutting machines is an inevitable choice for the development of large-scale production and improving production efficiency. It is an inevitable trend to use multi-wire cutting machines to process various types of wafers, and is especially suitable for batch processing of solar photovoltaic cell ultra-thin machine substrates.

In the 21st century technological progress and technological development, the technological content of modern multi-wire cutting machines has been different from that of the 1980s. Today's multi-wire cutting machines have integrated modern manufacturing technology, process technology, modern control technology, and modern sensors. Technology and new materials, such as AC servo motor and drive system, industrial control computer, motion control card and bus system, spindle oil mist lubrication cooling and gap sealing unit, constant tension fast wire routing, etc. Due to the selection of the above systems, the modern multi-wire cutting machine is suitable for the slicing of large-diameter IC silicon wafer photovoltaic cell substrate ultra-thin, gallium arsenide, silicon carbide, lithium niobate, optical glass and other hard and brittle materials. .

Chapter 1 The composition and characteristics of HCT multi-wire cutting machine

1.1 Equipment introduction

Swiss HCT company was established in 1984, it is the gestation period of multi-wire cutting machine, the company mainly focuses on multi-wire cutting machine, 10 years of sharpening a sword, in the mid-1990s, it launched E400SD, E500SD, DNC900/G and many kinds of large-scale multi-wire cutting machines. Quickly occupy the wafer cutting market. E500ED-8 and E400E-12 are 300mm equipment. The company's multi-wire square cutting machine can cut 525 square ingots at the same time, which is suitable for the square ingot processing of solar photovoltaic cells.

1.2 Equipment composition

HCT-B6 multi-wire cutting machine is composed of 6 parts: a cutting room, two pay-off rooms, a base, a slurry cylinder, a power distribution room, and a pressure chamber.

The cutting room is mainly composed of 4 rubber guide wheels and a wire net. The wire net is wound on the guide wheel and is located under the abutment. The length of the guide wheel is 1m40cm. When cutting, the 4 guide wheels in the cutting chamber drive the wire net to rotate at a high speed.

The pay-off room is composed of pay-off reel, take-up reel and pulley block.

The slurry tank is at the back of the machine, in order to form a backflow tank at the bottom of the machine. Then the bottom slurry is pumped to the upper nozzle by the air pressure chamber above the machine, and the flowing slurry flows back into the backflow tank, and then back Slurry tank. There is a filter screen in the slurry tank to filter out cutting impurities.

1.3 Equipment characteristics

The wire cutting mechanism of solar silicon wafers is that the machine guide wheel drives the steel wire during high-speed operation, so that the mortar mixed with polyethylene glycol and silicon carbide powder is sent to the cutting area by the steel wire, and the wire is pressed on the wire during high-speed operation of the steel wire. The workpiece is continuously rubbed to complete the cutting process.

HCT-B6 has the following features

(1) hct-b6 multi-wire cutting equipment integrates chemistry, physics, machinery, electrical and other technologies.

(2) It has high-precision 4-axis cable guide wheel drive technology. Increased cutting capacity.

(3) Cutting feed servo system. With the function of the automatic control system of wire tension, it can ensure the high efficiency of cutting under the condition of continuous wire.

(4) Using the slurry recovery system, the slurry can be directly taken out of the slurry tank for recycling. Save most of the slurry cost.

(5) The average thickness error of the sheet thickness is small, suitable for large-scale manufacturing.

2.1 Viscosity of cutting fluid

In the entire cutting process, the silicon carbide powder is suspended on the cutting fluid and cut by the steel wire, so the cutting fluid mainly plays the role of suspension and cooling.

1. The viscosity of the cutting fluid is an important guarantee for the suspension of silicon carbide powder. Due to the different system thinking of different machine development and design, the viscosity of the mortar is also different, that is, the viscosity of the cutting fluid is also different. For example, the Swiss wire cutting machine requires that the viscosity of the cutting fluid is not less than 55, while NTC requires 22-25, and Ernst & Young is as low as 18. Only the viscosity that meets the cutting standards required by the machine can ensure the uniform suspension of silicon carbide powder during the cutting process and the mortar to enter the cutting area through the mortar pipe and the steel wire stably.

2. Because the steel wire with mortar will generate high temperature due to friction in the process of cutting silicon material, the viscosity of the cutting fluid plays an important role in cooling. If the viscosity is not up to the standard, it will lead to poor fluidity of the liquid, and the temperature cannot be lowered to cause burns or breakage. Therefore, the viscosity of the cutting fluid ensures the temperature control of the entire process.

3. The ability of the wire cutting machine to cut silicon wafers is inseparable from the viscosity of the mortar. The viscosity of the mortar depends on the viscosity of the silicon wafer cutting fluid, the compatibility of the silicon wafer cutting fluid and the silicon carbide powder, the ratio of the silicon wafer cutting fluid to the silicon carbide powder, and the density of the mortar. Only the mortar viscosity that meets the requirements of the machine (for example, the NTC machine requires about 250) can improve the cutting efficiency and increase the yield during the cutting process.

4. The flow of mortar is in the high-speed movement of the steel wire. To complete the cutting of the silicon material, the mortar must be pumped from the storage box to the sand blasting nozzle by the mortar pump, and then sprayed onto the steel wire from the sand blasting nozzle. Whether the flow of the mortar is uniform and whether the flow can meet the cutting requirements, all play a key role in the cutting ability and cutting efficiency. If the flow rate cannot keep up, the cutting ability will be severely reduced, leading to line marks, wire breakage, and even machine alarms.

2.2 Wire cutting technology and influencing factors

<1> The cutting of solar silicon wafers is actually the cutting of steel wire with silicon carbide powder, so the grain type and granularity of the powder are the key to the smoothness and cutting ability of the silicon wafer surface. The grain shape is regular, and the cut silicon wafers will show a good finish; the uniform particle size distribution will improve the cutting ability of the silicon wafers.

〈2〉 Since HCT-B6 is a two-wire type, the steel wire speed must be different according to customer requirements. When the wire is routed in both directions, the steel wire speed starts to accelerate from the zero point in one direction to the specified speed in 2-3 seconds. After running for a period of time, it slowly decreases to the zero point in the original direction, and then slowly stops at the zero point for 0.2 seconds. It is a periodic cutting process in which the ground is accelerated to the specified speed in the reverse direction, and then slowly reduced to the zero point in the opposite direction. In the process of bidirectional cutting, the cutting ability of the wire cutting machine increases with the speed of the steel wire within a certain range, but it cannot be lower than or exceed the cutting ability of the mortar. If it is lower than the cutting capacity of the mortar, there will be line marks or even broken lines; on the contrary, if the cutting capacity of the mortar is exceeded, the mortar flow rate may not keep up, resulting in thick flakes or even line marks. At present, the HCT grade can maintain an average line speed of 13m/s.

<3> The tension of the steel wire is one of the core elements in the silicon wafer cutting process. Poor tension control is an important cause of thread marks, chipping, and even thread breakage.
Steel wire cutting line diagram, 1 is the pay-off wheel, 2 is the wire inlet, 3 is the guide wheel, 4 is the abutment (equipped with silicon blocks), 5 is the emergence opening, and 6 is the take-up wheel

1. When wiring is started, there will be knots between the old and new wires in the network; when there are knots in the wiring, the tension greater than 13N cannot be opened at the beginning. After the running line is completed, confirm the position of the knot; cut off the steel wire near the knot, and wind the thread from the next outlet directly on the take-up wheel. If the tension is too large, the knot will be easily torn when running.

2. The amount of tension during cutting will also affect the yield of silicon wafers. If the tension of the steel wire is too small, the bending of the steel wire will increase, the sanding capacity will decrease, and the cutting ability will decrease. As a result, line marks and the like appear.

If the tension of the steel wire is too high, the silicon carbide powder suspended on the steel wire will be difficult to enter the saw gap, cutting efficiency will be reduced, line marks will appear, etc., and the probability of wire breakage will be high.

2.3 Other factors affecting the yield rate and solutions in the process

1. Pay attention to the working conditions of the guide wheel. Once impurities appear on the guide wheel, it will cause jumpers and disconnections in the online network. Therefore, be sure to use an air gun to clean the surface of the guide wheel before wiring. If there is no jumper when the mortar is not opened after the wiring is completed, check whether there is any impurities or whether the guide wheel is damaged, and further eliminate the problem. If a jumper is found during the warm-up process after the mortar, check whether the filter in the return tank is damaged or not cleaned in time.

2. Be sure to check the pulley before cutting, and change the pulley after cutting twice. If a cut-through pulley is found during the inspection, replace it in time, whether the bearing at the pulley is loose; whether there is impurities or sand in the groove of the pulley. Once found, replace it immediately.

3. The filter screen of the cutting chamber, the slurry nozzles on the upper and lower layers, and the filter screen in the return tank need to be cleaned in time after the cutting is completed. Remove the broken silicon wafers that fall and remove the filtered impurities. Be sure to blow dry after cleaning. Because water will react with the slurry, the slurry will harden and become some hard small particles. Affect the cutting quality. It even caused a disconnection accident.

4. Be sure to check the surface of the silicon block and the pallet before cutting, remove the glue and dirt on the surface of the silicon block (the excess glue on the silicon block is best to be scraped off with a blade), and check the pallet after ensuring that there is no impurities Whether it is blocked in the middle groove. The silicon block can be loaded after everything is normal.

5. When an alarm is caused by insufficient cooling water or insufficient air pressure during cutting, in addition to turning on the water replenishment device or pressurizing device, the slurry supply during cutting must also be turned on first. Ensure the slurry density on the steel wire.

6. Do not start cutting immediately after the shutdown accident is eliminated. Let the cutting line run at low speed for a few seconds before starting to cut.