JP7353715B2 - Grinding method of workpiece - Google Patents

Description

The present invention relates to a method of grinding a workpiece by holding the workpiece on a chuck table and grinding the workpiece with a grinding wheel to obtain a resultant product with a predetermined thickness.

When forming a device chip to be mounted on an electronic device, first, devices such as an IC (Integrated Circuit) and an LSI (Large Scale Integration) are formed on the surface of a disk-shaped semiconductor wafer. At this time, a plurality of the devices are arranged in a matrix on the surface of the semiconductor wafer. Then, the semiconductor wafer is thinned by grinding from the back side, and the semiconductor wafer is divided into devices to form semiconductor chips.

Next, a plurality of semiconductor chips are mounted on a printed circuit board or the like. At this time, the electrodes of each semiconductor chip are connected to the respective target electrodes of the printed circuit board. Thereafter, the printed circuit board on which the semiconductor chip is mounted is sealed with resin to form a flat package substrate. This package substrate is ground from the back side to be thinned, and the package substrate is divided into semiconductor chips to obtain individual device chips.

Grinding of semiconductor wafers, package substrates, etc. is performed using a grinding device (see Patent Document 1). The grinding device includes a chuck table that suction-holds a workpiece such as a semiconductor wafer, and a grinding unit that grinds the workpiece suction-held by the chuck table. The grinding unit includes an annular grinding wheel at the lower end. Grinding wheels arranged in an annular shape are attached to the lower surface of the grinding wheel facing the upper surface of the chuck table.

When grinding a workpiece, first, the workpiece is placed on a chuck table, and the chuck table suction-holds the workpiece. At this time, the surface that is not to be ground is brought into contact with the chuck table so that the surface to be ground on which the workpiece is ground is exposed upward. Then, the chuck table and the grinding wheel are rotated, respectively, and the grinding wheel is lowered. Then, the grinding wheel moving on the annular orbit comes into contact with the surface to be ground of the workpiece, and the workpiece is ground.

Japanese Patent Application Publication No. 2002-200545

When a plurality of devices are formed on a semiconductor wafer, the semiconductor wafer may be warped due to forces generated in various films constituting the devices. Further, the package substrate may warp due to the force generated in the printed circuit board and the sealing resin included in the package substrate. With a grinding device, it is sometimes desired to grind a workpiece whose surface to be ground is curved in a concave shape.

When a warped workpiece is placed on a chuck table, the central part of the workpiece becomes lower than the outer circumference, and the outer circumference of the workpiece rises. When the workpiece is suctioned by the chuck table in this state, negative pressure (suction force) leaks from the gap between the outer peripheral portion and the chuck table, and the workpiece may not be held by suction. Therefore, when a warped workpiece is suctioned and held by a chuck table, the outer circumference of the workpiece is pressed from above to flatten the workpiece and suppress leakage of negative pressure. Conceivable.

However, when the force that warps the workpiece is strong, it is not easy to press the outer circumference of the workpiece with a force that deforms the workpiece to the extent that it can be suction-held by the chuck table. Further, even if the workpiece can be deformed into a flat shape, a force is generated in the workpiece that tends to return to its original shape, so there is a risk that the outer peripheral portion of the workpiece may rise again.

The present invention has been made in view of these problems, and its purpose is to stably hold a warped workpiece on a chuck table and to maintain the workpiece to a predetermined thickness. It is an object of the present invention to provide a method for grinding a workpiece until the workpiece is ground.

According to one aspect of the present invention, a disk-shaped first porous portion has an outer diameter smaller than the diameter of the workpiece, and a disk-shaped first porous portion surrounds the first porous portion and has an outer diameter corresponding to the diameter of the workpiece. an annular second porous section, a partition section disposed between the first porous section and the second porous section, and a frame surrounding the second porous section on the top surface. a chuck table that rotates around a rotation axis passing through the center of the upper surface and holds the workpiece by suction; and a grinding device that moves on an annular orbit passing through an area above the center of the upper surface of the chuck table. a grinding unit that is equipped with a grindstone and grinds the exposed back side of the workpiece with the grinding wheel while supplying grinding water to the workpiece that is suction-held by the chuck table; A method for grinding a workpiece, the workpiece having a curved concave portion lower than the outer circumferential portion thereof, from the back side until it reaches a first thickness, the front side facing the upper surface of the chuck table. The workpiece, whose center portion is suction-held by the first porous portion of the chuck table, is held by the grinding wheel of the grinding unit from the back side until it reaches a second thickness that is thicker than the first thickness. a first grinding step of grinding the workpiece, the center portion and the outer peripheral portion of which are suction-held by the first porous portion and the second porous portion of the chuck table, to the first thickness; A second grinding step of grinding the workpiece from the back surface side with the grinding wheel of the grinding unit until the workpiece becomes sharp is provided.

According to another aspect of the present invention, the first porous portion has a disk shape and has an outer diameter smaller than the diameter of the workpiece; an annular second porous part having a corresponding outer diameter; a partition disposed between the first porous part and the second porous part; and a frame surrounding the second porous part. , a chuck table that rotates around a rotating shaft passing through the center of the upper surface and suction-holds the workpiece, and a circular orbit passing through a region above the center of the upper surface of the chuck table. a grinding unit that is equipped with a grinding wheel that moves, and that grinds the exposed back side of the workpiece with the grinding wheel while supplying grinding water to the workpiece that is suction-held by the chuck table. A method for grinding a workpiece, in which the workpiece is warped in a concave manner so that the center portion thereof is lower than the outer circumferential portion thereof, is ground from the back surface until it reaches a first thickness, the method comprising: a first holding step in which the center portion of the workpiece is held by suction with the first porous portion of the chuck table, and after the first holding step, the a first grinding step of grinding the workpiece from the back side with the grinding wheel of the grinding unit until it has a second thickness that is thicker than the first thickness; and a first grinding step of grinding the workpiece from the back side with the grinding wheel of the grinding unit; and a second holding step of sucking and holding the center portion and the outer peripheral portion of the workpiece in the second porous portion, and after the second holding step, holding the workpiece until the first thickness is reached. A second grinding step of grinding the object from the back surface side with the grinding wheel of the grinding unit is provided.

According to still another aspect of the present invention, a disk-shaped first porous portion having an outer diameter smaller than the diameter of the workpiece; an annular second porous part having an outer diameter corresponding to the second porous part; a partition part disposed between the first porous part and the second porous part; and a frame surrounding the second porous part. and a chuck table that rotates around a rotating shaft passing through the center of the upper surface and holds the workpiece by suction, and an annular orbit that passes through a region above the center of the upper surface of the chuck table. a grinding unit that includes a grinding wheel that moves above the workpiece, and that grinds the exposed back side of the workpiece with the grinding wheel while supplying grinding water to the workpiece that is suction-held by the chuck table. In a grinding device, a method for grinding a workpiece, the workpiece being warped in a concave shape with a central portion lower than an outer peripheral portion, from the back side until it reaches a first thickness, the workpiece comprising: a first holding step of suctioning and holding the center portion of the workpiece with the first porous portion of the chuck table with the side thereof facing the upper surface of the chuck table; and after the first holding step; a grinding step of grinding the workpiece from the back side with the grinding wheel of the grinding unit until the workpiece has the first thickness, and while performing the grinding step, the second thickness of the chuck table is There is provided a method for grinding a workpiece, characterized in that a second holding step is performed in which the outer peripheral portion of the workpiece is held by suction in the porous portion of the workpiece.

Preferably, when grinding the workpiece, the grinding wheel moves from the area above the center of the top surface of the chuck table in the annular orbit to the frame body on the top surface of the chuck table. It contacts the back surface of the workpiece while advancing to the upper region.

Preferably, when the workpiece is sucked and held in the second porous part of the chuck table, the grinding water reaches the outer periphery of the second porous part from the second porous part to the workpiece. Suppresses leakage of suction force that acts on objects.

In the method for grinding a workpiece according to one aspect of the present invention, a chuck table has a first disc-shaped porous part and a second annular porous part surrounding the first porous part on its upper surface. A grinding device is used. Then, the workpiece is placed on the upper surface of the chuck table, and first, the center portion of the workpiece is held by suction with the first porous portion. Even if the workpiece is warped, it is relatively easy to suction and hold only the central portion of the workpiece.

When the workpiece is ground in this state, the outer peripheral portion is ground more intensively. Then, the force that warps the workpiece becomes weaker, and the force that causes the workpiece to return to its original shape after being deformed becomes smaller. This change becomes noticeable in the outer peripheral portion of the workpiece.

Therefore, when the workpiece has been ground to a certain extent, the second porous portion suction-holds the outer circumference of the workpiece, thereby suction-holding the entire area of the workpiece on the chuck table. Suction holding at this time is easier than suction holding the entire area of the workpiece before being ground. Moreover, the possibility that the outer peripheral portion of the workpiece will rise again is reduced. Therefore, the workpiece is stably and appropriately held under suction, and the workpiece can be stably ground until the thickness finally reaches the target first thickness.

Therefore, the present invention provides a method for grinding a workpiece, which stably holds a warped workpiece on a chuck table and grinds the workpiece to a predetermined thickness.

FIG. 2 is a perspective view schematically showing a grinding device. FIG. 2 is a perspective view schematically showing a chuck table and a workpiece. FIG. 2 is a cross-sectional view schematically showing how the center portion of the workpiece is held by suction in the first porous portion of the chuck table. FIG. 3 is a cross-sectional view schematically showing how a workpiece whose center portion is suction-held by a first porous portion of a chuck table is ground by a grinding wheel. FIG. 7 is a cross-sectional view schematically showing how the outer peripheral portion of the workpiece is held by suction in the second porous portion of the chuck table. FIG. 3 is a cross-sectional view schematically showing how a workpiece that is suction-held by the first porous part and the second porous part of the chuck table is ground. FIG. 3 is a top view schematically showing a region where a grinding wheel contacts a workpiece. FIG. 8(A) is a flowchart showing the flow of each step in one embodiment of the method for grinding a workpiece, and FIG. 8(B) is a flowchart showing the flow of each step in another embodiment of the method for grinding a workpiece. It is a flowchart which shows.

Embodiments according to the present invention will be described with reference to the drawings. In the method for grinding a workpiece according to the present embodiment, a warped workpiece is ground by a grinding device to be thinned. First, the workpiece to be ground will be explained. FIG. 2 schematically shows a disk-shaped wafer as an example of the workpiece 1. As shown in FIG.

The workpiece 1 is made of, for example, materials such as Si (silicon), SiC (silicon carbide), GaN (gallium nitride), GaAs (gallium arsenide), or other semiconductors, or sapphire, glass, quartz, etc. It is a substantially disk-shaped substrate made of material. Examples of the glass include alkali glass, non-alkali glass, soda lime glass, lead glass, borosilicate glass, and quartz glass.

On the surface 1a side of the workpiece 1, a plurality of devices such as ICs and LSIs are arranged in a matrix. By grinding the workpiece 1 from the back side 1b to make it thin and then dividing it into devices, individual semiconductor chips are obtained. Individual semiconductor chips are mounted and used in electronic devices such as mobile phones and personal computers. A semiconductor chip is used in a state sealed with, for example, a molding resin (sealing resin).

When manufacturing a packaged device chip, the semiconductor chip is first mounted on a printed circuit board or the like. At this time, the electrodes of each semiconductor chip are connected to the respective target electrodes of the printed circuit board. Thereafter, the printed circuit board on which the semiconductor chip is mounted is sealed with mold resin to form a package substrate. This package substrate is ground from the back side to be thinned and divided into semiconductor chips to obtain individual device chips.

On the surface of a semiconductor wafer on which a plurality of devices are formed, a plurality of metal films, insulating films, etc. constituting the devices are laminated. Then, the semiconductor wafer may be warped due to the force generated in each stacked film. Further, the package substrate may warp due to the force generated in the printed circuit board and the sealing resin included in the package substrate.

In the method for grinding a workpiece according to the present embodiment, a warped workpiece 1 such as a semiconductor wafer or a package substrate is ground. Hereinafter, a method for grinding a workpiece according to the present embodiment will be described using a case where the workpiece 1 is a semiconductor wafer as an example.

Next, a grinding device for grinding and thinning the workpiece 1 will be described. FIG. 1 schematically shows an example of a grinding device 2. As shown in FIG. The grinding device 2 shown in FIG. 1 includes a device base 4 that supports each component. The upper surface of the device base 4 is provided with an opening 4a. Inside the opening 4a, there is provided an X-axis moving table 8 on which a chuck table 6 for sucking and holding the workpiece 1 and a table base 6e for supporting the chuck table 6 are mounted.

The X-axis moving table 8 is movable in the X-axis direction by an X-axis moving mechanism (not shown). The X-axis moving table 8 is positioned in a carry-in/out area 10 where the workpiece 1 is attached/detached by the X-axis direction movement mechanism, and a processing area 12 where the workpiece 1 is ground.

The chuck table 6 is placed on the upper surface of the table base 6e. The upper surface of the chuck table 6 becomes a holding surface on which the workpiece 1 is placed. The chuck table 6 can apply negative pressure to the workpiece 1 placed on the holding surface and hold the workpiece 1 under suction. The table base 6e on which the chuck table 6 rests can rotate around an axis generally perpendicular to the holding surface. Then, the grinding device 2 grinds the workpiece 1 while the workpiece 1 is held under suction by the chuck table 6. The detailed configuration of the chuck table 6 will be described later.

A grinding unit 14 for grinding the workpiece 1 is arranged above the processing area 12 . A support section 16 is provided upright on the rear side of the device base 4, and the grinding unit 14 is supported by this support section 16. A pair of Z-axis guide rails 18 extending in the Z-axis direction are provided on the front surface of the support portion 16, and a Z-axis moving plate 20 is slidably attached to each Z-axis guide rail 18.

A nut portion (not shown) is provided on the back side (rear side) of the Z-axis moving plate 20, and a Z-axis ball screw 22 parallel to the Z-axis guide rail 18 is screwed into this nut portion. ing. A Z-axis pulse motor 24 is connected to one end of the Z-axis ball screw 22 . When the Z-axis ball screw 22 is rotated by the Z-axis pulse motor 24, the Z-axis moving plate 20 moves in the Z-axis direction along the Z-axis guide rail 18.

A grinding unit 14 for grinding the workpiece 1 is fixed to the lower front side of the Z-axis moving plate 20 . By moving the Z-axis moving plate 20 in the Z-axis direction, the grinding unit 14 can be moved in the Z-axis direction (processing feed direction).

The grinding unit 14 has a spindle 28 that is rotated by a motor connected to the proximal end. The motor is contained within the spindle housing 26. A disc-shaped wheel mount 30 is disposed at the tip (lower end) of the spindle 28, and an annular grinding wheel 32 that rotates as the spindle 28 rotates is attached to the lower surface of the wheel mount 30. Ru. The lower surface of the grinding wheel 32 is provided with grinding wheels 34 arranged in an annular manner.

The grinding wheel 34 includes abrasive grains such as diamond and a bond material that disperses and fixes the abrasive grains. When the spindle 28 is rotated to rotate the grinding wheel 32, the grinding wheel 34 rotates on an annular track. In the processing area 12 where the X-axis moving table 8 is positioned when grinding the workpiece 1, the center of the top surface of the chuck table 6 is located below the annular orbit along which the grinding wheel 34 moves. In other words, the grinding wheel 34 moves on the annular orbit passing through a region above the center of the top surface of the chuck table 6.

When grinding the upper surface of the workpiece 1 held under suction by the chuck table 6, as shown in FIG. 4, the chuck table 6 is rotated and the grinding unit 14 is lowered while rotating the grinding wheel 32. Then, the grinding wheel 34 moving on an annular orbit is brought into contact with the upper surface of the workpiece 1 to grind the workpiece 1.

Note that when the workpiece 1 is ground by bringing the grinding wheel 34 into contact with the workpiece 1, grinding debris is generated from the workpiece 1 and the grinding wheel 34, and heat is generated, increasing the temperature of the workpiece 1, etc. do. Therefore, in order to quickly remove grinding debris and heat from the workpiece 1, etc., when the workpiece 1 is ground by the grinding wheel 34, a liquid called grinding water is supplied to the workpiece 1, etc. . The grinding water is, for example, pure water.

By the way, when the X-axis moving table 8 is positioned in the loading/unloading area 10 and the workpiece 1 is loaded onto the chuck table 6, negative pressure is applied to the workpiece 1 from the chuck table 6, and the chuck table 6 The workpiece 1 is held by suction. At this time, if the workpiece 1 is not warped, negative pressure will not leak, and the workpiece 1 will be stably sucked and held.

However, as described above, the workpiece 1 that is the object of the grinding process may be warped. FIG. 2 includes a perspective view schematically showing a warped disk-shaped workpiece 1. As shown in FIG. The workpiece 1 has a central portion 1c lower than an outer circumferential portion 1d and is warped in a concave shape.

Note that the central portion 1c and the outer circumferential portion 1d of the workpiece 1 are regions each arbitrarily set on the warped workpiece 1, and their boundaries are not necessarily clear. The central portion 1c is a portion including the center of the workpiece 1, and the outer peripheral portion 1d is a portion surrounding the central portion 1c. The area other than the central portion 1c of the workpiece 1 is the outer peripheral portion 1d of the workpiece 1.

When it is desired to grind the workpiece 1 from the back surface 1b side, the workpiece 1 is placed on the chuck table 6 with the front surface 1a facing downward. When the warped workpiece 1 is placed on the chuck table 6, the central portion 1c of the workpiece 1 becomes lower than the outer peripheral portion 1d, and the outer peripheral portion 1d of the workpiece 1 rises. When the workpiece 1 is suctioned by the chuck table 6 in this state, negative pressure (suction force) leaks from the gap between the raised outer peripheral portion 1d of the workpiece 1 and the top surface of the chuck table 6, and the workpiece 1 may not be able to be sucked and held.

If the workpiece 1 cannot be held properly, the back surface 1b side of the workpiece 1 cannot be properly ground. Therefore, when the workpiece 1 is placed on the chuck table 6, the outer peripheral portion 1d of the workpiece 1 is pressed from above, and negative pressure is applied to the workpiece 1 while the workpiece 1 is deformed flat. It is also possible to do so.

However, in this case, since a force is generated in the workpiece 1 to return to its original shape, there is a possibility that the outer peripheral portion 1d of the workpiece 1 held by the chuck table 6 may rise again. Furthermore, if the force that warps the workpiece 1 is strong in the first place, it is not easy to press the outer peripheral portion 1d.

Therefore, in the method for grinding a workpiece according to the present embodiment, first, negative pressure is applied only to the central portion 1c of the workpiece 1, and the workpiece is Grind 1. Thereafter, the grinding of the workpiece 1 is further progressed while the outer peripheral portion 1d of the workpiece 1 is held under suction by the chuck table 6, and the workpiece 1 is thinned to the final thickness.

The chuck table 6 that can suction and hold the workpiece 1 section by section will be explained. FIG. 2 schematically shows a chuck table 6 that can individually apply negative pressure to the central portion 1c and outer peripheral portion 1d of the workpiece 1. The chuck table 6 includes a disk-shaped first porous part 6a having an outer diameter smaller than the diameter of the workpiece 1, and a disc-shaped first porous part 6a surrounding the first porous part 6a and having an outer diameter corresponding to the diameter of the workpiece 1. An annular second porous portion 6b is provided on the upper surface.

The chuck table 6 further includes a partition portion 6c disposed between the first porous portion 6a and the second porous portion 6b, and a frame body 6d surrounding the second porous portion 6b on the upper surface. . The frame body 6d accommodates a first porous portion 6a, a partition portion 6c, and a second porous portion 6b. When the workpiece 1 is placed on the chuck table 6, the central portion 1c of the workpiece 1 faces the first porous portion 6a, and the outer peripheral portion 1d of the workpiece 1 faces the second porous portion 6b. face to face.

The first porous portion 6a, the second porous portion 6b, the partition portion 6c, and the frame 6d are members formed of metal such as SUS, ceramics, or the like. Numerous holes are formed in the first porous portion 6a and the second porous portion 6b, which serve as transmission paths for negative pressure (suction force). The partition part 6c has a function of suppressing leakage of negative pressure (suction force), and is made of a member in which no holes are formed or holes smaller than those of the first porous part 6a and the second porous part 6b. It is a member that has.

3 and the like include a cross-sectional view schematically showing the chuck table 6. As shown in FIG. One end of a first suction path 36a is connected below the first porous portion 6a, and a first suction source 38a is connected to the other end of the first suction path 36a via a first switching portion 40a. Connected. Further, one end of a second suction path 36b is connected below the second porous portion 6b, and a second suction source is connected to the other end of the second suction path 36b via a second switching portion 40b. 38b is connected.

The first switching unit 40a has a function of switching between a communicating state and a blocked state of the first suction path 36a. When the first suction path 36a is in communication, the negative pressure generated by the first suction source 38a is applied to the center of the workpiece 1 placed on the chuck table 6 through the first suction path 36a and the first porous portion 6a. Acts on portion 1c.

The second switching section 40b has a function of switching between a communicating state and a blocking state of the second suction path 36b. When the second suction path 36b is in communication, the negative pressure generated by the second suction source 38b is applied to the outer circumference of the workpiece 1 placed on the chuck table 6 through the second suction path 36b and the second porous portion 6b. Acts on portion 1d.

The center of the upper surface of the chuck table 6 coincides with the center of the disk-shaped first porous portion 6a, and the chuck table 6 rotates around a rotating shaft 42 passing through the center of the upper surface. Note that the grinding wheel 34 of the grinding unit 14 moves on an annular orbit passing above the center of the upper surface of the chuck table 6.

In the method for grinding a workpiece according to the present embodiment, when grinding the workpiece 1 with the grinding wheel 34 of the grinding unit 14, first the central portion 1c of the workpiece 1 is held under suction by the first porous portion 6a. do. The upper surface of the first porous part 6a is covered with the central part 1c of the workpiece 1, and the partition part 6c is disposed between the first porous part 6a and the second porous part 6b. The negative pressure acting on the central portion 1c of the workpiece 1 from the porous portion 6a of the workpiece 1 is unlikely to leak to the outside. Therefore, the workpiece 1 is properly suction-held by the chuck table 6.

When the workpiece 1 is held under suction, the back surface 1b side of the workpiece 1 can be ground. In this case, since the workpiece 1 is ground with the outer peripheral portion 1d floating, the outer peripheral portion 1d is intensively ground and thinned. As a result, the outer peripheral portion 1d becomes thinner than the central portion 1c. Thereafter, the grinding wheel 34 also comes into contact with the central portion 1c, and the entire workpiece 1 is thinned.

When the workpiece 1 is ground and thinned, the force that was warping the workpiece 1 becomes weaker. Further, the force generated when the workpiece 1 is deformed to return to its original shape is reduced. Therefore, while grinding the workpiece 1, the second porous portion 6b suction-holds the outer peripheral portion 1d of the workpiece 1, so that the chuck table 6 suction-holds the entire area of the workpiece 1.

Compared to the case where the entire area of the workpiece 1 before being ground is suction-held by the chuck table 6, it is easier to suction-hold the entire area of the workpiece 1 which has been ground and thinned to some extent. Moreover, there is little risk that the outer peripheral portion 1d will rise again. Therefore, the entire area of the workpiece 1 is stably and properly suctioned and held by the chuck table 6, and the workpiece 1 can be stably ground.

Each step of the method for grinding a workpiece according to this embodiment will be described below. FIG. 8(A) is a flowchart showing the flow of each step in an example of the method for grinding a workpiece according to the present embodiment.

In this grinding method, first, a first holding step S10 is performed in which the central portion 1c of the workpiece 1 is suctioned by the first porous portion 6a of the chuck table 6. In the first holding step S10, first, the X-axis moving table 8 is moved to the loading/unloading area 10 so that the front surface 1a of the workpiece 1 faces the top surface of the chuck table 6. FIG. 2 is a perspective view schematically showing the workpiece 1 with the front surface 1a facing the upper surface of the chuck table 6. At this time, the central portion 1c of the workpiece 1 is positioned above the first porous portion 6a.

Then, the workpiece 1 is lowered and placed on the upper surface of the chuck table 6. Next, as shown in FIG. 3, the first switching unit 40a is activated to put the first suction path 36a into communication, and the negative pressure generated in the first suction source 38a is transferred to the first suction path 36a and the first suction path 36a. It acts on the central portion 1c of the workpiece 1 through the porous portion 6a of the workpiece 1. Then, the first porous portion 6a of the chuck table 6 can suck and hold the central portion 1c of the workpiece 1.

Note that a plurality of devices (not shown) such as ICs and LSIs are formed on the surface 1a side of the workpiece 1. Therefore, in order to protect the device etc. while the workpiece 1 is being ground, a protective tape (not shown) is applied to the surface 1a of the workpiece 1 before carrying out the first holding step S10. It may be worn. The protective tape is peeled off from the workpiece 1 after the grinding of the workpiece 1 is completed.

After carrying out the first holding step S10, a first grinding step S20 is carried out in which the workpiece 1 is ground by the grinding wheel 34 of the grinding unit 14. In the first grinding step S20, the chuck table 6 is rotated around the rotation axis 42, and the spindle 28 of the grinding unit 14 is also rotated. Then, the grinding unit 14 is lowered while supplying grinding water to the grinding wheel 34 and the workpiece 1, and the grinding wheel 34 is brought into contact with the back surface 1b of the workpiece 1. Then, the workpiece 1 is ground from the back surface 1b side.

FIG. 4 schematically shows a cross-sectional view of the workpiece 1 to be ground in the first grinding step S20. In the first grinding step S20, the workpiece 1 is ground until the workpiece 1 has a second thickness 46b that does not reach the first thickness 46a (see FIG. 6). Thereafter, a second holding step S30 is performed in which the entire area of the workpiece 1 is suction-held by the chuck table 6 by suction-holding the outer peripheral portion 1d of the workpiece 1 with the second porous portion 6b.

The grinding device 2 may include a thickness measuring unit (not shown) that measures the thickness of the workpiece 1 being ground. The thickness measuring unit has, for example, a probe that comes into contact with the back surface 1b of the workpiece 1. Using the measuring unit, it is possible to measure and monitor the thinning thickness of the workpiece 1 while the first grinding step S20 is being carried out.

In the first grinding step S20, for example, it is determined whether the thickness of the workpiece 1 has reached the second thickness 46b (S21). The first grinding step S20 is continued when the thickness of the workpiece 1 has not reached the second thickness 46b, and the second holding step S30 is continued when the thickness of the workpiece 1 has reached the second thickness 46b. will be implemented.

Here, the second thickness 46b will be explained. The second thickness 46b is appropriately set to a value larger than the first thickness 46a, which is the final finished thickness of the workpiece 1 in the workpiece grinding method according to the present embodiment.

When the workpiece 1 is ground by carrying out the first grinding step S20, as described above, the force that was giving warp to the workpiece 1 becomes weaker, and the force that is generated when the workpiece 1 is deformed becomes weaker. The force that tries to return to the original shape is reduced. As a result, the outer peripheral portion 1d of the workpiece 1 can be held by suction by the second porous portion 6b. That is, it becomes possible to implement the second holding step S30.

Therefore, the second thickness 46b, which is the target thickness of the workpiece 1 in the first grinding step S20, is set when the second porous portion 6b can suck and hold the outer peripheral portion 1d of the workpiece 1. The thickness of the workpiece 1 is set to . The second thickness 46b is a value that is appropriately set based on the type of workpiece 1, the conditions of the grinding to be performed, and the like. Note that it may be determined by other methods that the thickness of the workpiece 1 has reached the second thickness 46b and the second holding step S30 can be performed.

For example, it may be determined whether the second holding step S30 can be performed based on the amount of descent of the grinding unit 14 after the grinding wheel 34 contacts the back surface 1b of the workpiece 1 and grinding is started. Further, whether or not the second holding step S30 can be performed may be determined based on the elapsed time since grinding of the workpiece 1 is started. Furthermore, the output of the motor that rotates the spindle 28 may be monitored, and the determination may be made based on fluctuations in the output. Alternatively, the magnitude of the load applied to the table base 6e may be monitored and the determination may be made based on fluctuations in the load.

With these methods, knowledge regarding the degree of progress of grinding of the workpiece 1 can be obtained. Then, whether or not the second holding step S30 can be performed is determined based on the degree of progress. The determination as to whether the second holding step S30 can be carried out, that is, the determination as to whether the thickness of the workpiece 1 has reached the second thickness 46b (S21), is performed as described above. It may be carried out by methods other than measuring the thickness of.

Therefore, grinding the workpiece 1 to the second thickness 46b in the first grinding step S20 is synonymous with reaching a state where the second holding step S30 can be performed. That is, it does not necessarily mean that it is confirmed that the thickness of the workpiece 1 has reached a specific thickness, and the thickness of the workpiece 1 does not need to be directly measured. In the first grinding step S20, it can be said that the workpiece 1 has been ground to the second thickness 46b if a state is reached in which the second holding step S30 can be performed.

Furthermore, in the first grinding step S20, it is not necessary to determine whether or not the second holding step S30 can be performed. If the grinding of the workpiece 1 is started and the outer peripheral portion 1d of the workpiece 1 is then suction-held by the second porous portion 6b of the chuck table 6, the first grinding step S20 is completed. I can say that.

By the way, when a plurality of workpieces 1 are ground one after another by the grinding device 2, the degree of warpage occurring in each workpiece 1 is not necessarily the same. The criteria for determining whether or not the second holding step S30 can be performed may have to be determined by reflecting the degree of warpage of the workpiece 1.

Therefore, it is preferable that the grinding device 2 has a mechanism that can measure the degree of warpage of the workpiece 1. Moreover, before implementing the first grinding step S20, a warpage measuring step for measuring the degree of warpage of the workpiece 1 may be performed. The second thickness 46b, which is a criterion for determining whether or not the second holding step S30 can be performed, is set to a value that reflects the degree of warpage of the workpiece 1, for example. Ru.

Here, the degree of warpage of the workpiece 1 is determined by, for example, the curvature of the front surface 1a or the back surface 1b of the workpiece 1, the difference in height between the lowest point and the highest point of the workpiece 1, the It is expressed by an index such as the difference between the lowest point and the highest point on the back side 1b of 1. The mechanism that can measure the degree of warpage of the workpiece 1 is, for example, a three-dimensional measuring device that can irradiate light onto various parts of the workpiece 1 and detect reflected light, or a mechanism that can make contact with the top surface of the workpiece 1. It is a height measuring device etc. equipped with a probe.

When measuring the degree of warpage of the workpiece 1 using a three-dimensional measuring device, first, the three-dimensional shape of the workpiece 1 is measured. Then, the degree of warpage of the workpiece 1 is evaluated from the obtained information regarding the three-dimensional shape of the workpiece 1. Note that other information regarding the shape of the workpiece 1 can also be obtained from the measurement results by the three-dimensional measuring device. Therefore, conditions for grinding the workpiece 1 may be determined based on the other information regarding the shape of the workpiece 1. Furthermore, the finished thickness of the workpiece 1 may be corrected from the obtained information regarding the three-dimensional shape of the workpiece 1.

For example, when a three-dimensional measuring device is used, the height of the highest point of the workpiece 1 can be determined. Therefore, the height of the grinding unit 14 at the start of the first grinding step S20 may be determined based on the height of the highest point of the workpiece 1. The height position of the grinding unit 14 at the start of the first grinding step S20 is, for example, a position higher than the height of the highest point of the workpiece 1 by a predetermined margin height (air cut amount).

Next, the second holding step S30 will be explained. FIG. 5 schematically shows a cross-sectional view of the workpiece 1 when the second holding step S30 is performed. In the second holding step S30, the first porous portion 6a and the second porous portion 6b of the chuck table 6 suction hold the central portion 1c and outer peripheral portion 1d of the workpiece 1. More specifically, the second switching section 40b is operated to put the second suction path 36b into a communication state, and the negative pressure generated in the second suction source 38b is transferred to the second suction path 36b and the second porous section. 6b on the outer peripheral portion 1d of the workpiece 1.

As described above, the workpiece 1 that has been ground and thinned in the first grinding step S20 has a smaller warping force, and the workpiece 1 is not bent to its original shape when it is deformed. The force of trying to return becomes smaller. When the workpiece 1 is thinned, the degree of warpage of the workpiece 1 is reduced compared to before the workpiece 1 is ground, and the outer peripheral portion 1d of the workpiece 1 and the chuck table 6 becomes smaller. Therefore, when negative pressure (suction force) is applied to the workpiece 1 via the second porous portion 6b, the negative pressure is less likely to leak to the outside.

In particular, since grinding water is supplied to the grinding wheel 34 and the workpiece 1 when the workpiece 1 is ground, the outer peripheral portion 1d of the workpiece 1 and the second porous portion 6b of the chuck table 6 are The gap between and is partially or completely blocked by the grinding water 44. That is, the grinding water 44 makes it more difficult for the negative pressure (suction force) to leak to the outside.

Therefore, when negative pressure is applied to the workpiece 1 through the second porous portion 6b, the workpiece 1 is moved so that the outer peripheral portion 1d of the workpiece 1 approaches the second porous portion 6b of the chuck table 6. is deformed. Then, the entire area of the workpiece 1 comes into contact with the upper surface of the chuck table 6. If the workpiece 1 is further ground in this state, the center portion 1c and the outer peripheral portion 1d of the workpiece 1 can be ground to the same thickness.

Next, a second grinding step S40 is performed. FIG. 6 is a cross-sectional view schematically showing the workpiece 1 when the second grinding step S40 is performed. In the second grinding step S40, the grinding unit 14 is lowered, and the workpiece 1 is ground by the grinding wheel 34 of the grinding unit 14 from the back surface 1b side until it reaches the first thickness 46a.

The grinding device 2 includes, for example, the above-described thickness measuring unit (not shown) that measures the thickness of the workpiece 1. Then, in the second grinding step S40, the thickness of the workpiece 1 is monitored by the thickness measurement unit, and it is determined whether the thickness of the workpiece 1 has reached the first thickness 46a. (S41). The second grinding step S40 is continued when the thickness of the workpiece 1 has not reached the first thickness 46a, and when the thickness of the workpiece 1 has reached the first thickness 46a. The second grinding step S40 ends.

Here, the first thickness 46a is, for example, a finished thickness that is the final target thickness of the workpiece 1. However, the first thickness 46a is not limited to this. For example, the grinding device 2 may grind the workpiece 1 in two stages: rough grinding and finish grinding. Here, rough grinding refers to the process of grinding the workpiece 1 at high speed to a thickness that does not reach the finished thickness, and finish grinding refers to the process of relatively small grinding of the workpiece 1 to the finished thickness. This refers to the process of grinding under load.

When the grinding device 2 grinds the workpiece 1 in two stages, the grinding device 2 may include a plurality of grinding units. For example, the first grinding unit roughly grinds the workpiece 1, and the second grinding unit performs finish grinding of the workpiece 1.

In this case, the method for grinding a workpiece according to the present embodiment may be performed in one or both of the first grinding unit and the second grinding unit. The first thickness 46a in the grinding method performed in the first grinding unit is not the final finished thickness of the workpiece 1 but the target thickness value of the workpiece 1 during rough grinding. is set to

As described above, in the method for grinding a workpiece according to the present embodiment, the warped center portion 1c of the workpiece 1 is suction-held by the first porous portion 6a of the chuck table 6, and the workpiece is Grind 1. After the workpiece 1 has been ground to a certain extent, the outer peripheral portion 1d of the workpiece 1 with reduced warpage is held under suction by the second porous portion 6b of the chuck table, and the workpiece 1 is ground. Therefore, it is possible to appropriately grind the workpiece 1 which is warped to such an extent that it is difficult to suction and hold the entire area with the chuck table 6.

In addition, in the method for grinding a workpiece according to the present embodiment, after the first grinding step S20 is performed and the thickness of the workpiece 1 reaches the second thickness 46b, the grinding unit 14 is lowered. The second holding step S30 may be performed while the grinding of the workpiece 1 is stopped. Alternatively, even after starting grinding of the workpiece 1 and the thickness of the workpiece 1 reaches the second thickness 46b, the grinding unit 14 continues to descend, and the second holding step S30 is performed. Good too.

In other words, in the method for grinding a workpiece according to the present embodiment, even if the grinding of the workpiece 1 is stopped when the second porous portion 6b sucks and holds the outer peripheral portion 1d of the workpiece 1, the grinding of the workpiece 1 is continued. It doesn't matter which one is. Therefore, it is sufficient for the method of grinding a workpiece according to this embodiment to include the following two steps.

That is, in the first grinding step S20, the workpiece 1 whose central portion 1c is suction-held by the first porous portion 6a of the chuck table 6 is polished to a second thickness 46b that is thicker than the first thickness 46a. Grinding is performed using the grinding wheel 34 of the grinding unit 14 from the back surface 1b side until it becomes . In the second grinding step S40, the workpiece 1 with the central portion 1c and outer peripheral portion 1d held under suction by the first porous portion 6a and the second porous portion 6b of the chuck table 6 has a first thickness. Grinding is performed from the back surface 1b side using the grinding wheel 34 of the grinding unit 14 until it becomes 46a.

Next, the first porous part 6a of the chuck table 6 sucks and holds the center part 1c of the workpiece 1 to start grinding, and without stopping the grinding, the second porous part 6b moves the outer periphery of the workpiece 1. The case where the portion 1d is held under suction will be described in detail. FIG. 8(B) is a flowchart showing the flow of each step of the method for grinding the workpiece in this case. The method for grinding a workpiece shown in FIG. 8(B) is a modification of the method for grinding a workpiece shown in FIG. 8(A).

In the method for grinding the workpiece shown in FIG. A first holding step S50 of suctioning and holding the central portion 1c of is carried out. This first holding step S50 is similar to the above-described first holding step S10, so a description thereof will be omitted.

After the first holding step S50 is performed, a grinding step is started in which the workpiece 1 is ground from the back side 1b using the grinding wheel 34 of the grinding unit 14 until the first thickness 46a is reached (S60). While performing the grinding step, a second holding step S70 is performed in which the outer peripheral portion 1d of the workpiece 1 is held under suction by the second porous portion 6b of the chuck table 6.

The second holding step S70 is performed, for example, when the thickness of the workpiece 1 to be ground and thinned reaches the above-mentioned second thickness 46b (see FIG. 4). After the thickness of the workpiece 1 reaches the second thickness 46b, the second switching part 40b is actuated to apply negative pressure to the outer circumferential portion 1d of the workpiece 1, and the outer circumference of the workpiece 1 is reduced. The portion 1d is held under suction by the second porous portion 6b.

Note that the timing at which the second holding step S70 is performed is not limited to this. For example, after grinding of the workpiece 1 is started (S60), and before the thickness of the workpiece 1 reaches the second thickness 46b, the second switching part 40b is activated to switch the second suction path. 36b may be switched to a communicating state.

In this case, until the second porous portion 6b can suck and hold the outer peripheral portion 1d of the workpiece 1, that is, until the thickness of the workpiece 1 reaches the second thickness 46b, the Negative pressure (suction force) continues to leak from the gap between the porous portion 6b of No. 2 and the outer peripheral portion 1d. When the thickness of the workpiece 1 reaches the second thickness 46b, the workpiece 1 is deformed by the negative pressure and the outer peripheral portion 1d comes into contact with the second porous portion 6b. The outer peripheral portion 1d is suction-held by the second porous portion 6b.

In other words, when the workpiece 1 is ground and sufficiently thinned, when negative pressure is applied to the workpiece 1 through the second porous part 6b, the outer peripheral part 1d is Suction is held. On the other hand, if the workpiece 1 is not thinned sufficiently, that is, if the thickness of the workpiece 1 does not reach the second thickness 46b, the workpiece 1 is further ground to reduce the thickness. When the thickness reaches the second thickness 46b, the outer peripheral portion 1d is automatically sucked and held by the second porous portion 6b.

Even if grinding of the workpiece 1 is started with only the center portion 1c of the workpiece 1 being suction-held, if the entire area of the workpiece 1 is finally properly suction-held by the chuck table 6, The workpiece 1 is suitably ground until its thickness reaches a first thickness 46a. In this way, the grinding of the workpiece 1 does not need to be stopped when the second porous portion 6b sucks and holds the outer peripheral portion 1d of the workpiece 1.

Here, the moving direction of the grinding wheel 34 when grinding the workpiece 1 and the contact area between the workpiece 1 and the grinding wheel 34 will be explained. In each figure, the top surface of the chuck table 6 is depicted as being flat. However, in order to uniformly grind the surface of the workpiece 1, the top surface of the chuck table 6 has a conical shape with an extremely small height, and an extremely small slope is formed from the outer periphery to the center. There is.

The rotation axis 42 of the chuck table 6 and the axis of the spindle 28 of the grinding unit 14 are slightly deviated from parallel directions. The highest generating line of the conical generating lines forming the upper surface of the chuck table 6 and the lower surface of the grinding wheel 32 of the grinding unit 14 are substantially parallel to each other. When the workpiece 1 is held by the chuck table 6 and the grinding unit 14 is lowered while rotating the chuck table 6 and the grinding wheel 32, the grinding wheel 34 comes into contact with the workpiece 1 along the highest generatrix. .

FIG. 7 is a top view schematically showing the workpiece 1 that is suction-held by the chuck table 6 and the annular track 48 that is a path along which the grinding wheel 34 moves. FIG. 7 schematically shows the back surface 1b of the workpiece 1 that comes into contact with the workpiece 1 during grinding, the annular track 48, and the contact area 50. As shown in FIG. 7, the grinding wheel 34 begins to come into contact with the back surface 1b of the workpiece 1 when passing above the center of the chuck table 6, and when passing above the outer periphery of the workpiece 1, the grinding wheel 34 begins to contact the back surface 1b of the workpiece 1. It no longer comes into contact with the back surface 1b of the object 1.

Here, when grinding the warped workpiece 1, as the grinding wheel 34 in contact with the back surface 1b of the workpiece 1 moves along the annular track 48 and approaches the outer periphery of the workpiece 1, the grinding wheel 34 34 presses the raised outer peripheral portion 1d from above. Therefore, the gap between the workpiece 1 and the upper surface of the chuck table 6 is reduced. This makes it easy to suction and hold the outer peripheral portion 1d of the workpiece 1 with the second porous portion 6b.

However, when the grinding wheel 34 moves in the opposite direction, that is, the grinding wheel 34 contacts the workpiece 1 from the outer peripheral side of the workpiece 1 in the contact area 50 and passes above the center of the workpiece 1. The situation changes later when the grinding wheel 34 no longer contacts the workpiece 1. That is, in the outer circumferential portion 1d of the workpiece 1, a force acts in a direction in which the workpiece 1 is rolled up by the movement of the grinding wheel 34, and the outer circumferential portion 1d of the workpiece 1 may rise further. In this case, the outer peripheral portion 1d of the workpiece 1 is difficult to be sucked and held by the second porous portion 6b.

Therefore, when grinding the workpiece 1, the grinding wheel 34 moves from the area above the center of the top surface of the chuck table 6 on the annular track 48 to the area above the frame 6d on the top surface of the chuck table 6. It is preferable to contact the back surface 1b of the workpiece 1 while proceeding to the area. The rotational direction of the spindle 28 may be set to achieve this.

As described above, in the method for grinding a workpiece according to the present embodiment, the workpiece 1 is ground while each region of the workpiece 1 in which warpage has occurred is suctioned and held in stages by the chuck table 6. . Therefore, the workpiece 1 can be stably held on the chuck table 6 from the beginning to the end of grinding, and the workpiece 1 can be ground to a predetermined thickness.

Note that the present invention is not limited to the description of the above embodiments, and can be implemented with various modifications. For example, in the above embodiment, a case has been described in which two porous parts, the first porous part 6a and the second porous part 6b, are disposed on the upper surface of the chuck table 6. However, one embodiment of the present invention is not limited thereto. That is, three or more porous portions may be arranged on the upper surface of the chuck table 6.

For example, one or more additional annular porous parts may be arranged between the first porous part 6a and the second porous part 6b. In this case, since the warped workpiece 1 can be suction-held by the chuck table 6 in three or more stages, the workpiece 1 can be more easily transformed into a flat plate shape.

The structure, method, etc. according to the above embodiments can be modified and implemented as appropriate without departing from the scope of the objective of the present invention.

1 Workpiece 1a Front surface 1b Back surface 1c Central portion 1d Peripheral portion 2 Grinding device 4 Device base 4a Opening 6 Chuck table 6a First porous portion 6b Second porous portion 6c Partition portion 6d Frame 6e Table base 8 X-axis Moving table 10 Loading/unloading area 12 Processing area 14 Grinding unit 16 Support part 18 Z-axis guide rail 20 Z-axis moving plate 22 Z-axis ball screw 24 Z-axis pulse motor 26 Spindle housing 28 Spindle 30 Wheel mount 32 Grinding wheel 34 Grinding wheel 36a , 36b Suction path 38a, 38b Suction source 40a, 40b Switching part 42 Rotating shaft 44 Grinding water 46a, 46b Thickness 48 Annular orbit 50 Contact area

Claims (5)

a disk-shaped first porous part having an outer diameter smaller than the diameter of the workpiece; and an annular second porous part surrounding the first porous part and having an outer diameter corresponding to the diameter of the workpiece. a partition disposed between the first porous part and the second porous part, and a frame surrounding the second porous part on the upper surface, penetrating through the center of the upper surface. a chuck table that rotates around a rotation axis and holds the workpiece by suction;
A grinding wheel is provided that moves on an annular orbit passing through a region above the center of the upper surface of the chuck table, and the grinding wheel moves the workpiece held by suction on the chuck table while supplying grinding water to the workpiece. a grinding unit that grinds the exposed back side of the workpiece;
In a grinding device equipped with,
A method for grinding a workpiece, the workpiece being warped in a concave manner so that the center portion thereof is lower than the outer peripheral portion thereof, is ground from the back surface until it reaches a first thickness, the method comprising:
The workpiece whose front side faces the upper surface of the chuck table and whose center portion is suction-held by the first porous portion of the chuck table until it has a second thickness that is thicker than the first thickness. a first grinding step of grinding from the back surface side with the grinding wheel of the grinding unit;
The workpiece, whose center portion and outer peripheral portion are suction-held by the first porous portion and the second porous portion of the chuck table, is rotated from the back side by the grinding unit until it reaches the first thickness. a second grinding step of grinding with the grinding wheel;
A method for grinding a workpiece, comprising: a disk-shaped first porous part having an outer diameter smaller than the diameter of the workpiece; and an annular second porous part surrounding the first porous part and having an outer diameter corresponding to the diameter of the workpiece. a partition disposed between the first porous part and the second porous part, and a frame surrounding the second porous part on the upper surface, penetrating through the center of the upper surface. a chuck table that rotates around a rotation axis and holds the workpiece by suction;
A grinding wheel is provided that moves on an annular orbit passing through a region above the center of the upper surface of the chuck table, and the grinding wheel moves the workpiece held by suction on the chuck table while supplying grinding water to the workpiece. a grinding unit that grinds the exposed back side of the workpiece;
In a grinding device equipped with,
A method for grinding a workpiece, the workpiece being warped in a concave manner so that the center portion thereof is lower than the outer peripheral portion thereof, is ground from the back surface until it reaches a first thickness, the method comprising:
a first holding step in which the front surface side of the workpiece faces the upper surface of the chuck table, and the first porous portion of the chuck table suction-holds the center portion of the workpiece;
After the first holding step, a first grinding step of grinding the workpiece from the back side with the grinding wheel of the grinding unit until it has a second thickness that is thicker than the first thickness;
a second holding step of sucking and holding the central portion and the outer peripheral portion of the workpiece with the first porous portion and the second porous portion of the chuck table;
After the second holding step, a second grinding step of grinding the workpiece from the back side with the grinding wheel of the grinding unit until the first thickness is reached;
A method for grinding a workpiece, comprising: a disk-shaped first porous part having an outer diameter smaller than the diameter of the workpiece; and an annular second porous part surrounding the first porous part and having an outer diameter corresponding to the diameter of the workpiece. a partition disposed between the first porous part and the second porous part, and a frame surrounding the second porous part on the upper surface, penetrating through the center of the upper surface. a chuck table that rotates around a rotation axis and holds the workpiece by suction;
A grinding wheel is provided that moves on an annular orbit passing through a region above the center of the upper surface of the chuck table, and the grinding wheel moves the workpiece held by suction on the chuck table while supplying grinding water to the workpiece. a grinding unit that grinds the exposed back side of the workpiece;
In a grinding device equipped with,
A method for grinding a workpiece, the workpiece being warped in a concave manner so that the center portion thereof is lower than the outer peripheral portion thereof, is ground from the back surface until it reaches a first thickness, the method comprising:
a first holding step in which the front surface side of the workpiece faces the upper surface of the chuck table, and the first porous portion of the chuck table suction-holds the center portion of the workpiece;
After the first holding step, a grinding step of grinding the workpiece from the back side with the grinding wheel of the grinding unit until the first thickness is reached,
Grinding of a workpiece, characterized in that, while performing the grinding step, a second holding step is performed in which the outer peripheral portion of the workpiece is held by suction with the second porous portion of the chuck table. Method. When grinding the workpiece, the grinding wheel moves from the area above the center of the top surface of the chuck table in the annular orbit to the area above the frame on the top surface of the chuck table. 4. The method for grinding a workpiece according to claim 1, wherein the method contacts the back surface of the workpiece during the grinding process. When the workpiece is held by suction in the second porous part of the chuck table, the grinding water reaching the outer periphery of the second porous part acts on the workpiece from the second porous part. The method for grinding a workpiece according to any one of claims 1 to 4, characterized in that leakage of force is suppressed.

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