JP6757223B2 - Cutting tool - Google Patents

Description

The present invention relates to a cutting tool.

A bite wheel equipped with a bite tool is fixed to the tip of the spindle, and bumps on the surface of the WL-CSP (Wafer-level Chip Size Package) are swirled to make the height uniform, and IC (Integrated Circuit) chips, etc. There is known a tool cutting device that swirls and cuts the surface of a package substrate made of a resin or metal that is mounted and sealed with a resin to flatten the molded resin. In the tool cutting device, the holding surface of the chuck table that holds the work piece to be swiveled is made of a machinable material (for example, metal), and the holding surface is cut with a tool tool to swirl and cut the work piece. It is operated so as to have a flat finish (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2005-340324

The tool cutting device makes swivel cutting with a spindle rotated by a motor, but the column fixing the cutting unit is deformed (bent) due to the heat generated by the motor, and the finished thickness of the work piece fluctuates. I understood it.

The present invention has been made in view of such a point, and an object of the present invention is to provide a cutting tool capable of suppressing fluctuations in the finished thickness of a work piece.

In order to solve the above-mentioned problems and achieve the object, the tool cutting device of the present invention uses a chuck table for holding a work piece on a holding surface and a tool wheel including a tool tool mounted on the tip of a spindle. On the cutting unit that swirls and cuts the workpiece held on the chuck table, the machining feed unit that is installed on the device base and moves the chuck table relative to the machining feed direction parallel to the holding surface, and the device base. A tool cutting device provided with a cutting feed unit fixed to an erected column and moving the cutting unit in a direction orthogonal to the holding surface, and covered with an exterior cover accommodating each component. A temperature measuring device that measures the temperature of the atmosphere around the motor that rotates the spindle of the unit, and the temperature of the atmosphere when the holding surface of the chuck table is cut with the cutting unit to form a new holding surface. A temperature recording unit that records a reference temperature and a threshold temperature higher than the reference temperature, an exhaust unit that discharges the atmosphere to the outside of the exterior cover, and when the temperature of the atmosphere reaches the threshold temperature. It is characterized by including an exhaust unit control unit for operating the exhaust unit.

Further, the cutting tool may include a notification unit for notifying that the temperature of the atmosphere has become higher than the threshold temperature.

Therefore, the tool cutting device of the present invention measures the temperature of the atmosphere around the spindle motor during self-cutting to shape the holding surface and records it as the reference temperature, and the temperature of the atmosphere becomes a threshold temperature which is a predetermined value higher than the reference temperature. At that time, the atmosphere is exhausted to the outside of the exterior cover, the temperature of the atmosphere is lowered, and the column is prevented from being deformed. Therefore, it is possible to suppress fluctuations in the finished thickness of the workpiece.

FIG. 1 is a perspective view showing a configuration example of a cutting tool according to the first embodiment. FIG. 2 is a plan view showing an example of a workpiece of the cutting tool according to the first embodiment. FIG. 3 is a plan view showing the device of the workpiece shown in FIG. FIG. 4 is a cross-sectional view of a main part of the workpiece shown in FIG. 2 before the turning cutting process. FIG. 5 is a cross-sectional view of a main part of the workpiece shown in FIG. 2 after swivel cutting. FIG. 6 is a perspective view of a chuck table of the cutting tool according to the first embodiment. FIG. 7 is a cross-sectional view taken along the line VII-VII of FIG. FIG. 8 is a flowchart showing a machining operation of the cutting tool according to the first embodiment. FIG. 9 is a plan view showing a swirl cutting process of the cutting tool according to the first embodiment. FIG. 10 is another plan view showing the swirling cutting process of the cutting tool according to the first embodiment. FIG. 11 is a perspective view showing a configuration example of a cutting tool cutting device according to a modified example of the first embodiment.

The embodiment (embodiment) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited to the contents described in the following embodiments. In addition, the components described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Further, the configurations described below can be combined as appropriate. In addition, various omissions, substitutions or changes of the configuration can be made without departing from the gist of the present invention.

[Embodiment 1]
The cutting tool according to the first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a configuration example of a cutting tool according to the first embodiment. FIG. 2 is a plan view showing an example of a workpiece of the cutting tool according to the first embodiment. FIG. 3 is a plan view showing the device of the workpiece shown in FIG. FIG. 4 is a cross-sectional view of a main part of the workpiece shown in FIG. 2 before the turning cutting process. FIG. 5 is a cross-sectional view of a main part of the workpiece shown in FIG. 2 after swivel cutting.

The cutting tool 1 shown in FIG. 1 according to the first embodiment swivels and cuts the surface of the workpiece W flatly. In the first embodiment, the workpiece W to be machined by the cutting tool 1 is a disk-shaped semiconductor wafer or optical device wafer whose substrate SB is silicon, sapphire, gallium arsenide, or the like, or a package made of metal or resin. Boards, interposer boards, etc. As shown in FIG. 2, the work piece W has a device D formed in a plurality of regions partitioned by a plurality of intersecting scheduled division lines L (orthogonal in the first embodiment). As shown in FIG. 3, the surface of the device D is coated with the mold resin UF, and a plurality of bump BPs are exposed from the mold resin UF.

Further, as shown in FIG. 4, the bump BP formed on the surface of the substrate SB is covered with the mold resin UF in the workpiece W before the swivel cutting process. The workpiece W is subjected to a swirling cutting process by the cutting tool 1, the mold resin UF and the bump BP are formed flat, and the bump BP is exposed as shown in FIG. In the present invention, the workpiece W is not limited to the one shown in FIG.

Next, the cutting tool 1 according to the first embodiment will be described with reference to the drawings. FIG. 6 is a perspective view of a chuck table of the cutting tool according to the first embodiment. FIG. 7 is a cross-sectional view taken along the line VII-VII of FIG. As shown in FIG. 1, the cutting tool 1 includes an apparatus base 2, a chuck table 10, a cutting unit 20, a machining feed unit 30, and a cutting feed unit 40.

The chuck table 10 holds the workpiece W on the holding surface 10a. The chuck table 10 is formed in a disk shape by a metal material such as stainless steel. As shown in FIGS. 6 and 7, the chuck table 10 has an outer peripheral annular holding portion 11 formed on the outer peripheral portion and a suction recess 12 formed inside the outer peripheral annular holding portion 11, and a plurality of suction recesses 12 are formed in the suction recess 12. Support pin 13 is provided. In the first embodiment, the outer peripheral annular holding portion 11 is formed to have a width of about 1 mm, and the support pin 13 is formed into a columnar shape having a diameter of 1 mm. As shown in FIG. 7, the thickness of the holding surface 10a for holding the workpiece W is about 200 μm on the upper surfaces of the outer peripheral annular holding portion 11 and the plurality of support pins 13 in the chuck table 10 configured in this way. A plating layer 14 made of nickel or the like is formed.

The suction recess 12 formed in the chuck table 10 is communicated with a suction means (not shown) via a suction passage 15. By operating a suction means (not shown), the chuck table 10 applies a negative pressure to the suction recess 12 through the suction passage 15 to suck and hold the workpiece W placed on the holding surface 10a. At this time, the workpiece W is supported by the outer peripheral annular holding portion 11 and the plurality of support pins 13. The chuck table 10 is supported by a support base (not shown) that is rotatable around an axial center parallel to the Z-axis direction. The Z-axis direction is parallel to the vertical direction.

The cutting unit 20 swivels and cuts a workpiece W held on the chuck table 10 by a tool wheel 23 including a tool tool 22 mounted on the tip of a spindle 21. The cutting unit 20 includes a motor 24 that is supported by a column 3 erected on the apparatus base 2 via a cutting feed unit 40 and that rotates the spindle 21 around the axis P.

The machining feed unit 30 is installed on the apparatus base 2 and relatively moves the chuck table 10 in the Y-axis direction, which is the machining feed direction parallel to the holding surface 10a. By moving the support base supporting the chuck table 10 in the Y-axis direction, the machining feed unit 30 extends the chuck table 10 from the loading / unloading position where the cutting unit 20 is separated to the machining position below the cutting unit 20. To move.

The cut feed unit 40 is fixed to a column 3 erected on the apparatus base 2, and moves the cutting unit 20 in the Z axis direction, which is the cut feed direction orthogonal to the holding surface 10a. The column 3 is a casting, and is formed in a columnar shape erected from an end portion of the apparatus base 2 near the processing position. The cutting feed unit 40 lowers the cutting unit 20 to bring the tool tool 22 closer to the workpiece W held by the chuck table 10 at the machining position, and raises the cutting unit 20 to raise the cutting tool 22 to the chuck table at the machining position. Keep away from the workpiece W held at 10.

The machining feed unit 30 and the cut feed unit 40 include a well-known ball screw rotatably provided around the axis, a well-known pulse motor for rotating the ball screw around the axis, and a chuck table 10 or a cutting unit 20 on the Y-axis. It is provided with a well-known guide rail that supports it so as to be movable in the direction or the Z-axis direction.

Further, the cutting tool 1 includes cassettes 8 and 9, alignment means 4, carry-in means 5, carry-out means 6, cleaning means 60, carry-in / out means 7, temperature measuring device 70, and exhaust unit 80. And a control unit 100, and is covered with an exterior cover 50 that houses each component.

The exterior cover 50 covers the upper part of the apparatus base 2 and accommodates each component of the cutting tool 1.

The cassettes 8 and 9 are accommodators for accommodating the workpiece W, and are installed at the end of the apparatus base 2 near the loading / unloading position. One cassette 8 accommodates the workpiece W before the swivel cutting process, and the other cassette 9 accommodates the workpiece W after the swivel cutting process. Further, the alignment means 4 is a table for temporarily placing the workpiece W taken out from the cassette 8 and aligning the center thereof.

The carry-in means 5 has a suction pad, sucks and holds the workpiece W before the turning cutting process aligned by the alignment means 4, and carries it onto the chuck table 10 located at the carry-in / out position. The carry-out means 6 has a suction pad, and sucks and holds the workpiece W after the swirling cutting process held on the chuck table 10 located at the carry-in / carry-out position and carries it out to the cleaning means 60.

The cleaning means 60 cleans the workpiece W after the tool grinding process. The loading / unloading means 7 is, for example, a robot pick provided with a U-shaped hand 7a, and the U-shaped hand 7a sucks and holds the workpiece W for transport. Specifically, the loading / unloading means 7 carries out the workpiece W before the swivel cutting process from the cassette 8 to the positioning means 4, and transfers the workpiece W after the swivel cutting process from the cleaning means 60 to the cassette 9. Carry in.

The temperature measuring device 70 measures the temperature of the atmosphere around the motor 24 inside the exterior cover 50 and rotating the spindle 21 of the cutting unit 20. The temperature measuring device 70 is attached to the exterior cover 50 and is arranged in the vicinity of the motor 24. The temperature measuring device 70 outputs the measurement result to the control unit 100. The temperature measuring device 70 is composed of various temperature sensors such as a thermistor, a resistance thermometer, a thermocouple, or a radiation thermometer.

The exhaust unit 80 exhausts the atmosphere around the motor 24 inside the exterior cover 50 and rotating the spindle 21 of the cutting unit 20 to the outside of the exterior cover 50. The exhaust unit 80 is attached to the exterior cover 50 and is arranged in the vicinity of the motor 24. The exhaust unit 80 includes an exhaust pipe 81 that is attached to the exterior cover 50 and communicates inside and outside the exterior cover 50, and a fan (not shown) provided inside the exhaust pipe 81.

The control unit 100 controls each of the above-mentioned components constituting the cutting tool 1. That is, the control unit 100 causes the cutting tool 1 to perform a machining operation on the workpiece W. The control unit 100 includes a temperature recording unit 101 and an exhaust unit control unit 102.

The cutting tool 1 cuts the holding surface 10a of the chuck table 10 with the cutting unit 20 before the turning cutting of the workpiece W, and shapes (forms) a new holding surface 10a orthogonal to the Z-axis direction. Perform cutting. At this time, the axial center P of the cutting unit 20 of the cutting tool 1 is parallel to the Z-axis direction. When the cutting tool 1 performs swivel cutting, the column 3 and the like are deformed by the heat generated by the motor 24, and the axial center P of the cutting unit 20 is tilted in the Z-axis direction.

The temperature recording unit 101 is inside the exterior cover 50 and of the cutting unit 20 when the holding surface 10a of the chuck table 10 is cut by the cutting unit 20 and self-cutting is performed by shaping (forming) the new holding surface 10a. A reference temperature, which is the temperature of the atmosphere around the motor 24 that rotates the spindle 21, and a threshold temperature higher than the reference temperature are recorded. The predetermined value, which is the difference between the threshold temperature and the reference temperature, is the temperature at which the angle between the axis P of the spindle 21, that is, the cutting unit 20 and the Z-axis direction is within 2 degrees. The temperature recording unit 101 stores the relationship between the reference temperature and the predetermined value in advance, reads out the predetermined value from the stored relationship when the reference temperature is input from the temperature measuring device 70, calculates the threshold temperature, and calculates the threshold temperature. Record the threshold temperature.

The exhaust unit control unit 102 operates the exhaust unit 80 when the temperature of the atmosphere around the motor 24 that rotates the spindle 21 of the cutting unit 20 in the exterior cover 50 reaches the threshold temperature. The exhaust unit control unit 102 operates the exhaust unit 80 in the exterior cover 50 until the temperature of the atmosphere around the motor 24 that rotates the spindle 21 of the cutting unit 20 falls below the threshold temperature.

The control unit 100 includes an arithmetic processing device having a microcomputer such as a CPU (central processing unit), a storage device having a memory such as a ROM (read only memory) or a RAM (random access memory), and an input / output interface device. It is a computer that has and can execute computer programs. The arithmetic processing unit of the control unit 100 executes a computer program stored in the ROM on the RAM to generate a control signal for controlling the bite cutting device 1. The arithmetic processing unit of the control unit 100 outputs the generated control signal to each component of the bite cutting device 1 via the input / output interface device. Further, the control unit 100 is connected to a display means (not shown) composed of a liquid crystal display device for displaying a processing operation state, an image, or the like, or an input means used by an operator when registering processing content information or the like. .. The input means is composed of at least one of a touch panel provided on the display means, a keyboard and the like.

The function of the temperature recording unit 101 of the control unit 100 is realized by the arithmetic processing unit executing a computer program stored in the ROM on the RAM and recording the reference temperature and the threshold temperature in the storage device. The function of the exhaust unit control unit 102 of the control unit 100 is realized by the arithmetic processing unit executing the computer program stored in the ROM on the RAM.

Further, the cutting tool 1 includes a notification unit 200 for notifying that the temperature of the atmosphere around the motor 24 inside the exterior cover 50 and rotating the spindle 21 of the cutting unit 20 has become higher than the threshold temperature. The notification unit 200 notifies the operator of the bite cutting device 1 that the temperature has risen above the threshold temperature by generating light or sound.

Next, an example of the machining operation of the cutting tool will be described. FIG. 8 is a flowchart showing a machining operation of the cutting tool according to the first embodiment. FIG. 9 is a plan view showing a swirl cutting process of the cutting tool according to the first embodiment. FIG. 10 is another plan view showing the swirling cutting process of the cutting tool according to the first embodiment.

First, the operator attaches the cassette 8 containing the workpiece W before the swivel cutting process and the cassette 9 not accommodating the workpiece W to the apparatus base 2, and registers the machining information in the control unit 100. The cutting tool 1 starts the machining operation when instructed to start the machining operation.

In the machining operation, the control unit 100 of the cutting tool 1 cuts the holding surface 10a of the chuck table 10 with the cutting unit 20 before the turning cutting of the workpiece W, and a new holding surface orthogonal to the Z-axis direction. Self-cutting to shape 10a is performed (step ST1). In step ST1, the control unit 100 of the cutting tool 1 operates the machining feed unit 30 to move the chuck table 10 that does not hold the workpiece W toward the machining position, and the chuck table 10 is shown in FIG. Position at the indicated position. Then, the control unit 100 of the tool cutting device 1 rotationally drives the motor 24, rotates the chuck table 10 around the axis, and rotates the tool wheel 23 to which the tool tool 22 is attached in the direction indicated by the arrow in FIG. For example, it rotates at a rotation speed of 6000 rpm.

Next, the control unit 100 of the tool cutting device 1 lowers the cutting unit 20 to position the tool tool 22 at a predetermined cutting position. Then, the chuck table 10 is moved from the position shown in FIG. 9 to the position shown in FIG. 10 at a feed rate of, for example, 2 mm / sec. As a result, the outer peripheral annular holding portion 11 constituting the chuck table 10 and the plating layer 14 formed on the upper surfaces of the plurality of support pins 13 are turned by the cutting edge of the tool tool 22 that rotates with the rotation of the tool wheel 23. The new holding surface 10a is shaped (formed). The depth of turning the plating layer 14 may be about 5 μm. The control unit 100 of the cutting tool 1 records the measurement result of the temperature measuring device 70 in step ST1 as a reference temperature, generates a threshold temperature, and records the reference temperature and the threshold temperature.

Next, the control unit 100 of the cutting tool 1 performs a swirling cutting process on the workpiece W in the cassette 8 one by one (step ST2). In step ST2, the control unit 100 of the cutting tool 1 causes the loading / unloading means 7 to take out the workpiece W from the cassette 8 and carry it out to the positioning means 4. The control unit 100 of the cutting tool 1 causes the alignment means 4 to align the center of the workpiece W, and the workpiece W aligned with the loading means 5 is placed on the chuck table 10 located at the loading / unloading position. To bring it in. The control unit 100 of the cutting tool 1 causes the chuck table 10 to hold the workpiece W, and the machining feed unit 30 conveys the workpiece W to the machining position.

The control unit 100 of the tool cutting device 1 rotates the tool wheel 23, rotates the chuck table 10 around the axis, positions the tool tool 22 at a predetermined cutting position, and positions the surface of the workpiece W at the machining position. The tool tool 22 is cut into the work piece W, and the work piece W is subjected to a swivel cutting process to form a flat surface of the work piece W and expose the bump BP. The control unit 100 of the cutting tool 1 transports the workpiece W subjected to the swivel cutting process to the loading / unloading position, transports the workpiece W to the loading / unloading position, transports the workpiece W to the cleaning means 60, cleans the cleaning means 60, and then carries in / out. The work piece W is accommodated in the cassette 9 by the means 7. The control unit 100 of the cutting tool 1 takes out the next workpiece W from the cassette 8 and performs a turning cutting process.

The control unit 100 of the cutting tool 1 determines whether or not the temperature of the atmosphere detected by the temperature measuring device 70 has reached the threshold temperature based on the measurement result of the temperature measuring device 70 during the swirling cutting process. Step ST3). When the control unit 100 of the cutting tool 1 determines that the temperature of the atmosphere detected by the temperature measuring device 70 is less than the threshold temperature (step ST3: No), the control unit 100 swirls and cuts all the workpieces W in the cassette 8. It is determined whether or not the processing has been performed (step ST4). When the control unit 100 of the cutting tool 1 determines that all the workpieces W in the cassette 8 have not been subjected to the turning cutting (step ST4: No), the control unit 100 returns to step ST3 and returns to all the workpieces W in the cassette 8. When it is determined that the workpiece W has been subjected to swivel cutting (step ST4: Yes), the machining operation is terminated.

When the control unit 100 of the cutting tool 1 determines that the temperature of the atmosphere detected by the temperature measuring device 70 has reached the threshold temperature (step ST3: Yes), even during cutting of the work piece W with a cutting tool W The swivel cutting process is interrupted, the exhaust unit 80 is operated, and when the temperature is higher than the threshold temperature, the notification unit 200 is notified (step ST5), and the process returns to step ST3. Then, the control unit 100 of the cutting tool 1 operates the exhaust unit 80 until it is determined that the temperature of the atmosphere detected by the temperature measuring device 70 is lower than the threshold temperature (step ST3: Yes), and the temperature exceeds the threshold temperature. When the temperature is high, the notification unit 200 is notified (step ST5). When the control unit 100 of the cutting tool 1 determines that the temperature of the atmosphere detected by the temperature measuring device 70 is less than the threshold temperature (step ST3: Yes), the exhaust unit 80 and the notification unit 200 are stopped and swiveled. The cutting process is restarted and the process proceeds to step ST4. In the first embodiment, in step ST5, the turning cutting process was interrupted even during the cutting of the workpiece W, but in the present invention, after the turning cutting process of the workpiece W being machined is completed. , The turning cutting process may be interrupted, or the process may be continued.

As described above, the tool cutting device 1 according to the first embodiment measures the temperature of the atmosphere around the motor 24 that rotates the spindle 21 during self-cutting to shape (form) the new holding surface 10a, and measures the reference temperature. When the temperature of the atmosphere becomes higher than the threshold temperature, which is a predetermined value higher than the reference temperature, the atmosphere inside the exterior cover 50 is exhausted to the outside, the temperature of the atmosphere inside the exterior cover 50 is lowered, and the column 3 is deformed. In order to prevent this, it is possible to suppress fluctuations in the finished thickness of the workpiece W.

Next, the inventor of the present invention confirmed the effect of the cutting tool 1 according to the first embodiment by measuring the variation in the in-plane thickness of the workpiece W. The results are shown in Table 1. The product of the present invention in Table 1 measures the variation in the in-plane thickness of the workpiece W by the cutting tool 1 according to the first embodiment, and the comparative example relates to the first embodiment without the exhaust unit 80. The variation in the in-plane thickness of the workpiece W by the cutting tool 1 is measured. In both the product of the present invention and the comparative example, the thickness of a predetermined portion of the workpiece W to which the swirl cutting process is performed about 10 sheets after the self-cutting is measured, and the in-plane thickness variation is measured. ..

In the comparative example, the front side (cutting unit 20 side) of the column 3 expands due to the heat generated by the motor 24, the column 3 is in a state of warping rearward of the device, and X is formed from the center of the workpiece W held by the holding surface 10a. Both sides in the direction are lower than the center, and when the workpiece W is held on the chuck table 10 in FIG. 9 for processing, the upper and lower sides in FIG. 9 are thinner than the center of the workpiece W. .. According to the results in Table 1, the variation in the in-plane thickness of such a comparative example is 3 μm, whereas the variation in the in-plane thickness of the product of the present invention is 1 μm, so that the temperature of the atmosphere is higher than the reference temperature. By exhausting the atmosphere inside the exterior cover 50 to the outside when the temperature becomes higher than the threshold temperature higher than the predetermined value, the variation in the in-plane thickness of the workpiece W can be suppressed, and the finished thickness of the workpiece W can be suppressed. It became clear that fluctuations can be suppressed.

The present invention is not limited to the above embodiment. That is, it can be modified in various ways without departing from the gist of the present invention. For example, the cutting tool 1 of the first embodiment includes only one cutting unit 20, but as shown in FIG. 11, the present invention includes a plurality of cutting units 20 and a plurality of motors 24 as heat sources. It can also be applied to cutting equipment 1-2. FIG. 11 is a perspective view showing a configuration example of a cutting tool cutting device according to a modified example of the first embodiment. In FIG. 11, the same parts as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

1, 1-2 Tool Cutting Device 2 Device Base 3 Column 10 Chuck Table 10a Holding Surface 20 Cutting Unit 21 Spindle 22 Tool Tool 23 Tool Wheel 24 Motor 30 Machining Feed Unit 40 Cutting Feed Unit 50 Exterior Cover 70 Temperature Measuring Instrument 80 Exhaust Unit 101 Temperature recording unit 102 Exhaust unit control unit 200 Notification unit

Claims (2)

Installed on a chuck table that holds the work piece on the holding surface, a cutting unit that swirls and cuts the work piece held on the chuck table with a tool wheel including a tool tool attached to the tip of the spindle, and a device base. A machining feed unit that moves the chuck table relative to the machining feed direction parallel to the holding surface, and a notch that is fixed to a column erected on the apparatus base and moves the cutting unit in a direction orthogonal to the holding surface. A tool cutting device that includes a feed unit and is covered with an exterior cover that houses each component.
A temperature measuring device that measures the temperature of the atmosphere around the motor that rotates the spindle of the cutting unit, and
A temperature recording unit that records a reference temperature, which is the temperature of the atmosphere when the holding surface of the chuck table is cut by the cutting unit to form a new holding surface, and a threshold temperature higher than the reference temperature.
An exhaust unit that exhausts the atmosphere to the outside of the exterior cover,
A bite cutting device including an exhaust unit control unit that operates the exhaust unit when the temperature of the atmosphere reaches the threshold temperature. The cutting tool according to claim 1, further comprising a notification unit for notifying that the temperature of the atmosphere has become higher than the threshold temperature.

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