JP7427327B2 - How to grind the workpiece - Google Patents

Description

The present invention relates to a workpiece grinding method used when grinding a workpiece formed into a non-circular shape in plan view.

2. Description of the Related Art Device chips equipped with devices such as LSI (Large Scale Integration) have become essential components in electronic devices such as mobile phones and personal computers. A device chip is produced by, for example, dividing the surface of a wafer made of a semiconductor material such as silicon into multiple regions along dividing lines (street), forming devices in each area, and then dividing the wafer along these dividing lines. It is obtained by

After obtaining multiple device chips using the method described above, for example, place these multiple device chips on a substrate for CSP (Chip Size Package), and bond each device chip to the substrate using a method such as wire bonding. Connect to terminals, etc. Then, a plurality of device chips are sealed with resin or the like to form a package substrate, and this package substrate is divided into a plurality of package device chips corresponding to each device chip.

In this way, by sealing each device chip with resin or the like, it becomes possible to protect the device chips from external factors such as impact, water, light, and heat. Note that a package substrate obtained by sealing a device chip with a resin or the like may be formed in a non-circular shape (typically, a rectangular shape) in plan view.

In recent years, electronic devices have become smaller and thinner, and the package device chips mounted on these electronic devices are also required to be smaller and thinner. When manufacturing thin package device chips, for example, a package substrate before being divided into package device chips is made thinner by a method such as grinding (for example, see Patent Document 1).

Japanese Patent Application Publication No. 2015-205358

By the way, when grinding a non-circular workpiece such as a package board by rotating and contacting a plurality of grindstones arranged in an annular manner with each other, the workpiece after grinding It is difficult to make the thickness the same throughout. This is because the area of contact between the grindstone and the workpiece changes due to the rotation of the non-circular workpiece, and the pressure exerted from the grindstone on the workpiece is not constant. Note that as the contact area increases, the pressure applied from the grindstone to the workpiece decreases, making it difficult for grinding to proceed.

On the other hand, for example, in the above-mentioned Patent Document 1, the rotation speed of the workpiece is reduced in the diagonal direction where the area required for contact between the rectangular workpiece and the grinding wheel increases, and the workpiece is rotated in the direction away from the diagonal. A method has been proposed to increase the speed of rotation. In this method, by keeping the contact area between the grindstone and the workpiece constant per unit time, variations in the thickness of the workpiece after grinding are suppressed. However, this method requires complex control to optimize the speed of rotation of the workpiece.

The present invention has been made in view of these problems, and its purpose is to provide a workpiece grinding method that can suppress variations in thickness that occur in non-circular workpieces by simple control. That's true.

According to one aspect of the present invention, a holding table holding a non-circular workpiece and a grinding wheel to which a grindstone for grinding is fixed are each rotated, and the surface to be ground of the workpiece is rotated. A workpiece grinding method of grinding the workpiece by bringing the grindstone into contact with the workpiece, the method comprising : grinding the entire area of the workpiece in plan view so that the load acting on the workpiece from the grindstone becomes a first value. and after the first grinding step, the load changes from a second value smaller than the first value to a third value larger than the second value and smaller than the first value. a second grinding step of grinding the entire area of the workpiece in plan view so that the value changes to a value of A method of grinding a workpiece is provided, wherein a first value is a maximum value reached by the load, which increases over time of grinding the workpiece.

In one aspect of the invention, the rectangular workpiece may be ground.

Further, in one aspect of the present invention, in the second grinding step, after the grindstone is separated from the ground surface of the workpiece and the load is set to the second value, the grindstone is moved to the grinding surface of the workpiece. It is preferable to change the load to the third value by contacting the surface to be ground again.

Further, in one aspect of the present invention, the first value is a variation in the thickness of the workpiece that occurs due to the area of contact between the workpiece and the grindstone being different for each region of the workpiece. is set to a value that exceeds a tolerance value, and the second value and the third value are preferably set to values that reduce variations in the thickness of the workpiece that occur in the first grinding step.

In the workpiece grinding method according to one aspect of the present invention, the workpiece is ground so that the load acting on the workpiece from the grindstone becomes a first value, and then this load is smaller than the first value. The workpiece is ground to change from the second value to a third value that is greater than the second value and less than the first value. That is, after grinding the workpiece with a predetermined load, the workpiece is ground with a smaller load.

As the load acting on the workpiece from the grindstone increases, the variation in thickness of the workpiece after grinding increases. On the other hand, when the load acting on the workpiece from the grindstone is reduced, the variation in thickness that occurs in the workpiece after grinding is also reduced. Therefore, by controlling the load as in the workpiece grinding method according to one aspect of the present invention, variations in thickness that occur in non-circular workpieces can be suppressed to a small level.

FIG. 1 is a perspective view showing a grinding device. FIG. 2 is a cross-sectional view showing how a workpiece is ground. FIG. 3 is a graph showing the relationship between the load applied from the grinding wheel to the workpiece and time when the grinding wheel is lowered at a constant speed to grind the workpiece. FIG. 4 is a plan view schematically showing variations in the thickness of the workpiece after grinding. FIG. 5 is a graph showing the relationship between the load acting on the workpiece from the grinding wheel and time in the workpiece grinding method according to the present embodiment.

Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a perspective view showing a grinding device 2 used in the workpiece grinding method according to the present embodiment, and FIG. 2 is a side view showing how a workpiece 11 is ground by this grinding device 2. be. In addition, in FIG. 2, some elements are shown by cut planes. Further, in FIG. 2, the shapes of some elements are exaggerated for convenience of explanation. Furthermore, the X-axis direction (front-back direction), Y-axis direction (left-right direction), and Z-axis direction (vertical direction) used in the following description are perpendicular to each other.

As shown in FIG. 1, the grinding device 2 includes a base 4 on which each component is mounted. A columnar support structure 6 is provided at the rear end of the base 4. An opening 4a that is long in the X-axis direction is formed in the upper surface of the base 4. A ball screw type X-axis moving mechanism 8 and a cover 10 that partially covers the X-axis moving mechanism 8 are arranged in the opening 4a. The X-axis moving mechanism 8 includes an X-axis moving table 8a, and moves the X-axis moving table 8a in the X-axis direction. An operation panel 12 is installed in front of the opening 4a, which is used to input grinding conditions and the like.

A holding table (chuck table) 14 for holding a plate-shaped workpiece 11 (FIG. 2, etc.) is provided on the X-axis moving table 8a. The workpiece 11 is a package substrate formed into a rectangular shape in plan view using, for example, a semiconductor such as silicon or a sealing resin (see FIG. 4). In this embodiment, the first surface (surface to be ground) 11a of the workpiece 11 is ground.

However, the workpiece 11 only needs to be formed into a non-circular shape at least in plan view, and there are no major restrictions on its material, shape, structure, size, etc. For example, a substrate formed using materials such as other semiconductors, other resins, ceramics, and metals can also be used as the workpiece 11. A device such as an LSI (Large Scale Integration) may be provided on the second surface 11b of the workpiece 11 opposite to the first surface 11a (the surface that is not ground).

A part of the upper surface of the holding table 14 is a holding surface 14a for holding the workpiece 11. The holding surface 14a is configured to include a conical side surface in a part of the center, and is connected to a suction source (not shown) through a suction path 14b (FIG. 2) formed inside the holding table 14. There is. Moreover, the holding surface 14a is formed in a shape (rectangular shape) corresponding to the workpiece 11 in plan view.

By placing the workpiece 11 on this holding surface 14a and applying negative pressure from a suction source, the workpiece 11 can be sucked and held by the holding table 14. Although the shape of the side surface of the cone that forms part of the holding surface 14a is exaggerated in FIG. 2, in reality, the difference (height difference) between the highest point and the lowest point of the holding surface 14a is It becomes about 15 μm to 20 μm.

The holding table 14 is connected to a rotational drive source (not shown) such as a motor, and is rotated parallel to the Z-axis direction so that the apex 14c of the holding surface 14a, which corresponds to the apex of the cone, is the center of rotation. It rotates around a rotation axis or a rotation axis slightly tilted with respect to the Z-axis direction. Further, the holding table 14 is moved in the X-axis direction together with the X-axis moving table 8a by the above-mentioned X-axis moving mechanism 8.

A Z-axis moving mechanism 16 is provided on the front surface of the support structure 6. The Z-axis moving mechanism 16 includes a pair of Z-axis guide rails 18 that are generally parallel to the Z-axis direction, and a Z-axis moving plate 20 is attached to the Z-axis guide rails 18 in a slidable manner. There is. A nut (not shown) constituting a ball screw is fixed to the rear side (back side) of the Z-axis moving plate 20, and this nut has a screw shaft 22 that is generally parallel to the Z-axis guide rail 18. They are rotatably connected.

A Z-axis pulse motor 24 is connected to one end of the screw shaft 22 . By rotating the screw shaft 22 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 support 26 that protrudes forward is provided on the front (surface) of the Z-axis moving plate 20.

A grinding unit (processing unit) 28 for grinding the workpiece 11 is supported on the support 26 . Grinding unit 28 includes a spindle housing 30 that is secured to support 26 . A spindle 32 serving as a rotating shaft is rotatably housed in the spindle housing 30 .

A lower end portion of the spindle 32 is exposed to the outside of the spindle housing 30. A disc-shaped wheel mount 34 is provided at the lower end of the spindle 32. A disc-shaped grinding wheel 36 having approximately the same diameter as the wheel mount 34 is fixed to the lower surface of the wheel mount 34 with bolts or the like.

The grinding wheel 36 includes a disc-shaped (annular) wheel base 38 (FIG. 2) made of stainless steel, aluminum, or the like. The wheel base 38 has an upper surface and a lower surface that are generally parallel to each other, and a circular opening that penetrates the wheel base 38 from the upper surface to the lower surface is formed in the center thereof. Further, inside the wheel base 38, a flow path is provided for supplying a liquid (processing liquid) such as pure water downward.

On the lower surface of the wheel base 38, a plurality of grinding wheels 40, each made of a binder such as resin or metal with abrasive grains such as diamond or CBN (Cubic Boron Nitride) dispersed therein, are arranged in a ring. There are no particular restrictions on the type (material) of the binder that constitutes the grindstone 40, the material and size of the abrasive grains, but these may vary depending on, for example, the material of the workpiece 11, the flatness required for grinding, etc. It can be set arbitrarily.

When grinding the first surface 11a of the workpiece 11 using the grinding device 2, first, the entire second surface 11b of the workpiece 11 is brought into contact with the holding surface 14a of the holding table 14, and this holding surface 14a Apply negative pressure from a suction source to the As a result, the second surface 11b of the workpiece 11 is attracted by the holding table 14, and the workpiece 11 is held on the holding table 14 with the first surface 11a exposed upward.

After the workpiece 11 is held by the holding table 14, the holding table 14 is moved by the X-axis moving mechanism 8, and the grindstone 40 is moved to a position corresponding to the apex 14c of the holding surface 14a, for example, as shown in FIG. The relative positions of the holding table 14 and the grinding wheel 36 are adjusted so that they can pass through.

Next, the holding table 14 and the grinding wheel 36 are rotated in a predetermined direction at a predetermined number of rotations. The rotation speed of the holding table 14 is, for example, 10 rpm to 1000 rpm, and the rotation speed of the grinding wheel 36 is, for example, 1000 to 5000 rpm. However, the rotation speed of the holding table 14 and the rotation speed of the grinding wheel 36 are not limited to these.

Then, while supplying liquid (processing liquid) to the first surface 11a of the workpiece 11 through the channel of the wheel base 38, the grinding wheel 40 is brought into contact with the first surface 11a of the workpiece 11, and the grinding wheel 36 is rotated. lower at a predetermined speed. Thereby, as shown in FIG. 2, the workpiece 11 can be made thinner by grinding off the first surface 11a side of the workpiece 11 using the grindstone 40.

The speed at which the grinding wheel 36 is lowered is, for example, 0.1 μm/s to 1.0 μm/s, and the amount of liquid supplied is, for example, 1.0 L/min to 10.0 L/min. However, the speed at which the grinding wheel 36 is lowered and the amount of liquid supplied are not limited to these.

FIG. 3 is a graph showing the relationship between the load w acting on the workpiece 11 from the grinding wheel 36 and the time t when the grinding wheel 36 is lowered at a constant speed to grind the workpiece 11. Note that this load w is measured, for example, by a load sensor provided at the bottom of the holding table 14.

As shown in FIG. 3, from time _ts when the grindstone 40 contacts the workpiece 11 to a predetermined time _t1 , the load w acting on the workpiece 11 from the grindstone 40 increases as time passes. After the load w reaches the first value w ₁ at time t ₁ , the load w hardly changes until time t _e when grinding ends. Note that the time _te at which the grinding ends is determined based on, for example, the amount of descent of the grinding wheel 36 that is necessary when processing the workpiece 11 to a desired thickness.

By the way, when the workpiece 11, which is rectangular in plan view, is ground by the above-described method, grinding progresses more slowly in areas close to the diagonal of the rectangle than in areas away from the diagonal. This is because in the area close to the diagonal line, the workpiece 11 and the grinding wheel 36 (grinding stone 40) come into contact over a wider area than in the area away from the diagonal line, and the load (i.e., pressure) per unit area becomes smaller.

Therefore, when the workpiece 11, which is rectangular in plan view, is ground with a constant load, variations in the thickness of the workpiece 11 are likely to occur. A similar phenomenon occurs when grinding a non-circular workpiece with a constant load. FIG. 4 is a plan view schematically showing variations in the thickness of the workpiece 11 after grinding. Note that, in FIG. 4, thick regions within the workpiece 11 are shown with dense hatching, and thin regions within the workpiece 11 are shown with sparse hatching.

As shown in FIG. 4, the workpiece 11 after grinding is thick in areas close to the diagonal and thin in areas away from the diagonal. That is, the thickness of the workpiece 11 after grinding is maximum in the region A closest to the diagonal, and minimum in the region D furthest from the diagonal. More specifically, the workpiece 11 becomes thinner in the order of region A, region B, region F, region C, region E, and region D. In this way, with the above-described method in which the load w hardly changes after reaching the first value _w1 , the workpiece 11, which is rectangular (non-circular) in plan view, cannot necessarily be ground flat.

Therefore, in the workpiece grinding method according to the present embodiment, the load w is changed so that the variation in the thickness of the workpiece 11 is reduced. Specifically, the workpiece 11 is ground under conditions in which the load w generated by contact between the workpiece 11 and the grindstone 40 becomes a first value _w1 (first grinding step), and then the load w becomes the first value w1. Grinding the workpiece ₁₁ under conditions that change from a second value w ₂ smaller than the value w ₁ to a third value w ₃ larger than the second value w ₂ and smaller than the first value w 1 ( 2nd grinding step).

FIG. 5 is a graph showing the relationship between the load w acting on the workpiece 11 from the grinding wheel 36 and the time t in the workpiece grinding method according to the present embodiment. In the workpiece grinding method according to the present embodiment, the workpiece 11 exposed above is rotated while the holding table 14 holding the workpiece 11 and the grinding wheel 36 to which the grindstone 40 is fixed are rotated. The workpiece 11 is ground by bringing the grindstone 40 into contact with the first surface (surface to be ground) 11a.

The rotation speed of the holding table 14 is, for example, 10 rpm to 1000 rpm, typically about 300 rpm, and the rotation speed of the grinding wheel 36 is, for example, 1000 to 5000 rpm, typically about 1700 rpm. However, the rotation speed of the holding table 14 and the rotation speed of the grinding wheel 36 are not limited to these.

Further, the speed at which the grinding wheel 36 is lowered is, for example, 0.1 μm/s to 1.0 μm/s, typically about 0.6 μm/s, and the amount of liquid supplied is, for example, 1.0 L. /min to 10.0 L/min, typically about 4.0 L/min. However, the speed at which the grinding wheel 36 is lowered and the amount of liquid supplied are not limited to these.

As shown in FIG. 5, from the time _ts when the grindstone 40 contacts the workpiece 11 to the predetermined time _t1 , the load w generated by the contact between the workpiece 11 and the grindstone 40 increases over time. increase After the load w reaches the first value w ₁ at time t ₁ , the load w hardly changes until time t ₂ . Note that this first value _w1 is determined by conditions such as the size and material of the workpiece 11, the size of the grinding wheel 36, the material of the grindstone 40, and the speed at which the grinding wheel 36 is lowered. In this embodiment, the first value _w1 is approximately 55N.

At time _t2 , the grinding device 2 is operated so that the load w changes to a second value _w2 smaller than the first value _w1 . For example, by raising the grinding wheel 36 and separating the grindstone 40 from the first surface 11a of the workpiece 11, the load w can be changed to a second value _w2 smaller than the first value _w1 . can. Note that in this case, the second value _w2 becomes zero (ie, no load).

Thereafter, the grindstone 40 is brought into contact with the workpiece 11 again at time _t3 . Conditions such as the number of rotations of the holding table 14, the number of rotations of the grinding wheel 36, the speed at which the grinding wheel 36 is lowered, and the amount of liquid supplied are determined based on the grinding performed between time _t1 (time _ts ) and time _t2 . The conditions may be the same as those for (first grinding step).

Then, at time t _e when the load w reaches a third value w ₃ smaller than the first value w ₁ , grinding of the workpiece 11 is finished. That is, the grinding of the workpiece 11 is finished before the load w increases to the first value _w1 . The third value w ₃ is, for example, 3/4 or less of the first value w ₁ , preferably 2/3 or less of the first value w ₁ . Note that in this embodiment, the third value _w3 is set to about 30N.

In this way, by reducing the load w at the final timing of grinding, variations in the thickness of the workpiece 11 can be suppressed to a small level. The workpiece grinding method according to the present embodiment is based on the new knowledge that the larger the load w, the larger the variation in the thickness of the workpiece 11, and the smaller the load w, the smaller the variation in the thickness of the workpiece 11. be.

Note that there is no particular restriction on the above-described first value w ₁ , second value w ₂ , and third value w ₃ . For example, the first value _w1 is a variation in thickness that exceeds the allowable value (a variation in thickness that occurs due to the area of contact between the workpiece 11 and the grindstone 40 being different for each region of the workpiece 11). ) may be set to a value that occurs on the workpiece 11.

On the other hand, the second value w ₂ and the third value w ₃ can reduce the variation in the thickness of the workpiece 11 caused by grinding at the first value w ₁ (first grinding step). set to the value. However, the second value _w2 does not have to be zero (no load). That is, it is not necessary to completely separate the grindstone 40 from the first surface 11a of the workpiece 11.

Note that if the grindstone 40 is completely separated from the first surface 11a of the workpiece 11, the grindstone 40 will wear out when it comes into contact with the first surface 11a of the workpiece 11 again, so that so-called self-sharpening will occur. Easy to occur. Therefore, the workpiece 11 can be ground with the grindstone 40 in a better condition than when the grindstone 40 is not completely separated from the first surface 11a of the workpiece 11.

As described above, in the workpiece grinding method according to the present embodiment, after grinding the workpiece 11 with a predetermined load w (first value w ₁ ), a smaller load w (second value w 1 ) is applied. ₂ to the third value w ₃ ), the workpiece 11 is ground with a predetermined load w (the first value w ₁ ). Variations in thickness that occur can be suppressed to a small level.

Note that the present invention is not limited to the description of the embodiments described above, and can be implemented with various modifications. For example, in the embodiment described above, the holding table 14 including the holding surface 14a having a shape (rectangular shape) corresponding to the workpiece 11 in plan view is used; You may also use a holding table that includes: In this case, for example, a tape or the like that can cover the entire holding surface may be attached to the workpiece 11.

Furthermore, in the embodiment described above, the conditions for the grinding (second grinding step) performed between time t ₃ and time t _e are changed from the conditions for grinding performed between time t ₁ (time t _s ) and time t ₂ . Although the conditions are the same as those for grinding (first grinding step), they may be different. For example, the conditions for grinding performed between time t ₃ and time _te can be set so that the third value w ₃ becomes smaller.

In addition, the structures, methods, etc. according to the embodiments and modifications described above can be modified and implemented without departing from the scope of the objective of the present invention.

2: Grinding device 4: Base 4a: Opening 6: Support structure 8: X-axis moving mechanism 8a: X-axis moving table 10: Cover 12: Operation panel 14: Holding table (chuck table)
14a: Holding surface 14b: Suction path 14c: Vertex 16: Z-axis moving mechanism 18: Z-axis guide rail 20: Z-axis moving plate 22: Screw shaft 24: Z-axis pulse motor 26: Support tool 28: Grinding unit 30: Spindle Housing 32: Spindle 34: Wheel mount 36: Grinding wheel 38: Wheel base 40: Grinding wheel 11: Workpiece 11a: First surface (surface to be ground)
11b: Second surface A: Area B: Area C: Area D: Area E: Area F: Area

Claims (4)

While rotating a holding table holding a non-circular workpiece and a grinding wheel to which a grinding wheel is fixed, the workpiece is brought into contact with the grinding surface of the workpiece. A method for grinding a workpiece, comprising:
a first grinding step of grinding the entire area of the workpiece in plan view so that the load acting on the workpiece from the grindstone becomes a first value;
After the first grinding step, the load changes from a second value that is less than the first value to a third value that is greater than the second value and less than the first value. a second grinding step of grinding the entire area of the workpiece in plan view ;
The first grinding step and the second grinding step are performed under common grinding conditions,
A method for grinding a workpiece, wherein the first value is a maximum value reached by the load, which increases with the lapse of grinding time of the workpiece . 2. The method of grinding a workpiece according to claim 1, wherein the workpiece has a rectangular shape. In the second grinding step, the grindstone is separated from the surface to be ground of the workpiece to bring the load to the second value, and then the grindstone is brought into contact with the surface to be ground of the workpiece again. 3. The workpiece grinding method according to claim 1, further comprising changing the load to the third value. The first value is set to a value that causes variations in the thickness of the workpiece that occur due to the area of contact between the workpiece and the grindstone being different for each area of the workpiece to exceed a tolerance value. ,
The second value and the third value are set to values that reduce variations in the thickness of the workpiece that occur in the first grinding step. Method for grinding workpieces described in Crab.

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