JP7193969B2 - Rectangular substrate grinding method - Google Patents

Description

The present invention relates to a method of grinding a rectangular substrate.

In the manufacturing process of semiconductor devices, a plurality of semiconductor chips on which circuits such as LSIs are formed are mounted on a printed circuit board or the like, and after the electrodes of the semiconductor chips are bonded to the electrodes of the substrate, the front or back surface is covered with resin. A package substrate such as a CSP (Chip Size Package) substrate is formed by sealing.

As electronic devices have become smaller and thinner in recent years, there has been a strong demand for smaller and thinner semiconductor devices. It is manufactured by grinding and thinning. Such a package substrate may be formed in a rectangular (square or rectangular) shape, and in grinding a rectangular substrate, a rotating grinding wheel is brought into contact with the upper surface of the rectangular substrate held by suction on a chuck table. Grinding with the grinding wheel is continued until the rectangular substrate reaches a desired thickness.

In the rectangular substrate to be ground, the grinding area of the grinding wheel (the area in which the grinding wheel hits the rectangular substrate) that comes into contact with the rectangular substrate during grinding varies greatly, such as widening or narrowing within the rectangular substrate. Due to this difference, the grinding load on the rectangular substrate also changes, and in the state where the grinding area of the grinding wheel with respect to the rectangular substrate increases, the grinding load increases, the grinding force decreases, and the thickness of the rectangular substrate after grinding increases compared to other places. In a state where the grinding area of the grinding wheel with respect to the rectangular substrate is narrow, the grinding load is reduced and the grinding force is increased, so that the thickness of the rectangular substrate after grinding becomes thinner than other portions.
Since the grinding force varies in the rectangular substrate, there is a problem that the thickness of the rectangular substrate varies greatly after grinding. In particular, a rectangular substrate has a larger difference in the lengths of its short sides, long sides, and diagonals, which causes a greater variation in the grinding force within the rectangular substrate. There is a big problem.

In order to cope with this problem, as the grinding wheel approaches the grinding wheel in the diagonal direction of the rectangular substrate where the grinding area becomes larger, the rotation speed of the chuck table is increased, and as the grinding wheel moves away from the diagonal direction of the rectangular substrate, the holding table. There is a technique for suppressing thickness variations by lowering the rotational speed of and equalizing the grinding area per unit time (see, for example, Patent Document 1).

Japanese Patent No. 6292958

However, the technique described in Patent Document 1 poses a problem because the grinding apparatus needs to perform complicated control of rotation of the chuck table, rotation of the grinding wheel, and the like.
Therefore, in the case of grinding a rectangular substrate, there is a problem of suppressing variations in the thickness of the rectangular substrate after grinding, even if the grinding apparatus does not perform complicated control of the rotation of the chuck table and the like.

The present invention for solving the above-mentioned problems is a method for grinding a rectangular substrate to grind the back surface of the rectangular substrate to a desired finish thickness, wherein a grinding wheel attached to a spindle rotated by a motor of a grinding unit grinds a chuck. a holding surface grinding step of grinding a rectangular holding surface of the table having the same shape as the rectangular substrate and forming the holding surface of the chuck table into a curved surface by changing the grinding area of the grinding wheel; and the holding surface grinding step. a holding step of holding the front surface of the rectangular substrate on the holding surface of the chuck table that has been ground by the grinding unit; and a step of grinding a rectangular substrate in the state of a surface, wherein the curvature of the back surface caused by a difference in grinding area that occurs when grinding the rectangular substrate is removed in the holding surface grinding step by grinding the back surface into the same shape as the rectangular substrate. A method of grinding a rectangular substrate characterized by improving the accuracy of the thickness of the rectangular substrate after grinding by forming a similar shape in advance on the holding surface of a chuck table having the rectangular holding surface.

The holding surface of the chuck table is preferably made of the same material as the rectangular substrate.

A method for grinding a rectangular substrate according to the present invention includes grinding (self-grinding) a rectangular holding surface of a chuck table having the same shape as the rectangular substrate with a grinding wheel attached to a spindle rotated by a motor of a grinding unit, and A holding surface grinding step for forming a holding surface of the chuck table into a curved surface by a change in the grinding area of the grinding wheel caused by the difference in the length of the sides or diagonals of the rectangle, and the chuck table ground in the holding surface grinding step. a holding step of holding the front surface of the rectangular substrate on the holding surface of the rectangular substrate, and a rectangular substrate grinding step of grinding the back surface of the rectangular substrate held on the holding surface of the chuck table in a curved state by a grinding wheel attached to the grinding unit. , the curvature of the back surface of the rectangular substrate due to the difference in the grinding area that occurs when the rectangular substrate is ground is corrected by a chuck table having a rectangular holding surface having the same shape as the rectangular substrate in the holding surface grinding step. It is possible to improve the thickness accuracy of the rectangular substrate after grinding by forming the same in advance on the holding surface of .

By making the holding surface of the chuck table of the same material as the rectangular substrate, in the rectangular substrate grinding step, the grinding conditions for grinding the rectangular substrate can be set to be the same as those in the holding surface grinding step. It becomes possible to perform the substrate grinding step smoothly and easily.

FIG. 1A is a plan view showing an example of a chuck table. FIG. 1B is a perspective view showing an example of a chuck table. FIG. 2(A) is a side view of the chuck table and the grinding unit viewed from the lateral direction of the protrusion for explaining the holding surface grinding step. FIG. 2(B) is a side view of the chuck table and the grinding unit viewed from the longitudinal direction of the projection for explaining the holding surface grinding step. FIG. 3A is a side view of the convex portion of the chuck table after the holding surface grinding step is seen from the lateral direction. FIG. 3B is a side view of the convex portion of the chuck table after the holding surface grinding step, as seen from the longitudinal direction. FIG. 4A is a side view of the chuck table holding the rectangular substrate and the grinding unit viewed from the lateral direction of the convex portion for explaining the rectangular substrate grinding step. FIG. 4B is a side view of the chuck table holding the rectangular substrate and the grinding unit viewed from the longitudinal direction of the projection for explaining the rectangular substrate grinding step. FIG. 10 is a perspective view for explaining a problem in a conventional method for grinding a rectangular substrate;

Each step of the method for grinding a rectangular substrate according to the present invention will be described below.
(1) Holding surface grinding step The chuck table 3 illustrated in FIGS. A convex portion 31 and a convex portion 32 having a rectangular shape in a plan view are protruded from. Note that the rectangular shape includes a square shape and a rectangular shape. In the present embodiment, two projections 31 and 32 are arranged on the upper surface of the base 30 with a predetermined interval in the lateral direction (X-axis direction) of the projections 31 and 32 . For example, four or six rectangular projections may be provided on the upper surface of the base 30 at equal intervals in the horizontal plane (X-axis Y-axis plane), or one may be disposed.
For example, the length of the convex portion 31 (32) in the short direction is 69 mm and the length in the longitudinal direction is 232 mm.

For example, the convex portion 31 (32) is made of a material such as resin or alloy, and has a plurality of suction grooves and a plurality of suction holes penetrating therethrough in the thickness direction. It communicates with a suction source (not shown) through a channel. Then, the suction force generated by the suction by the suction source is transmitted to the holding surface 31a (32a), which is the upper surface of the projection 31 (32), through the suction grooves and suction holes. 3 sucks and holds the rectangular substrate W on the holding surface 31a (32a).
In FIGS. 1A and 1B, the holding surface 31a and the holding surface 32a of the chuck table 3 are in a state before being ground, and are substantially flat surfaces.

The configuration of the convex portion 31 (32) is not limited to the above example. The convex portion 31 (32) includes, for example, a rectangular plate-shaped suction portion made of a porous member or the like for sucking and holding the rectangular substrate W, and a frame surrounding and supporting the suction portion in a state in which the suction portion is fitted. may be provided. The suction portion communicates with a suction source (not shown) through a channel formed in the base portion 30, and the suction force generated by suction by the suction source is applied to the exposed surface of the suction portion (convex portions 31 (32)). The chuck table 3 sucks and holds the rectangular substrate W on the two holding surfaces 31a and 32a, respectively.

In the present embodiment, the rectangular substrate W shown in FIGS. 1A and 1B is a substrate made of the same resin or alloy as the holding surface 31a (32a) of the projection 31 (32). The rectangular substrate W is, for example, a rectangular substrate such as a CSP (Chip Size Package) or a QFN (Quad Flat NON-Leaded Package) in which a chip on which an integrated circuit such as an IC or LSI is formed is packaged with resin, or glass or the like. The substrate may be made of a hard brittle material such as sapphire.

As shown in FIGS. 2A and 2B, in the method of grinding a rectangular substrate according to the present invention, first, the flat holding surfaces 31a and 32a of the chuck table 3 are ground with the grinding wheel 24a of the grinding unit 2. Grind.
The grinding unit 2 includes a spindle 21 whose axial direction is the Z-axis direction, a motor 22 that rotationally drives the spindle 21, a mount 23 that is connected to the lower end of the spindle 21, and a lower surface of the mount 23 that is detachably attached. and a grinding wheel 24 . The grinding unit 2 can be reciprocated in the Z-axis direction by grinding feed means (not shown).

The grinding wheel 24 includes an annular wheel base 24b and a plurality of substantially rectangular parallelepiped grinding wheels 24a annularly arranged on the lower surface of the wheel base 24b. The grinding wheel 24a is formed, for example, by bonding diamond abrasive grains or the like with an appropriate binder.
The diameter of the grinding wheel 24 is set, for example, larger than the radius of the base 30 of the chuck table 3 and smaller than the diameter of the base 30 .

For example, inside the spindle 21, a channel (not shown) that communicates with the grinding water supply source and serves as a path for the grinding water is formed through the spindle 21 in the axial direction. is opened so that grinding water can be ejected toward the grinding wheel 24a.
2A and 2B, the chuck table 3 can reciprocate in the Y-axis direction relative to the grinding unit 2, and rotates around the axis in the Z-axis direction passing through the center of the chuck table 3. It is rotatable.

In the holding surface grinding step, the chuck table 3 is moved in the Y-axis direction to below the grinding unit 2, and the grinding wheel 24 provided in the grinding unit 2 and the holding surface 31a of the projection 31 and the holding surface 32a of the projection 32 are ground. are aligned. For example, as shown in FIGS. 2A and 2B, the alignment is performed by shifting the center of rotation of the grinding wheel 24 from the center of rotation of the chuck table 3 by a predetermined distance in the horizontal direction, and rotating the grinding wheel 24a. The trajectory is made to pass through the center of rotation of the chuck table 3 .

Here, in FIGS. 1A and 1B, the grinding wheel 24 provided in the grinding unit 2 and the holding surface 31a of the projection 31 and the holding surface 32a of the projection 32 are aligned as described above. In this case, the grinding area of the rotating grinding wheel 24a (the area where the grinding wheel 24a is in contact with the holding surface 31a (32a)) due to the different lengths of four sides or two diagonals of the holding surface 31a and the holding surface 32a Depending on the change, the extent to which the substantially flat holding surfaces 31a and 32a of the chuck table 3 before being ground are easily ground by the grinding wheel 24a is indicated by the shade of color.

In FIGS. 1(A) and 1(B), the relatively dark colored portions of the holding surface 31a (32a) of the convex portion 31 (32) indicate that the grinding wheel 24a is being ground against the holding surface 31a (32a) during grinding. This shows a portion that is difficult to grind because the grinding force of the grinding wheel 24a decreases as the area increases and the grinding load increases.
In FIGS. 1(A) and 1(B), the portions with relatively light color on the holding surface 31a (32a) of the convex portion 31 (32) indicate that the grinding wheel 24a is not ground against the holding surface 31a (32a) during grinding. Since the grinding force of the grinding wheel 24a increases as the area becomes narrower and the grinding load decreases, the locations that are likely to be ground are shown.

As shown in FIGS. 2A and 2B, as the motor 22 drives the spindle 21 to rotate, the grinding wheel 24 rotates about the axis in the Z-axis direction. Further, the grinding unit 2 descends in the -Z direction, and the grinding process is performed by bringing the grinding wheel 24a into contact with the holding surface 31a (32a) of the projection 31 (32). During grinding, since the chuck table 3 also rotates around the axis in the Z-axis direction, the grinding wheel 24a grinds the entire holding surface 31a (32a) of the projection 31 (32).
For example, during grinding, grinding water is supplied to the contact portion between the grinding wheel 24a and the holding surface 31a (32a) of the convex portion 31 (32) through the channel in the spindle 21 to cool and cool the contact portion. wash.

By performing the grinding process for a predetermined period of time, four sides or two diagonals of the holding surface 31a and the holding surface 32a of the chuck table 3 have different lengths as shown in FIGS. Due to the resulting change in the grinding area of the rotating grinding wheel 24a, the holding surface 31a and the holding surface 32a are ground into curved surfaces. Hereinafter, the curved holding surface 31a will be referred to as a holding surface 311a, and the curved holding surface 32a will be referred to as a holding surface 322a.
Then, the grinding unit 2 is raised, the grinding wheel 24a is separated from the holding surface 311a and the holding surface 322a, and the holding surface grinding step is completed.

The holding surface 311a and the holding surface 322a, which are curved surfaces shown in FIGS. It is determined by the ease (difficulty) of grinding by.

(2) Holding Step Next, the surfaces Wa of the two rectangular substrates W are respectively held on the holding surfaces 311a and 322a of the chuck table 3 ground in the holding surface grinding step. That is, as shown in FIGS. 4A and 4B, the lateral direction and the longitudinal direction are aligned, and the center of the rectangular substrate W and the center of the holding surface 311a (322a) of the convex portion 31 (32) are aligned. The rectangular substrate W is placed on the holding surface 311a (322a) such that the . A suction force generated by a suction source (not shown) is transmitted to the holding surface 311a (322a), whereby the chuck table 3 holds the rectangular substrate W by suction on the holding surface 311a (322a).
The rectangular substrate W held by suction has a curved back surface Wb following the curved holding surface 311a (322a) as a whole.

(3) Rectangular substrate grinding step Next, the back surfaces Wb of the two rectangular substrates W held on the holding surface 311a (322a) of the chuck table 3 by the grinding wheel 24a mounted on the grinding unit 2 are curved. Grind.
In the rectangular substrate grinding step, the chuck table 3 moves in the Y-axis direction to below the grinding unit 2, and the grinding wheel 24 provided in the grinding unit 2 and the two rectangular substrates W are aligned. For example, as shown in FIGS. 4A and 4B, the alignment is performed by shifting the center of rotation of the grinding wheel 24 from the center of rotation of the chuck table 3 by a predetermined distance in the horizontal direction, and rotating the grinding wheel 24a. The trajectory is made to pass through the center of rotation of the chuck table 3 .

As shown in FIGS. 4A and 4B, the grinding wheel 24 rotates about the Z-axis direction as the spindle 21 is driven to rotate by the motor 22 . Further, the grinding unit 2 descends in the -Z direction, and the grinding wheel 24a comes into contact with the rear surface Wb of each rectangular substrate W, thereby performing the grinding process. During grinding, the chuck table 3 also rotates around the axis in the Z-axis direction, so that the grinding wheel 24a grinds the entire curved back surface Wb of each rectangular substrate W. FIG.
For example, during grinding, grinding water is supplied to the contact portion between the grinding wheel 24a and the curved back surface Wb of each rectangular substrate W through the channel in the spindle 21 to cool and wash the contact portion. .

In the present embodiment, the rectangular substrate W is a substrate made of the same resin or alloy as the holding surface 311a (322a) of the projection 31 (32). The grinding processing conditions in the step (grinding feed speed in the −Z direction of the grinding unit 2, rotation speed of the grinding wheel 24, rotation speed of the chuck table 3, etc.) can be applied as they are.
On the other hand, when the rectangular substrate W is a substrate made of a material different from that of the holding surface 311a (322a) of the projection 31 (32), in the rectangular substrate grinding step, the grinding processing conditions in the previously performed holding surface grinding step (Grinding feed speed in the -Z direction of the grinding unit 2, rotation speed of the grinding wheel 24, rotation speed of the chuck table 3, etc.) are appropriately changed.

Here, for example, as in the conventional method of grinding a rectangular substrate, the rectangular substrate W is sucked and held by the holding surface 31a (32a) of the chuck table 3 shown in FIG. Problems in the case of grinding will be explained.
In FIG. 5, the center of rotation of the grinding wheel 24 is horizontally displaced from the center of rotation of the chuck table 3 holding two rectangular substrates W by a predetermined distance, and the rotation orbit of the grinding wheel 24a is shifted from the center of rotation of the chuck table 3. Positioned to pass through the center of rotation. In this state, the grinding unit 2 descends in the -Z direction, and the rotating grindstone 24a comes into contact with the rear surface Wb of each rectangular substrate W, thereby performing the grinding process. During grinding, the chuck table 3 also rotates around the axis in the Z-axis direction, so that the grinding wheel 24a grinds the entire curved back surface Wb of each rectangular substrate W. FIG.

In FIG. 5, the rectangular substrate W is changed in the grinding area of the rotating grinding wheel 24a (the area where the grinding wheel 24a is in contact with the rectangular substrate W) due to the four sides or two diagonals of the rectangular substrate W having different lengths. The gradation of color indicates how easily the is ground by the grinding wheel 24a.

In FIG. 5, the portion with a relatively dark color on the rear surface Wb of the rectangular substrate W held by the flat holding surface 31a (32a) has a larger grinding area of the grinding wheel 24a and an increased grinding load. 24a shows a portion that is difficult to grind because the grinding force of 24a is reduced.
In FIG. 5, the portion of the flat holding surface 31a (32a) with a relatively light color indicates that the grinding surface area of the grinding wheel 24a with respect to the holding surface 31a (32a) is narrowed, and the grinding load is reduced. Since the grinding force is increased, the locations that are likely to be ground are shown.
Therefore, in the conventional method of grinding a rectangular substrate, the rectangular substrate W after grinding is thickened at dark-colored portions of the back surface Wb and thinned at light-colored portions of the back surface Wb, resulting in poor grinding thickness uniformity. Also, there may arise a problem that the back surface Wb of the rectangular substrate W after grinding is curved due to the difference in the grinding area of the grinding wheel 24a.

On the other hand, in the method of grinding a rectangular substrate according to the present invention, a rectangular holding surface having the same shape as that of the rectangular substrate W on the chuck table 3 is driven by the grinding wheel 24a mounted on the spindle 21 that is rotationally driven by the motor 22 of the grinding unit 2. 31a (32a) is ground, and the holding surface 31a (32a) of the chuck table 3 is curved due to the change in the grinding area of the grinding wheel 24a caused by the difference in the length of the sides or diagonals of the rectangular holding surface 31a (32a). a holding surface grinding step for forming the surface 311a (322a); a holding step for holding the surface Wa of the rectangular substrate W on the holding surface 311a (322a) of the chuck table 3 ground in the holding surface grinding step; a rectangular substrate grinding step of grinding the back surface Wb of the rectangular substrate W held on the holding surface 311a (322a) of the chuck table 3 by the grinding wheel 24a mounted on the chuck table 3 in a curved surface state, wherein the rectangular substrate W is ground. In the holding surface grinding step, the holding surface 31a (32a) of the chuck table 3, which has a rectangular holding surface 31a (32a) having the same shape as that of the rectangular substrate W, is corrected for the curvature of the back surface Wb caused by the difference in the grinding area generated when grinding. , the thickness accuracy of the rectangular substrate W after grinding can be improved.

That is, in the rectangular substrate grinding step, a certain region of the rear surface Wb of the rectangular substrate W, which has been difficult to grind conventionally, is raised relatively higher than other regions with respect to the grinding surface of the grinding wheel 24a. In addition, grinding is performed in a state in which a certain region of the rear surface Wb of the rectangular substrate W, which was conventionally more easily ground, is lowered relative to the grinding surface of the grinding wheel 24a than other regions. can go on. Therefore, the area of the rear surface Wb of the rectangular substrate W which is more difficult to grind can be reduced compared to the conventional case where the rectangular substrate W is suction-held by the flat holding surface 31a (32a) of the chuck table 3 and ground. In the case of the grinding method according to the invention, it becomes easier to locally grind with the grinding wheel 24a. In addition, the area of the back surface Wb of the rectangular substrate W that was more likely to be ground is reduced compared to the conventional case where the rectangular substrate W is sucked and held by the flat holding surface 31a (32a) of the chuck table 3 and ground. In the case of the grinding method according to the invention, the grinding stone 24a is less likely to grind locally. As a result, the entire back surface Wb of the rectangular substrate W shown in FIGS. 4A and 4B is uniformly ground.

After the rear surface Wb of the rectangular substrate W has been ground until the rectangular substrate W has a desired finished thickness, the grinding unit 2 is raised, the grinding wheel 24a is separated from the two rectangular substrates W, and the rectangular substrate grinding step is performed. ends. Further, the suction holding of the rectangular substrate W by the chuck table 3 is released, so that the rectangular substrate W held so as to follow the curved holding surface 311a (322a) is moved to the rear surface on the holding surface 311a (322a). Wb becomes substantially flat.

It should be noted that the method of grinding a rectangular substrate according to the present invention is not limited to the above-described embodiment, nor is the configuration of the grinding unit 2 and chuck table 3 shown in the accompanying drawings limited to this. , can be appropriately changed within the range in which the effects of the present invention can be exhibited.

W: Rectangular substrate Wa: Front surface of rectangular substrate Wb: Back surface of rectangular substrate 3: Chuck table 30: Base 31, 32: Protrusions 31a, 32a: Holding surfaces 311a, 322a: Curved holding surface 2: Grinding unit 21: Spindle 22: Motor 23: Mount 24: Grinding Wheel 24a: Grinding Wheel 24b: Wheel Base

Claims (2)

A rectangular substrate grinding method for grinding the back surface of a rectangular substrate to a desired finished thickness, comprising:
A grinding wheel attached to a spindle rotated by a grinding unit motor grinds a rectangular holding surface of the chuck table having the same shape as the rectangular substrate. into a curved surface; and
a holding step of holding the surface of the rectangular substrate on the holding surface of the chuck table ground in the holding surface grinding step;
a rectangular substrate grinding step of grinding the back surface of the rectangular substrate held on the holding surface of the chuck table by a grinding wheel attached to the grinding unit so as to form a curved surface;
In the holding surface grinding step, the curvature of the back surface caused by the difference in the grinding area generated when the rectangular substrate is ground is transferred to the holding surface of a chuck table having the rectangular holding surface having the same shape as the rectangular substrate. A method of grinding a rectangular substrate, wherein the thickness accuracy of the rectangular substrate after grinding is improved by forming the same in advance. 2. The method of grinding a rectangular substrate according to claim 1, wherein the holding surface of said chuck table is made of the same material as said rectangular substrate.

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