Grinding Apparatus

The present invention relates to a grinding apparatus including a chuck table having a holding surface that is polygonal in plan view and a workpiece grinding method for grinding a workpiece held on the holding surface.

Integrated circuit (IC) packages are indispensable components for electronic appliances including mobile phones and personal computers. Downsizing and thinning of electronic appliances in recent years have caused demands for thinner IC packages. In order to thin the IC packages, a rectangular substrate is formed by sealing a plurality of semiconductor device chips disposed in a matrix by mold resin, and thereafter, one side (for example, a rear side) of the rectangular substrate is thinned by being ground by a grinding apparatus.

The grinding apparatus includes a chuck table that is rotatable about a rotational axis. A rotation center of this rotational axis is disposed at a position corresponding to a center of a surface (that is, a holding surface) on which a rectangular substrate is held. According to the shape of the rectangular substrate that is square or rectangular in plan view, the shape of the holding surface in plan view is also square or rectangular.

Above the chuck table, a grinding unit including a spindle is provided. On a lower end portion of the spindle, a circular ring-shaped grinding wheel is mounted. The grinding wheel has a circular ring-shaped base, on a lower surface of which a plurality of grindstones are disposed at substantially equal intervals along a circumferential direction of the base. When the grinding wheel rotates by rotation of the spindle, a circular ring-shaped grinding surface formed by trajectories of the plurality of grindstones passes over a center of the holding surface of the chuck table.

Grinding one side of the rectangular substrate by the grinding apparatus is, for example, performed in the following order. First, the other side (for example, the face side) of the rectangular substrate is held under suction on the holding surface of the chuck table. Next, the position of the chuck table is adjusted such that a center of the one side of the rectangular substrate and the trajectories of the plurality of grindstones overlap in a vertical direction. Subsequently, the grinding unit is moved downward at a predetermined grinding feed speed while both the chuck table and the spindle are being rotated.

While a portion that is part of the one side of the rectangular substrate and that comes into contact with the plurality of grindstones is ground, since the chuck table is rotating at the time of grinding, the one side of the rectangular substrate is ground in whole. However, in association with the rotation of the chuck table, an area of contact (grinding area) between the rectangular substrate and the plurality of grindstones alternately increases and decreases in a direction moving around the rotational axis.

For example, the area ground in the rectangular substrate when portions between the center of the one side of the rectangular substrate and each corner of the rectangular substrate are ground is larger than the area ground when portions between the center of the one side of the rectangular substrate and each side of the rectangular substrate are ground. Hence, when the one side of the rectangular substrate is ground, portions in the vicinity of the corners of the rectangular substrate tend to become relatively thick, while other portions tend to become relatively thin.

In light of such points, for the purpose of reducing thickness variations that occur at the time of grinding a rectangular substrate, there is proposed a method for grinding the holding surface of the chuck table before grinding the workpiece (see, for example, Japanese Patent Laid-open No. 2020-55080). The method described in Japanese Patent Laid-open No. 2020-55080 seeks to reduce thickness variations in the ground rectangular substrate by grinding in advance the holding surface and thereby making the shape formed on one surface of the holding surface due to the increase and decrease in the grinding area at the time of grinding the holding surface and the shape formed on one side of the rectangular substrate due to the increase and decrease in the grinding area at the time of grinding the rectangular substrate substantially the same.

However, the holding surface and the rectangular substrate are made of different materials. For example, the holding surface is formed by ceramics such as alumina, while the area to be ground in the rectangular substrate is formed by epoxy resin in which a filler made of silica is mixed. Moreover, the holding surface includes a frame area formed by non-porous dense ceramics and a porous area formed by porous ceramics. Such differences in material and structure make it typically difficult to make the shape of the ground holding surface and the shape of the ground one side of the rectangular substrate completely the same.

The present invention has been made in view of the problems described above, and one object thereof is to reduce a difference between a shape of a ground holding surface and a shape of a ground one side of a workpiece when the holding surface is polygonal in plan view.

In accordance with an aspect of the present invention, there is provided a grinding apparatus including a chuck table that has a holding surface polygonal in plan view and is rotatable about a predetermined rotational axis by a rotary drive source including a first motor, a grinding unit that includes a spindle mounted at a higher position than the holding surface and a spindle motor for rotating the spindle and has a grinding wheel mounted on the spindle, a moving unit that includes a second motor and moves the chuck table and the grinding unit relative to each other along a predetermined direction, a load detection unit that detects a load applied to one of or both the grinding unit and the chuck table, and a controller that includes a processor and a memory and receives information regarding the load from the load detection unit, in which the controller includes a load storage section that stores one of or both a predetermined load value and the information regarding the load, a holding surface grinding command section that controls the load applied to one of or both the grinding unit and the chuck table, by controlling a parameter related to grinding processing when the holding surface is ground by the grinding wheel, and a workpiece grinding command section that controls the load that is applied to one of or both the grinding unit and the chuck table and that is the same type of load as that controlled by the holding surface grinding command section, by controlling the parameter related to grinding processing when a workpiece held on the holding surface is ground, and the controller controls the parameter related to grinding processing such that the load controlled by the holding surface grinding command section and the load controlled by the workpiece grinding command section have the same value.

Preferably, the load detection unit includes at least any one of a first load sensor configured to detect a first load that is a load applied to the grinding unit, a second load sensor configured to detect a second load that is a load applied to the chuck table, or a load ammeter configured to measure a load current flowing in the spindle motor, the load current being a load of the spindle motor, the load applied to the grinding unit includes the first load and the load current, the load applied to the chuck table includes the second load, and the parameter related to grinding processing includes a relative moving speed of the chuck table and the grinding unit along the predetermined direction, a rotational speed of the chuck table, a rotational speed of the spindle, and a flow rate of grinding water to be supplied per unit hour.

Preferably, the parameter related to grinding processing is a relative moving speed of the chuck table and the grinding unit along the predetermined direction, the holding surface grinding command section controls the moving speed such that the load applied to one of or both the grinding unit and the chuck table has the predetermined load value, when the holding surface is ground by the grinding wheel, and the workpiece grinding command section controls the moving speed such that the load that is applied to one of or both the grinding unit and the chuck table and that is the same type of load as that controlled by the holding surface grinding command section has the predetermined load value, when the workpiece held on the holding surface is ground.

In accordance with another aspect of the present invention, there is provided a workpiece grinding method for grinding a workpiece held on a holding surface, polygonal in plan view, of a chuck table, after the holding surface is ground, the method including grinding the holding surface of the chuck table by a first grinding wheel mounted on a spindle, while detecting, by a load detection unit, a load applied to one of or both a grinding unit including the spindle and the chuck table that is rotatable about a predetermined rotational axis and bringing the grinding unit and the chuck table relatively close to each other along a predetermined direction, after the grinding the holding surface, holding the workpiece having a polygonal shape corresponding to the holding surface on the holding surface, and, after the holding, grinding the workpiece held on the holding surface by a second grinding wheel mounted on the spindle, while detecting, by the load detection unit, the load applied to one of or both the grinding unit and the chuck table and bringing the grinding unit and the chuck table relatively close to each other along the predetermined direction, in which a parameter related to grinding processing is controlled such that the load applied to one of or both the grinding unit and the chuck table and detected by the load detection unit in the grinding the holding surface and the load that is applied to one of or both the grinding unit and the chuck table and detected by the load detection unit in the grinding the workpiece and that is the same type of load as that controlled in the grinding the holding surface have the same value.

Preferably, the load applied to the grinding unit includes a first load applied to the grinding unit and a load current that is a load of a spindle motor that rotates the spindle, the load applied to the chuck table includes a second load applied to the chuck table, and the parameter related to grinding processing includes a relative moving speed of the chuck table and the grinding unit along the predetermined direction, a rotational speed of the chuck table, a rotational speed of the spindle, and a flow rate of grinding water to be supplied per unit hour.

Preferably, in the grinding the holding surface, the parameter related to grinding processing is controlled such that the load applied to one of or both the grinding unit and the chuck table has the same value as the load that is to be detected by the load detection unit when the workpiece is ground in the grinding the workpiece and that is known beforehand.

Preferably, in the grinding the workpiece, the parameter related to grinding processing is controlled such that the load applied to one of or both the grinding unit and the chuck table is of the same type and has the same value as the load detected by the load detection unit when the holding surface is ground in the grinding the holding surface.

Preferably, the workpiece grinding method includes, before the grinding the holding surface, setting the predetermined load value as a target value in the grinding the holding surface and the grinding the workpiece, in which the parameter related to grinding processing is controlled such that the load controlled has the predetermined load value in both the grinding the holding surface and the grinding the workpiece.

Preferably, the first grinding wheel that has last ground the holding surface in the grinding the holding surface and the second grinding wheel used throughout the grinding the workpiece are the same grinding wheel.

The controller of the grinding apparatus according to the aspect of the present invention includes the holding surface grinding command section and the workpiece grinding command section. The holding surface grinding command section controls the load applied to one of or both the grinding unit and the chuck table, by controlling the parameter related to grinding processing when the holding surface is ground by the grinding wheel.

In contrast, the workpiece grinding command section controls the load that is applied to one of or both the grinding unit and the chuck table and that is the same type of load as that controlled by the holding surface grinding command section, by controlling the parameter related to grinding processing when the workpiece held on the holding surface is ground.

That is, the controller controls the parameter related to grinding processing such that the load controlled by the holding surface grinding command section and the load controlled by the workpiece grinding command section have the same value, so that, compared to the case in which such control is not performed, the difference between the shape of the ground holding surface and the shape of the ground one side of the workpiece can be reduced.

Also in the grinding method according to the other aspect of the present invention, the difference between the shape of the ground holding surface and the shape of the ground one side of the workpiece can be reduced compared to the case in which controlling the parameter related to grinding processing to have the same load value is not performed. Hence, the thickness variation in the ground workpiece can be reduced.

The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.

An embodiment according to one aspect of the present invention is described with reference to the attached drawings.is a side elevational view, partly in cross section, of a grinding apparatus. Note that, in, some of the components are illustrated in functional blocks.

An X-axis, a Y-axis, and a Z-axis each illustrated inare perpendicular to one another. In the present specification, a direction parallel to the X-axis is referred to as an X-axis direction, a direction parallel to the Y-axis is referred to as a Y-axis direction, and a direction parallel to the Z-axis is referred to as a Z-axis direction. The Z-axis is parallel to a vertical direction and an up-down direction, and an XY plane corresponds to a horizontal plane perpendicular to the Z-axis.

The grinding apparatusincludes a basefor supporting or housing components. In an upper surface of the base, a rectangular parallelepiped recesswhich has a longitudinal portion disposed along the X-axis is formed. The recessis provided with a moving mechanismof a ball screw type.

The moving mechanismincludes a pair of guide rails (not illustrated). The pair of guide rails are disposed substantially parallel to the X-axis and fixed to the base. On an upper side of the pair of guide rails, a moving plateis attached in a slidable manner.

On a lower surface of the moving plate, a nutis provided. To the nut, a screw shaftis rotatably coupled via a plurality of balls (not illustrated). The screw shaftis disposed along the X-axis between the pair of guide rails.

To one end portion of the screw shaft, a drive sourcesuch as a servomotor or a step motor is coupled. When the screw shaftis rotated by the drive source, the moving platemoves along the X-axis. Above the moving plate, a chuck tablewhose outer shape is a disk shape is provided.

Here, with reference to, explanation is given on the chuck table.is a perspective view of the chuck table,is an A-A cross sectional view taken along line A-A of, andis a B-B cross sectional view taken along line B-B of.

In, the shape of a holding surfaceis illustrated in an exaggerated manner for the sake of description. Moreover, the holding surfaceillustrated inhas a shape that is available after a holding surface grinding step Sto be described later is performed but before a holding step Sto be described later is carried out, that is, a shape that is available immediately before a rectangular substrate (workpiece)is held thereon.

The chuck tablehas a non-porous dense disk-shaped first frameformed of ceramics such as alumina. The first frameincludes a large diameter portion which has an outer peripheral portion in which a plurality of screw holes are provided and a small diameter portion disposed concentrically with the large diameter portion.

On an upper surface of the small diameter portion of the first frame, a second framethat is square (that is, polygonal) in plan view is provided. Similarly to the first frame, the second frameis also formed of ceramics such as alumina and is a non-porous dense frame.

The second frameincludes a recessthat is square in plan view. To the recess, a square porous plateformed of ceramics such as alumina is fixed via an adhesive agent or the like. An outer shape of the porous plateis the same as an outer shape of the recess

On a bottom surface of the recess, a plurality of flow channels are formed. As illustrated in, the plurality of flow channels include a first flow channeldisposed on a bottom surface of the recessand a second flow channelthat is positioned at a center of the bottom surface of the recessand that penetrates the second framefrom the bottom surface of the recessup to a bottom surfaceof the second frame.

To the second frame, a vacuum apparatus (not illustrated) such as a vacuum pump and an ejector is connected via a rotary joint (not illustrated). The porous plateis a continuous porous material in which pores are connected continuously, and vacuum generated by the vacuum apparatus can be transmitted to an upper surface of the porous platethrough the first flow channel, the second flow channel, and the like.

An upper surface of the second frameand the upper surface of the porous plateare substantially mesh with each other and form the holding surfacethat holds under suction the rectangular substrate(see). The holding surfaceaccording to the present embodiment is square (that is, polygonal) in plan view, and each side of the holding surfaceis a straight line in plan view.

Yet, as illustrated in the perspective view of, a cornerof each side of the holding surfaceis protruding compared to an intermediate pointof each side. That is, when the second frameand the porous plate(that is, the holding member) are viewed in side elevation, one side of the holding surfaceis not a straight line but a curved line curved in such a manner that a central portion is slightly recessed (see).

illustrates the cross section of the chuck tablethat passes through a centerof the holding surfaceand the cornerof the holding surfaceand that is taken at a plane parallel to the upper surface of the first frame. As illustrated in, the centeris protruding upward compared to the cornersby a predetermined length Δ (for example, 25 μm).

Nevertheless, the amount of protrusion of the centerrelative to the cornersis sufficiently small compared to the length of each side of the holding surface. The length of one side of the holding surfacein plan view is a predetermined value within the range of 320 to 700 mm. In, the amount of protrusion of the centeris illustrated in an exaggerated manner.

The A-A cross section illustrated inincludes a conical areawhich has the centeras the vertex and a recessed curved surface areain which a height of the holding surfacegradually becomes lower from the cornertoward the center.

As described above, the holding surfacegradually becomes lower from the cornertoward the intermediate pointof one side along the one side of the holding surface(see an arrow C in). As illustrated in, in a cross section that passes through the intermediate pointof one side and the center, the recessed curved surface areadisappears.

The holding surfaceat an end face of the B-B cross section illustrated incorresponds to the two sides of an isosceles triangle. Note that, in, the cornerthat is positioned in a father direction on the sheet than the end face of the B-B cross section is positioned higher than the intermediate point

The holding surfacethat is square in plan view has the conical areaat the central portion and the recessed curved surface areain the vicinity of each of the cornersin such a manner as to fill the gap between the conical areaat the central portion and each of the four corners

The rectangular substrate(see) that is held under suction on the holding surfacehas, in plan view, a square shape that is substantially the same as the holding surface(a polygonal shape corresponding to the holding surface), and has substantially the same size as the holding surface

The rectangular substrateis formed by sealing a semiconductor package substrate including a die pad, a lead frame, and the like and a plurality of semiconductor device chips by molded resin (for example, epoxy resin in which a filler made of silica is mixed).

The rectangular substrateincludes one side (rear side)which is to be ground and a to-be-held side (face side)that faces the holding surfaceat the time of grinding. Here, other configurations of the grinding apparatusare described with reference to.

is a side elevational view, partly in cross section, illustrating a rotation mechanism and a support mechanism of the chuck table. In, some of the components are illustrated in functional blocks. The chuck tableis rotatably supported by an air bearing.

The air bearingincludes a rotor(a predetermined rotational shaft) that is coupled to a lower surface of the chuck table. The rotorhas a large diameter portionprovided on an apex in the longitudinal direction and a small diameter portionlocated on a lower side of the large diameter portion.