JP4371853B2 - Substrate cutting method - Google Patents

Description

  The present invention relates to a novel method for cutting a substrate made of an aluminum nitride sintered body. Specifically, the present invention provides a method for efficiently producing a chip having a good cutting edge accuracy.

  Ceramic materials represented by aluminum nitride, alumina, boron nitride and the like are widely used because they have excellent characteristics such as electrical characteristics, optical characteristics, and thermal characteristics. Among these ceramic materials, aluminum nitride, in particular, has not only thermal conductivity, but also has excellent properties in terms of insulation, dielectric properties, and thermal expansion characteristics, so it has rapidly spread as a highly functional heat dissipation substrate for semiconductor mounting. It's getting on.

  Such a heat dissipation board is usually manufactured by the following method. That is, the surface of the aluminum nitride sintered body is ground or polished as necessary to finish it to a certain surface roughness, and a metal thin film layer is formed on the surface. Such a metal layer includes a first thin film layer such as Ti, Cr, Ni—Cr, TaN, Al, Mo, W, and Zr, a second thin film layer such as Ni and Pt, Co, Cu, Au, Ag, and Pd. It is generally formed by forming the third thin film layer in this order.

  After the metal thin film layer is formed on the surface in this way, patterning is performed as necessary, and then the substrate is cut into chips, finished to the size and shape of the final product, and then formed on the metal thin film layer. An electronic element (for example, a laser diode) is mounted using thin film solder or the like.

  In the cutting of the substrate, as the electronic elements are miniaturized and densified, the processing accuracy has been required to be significantly improved in recent years.

  Conventionally, a rotary grinding wheel is generally used for cutting a substrate made of the aluminum nitride sintered body. The cutting device using this rotary grinding wheel is characterized by good economic efficiency because the device itself is simple and the processing speed is high. Various improved methods for cutting a workpiece with high accuracy using the grinding wheel have been proposed. For example, a dresser for supporting a dresser on a workpiece moving table for holding and moving the workpiece in parallel with the workpiece supported by the workpiece moving table and facing the grindstone from the normal direction. A method has been proposed in which a grinding machine provided with a holder is used for cutting so as to prevent wobble and tilt of the grindstone and improve the processing accuracy (see Patent Document 1).

  However, when a hard material such as an aluminum nitride sintered body is used by using a rotary grinding wheel, the substrate made of the aluminum nitride sintered body is a relatively fragile member. In the case of cutting, there is a problem that the occurrence of chipping at the end of the cut surface cannot be avoided.

  On the other hand, in recent years, the position accuracy at the time of cutting has increased, and the distance between the mounting position of the electronic element mounted on the chip obtained by cutting and the chip end has become closer, so that the end of the cut surface Occurrence of cracks in parts has greatly affected the yield of the obtained semiconductor products.

  On the other hand, a method using a laser has been proposed as a method for cutting a substrate (see Patent Documents 2 and 3).

  According to the above method, the chipping at the end of the cut surface can be effectively suppressed. However, cutting with a laser has a problem in industrial implementation because the cutting speed is slow and the processing time is remarkably long. Further, as the cutting depth increases, the tendency increases and the cutting accuracy also decreases. Furthermore, there is a concern that the aluminum nitride sintered body in the vicinity of the cut surface is altered by the use of a laser for a long time, and the characteristics such as thermal conductivity are deteriorated.

JP-A-4-13552 JP-A-7-284966 JP 2003-285192 A

  Therefore, an object of the present invention is to reduce the chipping of the cut end portion on the substrate surface in cutting a substrate made of an aluminum nitride sintered body, particularly a substrate having a metal thin film layer on the surface, and in a short time, the efficiency An object of the present invention is to provide a cutting method that can perform cutting well.

  The present inventors have intensively studied to solve the above problems. As a result, it is possible to form a corner of the substrate made of aluminum nitride sintered body by suppressing the chipping of the cut end by forming a groove in a part from the surface by laser processing, and rotation with a grinding width smaller than this groove By cutting the remaining portion with a grinding wheel to form a substrate, the grinding speed can be maintained sufficiently fast while having a surface portion in which chipping at the cutting end, which is a feature of laser, is suppressed, and the present invention. The inventors have found that the object can be achieved, and have completed the present invention.

  That is, according to the present invention, when cutting a substrate made of an aluminum nitride sintered body, a groove is formed by laser processing from the surface to a partial depth at the cutting position of the substrate, and the grinding width is smaller than the width of the groove. A substrate cutting method comprising cutting a substrate by grinding the remaining portion with a rotary grinding wheel.

  According to the substrate cutting method of the present invention, by forming an initial cutting groove by laser processing, a highly accurate processing end face can be secured on the surface layer portion, and the chip surface obtained by cutting has high precision on the chip surface. Parts can be mounted. Further, in the subsequent cutting, the remaining portion is cut with a rotating grinding wheel having a grinding width smaller than the width of the groove, so that the cutting can be industrially satisfied while maintaining the precision of the processed end. It became possible to carry out.

  Therefore, the substrate made of an aluminum nitride sintered body can be cut economically and precisely.

  In the cutting method of the present invention, a known substrate made of an aluminum nitride sintered body is used without particular limitation. Among them, the cutting method of the present invention is particularly effective particularly for crystals having an average particle diameter of about 1 to 10 μm constituting the aluminum nitride sintered body. Also, those having such a crystal grain size are suitable in the present invention because the accuracy by polishing the substrate surface can be increased.

  The shape of the substrate is not particularly limited, but the thickness is generally 50 μm to 5 cm, particularly 100 μm to 2 cm from the viewpoint of easy processing.

  Further, the substrate is an unprocessed substrate made of an aluminum nitride sintered body, various honing processing, lapping processing, mirror processing processing, etc. Examples thereof include a substrate made of an aluminum nitride sintered body in which a metal thin film layer is formed on the surface of the substrate by vapor deposition, sputtering, chemical vapor deposition (CVD), or the like.

  FIG. 1 is a process diagram showing a typical embodiment of the cutting method of the present invention. As shown in FIG. 1, in the cutting method of the present invention, (a) a substrate 1 made of the aluminum nitride sintered body is prepared, and (b) a partial depth (H) from the surface at the cutting position of the substrate 1. ), The groove 2 is formed by laser processing, and (c) the substrate 3 is cut by grinding the remaining portion 3 with a rotating grinding wheel having a grinding width (C) smaller than the width (B) of the groove. And

  In the cutting method of the present invention, first, the groove 2 is formed by laser processing from the surface of the substrate 1 made of the aluminum nitride sintered body to a partial depth.

  That is, when cutting with a rotating grinding grindstone without forming a groove by laser processing, chipping generated at the cutting end becomes large, so that chipping frequently occurs at the cutting end and a chip having a precise cut surface is obtained. It becomes difficult.

  Further, when the entire layer of the substrate is cut only by laser processing, not only a very long time is required, but also the above-mentioned inconvenience is concerned, so the depth of the groove formed by laser processing is the total thickness of the substrate. It needs to be a part. Thus, in cutting the substrate, the laser processing is interrupted and switched to another cutting means, and the advantages of both can be enjoyed without inheriting the respective defects.

As the laser used for the groove processing of the present invention, a known laser is used without particular limitation. For example _CO 2, YAG, include excimer laser. Moreover, although there is no restriction | limiting by a wavelength, generally it is preferable that it is a wavelength of 400 nm or less, especially 180-360 nm.

  The width of the groove formed by laser processing is not particularly limited as long as it is relatively larger than the cutting width of a rotating grinding wheel described later, but the cutting position may vary somewhat when cutting with a rotating grinding wheel. Therefore, it is preferable that the width of the groove formed by laser processing is wider by 10 μm or more than the cutting width by the grinding wheel.

  Note that if the groove width formed by laser processing is too large, the processing time may have to be lengthened. Therefore, the groove formed by laser processing must be 30 μm or less in width than the cutting width of the grinding wheel. Is preferred.

  The groove width (B) obtained by the laser processing can be adjusted, for example, by excimer laser by changing the mask or changing the magnification by the optical system.

  In the present invention, the depth (H) of the groove formed by the above laser processing may be a part of the entire layer of the substrate as described above, but it is 2 of the average crystal grain size of the aluminum nitride sintered body. 10 to 10 times and 50% or less of the thickness of the substrate made of the aluminum nitride sintered body effectively prevents the cutting edge from being chipped and prevents warping during substrate cutting. It is preferable for cutting the substrate more accurately. More preferably, the depth (H) of the groove is 2 to 5 times the average crystal grain size (d; μm) of the aluminum nitride sintered body and is 30 times the thickness of the substrate made of the aluminum nitride sintered body. % Or less.

  That is, the present inventors have found that when a polycrystalline material such as an aluminum nitride sintered body is cut with a rotary grinding wheel, the chips generated at the processed end are caused by dropping of crystal grains. And the knowledge that the depth of the groove when forming the groove by laser processing should be based on the size of the crystal grains in order to suppress the edge chipping caused by cutting with the rotating grinding wheel. Specifically, when a depth of twice or more the average crystal grain size of the aluminum nitride sintered body is grooved with a laser and then cut with a rotating grinding wheel, the crystal grains fall off when cutting with the rotating grinding wheel. I don't get up.

  Further, when 50% or more of the thickness of the substrate made of the aluminum nitride sintered body is grooved, the aluminum nitride sintered substrate tends to be warped, and the warped substrate is cut by a rotating grinding wheel. In this case, the cutting position may be inaccurate or the substrate may be cracked if it is forcibly fixed to the cutting device.

  In the present invention, when processing a substrate made of an aluminum nitride sintered body by the laser processing, metallic aluminum may be deposited on a portion exposed to high density energy of the substrate made of the aluminum nitride sintered body. It is preferable to employ a method in which nitrogen gas is blown to the processed part as gas.

  Moreover, the fixing method of the board | substrate at the time of the said laser processing is not restrict | limited, A well-known method can be used without a restriction | limiting. For example, vacuum suction, sticking with an adhesive sheet, sticking with a solid wax, sticking with an adhesive, etc. are applicable, and these may be used in combination.

  As the rotary grinding wheel used for the cutting of the present invention, a known one is used without particular limitation, but a grinding wheel using diamond abrasive grains is preferable. The diamond abrasive is a grinding wheel to which diamond abrasive is fixed using a binder. Natural or synthetic industrial diamond powder is used for the diamond abrasive grains, and the binder may be any method such as resin bond, metal resin bond, metal bond, vitrified bond, electrodeposition bond, and electroformed metal bond. Moreover, the whole grinding wheel may be comprised with the abrasive grain and the binder, and the part which does not relate to a cutting | disconnection may be comprised with other materials, such as a metal.

  In the present invention, the cutting width (C) by the above-mentioned rotary grinding wheel is not particularly limited as long as it is smaller than the width of the groove formed by the laser, but adverse effects such as meandering of the cutting groove and an increase in the wear amount of the wheel occur. It is preferable that the thickness is as thin as possible within the range. Specifically, it is preferably in the range of 50 to 95% with respect to the width of the groove formed by the laser.

  Further, the shape of the tip of a general grinding wheel is a square shape, but it may be R or tapered. Further, a method generally called multi-blade dicing, in which a large number of grindstones of the same shape are arranged in parallel on the same axis and rotated to cut a large number of cuts at a time, is particularly preferable because the economy is improved. is there.

  The average particle size (x; μm) of the abrasive grains in the grinding wheel used in the present invention is not particularly limited, but a particularly preferable range is 3d ≦ x ≦ 110 / d (d; average crystal of aluminum nitride sintered body) Particle diameter [μm]).

  The method for fixing the substrate at the time of cutting using the rotary grinding wheel is not particularly limited, and a known method can be used without limitation. For example, vacuum suction, sticking with an adhesive sheet, sticking with a solid wax, sticking with an adhesive, etc. are applicable, and these may be used in combination. Moreover, what is marketed can be used conveniently for the grinding machine which cut | disconnects.

  As the cutting method using the rotary grinding wheel targeted in the present invention, a known method can be used without limitation. For example, up cut, down cut, creep feed grinding, high speed stroke grinding and the like can be mentioned.

  Moreover, although the grindstone rotational speed should just be 5000 rpm or more, Preferably it is 20000 rpm or more. The upper limit of the rotational speed is not particularly limited, but is about 100,000 rpm, particularly about 60000 rpm.

  The substrate feed rate may be 300 mm / s or less, but is preferably 30 mm / s or less. There are no restrictions due to other processing conditions.

  Furthermore, the outer diameter of the grinding wheel used in the present invention is not particularly limited, and may be appropriately determined according to the substrate to be cut.

  As a preferred embodiment of the present invention, an embodiment using an adhesive sheet can be mentioned. That is, for example, polyester, polyethylene, polypropylene, polybutene, polybutadiene, vinyl chloride, vinyl chloride copolymer, ionomer resin, ethylene- (meth) acrylic acid copolymer, A known pressure-sensitive adhesive sheet having a structure in which a silicone pressure-sensitive adhesive, an acrylic pressure-sensitive adhesive, or the like is applied on a resin base material such as coalescence, ethylene- (meth) acrylic acid ester copolymer, polystyrene, polycarbonate, By cutting the substrate while leaving the pressure-sensitive adhesive sheet, it is possible to improve the handleability of the substrate after chip formation.

  Further, as another aspect of the cutting method of the present invention, it is possible to adopt an aspect in which the groove is formed by laser processing from both sides, and then the remaining portion is cut with a rotating grinding wheel. In this case, the said range is applied suitably for the depth of a groove | channel.

  The cutting method using the pressure-sensitive adhesive sheet in the above embodiment is such that after forming a groove by laser processing on one surface of the substrate, the pressure-sensitive adhesive sheet is pasted on the surface having the groove, and then the laser is applied to the other surface of the substrate. It can be cut into chips by forming grooves by machining and grinding with a rotating grinding wheel.

  In order to describe the present invention more specifically, examples and comparative examples will be described below, but the present invention is not limited to these examples.

Examples 1-5
Aluminum nitride sintered body substrates (50.8 mm × 50.8 mm × 5 mm × 30.8 mm × 3 μm) having three mirror surfaces (Ra <0.03 μm) of 3.3 μm, 4.4 μm, and 6.7 μm, each having a different average crystal grain size 0.3 mm), and an excimer laser processing machine (manufactured by OPTEC, MicroMaster, KrF) is used to make the laser incident from the upper surface of the aluminum nitride sintered substrate under an oscillation condition of an oscillation pulse of 200 Hz and an output of 10 mJ. Were formed from one end of the substrate to the other.

  Moreover, the board | substrate from which the depth of a groove | channel shown in Table 1 differs was obtained by changing the moving speed of the aluminum nitride sintered compact board | substrate at the time of groove | channel formation. 50 grooves formed by the above method were formed at intervals of 1 mm. The aluminum nitride sintered body substrate was fixed to an excimer laser processing machine by vacuum adsorption.

  A rotating grinding grindstone having an average grain size of 25 μm (B1A803SD600N50M51, 52D × 0.1T × 40H) and a thickness of 100 μm is used for an aluminum nitride sintered body substrate having grooves formed by an excimer laser. All of the 50 grooves are down-cut using a cutting machine (Disco 522, DAD522), with a grinding wheel rotation speed of 23000 rpm and a feed rate of 9 mm / s, in accordance with the grooves formed by the excimer laser. And cut. The aluminum nitride sintered substrate was attached to an adhesive sheet (UDV-100A) and fixed by vacuum suction with a porous chuck. In order to completely cut the substrate, the UV sheet was cut by 50 μm.

  Observe the processed end after cutting with a 200x measuring microscope, measure the maximum chip width of the cut end within one cut (50.8 mm), and perform this for all cuts. It was set as the processing end part chip width.

  Further, in each example, the warpage of the substrate after forming the groove by laser processing is calculated by measuring the difference between the edge and the center of the substrate using a surface roughness shape measuring instrument (manufactured by Tokyo Seimitsu, Surfcom 470A; trade name). The results are shown in Table 1.

  As understood from Table 1, in the embodiment, the processing end chip width is small and the processing time is short. Further, by setting the depth of the groove by laser processing to less than 50% of the total thickness of the substrate, it is possible to perform subsequent cutting with a rotating grinding wheel without warping.

Comparative Examples 1-6
Comparison of aluminum nitride sintered substrates (50.8 mm x 50.8 mm x 0.3 mm) with mirror finish (Ra <0.02 µm) with an average crystal grain size of 3.3 µm, 4.4 µm, and 6.7 µm In Examples 1 to 3, the grooves were not formed by the excimer laser, and only the cutting by the rotating grinding wheel of the example was performed. In Comparative Examples 4 to 6, the cutting was performed only by the excimer laser processing shown in the example. In Comparative Examples 1 to 3, the chip width at the machining end is larger than that in the example. In Examples 4 to 6, the chip end chip width is similar to that in the example, but the machining time is long.

Comparative Examples 7-9
An aluminum nitride sintered body substrate (50.8 mm × 50.8 mm × 0.3 mm) subjected to mirror finishing (Ra <0.02 μm) with an average crystal grain size of 3.3 μm, 4.4 μm, and 6.7 μm was used as an excimer. The width of the groove formed by laser was set to 109 μm, and the others were cut in the same manner as in the examples. That is, in Comparative Examples 7 to 9 in which the width of the groove formed by the excimer laser and the width of the rotating grinding wheel are the same, the machining time is the same as that of the example, but the chip width at the machining end is large.

Process drawing which shows the typical aspect of the cutting method of this invention

Explanation of symbols

1 Substrate made of sintered aluminum nitride 2 Groove 3 Remainder

Claims (3)

  When cutting a substrate made of an aluminum nitride sintered body, a groove is formed by laser processing from the surface to a partial depth at the cutting position of the substrate, and the remaining portion is formed by a rotating grinding wheel having a grinding width smaller than the width of the groove. A method of cutting a substrate, comprising cutting the substrate by grinding. In the cutting method, the depth of the groove formed by laser processing is 2 to 10 times the average crystal grain size of the aluminum nitride sintered body and less than 50% of the thickness of the substrate made of the aluminum nitride sintered body. The substrate cutting method according to claim 1 .   The substrate cutting method according to claim 1 or 2, wherein the substrate made of the aluminum nitride sintered body has a metal layer laminated on the surface thereof.

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