NL8403157A - WORKING OF WORKPIECES FROM BROS-CRUCKY MATERIALS. - Google Patents

Description

fc. »N032686 1

Machining workpieces from brittle crumbly materials.

The invention relates to the machining of workpieces of brittle crumbly materials with high hardness.

5 The machining of metal and non-metal materials by grinding is increasingly used in manufacturing technology, which pursues two development goals, namely on the one hand achieving the highest possible accuracy, surface quality and the least possible damage, and on the other 10 an increase in stock removal. Both purposes have hitherto been mutually exclusive, because, according to the current state of the art, the construction of the machines and especially the specification of the grinding tools must be specially designed to achieve one or the other optimum.

Two grinding methods are now known, namely "circumferential grinding" and "side grinding". The "circumferential grinding" is further developed than the "side grinding" and is partly already competitive in terms of cutting power and accuracy with regard to turning, milling and planing. The two different grinding methods according to the prior art have been described in depth in the technical literature, wherein the power limits in scientific works, specialist literature and product information are indicated and reflect the last state reached. Both of the aforementioned grinding methods have their own, partly overlapping areas of application, whereby they work optimally. In addition, side grinding is better for very hard, brittle and sensitive materials and very smooth surface surfaces. Non-metallic crystalline materials, which are used in large quantities in the form of very thin, large-area disks, for example, as substrates for electronic parts, are an exception in processing. · An example here is the processing of very thin workpieces in disk form made of silicon, germanium, sapphire, garnet, spinel and III-V compound, as these are increasingly used as a substrate for the manufacture of electronic parts worldwide. The lapping used exclusively at the start of the surface treatment becomes longer the more replaced by grinding with diamond-cut grinding wheels. This method was developed by the applicant ready for production.

The object of the present invention is to enable machining of materials that are improved in comparison with the prior art in machining 40 workpieces from highly brittle, friable, crystalline and often extremely hard materials, while the cutting process, inevitable changes of the upper material layers and the resulting damage, that is, the depth of destruction of the crystal layer in the vicinity of the surface, must be less than in the previously known and applied removal methods and at the same time improvement of the surface quality is achieved in order to reduce the number of subsequent processing steps necessary for such materials, such as for example pre-polishing and fine grinding

The damage and clearly visible machining marks on the ground surfaces increase the susceptibility to breakage and significantly change the electrical values of the workpieces, in particular of the sub-15 road disks, and have a very detrimental effect on subsequent treatments and diffusion processes · The less damage is the thinner the workpieces can be ground · Likewise, the material-saving grinding operation simplifies and shortens the subsequent operations, because removing the inevitable damage by etching is less expensive ·

Extremely brittle, friable, monocrystalline or polycrystalline materials, which are processed according to the invention, have a minimum Vickers hardness of 7000 N / mm ^ to a maximum of 25000 N / mm ^. The best known examples for such materials are AIII-BV compounds with a Vickers hardness up to 8500 * Germanium with a Vickers hardness up to 7500, silicon with a Vickers hardness up to 11500, spinel with a Vicker hardness up to 14000, as well as sapphire and gallium gadolinium Grenade (GGG) with a Vickers hardness of 19000 to 21500. Such materials are preferably used in electronics. In addition, super hard sinter materials such as silicon carbide SiC with a Vickers hardness of 15000 - 25500, silicon nitrite Si3N4 with a Vickers hardness of 15000 - 20000 (respectively 35000 with the single crystal) as well as boron carbide B4C with a Vickers hardness of 22500 to 31000 can be processed in an advantageous manner. . Such materials; 35 find application in machine building, engine building as well as construction building. A further preferred group of materials includes cutting ceramics with a Vickers hardness of 17000 to 28500 as well as Corundum AI2O3 with a Vickers hardness of 215000. These materials serve as non-metallic cutting materials.

The object is achieved according to the invention by using 8403157 * 3 the method of flat-side-transverse grinding for machining workpieces of extremely brittle, friable, crystalline materials and particularly preferred material is single crystal -line silicon. Polycrystalline silicon is also very suitable.

In contrast to the grinding process hitherto used for processing such materials, the flat-side-cross grinding comprises only two components of movement, namely rotation of the grinding wheel and the approach of the grinding wheel oriented perpendicular to the workpiece surface to be grinded. The starting movement, which has been regarded as a dominant active parameter in the grinding process used to process such materials, is eliminated.

The grinding process in flat-side cross grinding consists of immersing the rotating grinding disc into the surface of the workpiece, so that for this operation the designation "immersion grinding" is proposed. The grinding coating is preferably sized in such a way that the entire workpiece surface to be grinded is covered, but repetitive partial immersion grinding is also possible for very extended workpieces, the workpiece after each immersion grinding over the width of the grinding coating the grinding wheel shaft is shifted.

The flat-side cross grinding, which has hitherto only been used as relatively rough coarse stock removal with low surface requirements, has, in the optimum process control according to the invention, completely surprising with hard and very brittle materials, which vulnerable to crystal lattice destruction on the machined surface, resulting in exceptional material-saving and good machining behavior. Thus, the machining power is many times greater than the values known so far, although the achieved surface quality and the harmful change of the outer, with the grinding wheel in contact materials, are good in comparison with the hitherto specially developed for this purpose. machining methods.

Extremely brittle, friable, monocrystalline silicon can thereby be ground to a final thickness of about 80 µm, while the known grinding methods generally only control workpieces of a thickness greater than or equal to 160 µm. Measurements confirm that adverse changes in the crystal lattice of the material on the grinding surface are comparatively smaller than in the grinding methods used hitherto.

According to the invention, the very great advantage is furthermore obtained that the front side of the silicon wafer has had a final treatment when grinding the back sides and is generally coated with a final layer of relatively soft materials, which, during this grinding process, is the support side on the clamping point for the workpiece, is much less likely to be damaged by depressions and bruised places and that this prevents failure.

In practice, the most favorable grinding processes, in which the diamond-coated side grinding wheel is moved over the surface of the workpiece with a very slow progression movement and a small clamping depth, are based on a fine-grained grinding wheel with an elliptically rounded edge of the cutting edge, to achieve the required quality parameter. These optimum cutting behavior is not guaranteed to be reproducible in manufacturing machines, which leads to considerable quality fluctuations. In the grinding process according to the invention, on the other hand, only attention must be paid to the fact that the grinding coating is flat.

With a relatively fine-grained grinding wheel, machining capacities are achieved, which have hitherto only been achieved by very coarse-grained pre-grinding wheels, but the smoother grinding wheels inherent in the workpiece are even smoother, while at the same time improving the surface with the grinding wheel contacting material surface in the outer layer thereof is less changed or damaged. The flatness and roughness can still be considerably improved if, after the end of the "immersion grinding" feed, the workpiece is pulled out of the engagement area parallel to the grinding disc surface. The traces of the grain points protruding slightly further from the coating of the grinding wheel are thereby leveled. This extra processing step can be compared with the so-called "burn-out" in a greatly simplified form.

The use according to the invention of the method "flat-side cross grinding" for machining workpieces of brittle, friable materials with a high hardness creates a new grinding technology with many advantages.

Since no starting movement takes place, it is possible to construct a simpler and very stable machine. Known automatic grinders with one or more stations work with round tables as workpiece carrier and feed device, at which different outwardly increasing feed speeds occur. This drawback, which has a negative influence on the surface quality and the material load during the intervention of the abrasive grains, is eliminated because, as described above, 840 3 1 5 7 # 5 · a final "burn-out" as a rectilinear movement , for example, of the lathe head for the grinding shaft can be made, to obtain a very fine and even surface.

Normal multi-station round table grinders have the same feed rate at all grinding stations, regardless of whether pre-grinding, fine grinding or maximum fine grinding are used. In the flat-side-cross grinding used according to the invention, in which no starting movement takes place during the grinding process, the "burn-out movement" can in each case be individually and optimally adjusted with low machine costs, in general a linear "burn-out movement" only when last grinding station is necessary. Since the workpiece carrier is stationary during grinding, for example in the form of a round table moving rhythmically, a very precise and simple handling and unloading of workpieces is given.

A further advantage is that during this period a complete separation between the space between the grinding area and the area of supply and discharge is possible, which is very important with very precise workpieces, because the clamping point of the workpiece can be cleaned and clean. can be held until the next substrate disc is loaded. Small dust particles between the workpiece support and the substrate disc press on the surface and in the case of very thin substrate discs inevitably lead to the feared, localized cracks, which are called "crow's feet" because of their shape.

The present invention gives the extraordinarily great advantage of a much greater stock removal rate, with relatively low workpiece and tool loading.

This allows the grinding of brittle materials to very small thicknesses between 60 and 250 µm, preferably between 80 and 200 µm, because the crystal lattice of the material is advantageously only slightly changed. A further advantage is that, during grinding, the workpiece support table is firmly locked on the machine column and is therefore vibration-stable.

A further advantage of the present invention is low specific tooling costs, due to the long life of the grinding wheel, which is further promoted by the maximum possible number of grinding bodies participating in the grinding process, thereby reducing the grain load and reducing chip evacuation 40, with the constants acting on individual grain 840 31 5 7 rt 6

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and low-vibration cutting force, which can be displayed as a fixed space vector relative to the cutting plane. As a result of the not required starting movement, the breaking out of the grinding body from its binding is thereby delayed.

The grinding wheels required for the method according to the invention are straightforward and easy to manufacture. Generally, grinding bodies, preferably with diamond grain as a cutting material, will be attached to a base body in the form of discs, plates or strips. The spacings between the individual grinding elements, which are free of obligation, enhance the cooling effect and facilitate the removal of chips. The distance between the individual grinding elements or grinding segments is always smaller than the surface to be processed. In this way, a workpiece between two segments are clamped and when the grinding wheel is rotated a normal end grinding process is performed, whereby only the edges of the grinding segment become active. However, grinding wheels with a continuous coating, the dimensions of which are adapted to the size of the workpiece, can also be used advantageously.

In the method according to the invention, economically fine grains can be used, which causes smoother surfaces when grinding non-metallic materials.

The invention will now be explained in more detail with reference to the drawings, which show by way of example some embodiments of the invention.

Figure 1 shows a substrate of a characteristic size.

Figure 2 shows an embodiment of a device for carrying out the method according to the invention consisting of flat side cross grinding.

Figure 3 schematically shows the size relationships between grinding surfaces of the grinding wheel and the workpiece in a device according to figure 1.

Figure 4 schematically shows in Figures 4a to 4e examples 35 of advantageous embodiments of the grinding surfaces of grinding wheels for carrying out the method according to the invention.

The silicon substrate disk shown in Figure 1 has dimensions such as these are conditional for the manufacture of high power electronic components.

40 The embodiment of a device shown in figure 2 comprises 8403157 * 7: · consists of a basically block-shaped machine column 1, on the horizontal plane of which an intermittently rhythmically rotatable or horizontally sliding table 2, which can be clamped during the grinding process, receiving and for the further transport of the work pieces is mounted. A support 4 protrudes above the receiving location of the workpieces, to which are mounted the drive motor 8 and the grinding shaft 8, which carries the grinding disc 6 with the grinding surface 7 facing the workpieces. The support 4 is fixed to the column 1 vertically upwards and downwards with precise and rigid guide elements 9.

This vertical upward and downward movement can be initiated, for example, by an electrically driven feed shaft 10. This feed shaft 10 feeds the grinding wheel 6 according to the present invention into "immersion discs" down to the final dimension of the workpiece and with a rapid movement lifts the all support upwards. During this return movement of the support, the machined workpiece is removed from the area of the grinding wheel by intermittent turning or horizontal shifting of the table 2, at the same time a new workpiece to be machined is placed under the grinding wheel 20 and fixed in working position;

This simultaneous removal and loading takes place in coordination with the return movement of the support, so that no collision takes place between a new workpiece and the grinding wheel, as long as the transport movement is not closed and the workpiece carrier is clamped again.

Figure 3 shows a grinding wheel for carrying out the method according to the invention. The grinding disc 40 shown has a grinding surface 42 facing the workpiece 41, which completely covers the workpiece 41 fixedly applied during the grinding process and not subjected to an initial movement. In this way it is ensured that during grinding all grinding bodies of the grinding surface 42 become chip-removing.

Figure 4 schematically shows various embodiments of grinding body paints to be used according to the present invention.

Figure 4a shows a grinding surface formed from spheres of abrasive bodies. Figures 4b and 4c show grinding wheels, the grinding coatings of which are formed from rectangular and trapezoidal grinding coating elements 44, 45 respectively.

In Figures 4d and 4e, the abrasive coating elements are rod-shaped 840 31 57 * r 8 46 and arc-shaped 47, respectively. In all embodiments 4a to 4e, circular workpieces 41 are each drawn, it being seen that the abrasive coatings effectively cover the workpieces completely in the plane. In each of these 5 grinding wheel embodiments, it is ensured that during grinding, all grinding bodies of the grinding coating segments facing the workpiece become chip-removing. This is clearly in contrast to normal end grinding, in which only the grinding bodies of the grinding disc edge have a chip-removing effect.

A further advantage of the method according to the invention is the fact that the grinding load and the area of engagement of the grinding wheel on the workpiece are constant throughout the grinding time. This achieves a very even grinding pattern and a very stable grinding process.

The flat-side cross grinding according to the invention is described, for example, in the design of DIN 8589, part 11, page 10.

840 3 1 5 7

Claims (2)

1. Use of the flat-side cross grinding for machining disc-shaped workpieces of very hard, brittle-friable, crystalline materials with a Vickers hardness greater than 7000 H / m 2 to a thickness between 60 and 250 µm. Use of the flat-side cross grinding according to claim 1, for machining disc-shaped workpieces of very hard, brittle-friable, crystalline materials, preferably to a thickness between 10 80 and 120 µm 840 3 1 5 7