FR2554376A1 - PROCESS FOR SHAPING PIECES OF BROKEN MATERIALS AND APPLICATION OF THIS PROCESS - Google Patents

Abstract

APPLICATION OF THE PLANE-TO-PLANE CROSS-SECTIONAL GRINDING PROCESS TO SHAPING DISC-SHAPED PARTS CONSISTING OF A VERY HARD AND BREAKING CRYSTALLINE MATERIAL, RECTIFICATION PROCESS WHICH INCLUDES ONLY TWO MOVEMENT COMPONENTS, Namely the ROTATION OF WHEEL 6 AND THE APPROACH OF THE GRINDER. THE CRYSTALLINE 3 MATERIAL HAS A VICKERS HARDNESS OF GREATER THAN 7000NMM AND IS A THICKNESS BETWEEN 60 AND 250MM.

Description

PROCESS FOR SHAPING PIECES OF BROKEN MATERIALS AND APPLICATION

OF THIS PROCESS

  The present invention relates to the shaping of parts

  made of brittle materials of high hardness.

  The invention relates to improvements at the request of

  FR 83 08191 patent filed May 18, 1983 in the name of the plaintiff.

  The machining of metals and non-metallic materials by grinding is finding increasing use in techniques

  manufacturing, which tends towards two development goals, that is to say

  say, on the one hand, the achievement of the highest precision, the best surface quality and the lowest damage, and, on the other hand, an increase in the machining capacity. The two aims have been mutually exclusive up to now, because according to the current state of the art, the construction of the machine and, above all, the specification of the grinding tool had to be studied specially to achieve

  either of the optimal conditions.

  Nowadays, two methods of rectification are known,

  that is to say "tangential rectification", and "border rectification"

  tale or facial "." Tangential rectification "is more widely developed than facial rectification", and already occurs partially

  to compete, with regard to the capacity of usi-

  swimming and precision, turning, milling and planing.

  The two different rectification methods according to the state of the art are widely described in the technical literature, the capacity limits being

  indicated in scientific work, the litera-

  specialized information and product information,

  and reproducing each time, the last state reached.

  The two rectification methods indicated above have their own field of use, which partially overlap, where they present an optimal use. Indeed, for very hard, brittle and sensitive materials and very hard surfaces

  flat, the facial grinding method is preferred.

  non-metallic crystalline materials which are used in large quantities in the form of large area discs and very thin, for example, as

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  as a substrate for electronic components,

  occupy an exceptional place in shaping.

  An example on this subject is the shaping of very thin parts in the form of disks in silicon, germanium, sapphires, garnet, spinel and

  compounds of groups III-V of the peri-classification

  dique, as they are used more and more, worldwide, as a substrate for the manufacture of electronic components. Lapping exclusively used at the start of surface shaping is increasingly being replaced by grinding with diamond grinding wheels. This process was developed at the

production, by the plaintiff.

  The aim of the present invention is to allow, when shaping parts made from extremely brittle and often extremely hard crystalline materials, an improved machining capacity compared to the current state of the art, with removal of material sparing the material, the inevitable modifications of the upper layers of the material which intervene in a cutting process and the damage which results therefrom, namely the depth of the disturbances of the crystalline layer in the vicinity, having to be less than in removal methods currently known and used while an improvement in the surface quality is to be obtained at the same time to reduce the number of successive working phases necessary in the

  case of such materials, such as, for example,

  grinding, finishing polishing and

softening.

  The damage and traces of shaping clearly visible on the rectified surface increase the sensitivity to rupture and significantly modify the electrical characteristics of the parts in particular of the discs of substrate and have a very unfavorable effect on the consecutive treatments and

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  dissemination processes. The lower the damage, the thinner the workpieces can be. Likewise, shaping by rectification, sparing the material, simplifies and shortens the consecutive working phases, since the elimination of the inevitable damage by pickling is less complicated.

  Extremely brittle, monocris-

  tallins or polycrystallines which can be shaped according to the invention have a minimum Vickers hardness of 7000 N / mmn2, which can go up to a maximum value of 25000 N / mmn The known examples of such materials are compounds of groups IIIa-Vb having Vickers hardness up to 8500. Germanium * has Vickers hardness up to 7500, silicon - has Vickers hardness up to 11500, spinel has Vickers hardness up to 14000 as well as sapphire and gallium-gadolinium-garnet compounds ( GGG) having a Vickers hardness from 19000 to 21500. These types of materials find their particular

  use in electronics. In addition, we can also

  Advantageously, forming super-hard sintered materials such as silicon carbide SiC having a Vickers hardness of 15,000 to 25,500, 1 silicon silicon nitrite Si3N4: having a Vickers hardness of 15,000-20000 (or respectively 35,000 for the single crystal), as well than boron carbide B4C having a Vickers hardness of 22500 to 31000. These types of materials find use in the construction of machines, the construction of engines as well as the construction of installations. Another preferred group of materials includes cutting ceramics having a Vickers hardness of 17,000 to 28,500 as well as Al 203 corundum having a Vickers hardness of 21,500. These materials 2 3

  serve as a non-metallic cutting material.

  The objectives of the invention are achieved

  by applying the trans- rectification process

  side to side plan to the shaping of parts

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  made of an extremely crystalline material

  brittle. A material used particularly pre-

  fable is monocrystalline silicon. Silicon

  polycrystalline is also very satisfactorily

  doing. Unlike the rectification process hitherto used for the shaping of these types of materials, the transverse plane-to-plane rectification method only comprises two components of movement, namely the rotation of

  the grinding wheel and the approach of the grinding wheel directed perpendicular

  on the surface of the workpiece. The feed movement, which was considered in the grinding process hitherto used for shaping

  of these types of materials as a dominant parameter, is removed.

  The grinding process includes, as part of the plan-to-plan transverse grinding, a sinking of the rotating grinding wheel into the surface of the workpiece, so that

  proposed for this shaping the designation "rectified-

  dipping cation ". The abrasive lining is thus preferably dimensioned so that the entire surface of the part to be ground is covered, but, in the case of very large parts, repeating partial plunging is also possible, the piece after each plunge grinding being pushed along the width of the lining, towards the axis of the grinding wheel. The transverse plane-to-plane grinding, which was used until then only as relatively rough coarse machining with low quality requirements

  surface, has for consequence in the case of the orient-

  optimum performance of the method provided according to the invention, an exceptionally satisfactory machining behavior, sparing the material and this in an entirely surprising manner in the case of extremely hard materials

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  fragile which are subject to disturbances of the crystal lattice on the shaped surface. Thus, the machining capacity is several times greater than that currently known, although the surface quality obtained and the damaging modification of the layer of material located completely outside and coming into contact with the grinding wheel are comparatively good compared to the current shaping process specially developed

point for this purpose.

  It is thus possible to rectify mono- silicon

  crystalline, extremely brittle up to a final thickness of around 80 Nm, while in the case of known rectification processes, operations are generally only neutralized with parts with a thickness> 160 Nm. Measurements confirm that the unfavorable changes in the crystal lattice of the material on the rectification surface are comparatively smaller than in the processes

  rectification previously used.

  In accordance with the invention, there is moreover the very great advantage consisting in that during the aectification of the back side, the front side of the silica disc which undergoes a finishing treatment and which, in general, is covered with relatively material

  soft, constitutes, during this process of rec-

  tification ,, the application face on the location where the part is fixed, and is significantly less exposed to the risk of forming impressions and areas

  crushing, the rejects being thus avoided.

  The favorable grinding procedures that are used in practice, in which the diamond-grinded face grinding wheel is moved over the workpiece surface with very slow feed and shallow depth of cut, presupposes a fine-grained wheel with rounding of appearance

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  elliptical from the cutting edge, to obtain the required quality parameters. These optimum cutting ratios cannot be reproduced safely with finishing machines, which results in significant quality variations. In the case of the rectification process of the invention, on the other hand,

  it is only necessary to ensure that the lining abra-

sive be united.

  With a relatively fine-grained grinding wheel, machining capacities are obtained which were hitherto only obtained with discs of

  roughing with a very coarse grain, now

  however, or even by improving the smoother surface on the workpiece, thanks to the thinner grinding wheel, and in addition, by modifying or less disaggregating in its outer layer the surface of the material coming into contact with the grinding wheel. The uniformity and depth of roughness of the surface can be further improved considerably if, after the end of the "plunge grinding" pass, the workpiece is pulled, parallel to the surface of the grinding wheel, out of the contact area . The traces of the points of the grains protruding a little more from the lining of the grinding wheel are thus equalized. We can compare this additional step to "buffing"

in a very simplified form.

  The use according to the invention of the "transverse plane-to-plane rectification" method for shaping parts made of brittle materials of high hardness makes it possible to have a new technology for

  rectification with multiple advantages.

  As during the machining no advance movement takes place, this allows the construction of a very simple and very stable machine. Automatic grinding machines at one or more known stations (or stations) operate with circular tables as support for the workpiece and as advance installation

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  of room, circular tables in which are established da

  tesses d: avanoe n & e ssarily different etaugmentunt towards the ex-

  sorter. This convenlet, which has a negative effect on the stress

  tation of the material and the quality of the airface of the part during contact with the abrasive grain, is eliminated, since: it is possible, if necessary, to perform a final "buffing" as a linear movement, for example, of the grinding doll, to obtain a surface

  very fine and very regular. The automated systems

  additional rectification with circular table with several stations (or stations) have & all stations

  rectification, identical speed of advance, inde-

  pending a pre-rectification, a rectification

  fine tion or high precision grinding.

  In the method of transverse face-to-face face grinding, used according to the invention, and in which no advance movement takes place during the grinding process, the "buffing movement" can be adapted to each individual case and 0 optimally with minimal expense for the machine, since in general a "linear buffing movement" is not necessary until the last grinding station. As during grinding, the workpiece support, who has

  for example the shape of a circular progress table

  clocked, remains stationary, we obtain a loading and unloading of the part which are

  very precise and easy to use.

  Another advantage lies in the fact that, during this period, a complete separation, in the space, between the field of grinding and the field of loading and unloading, is possible, which is of great importance in the case of parts. very precise, because the attachment points or locations of the part can be cleaned and kept clean until the next SubstMt disc is put in place. Of

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  dust particles inserted in small quantity between the support surface of the part and the substrate discs, exert a pressure on the surface causing inevitably in the case of very thin substrate discs, the formation of the dreaded local cracks which are called

  because of their "crow's feet" conformation.

  The invention produces the exceptional advantage of a considerably higher machining capacity accompanied by relatively high stress.

less of the workpiece and the tool.

  This allows the rectification of more brittle materials with very small thicknesses between and 250 Dm, preferably between 80 and 200 gm, because advantageously, the crystal lattice of the material is only very slightly modified. Another advantage is that, during grinding, the workpiece table is securely locked on the support.

  machine and is therefore very stable against oscillations.

  The present invention offers another advantage concerning the very low prices of the specific tools which result from the long life of the grinding wheel and which also contributes significantly to the fact that the maximum possible number of grinding bodies participates in the grinding process. , which reduces the load on the grains and facilitates the removal of chips, the cutting force, which acts constantly and with little vibration on each grain that can be represented, with regard to the polishing surface, as a fixed vector in space. Thanks to the fact that the advance movement is not necessary, this avoids the tearing of the

gMns of binder furniture.

  The grinding wheels necessary for the process of the invention are not complicated and are easy to manufacture. In general, grinding bodies are fixed, preferably consisting of diamond grains as

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  cutting material, in the form of discs, plates

  or bands, on a base body. The inter-

  media which, therefore, remain free between individual grinding elements enhance the cooling effect and facilitate removal

  shavings. The distance between the grinding elements

  individual cation or rectification segments

  cation is In addition, each time, smaller than the surface to be shaped. In this way, a picene is prevented from being wedged between two grinding segments and that, during the rotation of the grinding wheel, takes place a traditional process of frontal grinding, where only the edge of the grinding segment acts. However, it is also possible to advantageously use grinding wheels provided with a continuous lining the dimensions of which are

  determined according to the size of the room.

  In the grinding according to the invention, economically finer grains can be used, which, for grinding non-material

  metallic, give better finished surfaces.

  To better understand the object of the present invention, we will describe below,

  title of examples purely illustrative, and not limited to

  several embodiments shown

in the accompanying drawings.

  In these drawings, Figure 1 shows a substrate disc of a typical size; FIG. 2 represents an embodiment of a device for the implementation according to the invention of the transverse plan-to-plan rectification process; Figure 3 is a schematic representation of the rough proportions between the grinding surface of the grinding wheel and the workpiece in the case of a device according to Figure 2; and

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  FIGS. 4a to 4e are respective schematic representations of examples of advantageous configurations of the grinding surfaces of grinding wheels

  for implementing the method of the invention.

  The silicon support disc shown in Figure 1 has dimensions as provided for the manufacture of high power electronic components. The embodiment of a device shown in Figure 2 consists of a machine support 1 mainly in the form of a parallelepiped, on the upper horizontal surface of which is arranged for receiving or transporting the parts 3, a table 2 that you can rotate in a clocked fashion or that can be moved horizontally,

  and which can be fixed during the rectification process.

  The coin receiving device is surmounted by

  a support 4, on which are fixed the drive motor

  8 and the grinding spindle 5, which carries the grinding wheel 6 with the grinding surface 7 facing the workpieces. The support 4 is mounted movable vertically up and down by means of

  guide 9, precise and rigid, on the support 1.

  This vertical upward and downward movement can, for example, be obtained by an electrically controlled approach pin 10. This approach spindle 10 advances the grinding wheel 6 downwards, according to the invention, in "plunge rectification" until the final measurement of the part and lifts the entire support in rapid movement, upwards. During this return movement of the support, the finished part is moved away from the grinding zone by the clockwise rotation or by the horizontal displacement of the table 2, and, at the same time, a new part to be shaped is

  brought under the grinding wheel and put in working position.

  These simultaneous loading and unloading

  dual in synchronism with the return movement of the support so that there is no collision there

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  between the new part and the grinding wheel, as long as the transport movement is not finished and the

  workpiece support has not been locked again.

  FIG. 3 shows a grinding wheel for implementing the method of the invention. The grinding wheel 40 shown has a grinding or polishing surface 42 facing the part 41 which, during the grinding process, completely covers, by its surface, the part 41 held securely and not subjected to a movement of advance. In this way, it is ensured that during the grinding, all the abrasive bodies of the grinding surface 42

  work effectively to remove chips.

  Figures 4a to 4e represent in a hatic way, various possibilities of surface configuration

  abrasive bodies which can be used according to the invention.

  FIG. 4a represents a surface of

  rectification formed by pads 43 of abrasive bodies.

  Figures 4b and 4c show grinding wheels whose abrasive linings are formed from abrasive lining elements 44, 45 respectively of square shape.

and trapezoidal.

  In the case of FIGS. 4d and 4e, the elements of the abrasive lining are respectively shaped in the form of rods 46 and dacs 47. In all the embodiments of FIGS. 4a to 4e, parts 41 have been shown respectively of circular shape and you can see that the abrasive linings completely cover the parts on the surface effectively. In each of these grinding wheel embodiments, it is ensured that, during grinding, all of the abrasive bodies of the abrasive lining segments facing the workpiece will be effective in removing the

  shavings. This is clearly contrary to rectification.

  traditional frontal or facial cation, according to which only the abrasive bodies of the edge of the grinding wheel

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used to remove chips.

  Another advantage of the invention lies in the fact that the grinding load and the contact area of the grinding wheel on the workpiece are constant throughout the time of grinding. We can thus obtain a very regular image of the rectification.

  and a very stable rectification process.

  The transverse rectification process

  plan against plan, or plane rectification trans-

  lateral, facial, is described for example in the

  draft standard DIN 8589, part 11, page 10.

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Claims (2)

  1. Application of the plan-to-plan transverse rectification process to the shaping of disc-shaped parts consisting of a very hard and brittle crystalline material, rectification process which comprises   only two components of movement, namely the rota-   tion of the grinding wheel and approach to the grinding wheel, characterized in that the crystalline material has a Viekers hardness greater than 7000 N / mmn2 and is of a thickness included between 60 and 250 pm.   2. Application of the trans- rectification process   planar against planar versal according to claim 1 for forming disc-shaped parts consisting of a very hard and brittle crystalline material preferably having   a thickness between 80 and 120 μm.