阅读说明：本技术 一种晶圆化学机械研磨工艺 (Wafer grinding mechanical grinding process ) 是由 刘虎 于 2021-08-27 设计创作，主要内容包括：本发明公开了一种晶圆化学机械研磨工艺,涉及晶圆加工领域,为解决现有技术中的化学研磨速率较慢,晶圆的研磨效果差,不方便调整研磨位置的问题。所述研磨台底座的上方安装有工作台底座,所述工作台底座的内部安装有抽气泵,所述工作台底座的上端安装有研磨垫,所述研磨垫的两侧均设置有活动套筒,所述活动套筒的内部安装有电动喷头,所述研磨垫的上方设置有连接支撑架,所述连接支撑架的两侧均安装有第一电动缸,所述连接支撑架的下端安装有加强筋,所述加强筋的下端两侧均安装有固定防护罩,两个所述固定防护罩之间安装有磨辊电动机,所述磨辊电动机的下端安装有研磨辊头,所述研磨辊头的外部设置有清扫板。(The invention discloses a wafer chemical mechanical polishing process, relates to the field of wafer processing, and aims to solve the problems that in the prior art, the chemical polishing speed is low, the polishing effect of a wafer is poor, and the polishing position is inconvenient to adjust. The grinding table is characterized in that the workbench base is installed above the grinding table base, an air pump is installed inside the workbench base, a grinding pad is installed at the upper end of the workbench base, movable sleeves are arranged on two sides of the grinding pad, electric spray heads are installed inside the movable sleeves, a connecting support frame is arranged above the grinding pad, first electric cylinders are installed on two sides of the connecting support frame, reinforcing ribs are installed at the lower end of the connecting support frame, fixed protective covers are installed on two sides of the lower ends of the reinforcing ribs, grinding roller motors are installed between the fixed protective covers, grinding roller heads are installed at the lower ends of the grinding roller motors, and cleaning plates are arranged outside the grinding roller heads.)

1. A wafer grinding process comprises a grinding table base (1), and is characterized in that: the grinding table is characterized in that a working table base (23) is installed above the grinding table base (1), an air pump (28) is installed inside the working table base (23), a grinding pad (25) is installed at the upper end of the working table base (23), movable sleeves (22) are arranged on two sides of the grinding pad (25), electric spray heads (29) are installed inside the movable sleeves (22), a connecting support frame (14) is arranged above the grinding pad (25), first electric cylinders (15) are installed on two sides of the connecting support frame (14), reinforcing ribs (16) are installed at the lower end of the connecting support frame (14), fixed protective covers (17) are installed on two sides of the lower end of each reinforcing rib (16), grinding roller motors (18) are installed between the fixed protective covers (17), and grinding roller heads (19) are installed at the lower ends of the grinding roller motors (18), a cleaning plate (35) is arranged outside the grinding roller head (19), a second electric cylinder (34) is arranged on one side of the cleaning plate (35), a movable sliding plate (6) is arranged at the upper end of the first electric cylinder (15), a connecting moving block (8) is arranged at the upper end of the movable sliding plate (6), a threaded lead screw (9) penetrates through the connecting moving block (8), and a fixed top plate (7) is arranged above the threaded lead screw (9); the wafer chemical mechanical polishing process comprises the following steps:

the method comprises the following steps: placing the wafer above the grinding pad (25), opening the air suction pump (28), and fixing the wafer on the upper end face of the grinding pad (25);

step two: the grinding fluid is sprayed by an electric spray head (29) in the movable sleeve (22), and the angle of the movable sleeve (22) is continuously adjusted in the spraying process;

step three: extending a first electric cylinder (15), driving a grinding roller head (19) to carry out chemical grinding work on the surface of the wafer, adjusting the position of a movable sliding plate (6) to drive the grinding roller head (19) to adjust the position, and adjusting the angle of a grinding roller motor (18) to adjust the angle of the grinding roller head (19);

step four: in the cleaning process, a second electric cylinder (34) is extended, the second electric cylinder (34) drives a cleaning plate (35) to be attached to the grinding roller head (19), so that the grinding roller head (19) can clean the powder ground on the surface in the grinding process.

2. The wafer chemical mechanical polishing process of claim 1, wherein: the grinding table protective cover (24) is arranged outside the grinding pad (25), an air suction hole (26) is formed in the upper end face of the grinding pad (25), an air suction pipe (27) is installed at the lower end of the air suction hole (26), and the air suction pipe (27) is connected with an air suction pump (28) in a sealing mode.

3. The wafer chemical mechanical polishing process of claim 1, wherein: anti-skidding callus on sole (4) are installed to the below of grinding table base (1), screw thread telescopic link (3) are installed to the upper end of anti-skidding callus on sole (4), screw thread telescopic link (3) extend to grinding table base (1) inside and grinding table base (1) threaded connection, the lower extreme fixed connection of anti-skidding callus on sole (4) and screw thread telescopic link (3), just the up end of grinding table base (1) is provided with calibration bubble.

4. The wafer chemical mechanical polishing process of claim 1, wherein: the front end face of the grinding table base (1) is provided with a ventilation hole (2), support frames (5) are mounted on two sides of the grinding table base (1), and a positioning block is mounted between each support frame (5) and the grinding table base (1).

5. The wafer chemical mechanical polishing process of claim 1, wherein: the novel connecting device is characterized in that a stepping motor is mounted inside the fixed top plate (7) and is connected with the threaded lead screw (9) through synchronous belt transmission, the connecting moving block (8) is connected with the fixed top plate (7) through a sliding groove in a sliding mode, the connecting moving block (8) is connected with the threaded lead screw (9) through threads, the connecting moving block (8) is fixedly connected with the movable sliding plate (6), and the movable sliding plate (6) is connected with the movable sliding plate through a sliding rail support frame (5) in a sliding mode.

6. The wafer chemical mechanical polishing process of claim 1, wherein: remove and install movable shockproof pole (10) between slide (6) and joint support frame (14), activity shockproof pole (10) is provided with two sets ofly, and is two sets of connection sliding block (11) are all installed to the lower extreme of activity shockproof pole (10), the both ends of activity shockproof pole (10) all through the connecting axle respectively with be connected sliding block (11) and remove slide (6) swing joint, location lagging (12) are installed to one side of connecting sliding block (11), the lower extreme and the location lagging (12) sliding connection of connecting sliding block (11), just install damping spring (13) between activity shockproof pole (10) and the location lagging (12).

7. The wafer chemical mechanical polishing process of claim 1, wherein: the strengthening rib (16) are provided with two sets ofly, two sets of strengthening rib (16) all with joint support frame (14) welded connection, just fixed protection casing (17) are installed to the lower extreme inboard of strengthening rib (16), fixed protection casing (17) are provided with two, two servo motor (31) and balancing weight (33) are installed respectively to the inside of fixed protection casing (17), install bearing frame (32) between fixed protection casing (17) and grinding roller motor (18), just the one end of the electronic jar of second (34) extends to the inside and fixed protection casing (17) fixed connection of fixed protection casing (17).

8. The wafer chemical mechanical polishing process of claim 1, wherein: grinding fluid storage box (20) are all installed to the both sides of workstation base (23), telescopic bracket (21) are installed to the upper end of grinding fluid storage box (20), just the internally mounted electric pump of grinding fluid storage box (20), and electric pump and electric nozzle (29) pass through connecting pipe sealing connection, electric motor (30) are installed to the rear end of movable sleeve (22), electric motor (30) and telescopic bracket (21) fixed connection, just electric motor (30) are connected with movable sleeve (22) transmission through the connecting axle.

Technical Field

The invention relates to the technical field of wafer processing, in particular to a wafer grinding process by a wafer chemical machine.

Background

Chemical Mechanical Polishing (CMP), wafer fabrication, and photolithography, with the progress of process technology and the reduction of wire and gate dimensions, have increasingly required the flatness of the wafer surface, and IBM corporation developed the introduction of CMOS products in 1985 and succeeded in producing 64MB of DRAM in 1990. Since 1995, CMP technology has rapidly developed and has been used in the semiconductor industry in large numbers. Chemical mechanical polishing (cmp) is also called chemical mechanical polishing (cmp), and the principle of cmp is a processing technology combining chemical corrosion and mechanical removal, and the only technology in mechanical processing can achieve global surface planarization.

The chemical mechanical polishing technology combines the advantages of chemical polishing and mechanical polishing. The method has the advantages that the method is simple in chemical grinding, high in surface precision, low in damage and good in integrity, surface and sub-surface damage is not easy to occur, but the existing chemical grinding speed is low, the grinding effect of a wafer is poor, and the grinding position is not convenient to adjust; therefore, there is a need in the market to develop a wafer grinding process to help people solve the existing problems.

Disclosure of Invention

The present invention provides a wafer chemical mechanical polishing process to solve the problems of slow chemical polishing rate, poor wafer polishing effect and inconvenience in adjusting polishing position in the prior art.

In order to achieve the purpose, the invention provides the following technical scheme: a crystal circle learning mechanical grinding process comprises a grinding table base, wherein a workbench base is installed above the grinding table base, an air pump is installed inside the workbench base, a grinding pad is installed at the upper end of the workbench base, movable sleeves are arranged on two sides of the grinding pad, an electric spray head is installed inside each movable sleeve, a connecting support frame is arranged above each grinding pad, first electric cylinders are installed on two sides of the connecting support frame, reinforcing ribs are installed at the lower ends of the connecting support frame, fixed protective covers are installed on two sides of the lower ends of the reinforcing ribs, a grinding roller motor is installed between the two fixed protective covers, a grinding roller head is installed at the lower end of the grinding roller motor, a cleaning plate is arranged outside the grinding roller head, a second electric cylinder is installed on one side of the cleaning plate, and a movable sliding plate is installed at the upper end of the first electric cylinder, a connecting moving block is arranged at the upper end of the moving sliding plate, a threaded lead screw penetrates through the connecting moving block, and a fixed top plate is arranged above the threaded lead screw; the wafer chemical mechanical polishing process comprises the following steps:

the method comprises the following steps: placing a wafer above a grinding pad, opening an air suction pump, and fixing the wafer on the upper end face of the grinding pad;

step two: spraying the grinding fluid through an electric nozzle in the movable sleeve, and continuously adjusting the angle of the movable sleeve in the spraying process;

step three: extending a first electric cylinder to drive a grinding roller head to perform chemical grinding work on the surface of the wafer, adjusting the position of a movable sliding plate to drive the grinding roller head to adjust the position, and adjusting the angle of a grinding roller motor to adjust the angle of the grinding roller head;

step four: in the clearance process, the electronic jar of extension second, the electronic jar of second drives cleaning board and grinds the first laminating of roller, makes the roller head of grinding in the grinding process, and the powder of surface grinding clears up simultaneously.

Preferably, a grinding table protective cover is arranged outside the grinding pad, an air suction hole is formed in the upper end face of the grinding pad, an air suction pipe is installed at the lower end of the air suction hole, and the air suction pipe is connected with an air suction pump in a sealing mode.

Preferably, the antiskid callus on the sole is installed to the below of grinding table base, the screw thread telescopic link is installed to the upper end of antiskid callus on the sole, the screw thread telescopic link extends to grinding table base inside and grinding table base threaded connection, the lower extreme fixed connection of antiskid callus on the sole and screw thread telescopic link, just the up end of grinding table base is provided with calibration bubble.

Preferably, the front end face of the grinding table base is provided with a ventilation hole, the two sides of the grinding table base are both provided with a support frame, and a positioning block is arranged between the support frame and the grinding table base.

Preferably, a stepping motor is installed inside the fixed top plate, the stepping motor is connected with the threaded lead screw through a synchronous belt in a transmission mode, the connecting moving block is connected with the fixed top plate through a sliding groove in a sliding mode, the connecting moving block is connected with the threaded lead screw in a threaded mode, the connecting moving block is fixedly connected with the movable sliding plate, and the movable sliding plate is connected with the sliding support through a sliding rail support frame in a sliding mode.

Preferably, movable shockproof rods are installed between the movable sliding plate and the connecting support frame, the movable shockproof rods are provided with two groups, two groups of connecting sliding blocks are installed at the lower ends of the movable shockproof rods, the two ends of each movable shockproof rod are respectively movably connected with the connecting sliding blocks and the movable sliding plate through connecting shafts, a positioning sleeve plate is installed on one side of each connecting sliding block, the lower end of each connecting sliding block is slidably connected with the corresponding positioning sleeve plate, and a damping spring is installed between each movable shockproof rod and each positioning sleeve plate.

Preferably, the strengthening rib is provided with two sets ofly, two sets of the strengthening rib all with joint support frame welded connection, just fixed protection casing is installed to the lower extreme inboard of strengthening rib, fixed protection casing is provided with two, two servo motor and balancing weight are installed respectively to the inside of fixed protection casing, install the bearing frame between fixed protection casing and the grinding roller motor, just the one end of the electronic jar of second extends to the inside and the fixed protection casing fixed connection of fixed protection casing.

Preferably, the lapping liquid storage box is all installed to the both sides of workstation base, telescopic bracket is installed to the upper end of lapping liquid storage box, just the internally mounted electric pump of lapping liquid storage box, and electric pump and electric nozzle pass through connecting pipe sealing connection, electric motor is installed to movable sleeve's rear end, electric motor and telescopic bracket fixed connection, just electric motor passes through the connecting axle and is connected with movable sleeve transmission.

Compared with the prior art, the invention has the beneficial effects that:

1. the invention arranges a wafer above a grinding pad through the arrangement of a grinding table base, opens an air suction pump to fix the wafer on the upper end surface of the grinding pad, can suck air through an air suction hole on the surface of the grinding pad to ensure that the joint effect between the wafer and the surface of the grinding pad is better, so that the working effect of the wafer is improved, can drive a connecting moving block to move through the rotation of a threaded lead screw, so that a moving sliding plate and a connecting support frame are moved, thereby the position of a grinding roller head is moved to adapt to different positions, can drive a grinding roller motor and the grinding roller head to adjust the angle through a servo motor in a fixed protective cover, so as to adapt to wider grinding angles, has simple structure and convenient use, can improve the fixing effect of the connecting support frame through reinforcing ribs, reduces the shake of the grinding roller head in the working process by matching with a movable shockproof rod at the upper end, and improves the stability of the grinding roller head, further improve the effect of chemical milling, conveniently adjust the position, adaptability is wide.

2. According to the invention, through the arrangement of the movable sleeve, in the working process, the electric spray head in the movable sleeve can be used for spraying the grinding fluid, the electric pump in the grinding fluid storage box can be used for guiding the grinding fluid into the electric spray head, and the electric motor can adjust the spraying angle of the electric spray head, so that the spraying position of the grinding fluid is wider, the grinding fluid can be more uniformly covered, and the grinding effect is improved.

Drawings

FIG. 1 is a schematic diagram of a wafer chemical mechanical polishing apparatus according to the present invention;

FIG. 2 is a top view of a polishing pad of the present invention;

FIG. 3 is an internal structural view of a polishing table base according to the present invention;

FIG. 4 is a schematic view of a movable sleeve of the polishing platen of the present invention;

fig. 5 is an internal structure view of the fixing guard of the present invention.

In the figure: 1. a grinding table base; 2. a ventilation hole; 3. a threaded telescopic rod; 4. anti-skid foot pads; 5. a support frame; 6. moving the sliding plate; 7. fixing a top plate; 8. connecting a moving block; 9. a threaded lead screw; 10. a movable shock-proof rod; 11. connecting the sliding blocks; 12. positioning a sleeve plate; 13. a damping spring; 14. connecting a support frame; 15. a first electric cylinder; 16. reinforcing ribs; 17. fixing a protective cover; 18. a grinding roller motor; 19. grinding the roller head; 20. a grinding fluid storage tank; 21. a telescopic support frame; 22. a movable sleeve; 23. a table base; 24. a grinding table protective cover; 25. a polishing pad; 26. an air exhaust hole; 27. an air exhaust pipe; 28. an air pump; 29. an electric shower head; 30. an electric motor; 31. a servo motor; 32. a bearing seat; 33. a balancing weight; 34. a second electric cylinder; 35. and (4) cleaning the board.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.

Referring to fig. 1-5, an embodiment of the present invention is shown: a crystal circle learning mechanical grinding process comprises a grinding table base 1, a working table base 23 is installed above the grinding table base 1, an air suction pump 28 is installed inside the working table base 23, a grinding pad 25 is installed at the upper end of the working table base 23, movable sleeves 22 are arranged on two sides of the grinding pad 25, an electric spray head 29 is installed inside the movable sleeves 22, a connecting support frame 14 is arranged above the grinding pad 25, first electric cylinders 15 are installed on two sides of the connecting support frame 14, reinforcing ribs 16 are installed at the lower end of the connecting support frame 14, fixed protective covers 17 are installed on two sides of the lower end of each reinforcing rib 16, a grinding roller motor 18 is installed between the two fixed protective covers 17, a grinding roller head 19 is installed at the lower end of the grinding roller motor 18, a cleaning plate 35 is arranged outside the grinding roller head 19, a second electric cylinder 34 is installed on one side of the cleaning plate 35, a movable sliding plate 6 is installed at the upper end of each first electric cylinder 15, a connecting moving block 8 is installed at the upper end of the moving sliding plate 6, a threaded lead screw 9 penetrates through the connecting moving block 8, and a fixed top plate 7 is installed above the threaded lead screw 9; and a wafer chemical mechanical polishing process comprises the following steps:

the method comprises the following steps: placing the wafer above the polishing pad 25, turning on the suction pump 28, and fixing the wafer on the upper end surface of the polishing pad 25;

step two: the grinding fluid is sprayed by an electric nozzle 29 in the movable sleeve 22, and the angle of the movable sleeve 22 is continuously adjusted in the spraying process;

step three: extending the first electric cylinder 15 to drive the grinding roller head 19 to perform chemical grinding work on the surface of the wafer, adjusting the position of the movable sliding plate 6 to drive the grinding roller head 19 to adjust the position, adjusting the angle of the grinding roller motor 18 to adjust the angle of the grinding roller head 19, rotating the threaded lead screw 9 to drive the connecting moving block 8 to move, moving the movable sliding plate 6 and the connecting support frame 14 to move, so that the position of the grinding roller head 19 is moved to adapt to different positions, and driving the grinding roller motor 18 and the grinding roller head 19 to adjust the angle through the servo motor 31 in the fixed protective cover 17 to adapt to wider grinding angles;

step four: in the cleaning process, the second electric cylinder 34 is extended, the second electric cylinder 34 drives the cleaning plate 35 to be attached to the grinding roller head 19, and the powder ground on the surface of the grinding roller head 19 is cleaned simultaneously in the grinding process.

Further, a grinding table protective cover 24 is arranged outside the grinding pad 25, an air suction hole 26 is formed in the upper end face of the grinding pad 25, an air suction pipe 27 is installed at the lower end of the air suction hole 26, the air suction pipe 27 is hermetically connected with an air suction pump 28, a wafer is placed above the grinding pad 25, the air suction pump 28 is opened, the wafer is fixed to the upper end face of the grinding pad 25, air can be sucked through the air suction hole 26 in the surface of the grinding pad 25, the attaching effect of the wafer and the surface of the grinding pad 25 is better, and the working effect of the wafer is improved.

Further, anti-skidding callus on the sole 4 is installed to grinding table base 1's below, threaded telescopic rod 3 is installed to anti-skidding callus on the sole 4's upper end, threaded telescopic rod 3 extends to grinding table base 1 inside and grinding table base 1 threaded connection, anti-skidding callus on the sole 4 and threaded telescopic rod 3's lower extreme fixed connection, and grinding table base 1's up end is provided with calibration bubble, through rotating threaded telescopic rod 3, make grinding table base 1's gradient adjust, the cooperation calibration bubble can keep grinding pad 25's angle steady.

Further, the front end face of the grinding table base 1 is provided with the vent hole 2, the two sides of the grinding table base 1 are provided with the support frames 5, the positioning blocks are arranged between the support frames 5 and the grinding table base 1, the movable sliding plate 6 slides in the support frames 5, and the position of the movable sliding plate 6 can be kept stable through the support frames 5.

Further, the internally mounted of fixed roof 7 has step motor, and step motor passes through synchronous belt drive with screw lead screw 9 and is connected, connects movable block 8 and fixed roof 7 and passes through spout sliding connection, and connects movable block 8 and screw lead screw 9 threaded connection, connects movable block 8 and 6 fixed connection of removal slide, and removes slide 6 and pass through 5 sliding connection of slide rail support frame, and step motor drives screw lead screw 9 and rotates, drives and connects movable block 8 and remove for removal slide 6 removes with joint support frame 14.

Further, install movable shockproof pole 10 between movable sliding plate 6 and the joint support frame 14, movable shockproof pole 10 is provided with two sets ofly, connecting sliding block 11 is all installed to the lower extreme of two sets of movable shockproof poles 10, the both ends of movable shockproof pole 10 all through the connecting axle respectively with connecting sliding block 11 and movable sliding plate 6 swing joint, location lagging 12 is installed to one side of connecting sliding block 11, the lower extreme of connecting sliding block 11 and location lagging 12 sliding connection, and install damping spring 13 between movable shockproof pole 10 and the location lagging 12, grinding roller head 19 is after rotating, the vibrations that joint support frame 14 of grinding roller head 19 upper end received, damping spring 13 of accessible movable shockproof pole 10 lower extreme cushions, thereby reduce the shake of joint support frame 14 and grinding roller head 19, and improve the working effect.

Further, the strengthening rib 16 is provided with two sets ofly, two sets of strengthening ribs 16 all with joint support frame 14 welded connection, and the lower extreme inboard of strengthening rib 16 installs fixed protection casing 17, fixed protection casing 17 is provided with two, servo motor 31 and balancing weight 33 are installed respectively to the inside of two fixed protection casings 17, install bearing frame 32 between fixed protection casing 17 and the grinding roller motor 18, and the one end of the electronic jar 34 of second extends to the inside of fixed protection casing 17 and fixed protection casing 17 fixed connection, and can improve joint support frame 14's fixed effect through strengthening rib 16.

Further, the lapping liquid storage box 20 is all installed to the both sides of workstation base 23, telescopic support frame 21 is installed to the upper end of lapping liquid storage box 20, and the internally mounted electric pump of lapping liquid storage box 20, and the electric pump passes through connecting tube sealing connection with electric shower nozzle 29, electric motor 30 is installed to the rear end of movable sleeve 22, electric motor 30 and telescopic support frame 21 fixed connection, and electric motor 30 is connected with movable sleeve 22 transmission through the connecting axle, the leading-in electric shower nozzle 29 of lapping liquid is with the electric pump of inside lapping liquid storage box 20 of accessible, and the angle that electric motor 30 adjustable electric shower nozzle 29 sprayed, thereby can make the position that the lapping liquid sprayed more extensive, can make the lapping liquid cover more evenly, improve the grinding effect.

The working principle is as follows: when the grinding table is used, a wafer is placed above a grinding pad 25, the inclination of a grinding table base 1 is adjusted by rotating a threaded telescopic rod 3, the angle of the grinding pad 25 can be kept stable by matching with calibration bubbles, an air suction pump 28 is opened to fix the wafer on the upper end surface of the grinding pad 25, air suction can be performed through an air suction hole 26 on the surface of the grinding pad 25, the bonding effect of the wafer and the surface of the grinding pad 25 is better, the working effect of the wafer is improved, grinding fluid is sprayed through an electric spray head 29 inside a movable sleeve 22, the angle of the movable sleeve 22 is continuously adjusted in the spraying process, the grinding fluid can be guided into the electric spray head 29 through the electric pump inside a grinding fluid storage box 20, and the electric motor 30 can adjust the spraying angle of the electric spray head 29, so that the spraying position of the grinding fluid can be wider, the grinding fluid can be more uniformly covered, and the grinding effect is improved, extend first electronic jar 15, drive grinding roller head 19 and carry out the chemical milling work to the wafer surface, the position of adjustment movable sliding plate 6 drives grinding roller head 19 adjustment position, the angle of adjustment grinding roller motor 18, make grinding roller head 19's angle adjust, step motor drives screw lead screw 9 and rotates, it removes to drive connection movable block 8, make movable sliding plate 6 and joint support frame 14 remove, in the clearance process, extend electronic jar 34 of second, electronic jar 34 of second drives sweeping board 35 and the laminating of grinding roller head 19, make grinding roller head 19 in the course of lapping, the powder of finish is cleared up simultaneously, can be favorable to subsequent work.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.