WO2014174350A1

WO2014174350A1 - Wire saw

Info

Publication number: WO2014174350A1
Application number: PCT/IB2014/000428
Authority: WO
Inventors: Simon Habegger
Original assignee: Meyer Burger Ag
Priority date: 2013-04-24
Filing date: 2014-03-26
Publication date: 2014-10-30
Also published as: CN105142867A

Abstract

The invention relates to a wire saw (1), preferably a wafer cutting saw, comprising: a cutting wire (3), preferably forming a wire web, for cutting a workpiece (2), application means (6) for applying a cutting fluid to the cutting wire (3), wire breakage sensing means (8) for detecting a broken cutting wire (3), - a shield (7) for shielding the wire breakage sensing means (8) from the cutting fluid coming from the application means (6), wherein the application means (6), the wire breakage sensing means (8) and the shield (7) form within the wire saw (1) a constructional unit (10).

Description

Wire saw

[001] The invention refers to a wire saw comprising: a cutting wire, preferably forming a wire web, for cutting a workpiece, application means for applying a cutting fluid to the cutting wire, - wire breakage sensing means for detecting a broken cutting wire, a shield for shielding the wire breakage sensing means from the cutting fluid coming from the application means.

[002J Wafers, e.g. for use in solar cells or semiconductor industry, are cut from a block (also called brick or ingot) in a wire saw employing a wire and abrasives. Usually abrasives are suspended in a slurry (in this application also called cutting fluid) that is supplied to the wire web, e.g. by means of a spray means. Nowadays, wafers are cut more and more using fixed abrasives, which are directly attached to the cutting wire. Such wire is e.g. called a diamond wire. Also in the latter case a cutting fluid may be used, e.g. for high quality cuts and for cooling purposes. [003] JP2004114249A as closest prior art discloses a wire saw with a slurry supply, a wire breakage detector and a protection means for protecting the wire breakage detector from slurry. The slurry supply is arranged above the wire web for cutting the workpiece, the protection means is arranged between the upper and the lower wire web and the wire breakage detector is arranged below the lower wire web. The maintenance and exchange of these parts is very costly and time-consuming, since they are difficult to access.

[004] The cutting wire is grounded and an electrically conductive detection bar, to which voltage is applied, is positioned and mounted under the wire web and is electrically insulated from the wire web. The breaking of the cutting wire is detected by detecting a voltage drop caused by a contact of the broken cutting wire with the detection bar. There are some disadvantages in connection with such a solution:

[005] The splash protection means (between the upper and the lower wire web) can easily crash with the cutting wire when removing the protection means (for cleaning) between cuts. The wire may break or jump out of a rill in the wire guide rolls. This impacts the saw up-time and the cutting wire lifetime adversely.

[006] The wire breakage detector is not installed operator-friendly. It is hard to access and to clean. Not cleaning the detector may lead to malfunctioning of the wire breakage 5 detector because it gets covered with an isolating layer of debris, thus not establishing the needed connection to ground of a wire touched it.

[007] The slurry supply in form of a spray means is spraying too wide. There is no control which leads to an inaccurate fluid flow distribution. The fluid may thus establish an electrically conductive path between the wire web and the wire breakage detector, i o leading to undesired stops of the wire saw.

[008] Three parts has to be handled during manufacturing and for maintenance (wire breakage detector, slurry supply, splash protection means).

[009] The spray nozzles get dirty or even clogged and have to be examined and cleaned regularly. The same holds for the wire breakage detector: fluid gets deposited 15 on them, making the contact resistance with broken wires larger.

[0010] JP9262829A discloses a wire saw with slurry supply means. In order to lower generation of cracking of a wafer during cutting, plates are provided laterally from the slurry supply means. The plates prevent that excess slurry reaches the workpiece to be cut.

20 [001 ] JP11070456A discloses a wire saw with cutting fluid nozzles installed along the wire web in a region between the wire guiding rolls and the workpiece path. During the cutting process cutting fluid is sprayed towards the wire web.

[0012] JP2000218501A discloses a wire saw. To provide an easily maintainable wire saw, the wire guiding rolls are partitioned by a pair of brackets. Thereby, a slurry

25 supplied to a wire row is spread only to the inside of the brackets. A duct for wiring or piping is provided between the spindle brackets. Thereby, the slurry is not splashed directly to the piping and wiring.

[0013] DE112008002790T5 discloses a wire saw with a slurry supply and a movable protection means may comprise a plate, a plate- or block-shaped slurry splash preventing member.

[0014] US2011048396A1 discloses wire saw with a slurry blocking plate, extending in the direction along the wire web. The slurry blocking plate is pivotably fixed at a base point.

[0015] The problems in prior art arise due to costly and time-consuming manufacturing, repair and maintenance, particularly cleaning, procedures. The arrangement of the cutting fluid application means, the shield and the wire breakage sensing means does not allow an ease access (miss-handling, long down times). Furthermore, the quality of the wafers is adversely influenced by the cutting fluid splashing towards the workpiece and by a not reliable detection capability of prior art wire breakage detectors.

[0016] The object of the invention is to solve this problem and to provide a wire saw allowing: easy access to all parts (wire breakage sensing means, shield and cutting fluid application means), no wire damaging by handling errors in any component part mentioned above, and, preferably, an accurate fluid flow distribution over the whole wire web leading to better wafer quality.

[0017] Especially in the field of cutting wafers cutting quality it is essential. This comprises the aspects of reliably cutting (application of cutting fluid) and reliably detecting broken wires (wire breakage sensing means). [0018] This object is achieved by a wire saw as mentioned above, wherein the application means, the wire breakage sensing means and the shield form within the wire saw a constructional unit.

[0019] The inventive solution combines three functions within one unit. This allows to build the parts very compact and space-saving and facilitate handling during

manufacturing and cleaning. The functions of the constructional unit are as follows: lubricating the cutting wire with cutting fluid: e.g. providing slurry to the wire web and/or cooling and/or cleaning the (diamond) wire; detecting broken cutting wires and preventing the cutting fluid from being applied to the wire breakage sensing means and thus from covering the sensing means and/or from establishing an electrically

conductive path between the application means and/or cutting wire and the wire breakage sensing means, all this in a small area. Generally, the shield prevents the cutting fluid from being sprayed in all directions causing undesired and uncontrolled (direct or indirect) fluid distribution towards the wire web and/or the brick, ingot or core to be cut. [0020] The shield is arranged between the application means and the wire breakage sensing means, i.e. the application means and the wire breakage sensing means are arranged on opposite sides of the shield. Thus, the shield separates the wire breakage sensing means from an area through which the cutting fluid path, e.g. shaped as a spray cone or a jet, extends between the application means and the cutting wire. [0021] The shield is adapted such, that it is capable of shielding the wire breakage sensing means from cutting fluid coming directly from the application means and from cutting fluid coming indirectly from the application means, namely via the cutting wire and/or the wire guide roll. In the latter case the cutting fluid coming from the application means is deflected and/or transported by the cutting wire and/or the wire guide roll towards the wire breakage sensing means. The cutting fluid splashes off the wire web and/or wire guide roll.

[0022] For shielding the wire breakage sensing means from cutting fluid coming directly from the application means the shield is arranged between the application means and the wire breakage sensing means. For shielding the wire breakage sensing means from cutting fluid coming indirectly from the application means - via the cutting wire and/or the wire guide roll - the shield is arranged close to the cutting wire (wire web).

[0023] The object of the shield is to reduce the amount of cutting fluid in the direction towards wire breakage sensing means. The effect of shielding should be such, that the electrical conductivity between cutting wire and wire breakage sensing means communicated by the cutting fluid is significantly lower than that communicated by a broken wire section touching the wire breakage sensing means. Although preferred, it is not necessary to provide a complete (100%) shielding. The shielding should at least provide a significant difference in electrical conductivity (cutting fluid vs. broken wire). [0024] The application means may be any means directing a cutting fluid towards the improving the cutting process, for cooling components, particularly the cutting wire, and/or preventing components from damage. The cutting fluid may e.g. comprise slurry having abrasives and/or cooling liquid, etc.

[0025] If the wire breakage sensing means is made from an electrically conductive material and forms a part of an electrical contact detector, the following embodiments are preferred. The wire breakage sensing means as part of a detector must be electrically isolated as much as possibly from the cutting fluid leaving the application means (e.g. spray head).

[0026] The wire breakage sensing means should be placed on an electrically insulating material. Alternatively, the shield may be made of electrically insulating material, to which the wire breakage sensing means is mounted.

[0027] The shield may be covered (inside and/or outside) with an insulation material to prevent a conductive path from being formed as cutting fluid rains down.

[0028] The shield is placed such that the cutting fluid (e.g. spray, jet) does not create an electrically conductive path from the wire web to the wire breakage sensing means.

[0029] Preferably, only a small gap is formed between the cutting wire and the shield, the gap being smaller than the distance between the cutting wire and the wire breakage sensing means. Here, it is especially beneficial for the shield to be made of an isolating material or to be covered with it. The shield extends much closer towards the cutting wire than the wire breakage sensing means, i.e. the distance between cutting wire and shield is smaller than the distance between cutting wire and wire breakage sensing means. In this way, cutting fluid coming thru the gap between cutting wire and shield does not immediately touch the wire breakage sensing means.

[0030] The shield preferably has a wall-like structure (preferably adapted to the local shape of the wire web) preventing the cutting fluid as coming from the application means to cover the wire breakage sensing means.

[0031] Preferably, in order to achieve a very compact constructional unit, the

application means, the wire breakage sensing means and the shield face towards the same cutting wire section and are arranged in immediate vicinity to each other, most preferably they are mounted to each other. [0032] Preferably, the application means, the shield and the wire breakage sensing means forming the constructional unit are arranged on the same side of the cutting wire. This allows a simple construction and mounting and allows to remove all components of constructional unit by a single operational step. On the same side of the cutting wire' includes the options, that the components of the constructional unit may be arranged inside or outside of the loop formed by the cutting wire (web).

[0033] Other alternatives of the invention are characterized by the fact, that the application means, the shield and the wire breakage sensing means forming the constructional unit are arranged in the same, adjacent area with respect to a cutting wire section and/or face towards the same part or sector of the cutting wire. Preferably, the application means, the shield and the wire breakage sensing means forming the constructional unit are in immediate vicinity to each other.

[0034] Preferably, the application means, the shield and the wire breakage sensing means are arranged one after another with respect to the moving direction of the cutting wire. This allows a space-saving construction and provides a reliable functioning of all components of the constructional unit in connection with the cutting wire. Preferably, the wire breakage sensing means is mounted upstream of the application means with respect to the moving direction of the cutting wire (downstream being the direction the wire moves; cutting wire moves only in one direction). This arrangement prevents fluid from being tossed onto the wire breakage sensing means.

[0035] A 'direction' of cutting wire movement (characterizable by means of a double arrow) is also defined in the pilgrim mode, i.e. the cutting wire moves alternately in opposite directions.

[0036] Preferably, the application means, the shield and the wire breakage sensing means are arranged directly adjacent to each other.

[0037] Preferably, the application means, the shield and the wire breakage sensing means forming the constructional unit are supported within the wire saw by a common support structure. Production, maintenance and repair are very simple, since all components of the constructional unit have a common mounting to a base structure of the wire saw. [0038] Preferably, the application means comprises spray means for spraying the cutting fluid to the cutting wire. Spray means allow a controllable and uniform cutting fluid distribution towards the cutting wire/wire web. The spray means may comprise a plurality of spray nozzles arranged along the width of the wire web and lubricating the wire web with cutting fluid, e.g. cooling fluid or slurry (abrasives).

[0039] Preferably, the wire breakage sensing means is mounted on the shield. This allows a very compact and stable construction.

[0040] Preferably, the application means is mounted on the shield. This also constitutes a compact and space-saving solution.

[0041] Preferably, the application means is surrounded by a housing which opens towards the cutting wire and wherein the shield is formed by a wall of the housing, and wherein preferably the application means is mounted on the housing. The housing may provide a spatial limitation of the cutting fluid path (spray cone, jet) towards the cutting wire and at the same time provides the shield in form of a housing wall. This solution thus combines the functions in an elegant way.

[0042] Preferably, the wire breakage sensing means is formed from an electrical conductive material for detecting an electrical contact between a broken cutting wire and the wire breakage sensing means. The wire breakage sensing means is part of a detector forming an electrical circuit when a broken wire touches the wire breakage sensing means. The shield prevents that the cutting fluid establishes an electrical connection between the cutting wire and the wire breakage sensing means and that a current flows from the cutting wire/wire web, via the cutting fluid to the wire breakage sensing means. The resistance in the path from the cutting wire/wire web to the wire breakage sensing means via the cutting fluid should be significantly greater than via broken wires, preferably by at least a factor 2, more preferably by a least a factor 5 or still better by at least a factor 0.

[0043] Preferably, the wire breakage sensing means is formed by a bar, extending perpendicular to the cutting wire. The bar has at least a length corresponding to the width of the wire web (extension of the wire web perpendicular to the cutting wire orientation). Here, a broken wire can be detected at any position throughout the wire [0044] Preferably, the constructional unit faces towards a wire guiding roll of the wire saw. In this region the constructional unit is very easy to access. Where wire break detectors as wire breakage sensing means are normally placed below the wire web (according to prior art), it was found that it can also be placed next to the wire guide rolls, enabling easy access (according to a preferred embodiment of invention).

Furthermore, the cutting wire sections supported by the wire guiding rolls are not so sensitive to mechanical stress. The cutting fluid may be sprayed onto the wire web , where it lays on the wire guiding rolls. This prevents the wire web from being impaired, e.g_: by pairing of wires, pushing the wires aside, making the wafers less flat, etc. Also the fluid is not sprayed into the rills of the wire guide rolls since these are covered by the wires.

[0045] Preferably, the constructional unit is releasable mounted to the wire saw. Repair and maintenance is simple, since it is not necessary to remove the individual

components individually. The term 'releasable' constructional unit should be understood such, that the constructional unit is completely removable from the wire saw and/or that the constructional unit is movable within (relative to) the wire saw, e.g. between a working position and a maintenance position.

[0046] Preferably, the constructional unit is movably mounted within the wire saw such that the constructional unit is movable between a working position in the vicinity of the cutting wire and a maintenance position distanced from the cutting wire, preferably by means of a guide or a pivot mechanism. This guarantees that the constructional unit follows a defined path within the wire saw reducing the probability of wire damage. Also in the working position there is a small distance between the constructional unit and the cutting wire (gap), however, in the maintenance position the distance of the

constructional unit from the cutting wire is of course larger.

[0047] Preferably, in the maintenance position of the constructional unit the opening of the housing, which in the working position of the constructional unit faces towards the cutting wire, faces away from the cutting wire, preferably in the direction of an operator's access opening in the wire saw. This allows an optimal access for maintenance, cleaning purposes and repair without the danger of damaging the cutting wire.

[0048] Preferably, the constructional unit may be rotatable such that in an inspection or maintenance position, the application means (e.g. spray nozzles) and wire breakage sensing means are easily accessible and/or visible or even protrude from the wire saw. Again damaging the cutting wire during maintenance is prevented this way.

[0049] Preferably, the wire saw has at least two constructional units each comprising an application means for applying a cutting fluid to the cutting wire, a wire breakage sensing means for detecting a broken cutting wire and a shield for shielding the wire breakage sensing means from the cutting fluid coming from the application means. E.g. one constructional unit may face towards a wire guiding roll and the other constructional unit may face to a second wire guiding roll, yielding a more uniform cutting fluid distribution over the whole wire web. [0050] Preferably, the application means comprises control means for controlling the application rate of cutting fluid to the cutting wire. The control means, e.g. screws are accessible form outside of the constructional unit and may be easily adjusted

[0051] Preferably, the constructional unit according to the invention is arranged in the vicinity of the access door of the wire saw to the cutting space. [0052] In an alternative wording of a preferred embodiment the wire saw (e.g. using fixed abrasive or slurry) having a constructional unit containing: a spray unit for the cutting fluid (cooling fluid, slurry, etc.) for spraying it onto the cutting wire, a wire breakage sensing means, consisting of a conductive material that is on a first electrical potential, the cutting wires being on a second electrical potential, the

conductive material being placed so that broken wires touch it and the current flowing thru the wire breakage sensing means or the change in its electrical potential being used to detect wire breakage. a shield for the spray means, wherein the wire breakage sensing means and the spray means being arranged on opposite sides of the shield.

[0053] The shield preventing the cutting fluid or slurry form being (directly or indirectly) sprayed onto the wire web as well as preventing the fluid from establishing an

electrically conductive path from the spray means to the wire breakage sensing means. Otherwise a current could flow from the wire web, via the medium to the wire breakage detector. The resistance in the path from the wire web to the wire breakage sensing means via the cutting fluid should be significantly greater than via broken wires, say at least a factor 2, preferably a factor 5 or still better a factor 10. [0054] This embodiment is characterized by the spatial distribution of the components (close together), mechanical structure (common mounting means for all components of the constructional unit), i.e. the individual components do not have their own mounting means to a base structure of the wire saw).

[0055] Preferably, the wire saw is a wafer cutting wire saw and the cutting wire forms a wire web for cutting an ingot, brick or core into a plurality of wafers.

[0056] Further embodiments of the invention are indicated in the figures and in the dependent claims. The list of reference marks forms part of the disclosure. The invention will now be explained in detail by the drawings. In the drawings:

Fig. 1 shows a wire saw according to the invention,

Fig. 2 shows the wire saw of Fig. 1 with the constructional unit being pivoted away from the cutting wire,

Fig. 3 shows a wire saw in detail with the constructional unit being located in the working position,

Fig. 4 shows the wire saw of Fig. 3 with the constructional unit being located in the maintenance position,

Fig. 5 shows the constructional unit and its support structure according to the invention, Fig. 6 shows in a cross-section the constructional unit in the working position.

[0057] Fig. 1 shows a wire saw 1 in form of a wafer cutting saw, comprising a cutting wire 3 forming a wire web for cutting a workpiece 2, e.g. an ingot, brick or core, which is moved through the wire web (vertical arrow). The cutting wire 3 is supported and driven by wire guiding rolls 4. The moving direction of the cutting wire is indicated by the arrow M. Note, that for a diamond wire, normally the wire moves in two directions. In this case the arrow M in Fig. 1 would point to the left and to the right. According to the invention the wire saw 1 has a constructional unit 10 comprising an application means 6 for applying a cutting fluid (e.g. slurry, cooling liquid and/or cleaning liquid) to the cutting shield 7 for shielding the wire breakage sensing means 8 from the cutting fluid coming from the application means 6.

[0058] The wire breakage sensing means 8 is preferably arranged upstream of the shield 7. Firstly, in this way the cutting fluid is transported by the wire web away from the sensing means 8 and secondly, a broken wire can more easily touch the sensing means 8. If the cutting wire 3 runs in both directions (pilgrim mode) the wire breakage sensing means 8 may be provided upstream and downstream relative to the application means 6. In this case two shields 7 may be provided each separating a wire breakage sensing means 8 from the application means 6. [0059] If two (or more) constructional units 10 are provided, the wire breakage sensing means 8 may be positioned on different sides (i.e. one of them downstream and one of them upstream) as shown in Fig. 2. It also may be enough to place them on the same side as shown in Fig. 1. One or multiple constructional units 10 may be provided and do not have to be identical. [0060] The application means 6, the shield 7 and the wire breakage sensing means 8 forming the constructional unit 10 are arranged on the same side of the cutting wire 3.

[0061] The application means 6, the shield 7 and the wire breakage sensing means 8 are arranged one after another with respect to the moving direction M of the cutting wire 3. Here, the shield 7 separates the wire breakage sensing means 8 from the application means 6 or the area through which the cutting fluid path 19 (Fig. 6) extends from the application means 6 towards the wire web, respectively.

[0062] As indicated in Fig. 1 the wire breakage sensing means 8 is part of a detector. A measurement device 20 is electrically connected to the cutting wire 3, e.g. via a wire guiding roll 4, and is also electrically connected to the wire breakage sensing means 8. An electrical contact between a broken wire and the wire breakage sensing means 8 can be detected by the measurement of e.g. the electrical resistance, voltage change or current by means of the measurement device 20.

[0063] The collecting means 5 between the wire guiding rolls 4 and having an U- shaped profile is provided for collecting chips (broken off of wafers) and wafers (that detached themselves from the holding beam on which the workpiece 2 is attached). If these large wafer parts (not swarf) would fall onto the lower part of the wire web, they would damage the wire guiding rolls 4 and the cutting wire 3.

[0064] Fig. 1 shows the constructional unit 10 in a working position in immediate vicinity of the cutting wire 3 and Fig. 2 shows one of the constructional units 10 in the maintenance position, distanced from the cutting wire 3. In the embodiment shown the constructional unit 10 is rotatably mounted within the wire saw 1 , i.e. rotatably mounted to a base structure of the wire saw 1 .

[0065] Fig. 3 and 4 show in a perspective view a wire saw 1 according to the invention. The constructional unit 10 further comprises an electrical insulation 9 on which the wire breakage sensing means 8 is mounted. The wire breakage sensing means 8 is made of an electrical conductive material for detecting an electrical contact between a broken cutting wire 3 and the wire breakage sensing means 8. In the present embodiment the wire breakage sensing means 8 is formed by a longitudinal bar, extending perpendicular to the cutting wire 3. The length of the bar corresponds at least the width of the wire web. The electrical insulation 9 electrically insulates the bar from other components of the constructional unit 10.

[0066] As can be seen from Fig. 3 and 4 the constructional unit 10 as such has longitudinal extension along the width of the wire web.

[0067] The application means 6, the shield 7 and the wire breakage sensing means 8 and other components (e.g. electrical insulation, housing, etc.) of the constructional unit 10 are supported within the wire saw 1 by a common support structure 11. The common support structure 1 1 connects the constructional unit 10 to a base structure 14 of the wire saw 1. On the base structure 14 also the wire guiding rolls 4 are rotatably mounted. The constructional unit 10 as a whole is releasable mounted to the wire saw 1. For this purpose only the common support structure 1 1 has to be detached from the base structure 14.

[0068] The constructional unit 10 further comprises a cutting fluid inlet 15 for receiving the cutting fluid and a control means 16 for controlling the application rate of the cutting fluid to the wire web. [0069] In the embodiments of Fig. 3 and 4 the constructional unit 10 is movably mounted within the wire saw 1 such that the constructional unit 0 is movable between a working position (Fig. 3) in the vicinity of the cutting wire 3 and a maintenance position (Fig. 4) distanced from the cutting wire 3. The support structure 1 1 comprises a guide 12, preferably cooperating with adjusting means 13 for exactly adjusting the working position of the constructional unit 10. The constructional unit 10 is slidably supported by the guide 12.

[0070] Alternatively, a pivot mechanism may be used for moving the constructional unit 10 from the working position to the maintenance position and vice versa (schematically indicated in the embodiment of Fig. 1 and 2).

[0071] Preferably, in the maintenance position of the constructional unit 10 the opening of the housing 18, which in the working position of the constructional unit 10 faces towards the cutting wire 3, faces away from the cutting wire 3 (Fig. 2), preferably in the direction of an operator's access opening in the wire saw 1.

[0072] Fig. 5 shows the constructional unit 10 with its support structure 1 1 from the side facing in the working position towards the wire web.

[0073] The application means 6 comprise a plurality of spray means 17 in form of nozzles for spraying the cutting fluid to the cutting wire 3.

[0074] The application means 6 is surrounded by a housing 18 which opens towards the wire web. The opening of the housing 18 facing - at least in the working position of the constructional unit 10 - towards the cutting wire 3 is seen in Fig. 6. The shield 7 is formed by a wall of the housing 18 and the application means 6 is mounted on the housing 18.

[0075] As can be seen from the cross-sectional view of Fig. 6 the wire breakage sensing means 8 is mounted on the shield 7 via the electrical insulation 9.

[0076] The application means 6 comprise control means 16 (e.g. in form of adjusting screws) for controlling or adjusting the position of the application means 6.

[0077] In another embodiment the application means 6 may comprise control means for controlling the application rate of cutting fluid to the cutting wire 3. The control means when operated from outside the constructional unit 0 change the amount of nozzle opening.

[0078] Fig. 6 shows a gap between the cutting wire 3 and the shield 7, wherein the gap is smaller than the distance between the cutting wire 3 and the wire breakage sensing means 8. The shield 7 extends much closer towards the cutting wire 3 than the wire breakage sensing means 8, i.e. the distance between cutting wire 3 and shield 7 is smaller than the distance between cutting wire 3 and wire breakage sensing means 8. In this way, cutting fluid coming thru the gap between cutting wire 3 and shield 7 does not immediately touch the wire breakage sensing means 8.

[0079] The shield 7 is arranged between the application means 6 and the wire breakage sensing means 8, i.e. the application means 6 and the wire breakage sensing means 8 are arranged on opposite sides of the shield 7. Thus, the shield 7 separates the wire breakage sensing means 8 from an area through which the cutting fluid path 19, e.g. shaped as a spray cone or a jet, extends between the application means 6 and the cutting wire 3.

[0080] Also visible in Fig.6 is an outlet 21 for the cutting fluid. This outlet 21 prevents the unit 10 becomes filled with cutting fluid.

[0081] As can be seen from Figs. 1 to 4 the constructional unit 10 faces - in its working position - towards a wire guiding roll 4 of the wire saw 1.

[0082] Preferably the wire saw 1 has at least two constructional units 10 each comprising an application means 6 for applying a cutting fluid to the cutting wire 3, a wire breakage sensing means 8 for detecting a broken cutting wire 3 and a shield 7 for shielding the wire breakage sensing means 8 from the cutting fluid coming from the application means 6. This allows for a more uniform distribution of cutting fluid towards the wire web and a more reliable wire breakage detection.

[0083] The invention is not restricted to the embodiments shown. Support structure, spatial arrangement, movable mounting and other components may be changed within the scope of the invention. List of reference marks

1 wire saw

2 workpiece

3 cutting wire

4 wire guiding roll

5 collecting means

6 application means

7 shield

8 wire breakage sensing means 9 electrical insulation

10 constructional unit

1 1 support structure

12 guide

13 adjusting means

14 base frame

15 fluid inlet

16 control means

17 spray means

18 housing

19 cutting fluid path

20 measurement device

21 outlet for cutting fluid

M moving direction of the cutting wire 3

W width of the wire web

Claims

1. Wire saw (1 ), preferably a wafer cutting saw, comprising:

- a cutting wire (3), preferably forming a wire web, for cutting a workpiece (2), - application means (6) for applying a cutting fluid to the cutting wire (3),

- wire breakage sensing means (8) for detecting a broken cutting wire (3),

- a shield (7) for shielding the wire breakage sensing means (8) from the cutting fluid coming from the application means (6), wherein the application means (6), the wire breakage sensing means (8) and the shield (7) form a constructional unit (10).

2. Wire saw according to claim 1 , wherein the application means (6), the shield (7) and the wire breakage sensing means (8) forming the constructional unit (10) are arranged on the same side of the cutting wire (3).

3. Wire saw according to claim 1 or 2, wherein the wire breakage sensing means (8), the shield (7) and the application means (6) are arranged one after another with respect to the moving direction (M) of the cutting wire (3).

4. Wire saw according to one of the preceding claims, wherein the application means (6), the shield (7) and the wire breakage sensing means (8) forming the

constructional unit (10) are supported within the wire saw (1 ) by a common support structure ( 1 ).

5. Wire saw according to one of the preceding claims, wherein a gap is formed

between the cutting wire (3) and the shield (7), the gap being smaller than the distance between the cutting wire (3) and the wire breakage sensing means (3).

6. Wire saw according to one of the preceding claims, wherein the application means (6) comprises spray means (17) for spraying the cutting fluid to the cutting wire (3).

7. Wire saw according to one of the preceding claims, wherein the wire breakage sensing means (8) is mounted on the shield (7) and/or wherein the application means (6) is mounted on the shield (7).

8. Wire saw according to one of the preceding claims, wherein the application means 5 (6) is surrounded by a housing (18) which in a working position of the constructional unit (10) opens with an opening towards the cutting wire (3) and wherein the shield (7) is formed by a wall of the housing (18), and wherein preferably the application means (6) is mounted on the housing (18).

9. Wire saw according to one of the preceding claims, wherein the wire breakage0 sensing means (8) is formed from an electrical conductive material for detecting an electrical contact between a broken cutting wire (3) and the wire breakage sensing means (8), and/or wherein the wire breakage sensing means (8) is formed by a bar, extending perpendicular to the cutting wire (3).

10. Wire saw according to one of the preceding claims, wherein the constructional unit5 (10) faces towards a wire guiding roll (4) of the wire saw ( ).

1 1. Wire saw according to one of the preceding claims, wherein the constructional unit (10) is releasable mounted to the wire saw (1).

12. Wire saw according to one of the preceding claims, wherein the constructional unit (10) is movably mounted within the wire saw (1) such that the constructional unito (10) is movable between a working position in the vicinity of the cutting wire (3) and a maintenance position more distanced from the cutting wire (3), preferably by means of a guide (12) or a pivot mechanism

13. Wire saw according to claim 8 and claim 12, wherein in the maintenance position of the constructional unit (10) the opening of the housing (18), which in the working5 position of the constructional unit ( 0) faces towards the cutting wire (3), faces away from the cutting wire (3), preferably in the direction of an operator's access opening in the wire saw (1 ).

14. Wire saw according to one of the preceding claims, wherein the wire saw (1) has at least two constructional units (10) each comprising an application means (6) for0 applying a cutting fluid to the cutting wire (3), a wire breakage sensing means (8) for detecting a broken cutting wire (3) and a shield (7) for shielding the wire breakage sensing means (8) from the cutting fluid coming from the application means (6).

15. Wire saw according to one of the preceding claims, wherein the application means (6) comprises control means (16) for controlling the application rate of cutting fluid to the cutting wire (3).