DE102014109791B4 - Laser ablation process and element made of brittle material - Google Patents

Abstract

Method for producing a recess (6) in an element (2) made of brittle-hard material, in which a laser beam (40) with laser pulses (41) is directed onto the surface (20) of the element (2) by means of a pulsed laser (4), wherein the laser pulses (41) generate a plasma (8) with vaporized material on the surface (20) and thus material is ablated from the surface (20) of the element (2), and wherein the laser beam (40) is guided over the surface (20) of the element (2) at a feed rate of at most 30 mm/s, so that successive laser pulses (41) strike different locations on the surface (20) of the element (2), and wherein the pulse frequency and the feed rate of the laser beam (40) on the surface (20) of the element (2) are set such that the light spots (42) of successive laser pulses (41) of the laser beam (40) overlap on the surface (20) of the element (2) and the plasma (8) generated by the preceding laser pulse (41) still exists when a laser pulse (41) impinges, and wherein the laser pulses (41) remove material to a depth in the range between 30 µm and 150 µm.

Description

The invention generally relates to material processing with lasers. In particular, the invention relates to the insertion of depressions, such as trenches in brittle-hard materials, as well as elements made of brittle-hard material with trench-shaped depressions.

US 2012 / 0 196 454 A1 relates to the laser-based modification of a workpiece, wherein focusing and directing laser pulses onto the workpiece is performed at a pulse repetition rate sufficiently high so that material is efficiently removed from the area, reducing the amount of unwanted material compared to a lower repetition rate.

DE 10 2005 037 412 A1 relates to a laser machining method for forming a laser groove along dividing lines by applying a pulse laser beam along the dividing lines formed on a workpiece, the method comprising the steps of forming the focal point of the pulse laser beam in the shape of an oval, positioning the long axis of the oval focal point along each of the dividing lines, and moving the focal point and the workpiece along the dividing line relative to each other.

JP 2006 - 36 602 A relates to a ceramic component having a recessed part on at least one main surface and being constructed from a main component and a plurality of additional components, wherein the recessed part is formed by heat irradiation and wherein there is substantially no melt layer of the ceramic forming the main component on the surface layer of the recessed part.

EP 2 246 146 A1 relates to a laser processing method comprising directing pulsed laser light onto a surface of a substrate made of brittle material and a laser light scanning step for scanning laser light along a planned scribe line, the method comprising certain parameters for the laser intensity of the pulsed laser light and the value resulting from multiplying the amount of heat supplied by the linear expansion coefficient of the brittle material and the number of pulses within a square that describes the diameter of the condensed light of the pulsed laser.

The EP 0 931 620 A1 describes a device and a method for laser ablation of quartz glass with a laser whose light wavelength of 266 nm is longer than the absorption edge of quartz glass at 170 nm and less. In this method, the laser is directed through the quartz glass onto a target. This creates a plasma cloud on the target that spreads between the quartz glass and the target. Material is then ablated from the quartz glass using this secondary plasma cloud. This method is very complex and slow. The laser is operated at a pulse frequency of 1 Hz in order to provide sufficient pulse energy for the indirect ablation.

From the JP 2000 - 348 621 A A process is known in which a glass solder seam between the screen and the funnel of cathode ray tubes is loosened or loosened by means of a laser. The loosening or loosening takes place by briefly evaporating the glass inside the glass seam.

This procedure therefore causes immediate, deep damage, which in itself is beneficial in order to be able to easily separate the two parts from each other.

The JP 2000 - 348 621 A The process described is intended to separate the screen and funnel for recycling. The exact course of the breaking edge is not important here.

However, the process will not be suitable for reliably ensuring a very precise course of the fracture edge. Another difficulty arises if the ablation and separation of the parts are to be separated in time. Ageing phenomena can occur here, especially with glass. Chemical changes to the surface cause a change in the breaking force. This change can also be inhomogeneous, so that the required breaking force varies locally and the fracture edge can therefore run differently.

It would therefore be desirable to be able to introduce predetermined breaking points into an element made of brittle-hard material in such a way that the element can be cleanly divided with a defined breaking force even long after the predetermined breaking point has been inserted.

Even with depressions for purposes other than inserting a predetermined breaking point, the laser ablation process has the problem that the depth of such a depression depends on the laser power. However, the laser power can decrease significantly during operation, especially with lasers in the UV wavelength range due to the higher energy density and thus negative influence on the optical elements (even to the point of destruction). It would be desirable if the depth of an ablated depression could be adjusted as independently as possible from the laser power.

This object is achieved by the subject matter of the independent claims. Advantageous embodiments and further developments of the invention are specified in the dependent claims.

It was found that by choosing the right process parameters for laser ablation, a self-regulating process is obtained that remains stable even when the laser power drops by more than 40%, provided the pulse energy does not fall below the ablation threshold.

Accordingly, the invention provides a method for producing a recess in an element made of brittle-hard material, in which a laser beam with laser pulses is directed onto the surface of the element by means of a pulsed laser, the laser pulses generating a plasma with vaporized material on the surface and thus ablating material from the surface of the element, and the laser beam being guided over the surface of the element at a feed rate of at most 30 mm/s so that successive laser pulses hit different locations on the surface of the element, and the pulse frequency and the feed rate of the laser beam on the surface of the element are set so that the light spots of successive laser pulses of the laser beam overlap on the surface of the element and the plasma generated by the previous laser pulse still exists when a laser pulse hits, and the laser pulses are used to remove material with a thickness or to a depth in the range between 30 µm and 150 µm.

When removing material by laser ablation with a pulsed laser, particularly an ultrashort pulse laser, the self-regulating process described above occurs at very low scanning speeds in such a way that the impact points of the pulses overlap. What is surprising is that when the plasma generated by a previous pulse overlaps in time and space with the subsequent pulse, the removal depth is almost independent of the laser power over a wide power range of the laser. The following mechanism is suspected: The first pulses evaporate the material to a certain depth, creating a plasma. When a certain energy level is reached, this plasma shields the material underneath from further laser radiation. This means that even when the laser power decreases significantly, the removal depth decreases only slightly or not at all.

It has also been shown that the stability of the process, or the constancy of the removal depth, is particularly pronounced when the laser spot is held at a fixed location/point, i.e. the laser beam is stationary and the element to be processed is moved. In other words, according to a further development of the invention, the element made of brittle-hard material is moved relative to the laser beam to generate a feed of the laser beam.

According to one embodiment of the invention, without limitation to a specific embodiment, a pulsed Nd-YAG laser is used as the laser.

According to a further preferred development of the invention, the laser beam is frequency multiplied. A frequency multiplier is provided for this purpose. If an Nd:YAG laser with a wavelength of 1064 nm is used, a KDP crystal, for example, is suitable as a frequency doubler in order to generate green light with a wavelength of 532 nm. The laser beam is then directed onto the surface of an element to be treated made of brittle material using a focusing optic.

According to a further development of the invention, the frequency of the laser beam is tripled. If an Nd:YAG laser is tripled with the frequency multiplier, the wavelength of the laser pulses hitting the surface of the element is 355 nm, i.e. a wavelength in the ultraviolet spectral range. In general, the two light wavelengths mentioned above, generally light wavelengths of less than 600 nm, are particularly suitable for processing glass as a brittle material. In general, without being restricted to a specific embodiment, a development of the invention therefore provides that the recess is created with a laser beam with a light wavelength of less than 600 nm.

In general, without being limited to a specific embodiment, the method according to the invention is particularly suitable for producing a recess in a glass element. Preferred types of glass for this purpose are borosilicate glasses, including aluminoborosilicate glasses.

With the invention, almost any geometry of depressions can be created by appropriately guiding the laser beam over the surface. However, it is generally preferred that a depression in the form of a trench is inserted into the element.

With the invention, by appropriately guiding the laser beam over the surface Almost any geometry of depressions can be created. However, it is generally preferred that a depression in the form of a trench is inserted into element 2.

In general, without being limited to a specific embodiment, a laser is operated with a pulse frequency of at least 10 kHz, preferably at least 50 kHz. With these high pulse frequencies, the process can be carried out economically with sufficient feed rates. In particular, these pulse frequencies can ensure that the plasma is still maintained between the individual pulses.

The plasma still present above the surface when the next laser pulse hits counteracts variations in the laser power. If the laser power drops, the plasma is weaker when the next laser pulse arrives. This also weakens the shielding effect of the plasma, so that the laser light penetrates more easily to the surface of the element to be processed.

In this way, the laser pulses can be used to remove material with a thickness or depth in the range between 30 µm and 150 µm. The self-regulating mechanism allows the removal depth to be kept very constant within the range specified above. According to one embodiment of the invention, the removal depth is approximately 80 µm. The invention is therefore generally particularly suitable for introducing the smallest structures into the material.

In order to ensure a spatial overlap of small light spots for inscribing fine structures in the element to be processed, it is generally preferred according to the invention, without limitation to a specific example, if the laser beam is guided over the surface of the element at a feed rate of at most 22 mm/s.

Furthermore, it is preferred that the laser beam is focused such that the light spot on the surface of the element has a diameter of at most 70 µm, preferably at most 50 µm, in order to be able to produce fine structures.

According to a further development of the invention, it is generally provided that an element in the form of a tube is provided which has an axial section with an enlarged circumference, wherein a circumferentially encircling recess is inserted in the axial section with an enlarged circumference.

Without being limited to a specific embodiment, according to a preferred embodiment of the invention, a recess with a width of at most 50 µm is produced.

Due to the comparatively slow ablation process according to the invention due to the spatial overlap of the laser pulses, a deep depression can generally be created in just one pass of the laser beam, without being restricted to specific embodiments. In general, a further development of the invention provides for a depression of at least 30 µm, preferably at least 50 µm, to be created in a single pass of the laser beam. According to the invention, the feed rates are 30 mm/s or less. According to one embodiment, the ablation takes place at a feed rate of 15 mm/s with a laser repetition frequency of around 100 kHz. At first glance, this slow processing appears to be disadvantageous. However, the slow processing time is hardly significant, particularly when processing thin tubes, in particular capillaries, since the circumference and thus the distance to be covered by the laser beam are correspondingly short.

The method is used to produce depressions in particular which have a high aspect ratio between width and depth. In general, without being restricted to specific embodiments, an element made of brittle material is provided which has at least one trench-shaped depression whose depth is at least as great as its width, the width of the depression being, as already stated above, at most 50 µm and the depth between 30 µm and 150 µm, preferably between 50 µm and 100 µm.

Without being limited to specific embodiments, a further development of the invention provides that the side walls of the recess have an opening angle on the surface of the element which is at most 45°.

The invention is described in more detail below, also using exemplary embodiments and with reference to the figures. In the figures, the same reference symbols designate the same or corresponding elements.

• 1 schematisch einen Aufbau zur Durchführung des erfindungsgemäßen Verfahrens,
• 2 einen alternativen Aufbau,
• 3 schematisch im Querschnitt ein verfahrensgemäß bearbeitetes Rohr,
• 4 eine mikroskopische Seitenaufnahme eines Rohres,
• 5 eine mikroskopische Aufnahme der Bruchkante eines an der Vertiefung gebrochenen Rohres,
• 6 einen Querschnitt durch ein Element aus sprödhartem Material, vorzugsweise Glas.

They show:

• 1 schematically shows a structure for carrying out the method according to the invention,
• 2 an alternative structure,
• 3 schematic cross-section of a pipe processed according to the process,
• 4 a microscopic side view of a pipe,
• 5 a microscopic image of the fracture edge of a pipe broken at the depression,
• 6 a cross-section through an element made of brittle material, preferably glass.

1 shows a schematic structure of a device 1 for carrying out the method according to the invention for producing a recess in an element 2 made of brittle material. The device 1 comprises a laser 4 for emitting a pulsed laser beam 40. The laser beam 40 is therefore made up of a sequence of laser pulses 41. For example, a laser with an output power of approximately 40 µJ per pulse can be used.

A pulsed Nd-YAG laser is used as laser 40.

In the 1 In the example shown, the laser beam 40 is frequency multiplied. A frequency multiplier 43 is provided for this purpose. If an Nd:YAG laser with a wavelength of 1064 nm is used, a KDP crystal, for example, is suitable as a frequency doubler in order to generate green light with a wavelength of 532 nm. The laser beam 40 is then directed by means of a focusing optics 44 onto the surface 20 of an element 2 to be treated, made of brittle-hard material.

For example, it is intended to triple the frequency of the laser beam 40. If an Nd:YAG laser is tripled using the frequency multiplier 43, the laser pulses 40 striking the surface 20 of the element 2 have a wavelength of 355 nm, i.e. a wavelength in the ultraviolet spectral range. In general, the two light wavelengths mentioned above, generally light wavelengths of less than 600 nm, are particularly suitable for processing glass as a brittle material. It is therefore intended, for example, that the recess 6 is created with a laser beam 40 with a light wavelength of less than 600 nm.

The method is particularly suitable for producing a recess 6 in a glass element. Preferred glass types for this are borosilicate glasses including aluminoborosilicate glasses.

By appropriately guiding the laser beam over the surface, almost any geometry of recesses 6 can be created. It is preferred that a recess 6 is inserted into the element 2 in the form of a trench.

In the 1 In the example shown, three laser pulses 41 are shown for illustration purposes only, which are located between the laser 4 and the surface 20 of the element 2. Typically, however, repetition frequencies and distances are used which are so low that the laser pulse 20 fills the optical path between the laser 4 and the surface 20.

The focusing optics 44 now collimates the laser beam 40 onto a light spot 42 on the surface 20 of the element. The light spot 42 is preferably as small as possible, so that the light spot 42 represents the focus of the laser beam 40 generated by the focusing optics. The laser pulses 41 generate a plasma 8 with vaporized material of the element 2 on its surface 20, so that material is ablated from the surface 20 of the element 2. In order to generate an elongated depression 6, the laser beam 4 is guided over the surface 20 of the element, so that successive laser pulses 41 hit different locations on the surface 20 of the element 2.

One possibility is to deflect the laser beam 40. According to a preferred embodiment of the invention, however, the element 2 made of brittle material is moved relative to the laser beam 4 to generate a feed of the laser beam 40. For this purpose, in the 1 In the example shown, a device 10 is provided for guiding the laser beam 40 over the surface 20 of the element 2. In this example, the device 10 comprises a carriage 101 on which the element 2 is arranged. The carriage 101 and thus also the element 2 are moved relative to the stationary laser 4 in a direction transverse to the direction of impact of the laser 4, so that an elongated depression 6 is produced which extends along the direction of movement of the element 2.

After the end of a laser pulse 41, the plasma 8 collapses due to the lack of heating power from the laser beam 4 until the next impinging laser pulse 41 generates a new plasma 8 and the ablation process is continued. According to the invention, however, the pulse frequency and the feed speed of the laser beam 40 on the surface 20 of the element 2 are set such that the light spots 42 of successive laser pulses 41 of the laser beam 40 overlap on the surface 20 of the element 2 and the plasma 8 generated by the previous laser pulse 41 still exists when a laser pulse 41 impinges.

The laser 4 is operated with a pulse frequency of at least 10 kHz, preferably at least 50 kHz. With these high pulse frequencies, the process can be carried out economically with sufficient feed rates. In particular, these pulse frequencies can ensure that the plasma is still maintained between the individual pulses.

The plasma still present above the surface when the next laser pulse 41 hits counteracts variations in the laser power. If the laser power drops, the plasma is weaker when the next laser pulse arrives. This also weakens the shielding effect of the plasma 8, so that the laser light penetrates more easily to the surface 20 of the element 2 to be processed.

In this way, the laser pulses 41 can be used to remove material with a thickness or depth in the range between 30 µm and 150 µm. The self-regulating mechanism allows the removal depth to be kept very constant within the range specified above. For example, the removal depth is around 80 µm. The method is therefore particularly suitable for introducing the smallest structures into the material.

2 shows a variant of the 1 device shown 1.

In order to ensure a spatial overlap of small light spots 42 for inscribing fine structures in the element to be processed, it is preferred if the laser beam 40 is guided over the surface 20 of the element 2 at a feed rate of at most 22 mm/s.

Furthermore, it is preferred that the laser beam 40 is focused such that the light spot 42 on the surface 20 of the element 2 has a diameter of at most 70 µm, preferably at most 50 µm, in order to be able to produce fine structures.

2 shows a variant of the 1 This variant is generally based on the fact that the element 2 made of brittle-hard material is rotated in order to guide the laser beam 40 over the surface of the element 2. The device for guiding the laser beam 40 over the surface 20 of the element 2 comprises a rotation device 102, for example with a chuck in which the element 2 is clamped and which is driven by a motor with a gear reduction. This embodiment of the invention is particularly suitable for, as also in 2 shown, circumferentially extending recesses are inserted into the lateral surface of an element 2 in the form of a tube 22, particularly preferably in a glass tube.

When using the method according to the invention, there is a further advantage that makes the invention particularly suitable for processing tubular elements. The plasma, which still exists during the subsequent laser pulse 41, also has the effect of suppressing ablation of material on the surface facing away from the laser beam due to the shielding. In the case of an element 2 in the form of a tube, this surface is its inside. If ablation occurs on the inside, particles can be deposited inside the tube. Depending on the application, such particles and other deposits from the ablation can be very disruptive.

A recess 6, as inserted using the method according to the invention, can form a predetermined breaking point according to one embodiment of the invention. The element 2 can then be separated at the predetermined breaking point after the recess 6 has been inserted. A recess in the form of a trench is particularly suitable for forming a predetermined breaking point.

Glass elements that are to be broken at a defined point are used in the analytical and medical fields, among others. Ampoules are an example. As already explained above, one problem is to be able to introduce predetermined breaking points into an element made of brittle material in such a way that the element can be cleanly broken with a defined breaking force even long after the predetermined breaking point has been inserted. It turns out that the method according to the invention is particularly suitable for inserting predetermined breaking points that satisfy this condition.

The problem of creating a clean break edge is further exacerbated if the element is to be separated at a particularly stable point. This is the case, for example, with capillary tubes that have a section-by-section expansion of the diameter. Such glass capillaries that are separated at the expansion in the area of the maximum diameter are used in chemical analysis, particularly in immunological tests. The expansion serves as a reaction reservoir and the subsequent thinner capillary section is used to absorb particles that form during the reaction, such as agglutinates.

For example, it is provided that an element 2 is provided in the form of a tube 22, which has an axial section 23 with an extended circumference, wherein a circumferential recess 6 is inserted in the axial section 23 with an extended circumference. In 3 such a tube 22 is shown schematically in cross-section. The tube 22 has the shape of a capillary. In the axial section 23, the inner and outer diameters of the capillary expand. At the same time, the wall thickness of the tube 22 also tapers towards the axial position with the maximum outer diameter.

Such a tube 22 can be produced in particular by a method for forming a glass tube, in particular a
capillary tube, in a forming section, wherein the tube 22 has one or
two open ends. The tube 22 is held and fixed with a holding device. The holding device preferably comprises a
first fixing section 14 and a second fixing section. The tube 22 is then heated between the first and second fixing sections. The heating is preferably carried out with a between the first and the second
second fixing section arranged heating pipe, which surrounds the pipe 22 in a ring shape. A gas flow is provided by means of a gas source and introduced into the pipe 22 via at least one of the open ends with a connector that communicates with the gas source. In other words, the pressure inside the pipe 22 is increased compared to the environment by means of a gas source. The set pressure inside causes a radial expansion of the pipe 22 in the forming section softened by the heating. This forming section is thus formed into the axial section 23 with an expanded diameter.

The tube 22 thus formed can then be provided with a recess 6 in the axial section 23 with the aforementioned circumferentially extending recess 6 by laser ablation using the method according to the invention. The recess preferably runs all the way around and thus has the shape of a ring-shaped closed notch or a ring-shaped closed trench.

Furthermore, it is also preferred that the recess 6 is inserted at or near the axial position of the tube 22 with the maximum diameter of the section 23.

This creates a predetermined breaking point which, after the tube has broken at the recess 6, provides two glass parts with essentially equal-sized extensions at their respective ends, preferably serving as a reaction space.

4 shows a microscopic image of such a tube 22. In particular, a section of the tube 22 with the axial section 23 is shown. The circumferential depression 6 in the form of an annular groove in the area of the maximum diameter of the axial area 23 can be clearly seen. It can also be seen from the scale of 500 µm that the depression 6 is very narrow. For example, it is intended that a depression 6 with a width of at most 50 µm is produced.

The recesses 6 that can be produced using the method according to the invention are typically also characterized by steep walls, so that the recesses 6, for a given width, extend deep into the brittle material of the element 2. This is also shown in the example of the 5 clearly. 5 shows a view of the front side of a 4 processed tube 22. The tube 22 was broken into two parts. The end face of the tube 22 thus obtained accordingly runs along the plane perpendicular to the longitudinal axis of the tube 22 at the axial position of the maximum diameter of the region 23.

The recess 6 extends as in the 3 and 4 shown examples from the outside 25 of the tube 22 to a depth that is less than the wall thickness of the tube 22. When the element 2, or here the tube 22, breaks at the predetermined breaking point formed by the recess 6, a fracture surface 26 is created which extends from the recess 6 to the side of the element 2 opposite the side with the recess 6. In the case of a tube 22, this opposite side is formed by the inside 24 of the tube 22.

The fracture surface 26 and the wall of the former depression 6 are visible in the image of the 5 can be clearly seen from the different surface textures. The fracture surface 26, which appears bright in the image, is very smooth, while the wall remaining from the depression 6 has a certain roughness due to the ablation process.

Due to the comparatively slow ablation process according to the invention due to the spatial overlap of the laser pulses, a deep depression can be created with just one pass of the laser beam. For example, it is provided that a depression of at least 30 µm, preferably at least 50 µm, is created with a single pass of the laser beam. According to the invention, the feed speeds are 30 mm/s or less. According to one embodiment, the ablation is carried out with a feed speed of 15 mm/s at a laser repetition frequency of about 100 kHz. At first glance, this slow processing appears to be disadvantageous. However, it is particularly important when processing thin tubes 22, especially capillaries, as shown in the examples of 3 to 5 As can be seen from the figures, the slow processing time is of little consequence, since the circumference and thus the distance to be covered by the laser beam are correspondingly short. For example, the tube 22 of the 4 In the example shown, the tube only has a diameter of about 1.5 mm at the location of the recess 6. At a feed rate of 15 mm/s, the processing time is therefore only about 0.3 s. The processing time is therefore typically less than the time used to fix the tube.

The removal depth D is in 5 marked with a double arrow and is approximately 80 µm. Such a removal depth is typical for the above-mentioned pulse frequencies of at least 50 kHz.

A trench-shaped depression inserted using the method according to the invention has a number of characteristics that make it particularly suitable as a long-term stable predetermined breaking point. In particular, the breaking force required for breaking can be kept essentially constant almost independently of the storage period. In comparison, this is not the case with the usual scratching, since the scratch can partially heal, particularly under the influence of moisture. This can cause the required breaking force to increase locally. Conversely, storage under stress can lead to stress corrosion cracking, which can lead to a locally reduced required breaking force or even to premature breakage. Both effects can occur simultaneously, so that overall the required breaking force becomes inhomogeneous along the predetermined breaking point. If there is a time delay between scratching and breaking, this can lead to blurred and unclean breaking edges.

In contrast, a recess 6 inserted according to the invention is suitable as a predetermined breaking point for a time-delayed breaking, whereby further processing steps can also be carried out between the insertion of the recess and the breaking. In particular, a cleaning step with an aqueous medium and/or a coating step can take place between scratching and breaking. Water in particular otherwise leads to the above-mentioned phenomena of crack healing and stress corrosion cracking. A preferred application of such a product is a sample carrier (also in the form of a sample container) for medical, biological or chemical samples.

According to one embodiment of the invention, a method is therefore provided for further processing and using a sample carrier with an element made of brittle-hard material, wherein an element 2 made of brittle-hard material, preferably made of glass, is provided with at least one recess 6, which serves as a predetermined breaking point, is cleaned with an aqueous medium after the recess 6 has been inserted, is then optionally coated and is then broken at the predetermined breaking point. In the case of tubular sample carriers, such as those used in the 3 until 5 show, a further cleaning step can be carried out after breaking before filling the pipe with a sample.

The following are based on 6 the characteristics of a product that can be produced using the process according to the invention are described. 6 shows a cross-section through an element 2 made of brittle material, preferably glass, wherein a section of the element 2 is shown with two examples of depressions 6 according to the invention, designed in the shape of a trench for the purpose of a predetermined breaking point.

The method is used to produce depressions 6 that have a high aspect ratio between width and depth. In both cases, 6 In the examples shown, the depth D is greater than the width B of the depression 6. For example, an element 2 made of brittle-hard material is provided, which has at least one trench-shaped depression 6, the depth of which is at least as great as its width, the width of the depression, as already stated above, being at most 50 µm and the depth between 30 µm and 150 µm, preferably between 50 µm and 100 µm. Furthermore, as with both in 6 In the examples shown, the two side walls 60, 61 run towards each other starting from the surface of the element 2. The side walls can run towards each other essentially in a straight line, as in the embodiment shown on the right, or with a curve, as in the example shown on the left.

In both cases, the opening angle α of the side walls 60, 61 is marked on the surface 20 of the element 2. The opening angle α, i.e. the angle of opposite wall sections of the walls 60, 61 to each other, is smaller in the case of the side walls curved towards each other shown on the left than in the case of straight side walls.

For example, it is provided that the side walls 60, 61 of the recess have an opening angle α on the surface 20 of the element 2, which is at most 45°. If a typical depth D of the recess 6 of approximately 80 µm and a width of 50 µm is assumed, an opening angle of approximately 35° results in the embodiment shown on the right.

The comparatively small opening angle is favorable for generating high tensile stresses at the tip 63 of the recess 6 when the element 2 is subjected to a bending stress and thus enabling the element 2 to be easily separated at the recess.

On the other hand, a very pointed depression 6 can lead to phenomena similar to crack healing. In depressions produced according to the invention, however, a rounding of the tip 63 is evident. Although the rounding leads to slightly increased fracture stresses, this rounding leads to a predetermined breaking point that is stable over the long term, even with regard to cleaning processes when in contact with aqueous media. The radius R of the tip 63 is generally less than 1 µm, but at least 50 nm.

In summary, the method according to the invention can be used to produce an element 2 made of brittle-hard material which has a trench-shaped depression 6, wherein the trench-shaped depression is produced with a width of at most 50 µm and a depth of at most 150 µm, preferably at most 100 µm, wherein the side walls of the depression 6 on the surface 20 of the element 2 have an opening angle of less than 45° and wherein the two side walls 60, 61 of the depression 6 converge in a tip 63 which has a radius in the range of 0.05 µm to 1 µm.

For the purpose of a predetermined breaking point, it is still less sensible to provide very large wall thicknesses or thicknesses of the element 2 in order not to make the breaking force required too high. Thicknesses of the element at the recess 6 in the range of 200 µm to 2 mm are preferred. The depth of the recess is not included in this information, so the thickness is measured from a point next to the recess.

It is clear to the person skilled in the art that the invention can be varied in many ways within the scope of the subject matter of the patent claims. In particular, the features of the individual embodiments can also be combined with one another.

list of reference symbols

1

device for producing a depression

2

element made of brittle material

4

Laser

6

deepening

8

plasma

10

Device for guiding the laser beam 40 over the surface 20 of the element 2

20

surface of 2

22

Pipe

23

axial section of 22 with extended circumference

24

inside of 22

25

outside of 22

26

fracture surface

40

laser beam

41

laser pulse

42

light spot

43

frequency multiplier

44

focusing optics

60, 61

side walls of 6

63

top of 6

101

Sleds

102

rotation device

Claims (15)

Method for producing a recess (6) in an element (2) made of brittle-hard material, in which a laser beam (40) with laser pulses (41) is directed onto the surface (20) of the element (2) by means of a pulsed laser (4), wherein the laser pulses (41) generate a plasma (8) with vaporized material on the surface (20) and thus material is ablated from the surface (20) of the element (2), and wherein the laser beam (40) is guided over the surface (20) of the element (2) at a feed rate of at most 30 mm/s, so that successive laser pulses (41) strike different locations on the surface (20) of the element (2), and wherein the pulse frequency and the feed rate of the laser beam (40) on the surface (20) of the element (2) are set such that the light spots (42) of successive laser pulses (41) of the laser beam (40) overlap on the surface (20) of the element (2) and the plasma (8) generated by the preceding laser pulse (41) still exists when a laser pulse (41) impinges, and wherein the laser pulses (41) remove material to a depth in the range between 30 µm and 150 µm. Method according to the preceding claim, characterized in that the element (2) made of brittle material is Laser beam (40) is moved to generate a feed of the laser beam (40). Method according to the preceding claim, characterized in that the element (2) made of brittle-hard material is rotated. Method according to one of the preceding claims, wherein the recess (6) is produced in a glass element. Method according to one of the preceding claims, characterized in that a recess (6) in the form of a trench is inserted into the element (2). Method according to one of the preceding claims, characterized in that the recess (6) forms a predetermined breaking point and the element (2) is separated at the predetermined breaking point after the insertion of the recess (6). Method according to one of the preceding claims, characterized in that an element (2) in the form of a tube (22) is provided which has an axial section (23) with an enlarged circumference, wherein a circumferential recess (6) is inserted in the axial section (23) with an enlarged circumference. Method according to one of the preceding claims, characterized in that the laser beam (40) is guided over the surface (20) of the element (2) at a feed rate of at most 22 mm/s. Method according to one of the preceding claims, characterized in that the laser (4) is operated with a pulse frequency of at least 10 kHz, preferably of at least 50 kHz. Method according to one of the preceding claims, characterized in that the recess (6) is produced with a laser beam (40) with a light wavelength of less than 600 nm. Method according to one of the preceding claims, characterized in that the laser beam (40) is focused such that the light spot (42) on the surface (20) of the element (2) has a diameter of at most 70 µm, preferably at most 50 µm. Method according to one of the preceding claims, characterized in that a recess (6) with a width of at most 50 µm is produced. Method according to one of the preceding claims, characterized in that a depression of at least 30 µm, preferably at least 50 µm, is produced by a single pass of the laser beam. Element (2) made of brittle-hard material, which has a trench-shaped depression (6), wherein the trench-shaped depression (6) has a width of at most 50 µm and a depth of at most 150 µm, preferably at most 100 µm, wherein the side walls of the depression (6) on the surface (20) of the element (2) have an opening angle of less than 45° and wherein the two side walls (60, 61) of the depression 6 converge in a tip (63) which has a radius in the range of 0.05 µm to 1 µm. Element (2) according to the preceding claim, wherein its thickness at the recess (6) is in the range of 200 µm to 2 mm.

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