EP4185434A2

EP4185434A2 - Apparatus and method for joining at least two joining partners

Info

Publication number: EP4185434A2
Application number: EP21748550.7A
Authority: EP
Inventors: Felix Zimmermann
Original assignee: Trumpf Laser und Systemtechnik GmbH
Current assignee: Trumpf Laser und Systemtechnik GmbH
Priority date: 2020-07-22
Filing date: 2021-07-20
Publication date: 2023-05-31
Also published as: CN116096526A; WO2022018069A2; WO2022018069A3; KR20230038578A; US20230166360A1

Abstract

The invention relates to a method for joining at least two joining partners (30, 31), wherein the at least two joining partners (30, 31) are joined to each other using ultrashort laser pulses of a laser beam of an ultrashort pulse laser (1), at least one of the joining partners (30, 31) being substantially transparent to the ultrashort laser pulses of the ultrashort pulse laser (1); prior to the joining operation, a coating (32) is applied to at least one of the joining partners (30, 31), and the coating (32) is placed between the joining partners (30, 31), the coating (32) having physical properties similar to at least one of the joining partners (30, 31) and/or comprising a chemical constituent similar to at least one of the joining partners (30, 31).

Description

Device and method for joining at least two joining partners

technical field

The present invention relates to a device and a method for joining at least two parts to be joined, the at least two parts to be joined being joined to one another by means of ultra-short laser pulses of a laser beam from an ultra-short-pulse laser.

State of the art

In order to join at least two joining partners, it is known to apply a laser beam to the respective joining partners in order in this way to generate a melt through energy absorption in the zone exposed to the laser beam, which melt forms a weld seam between the joining partners after the melt has solidified.

It is known to place the focus or focal zone of the laser beam in the boundary surface or in an area around the common boundary surface of the two joining partners for joining a transparent joining partner with a non-transparent joining partner or for welding two transparent joining partners. The processing laser beam passes through one of the transparent joining partners and generates a melt in the area of the interface between the two joining partners.

If you focus ultra-short laser pulses, ie laser pulses in the picosecond range or in the femtosecond range (eg 50 fs -50 ps), in the volume of glass, eg quartz glass, the high intensity in the focus leads to non-linear absorption processes. Depending on the laser parameters, various material modifications can be made to the glass. If the time between the successive ultra-short laser pulses is shorter than the heat diffusion time, this leads to heat accumulation or a temperature increase in the glass in the focus area. With each of the successive pulses, the temperature can then be increased to the melting temperature of the glass and finally the glass can be locally melted. When joining joining partners, the breaking strength of the subsequent weld seam can be determined on the one hand by the laser parameters. On the other hand, the stability of the connection also depends on the materials and the material composition of the joining partners.

It is known from US 2015/0027168 A1 to insert a coating between the joining partners, to position the laser focus in the coating and to initiate a joining process by heating the coating. This has the disadvantage that the joining behavior of the joining partners is difficult to control via the method.

Presentation of the invention

Proceeding from the known state of the art, it is an object of the present invention to provide an improved method for joining at least two joining partners, as well as a corresponding device for carrying out the method.

The object is achieved by a method for joining at least two joining partners with the features of claim 1. Advantageous developments result from the dependent claims, the description and the figures.

Accordingly, a method for joining at least two joining partners is proposed, wherein the at least two joining partners are joined to one another by means of ultrashort laser pulses of a laser beam from an ultrashort pulse laser, wherein at least one joining partner is essentially transparent to the ultrashort laser pulses of the ultrashort pulse laser, and a coating is applied before joining at least one of the joining partners is applied and the coating is arranged between the joining partners, the coating comprising physical properties similar to at least one joining partner and/or a chemical component similar to at least one joining partner.

The coating here leads to an improvement in the joint connection. In particular, with the same process parameters, the breaking strength of the connection of the joining partners joined with the coating can be greater than the breaking strength of the connection if it had been joined without the coating.

The joining laser provides the ultra-short laser pulses, i.e. laser pulses in the picosecond or femtosecond range. The ultra-short laser pulses move along a trajectory determined by the optics of the joining laser, the so-called laser beam. An ultra-short laser pulse from the joining laser is also called a joining pulse. The laser can also provide pulse trains, so-called bursts, made up of ultra-short laser pulses, with each burst comprising the emission of several laser pulses. In particular, so-called GHz bursts can also be provided, with the repetition rate of the individual laser pulses being up to 50 GHz, for example.

Substantially transparent means that the at least one joining partner has a transparency of more than 50% for the wavelength of the laser beam. The transparency of the at least one joining partner has the advantage that the joining laser can be focused through the transparent joining partner, so that the joining area can be localized at the interface of both joining partners. In the case of two transparent joining partners, both irradiation directions are possible.

The first joining partner can be transparent, for example, and the second joining partner can be opaque. For example, the first joining partner can consist of quartz glass and the second can consist of aluminum. However, both joining partners can also be transparent.

Before the joining process, the coating is applied to at least one of the joining partners, for example vapor-deposited, so that the coating is firmly connected to the joining partner. However, the coating can also be sprayed or brushed on, for example, or spun on and baked, for example, in a so-called rotary coating process. In particular, it is also possible for the coating to be applied only locally to the joining partner, with the coating only being applied where a welded joint of the joining partners is to be produced in the subsequent process. This can be done, for example, by masking the joining partner, so that the coating is only arranged on the unmasked areas of the joining partner.

The at least one joining partner with the coating is then oriented to the other joining partner in such a way that the coating comes into contact with the other joining partner. The coating is thus arranged between the joining partners. In other words, the coating then lies in the interface between the two parts to be joined. The interface lies in the joining area.

Similar physical properties of the coating and the at least one joining partner can include, for example, similar transmission of the laser wavelength, similar melting temperature, similar thermal expansion, similar crystal structure or lattice structure, etc. Similar chemical components of the coating of at least one joining partner can include, for example, a similar chemical composition, in particular elements of the same chemical group with similar electronegativity, similar chemical compounds and in particular the same elements.

In the joining area, heat is accumulated as a result of successive absorption of the ultra-short laser pulses, provided the pulse rate of the joining beam is greater than the rate of heat transport through material-specific heat transport mechanisms, in particular through heat diffusion.

Due to the increasing temperature in the material of at least the first joining partner from joining pulse to joining pulse, the melting temperature of the material of the joining partner can finally be reached, which leads to local melting of the material of the first joining partner into which the joining beam enters. In particular, the coating can also be melted here.

The joining area is understood to be that area of the joining partners and the coating in which the ultra-short laser pulses are introduced and in which the material is melted. Alternatively, the entirety of the locally melted material in the joining area can also be referred to as a melt bubble. Irrespective of the name, the resulting melt can bridge the common interface of the joining partners and permanently connect the joining partners to one another when cooling down. This results in a mixing of the melted components of the joining partners and the coating, and then a bond is formed. In particular, the chemical and physical structure of the joining partners can also change here, so that a particularly stable joining modification is formed. The cooled melt, which connects the joint partners to one another or produces the weld seam, is referred to as a joint modification.

In order to melt the material in the joining area, for example between 2 and 10 ultra-short laser pulses and/or bursts can be introduced into the material and successively absorbed. From a spatial perspective, this plurality of ultra-short laser pulses and/or bursts are introduced into the material in a laser spot for the intended material processing, i.e. in the spatial extent of the respective focus area of the laser in the material. The number of laser pulses introduced at a single location is referred to as the pulse overlap. Pulse overlap can be viewed as a measure of heat accumulation.

For example, if there is no feed and all laser pulses are entered at the same location in the material, the pulse overlap is at a maximum. If, on the other hand, there is a feed between the material and the laser spot, the pulse overlap can decrease depending on the ratio of pulse frequency (repetition rate) and feed speed. If the feed rate is too high, the laser spots no longer overlap in the material and the laser spots lie side by side.

The number of ultra-short laser pulses and/or bursts per location in the material is given by the product of the laser spot size SG and the repetition rate P per feed rate VG. The pulse overlap is given by SG * P / VG, for example. The pulse overlap describes the spatial range over which the ultra-short laser pulses and/or bursts are emitted into the material.

The average laser power can be between 0.5 W and 50 W, with the average power being defined as the product of the pulse energy of the individual pulses, possibly the number of pulses in the burst, and the repetition rate of the pulses. This provides enough laser power to melt the material.

At least one joining partner can be a metal or a semiconductor or an insulator or a combination thereof, in particular a glass ceramic or a crystal or a polymer.

For example, the material can include a steel alloy and/or a carbon compound and/or an iron compound and/or an aluminum compound and/or a calcium fluoride compound and/or a silicon compound, in particular a silicon oxide compound or a copper compound.

For example, the material can be a glass, for example a quartz glass, or a silica glass, or a Corning Eagle glass. For example, the material can be steel. For example, the material can be copper or calcium fluoride.

The coating can include at least one chemical component that is present in one of the joining partners. A coating on a joining partner that includes a component that is present in one of the joining partners can result in the atoms on the surface of the joining partner now being exposed to different bonding forces at the interface between the coating and the volume material of the joining partner. This can result in the mixing process in the melt bubble taking place in a particularly advantageous manner, for example a homogeneous mixture of the joining partners and the coating is produced and a particularly stable joint connection or weld seam is produced as a result during cooling.

For example, before joining steel and sapphire (AI2O3), an aluminum coating can be applied to one of the joining partners. Since aluminum is present at least in sapphire, the aluminum layer functions, for example, as a mediator and exchange layer during the actual joining process.

The laser beam can have a focal zone that is elongated in the beam direction, with the focal zone being able to overlap with the coating and the focal zone being able to penetrate the two mutually facing boundary surfaces of the joining partners and/or the focal zone being able to penetrate at least one of the two mutually facing boundary surfaces of the joining partners.

Due to a focal zone that is elongated in the direction of the beam, the average power is distributed over a part of the layer system thickness, so it can also extend into the volume of the material of one or both joining partners. Since a larger area is heated overall, high thermal gradients and pressure gradients in and against the direction of jet propagation are reduced, so that cracking can be prevented as a result. In addition, it is also possible to melt a larger area of the layer system and thus join it together. This leads in particular to more stable joints. Another advantage of an elongated focal zone is the increased tolerance to positional deviations. For example, the joining partners cannot lie exactly flat on top of each other, but enclose a gap. It is also possible that both joining partners have a certain surface roughness. These distances can be bridged by an elongated focal zone.

Since the focal zone overlaps with the coating, it is possible in particular for the laser energy to also be introduced into the coating and the coating to be melted as a result.

Since the focus zone penetrates the two mutually facing boundary surfaces of the joining partners, it is ensured that the laser energy can be introduced into both joining partners, so that both joining partners can be melted. This can lead to an improvement in the connection, since the joining partners mix better in the melt bubble. In particular, the mutually facing boundary surfaces of the joining partners are the boundary surfaces that border on the coating.

Because the focus zone penetrates at least one interface of the joining partner that faces away, i.e. in particular penetrating an interface of the joining partner that faces away from the coating, i.e. that in particular is not in contact with the coating, it is ensured that the joining partner is heated over a larger area. This can lead to the joining partner also melting in a larger area. In particular, however, this can also lead to the thermal gradient that occurs during joining extending over a larger area and as a result the overall compressive and tensile stress in the joining partner is locally reduced and/or redistributed. In this way, in particular, cracking can be prevented.

The laser beam can melt at least one of the joining partners locally, preferably melt at least one of the joining partners and the coating locally, or melt both joining partners locally, particularly preferably locally melting both the joining partners and the coating.

By only melting one part to be joined, it is ensured that a melt bubble is created which can bridge the interface between the two parts to be joined, so that a connection is formed between the two parts to be joined.

If a joining partner and the coating are melted locally, it is ensured that the material of the joining partner mixes better with the coating and a more stable joint can be formed with the other joining partner.

If both joining partners melt locally, it is ensured that the materials of the joining partners mix, so that an even more stable joint can be produced between the two joining partners.

If both the joining partners and the coating melt locally, the joining partner material also mixes with the coating material, so that a particularly stable joint between the two joining partners can be produced.

The laser beam can be a quasi non-diffracting laser beam, preferably a Gauss-Bessel beam. Non-diffracting rays obey the Helmholtz equation:

V ² U(x,y,z)+k ² U(x,y,z)=0 and show a clear separability into a transversal and a longitudinal dependency of the form U(x,y,z)=Ut(x, y)exp(ikzz) on. Here k=oj/c is the wave vector with its transversal and longitudinal components k ² =kz ² +kt ² and Ut(x,y) is an arbitrary complex-valued function that only depends on the transversal coordinates x,y. The z-dependence in the direction of beam propagation in U(x,y,z) leads to a pure phase modulation, so that the associated intensity I of the solution is propagation-invariant or non-diffractive: l(x,y,z) = |U(x, y,z)| ² = l(x,y,0).

This approach provides different solution classes in different coordinate systems, such as Mathieu rays in elliptic-cylindrical coordinates or Bessel rays in circular-cylindrical coordinates. Experimentally, a large number of non-diffracting beams can be realized to a good approximation, i.e. quasi non-diffracting beams. In contrast to the theoretical construct, these lead only to a finite performance. The length L of the propagation invariance of these quasi non-diffracting rays is also finite.

Furthermore, we define the transversal dimensions of local intensity maxima as the transversal focal zone or as the diameter of the beam profile for quasi-non-diffracting rays d ^ND o as the shortest distance between directly adjacent, opposite intensity minima.

The longitudinal extent of the focal zone in the direction of beam propagation of these intensity maxima, which are almost propagation-invariant, indicates the characteristic length L of the quasi-non-diffracting beam. This is defined by the intensity drop to 50%, starting from the local intensity maximum in the positive and negative z-direction, i.e. in the direction of propagation. A quasi-non-diffracting ray is present if and only if for d ^ND o=d ^GF o, i.e. similar transverse dimensions, the characteristic length L clearly exceeds the Rayleigh length of the associated Gaussian focus, for example if L>10ZR.

Quasi-Bessel rays or Bessel-like rays, also referred to here as Bessel rays, are known as a subset of the quasi-non-diffracting rays. The transversal field distribution Ut(x,y) in the vicinity of the optical axis obeys a Bessel function of the first kind of order n to a good approximation production are widespread. Thus, the illumination of an axicon in a refractive, diffractive or reflective design with a collimated Gaussian beam allows the formation of the Bessel-Gaussian beam. The associated transversal field distribution in the vicinity of the optical axis obeys a good approximation to a Bessel function of the first kind of order 0, which is enveloped by a Gaussian distribution. Bessel-Gauss beams thus have a radially symmetrical beam cross section, so that the intensity of the laser beam perpendicular to the beam propagation direction only depends on the distance from the optical axis. This has the advantage that the properties of the joint connection are independent of the weld seam geometry.

As a result, a significantly larger focus position tolerance can be achieved when joining. Thus, for example, the influence of local ripples in the glass and the focus adjustment is reduced. Accordingly, it can be advantageous to use a quasi-non-diffracting beam, in particular a Bessel beam, for joining, since larger gaps can be bridged with this, among other things, and the focal position tolerance thus becomes larger. The proposed method can thus be used in a further area of application - for example even when the workpieces to be joined are not perfectly flat on one another in the area of the desired weld seam and there is a corresponding gap between the workpieces.

Typical Bessel-Gauss beams that can be used for joining have, for example, a diameter of the central intensity maximum on the optical axis of d ^ND o=2.5 pm.

A Gaussian focus with d ^ND o=d ^GF o=2.5 pm, on the other hand, is characterized by a focus length in air of only Z _R =5 pm at A=1 pm. In these cases, which are relevant for material processing, L»10ZR can even apply.

In addition, focus zones with a length of between 150 μm and 500 μm are preferred for joining, with a length of 300 μm being particularly preferred for producing large connection cross-sections or for producing wide weld seams. Before joining, the coating can be applied to one of the joining partners, with the coating comprising at least one component that is present in the other joining partner. In particular, the coating can also include components that are present in both joining partners.

As a result, a particularly stable connection can be established between the joining partners.

For example, an aluminum layer (AI) can be applied to a joining partner made of sapphire (AI2O3) and then joined with a joining partner made of a blasting alloy (comprising Fe, C and Al).

For example, a layer of amorphous silicon oxide (S1O ₂ ) can be applied to a joining partner made of calcium fluorite (CaF ₂ ) and joined to a joining partner made of quartz glass (S1O ₂ ).

For example, a layer of copper (Cu) can be applied to a joining partner made of Corning Eagle Class (for example alkaline earth metal boron aluminum silicate) and joined with a joining partner made of copper (Cu).

For example, a layer of amorphous silicon oxide (S1O ₂ ) can also be applied to a joining partner made of copper (Cu) and joined with a joining partner made of Corning Eagle Class.

The coating can be thicker than three monolayers of coating material.

This has the advantage that the coating can be applied to the entire surface of the joining partner. In particular, there are no holes in the coating, so that the joining partner can be joined equally well everywhere.

A monolayer is a layer that is exactly one atom or one molecule of the material of the coating thick. A three monolayer thick layer is three atoms or three molecules of the coating material thick.

The coating can be applied to one of the joining partners by means of physical vapor deposition, chemical vapor deposition, sputtering or another vaporization process. A particularly uniform layer growth on the joining partner can be achieved by one of these known methods mentioned above. In particular, these processes can also be used on an industrial scale.

In all of the aforementioned methods, a substrate containing the chemical components of the coating is vaporized, with the vapor being deposited on the part to be joined and the coating forming on the surface of the part to be joined.

The absorption of the laser beam by the coating can be low, preferably less than 50%, and/or the absorption of the laser beam by the coating can be lower than by at least one joining partner.

This has the advantage that the laser beam can be at least partially transmitted through the coating and can reach the other joining partner in order to heat the other joining partner. In particular, it can be achieved that both parts to be joined are melted in order to achieve a stable connection of the two parts to be joined.

However, there can be finite absorption of the laser beam in the coating, so that the coating is also heated and melted. This ensures that the materials of the two joining partners and the coating mix with each other in the melt bubble and a particularly stable connection of the joining partners is thus achieved.

The wavelength of the ultra-short laser pulses can be between 200 nm and 5000 nm, preferably 1030 nm, and/or the pulse duration of a laser pulse can be between 50 fs and 10 ps, preferably 400 fs, and/or several laser pulses can be emitted in one pulse train where the repetition rate of the laser pulses in the pulse train is between 1 kHz and 50 GHz, and/or individual laser pulses can be emitted, where the repetition rate of the individual laser pulses is between 1 kHz and 50 MHz, and/or the numerical aperture of the focused laser beam can be between 0.1 and 0.7 and/or the fluence in the focus can be greater than 0.01 J/cm ² and/or the raw beam diameter can preferably be 5 mm and/or the average laser power can be between 0.5 W and 50 W lie.

These parameters allow the joining process to be optimized for numerous material combinations.

For example, the wavelength of the ultra-short laser pulse can be 1030 nm, with the pulse duration of a single pulse being 400 fs, 2 pulses per burst are emitted, the pulse spacing is 20 ns, which corresponds to a pulse repetition rate of 50 MHz, the bursts a Have a repetition rate of 200 kHz, the numerical aperture is 0.25, the fluence in the focus is between 5 and 100 J/cm ² , for example 75 J/cm ² , and the average laser power is 5W.

The laser pulse energy can be modulated in time from pulse to pulse, the modulation rate being between 100 Hz and 10 kHz, the modulation form preferably being sin ² -shaped or triangular.

Temporally modulated means that the pulse energy is changed during a modulation period, the modulation period being given by the inverse modulation rate. The modulation rate indicates the time scale on which the modulation form is repeated. In particular, a modulation of the pulse energy means that the pulse energy can become larger or smaller during the modulation period. The modulation form indicates which mathematical function the pulse energy follows during the modulation period.

The modulated pulse energy from pulse to pulse means that there are times when less pulse energy is introduced into the joining partner(s) and temperature relaxation can take place, or there are times when more energy can be introduced than without the modulation. Crack formation can thus be controlled and/or avoided.

For example, a temporal modulation can be achieved by varying the intensity of the joining pulses. For example, a strong joining pulse can be emitted followed by two joining pulses with half the intensity. However, the temporal modulation also means that the laser then emits a strong joining pulse, followed by two weakened joining pulses.

The ultra-short laser pulses of the laser beam can be introduced into the material together with an additional laser beam, the additional laser beam being a continuous wave laser beam or carrying pulses with a pulse length between 1 ns and 100 ps.

When another laser beam hits the material of the joining partner(s), the temperature in the material is increased so that the thermal gradient when joining the joining partner is smaller. This can prevent cracking.

The laser beam and the joining partners can be moved and/or positioned relative to one another.

Moving relative to one another can mean that either the laser beam or the layer system or both the laser beam and the layer system are moved. This can be achieved that the laser beam brings in joints at different locations of the joint partners. In particular, this makes it possible to produce a continuous weld seam between the two joining partners.

The movement can take place with a feed, with laser pulses or laser pulse trains being able to be introduced continuously into the joining partners during the feed. A positioning of the joining partners relative to the laser beam consists in bringing the focus zone of the laser beam into the desired penetration depth and into the desired location.

The object set above is also achieved by a device for joining at least two joining partners with the features of claim 16. Advantageous developments of the device result from the dependent claims and the present description and the figures.

Accordingly, a device for joining two joining partners is proposed, comprising an ultra-short-pulse laser that is set up to provide a laser beam that carries ultra-short laser pulses, a feed device that is set up to move and/or move the joining partners and the laser beam relative to one another position, focusing optics that are set up to generate an intensity increase of the laser beam, the focusing optics comprising beam shaping optics that are set up to impress the laser beam with a focus zone that is elongated in the direction of beam propagation, the at least two joining partners using ultrashort laser pulses of the laser beam of the ultrashort pulse laser are joined together, wherein at least one joining partner is substantially transparent to the ultra-short laser pulses of the ultra-short pulse laser, and wherein a coating is applied to at least one of the joining partners before joining and the Coating is arranged between the joining partners, with the focal zone overlapping with the coating and the focal zone penetrating the two mutually facing boundary surfaces of the joining partners and/or the focal zone penetrating at least one of the two mutually facing boundary surfaces of the joining partners, the coating having physical properties similar to at least one joining partner Includes properties and / or a chemical component similar to at least one joining partner.

A feed device is a device that can be moved in at least two spatial axes and can, for example, be an XY table or an XYZ table. The feed device can, for example, have a fastening device on which the joining partners can be fixed. A fixation can be accomplished, for example, by gluing or clamping. A fixation can also work via negative air pressure using a suction device.

Furthermore, a feed device can be moved or shifted in an automated or motorized manner with a feed. The feed here is a movement with a feed rate, the feed taking place along a feed trajectory.

Because the feed device moves the material relative to the laser beam, the laser beam is guided over the material along a feed trajectory, which makes it possible to process and in particular to join the material at the locations of the feed trajectory.

The beam shaping optics can comprise a spatial light modulator or a diffractive optic element or an axicon or an acousto-optic deflector. A beam shaping optics can in particular also include a lens for focusing the laser beam.

A spatial light modulator makes it possible to fan out the process beam to a given geometry, for example round, square or star-shaped. A diffractive element also allows the process beam to be fanned out spatially to a given geometry. An axicon is a conically ground optical element that can impress a quasi-non-diffracting beam profile on a Gaussian laser beam as it passes through.

An acousto-optical deflector makes it possible to periodically deflect the process beam over time, so that in particular Lissajous figure-shaped heating patterns can be generated in the interface, so that a larger area is heated. The deflection using an acousto-optical deflector also allows a randomized movement pattern, so-called random access scanning, which enables the rapid scanning of any heating pattern.

In this case, the focusing optics can in particular comprise an optics system which enables an enlarging or reducing imaging of the beam profile in the joining partners. In particular, the lens system can be used to shift the focal zone in or against the direction of beam propagation in order to place the focal zone in the boundary layer of the two joining partners and to enable the laser pulse energy to be introduced into the boundary layer.

The focusing optics can include a distance sensor, preferably include a confocal distance sensor, which is adapted to the distance and / or the positioning of the To regulate joining partners relative to a reference point in space. The focusing optics may include a camera configured to regulate the establishment of the laser focus.

In particular, this makes it possible for the focus zone to be placed in the boundary layer of the two joining partners. In addition, unevenness on the material surface can also be compensated for, so that the focus zone can also be guided along an inclined plane if the joining partners are not mounted exactly level with each other or are installed at an angle. This increases the tolerance range for the joining process, so that stable joints are made possible.

BRIEF DESCRIPTION OF THE FIGURES Preferred further embodiments of the invention are explained in more detail by the following description of the figures. show:

Figure 1 is a schematic representation of the method with quasi-non-diffractive

rays;

FIG. 2 shows a schematic representation of the method with Gaussian beams; Figure 3A, B, C, D is a schematic representation of the quasi non-diffracting beams;

FIG. 4A, B shows a schematic representation of the time modulation of the laser pulses; and

FIG. 5 shows a schematic representation of the device for carrying out the method.

Detailed description of preferred exemplary embodiments

Preferred exemplary embodiments are described below with reference to the figures. Elements that are the same, similar or have the same effect are provided with identical reference symbols in the different figures, and a repeated description of these elements is sometimes dispensed with in order to avoid redundancies.

FIG. 1 shows a schematic cross section of two joining partners 30, 31 to be joined. A coating 32 is applied to one of the joining partners 30, 31, with the joining partners 30, 31 being oriented in particular in such a way that the coating 32 is arranged between the two joining partners 30, 31. Each joining partner 30, 31 has a thickness D0, D1. The coating 32 has physical and/or chemical properties similar to those of at least one of the joining partners 30, 31.

For example, the coating 32 can have a component in the form of a chemical element and/or molecule that is present in the joining partner 31 . In particular, the coating 32 can be arranged on the joining partner 30 and have a thickness S that is greater than three monolayers of the material of the coating. This ensures a continuous coating 32 on the joining partner 30 . In this case, the coating 32 can have been applied to the joining partner 30 in particular by means of a vapor deposition method, such as sputtering, for example.

The ultra-short pulse laser 1 makes the ultra-short laser pulses of the laser beam 10 available. These can be introduced into the joining partners 30, 31 and the coating 32 in the form of individual laser pulses or in the form of pulse trains. The laser wavelength can be between 200 nm and 5000 nm and/or the repetition rate of the individual pulses can be between 100 Hz and 50 Hz and/or the repetition rate of the pulses in a pulse train can be between 1 MHz and 50 GHz and/or the number of pulses per pulse train can be between 2 and 5 and/or the laser pulse duration can be between 10fs and 50ps. In particular, the average laser power can be between 0.5W and 50W.

The laser beam is guided through focusing optics 4 which include beam-shaping optics 2 . In this case, the beam-shaping optics 2 can be, for example, an axicon or a diffractive optical element. The beam-shaping optics 2 impose a quasi-non-diffracting beam shape on the laser beam 10 of the ultrashort pulse laser, for example a Bessel beam shape or a Bessel-Gaussian beam shape, as shown in more detail in FIG. What is achieved in particular is that the laser beam 10 has an elongated focal zone 100 .

The quasi-non-diffracting laser beam 10 is focused by suitable focusing optics 4 in such a way that the focus zone 100 , ie the area of the excess intensity of the laser beam 10 , approximately coincides with the coating 32 . For example, the fluence in the focal zone can be over 0.01 J/cm ² . In particular, the insertion depth of the focus zone 100 relative to the first joining partner 30 can be determined here by focusing.

The focal zone 100 overlaps with the coating 32 and penetrates the two mutually facing boundary surfaces of the joining partners. In particular, this means that the focus zone 100 is at least partially in the volume material of the joining partners 30, 31, so that in both joining partners 30, 31 energy of the laser 1 can be deposited. However, the focus zone 100 does not penetrate the sides of the joining partners 30, 31 that are remote from the coating 32. In particular, the focal zone 100 is therefore completely within the two joining partners 30, 31, so that the focal zone 100 is shorter in the beam propagation direction than the sum of the thicknesses D0, D1 of the joining partners 30, 31. This ensures that the ultra-short laser pulses of the ultra-short-pulse laser 1 introduce the joining modification 5 within the joining partners 30, 31 and, in particular, that the outer surfaces of the joining partners 30, 31 are not modified.

In order to cause the laser beam 10 to overlap with the coating 32 , the first joining partner 30 in the beam propagation direction must be transparent to the wavelength of the laser 1 . Both joining partners 30, 31 can also be transparent to the wavelength of the laser 1, so that the laser beam 10 can also be focused by the joining partner 31 in the beam propagation direction. In particular, the coating 32 may absorb less than 50% of the laser energy of the laser beam 10, so that the laser beam 10 is transmitted through the joining partner 30 in the beam propagation direction, is then transmitted through the coating 32 and finally is transmitted into the joining partner 31. This ensures in particular that all the materials involved, namely the two joining partners 30, 31 and the coating 32, can be melted.

For this purpose, the joining partners 30, 31 can comprise a metal and/or a semiconductor and/or an insulator or a combination thereof; in particular, the joining partners can comprise a glass ceramic or a crystal or a polymer.

For example, the joining partner 31 can consist of sapphire (AI203), an aluminum layer (AI) can be arranged on the joining partner 31 and the joining partner 30 can consist of a blasting alloy (comprising Fe, C and Al).

For example, the joining partner 30 can consist of calcium fluorite (CaF 2 ), a layer of amorphous silicon oxide (SiO 2 ) can be arranged on the joining partner 30 and the joining partner 31 can be quartz glass (SiO 2 ).

In the focus zone 100, successive laser pulses are absorbed in such a way that the material of the joining partners 30, 31 and the coating 32 melts and connects across the interface 32 to the other joining partner 30, 31 in each case. But it can also melt only one of the joining partners 30, 31, or only one of the joining partners 30, 31 and the coating 32, or both joining partners 30, 31, or both joining partners 30, 31 and the Coating 32 melt. As soon as the melt cools down, a permanent connection of the two joining partners 30, 31 is created.

In other words, the two joining partners 30, 31 are joined to one another in the area in which the focus zones 100 are positioned. This area, in which the melting and joining of the materials and the subsequent cooling of the melt takes place and in which the actual joining takes place, is also referred to as the joining area. The cooled melt and material connection of the joining partners 30, 31 forms the joining modification 5 or the weld seam. In particular, the coating 32 brings about an improvement in the connection, since, for example, the mixing processes in the melt proceed particularly advantageously. The coating 32 functions as a kind of adhesion promoter between the joining partners 30, 31.

In particular, with the same process parameters, the breaking strength of the connection of the joining partners 30, 31 joined with the coating is greater than the breaking strength of the connection of the joining partners 30, 31 joined without the coating.

The same structure as in FIG. 1 is shown in FIG. 2, with a Gaussian laser beam 10 being made available by focusing optics 4 . In particular, a symmetrical Gaussian beam profile can thereby be achieved, as a result of which the joining modifications 5 introduced are radially symmetrical and thus do not cause any stress peaks in the joining partners 30, 31. In particular, the Gaussian beam profile nevertheless shows a slightly elongated focal zone 100, which both overlaps with the coating 32 and penetrates the mutually facing boundary surfaces of the joining partners 30, 31.

FIG. 3A shows the intensity profile and beam cross section of a quasi-non-diffracting laser beam 10. In particular, the quasi-non-diffracting beam 10 is a Bessel-Gaussian beam. In the beam cross-section in the xy plane, the Bessel-Gauss beam has radial symmetry, so that the intensity of the laser beam only depends on the distance from the optical axis. In particular, the transverse beam diameter d ^ND o is between 0.25 pm and 10 pm.

FIG. 3B shows the longitudinal beam cross section, ie the beam cross section in the direction of beam propagation. The beam cross-section has an elongated focal zone 100 that is about 300 pm in size. The focal zone 100 is thus significantly larger in the direction of propagation than the beam cross-section in the x-y plane, so that an elongated focal zone 100 is present. Analogously to FIG. 3A, FIG. 3C shows a Bessel beam which has a non-radially symmetrical beam cross section. In particular, the beam cross-section appears stretched in the y-direction, almost elliptical.

FIG. 3D shows the longitudinal focal zone 100 of the Bessel beam, which again has an extension of about 3 pm. Accordingly, the Bessel beam also has a focal zone 100 that is elongated in the beam propagation direction.

A temporal modulation of the laser pulse energy from pulse to pulse is shown in FIG. 4A. In particular, the modulation rate can be between 100 Hz and 10 kHz. The modulation form is sine ² -shaped, so that the successive pulses differ in their pulse energy according to the sine ² function. Analogous to this, a temporal modulation of the laser pulse energy from pulse to pulse is shown in FIG. 4B, the modulation form being triangular here. The laser pulse energy follows a triangular function.

The modulation forms shown make it possible for the joining partners 30, 31 to cool down slightly between the introduction of the pulses with the maximum power shown, so that cracking in the material of the joining partners 30, 31 is prevented.

A device for carrying out the method is shown schematically in FIG. In particular, a feed device 6 is shown, on which the joining partners 30,31 are mounted. The feed device 6 is an XY table, so that the joining partners 30, 31 mounted on it can be moved in the XY direction. The feed device 6 moves the joining partners 30, 31 under the laser beam 10 with a feed V, with the laser 1 emitting laser pulses, however, with a repetition rate. In particular, the focus zone 100 is thus moved and/or positioned relative to the joining partners 30,31. The emission of the laser pulses consequently results in a continuous weld seam 5, through which the two joining partners 30, 31 are firmly connected to one another.

The focusing optics 4 of the device can include a distance sensor 40 which measures the distance between the joining partners 30, 31 relative to a reference point in space. In particular, the focusing optics can also include a camera 42 with which the establishment of the laser focus can be regulated. Both the camera 42 and the distance sensor 40 can be connected to the feed device 6 and to the focusing optics 4, so that the distance values of the distance sensor 40 or the focus values of the camera 42 can be coupled to the focusing optics 4 and the feed device 6. This ensures that the focus zone 100 can always be placed at the desired point in the joining partner 30,31. In particular, an undesired melting of the joining partners 30, 31, for example on the surface, can thereby be avoided. This also makes it possible to produce a continuous weld seam in a desired geometry between the joining partners 30, 31.

As far as applicable, all individual features that are presented in the exemplary embodiments can be combined with one another and/or exchanged without departing from the scope of the invention.

Reference character list

1 laser

10 laser beams

100 focal zone 2 beam shaping optics

30 joining partners

31 joining partners

32 coating

4 focusing optics 40 distance sensor

42 camera

5 joining modification

6 Feed device DO Thickness of the joining partner

D1 Thickness of the joining partner

S thickness of the coating

Claims

Expectations

1 . Method for joining at least two joining partners (30, 31), wherein the at least two joining partners (30, 31) are joined to one another by means of ultra-short laser pulses of a laser beam from an ultra-short pulse laser (1), wherein at least one joining partner (30, 31) is essentially transparent to the ultra short

laser pulses of the ultra-short pulse laser (1), and with a coating (32) being applied to at least one of the joining partners (30, 31) before joining and the coating (32) being arranged between the joining partners (30, 31), characterized in that that the coating (32) comprises physical properties similar to at least one joining partner (30, 31) and/or a chemical component similar to at least one joining partner (30, 31).

2. The method according to claim 1, characterized in that at least one joining partner (30, 31) is a metal or a semiconductor or an insulator or a combination thereof, in particular a glass ceramic or a crystal or a polymer.

3. The method according to claim 1 or 2, characterized in that the coating (32) comprises at least one chemical component which is present in a joining partner (30, 31).

4. The method according to any one of the preceding claims, characterized in that the

The laser beam (10) has a focal zone (100) that is elongated in the beam direction, the focal zone (100) overlaps with the coating (32) and the focal zone (100) penetrates the two mutually facing boundary surfaces of the joining partners (30, 31) and/or the focal zone (100) penetrates at least one of the two opposite boundary surfaces of the joining partners (30, 31).

5. The method according to any one of the preceding claims, characterized in that the laser beam (10) locally melts at least one of the joining partners (30, 31), preferably at least one of the joining partners (30, 31) and the coating (32) melts locally, or both parts to be joined (30, 31) melt locally, particularly preferably both the parts to be joined (30, 31) and the coating (32) melt locally.

6. The method according to any one of the preceding claims, characterized in that the laser beam (10) is a quasi-non-diffracting laser beam, preferably a Gauss-Bessel beam.

7. The method according to any one of the preceding claims, characterized in that before joining, the coating (32) is applied to a joining partner (30, 31), the coating (32) comprising at least one component which is present in the other joining partner (30 , 31) is present.

8. The method according to any one of the preceding claims, characterized in that the

Coating (32) is thicker than three monolayers of the material of the coating (32).

9. The method according to any one of the preceding claims, characterized in that the coating is applied to one of the joining partners (30, 31) by means of physical vapor deposition, chemical vapor deposition, sputtering or another vaporization process.

10. The method according to any one of the preceding claims, characterized in that the breaking strength of the connection of the joining partners (30, 31) joined with the coating is greater with the same process parameters than the breaking strength of the connection of the joining partners (30, 31) joined without the coating ).

11. The method according to any one of the preceding claims, characterized in that the

Absorption of the laser beam (10) by the coating (32) is low, preferably less than 50% and/or the absorption of the laser beam (10) by the coating (32) is less than by at least one joining partner (30, 31).

12. The method as claimed in one of the preceding claims, - the wavelength of the ultra-short laser pulses is between 200 nm and 5000 nm, preferably 1030 nm, and/or

- the pulse duration of a laser pulse is between 50 fs and 10 ps, preferably 400 fs, and/or - Several laser pulses are emitted in a pulse train, the repetition rate of the laser pulses in the pulse train being between 1 kHz and 50 GHz, and/or

- Individual laser pulses are emitted, the repetition rate of the individual laser pulses being between 1 kHz and 50 MHz, and/or

- the numerical aperture of the focused laser beam is between 0.1 and 0.7 and/or

- the fluence at the focus is greater than 0.01 J/cm ² , and/or

- the raw beam diameter is preferably 5 mm,

- the average laser power is between 0.5 W and 50 W.

13. The method according to any one of the preceding claims, characterized in that the laser pulse energy is modulated in time from pulse to pulse, the modulation rate being between 100 Hz and 10 kHz, the modulation form preferably being sine ² -shaped or triangular.

14. The method according to any one of the preceding claims, characterized in that the ultra-short laser pulses of the laser beam (10) are introduced into the material together with a further laser beam (101), the further laser beam being a continuous wave laser beam or pulses with a pulse length between 1 ns and 100 hp leads.

15. The method according to any one of the preceding claims, characterized in that the laser beam (10) and the joining partners (30, 31) are moved and/or positioned relative to one another.

16. Device for joining two joining partners (30, 31), comprising an ultra-short pulse laser (1) which is set up to provide a laser beam (10) which guides ultra-short laser pulses, a feed device (6) which is set up for the joining partners (30, 31) and to move and/or position the laser beam (10) relative to one another, focusing optics (4) which are set up to generate an intensity increase of the laser beam, the focusing optics (4) comprising beam shaping optics (2). , the is set up for this purpose to impress the laser beam (10) with a focus zone that is elongated in the direction of beam propagation, the at least two joining partners (30, 31) being joined to one another by means of ultrashort laser pulses of the laser beam (10) of the ultrashort pulse laser, with at least one joining partner (30, 31) essentially transparent for the ultra-short

Laser pulses of the ultra-short pulse laser (1), and wherein a coating (32) is applied to at least one of the joining partners (30, 31) before joining and the coating (32) is arranged between the joining partners (30, 31), the focal zone (100) overlaps with the coating (32) and the focus zone (100) penetrates the two mutually facing boundary surfaces of the joining partners (32) and/or the focal zone (100) penetrates at least one of the two facing away boundary surfaces of the joining partners (30, 31). characterized in that the coating (32) to at least one joining partner (30, 31) similar physical

Properties and/or a chemical component which is similar to at least one joining partner (30, 31).

17. The device according to claim 16, characterized in that the focusing optics (4) comprises a distance sensor (40), preferably a confocal distance sensor, which is set up to determine the distance and/or the positioning of the joining partners

(30, 31) relative to a reference point in space.

18. Device according to claim 15, characterized in that the focusing optics (4) comprises a camera (42) which is set up to regulate the establishment of the laser focus.