DE102020119307A1 - Process for joining at least two joining partners - Google Patents

Abstract

The present invention relates to a method for joining at least two joining partners (3), the at least two joining partners (3) being joined to one another by means of ultra-short laser pulses from a joining laser (1), with at least one joining partner (3) being essentially transparent to the ultra-short laser pulses of the Joining laser (1), a material modification (20) being introduced into at least one of the joining partners (3) before and/or after joining.

Description

technical field

The present invention relates to a method for joining at least two joining partners, the at least two joining partners being joined to one another by means of ultra-short laser pulses from a joining laser.

State of the art

To join two parts to be joined, it is known to apply a laser beam to the respective parts to be joined in order to generate a melt through energy absorption in the zone exposed to the laser beam, which melt forms a weld seam between the parts to be joined 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, i.e. laser pulses in the picosecond range or in the femtosecond range (e.g. 50 fs -50 ps), in the volume of glass, e.g. 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 partners, high temperatures occur due to the strong local energy input from the focused joining beam, which are not present in the surrounding material areas. Accordingly, the heat required for processing - for example for the production of a weld seam - leads to tensile and compressive stresses in the surrounding material areas. Depending on the type of glass, these tensile and compressive stresses can be distributed radially and/or orthoradially, for example.

These tensile and compressive stresses can also weaken the joint partners that are joined, for example when subjected to a bending load. The reason for this lies in the changed material properties in the joining partner induced by the joining jet and the melting. For example, due to the high cooling rate during the joining process, the weld seam can have a different density compared to the starting material. Depending on the type of glass selected, there may be a compression in the case of abnormal glasses and a thinning in the case of normal glasses. This change in density creates a local weakening of the material, which, depending on the type of load applied, can reduce the resulting connection strength compared to the volume material.

In U.S. 8,314,359 B2 such as U.S. 9,625,713 B2 systems and methods are described in which two optically transparent materials are melted locally in the area of the common interface using ultra-short laser pulses and are thus finally welded together.

Presentation of the invention

It is therefore the object of the invention to improve the method for joining joining partners.

The above task is solved by a method for joining at least two joining partners with the features of claim 1. Advantageous developments of the method result from the dependent claims and the present 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 together using ultra-short laser pulses of a joining laser, wherein at least one of the joining partners is essentially transparent to the ultra-short laser pulses of the joining laser. According to the invention, at least one material modification is introduced into at least one of the joining partners before and/or after joining.

This has the advantage that a weakening of the material of the joining partner as a result of the joining process can be prevented by the targeted pre- and/or post-treatment, or the weakening of the material can be reduced or healed or compensated for by the joining process.

The introduction of the material modification before and/or after the joining can reduce stresses in the joining partners, which emanate from the joining modification (i.e. the weld seam), and thus improve the strength of both the resulting joined association and the individual joining partners mend The process thus makes it possible to increase the mechanical strength of ultra-short-pulse joined joining partners so that they become more resistant to bending and tensile loads. Furthermore, the optical quality of the joining partners and the joining modification is also improved, if this should be of importance when joining glasses, for example.

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 on a trajectory determined by the optics of the joining laser, which essentially corresponds to the specified trajectory of the joint to be produced. 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 1000 GHz, for example.

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.

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.

Heat is accumulated in the joining area as a result of successive absorption of the ultra-short laser pulses, provided that 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. The joining area is therefore understood to be that area of the joining partner 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. In particular, the network structure of the joining partners can also change. The cooled melt, which connects the joint partners to one another or produces the weld seam, is then 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. In the case of a Gaussian laser beam, the laser spot is defined, for example, via the double beam waist.

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, 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 or bursts. This provides enough laser power to melt the material.

In addition to the degree of heat accumulation and other parameters, the size of the joining area is also determined by the beam geometry, in particular the focus diameter of the Joining beam, determined. The beam geometry describes the spatial configuration of the laser beam and other beam properties such as certain diffraction properties of the laser beam.

A joining beam can be a Gaussian laser beam, for example. A Gaussian laser beam is characterized by the fact that the beam profile, i.e. the cross section through the intensity distribution of the laser beam perpendicular to the direction of propagation of the laser beam, essentially corresponds to a Gaussian bell curve.

The focus zone d ^GF _{0 of} a Gaussian beam, the Gaussian focus, or the diameter of the Gaussian beam or the Gaussian profile, is defined on the one hand by the second moments or the variance of the Gaussian curve. On the other hand, the focal zone d ^GF _{0 is} defined by the associated characteristic length, the Rayleigh length z _R =π(d ^GF ₀ ) ² /4λ, as the distance from the focal position at which the beam cross section has increased by a factor of 2.

und weisen eine klare Separierbarkeit in eine transversale und eine longitudinale Abhängigkeit der Form $$\text{U}\left(\text{x}\text{,y}\text{,z}\right)={\text{U}}_{\text{t}}\left(\text{x}\text{,y}\right)\text{exp}\left({\text{ik}}_{\text{z}}\text{z}\right)$$

auf. Hierbei ist k=ω/c der Wellenvektor mit seinen transversalen und longitudinalen Komponenten k²=k_z ²+k_t ² und Ut(x,y) eine beliebige komplexwertige Funktion, die nur von den transversalen Koordinaten x,y abhängt. Die z-Abhängigkeit in Strahlausbreitungsrichtung in U(x,y,z) führt zu einer reinen Phasenmodulation, so dass die zugehörige Intensität I der Lösung propagationsinvariant beziehungsweise nicht-beugend ist: $${\left|\left(\text{x}\text{,y}\text{,z}\right)=|\text{U}\left(\text{x}\text{,y}\text{,z}\right)\right|}^2=\text{I}\left(\text{x}\text{,y}\text{,0}\right).$$

However, a joining beam can also be a virtually non-diffracting beam. Non-diffracting rays obey the Helmholtz equation: $${\nabla }^2\text{u}\left(\text{x}\text{y}\text{e.g}\right)+{\text{k}}^{\text{2}}\text{u}\left(\text{x}\text{y}\text{e.g}\right)=0$$

and show a clear separability into a transverse and a longitudinal dependence of the shape $$\text{u}\left(\text{x}\text{y}\text{e.g}\right)={\text{u}}_{\text{t}}\left(\text{x}\text{y}\right)\text{ex}\left({\text{ik}}_{\text{e.g}}\text{e.g}\right)$$

on. Here k=ω/c is the wave vector with its transversal and longitudinal components k ² =k _z ² +k _t 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: $${\left|\left(\text{x}\text{y}\text{e.g}\right)=|\text{u}\left(\text{x}\text{y}\text{e.g}\right)\right|}^2=\text{I}\left(\text{x}\text{y}\text{,0}\right).$$

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 transverse dimensions of local intensity maxima as the shortest distance of directly adjacent, opposite intensity minima as the transverse focal zone or as the diameter of the beam profile for quasi-non-diffracting rays d ^ND _{0 .}

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 ₀ ≈D ^GF ₀ , i.e. similar transverse dimensions, the characteristic length L clearly exceeds the Rayleigh length of the associated Gaussian focus, for example if L>10z _R .

Quasi-Bessel rays or Bessel-like rays, also called Bessel rays here, are known as a subset of the quasi-non-diffracting rays. Here, 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 transverse 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.

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 ₀ =2.5 μm. A Gaussian focus with d ^ND ₀ ≈d ^GF ₀ =2.5 µm, on the other hand, is characterized by a focus length in air of only z _R ≈5 µm at λ=1 µm. In these cases, which are relevant for material processing, even L>>10z _{R can} apply.

Around the area to be joined, the part to be joined also partially heats up due to the absorption of the joining beam and the subsequent heat transport, depending on the heat diffusion time, the laser absorptivity of the glass and the joining pulse rate. Due to the large temperature gradients that occur around the joint area, material stresses can occur during cooling, which promote crack formation. In particular, both tensile and compressive stresses can arise around the joining area. These stresses can be distributed radially and/or ortho-radially, for example.

The joint modification area is understood to be the area in which there are material stresses in the cooled state that originate from the joining process. The joint modification area includes, for example, the entire area in which the effects of the joining can be measured using the tensile and compressive stresses. This can be the area in which the material, viewed spatially, returns to its original state from the joint modification in the area.

In order to prevent crack formation under mechanical stress, a material modification is introduced into at least one joining partner before and/or after the actual joining in order to reduce the tensile and compressive stresses in the joining area or derive them from them or to redirect the stress and thus local to avoid voltage peaks.

The material modification that is introduced before and/or after the introduction of the actual joining modification must be distinguished from the actual joining modification, i.e. the weld seam introduced between and in the joining partners.

A material modification is generally a permanent, structural change in the joining partner in thermal equilibrium.

By introducing the material modification, for example, the network structure of a glass can be modified and, for example, a lower fictitious temperature of the glass can be achieved. The refractive index and/or the density can also be modified compared to the starting material.

By introducing the material modification before and/or after the actual joining in at least one of the joining partners, a modification of the structure, in particular the crystalline structure and/or the amorphous structure and/or the network structure of the glass and/or the chemical structure and/or or the mechanical structure, the material of the joining partner.

By introducing the material modification before and/or after the actual joining, a change in the composition, in particular the chemical composition, of the joining partner can also be achieved. However, a material modification can also be a change in a physical property, for example the strength and/or the flexural strength and/or the tolerance of the material to bending forces and shearing forces as well as shear and tensile stresses.

A material modification can in particular be a local change in density, which can also be dependent on the selected material of the joining partner, in particular its type of glass. In particular, a local change in density can occur in connection with a change in the network structure due to rapid material cooling.

The material modification introduced into the at least one joining partner before and/or after the actual joining can preferably be introduced locally in such a way that stresses in the joining partner are concentrated in the area around the material modification. In particular, the material modification can divert stresses in the joining partner from the joint modification and/or limit the stresses to the area around the material modification.

By introducing the material modification before and/or after the actual joining, the chemical composition of the material can also be changed, for example, so that the changed local chemical bonding forces result in different flexural strengths, for example.

A material modification is introduced when it has a permanent effect on the joining partner and its internal structure. This includes in particular surface modifications and joint modifications.

For example, a material modification before and/or after the actual joining in Form a coating of a joining partner are introduced and lead to the fact that the atoms on the surface of the joining partner are now exposed to other binding forces at the interface between the coating and volume material of the joining partner. However, since the atoms on the surface of the joining partner are part of the joining partner, a material modification has already been introduced here. For example, a coating on the joining partner can affect the flexural strength of the joining partner.

For example, local heating or even melting in the volume material of the joining partner and subsequent cooling can also lead to crystallization of the joining partner.

For example, the local introduction of foreign atoms or ions, such as by doping, can lead to a permanent modification of the chemical structure of the joining partner.

The material modification can be introduced into one of the joining partners, but it can also be introduced into both joining partners or into all joining partners. In particular, different material modifications can be introduced into different joining partners. Different material modifications can also be introduced into a joining partner.

For example, a first material modification can be introduced into the first joining partner by global thermal annealing of the amorphous glass structure, and then a second local material modification can be introduced by ion implantation.

The wavelength of the ultra-short laser pulses can be between 200 nm and 5000 nm, in particular 1030 nm. The pulse duration of a laser pulse can be between 10 fs and 50 ps, in particular 400 fs. A plurality of laser pulses can be emitted in a burst, with the repetition rate of the burst being between 1 kHz and 50 MHz, preferably 100 kHz to 400 kHz, particularly preferably 200 kHz. The repetition rate of the individual laser pulses can be between 1 kHz and 1000 GHz, preferably between 1 MHz and 50 MHz. The numerical aperture of the focused laser beam can be between 0.1 and 0.7, preferably 0.25. The fluence in the focus can be greater than 0.01 J/cm ² . In this case, the raw beam diameter can preferably be 5 mm.

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 have a repetition rate of 200 kHz, the numerical aperture is 0.25 and the fluence in the focus is between 50 and 100 J/cm ² , for example 75 J/cm ² .

These parameters allow a material modification to be introduced into one of the two joining partners before and/or after the actual joining.

The roughness of the upper joining partner can be less than 200 nm. For example, the upper joining partner, ie the joining partner through which the laser beam is focused or through which the laser beam falls first, can have a roughness of less than 100 nm.

This has the advantage that the laser beam focused by the joining partner is not scattered, or only slightly, at the roughness, so that as much laser energy as possible can be introduced into the joining partner.

The laser beam can be radiated perpendicularly to the interface of the joining partners. For example, the laser beam can thus be introduced parallel to the surface normal of the interface.

Under normal incidence, the reflection of the laser beam at the interface or interfaces is minimized. A vertical incidence of the laser beam thus enables as much laser energy as possible to be introduced into the joining partner or partners.

Before joining, a material modification in the form of a coating can be applied to at least one joining partner, with the coating preferably comprising at least one component that is present in one of the two joining partners.

A coating on a joining partner 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 bulk material of the joining partner. In particular, however, coatings can be used, with at least one component of the coating also being a component of one of the two joining partners.

For example, before joining steel and sapphire (Al ₂ O ₃ ), 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 joining partners can thus be joined particularly easily.

The joining beam of the joining laser can be spatially and/or temporally modulated.

This has the advantage that the laser power introduced into the joining partner can be adapted to the local conditions and that a coherent joining modification can be produced.

Spatially modulated means that the joining beam moves along a specific trajectory through or along the joining partner with a feed rate and a feed rate. Temporally modulated means that the joining beam changes on a certain time scale. In both cases, a modulation preferably includes a spatially/temporally recurring pattern. The modulation frequency is then preferably between 50 Hz and 10 kHz.

For example, spatial modulation can be achieved by moving the laser beam along a trajectory. The trajectory depicts the course of the desired joining modification. However, a spatial modulation can also be achieved by the joining beam sweeping over the trajectory several times.

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 joining beam can be regulated in the focus position.

This has the advantage that the location at which the joining partner is to be melted or the joining pulse is to be placed can be precisely determined. In particular, longitudinal joint modifications in the thickness direction, ie parallel to the surface normal, of the joint partner can also be produced in this way.

For example, the focal position can be regulated using a height-adjustable table. However, it is also possible for the focal position to be regulated by varying the focus of an objective imaging the processing laser beam. In particular, it is possible for the focal position to be regulated automatically, for example coupled with a distance sensor. In this way, the joining pulses can always be placed in a joining partner at the same distance from the interface between the joining partners via the distance between the joining partner surface and a certain reference surface.

The material modification can be introduced before and/or after the actual joining process.

This has the particular advantage that the introduction of the material modification before and/or after the actual joining can be carried out separately in time and/or space from the actual joining process and/or the joining process device.

Before joining means that the material modification is finally introduced before the joining modification for joining the joining partners is introduced. This means in particular that the pre-treatment of the material is completed before the joining modification is introduced and in particular before the weld seam is introduced. This also means that extensive cooling, hardening, etc. should be completed before the weld seam is made.

Time after the joining means that the joining process has already been completed for the post-treatment and the joining modification has already been introduced. In particular, the joining partners are already finally connected to one another at this point in time.

In the case of multi-step joining methods or the processing of several interfaces, the time before or after the introduction of the joining modification refers to the respective concrete joining process. In other words, the material modification can be introduced before the respective joining. A post-treatment after a first joining then becomes a pre-treatment of the joining partner for a second joining.

In particular, the order of the process steps can vary or be repeated, e.g. if several interfaces or joining modifications have to be processed or carried out separately.

For example, a material modification in the form of a coating can be applied to the first joining partner. After the coating has been applied, you can continue with the first joining partner at another work station that is spatially separate from the coating station. For example, the coated first joining partner can be joined to another joining partner at the further work station by introducing a corresponding joint modification at the interface.

For example, a further material modification can then be introduced into the second joining partner at a third work station by means of ion implantation. For example, a further material modification can then be introduced at a different point, and in a further step the joining partners can be joined at the other point.

The material modification can be spatially localized in the joining partner.

Spatially localized here means that the material modification is introduced into a part of the joining partner. In particular, spatially localized here means that the material modification is located within the joining modification area or at least that the material modification area overlaps with the joining modification area.

Analogously to the joining modification area, the material modification area is created around the material modification.

By introducing the material modification in a spatially localized manner in the joining modification area, the tensile and compressive stresses from the joining process can be redirected and/or derived from the material modification. For example, a particularly large tensile and compressive stress from the joining process can be distributed over a spatially larger area by means of a special pattern of material modification. This effectively removes the tension from the joining area so that the joining partners can be exposed to greater tensile and compressive forces before they break or are permanently deformed or, for example, the joint modification or the weld seam breaks.

In this overlap, the tensile and compressive stresses from the joining process are indirectly related to the material modification. Thus, for example, via long-range interactions, stress can be relieved from the joint modification to a significantly larger area, which is composed of the joint modification area and the material modification area. Due to the fact that there is less tensile and compressive stress in the joint modification, the joint area can be subjected to greater loads before the maximum tensile and compressive stress is reached in the joint area.

The material modification can be introduced by laser irradiation using a processing laser and/or XUV or EUV irradiation and/or X-ray irradiation and/or chemical hardening and/or thermal hardening and/or ion implantation.

The material modification can be introduced by laser irradiation using a processing laser. As in the joining process, the laser irradiation can cause local melting or at least heating of the joining partner. Local melting or heating and subsequent cooling can, for example, locally change the amorphous structure or the crystalline structure of the joining partner. Similar to the joining modification, local tensile and compressive stresses can occur.

The material modification can be introduced by XUV or EUV irradiation and/or X-ray irradiation. XUV refers to electromagnetic radiation in the extreme ultraviolet wavelength range (0.1 nm-10 nm). EUV refers to electromagnetic radiation in the extreme ultraviolet wavelength range (10 nm -121 nm). By irradiating the joining partner with EUV rays or X-rays, for example, the chemical reactivity of the atoms on the surface of the joining partner can be increased for a short period of time, so that chemical reactions with the surrounding medium, e.g. the ambient air and ambient humidity, start and, for example, the atoms on the surface of the Joining partners enter into oxide compounds.

The material modification can be done by chemical hardening. With chemical hardening, the joining partner is immersed in a chemical hardening bath, whereby the chemical substance in the hardening bath reacts with the material of the joining partner and thus leads to a chemical change in the material of the joining partner. The chemical change can lead to hardening and scratch resistance of the joining partner.

During thermal hardening, the joining partner is heated to a predefined temperature and abruptly cooled, causing tensile and compressive stresses in the joining partner.

The material modification can be introduced by means of ion implantation. Similar to the semiconductor doping process, foreign atoms are accelerated onto the surface of the joining partner, where they then blend into the atomic landscape of the joining partner surface. The absorption of the ion can in particular only take place in the volume material of the joining partner.

The processing laser can be the joining laser.

This has the advantage that only one laser has to be used for joining and introducing the material modifications.

The processing laser can be a separate CO2 laser and aligned collinearly with the joining beam and/or the processing beam can be spatially and/or temporally modulated and/or the focus position can be regulated.

This has the advantage that the processing laser can be modulated and moved independently of the joining laser. Furthermore, pre- and/or post-treatment and the actual joining process can be separated from one another in terms of time and space.

Collinear can mean that the machining beam and the joining beam hit the joining partner in parallel. In particular, collinear can also mean that the processing beam and the joining beam have the same focal position, ie are focused on the same plane.

For example, the joining jet can impinge on the surface of the joining partner at an angle of, for example, 10°. During the subsequent post-processing, the processing beam can also strike the surface of the joining partner at an angle of, for example, 10°.

The material modification can take place by introducing the processing beam along the joining path or along one or more parallel offset joining paths.

This has the advantage that a material modification is carried out uniformly along the trajectory of the joining beam, so that the influence of the material modification on the joining modification is the same everywhere.

A machining beam is offset parallel to the joining beam if the machining beam and joining beam are moved in the same way, but start from different starting points.

For example, the processing beam can be moved along the trajectory of the joining beam. Then the trajectory of the machining beam and the joining beam as well as the starting point are the same. However, a material modification can also be introduced into the joining partner along a parallel offset trajectory of the joining beam. The changes in direction along the trajectory of the machining beam to the joining beam are then the same, but the starting points are different.

A defined modification time can be used in the XUV or EUV irradiation and/or in the chemical hardening and/or in the ion implantation in order to achieve the pre- and/or post-treatment.

The modification time is the period of time that the joining partner treated with the pre- and/or post-treatment is exposed to the material modification process.

This has the advantage that the penetration depth of the material modification can be controlled. However, the method for material modification can only bring about a material change after a certain time, so that a minimum time should not be undercut, or after a certain time a material modification comes to a standstill, so that further treatment would then be inefficient.

For example, the joining partner can be exposed to the chemical hardening bath for five minutes. Depending on the combination of materials, it may be that the chemical hardening bath only takes effect after one minute and causes material modifications. It is also possible that the chemical hardening bath has no further effect after two more minutes. A modification time of five minutes is then sufficient to achieve the maximum possible material modification.

During XUV or EUV irradiation and/or x-ray irradiation and/or chemical hardening and/or during ion implantation, a material modification can be introduced in a localized manner through a processing mask. The localization is preferably provided in the joining area.

A processing mask can be a photolithographic exposure mask and/or a chemical resist mask and/or a mechanical mask.

In the case of a photolithographic exposure mask, a shielding coating, for example, is applied to a mask carrier, for example a glass, wherever the XUV or EUV rays and/or the X-rays should not impinge on the joining partner. If the photolithographic exposure mask is placed on the joining partner and then irradiated with one of the aforementioned types of radiation, the rays then pass through the free areas of the exposure mask into the joining partner and cause a material modification there.

The photolithographic exposure mask has the advantage that the processing mask only once has to be made and can then be used with a large number of joining partners.

A chemical resist mask is, for example, a mask that can be applied directly to the joining partner using a so-called photoresist and a corresponding writing process, for example using an electron beam. The areas described can be removed in a subsequent etching process.

This has the advantage that ions or a chemical hardening bath can now also hit the joining partner directly through the areas in the mask that are freed up in this way.

A mechanical mask is to be understood analogously to a chemical paint mask, i.e. it has mechanically free areas for the passage of ions or rays. In contrast to the resist mask, however, the mask is not tied to the joining partner, but can be removed, similar to the photolithographic exposure mask.

This has the advantage that the mask can be used for a large number of joining partners.

The thermal curing can be carried out with a spatially and/or temporally modulated heat source, preferably an oven or a processing laser.

For example, the oven can have a temperature gradient, so that the material modification of the joining partner is spatially variable and therefore modulated. However, the heating source can also be modulated in time. For example, a deeper penetration of the heat into the joining partner can be achieved by means of heat waves. In the case of a joining partner that is partially metallic, for example, a standing heat wave can be generated by heat waves running in opposite directions, so that the material modification is only introduced where the antinodes of the heat wave interfere constructively.

However, it is also possible that the material modification is introduced by placing the joining partner on a hot plate so that its surface is modified. It is also possible that the joining partner is heated up globally by the oven and thus changes its overall amorphous or crystalline structure.

character list

• 1 zeigt einen schematischen Querschnitt zweier zu fügender Fügepartner mit dem fokussierten Fügestrahl;
• 2A,B zeigen schematisch einen Fügemodifikationsbereich;
• 3 zeigt eine schematische Darstellung einer Trajektorie eines Fügestrahls und eines Bearbeitungsstrahls; und
• 4A,B zeigen einen schematischen Querschnitt verschiedener Fügepartner mit eingebrachten Materialmodifikationen.

Preferred further embodiments of the invention are explained in more detail by the following description of the figures. show:

• 1 shows a schematic cross section of two joining partners to be joined with the focused joining beam;
• 2A,B schematically show a joint modification area;
• 3 shows a schematic representation of a trajectory of a joining beam and a machining beam; and
• 4A,B show a schematic cross-section of various joining partners with introduced material modifications.

Detailed description of preferred 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.

In 1 a cross section of two joining partners 3 to be joined is shown schematically. The joining beam 1 of a joining laser is focused in such a way that the maximum intensity, ie the area with the smallest joining beam waist, roughly coincides with the common interface 5 of the two joining partners 3 . At the boundary surface 5, laser pulses are successively absorbed in the joining region 10 in such a way that the material of the joining partner 3 melts and connects across the boundary surface 5 to the other joining partner 3 in each case. As soon as the melt cools down, the joining modification 11 creates a permanent connection between the two joining partners 3. In other words, the two joining partners are joined to one another in this area. 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 referred to here as the joining area 10 . The cooled melt and material connection of the joining partners 3 forms the joining modification 11 .

The resulting joining modification areas are shown schematically in FIGS 2A and 2 B shown.

Around the joint area 10 and the joint modification 11, a joint modification area 12 can form in the respective joint partners 3 during cooling, in which area tensile and compressive stresses 6 are present. These tensile and compressive stresses 6 can, for example, build up in the material volume of one or both joining partners 3 due to the locally limited heat introduced during the joining process and the subsequent cooling form. The joining itself can also cause tensile and compressive stresses 6 in the material volume of one or both joining partners 3 if the material melted during joining has a different volume requirement than the non-melted material, for example.

This already results, for example, from the gap occurring between the joining partners 3 at the interface 5, which gap is bridged with melted material.

In order to reduce the occurrence of tensile and compressive stresses 6 in the material volume of one or both joining partners 3 compared to conventional methods, a material modification 20 is introduced into at least one of the joining partners 3 before and/or after the actual joining of the joining partners 3.

If the material modification 20 is introduced into one of the joining partners 3 before the actual joining, the joining area 10 or the joining modification 11 is understood to mean the area of the respective joining partner 3 in which the actual joining is to take place using the joining beam 1, or the joining modification 11 is to be created. The joining area 10 and the joining modification 11 are therefore also to be regarded as the “planned” joining area 10 or “planned” joining modification 11 . It also applies to the joint modification area 12 that this can be viewed as the “planned” joint modification area 12 .

In 2A a schematic plan view of the interface 5 between two joining partners 3 is shown, with the joining modification 11 already introduced causing tensile and compressive stresses 6 in the joining modification area 12 . These tensile and compressive stresses 6 are not limited to the joining modification 11, but extend into the material volume of the joining partners 3. This area, in which the tensile and compressive stresses 6 act, is also referred to herein as the joint modification area 12 . In order to reduce the tensile and compressive stresses 6 in the joint modification area 12, material modifications 20 are introduced into the at least one of the joint partners 3 in a targeted manner. The material modifications 20 derive and/or redirect the tensile and compressive stresses 6 arising from the joining modification 11, so that the joining of the joining partners 3 does not negatively influence the mechanical resilience of the joined joining partners 3.

A material modification 20 can be introduced into the joining partner 3 in various ways. The material modification 20 can, for example, be introduced after the actual joining by locally heating the joining partner 3 with a processing laser beam 2, so that the fictitious temperature of the joining partner 3, which serves as a measure of the state of the network structure, is reduced and thus stresses within the joining modification and reduced around the joining modification.

The material modification before and/or after the actual joining can also be introduced by ion implantation. The ion implantation changes the electrochemical structure locally, for example due to long-range binding forces.

The material modification before and/or after the actual joining can be carried out, for example, by XUV and/or EUV and/or X-ray irradiation, which increases the chemical reactivity of the joining partner surface for a short time and the now reactive joining partner forms oxide compounds through interaction with the ambient air generated on its surface.

Around this material modification 20 , tensile and compressive stresses 6 can also develop analogously to the joint modification area 12 , which then propagate in the material modification area 22 in the joint partner 3 . In the material modification area 22 the material of the joining partner 3 gradually changes from its state modified by the material modification 20 to its original state in the surrounding material. Only at a sufficiently large distance from the material modification 20 is the material of the joining partner 3 in its original state.

The material modification area 22 around the material modification 20 overlaps with the joining modification area 12. In this overlap 4, the tensile and compressive stresses 6 from the joining modification 11 to the material modification 20 are indirectly connected. For example, tensile and compressive stress can be transferred to the changed electrochemical bond in the area 22 via the overlap 4 . Thus, the stress from the joining partner 3 is distributed over a significantly larger area, which is made up of the joining modification area 12 and the material modification area 22 . Tensile and compressive stress 6 is thus also derived from and/or diverted from the joint modification area 12 . Due to the fact that there is less tensile and compressive stress 6 around the joint modification region 12, the joined partners 3 to be joined can be subjected to greater loads before the maximum tensile and compressive stress of the joint modification 11 is reached.

In particular, the material modification 20 can also be introduced directly into the joint modification area 12 . This is schematic in 2 B shown. If the material modification 20 is introduced directly in the joint modification area 12, the two modifications are coupled more directly, so that a significantly more effective diversion and/or derivation of tensile and compressive stresses 6 can take place.

In particular, the material modification 20 can also be introduced directly into or on the joining modification 11 (not shown). For example, the joint modification 11 can be heated with a processing laser beam 2, so that the tensile and compressive stresses 6 in the joint modification 11 and in the joint modification area 12 are reduced and thus make the joint connection more durable even under loads.

In order to achieve the greatest possible diversion and/or derivation of the tensile and compressive stresses 6 from the joint modification 11 and the joint modification area 12, it makes sense to match the shape and/or the spread of the joint modification 11 in the joint partner 3 with the shape and/or the To correlate propagation of the material modification 20 in the joining partner.

In 3 a schematic representation of the trajectory of the joining beam 1 and the machining beam 2 is shown for this purpose. Both trajectories are offset from each other, i.e. they have different starting points, but have the same changes in direction along the trajectory. In particular, they are thus offset in parallel. After the two joining partners 3 have been joined along the trajectory of the joining beam 1, a correspondingly shaped material modification 20 can be introduced into at least one of the joining partners along the parallel offset trajectory with the processing beam 2. The shape of the introduced material modification 20 thus correlates with the joining modification 11. For example, the distance from a point of the trajectory of the joining beam 1 to the corresponding point of the trajectory of each machining beam 2 is always the same. As a result, the tensile and compressive stresses 6 from the joining modification 11 can be discharged and/or diverted uniformly into the material modification area 22 and the material modification 20 .

The introduction of the material modification into the joining partner 3 before and/or after the actual joining can be carried out with the same ultra-short pulse laser as in the joining process. For this purpose, other process parameters such as the focusing, the feed along the trajectory, as well as the power/pulse energy or the beam shape may have to be adjusted accordingly.

The joining partner 3 can be fused silica, for example. To introduce the material modification into the joining partner 3 before and/or after the actual joining, the average power of the ultrashort pulse laser can be 15 W, for example, with four laser pulses being emitted per burst at a distance of 20 ns, with the repetition rate of the burst being 200 kHz . The numerical aperture when focusing can be, for example, 0.1-0.7 and is typically 0.25. The feed can be 1 mm/s up to 50 mm/s, for example.

The joining partner 3 can also be borosilicate glass. To introduce the material modification into the joining partner 3 before and/or after the actual joining, the average power of the ultrashort pulse laser can be 3 W, with two laser pulses being emitted with a spacing of 20 ns per burst, with the repetition rate of the burst being 100 kHz to 400 can be kHz. The numerical aperture when focusing can be, for example, 0.1-0.6 and is typically 0.25. The feed can be 5 mm/s up to 50 mm/s, for example.

The joining partner 3 can also be sapphire. To introduce the material modification into the joining partner 3 before and/or after the actual joining, the average power of the ultrashort pulse laser can be 6 W, with the repetition rate of the individual pulses being 200 kHz to 500 kHz. The numerical aperture when focusing can be, for example, 0.1-0.6 and is typically 0.25. The feed can be 50 mm/s, for example.

The joining partner 3 can also be Corning Eagle Glass, whereas the other joining partner can be copper. To introduce the material modification into the joining partner 3 before and/or after the actual joining, the average power of the ultrashort pulse laser can be 1.5 W, with the repetition rate of the individual pulses being 500 kHz. The numerical aperture when focusing can be, for example, 0.1-0.6 and is typically 0.25. The feed can be 1 mm/s, for example.

A variety of configurations of the material modification 20 are possible. In particular, due to the different modification methods, such as laser irradiation, XUV, EUV and X-ray irradiation, as well as chemical hardening and ion implantation, different characteristics and in particular different insertion depths in the joining partner 3 are possible.

In the 4 are schematically different forms and characteristics of material modifications 20 shown. The material modifications 20 are shown hatched. Shown here are cross sections through the two joining partners 3.

In particular, a pretreatment of the joining partner is shown in the top line of the figure, since the material modifications 20 have already been introduced into the joining partner and no joining modification 11 is yet present. The introduction of the joining modification 11 into the pretreated joining partner 3 is shown in the lower half of the figure. In this case, the joining beam 1 can be moved, for example, along the y-axis perpendicular to the image plane. The procedure for the post-treatment of the joining partners 3 is analogous.

In 4A the material modification 20 was inserted along the entire surface at the interface between the joining partners 3. This can be the result of a chemical hardening process, for example. The half of the figure below shows that the joining beam 1 is placed in the material modification 20 . This ensures that the joint modification area 12 has a large overlap with the material modification 20 and the material modification area 22 .

In 4B a material modification 20 is shown, which is localized to a region at the interface 4 of the joining partners 3 . Such a material modification 20 originates, for example, from a method in which a processing mask was used. In this case, too, the figure below shows that the joining beam 1 is placed in the material modification 20 .

In 4C several material modifications 20 are shown. The material modifications 20 are introduced into both joining partners 3 . This can be accomplished, for example, by the processing beam 2 of a processing laser. The trajectories that the processing beam 2 has covered in the image plane are parallel to one another, but offset from one another. The joining beam 1 is now placed exactly between the material modifications 20. Thus, in each material modification 20, tensile and compressive stresses can be derived from the joining process in a targeted manner.

In 4D other forms of material modification 20 are shown. The material modifications 20 extend from the interface 5 of the joining partners 3 into the respective volume material. A material modification 20 localized in this way can originate, for example, from an ion implantation process, in which case a corresponding processing mask was used. Here, too, the joining beam 1 is focused on the interface 5 between the material modifications 20 .

In 4E Another form of material modification 20 is shown. The material modification 20 extends from the interface 5 into the bulk material, the entire material modification 20 having multiple points of contact at the interface 5 and still being coherent. Such a material modification 20 can be created, for example, by a corresponding processing beam 2, the focal position along the z-axis being varied depending on the x-position. The processing beam 2 only modifies the material in its focus. Here, too, the joining beam 1 is placed centrally in the material modification 20 .

As far as applicable, all of the 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 List

1

joining beam

10

joining area

11

joint modification

12

joint modification area

2

machining beam

20

material modification

22

material modification area

3

joining partner

4

overlap

5

interface

6

tensile and compressive stress

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• US8314359B2 [0007]
• US 9625713 B2 [0007]

Claims (15)

Method for joining at least two joining partners (3), the at least two joining partners (3) being joined to one another by means of ultra-short laser pulses from a joining laser (1), at least one joining partner (3) being essentially transparent to the ultra-short laser pulses from the joining laser (1). , characterized in that a material modification (20) is introduced into at least one of the joining partners (3) before joining and/or after joining. procedure after claim 1 , characterized in that - 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 10 fs and 50 ps, preferably 400 fs, and/or - several laser pulses are emitted in a burst, the repetition rate of the burst being between 1 kHz and 50 MHz, preferably 100 kHz to 400 kHz, particularly preferably 200 kHz, and/or - the repetition rate of the individual laser pulses being between 1 kHz and 1000 GHz is, preferably between 1 MHz and 50 MHz, and/or - the numerical aperture of the focused laser beam is between 0.1 and 0.7, preferably 0.25, and/or - the fluence in the focus is greater than 0, 01 J/cm ² and/or the raw beam diameter is preferably 5 mm. Method according to one of the preceding claims, characterized in that the average power of a laser spot is between 0.5 W and 50 W. Method according to one of the preceding claims, characterized in that the roughness of the upper joining partner (3) is less than 200 nm. Method according to one of the preceding claims, characterized in that the joining beam of the joining laser (1) is irradiated perpendicularly to the interface of the joining partners. Method according to one of the preceding claims, characterized in that before the joining, a material modification (20) in the form of a coating is applied to at least one joining partner (3), the coating preferably comprising at least one component which is present in one of the two joining partners (3 ) is available. Method according to one of the preceding claims, characterized in that the joining beam of the joining laser (1) is spatially and/or temporally modulated. Method according to one of the preceding claims, characterized in that the joining beam (1) is regulated in the focal position. Method according to one of the preceding claims, characterized in that the material modification (2) by laser irradiation by means of a processing laser (2) and / or by means of XUV or EUV irradiation and / or by means of X-ray irradiation and / or by means of chemical hardening and / or by means of thermal Hardening and / or is introduced by ion implantation. procedure after claim 9 , characterized in that the joining laser (1) is used as the processing laser (2). procedure after claim 9 , characterized in that a CO2 laser is used as the processing laser (2) and the processing laser beam is aligned collinear to the joining beam (1) and/or the processing laser beam is spatially and/or temporally modulated and/or the focus position is regulated. Procedure according to one of claims 9 until 11 , characterized in that the material modification (20) is carried out by introducing the processing beam (2) along the joining path or along one or more parallel offset joining paths. Method according to one of the preceding claims, characterized in that the material modification (20) is introduced spatially localized in the joining partner (3). Procedure according to one of Claims 10 until 13 , characterized in that a material modification (20) is locally introduced with the aid of a processing mask during the XUV or EUV processing and/or the X-ray irradiation and/or the chemical hardening and/or during the ion implantation. Procedure according to one of Claims 10 until 14 , characterized in that the thermal hardening is carried out with a spatially and/or temporally modulated heat source, preferably a heating oven.

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