CN110856886A

CN110856886A - Soldering method for connecting a transparent first substrate and a non-transparent second substrate and use thereof

Info

Publication number: CN110856886A
Application number: CN201910758281.XA
Authority: CN
Inventors: S·鲁斯; J·维杜威尔特; M·赛勒; C·诺伊格鲍尔; B·菲拉; F·克莱克纳
Original assignee: Trumpf Laser und Systemtechnik GmbH
Current assignee: Trumpf Laser und Systemtechnik GmbH
Priority date: 2018-08-16
Filing date: 2019-08-16
Publication date: 2020-03-03
Also published as: DE102018120011A1; DE102018120011B4

Abstract

The invention relates to a soldering method for connecting a transparent, aluminum oxide-containing first substrate (10) to an opaque second substrate (12), in particular comprising or consisting of aluminum, comprising a step of placing the first substrate (10) against the second substrate (12) and a step of irradiating a contact surface (34) between the first and second substrates (10, 12) by means of a laser beam (18, 24) in order to solder the first and second substrates (10, 12). The invention also relates to the use of the welding method for fixing a transparent aluminum oxide-containing disk (10) to a housing (12) of an electronic and/or optical device.

Description

Soldering method for connecting a transparent first substrate and a non-transparent second substrate and use thereof

Technical Field

The invention relates to a soldering method for connecting a transparent, aluminum oxide-containing first substrate to an opaque, second substrate, which in particular comprises aluminum or consists of aluminum. The invention also relates to the use of such a welding method for fixing a transparent aluminum oxide-containing disk to a housing of an electronic or optical device, in particular a housing made of aluminum.

Background

Various products are known whose casing is constructed from transparent and non-transparent materials. Typical examples are electronic appliances or appliances in the medical technology and optics field. In order to ensure proper operation and proper function, it may be a requirement of such appliances that the different materials used are connected to one another in a liquid-tight and/or gas-tight manner.

Aluminum is widely used for the housing member in the above products because of its relatively small weight compared to other metals. It is also known to insert an alumina-containing disk as a transparent material, for example corundum, in particular synthetic corundum, also known as sapphire glass, into the housing of the product. These discs are characterized by a high stiffness and a corresponding high scratch resistance, which may be advantageous for many applications.

For joining these materials, adhesive bonding methods are mainly used, in which the surfaces to be joined to one another are joined to one another in a cohesive manner by means of an adhesive.

However, the adhesive bond thus produced generally suffers from a reduction in holding power under the influence of environmental influences, such as thermal stress or changing air humidity. The handling of the adhesive in the joining process is also complicated, since, for example, the adhesive poses a high risk of contamination of the materials to be joined and of the joining apparatus. However, it is not desirable for the optically active region of the transparent substrate to be contaminated during use in the optical component, and therefore the contamination must be removed again in a laborious subsequent processing step.

Soldering methods for joining such materials are also known, in which a solder is heated and applied in liquid form to the surfaces of the materials to be joined. In this case, the solder generally has a temperature below the melting temperature of the materials to be joined. After the positioning of the materials to be joined and the solder solidification, a cohesive connection is produced.

Disclosure of Invention

Starting from the known prior art, the object of the present invention is to provide an improved bonding method for connecting a transparent, aluminum oxide-containing first substrate to an opaque, in particular aluminum-containing second substrate. Further, the use of this joining method should be explained.

This is solved by a welding method having the features of claim 1. Advantageous further developments emerge from the dependent claims, the description and the drawings.

Accordingly, a soldering method for connecting a transparent, aluminum oxide-containing first substrate to an opaque, second substrate, which in particular comprises aluminum or consists of aluminum, is proposed. The welding method comprises a step of attaching the first substrate to the second substrate and a step of irradiating a contact surface between the first and second substrates with a laser beam to weld the first substrate to the second substrate.

In the proposed method, energy is introduced by irradiating the contact surface between the first and second substrate with a laser beam, so that a targeted local melting of the first and/or second substrate takes place at the contact surface, and the materials melted in this way are welded together after solidification. More precisely, after the solidification process of the molten material, the first and/or second substrate forms a cohesive connection in the region of the contact surface.

The connection between the first and second substrates by soldering may be of a chemical and/or mechanical nature.

In contrast to the joining methods known from the prior art, the introduction of additional material, for example in the form of adhesive or solder, between the components to be joined to produce a cohesive and/or chemical bond can be prevented. In this way, the method for joining or joining the first and second substrates can be simplified, since handling and application of the joining agent tool, for example in the form of an uncured adhesive or a liquid solder, can be dispensed with. Furthermore, the method steps for applying the first substrate to the second substrate and thus for positioning the components to be connected relative to one another can be carried out more simply and more precisely. Therefore, contamination of the member to be connected by the bonding agent can also be avoided.

This is advantageous in particular when joining the substrates, that is to say the transparent, aluminum oxide-containing first substrate and the opaque, in particular aluminum-containing or aluminum-containing second substrate, so that ultimately the transparent hard component can be soldered to the opaque metal component. The optical quality and the perfection of the transparent first substrate are not impaired or not substantially impaired here. Contamination of the transparent substrate by adhesive residues can be avoided in particular.

The proposed method is accordingly preferably provided for connecting a transparent, aluminum oxide-containing first substrate to a second substrate composed of aluminum.

More precisely, the first substrate may be made of or comprise corundum. For example, the first substrate may be made of or comprise sapphire. Furthermore, the first substrate may be made of or comprise synthetic corundum, wherein synthetic corundum is also referred to as sapphire.

According to the present disclosure, the term "transparent" refers to a property of the first substrate that is transparent or transparent to light having a wavelength in the visible range and/or to a laser beam impinging on the contact surface, i.e. to light having the wavelength of the laser beam. Here, however, "transparent" is not necessarily to be understood as a transmission of 100%, but a part of the incident light can also be absorbed or reflected in the first substrate. By partially absorbing the laser beam guided through the transparent substrate, heat can also be introduced into the first substrate when the contact surface is irradiated with the laser beam.

Accordingly, the term "opaque" is understood at present as meaning a property of the second substrate that is opaque or opaque to light having a wavelength in the visible range and/or to laser radiation impinging on the contact surface. Accordingly, light impinging on the opaque substrate is substantially completely absorbed and reflected.

The term "substrate" is currently understood in general as a material to be treated or a component to be treated. The first and second substrates in the proposed soldering method may have any shape as long as the accessibility of the contact face between them to the laser beam can be ensured. For example, the first substrate may be plate-shaped and in particular provided in the form of a plate, for example in the form of a planar plate or a curved plate.

The second substrate may have a shape complementary to the first substrate. In particular, the second substrate may have a shape that matches the outer contour of the first substrate. For example, the first and second substrates can be provided such that they at least partially overlap in the region of the outer contour of the first substrate in the state of abutting one another. Here, the contact surface may be formed in an overlapping region between the first and second substrates. A lap weld is thus produced during the welding, wherein the welded part is located between the two substrates. The first substrate and the second substrate may constitute at least a part of a housing for an electronic appliance or an optical appliance, for example.

In the proposed welding method, the irradiation of the contact surface can be carried out in such a way that the laser beam is guided through the first (transparent) substrate in the direction of the contact surface. In this way, good accessibility of the contact surface to the laser beam can be ensured and a targeted, local melting and welding of the first and second substrates can be achieved accordingly.

The formation of the lap weld can accordingly be formed therefrom: the laser beam is directed through the transparent substrate onto the contact area.

In general, a Laser beam is understood to be a Light beam generated by a Laser (abbreviation of Laser, Light Amplification by modulated emission of Radiation). Such laser radiation generally has a large coherence length, is bundled, is present in a narrow wavelength range, and-at least for lasers used for material processing-is high-energy.

The radiation generated by the laser for the welding method described above can be emitted by the radiation source either continuously or in pulses.

In the use described here, the laser beam is irradiated in a focal spot onto the contact surface between the first and second substrate after the preceding beam shaping. Thus, the focal spot describes a spatially delimited region of the contact surface. The contact surface regions not irradiated by the laser beam are not to be understood as focal spots. In other words, the focal spot typically has a small spatial extension compared to the contact surface between the first and second substrate, so that simultaneous machining of the entire contact surface is generally not possible. But a continuous processing of the contact surfaces is necessary when it is desired to join the two substrates across the entire contact surfaces. However, the joining of the first and second substrates may also be carried out only in selected sections or regions of the contact surface, for example by spot welding or intermittent wire bonding.

In order to be able to achieve locally defined and thus targeted melting of the material, the focal spot may have a width of 3 μm to 35 μm, for example 4 μm to 12 μm, preferably 8 μm or 32 μm. Alternatively, the focal spot may also have a width of more than 35 μm. The width of the focal spot can be adjusted in particular depending on the desired intensity of the laser radiation on the contact surface and the desired size of the weld spot or the desired width of the weld seam. The focal spot preferably has a substantially circular contour. However, the actual shape of the focal spot results from the beam shaping of the laser beam (in particular by collimation and/or widening and/or focusing of the laser beam), the geometrical relationship between the irradiated shaped laser beam and the contact surface between the substrate and the surface properties of the contact surface.

In a further development of the welding method, a step of focusing the laser beam can be provided. The laser beam is focused by the optical unit before the laser beam impinges on the contact surface and/or before it is guided through the first substrate. The energy of the laser beam can be focused on the focal spot in this way, so that precise and rapid machining can be achieved and thus the accuracy of the welding method is improved.

The focal point of the laser beam is preferably located in the plane formed by the contact surfaces, so that the energy input at the contact surfaces is maximized. Depending on the configuration of the method, however, the focal point of the laser beam can also be arranged in the first or second substrate.

The optical unit may be provided in particular for bundling the focused laser beam in the focal spot in the plane of the contact surface between the substrates and thus providing a laser beam with a high intensity in the focal spot. The focal spot is predefined by the structural configuration of the optical unit and has a defined distance to the optical unit. More precisely, the focal spot is located after the optical unit in the irradiation direction in the beam path of the laser beam. The step of irradiating the contact surface is preferably performed such that the focal spot coincides with the contact surface.

The optical unit may comprise an objective lens, i.e. a lens system, or a converging lens. More precisely, the objective lens may provide a magnification or demagnification of 2 to 20 times, for example 10 times. Alternatively or additionally, the objective lens may have a numerical aperture between 0.25 and 0.75, for example substantially 0.5. Alternatively or additionally, the objective lens may have a focal length between 10mm and 50mm, for example substantially 20 mm. Depending on the desired size and intensity of the focal spot, an objective lens having a focal length of more than 50mm, for example 56mm or 100mm or more than 100mm, may also be used.

The optical unit may be provided in particular for focusing the preferably already collimated laser beam injected therein in such a way that the focused laser beam impinges on a focal spot having a substantially circular focal spot cross section with a desired diameter, for example a diameter of 3 μm to 35 μm, for example 32 μm.

In order to adjust the desired width or the desired diameter of the focal spot cross section, the focal length of the optical unit, in particular of the objective lens, can be adjusted accordingly depending on the incident laser beam. For example, the light entering the optical unit may have a substantially circular beam cross-section (initial beam diameter) with a diameter between 4.5mm and 10 mm.

The laser beam incident on the optical unit can also be widened, for example by a factor of 1.1 to 10, preferably by a factor of 2, before penetrating the objective. By widening, a further objective lens can be used, for example with a double focal length when widening by a factor of 2, in order to obtain the same properties of the focal spot.

Additionally or alternatively, a widening of the laser beam can be carried out in order to influence the size of the focal spot in this way.

In a further embodiment, the contact surface between the first and second substrate can be irradiated by means of a pulsed laser beam. In other words, pulsed laser pulses can be used in order to locally melt and thus weld the substrates to be joined. A "pulsed laser beam" is understood to mean a laser beam which impinges on the contact surface discontinuously, but intermittently. In other words, the laser beam impinges on the contact surface during a predetermined irradiation time window, so-called pulses, which are interrupted by a predetermined rest period in which no irradiation of the contact surface takes place.

The use of a pulsed laser beam enables the melting of the material of the first and/or second substrate to be carried out in a particularly targeted manner. The heat input into the substrates to be connected can therefore be better controlled and the size of the solder bubble which can be produced by irradiation can accordingly be locally limited in the first and/or second substrate.

Furthermore, laser types which do not allow continuous operation (continuous wave laser) can also be used by using pulsed laser beam sources. For example, Q-switched lasers, mode-coupled lasers or pulse-pumped lasers can therefore be used as beam sources for the welding methods currently proposed.

The laser beam of the pulses can be generated by means of a short-pulse laser for generating laser pulses having a pulse duration in the nanosecond range. The pulsed laser beam thus produced can in particular have a pulse duration of less than 1 ns. Alternatively, the pulsed laser beam may also have a pulse duration of greater than or equal to 1 ns.

In the proposed welding method, the melting of the first and/or second substrate is carried out in such a way that the pulsed laser beam is absorbed by the first and/or second substrate. Here, the absorption in the second (opaque) substrate proceeds substantially linearly, so that also higher pulse durations, for example of 100ns, can be set.

Preferably, the pulsed laser beam can be provided by means of an ultrashort pulse laser for generating a laser beam having a pulse duration in the picosecond or femtosecond range. The pulsed laser beam generated in this way can in particular have a pulse duration of less than 10ps, preferably less than 1ps or less than 1 fs. For example, the pulsed laser beam may have a pulse duration of at most 400fs, for example 300 fs. In another embodiment, the pulse duration may also be 6 ps.

Preferably, the laser beam has a laser power of 20W or less, in particular a laser power between 2W and 15W, for example 6W. Alternatively, the laser beam may have a laser power of more than 20W, for example 50W. Alternatively or additionally, the pulsed laser beam preferably provides a pulse energy of at most 20 μ J, in particular a pulse energy between 2 μ J and 12 μ J, but also pulse energies greater than 20 μ J. Alternatively or additionally, the pulsed laser beam may have a repetition rate of between 250kHz and 1000kHz, in particular 500 kHz.

As mentioned above, the laser beam influencing the contact surface can be defined or influenced by a number of different parameters, for example by the focal spot size on the contact surface, the pulse duration, the laser power, the pulse energy, the repetition rate, etc. These parameters can be varied individually or simultaneously, in particular in relation to one another, in order to influence the melting process of the first and/or second substrate. For example, these parameters may vary depending on the first and second substrates (e.g. in particular depending on their material construction scheme) or depending on the time specification for the soldering method.

For example, the welding of the first substrate to the second substrate can also be carried out with a laser power of 50W with a 6ps laser pulse and a focal spot having a diameter of 32 μm.

The welding method can be carried out in such a way that several hundred successive pulses impinge on the focal spot on the contact surface in order to melt the first and/or second substrate. As a result, the material of the first and/or second substrate is heated above its respective melting temperature and is correspondingly melted, wherein a cohesive and/or chemical bond is produced when the melted material subsequently solidifies. Since a part of the radiated energy can be absorbed when traversing the first substrate, the melting of the first substrate can also take place in a region arranged in front of the focal spot in the beam direction.

In one embodiment, the irradiation of the contact surface can be carried out by: the average laser power of a pulse sequence comprising a predetermined number of laser beam pulses, in particular one single laser beam pulse or four or eight laser beam pulses, is increased compared to temporally adjacent pulses. This can be achieved in particular by: the pulse duration of the laser beam pulses of the pulse sequence is increased, wherein the pulse energy is kept constant. In this way, it is possible to increase the average power at least for a short time, i.e. for a limited number of pulse sequences, in order to thus reduce the time required for soldering the first and second substrates. This mode of operation of the laser unit emitting the laser beam is also known under the concept of the Burst function.

As mentioned above, the method comprises the step of abutting the first substrate against the second substrate. In this way, the first and second substrates can be brought into touch contact and in particular positioned relative to each other before they are soldered. The step of attaching the first and second substrates can be carried out by gluing (antisternen) the surfaces of the first and second substrates to be attached to each other.

The term "adhesion" is understood in general as a bonding method in which the parts to be connected, in particular the surfaces thereof, are connected or fixed to one another by molecular attractive forces, in particular adhesive forces. The step of adhering may in particular comprise the step of cleaning the surfaces to be connected before they are placed in touching contact with each other. In this way a strong attraction between the parts to be connected can be achieved.

It is previously known that the quality of the connection formed by soldering may be related to the size of the gap between the first and second substrates when the contact surfaces are irradiated. In particular, a small gap between the first and second substrate may have a positive effect on the quality of the connection.

Accordingly, the surfaces to be connected of the first and second substrates may preferably be provided smoothly, i.e. with a small average roughness. For example, the surfaces to be connected of the first and/or second substrates may have an average roughness of 10 μm or less. The surface to be connected of the first substrate preferably has an average roughness of at most 20nm or 5 nm. The surface to be connected of the second substrate can in particular have an average roughness of at most 300nm, preferably at most 180 nm. In this way, the size of the gap between the substrates lying against one another can be reduced. Furthermore, this may improve the adhesion of the first and second substrates, since the connection caused by molecular attraction may be made stronger by the smaller gap and the consequent smaller distance between the first and second substrates.

In order to ensure such surface properties of the first and second substrates, the proposed method may comprise the step of smoothing the surfaces of the first and second substrates that abut each other. Accordingly, the step of smoothing may be performed such that the surfaces to be connected of the first and/or second substrates have an average roughness of 10 μm or less. The surface to be connected of the first substrate preferably has an average roughness of at most 20nm or 5nm and/or the surface to be connected of the second substrate preferably has an average roughness of at most 300nm, preferably at most 180 nm.

In general, the irradiation of the contact surface can be carried out in such a way that at least one weld seam extending along the contact surface is formed. Alternatively or additionally, the irradiation of the contact surface may be carried out such that the first and second substrates are welded to one another point by point along the contact surface.

In a further development, the welding method further comprises the step of moving the substrate to be welded and the laser beam or the focal spot relative to each other. To this end, the substrates to be welded may be moved together relative to the laser beam and/or the focal spot.

More precisely, the relative movement between the substrate to be welded and the laser beam can take place in the region of the contact surface in a direction transverse to the beam direction of the laser beam. The focal spot may be moved along the contact surface in this way. Alternatively or additionally, the relative movement between the substrate to be welded and the laser beam may be performed in a direction along the beam direction. The relative position between the contact surface and the focal spot may be changed or adjusted in this way. The substrate to be welded and the laser beam or focal spot may also be moved rotationally relative to each other. In other words, the substrate to be welded and the laser beam or focal spot may be twisted or flipped relative to each other.

The relative movement, in particular the rotational movement and/or the translational movement, between the substrate and the laser beam or the focal spot can be controlled by means of cnc (computerized Numerical control). Such CNC controls are known to those skilled in the art and are therefore not elaborated in the present disclosure.

In order to produce a weld seam extending along the contact surface, the step of irradiating the contact surface and the step of moving the substrate to be welded and the laser beam or focal spot relative to each other may be performed simultaneously. The substrate to be welded and the laser beam can be moved continuously relative to one another while the contact surface is irradiated. Here, the speed of the relative movement between the substrate to be welded and the laser beam can be adjusted depending on the average power of the laser beam and/or its repetition rate. In this way, it is ensured that energy sufficiently high for the material-bound and/or chemical bonding is introduced into the material of the first and/or second substrate, in particular a sufficient number of pulses act on the material.

Alternatively or additionally, the step of irradiating the contact surface and the step of moving the substrate to be welded and the laser beam or the focal spot relative to each other may be performed one after the other. In other words, the step of moving the substrate to be welded and the laser beam or the focal spot relative to each other may be performed without simultaneously performing the step of irradiating the contact surface.

When soldering the substrates to one another point by point, the substrates can first be moved individually to a single soldering position on the contact surface, so that the soldering position coincides with the focal spot. For this purpose, the substrate is moved relative to the focal spot. The relative position between the substrate and the laser beam or focal spot remains constant while a single welding position is irradiated. In order to generate a corresponding welding bubble at each welding position, several hundred successive pulses can be applied to the welding position. For this purpose, the welding position coinciding with the focal spot can be irradiated by means of a pulsed laser beam for several milliseconds. In this way, it is possible to achieve that the focal point of the laser beam always coincides with the desired irradiation position and is located, for example, always exactly in the plane formed by the contact surfaces or at a predefined penetration depth in the first or second substrate, in order to achieve a firm weld spanning the length of the weld seam or the number of weld spots in this way.

In a further development, the method can also comprise the step of determining the position of the substrate to be welded, in particular the contact surface, relative to the focal spot and/or the laser beam. This can be done, for example, using a confocal sensor. The step of moving the substrate to be welded and the laser beam or the focal spot relative to one another can be carried out in such a way that the focal spot coincides with the region to be irradiated on the contact surface.

Furthermore, the step of irradiating the contact surface may be performed such that a continuous, in particular closed, weld seam, for example a substantially circular weld seam, is produced between the first and second substrates. In order to increase the security of the connection between the substrates, a further weld seam running parallel to the weld seam on the contact surface can be produced in a further step.

The above object is also achieved by a welding method as described above with the features of claim 15. Advantageous embodiments of the invention result from the present description and the drawings.

Accordingly, use of a welding method having the above features is provided. The features described above in connection with the welding method are correspondingly considered to be disclosed for the proposed use.

The use of a soldering method is provided for fixing a transparent aluminum oxide-containing disk to a housing, in particular comprising aluminum or consisting of aluminum, of an electronic and/or optical device. The electronic appliance may be, for example, a mobile phone or a computer, preferably a laptop or tablet computer. The optical instrument may be, for example, a camera, an endoscope or an objective lens.

Drawings

Further embodiments of the invention are preferably elaborated by the following description of the figures. The drawings herein show schematically:

FIG. 1 illustrates a welding method in flow chart form;

FIG. 2 is a perspective view of a welding device used in the welding method illustrated in FIG. 1;

FIG. 3 is a longitudinal cross-sectional view of a component manufactured by the welding method shown in FIG. 1 and the welding apparatus shown in FIG. 2; and

fig. 4 a top view of the component shown in fig. 3.

Detailed Description

Preferred embodiments are described below with the aid of the figures. In this case, identical, similar or identically functioning elements in different figures are provided with the same reference symbols and a repeated description of these elements is partly omitted in order to avoid redundancy.

A flow chart illustrating the welding method is shown in fig. 1. The soldering method is provided, for example, for connecting a transparent, aluminum oxide-containing first substrate 10 to an opaque, aluminum-containing second substrate 12, as shown in fig. 2.

More precisely, the first substrate 10 may comprise or be produced from corundum, in particular synthetic corundum, for example sapphire, and may have the shape of a disk which is bonded and/or chemically bonded to the housing component formed by the second substrate 12. The housing component in the form of the second substrate 12 constitutes, for example, a housing of an electronic appliance and/or an optical appliance. The first substrate 10 and the second substrate 12 can be connected to form a housing part with a transparent plate, for example for producing a display, a smartphone or a tablet computer, by means of a cohesive and/or chemical connection, as described below.

A soldering method is disclosed below, by means of which a transparent aluminum oxide-containing disk in the form of a first substrate 10 can be fixed to a housing component made of aluminum in the form of a second substrate 12. The soldering method can be used, for example, to embed a transparent aluminum oxide-containing disk in a mobile telephone housing and to solder it in such a way that the disk serves as a protection for the camera lens of the mobile telephone. Here, the disk can be inserted into the housing and welded thereto in such a way that the light passes through the disk into the camera lens. The disc may also be constructed as a protective cover for the display of the mobile phone located therebelow.

The first and

second substrates

10, 12 are provided in a first step S1 of the soldering method. Subsequently, in a second step S2, the surfaces of the first and

second substrates

10, 12 to be connected to each other are smoothed. For this purpose, the respective surface can be treated, for example, by means of polishing, grinding and/or honing, and its surface quality is thus improved. In a smoothing method step S2, the first and

second substrates

10, 12 are processed in such a way that, after the end of the smoothing, an average roughness of at most 5nm is present at the surface to be joined of the first substrate 10 and a roughness of at most 180nm is present at the surface to be joined of the second substrate 12. Alternatively, a larger average roughness, for example, an average roughness of 10 μm, may be present on the surfaces to be connected of the first and

second substrates

10, 12.

In a next step S3, the first substrate 10 is brought flush against the second substrate 12 and held in a positionally stable manner. This can be achieved particularly preferably by gluing the surfaces to be connected of the first and

second substrates

10, 12, whereby the surfaces to be connected are already connected to one another in a positionally stable manner by means of molecular attractive forces, in particular adhesive forces.

The

substrates

10, 12 positioned relative to one another in this way are welded to one another in a method step S4 of irradiating the contact surface between the first and

second substrates

10, 12. This takes place using the welding device 14 shown in fig. 2 and described in detail below.

The welding device 14 comprises a laser unit 16, for example in the form of an ultrashort pulse laser, for generating a pulsed laser beam 18. In a first mode of operation, the laser unit generates a pulsed laser beam having a pulse duration of substantially 300 fs. Alternatively, the pulse duration may be greater. The pulsed laser beam 18 thus generated has a laser power between 2W and 20W, a pulse energy between 2 μ J and 12 μ J and a repetition rate of substantially 500 kHz. Alternatively, the laser power, pulse energy and/or repetition rate may also be lower or higher.

Furthermore, the laser unit 16 may be operated in a burst mode of operation, in which the average laser power is increased compared to the first mode of operation. This is done by increasing the pulse duration for a pulse sequence comprising one to eight laser beam pulses, wherein the pulse energy is kept constant. This makes it possible to increase the average power and thus to reduce the time necessary for soldering the first and

second substrates

10, 12, at least for a short time, that is to say for a limited number of pulse sequences.

The laser beam 18 generated by the laser unit 16 is guided by the deflection unit 20 in the direction of an optical unit 22 in the form of an objective lens for focusing the laser beam 18. In an exemplary configuration, the objective lens has a magnification of 10 times, a numerical aperture of 0.5, and a focal length of 22 mm. Alternatively, the focal length of the objective lens may be larger. For example, the focal length may be substantially 100 mm. The laser beam 18 impinging on the objective has, for example, a circular beam cross section with a diameter of between 4.5mm and 5.5 mm.

While traversing the optical unit 22, the laser beam 18 is focused onto a focal spot located behind the optical unit 22 in the direction of the beam path. In the focal spot, the focused laser beam 24 has a circular beam cross section with a diameter of between 3 μm and 35 μm. Alternatively, the diameter may also be larger than 35 μm or smaller than 3 μm.

For example, the soldering of the first substrate 10 to the second substrate 12 can also be effected with a laser power of 50W with 6ps laser pulses and a focal spot having a diameter of 32 μm.

The optical unit 22 and the corresponding focal spot can be moved in translation along the Z-axis relative to the support 26 receiving the

substrates

10, 12 to be connected, as indicated in fig. 2 by the arrow Z. For this purpose, a first actuator is provided which can be actuated by the control unit 28. The control unit 28 is preferably a CNC control unit which actuates the first actuator such that the focal spot coincides with the contact surface between the surfaces to be connected of the first and

second substrates

10, 12.

The welding device 14 is provided for irradiating the contact surface between the first and

second substrates

10, 12 by means of a pulsed and focused beam 24, in order to be able to achieve a local melting of the first and/or

second substrate

10, 12 and thus a corresponding welding. The laser beam 24 is guided through the first (transparent to the laser beam) substrate 10 in the direction of the contact surface. The laser beam 24 impinges with its focal spot on the contact surface.

As mentioned above, the support 26 is provided for receiving the

substrates

10, 12 to be joined. The

substrates

10, 12 are fixed relative to the carrier 26. The support 26 is movable in translation along an X-axis and a Y-axis perpendicular to the X-axis, as indicated in fig. 2 by arrows X and Y, which are perpendicular to the Z-axis. In addition, the support 26 can be manipulated to rotate about the X and Y axes, that is, to tip. For this purpose, at least one second actuator is provided, which is connected to the control unit 28.

Furthermore, the soldering device 14 comprises a confocal sensor 30 which is provided for determining the position of the

substrates

10, 12 to be connected, in particular the position of the contact surface between the substrates. In this way, the position of the focal point of the laser beam 24 can be controlled and correspondingly tracked by an actuator acting in the Z direction.

The irradiation of the contact surface between the first and

second substrates

10, 12 by means of the pulsed and focused laser beam 24 can be carried out in such a way that the

substrates

10, 12 are welded to one another point by point. For this purpose, the

substrates

10, 12 can be moved successively along the contact surface to different, predefined welding positions, so that the focal spots successively coincide with the respective welding positions.

The movement into the welding position is effected by means of a control unit 28, which actuates the first actuator and the at least one second actuator in such a way that the

substrates

10, 12 to be connected are moved relative to the focal spot. Once moved to the welding position, the control unit 28 controls the welding device 14 in such a way that the pulsed laser beam 18 generated by the laser unit 16 is guided through the optical unit 22 and irradiates the contact surface between the first and

second substrates

10, 12 at the respective welding position. The relative position between the substrates to be processed 10, 12 and the focal spot remains unchanged during irradiation of the corresponding welding positions. In other words, the irradiation of the contact surfaces and the movement of the

substrates

10, 12 to be connected relative to the focal spot take place successively, i.e. one after the other.

Alternatively or additionally, the irradiation of the contact surface between the first and

second substrates

10, 12 by means of the pulsed and focused laser beam 24 can be carried out such that a weld 32 is produced along the contact surface, as shown in fig. 2. In order to produce such a weld seam 32, the irradiation of the contact surfaces and the movement of the substrates to be connected 10, 12 relative to the focal spot are carried out simultaneously in the welding process. More precisely, the

substrates

10, 12 to be connected are moved continuously relative to the focal spot or laser beam 24 while the contact surfaces are irradiated. The control unit 28 is arranged for adjusting the speed of said relative movement in dependence of the average power of the laser beam 24 and its repetition rate.

In the welding method, the

substrates

10, 12 to be connected together with the substrate 26 can be moved relative to the laser beam 24 or the focal spot by means of at least one second actuator along the X and Y axes, i.e. in a direction transverse to the irradiation direction of the laser beam 24, and by means of the first actuator along the Z axis, i.e. in the irradiation direction of the laser beam 24. The control unit 28 is provided for carrying out the step of moving the

substrates

10, 12 relative to one another in relation to the laser beam 24 or the focal spot depending on the contact surface position determined by the confocal sensor 30. The control unit 28 actuates the respective actuator in such a way that the focal spot coincides with the region to be irradiated on the contact surface between the

substrates

10, 12.

Fig. 3 shows a longitudinal section through a component produced by the welding method and the welding device 14, in which section a transparent, aluminum oxide-containing first substrate 10 is welded to a second substrate 12 made of aluminum.

As shown in fig. 4, the welding method is carried out in such a way that a closed, circular first weld 36 and a parallel, closed second weld 38 are produced by irradiating the contact surface 34 between the

substrates

10, 12.

Fig. 4 shows a top view of the component, wherein the

welds

36, 38 and the contact face 34 are visible due to the transparent nature of the first substrate 10. The first and

second welds

36, 38 provide a material-locking and/or chemical connection between the first and

second substrates

10, 12. The first substrate 10 covers the inner chamber 40 of the member. By providing two

closed welds

36, 38 parallel to each other, the connection formed by the

welds

36, 38 is redundant and thus has an increased safety.

The weld seams 36, 38 shown in top view in fig. 4 are shown in cross section in fig. 3. The weld seam is produced in this way: the contact surface between the

substrates

10, 12 is irradiated by means of a pulsed laser beam 24 guided through the first substrate 10. While traversing the first substrate, a portion of the irradiation energy is absorbed by the first substrate 10, which in the drawing shown in fig. 3 results in melting of the material of the first substrate 10 above the weld seams 36, 38. This can be seen on the melting zone 42 shown in fig. 3, which is arranged above the weld seams 36, 38 and is produced by solidification of the thus melted material of the first substrate above the weld seams 36, 38.

All individual features shown in the embodiments can be combined with each other and/or substituted for each other as long as they can be used, without departing from the scope of the invention.

List of reference numerals

10 first substrate

12 second substrate

14 welding device

16 laser unit

18 pulsed laser beam

20 deflection unit

22 optical unit

24 focused and pulsed spotlight beam

26 support

28 CNC control unit

30 confocal sensor

32 welding seam

34 contact surface

36 first closed weld

38 second closed weld

40 inner chamber

42 melting zone in the first substrate

Claims

1. Soldering method for connecting a transparent, aluminum oxide-containing first substrate (10) to an opaque, second substrate (12), in particular comprising or consisting of aluminum, comprising the following steps:

-abutting the first substrate (10) against the second substrate (12); and is

-irradiating a contact surface (34) between the first and second substrates (10, 12) by means of a laser beam (18, 24) for welding the first and second substrates (10, 12).

2. Welding method according to claim 1, wherein the first substrate (10) comprises or consists of corundum, in particular synthetic corundum, such as sapphire.

3. Welding method according to claim 1 or 2, wherein the laser beam (24) is directed through the first substrate in the direction of the contact face (34) and/or the laser beam (24) is focused on the contact face (34) into a focal spot, in particular having a diameter of substantially 3 μ ι η to 35 μ ι η, preferably having a diameter of 8 μ ι η or 32 μ ι η.

4. Welding method according to one of the preceding claims, wherein the laser beam (18) is guided through an optical unit (22) for focusing the laser beam (18) on a focal spot in the contact surface (34), wherein the optical unit in particular has an objective with a magnification of 2-20 times, preferably 10 times, and/or an objective with a numerical aperture between 0.25 and 0.75, preferably a numerical aperture of 0.5, and/or an objective with a focal length of substantially 10mm to 100mm, preferably 20 mm.

5. Welding method according to one of the preceding claims, wherein the contact surface (34) is irradiated by means of a pulsed laser beam (24), in particular having a pulse duration of at most 100ns or at most 400fs, for example 6ps or 300 fs.

6. Welding method according to claim 5, wherein the laser beam (18, 24) provides a laser power of at most 20W, preferably between 2W and 15W, and/or a laser energy of 20W to 60W, such as 50W, and/or a pulse energy of at most 20 μ J, preferably between 2 μ J and 12 μ J, and/or has a repetition rate of between 250kHz and 1000kHz, preferably 500 kHz.

7. Welding method according to one of the preceding claims, wherein the irradiation of the contact surface (34) is carried out in such a way that the average laser power of a pulse sequence comprising a predetermined number of laser beam pulses, in particular one laser pulse or four or eight laser beam pulses, is increased in comparison to temporally adjacent pulses, in particular by an increase in the pulse duration.

8. Soldering method according to one of the preceding claims, in which the bonding of the surfaces of the first and second substrates (10, 12) to be brought into abutment with one another takes place in the step of abutment of the first and second substrates (10, 12).

9. Soldering method according to one of the preceding claims, further comprising a step of smoothing the surfaces of the first and second substrates (10, 12) which are to be placed against one another, wherein the smoothing is carried out in particular in such a way that the surfaces of the first and/or second substrates (10, 12) which are to be connected have an average roughness of at most 10 μm.

10. Welding method according to one of the preceding claims, wherein the laser beam (18, 24) influences the contact surface (34) in such a way that a weld seam (32, 36, 38) is produced along the contact surface (34) and/or the first and second substrates (10, 12) are welded point by point along the contact surface.

11. Welding method according to one of the preceding claims, further comprising the step of moving the substrate (10, 12) to be welded and the laser beam (24) or the focal spot relative to each other, in particular in a direction transverse to the irradiation direction of the laser beam, in the region of a contact surface and/or in a direction along the irradiation direction, wherein the step of irradiating the contact surface (34) and the step of moving the substrate (10, 12) to be welded and the laser beam (24) or the focal spot are carried out simultaneously and/or one by one.

12. Welding method according to claim 11, wherein the substrates (10, 12) to be welded and the laser beam (24) are moved continuously relative to each other while irradiating the contact surface (34), wherein the speed of the relative movement between the substrates (10, 12) to be welded and the laser beam (24) is adjusted in dependence on the average power of the laser beam (24) and/or its repetition rate.

13. Welding method according to one of the preceding claims, further comprising the step of determining the position of the substrate (10, 12) to be welded relative to the focal spot, in particular using a confocal sensor (30), wherein in particular the step of moving the substrate (10, 12) to be welded and the laser beam (24) or the focal spot relative to each other is carried out such that the focal spot coincides with the region to be irradiated on the contact surface (34).

14. Welding method according to one of the preceding claims, wherein a continuous, in particular closed, weld seam (36), for example a substantially circular weld seam, is produced by irradiating the contact surface (34), wherein in particular a further weld seam (38) is produced which extends parallel to the weld seam (36) on the contact surface (34).

15. Use of a soldering method according to one of the preceding claims for fixing a transparent aluminum oxide-containing disk (10) to a housing (12) of an electronic and/or optical device, in particular comprising aluminum.