Hermetically sealed enclosure and method for designing the welded joint for such an enclosure

Abstract

A method for designing a laser weld between a base substrate (10) and a cover substrate (14) of an enclosure (1) is proposed, wherein the base substrate (10) has a functional area (20), and the cover substrate (14), which is in contact with the base substrate (10), covers the functional area (20), wherein the base substrate (10) and the cover substrate (14) are directly and hermetically bonded to each other via at least one laser bond line (2), so that the functional area (20) is hermetically enclosed inside the formed enclosure (1). It is provided that a minimum shear force F is required for the bond between the cover substrate (14) and the base substrate (10). min The minimum length L that the laser welding is supposed to withstand is specified by an empirically determined force per laser bond line length P. minfor the total length of all bond lines (2) is determined and a contact area width B is chosen such that a ratio A i / A w formed from a contact surface A i , where the base substrate (10) and the cover substrate (14) can touch, and a laser bonding area A swept over by the laser bonding lines (2) with a width w w in the range of 1 to 10. Further aspects of the invention relate to such an enclosure (1) and a sensor unit and / or medical implant comprising such an enclosure (1).

Description

[0001] The invention relates to a hermetically sealed enclosure comprising a base substrate having a functional area and a cover substrate which is in contact with the base substrate and covers the functional area, wherein the base substrate and the cover substrate are directly and hermetically connected to each other via at least one laser bond line, and wherein the functional area is hermetically enclosed within the formed enclosure. The invention further relates to a method for creating the laser weld between the substrates and to the use of such an enclosure.

[0002] Hermetically sealed enclosures are designed, for example, to protect a component or components inside the enclosure from harsh environmental conditions. Applications for such hermetically sealed enclosures can be found in electronics applications to protect sensitive electronic components, and in optics applications to encapsulate optical components. Further applications include medical implants, microfluidic chips, augmented reality, and mobility sensors (e.g., pressure sensors).

[0003] Transparent materials such as glass are particularly desirable for housings in optical applications. However, glass materials also offer advantages over conventional metal housings, such as those made of titanium, in electronic applications where wireless communication or wireless charging is required, as these materials do not shield the radiation used.

[0004] An example of such a hermetically sealed enclosure is known from EP 3 812 352 A1. The enclosure comprises at least a base substrate and a cover substrate, which form the housing and enclose a functional area inside. The cover substrate and the base substrate, which are selected, for example, from a glass material, are joined together by laser bonding.

[0005] A method for producing a transparent part to protect an optical component using a laser method for generating laser bond lines is also known from European patent EP 3 012 059 B1.

[0006] German patent DE 10 2020 117 194 A1 discloses a hermetically sealed enclosure comprising a cover substrate and a second substrate in direct contact with it. The substrates are hermetically bonded directly using a laser bonding line.

[0007] In these known laser processes, two substrates are placed on top of each other, and any remaining gap or space between the substrates is sealed by performing laser welding, so that the connection between the two substrates is hermetically sealed.

[0008] The resulting housings must meet high mechanical requirements, especially when used as implants. One measure of the mechanical strength of the connection between two housing parts is its resistance to shear forces. The higher the stability of the connection, the greater the shear forces it can withstand without loosening. When joining two substrates, the shear force resistance depends on the size of the contact area between them.

[0009] To ensure sufficient shear strength, conventional hermetic enclosures have comparatively thick walls, which can be several millimeters thick. Besides increasing the wall thickness, it is also possible to design the parts to be joined so that they have a positive fit. However, this also requires considerable installation space and is particularly complex for components made of glass and similar materials. This makes a particularly compact design of the hermetic enclosures difficult.

[0010] From US 2015 / 0102315A1, a display arrangement comprising a display substrate and a sealing element is known. The display arrangement additionally features a reinforcing element arranged on an outer surface of the sealing element, wherein the shear stress and the hardness of the reinforcing element are a function of the sum of the thicknesses of the display substrate and the sealing element.

[0011] DE 10 2021 129 411 A1 discloses a hermetically sealed arrangement comprising a transparent substrate and a metal foil arranged adjacent to the transparent substrate. The substrate and the metal foil are joined by at least one laser joining line or a plurality of tack points.

[0012] GB 2 583 090 A discloses a method for joining two substrates using a laser and an interface material arranged between the substrates.

[0013] One object of the invention can therefore be seen as providing a hermetic enclosure which has particularly thin walls and simultaneously meets the mechanical requirements. A further object of the invention can be seen as providing a method for designing a laser weld between components of an enclosure, with which, starting from a given mechanical requirement, a particularly compact and at the same time sufficiently durable enclosure can be obtained. Disclosure of the invention

[0014] A method for designing a laser weld between a base substrate and a cover substrate of an enclosure is proposed. The enclosure to be formed comprises at least the base substrate with a functional area and the cover substrate. The cover substrate is in contact with the base substrate and covers the functional area. The base substrate and the cover substrate are directly and hermetically bonded to each other via at least one laser bond line, so that the functional area is hermetically enclosed within the formed enclosure. It is stipulated that a minimum shear strength F is required for the bond between the cover substrate and the base substrate. min is specified, which the laser welding should withstand, and that the sum of the lengths L ges All laser bonding lines are chosen to be larger than a required minimum length L min the length of all laser bond lines, where L min =F min / P is determined by dividing the given minimum shear force F min by an empirically determined force per laser bond line length P and whereby a contact area width B, measured in the plane of the end face of the base substrate facing the cover substrate as the shortest distance between the functional area and the outer surface of the enclosure, is chosen such that a ratio J=A i / A w formed from a contact surface A i , where the base substrate and the cover substrate can touch, and a laser bonding area A swept over by the laser bonding lines with a width w w on the end face of the base substrate facing the covering substrate, in the range of 1 to 10.

[0015] Preferably, a number N of closed paths of laser bond lines with width w and a distance H between the centers of two adjacent laser bond lines of at least width w is arranged around the functional area, wherein the number N is determined as the smallest number N for which the total length L ges The number N of all laser bond lines formed is multiplied by the length of an outline line that limits the functional area, and is greater than the minimum length L. min .

[0016] For the purposes of this application, a contact surface is the intersection of the inclined surfaces of the two substrates to be brought into contact. The touch contact area refers to a portion of the contact surface where the distance between the two substrates is so small that it is no longer optically measurable. In particular, within the touch contact area, the distance between the surfaces of the adjacent substrates is less than 250 nm. Generally, the contact area is greater than or equal to the touch contact area.

[0017] In other words, two substrates are first arranged next to each other, for example, stacked on top of each other, with gravity pressing the typically upper substrate against the second. The orientation above or below is merely descriptive, as the substrates can naturally assume any orientation in space, and even a side-by-side arrangement should not leave the protected area. The two substrates are typically positioned with a larger side of their dimensions touching each other.

[0018] If both substrates were perfectly flat, without any depressions, raised areas, or curvatures whatsoever—a feat only theoretically achievable—the first and second substrates would be in complete contact with each other. The two substrates would therefore touch at every point on their aligned surfaces. This is generally not attainable in practical construction. Instead, substrates are, even if only to a very small degree, still curved, inclined, or have depressions or raised areas, so that complete contact is achieved only in exceptional cases.

[0019] The functional area enclosed by the housing can, in particular, be a cavity designed to receive a functional element. The cavity has a base and side walls provided by the base substrate and a cover surface provided by the cover substrate. In this embodiment, the thickness of the side walls corresponds to the width of the contact surfaces.

[0020] In other examples of encapsulation, the functional area can be a functionalized area of ​​the base substrate. Such functionalization can be achieved, for example, by applying a coating and / or by structuring the surface.

[0021] The functional area is hermetically sealed by the weld. Hermetically sealed in this context refers specifically to an enclosure that has a helium leakage rate of less than 1 × 10⁻⁶. -8exhibits mbar·l / sec and preferably in the range of 1·10 -10 mbar· l / sec up to 1·10 -9 mbar· l / sec

[0022] The weld is formed by introducing at least one laser bond line or laser welding line. The weld is preferably performed using an ultrashort pulse laser. Typical pulse widths are in the range of 100 fs to 100 ps. A method for performing such a weld with one or more laser welding lines is known, for example, from EP 3 012 059 B1.

[0023] The laser weld line has a height HL in a direction perpendicular to its joining plane. The joining plane is the direction in which the adjacent or successive beam points are placed. Typically, laser welding is performed from a top-down perspective; that is, the substrate stack lies, for example, on a surface—such as a table—and the laser is directed from above, at least through the uppermost substrate layer—or through several substrate layers—to the location of the beam focus. The height HL is therefore measured in the direction of the laser beam, while the width w of the laser weld line is measured perpendicular to the direction of the laser beam.

[0024] The width w of the area modified by the laser beam varies along the depth T of the treated area, i.e., along the laser beam direction. The information provided in this application regarding the width w of the laser weld line refers to the plane of the contact surface between the substrates joined by the laser weld line. Within this plane, the width w is understood to be the area within which material changes were caused by the laser treatment. Such material changes resulting from the laser treatment are caused by heating above the glass transition temperature T. gand / or the melting temperature of the materials involved and subsequent cooling. This laser treatment creates a metallurgical bond between the two substrates in the treated area without the need for additional bonding materials. For optically transparent materials, the material change caused by the laser treatment can be detected, for example, by measuring a refractive index deviation compared to the untreated material. A cross-section can be examined under a light microscope for this purpose. In particular, a change in refractive index of more than 1 × 10⁻⁶ can be detected. -5 They can be used as markers for material changes and, accordingly, for determining the width w. A microscopic image of such a cross-section is shown in Fig. 10 can be seen and is described in more detail below.

[0025] The laser welding process can be used to join a wide variety of materials, whereby at least the substrate which points towards the laser source should be at least partially transparent to the laser used.

[0026] The generated laser welding lines or laser bonding lines are arranged around the functional area such that a closed area surrounding the functional area is formed by the laser bonding surface in a contact plane corresponding to the end face of the base substrate facing the cover substrate. In the case of a cuboid enclosure, one or more straight laser bonding lines can be arranged on each of the four sides bounding the functional area, with the laser bonding lines potentially overlapping at the four corners. The one or more laser bonding lines can, in particular, run parallel to the side walls. It is also possible to arrange one or more closed laser bonding lines, for example, parallel to an outline of the functional area.

[0027] For the hermetic enclosure of the functional area, at least one laser bond line must be laid completely around it. This criterion can also be met by several individually written laser bond lines that overlap at intersection points, thereby forming a closed path around the functional area. Each of these closed paths then corresponds, in the context of the procedure, to a laser bond line arranged around the functional area, where the number of lines is N=1 for exactly one such path and, for example, N=2 for exactly two closed paths. This is necessary to meet the specified minimum shear force F. min A single such closed laser bonding line is sufficient to achieve the specified minimum length L minTo exceed the target value, the number N of laser bonding lines surrounding the functional area can be chosen to be N=1. In this case, there are no laser bonding lines arranged adjacent to each other in the sense of the method.

[0028] Preferably, several laser bonding lines are introduced in the form of several such closed paths, with adjacent laser bonding lines that run within the area defined by the respective contact surface width preferably arranged parallel to each other. Laser bonding lines that are separated from each other by the functional area are not considered adjacent.

[0029] A distance H between the centers of two adjacent laser bond lines with width w is preferably chosen in the range of 1 w to 5 w, preferably in the range of 1.01 w to 2.5 w, and particularly preferably in the range of 1.05 w to 2 w. This prevents the laser bond lines from overlapping, except where different laser bond lines may be crossing.

[0030] By providing a distance between two adjacent, especially parallel, laser bonding lines of at least the width of the laser bonding lines, it is ensured that the substrate material is processed only once, except at laser bonding line intersections, for example, at the four corners around a rectangular functional area. Furthermore, the specified upper limit for the distance allows for a particularly compact design of the laser bonding surface. The contact area width B can thus be made very small while still providing sufficient space for the formation of the laser bonding lines.

[0031] Preferably, the contact area width B is selected in the range of 100 µm to 1000 µm. The precise selection of the contact area width B depends on various criteria, such as the material of the base substrate, the material of the cover substrate, the dimensions of the enclosure, and / or the type of functional area. If a cavity is provided as the functional area, the contact area width B determines the thickness of the sidewalls of the functional area. The contact area width is preferably selected to be at least large enough to ensure sufficient mechanical stability of the sidewall.

[0032] Preferably the contact area width B is chosen to be greater than 200 µm, particularly preferably greater than 300 µm, more preferably greater than 400 µm and most preferably greater than 500 µm.

[0033] The larger the contact area width B is chosen, the larger the enclosure becomes in relation to the enclosed functional area. Accordingly, it is preferred to choose a contact area width B of less than 750 µm, particularly preferably less than 500 µm, and most preferably less than 400 µm. The minimum contact area width is limited by the width w of a laser bond line and is therefore preferably chosen to be greater than 30 µm, particularly preferably greater than 50 µm, and most preferably greater than 100 µm.

[0034] The width w of the laser bonding lines is preferably selected in the range of 20 µm to 75 µm, and particularly preferably in the range of 30 µm to 60 µm. For example, a width w of 50 µm is selected. This range is optimally chosen to ensure that sufficient energy can be supplied by the laser for welding the two substrates. It is particularly advantageous if the width w is essentially constant across all laser bonding lines. Accordingly, it is preferred if the width w of all laser bonding lines is constant over the total length L. ges The width of the laser bond lines varies by at most 30%, particularly preferably at most 20%, and most preferably at most 10%. Since the width w depends on the position of the laser's focal point relative to the contact plane, the use of a laser processing method with precise control of the laser focus's distance from the contact plane is preferred. A suitable method is known, for example, from EP3012059B1.

[0035] For the most compact enclosure possible, the fill factor J=A should be used. i / A w formed from a contact surface A i , where the base substrate and the cover substrate can touch, and a laser bonding area A swept over by at least one laser bonding line with a width w w The fill factor J should be chosen as small as possible. Accordingly, it is particularly preferred to choose a fill factor J in the range of 1 to 5, and most preferably in the range of 1 to 2.

[0036] According to the proposed method, the total length of the applied laser bonding lines, and thus the laser bonding area A, is to be determined. wThe weld thickness must be chosen to ensure a specified resistance of the weld joint to applied shear forces. Shear forces, in this context, are understood to be forces acting perpendicular to the plane of contact between the two substrates, forces which, without a connection between them, would lead to a displacement of the substrates relative to each other.

[0037] The inventors have determined that the shear strength of the weld increases linearly with the total length of the non-overlapping laser bond lines. For the non-overlapping criterion, small overlaps, for example at intersection points of laser bond lines running at right angles to each other and arranged around a rectangular functional area, can be neglected due to the small area of ​​these intersections. Accordingly, when specifying the minimum shear force F min, against which the weld joint is to be resistant, and an empirically determined constant P for the force increase per unit length, the required minimum length of the sum of the laser bond lines via the relationship L min =F min / P can be determined. The total length L gesThe length of the applied laser bond lines, particularly in the case of parallel laser bond lines running around the functional area, can be determined as an integer multiple of the length of a contour line around the functional area. The slight increase in the actual length of the circumferential laser bond lines due to the fact that the laser bond lines are not overlapping can be disregarded because of the small width of the laser bond lines. Similarly, small additional bond line segments, which can occur when manufacturing a large number of enclosures by processing a wafer and subsequently singulating the enclosures, can also be disregarded due to their short length.

[0038] The constant P is specific to the materials of the substrates to be joined and the selected width of the laser bond line and can be easily determined empirically by producing several test specimens, for example 30 pieces, in which a first substrate made of a cover substrate material is joined to a second substrate made of a base substrate material with laser bond lines, where the total length L ges The laser bonding lines are chosen to be identical for the test specimens. Subsequently, the shear strength of the test specimens is determined by applying an increasing shear force to the connection between the first and second substrates, determining the force at which the connection fails, and evaluating a failure probability distribution.

[0039] The minimum shear force F minThe shear force against which the weld joint is to be resistant is preferably not specified larger than necessary, so that the weld joint itself, and consequently the entire enclosure, can be designed as compactly as possible. Preferably, the specification is based on the mechanical requirements of the enclosure. One criterion can be, in particular, that the minimum shear force is related to other force resistances of the substrates. The minimum shear force F is preferably used for this purpose. min specify in such a way that several test specimens are produced, in which a first substrate made of a cover substrate material is joined with a second substrate made of a base substrate material using laser bonding lines so that these are subject to a minimum shear force F min are designed and when applying this minimal shear force F minmore than 50%, preferably more than 75%, particularly preferably more than 90%, most preferably 95% of the test specimens do not break along the contact surface due to failure of the weld joint, but break at other locations, particularly at an edge of one or more of the substrates.

[0040] To determine the failure rate, several identical test specimens can be produced, similar to determining the empirical constant P. For example, 30 specimens in which two substrates are welded together by introducing laser bond lines. The total length of the laser bond lines is determined according to the shear force F to be tested. minThe test specimens are then increasingly subjected to a shear force. The point at which a test specimen mechanically fails can easily be determined by visual inspection. If the weld fails, the individual substrates are separated again, but essentially without further damage. If the number of test specimens that do not break along the contact surface due to weld failure is within the intended range, for example, more than 75%, then the tested shear force F is min correctly selected. Otherwise, the test is repeated for a higher or lower shear force to be tested, depending on the result.

[0041] After the weld joint has been designed, steps for manufacturing the housing can follow. These steps can include, in particular, providing the substrates and, if necessary, cleaning the substrate surfaces, stacking the substrates (possibly inserting a functional element into a functional area), and applying the laser bond lines.

[0042] The manufacturing process can be designed to produce a large number of enclosures in a single pass. For this purpose, large wafers are initially used instead of substrates already cut to the final size of the enclosure. These wafers are stacked layer by layer and joined together by laser welding. The individual enclosures are then separated by cutting the resulting wafer stack. In such a process, the laser bond lines can be arranged along a grid pattern, with each functional area enclosed by four laser bond lines forming a rectangle.

[0043] Another aspect of the invention is the provision of a hermetically sealed enclosure. The proposed hermetically sealed enclosure comprises a base substrate, which has a functional area, and a cover substrate, which is in contact with the base substrate and covers the functional area. The base substrate and the cover substrate are directly and hermetically bonded to each other via at least one laser bonding line, and the functional area is hermetically enclosed within the formed enclosure. Furthermore, it is provided that a ratio J=A i / A w formed from a contact surface A i , where the base substrate and the cover substrate can touch, and a laser bonding area A swept over by at least one laser bonding line with a width w w on the end face of the base substrate facing the covering substrate in the range of 1 to 10, wherein a contact area width B, measured in the plane of the end face of the base substrate facing the cover substrate as the shortest distance between the functional area and the outside of the housing, lies in the range of 100 µm to 1000 µm.

[0044] The proposed housing is particularly compact because the contact surface width B is designed such that the laser bonding surface A w as large a part as possible of the total contact area A i fills out.

[0045] In previously known hermetic enclosures obtained by laser welding of substrates, it was assumed that a significant portion of the mechanical stability is provided by the largest possible contact area, and that the laser bonding area is essentially required to ensure the hermetic enclosure of the functional area. Due to the size of the laser bonding area compared to the total contact area A, itypically small laser bonding area A w Regarding the laser bonding area A, the following has been recorded so far w even assumed only a small contribution to mechanical stability, especially to resistance to shear forces.

[0046] Furthermore, it was surprisingly found that maximizing the shear strength of the weld joint between the two substrates is not advantageous, as in this case the enclosure fractures uncontrollably at other points under the influence of large mechanical forces. Therefore, further weld lengthening does not contribute to an improvement in the overall strength of the enclosure. Moreover, the "unnecessary" welds in this way require a larger contact area and thus increase the "footprint" of the enclosure. Accordingly, it is preferable to specify not only a lower limit but also an upper limit for the shear strength.

[0047] The laser bonding area A, which is swept by at least one laser bonding line, is preferred for this purpose. w selected such that the connection between the cover substrate and the base substrate has a failure shear force in the range of 10 N to 1000 N, preferably 50 N to 500 N, particularly preferably in the range of 100 N to 400 N.

[0048] The overall length L is preferred. ges The laser bond lines of the enclosure are determined according to one of the design methods described herein. It is particularly preferred if the specified minimum shear force F min , which is intended to withstand laser welding, corresponds to this failure shear force in the range of 10 N to 1000 N.

[0049] Since the enclosure can be obtained using one of the described methods, features described within the framework of one of the methods also apply to the enclosure, and conversely, features disclosed within the framework of the enclosure also apply to the methods.

[0050] Preferably, the welding is carried out with several laser bonding lines, wherein the laser bonding lines have a width w and a distance H between the centers of two adjacent laser bonding lines is selected in the range of 1 w to 5 w, preferably in the range of 1.01 w to 2.5 w and particularly preferably in the range of 1.05 w to 1.5 w.

[0051] The width w of the laser bond lines is preferably in the range of 20 µm to 75 µm, particularly preferably 30 µm to 60 µm. For example, the laser bond lines are 50 µm wide. It is particularly advantageous if the width w is essentially constant across all laser bond lines. Accordingly, it is preferred if the width w of all laser bond lines is constant over the total length L. ges The laser bonding lines vary by a maximum of 30%, preferably a maximum of 20%, and most preferably a maximum of 10%.

[0052] The housing is preferably designed to be as compact as possible. This is achieved by keeping the portion of the contact area not occupied by the laser bonding surface as small as possible, and consequently, by also minimizing the contact area width B. For this purpose, it is preferably provided that the end face of the base substrate facing the cover substrate, which forms the contact area A, i The contact area corresponds to at least 20% being covered with laser bond lines, and thus J lies in the range of 1 to 5. Particularly preferred is at least half of the contact area A being covered by laser bond lines. i covered with laser bond lines, where J is then in the range of 1 to 2.

[0053] The covering substrate is preferably designed as a transparent thin-film substrate, wherein the covering substrate has a thickness of less than 200 µm, preferably less than 170 µm, particularly preferably less than 125 µm, and preferably greater than 10 µm, particularly preferably greater than 20 µm. This allows the dimensions of the enclosure to be made particularly compact, even in the stacking direction of the substrates.

[0054] The covering substrate can be provided in the form of a thin-layer substrate and welded to the base substrate. Alternatively, a thicker substrate can be thinned by material removal after bonding it to the base substrate.

[0055] The cover substrate and the base substrate border at contact surface A. i directly adjacent to each other, so that the connection in the laser bonding area A swept over by at least one laser bonding line wThe housing is free of foreign materials, in particular free of bonding materials such as adhesives, glass frit, or absorbent layers. Since no foreign materials were used in sealing the housing, contamination of the functional area, for example by components of an adhesive, is avoided.

[0056] The functional area can be designed as a cavity. Such a cavity is preferably configured to receive a functional element, so that one or more functional elements can be accommodated in the cavity of such an enclosure. The cavity has a bottom surface and side walls provided by the base substrate, and a top surface provided by the cover substrate. In this embodiment, the thickness of the side walls corresponds to the width of the contact surfaces.

[0057] The base substrate can comprise a planar bottom substrate forming the floor area of ​​a cavity-shaped functional area, and an intermediate substrate forming the side walls of the cavity with an end face facing the cover substrate. The bottom substrate and the intermediate substrate are preferably hermetically bonded to each other via at least one laser bond line. The method described herein can be applied analogously to the design of this welded joint, and the welded joint can be designed analogously to the connection between the cover substrate and the base substrate described herein.

[0058] Alternatively or additionally, the base substrate can be designed as a functional area in the form of a depression with a base and side walls, which together with the cover substrate as the lid form a cavity. Such depressions can be created, for example, by grinding or etching.

[0059] In other examples of encapsulation, the functional area can be a functionalized area of ​​the base substrate. Such functionalization can be achieved, for example, by applying a coating and / or by structuring the surface.

[0060] The cover substrate and / or the base substrate preferably consist of a glass, a glass-ceramic, silicon, sapphire, or a combination of the aforementioned materials. Borosilicate glasses are particularly suitable as glass materials.

[0061] The invention also relates to the use of the proposed housing as an enclosure for a sensor unit and / or a medical implant. In these applications, the hermetic seal and the achievable compact dimensions of the housing are particularly advantageous. With thin walls and a contact surface width of, for example, 500 µm, the housing is only marginally larger than the functional element it contains.

[0062] Furthermore, a sensor unit and / or medical implant is comprised of one of the housings described herein. Preferably, the housing has a cavity that encloses a functional element of the sensor unit and / or the medical implant.

[0063] An example of an enclosure comprises a base substrate and an intermediate substrate, which together form a base substrate, as well as a cover substrate. All substrates consist of borosilicate glass, which is available, for example, under the name BOROFLOAT 33. The base substrate and the intermediate substrate have a thickness of 1.1 mm, and the cover substrate has a thickness of 500 µm. The length and width of the substrates are each 5 mm. By selecting a contact surface width B of 500 µm, a cavity with side walls and a lid wall with a thickness of 500 µm is provided.

[0064] Example for determining the empirical parameter P: Samples were prepared in which two substrates made of a floated borosilicate flat glass, available under the name BOROFLOAT® 33, with a length and width of 5 mm and a thickness of 1.1 mm, were stacked on top of each other. To verify the assumption that the shear force is linear with respect to the total length of the laser bond lines, a first type 1 laser bond line with a total length L was used. ges of 20 mm were inscribed. In a second type 2, laser bonding lines with a total length L were used. ges of 40 mm and in a third type 3, laser bonding lines with a total length L were used. gesThe laser bond lines are inscribed with a cross-section of 60 mm. In principle, the laser bond lines can be applied to any geometry. In this example, half of the bond line length was inscribed along a first direction and the other half along a second, perpendicular direction, creating a "+" shape. The overlap of the laser bond lines at the center of this cross shape can be neglected due to its small area.

[0065] Thirty samples of each of the three substrate types were prepared, and the shear force at which the bond between the two substrates failed was determined for each sample. This was done using an apparatus in which two superimposed plates could be sheared against each other with a defined force. Each plate had a recess whose shape and depth corresponded, within a small tolerance, to the dimensions of the substrates. Accordingly, the sidewalls of the recesses closely abut the lateral surfaces of the respective substrates. To determine the shear force at which a bond between the two substrates of one of the samples failed, a sample was placed between the two plates, and the two plates were slid against each other at a rate of 1.5 mm / min, during which time the force was measured.If the connection fails, the specimen no longer resists displacement, which is detected by an abrupt drop in the measured force. The shear force at which the connection failed is then the highest force measured during the displacement or shearing of the two plates.

[0066] The measurement is repeated for all samples, recording the shear force at which the bond between the two substrates of a sample fails. The measurement results for the cumulative probability KP are shown in a double-logarithmic plot in Fig. 6 applied.

[0067] By adjusting the parameters of a distribution function p(F) for the cumulative failure probability at a shear force of F, a failure shear force Fv can be determined at which the corresponding sample type fails. The distribution function p(F) is given by p(F)=100%⋅(1−e−FzFV), where the parameter z specifies the width of the distribution function and can also be determined by adjusting the parameter.

[0068] For a confidence interval of 95%, the following results for the failure shear force Fv are obtained for the three sample types, which are also shown in Fig. 7 as a function of the total length L ges the laser bonding lines are shown: Fv=107.9(101.8…114.3)N Fv=144.1(139.6…148.8)N Fv=219.6(206.6…233.6)N

[0069] By fitting an affine function, it is readily apparent that the samples, without laser welding (i.e., for a laser bond line length of 0), already exhibit a non-zero failure shear force of approximately 45 N. This basic contribution to shear strength is attributed to the adhesion forces across the optical interface area A. cattributed. Furthermore, it is evident that for every mm of laser bond line, the shear strength increases by approximately 2.8 N.

[0070] For the material pairing used for the two sample types 1 to 3, an empirical constant P of 2.8 N / mm is determined accordingly.

[0071] Since this is a linear relationship, it is sufficient for an empirical determination of the constant P to perform this measurement on a single sample type for the material pairing under investigation.

[0072] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0073] Preferred embodiments and configurations of the invention are shown in the drawings and are explained in more detail in the following description, wherein identical reference numerals refer to identical or similar or functionally identical components or elements.

[0074] This is shown in schematic form Fig. 1 a perspective view of two substrates connected by a laser bond line, Fig. 2 a top view of a hermetic enclosure, Fig. 3 a sectional view of the hermetic enclosure from the side, Fig. 4. A section through laser bond lines along the welding direction, Fig. 5. Cut through laser bond lines perpendicular to the welding direction. Fig. 6 A diagram of the failure probability of laser-welded specimens in the shear test for three different total lengths of the laser bond lines against applied shear force, Fig. 7 a diagram of the characteristic failure force of the laser-welded specimens against the total length of the laser bond lines, Fig. 8 a diagram of the determined empirical constant for bond strength per length, Fig. 9 a microscopic image of a cross-section of two substrates joined together by laser bond lines, Fig. 10 Three examples of fracture patterns for the failure of the weld joint when the failure shear force is exceeded, and Fig. 11 Three examples of fracture patterns in which one or both substrates have broken due to the application of force without prior failure of the weld joint.

[0075] In Fig. Figure 1 shows a perspective view of two substrates 3 and 4 connected by a laser bonding line 2. A first substrate 3 is placed on top of a second substrate 4, so that the two substrates 3 and 4 are in direct contact. The surface where the two substrates 3 and 4 touch is called the contact area A. i designated.

[0076] If the surfaces of the two substrates 3, 4 are smooth, the overlapping surfaces have a distance from each other that can no longer be determined optically. This is typically the case at a distance of less than approximately 250 nm. At such small distances, adhesive forces occur between the two substrates 3, 4 as soon as they are placed together. These adhesive forces occur in a region known as the contact area A. c is designated. The contact surface A c is smaller than the total contact area A i .

[0077] For hermetically sealing the connection of the two substrates 3, 4 in the area of ​​contact surface A c Laser welding is performed by introducing a laser bond line 2. Along the laser bond line 2, material is melted with an ultrashort pulse laser and then cools again, so that the two substrates 3, 4 bond together when they are in contact as in the area of ​​the contact surface A. c very closely adjacent to each other. In a laser bonding area A created by laser welding w The two substrates 3 and 4 are bonded together in a metallurgical manner, so that there is no longer a gap between them. The width of the laser bond lines 2 is thin, approximately 20 µm to 75 µm, so that in the Fig. 1 as an example of full-surface bonding of the substrates 3,4 only a very small part of the contact area A c or the contact surface A i additionally welded by laser treatment.

[0078] Surprisingly, it was found that the contribution to the shear strength of the connection between the two substrates 3, 4 by the laser bonding surface A w , despite the in the Fig. 1. The example shown has a very small area compared to the total contact area A. i and the contact surface A c , is much larger than the contribution of the adhesive forces in the area of ​​the contact surface A c The laser bonding area A w It can therefore be used not only to hermetically seal a gap existing between the two substrates, but also to increase the resistance of the connection to acting shear forces.

[0079] Fig. Figure 2 shows a top view of an embodiment of a hermetic enclosure 1. The enclosure has a length a, a width b and a height c (compare Fig. 3) on. In the housing 1, a functional area 20 is formed in the form of a cavity 21, into which a functional element 22, such as a sensor or a transponder, is hermetically encapsulated.

[0080] Typical dimensions of an enclosure are a = 5 mm, b = 5 mm, c = 2.5 mm, but larger and flatter (e.g. a = 10 mm, b = 5 mm, c = 0.9 mm) or more compact (a = 3 mm, b = 4 mm, c = 2 mm) are also possible.

[0081] To form the enclosure 1, a cover substrate 14 is placed on a base substrate 10 (compare Fig. 3) placed and touches the base substrate 10 at contact surface A i The contact area A i corresponds to an end face of 16 of the base substrate 10, compare Fig. 3.

[0082] The cover substrate 14 is hermetically sealed to the base substrate 10 via several laser bonding lines 2. These laser bonding lines 2 run parallel to the side walls of the cavity 21, which in the illustrated example is rectangular and therefore has four side walls. In this example, two bonding lines 2 run parallel to each of the side walls of the cavity, with the thickness of the side walls corresponding to a contact area width B. Only those bonding lines 2 that are not separated from each other by the functional area 20 or the cavity 21 are considered adjacent. In this example, the laser bonding lines 2 form two closed rectangular paths around the functional area 20.

[0083] The in Fig. The enclosure shown in Figure 2 was obtained from a wafer stack in which a wafer for the base substrate 10 and a wafer for the cover substrate 14 were placed on top of each other and bonded together. This resulted in a wafer stack comprising a multitude of interconnected enclosures 1. The laser bond lines 2 were applied across the entire width or length of the wafer stack. The individual enclosure 1, as shown in Figure 2, is formed by the individual wafers 1. Fig. The image shown in 2 was obtained by separating the numerous enclosures.

[0084] Fig. Figure 3 shows a cross-sectional view of the hermetic enclosure 1 of the Fig. 2 from the side along the in Fig. 2. Section line marked AA.

[0085] In the sectional view of the Fig. Figure 3 shows that the base substrate 10 in this embodiment consists of a base substrate 11 and an intermediate substrate 12. The base substrate 11 and the intermediate substrate 12 were hermetically bonded via several laser bond lines 2, analogous to the bond between the cover substrate 14 and the base substrate 10 or the intermediate substrate 11.

[0086] The side walls of the formed cavity 21 are formed by the intermediate substrate 12, and the bottom of the cavity 21 is formed by the bottom substrate 11. In the example shown, the functional element 22 is arranged inside the cavity 21 on the bottom substrate 11.

[0087] Fig. Figure 4 shows a section through laser bond lines 2 along the welding direction. The welding direction is the direction along which the laser beam was guided over the substrates 11, 12, 14 to be joined, with the individual pulses overlapping several times locally, so that a weld seam is formed by heat accumulation above the focal points (32). The cross-section of the seam is pear-shaped and is referred to as the welding pear 30. The welding pear 30 represents the area of ​​the substrates 11, 12, 14 that was treated by the respective laser pulse such that the material exceeded the glass transition temperature T. G or the melting temperature has been heated, allowing the adjacent substrates 11, 12, 14 to bond together. The scan speed, in conjunction with the pulse repetition rate of the ultrashort pulse laser, is selected such that a continuous laser bonding region is created in the area of ​​laser bond line 2.

[0088] The laser beam is focused such that a focal point 32 is placed at a distance T from the connection plane between the two respective substrates 11, 12, 14. Starting from the focal point 32, the energy transferred from the laser pulse to the respective substrate 11, 12, 14 then forms the welding bulb 30 with a height HL.

[0089] Fig. Figure 5 shows a cross-section through laser bond lines 2 perpendicular to the welding direction. This cross-sectional view shows that the respective laser bond lines 2 have a width w relative to the bonding plane between the substrates 11, 12, 14 to be joined—in this case, between the base substrate 11 and the intermediate substrate 12, and again between the intermediate substrate 12 and the cover substrate 14. Since the width of the welding bulbs 30 varies along their height HL, the width w of the laser bond lines 2 can be adjusted by selecting the depth T of the focal point 32 relative to the respective bonding plane. A distance H between any two adjacent laser bond lines 2, measured from center to center, is preferably chosen such that the laser bond lines 2 do not overlap. Accordingly, the distance H is greater than or equal to the width w.Furthermore, the aim is to make the enclosure 1 as compact as possible and accordingly to the contact surface width B, which here corresponds to the width of the side wall of the cavity 21, compare . Fig. 3. To choose as small as possible. Accordingly, the distance between two laser bonding lines 2 is preferably chosen to be no more than five times the width w.

[0090] Fig. Figure 6 shows a double-logarithmic plot of the cumulative failure probability of laser-welded specimens in a shear test for three different total lengths of the laser bond lines against the applied shear force in N. A first curve 101 shows the cumulative failure probability for 30 specimens with a total laser bond line length of 20 mm, a second curve 102 shows the cumulative failure probability for 30 specimens with a total laser bond line length of 40 mm, and a third curve 103 shows the cumulative failure probability for 30 specimens with a total laser bond line length of 60 mm.

[0091] Fig. Figure 7 shows a diagram of the characteristic failure force of the laser-welded specimens against the total length of the laser bond lines. A fitted affine function can be used to determine the empirical constant P. The slope of the function corresponds to the constant P. The y-intercept corresponds to that of a contact area A. c , compare Fig. 1. provided adhesive force.

[0092] Fig. Figure 8 shows a diagram of the determined empirical constant P for the bond strength per unit length for the three curves 101, 102, 103; compare Fig. 6. It can be seen that, within the error tolerance, the obtained values ​​for the constant p are independent of the laser bond line length of the respective test specimens.

[0093] Fig. Figure 9 shows a microscopic image of a cross-section of two substrates 10, 14 bonded together by laser bond lines 2, using borosilicate glass substrates 10, 14 as an example. The laser bond lines 2 are clearly visible due to the changes in refractive index that occur during heating and cooling.

[0094] Fig. Figure 10 shows three examples (a, b, and c) of fracture patterns for the failure of a welded joint between two substrates when the failure shear force is exceeded. It is clearly visible that the two substrates separated from each other along the weld seams or laser bond lines essentially without further damage.

[0095] Fig.Figure 11 shows three examples (a, b, c) of fracture patterns in which one or both substrates have fractured due to force without prior failure of the weld. It is clearly visible that the fracture lines do not run along the original surfaces of the substrates, but rather that the substrates themselves have been destroyed. Parts of the respective substrates have chipped off.

[0096] Although the present invention has been described using preferred embodiments, it is not limited to these, but can be modified in many ways. Reference symbol list A i Contact surface A c Touch contact surface A w Laser bonding surface 1 Enclosure 2 laser bonding lines 3 first substrate 4 second substrate 10 Base substrate 11 Soil substrate 12 Intermediate substrate 14 Cover substrate 16 Front surface 20 Functional area 21 Cavity 22 Functional element 30 welding torches 32 Focus Point A section line a length of enclosure b Wide enclosure c Height of enclosure B Contact surface width HL height laser bonding line T Depth Laser Bond Line w Wide laser bonding line H Distance between two laser bond lines 101 first curve 102 second curve 103 third curve KW cumulative probability of failure S Shear force p empirical constant Fv failure shear force L Laser bonding line length

Claims

[1] Method for designing a laser weld between a base substrate (10) and a cover substrate (14) of an enclosure (1), wherein the base substrate (10) has a functional area (20), and the cover substrate (14), which is in contact with the base substrate (10), covers the functional area (20), wherein the base substrate (10) and the cover substrate (14) are directly hermetically sealed together via at least one laser bond line (2), so that the functional area (20) is hermetically enclosed inside the formed enclosure (1), characterized by , that a minimum shear force F is required for the connection between the cover substrate (14) and the base substrate (10). min specified, which the laser welding should withstand, and that the sum of the lengths L ges all laser bonding lines (2) are chosen to be larger than a required minimum length L min the length of all laser bond lines (2), where L minis determined by dividing the given minimum shear force F min by an empirically determined force per laser bond line length P L min =F min / P, and that a contact surface width B, measured in the plane of an end face (16) of the base substrate (10) facing the cover substrate (14) as the shortest distance between the functional area (20) and the outer surface of the enclosure (1), is chosen such that a ratio J=A i / A w formed from a contact surface A i , where the base substrate (10) and the cover substrate (14) can touch, and a laser bonding area A swept over by the laser bonding lines (2) with a width w w on the end face (16) of the base substrate (10) facing the cover substrate (14) in the range of 1 to 10. [2] Method according to claim 1, characterized by, that a number N of closed paths of laser bond lines (2) with width w and a distance H between the centers of two adjacent laser bond lines (2) of at least width w is arranged around the functional area (20), wherein the number N is determined as the smallest number N for which the total length L ges all laser bond lines (2) formed from the number N multiplied by the length of an outline line which limits the functional area (20) is greater than the minimum length L min [3] Method according to claim 1 or 2, characterized by , that the distance H between the centers of two adjacent laser bond lines (2) with width w is selected in the range of 1 w to 5 w, preferably in the range of 1.01 w to 2.5 w and particularly preferably in the range of 1.05 w to 2 w. [4] Method according to any one of claims 1 to 3, characterized by , that the contact area width B is chosen in the range of 100 to 1000 µm. [5] Method according to any one of claims 1 to 4, characterized by , that the width w of the laser bond lines (2) is preferably chosen in the range of 30 µm to 60 µm in the range of 20 µm to 75 µm. [6] Method according to any one of claims 1 to 5, characterized by , that the force per laser bond line length P is empirically determined by producing several test specimens in which a first substrate (3) made of a cover substrate material is joined to a second substrate (4) made of a base substrate material with laser bond lines (2), wherein the total length L ges the laser bonding lines are chosen to be the same for the test specimens, the shear strength of the test specimens is determined by applying an increasing shear force to the connection of the first (3) and second substrate (4), determining the force at which the connection is destroyed and evaluating a failure probability distribution. [7] Method according to any one of claims 1 to 6, wherein, wherein the minimum shear force F min is specified in such a way that when producing several test specimens, in which a first substrate (3) made of a cover substrate material is joined with a second substrate (4) made of a base substrate material by laser bond lines (2) such that these are responsible for a minimum shear force F min are designed and when applying this minimal shear force F min more than 50%, preferably more than 75%, particularly preferably more than 90%, most preferably 95% of the specimens do not break along the contact surface due to failure of the weld joint, but break at other locations, in particular at an edge of one or more of the substrates (3, 4). [8] Hermetically sealed enclosure (1) comprising a base substrate (10) having a functional area (20) and a cover substrate (14) which is in contact with the base substrate (10) and covers the functional area (20), wherein the base substrate (10) and the cover substrate (14) are directly hermetically connected to each other via at least one laser bond line (2) and wherein the functional area (20) is hermetically enclosed inside the formed enclosure (1), characterized by , that a ratio J=A i / A w formed from a contact surface A i , where the base substrate (10) and the cover substrate (14) can touch, and a laser bonding area A swept over by at least one laser bonding line (2) with a width w w on the surface of the interface between base substrate (10) and cover substrate (14) lies in the range of 1 to 10, wherein a contact area width B, measured in the plane of the end face (16) of the base substrate (10) facing the cover substrate (14) as the shortest distance between the functional area (20) and the outer surface of the housing (1), lies in the range of 100 µm to 1000 µm. [9] Enclosure (1) according to claim 8, characterized by , that the area A swept by at least one laser bond line (2) w is selected such that the connection between the cover substrate (10) and the base substrate (14) has a failure shear force in the range of 10 N to 1000 N, preferably 50 N to 500 N, particularly preferably in the range of 100 N to 400 N. [10] Enclosure (1) according to claim 8 or 9, characterized by that the total length L ges the laser bonding lines (2) are selected according to a design method according to one of claims 1 to 6. [11] Enclosure (1) according to any one of claims 8 to 10, characterized by, that more than one laser bonding line (2) is present, wherein the laser bonding lines (2) have a width w and a distance H between the centers of two adjacent laser bonding lines (2) is selected in the range of 1 w to 5 w, preferably in the range of 1.01 w to 2.5 w and particularly preferably in the range of 1.05 w to 2 w. [12] Enclosure (1) according to any one of claims 8 to 11, characterized by , that the covering substrate (14) is designed as a transparent thin-film substrate, wherein the covering substrate (14) has a thickness of less than 200 µm, preferably less than 170 µm, particularly preferably less than 125 µm and preferably has a thickness greater than 10 µm, particularly preferably greater than 20 µm. [13] Enclosure (1) according to any one of claims 8 to 12, characterized by , that the cover substrate (14) and the base substrate (10) at the contact surface A idirectly adjacent to each other, so that the connection in the laser bonding area A swept by at least one laser bonding line (2) w is free from foreign materials, in particular free from bonding materials such as adhesives or glass frit or an absorbent layer. [14] Enclosure (1) according to any one of claims 8 to 13, characterized by, that the base substrate (10) comprises a planar bottom substrate (11) which forms the bottom surface of a functional area (20) designed as a cavity (21), and an intermediate substrate (12) which forms the side walls of the cavity (21) with an end face facing the cover substrate (14), and that the bottom substrate (11) and the intermediate substrate (12) are hermetically tightly connected to each other via at least one laser bond line (2), or that in the base substrate (10) a functional area (20) is formed in the form of a depression with a bottom surface and side walls which together with the cover substrate (14) as the cover surface form a cavity (21). [15] Enclosure (1) according to any one of claims 8 to 14, wherein the cover substrate (14) and / or the base substrate (10) consists of glass, glass ceramic, silicon, sapphire or a combination of the aforementioned materials. [16] Enclosure (1) according to any one of claims 8 to 15, characterized by, that the width w of the laser bond lines (2) is in the range of 20 µm to 75 µm, preferably 30 µm to 60 µm, and / or that the width w of all laser bond lines (2) over the total length L ges the laser bonding lines (2) vary by a maximum of 30%, preferably a maximum of 20%, particularly preferably a maximum of 10%. [17] Sensor unit and / or medical implant comprising a housing (1) according to at least one of claims 8 to 16 or obtained by design via a method according to one of claims 1 to 7.

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