Hermetically sealed housing and method for designing welded connection of such housing

Abstract

The invention relates to a method for arranging a laser welding connection between a base substrate (10) and a cover substrate (14) of a housing (1), the base substrate (10) having a functional region (20), the cover substrate (14) being in contact with the base substrate (10) and covering the functional region (20), the base substrate (10) and the cover substrate (14) being directly connected to one another in a gas-tight manner via at least one laser bonding wire (2), the functional region (20) is sealed in a gas-tight manner in the interior of the housing (1). According to the invention, a minimum shear force Fmin is preset for the connection between the cover substrate (14) and the base substrate (10), to which the laser welding will be carried out, for the total length of all the laser bonding wires (2), a minimum length Lmin is determined by a force per unit laser bonding wire length P, which is determined according to experience, and the minimum length Lmin is determined by a force per unit laser bonding wire length P, for the total length of all the laser bonding wires (2). And a contact surface width B is selected such that a ratio Ai / Aw formed by a contact surface Ai at which the base substrate (10) and the cover substrate (14) can touch each other, and a laser bonding surface Aw swept by a laser bonding line (2) having a width w, is in the range of 1 to 10, the ratio Ai / Aw being formed by the contact surface Ai, at which the base substrate (10) and the cover substrate (14). Other aspects of the invention relate to such a housing (1) and a sensor unit and / or a medical implant comprising such a housing (1).

Description

Technical Field

[0001] The invention relates to a hermetically sealed housing, comprising a base substrate having a functional area and a cover substrate, the base substrate having a functional area, the cover substrate being in contact with the base substrate and covering the functional area, wherein the base substrate and the cover substrate are directly connected to each other in a hermetically sealed manner via at least one laser bonding line, and wherein the functional area is hermetically enclosed in the interior of the formed housing. The invention also relates to a method for laying out a solder connection between the substrates and the use of such a housing. Background Art

[0002] Hermetically sealed housings are intended, for example, to protect one or more components inside the housing from adverse environmental conditions. Fields of application for such hermetically sealed housings may be, for example, electronic applications for protecting sensitive electronic components and optical applications for encapsulating optical components. Other applications are in particular in the fields of medical implants, microfluidic chips, augmented reality and mobile sensor technology (e.g. pressure sensors).

[0003] Transparent materials such as glass for housings are particularly desirable for use in optical applications. Furthermore, in electronic applications requiring wireless communication or wireless charging, glass materials have advantages over conventional metal housings, such as those made of titanium, because the glass material does not shield the radiation used.

[0004] An example of such a hermetically sealed housing is known from EP 3812352 A1. The housing comprises at least a base substrate and a cover substrate, which form a housing and enclose the functional area internally. The cover substrate and the base substrate, which are selected from glass materials, are connected to each other by performing laser bonding wires, for example.

[0005] A method for producing a transparent part for protecting an optical component using a laser method for producing a laser joining line is known from European Patent Document EP 3 012 059 B1.

[0006] In these known laser methods, two substrates are placed one on top of the other and any spacing or gap between the substrates that may still exist is sealed by laser welding, so that the connection between the two substrates is hermetically sealed.

[0007] The resulting housing must meet high mechanical requirements, especially when used as an implant. The degree of mechanical strength of the connection of two housing parts is the ability to withstand shear forces. The higher the stability of the connection, the higher the shear forces it can withstand without loosening. When connecting two substrates, the shear force resistance depends on the size of the contact surface at which the two substrates touch each other.

[0008] In order to ensure sufficient shear force resistance, known gas-tight housings therefore have relatively high wall thicknesses, which can be several millimeters. In addition to increasing the wall thickness, the components to be connected can also be designed so that they have a form-fitting connection. However, this also requires a lot of installation space and is expensive, especially when the components are made of glass or the like. This makes a particularly compact design of the gas-tight housing difficult. Summary of the invention

[0009] It can therefore be an object of the invention to provide a gas-tight housing which has particularly thin walls and at the same time meets mechanical requirements. Another object of the invention can be to provide a method for arranging welded connections between components of a housing, by means of which a particularly compact and at the same time sufficiently robust housing can be obtained based on predefined mechanical requirements.

[0010] A method for arranging laser welding between a base substrate and a cover substrate of a housing is proposed. The housing to be formed has at least a base substrate and a cover substrate, the base substrate having a functional area. The cover substrate is in contact with the base substrate and covers the functional area. The base substrate and the cover substrate are directly connected to each other in a hermetic and sealed manner via at least one laser bonding line, so that the functional area is hermetically enclosed in the interior of the housing formed. It is proposed that a minimum shear resistance F is predefined for the connection between the cover substrate and the base substrate. min , the laser weld should withstand the minimum shear force, and the total length of all laser joint lines L ges The required minimum length L is selected to be greater than the length of all laser bond lines. min , where the minimum shear force F is set min Divide by the empirically determined force per unit laser bond line length P to determine L min =F min / P,

[0011] And among them, The contact surface width B, measured in the plane of the end surface of the base substrate facing the cover substrate as the shortest distance between the functional area and the exterior of the housing, is selected such that the contact surface A i and laser bonding surface A w The composition ratio J=A i / A w In the range of 1 to 10, where the contact surface A i The base substrate and the cover substrate can touch each other, and the laser bonding surface A swept by the laser bonding line having a width w w Located at the end surface of the base substrate facing the cover substrate.

[0012] Preferably, N closed paths of laser joining lines having a width w and a spacing H between the midpoints of two adjacent laser joining lines of at least width w are arranged around the functional area, wherein the number N is determined as a minimum number N for which the total length L of all laser joining lines is obtained by multiplying the number N by the length of the contour line defining the functional area. ges Greater than the minimum length L min .

[0013] In the present application, the contact surface is the cross section of the mutually facing surfaces of the two substrates to be brought into contact. The contact surface is understood to be a sub-surface of the contact surface in which the distance between the two substrates is so small that it is no longer possible to measure this distance optically. In particular, in the region of the contact surface, the distance between the surfaces of adjacent substrates is less than 250 nm. In this case, the contact surface is usually greater than or equal to the contact surface.

[0014] In other words, firstly the two substrates are arranged adjacent to one another, i.e., for example stacked one on top of the other, wherein gravity presses the usually first substrate located on top onto the second substrate. The orientation above or below is merely descriptive here, since the substrates can of course adopt any orientation in space and an arrangement next to one another should not deviate from the scope of protection. The two substrates are usually arranged with their extended larger sides against one another.

[0015] If the two substrates are designed to be absolutely flat, i.e. completely without depressions, protrusions or cambers, which is only theoretically possible in an absolute state, the first and second substrates will touch each other over their entire surface. The two substrates would thus touch each other at all points of their surfaces that are aligned with each other. This is usually not possible in practical construction. In practice, even if the substrates are bent, tilted, curved, depressed or convex to a very small extent, complete contact can only be achieved in absolutely exceptional cases.

[0016] The functional area surrounded by the housing can be a cavity, in particular, for accommodating the functional element. The cavity has a bottom surface and side walls provided by the base substrate and has a top surface provided by the cover substrate. In this embodiment, the thickness of the side wall corresponds to the width of the contact surface.

[0017] In other examples of the housing, the functional area may be a functionalized area of ​​the base substrate. Such functionalization may be achieved, for example, by applying a coating and / or by surface structuring.

[0018] The functional area is hermetically sealed by the welded connection. In this context, hermetically sealed is understood to mean that the housing has a thickness of less than 1×10 -8 mbar·l / sec, preferably 1×10 -10 mbar·l / sec to 1×10 -9 Helium leak rates in the mbar·l / sec range.

[0019] The welded connection is produced by introducing at least one laser joining line or laser welding line. The welded connection is preferably produced using an ultrashort pulse laser. Typical pulse widths are in the range of 100 fs to 100 ps. A method for implementing such laser welding with one or more laser welding lines is known, for example, from EP 3 012 059 B1.

[0020] The laser weld line has a height HL in a direction perpendicular to its connection plane. The connection plane is the direction in which adjacent or successively consecutive beam points are arranged. Usually, laser welding is performed from a top-down perspective, i.e. the substrate stack is, for example, located on a surface, such as a table, and the laser is directed from above through at least the uppermost substrate layer or through a plurality of substrate layers to the location of the beam focus. Therefore, the height HL is 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.

[0021] The width w of the area modified by the laser beam varies along the depth T of the processed area, i.e. along the direction of the laser beam. The information given in the present application about the width w of the laser weld line relates to the plane of the contact surface between the substrates connected by the laser weld line. In this plane defined in this way, the width w is understood to be the area within which a material change is caused by the laser treatment. This material change caused by the laser treatment is caused by heating above the glass transition temperature T g The laser treatment is carried out by bringing the two substrates to a material connection in the processing region without the need for additional connecting material. In the case of optically transparent materials, the material changes caused by the laser treatment can be detected, for example, by measuring the refractive index deviation relative to the untreated material. For this purpose, for example, a cross section can be examined with an optical microscope. In particular, a refractive index greater than 1×10 -5 The refractive index change of the material is used as a marker for the change in the material and is used to determine the width w accordingly. A microscopic image of such a cross section is Fig.10 and described in detail below.

[0022] By means of laser welding methods, a plurality of materials can be joined to one another, wherein at least the substrate pointing in the direction of the laser source should be at least partially transparent to the laser light used.

[0023] The generated laser welding lines or laser joining lines are arranged around the functional area so that a closed area surrounding the functional area is formed by the laser joining surface in the contact plane corresponding to the end face of the base substrate facing the cover substrate. In the case of a rectangular housing, one or more straight laser joining lines are arranged on each of the four sides defining the functional area, wherein the laser joining lines can overlap in the four corners. The one or more laser joining lines can in particular extend parallel to the side walls. It is also possible to arrange one or more closed laser joining lines, for example, parallel to the contour line of the functional area.

[0024] In order to hermetically close the functional area, it is necessary that at least one laser joining line extends around the functional area without any gaps. However, this criterion can also be met by a plurality of individually written laser joining lines, which overlap at the intersection and simultaneously form a closed path around the functional area. In the method, each such closed path corresponds to a laser joining line arranged around the functional area, wherein in the case of exactly one such path the number N=1, for example in the case of exactly two closed paths the number N=2. If a single closed laser joining line of this type is sufficient to meet the predefined minimum shear force F min With a minimum length L min , then the number N of laser joining lines surrounding the functional region can be selected to be N=1. In this case, there are no adjacently arranged laser joining lines as defined by the method.

[0025] Preferably, a plurality of laser joining lines are introduced in the form of a plurality of such closed paths, wherein adjacent laser joining lines extending in an area defined by the respective contact surface width are preferably arranged parallel to one another. Laser joining lines separated from one another by functional areas are not considered adjacent here.

[0026] Preferably, the spacing H between the centers of two adjacent laser joining lines having a width w is selected in the range of 1w to 5w, preferably in the range of 1.01w to 2.5w, particularly preferably in the range of 1.05w to 2w. This avoids overlapping of the laser joining lines, except for any possible crossings of different laser joining lines.

[0027] By providing a spacing between two adjacent laser joining lines, in particular running parallel to one another, which is at least equal to the width of the laser joining lines, it is achieved that the material of the substrate is processed only once, except for the intersection points of the laser joining lines (for example at the four corners around the rectangular functional area).

[0028] On the other hand, the upper limit set for the spacing allows a particularly compact arrangement of the laser joining surfaces. The contact surface width B can thus be selected to be particularly small, but still provide sufficient space for forming the laser joining line.

[0029] Preferably, the contact surface width B is selected in the range of 100 μm to 1000 μm. The exact selection of the contact surface width B depends on various criteria, such as the material of the base substrate, the material of the cover substrate, the size of the housing and / or the type of functional area. If a cavity is provided as the functional area, the contact surface width B predetermines the thickness of the side wall of the functional area. The contact surface width is preferably selected to be at least large enough to ensure that the mechanical stability of the side wall is sufficiently high.

[0030] Preferably, the contact surface width B is selected to be greater than 200 μm, particularly preferably greater than 300 μm, more preferably greater than 400 μm, most preferably greater than 500 μm.

[0031] However, the larger the contact surface width B is selected, the larger the housing becomes relative to the enclosed functional area. Therefore, preferably, the contact surface width B should be selected to be less than 750 μm, particularly preferably less than 500 μm, and particularly particularly less than 400 μm. The minimum contact surface width is limited by the width w of the laser joining line and is therefore preferably greater than 30 μm, particularly preferably greater than 50 μm, and particularly particularly preferably greater than 100 μm.

[0032] The width w of the laser joining line is preferably selected in the range of 20 μm to 75 μm, particularly preferably in the range of 30 μm to 60 μm. For example, the width w is selected to be 50 μm. This range is optimally selected so that sufficient energy can be introduced via the laser to weld the two substrates. It is particularly advantageous here that the width w remains essentially constant over the entirety of the laser joining line. Therefore, it is preferred that the width w of all laser joining lines is within the total length L of the laser joining line. ges The width w varies by at most 30%, particularly preferably by at most 20%, and most preferably by at most 10%. Since the width w is related to the position of the focal point of the laser relative to the contact plane, it is preferred to use a laser processing method by precisely controlling the distance between the laser focal point and the contact plane. Suitable methods are known, for example, from EP3012059B1.

[0033] For the most compact housing possible, the contact surface A i and laser bonding surface A w The obtained volume coefficient J=A i / A w Should be selected as small as possible, where the contact surface A i The base substrate and the cover substrate can touch each other, and the laser bonding surface A w The at least one laser joining line having a width w is swept through. Therefore, it is particularly preferred that the volume factor J is selected in the range of 1-5, more preferably in the range of 1-2.

[0034] According to the proposed method, the total length of the introduced laser joint line and thus the laser joint surface Aw The intended resistance is chosen to be just large enough that the soldered connection offers shear forces acting on it. The term shear forces is here in particular understood to mean forces acting on the substrates perpendicularly to the plane of the connection of the two substrates and which would cause the substrates to move relative to each other without a connection between them.

[0035] The inventors have found that the shear resistance of the welded connection increases linearly with the total length of the non-overlapping laser joining lines. For the non-overlapping criterion, small overlaps at the intersections of the laser joining lines, for example, which run at right angles to one another and are arranged around a rectangular functional area, can be neglected here, since the area of ​​these intersections is very small. Therefore, the minimum shear force F that the welded connection is to withstand is set. min When P is the empirically determined constant for the force increase per unit length, the required minimum length of the total laser bond line can be determined by the following relationship:

[0036] L min =F min / P.

[0037] The total length of the introduced laser bonding line L ges In particular, in the case of laser joining lines extending parallel around the functional area, it can be determined as an integer multiple of the length of the contour line around the functional area. Since the laser joining lines are not designed to overlap, a small increase in the actual length of the surrounding laser joining line can again be neglected here due to the small width of the laser joining line. Small additional joining line segments that may occur when producing a plurality of housings by processing wafers and subsequently separating the housings can also be neglected due to their small length.

[0038] The constant P is specific to the material of the substrates to be connected and to the selected laser joining line width and can be determined empirically in a simple manner by producing a plurality of, for example, 30 test pieces, in which a first substrate made of the cover substrate material is joined to a second substrate made of the base substrate material by means of a laser joining line, wherein the total length L of the laser joining line is set to ges The shear resistance of the specimen is then determined by applying an increased shear force to the connection of the first substrate and the second substrate, determining the force at which the connection breaks, and evaluating the failure probability distribution.

[0039] Minimum shear force F that the welded connection should withstand min The force is preferably not greater than the required force, so that the welded connection itself and thus the housing as a whole can be designed as compactly as possible. Preferably, the presetting is based on the mechanical requirements of the housing. One criterion can be, in particular, the minimum shear force in relation to the resistance of the substrate to other forces. Preferably, the minimum shear force F is set to this end. minIt is provided that when producing a plurality of test pieces, a first substrate made of the cover substrate material is connected to a second substrate made of the base substrate material by laser welding lines, so that these laser welding lines are designed for a minimum shear force F min , and make the minimum shear force F min When the welding connection fails, more than 50%, preferably more than 75%, particularly preferably more than 90%, and most preferably 95% of the test specimens do not break along the contact surface due to welding connection failure, but break at other locations, especially at one or more edges of the substrate.

[0040] To determine the failure rate, a plurality of identical test specimens, for example 30 test specimens, can be produced in a similar manner to the determination of the empirical constant P, in which two substrates are welded to one another by introducing a laser joining line. The total length of the laser joining line is determined according to the shear force F to be tested. min The test piece is then gradually subjected to the shear force. The location of the mechanical failure of the test piece can be determined simply by visual inspection of the test piece. If the solder connection fails, the individual substrates are separated again, but there is essentially no further damage. If the number of test pieces that do not break along the contact surface due to the failure of the solder connection is within the expected range, for example greater than 75%, the shear force F of the test is min If the selection is correct, repeat the test for a higher or lower shear force to be tested, depending on the test results.

[0041] After the solder connection has been laid out, the steps for producing the housing can follow. These steps may include, in particular, providing the substrates and, if necessary, cleaning the surfaces of the substrates; placing the substrates on top of one another, if necessary, introducing functional elements into the functional region; and introducing the laser bonding wires.

[0042] In particular, it can be provided during production that a plurality of housings are produced in one process. For this purpose, firstly, instead of a substrate, a large wafer cut to the final size of the housing is provided, which is stacked one on top of the other in layers and connected to one another by laser welding. The individual housings are then separated by cutting the resulting wafer stack. In such a process, it can be provided that the introduced laser bonding lines are written along a grid pattern, wherein a functional area is respectively surrounded by four laser bonding lines forming a rectangle.

[0043] Another aspect of the present invention provides a hermetically sealed enclosure. The proposed hermetically sealed enclosure comprises a base substrate and a cover substrate, the base substrate having a functional region, the cover substrate being in contact with the base substrate and covering the functional region, wherein the base substrate and the cover substrate are directly hermetically sealed to each other via at least one laser bonding line, and wherein the functional region is hermetically enclosed within the formed enclosure. It is also provided that:

[0044] By contact surface A iand laser bonding surface A w The composition ratio J=A i / A w In the range of 1 to 10, where the contact surface A i The base substrate and the cover substrate can touch each other, and the laser bonding surface A swept by at least one laser bonding line having a width w w Located at the end surface of the base substrate facing the cover substrate, wherein The contact surface width B, which is the shortest distance between the functional region and the outside of the housing, measured in a plane of the end surface of the base substrate facing the cover substrate is in the range of 100 μm to 1000 μm.

[0045] The proposed housing is particularly compact since the contact surface width B is designed such that the laser joint surface A w Occupies the entire contact surface A i as large a portion as possible.

[0046] In the case of a gas-tight housing obtained by laser welding of substrates known in the prior art, it is assumed that a large part of the mechanical stability is provided by the largest possible contact surface and that the laser joint surface is essentially required to ensure a gas-tight seal of the functional area. i Compared with laser bonding surface A w Usually small, so it was previously assumed that the laser joint surface A w The contribution of the material itself to mechanical stability, especially shear resistance, is very small.

[0047] Furthermore, it was surprisingly found that maximizing the shear resistance of the welded connection between the two base plates is not advantageous, since in this case the housing breaks uncontrollably when subjected to large mechanical forces at other locations. Therefore, further weld extension does not contribute to improving the overall strength of the housing. Furthermore, a weld that is "unnecessary" in this way requires a larger contact surface and thus increases the "footprint" of the housing. It is therefore preferred to predetermine not only a lower limit but also an upper limit for the shear resistance.

[0048] Preferably, for this purpose, the laser joining surface A swept by at least one laser joining line is w The connection between the cover substrate and the base substrate is selected such that it has a shear failure 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.

[0049] Preferably, the total length L of the laser bonding line of the housing is ges It is particularly preferred that the minimum shear force F that the laser welding should withstand is set to min Corresponding to failure shear forces in the range of 10N to 1000N.

[0050] Since the housing can be obtained by using one of the described methods, features described in one of the methods also apply to the housing and vice versa features disclosed within the scope of the housing also apply to the method.

[0051] Preferably, welding is performed by means of a plurality of laser joining lines, wherein the laser joining lines have a width w and the spacing H between the centers of two adjacent laser joining lines is selected in the range of 1w to 5w, preferably in the range of 1.01w to 2.5w, particularly preferably in the range of 1.05w to 1.5w.

[0052] The width w of the laser joining line is preferably selected in the range of 20 μm to 75 μm, particularly preferably in the range of 30 μm to 60 μm. For example, the laser joining line is 50 μm wide. It is particularly advantageous here that the width w remains essentially constant over the entirety of the laser joining line. It is therefore preferred that the width w of all laser joining lines is within the total length L of the laser joining line. ges The above variation is at most 30%, particularly preferably at most 20%, most preferably at most 10%.

[0053] The housing is preferably designed to be as compact as possible. This is achieved by keeping the portion of the contact surface that is not occupied by the laser bonding surface as small as possible and thus also making the contact surface width B as small as possible. For this purpose, it is preferred that the end surface of the base substrate facing the cover substrate (which corresponds to the contact surface A) i ) is covered by the laser bonding line, and J is therefore in the range of 1 to 5. Particularly preferably, the contact surface A i At least half of is covered by the laser bonding line, wherein J is in the range of 1 to 2 in this case.

[0054] The cover substrate is preferably designed as a transparent thin-layer substrate, wherein the cover substrate has a thickness of less than 200 μm, preferably less than 170 μm, particularly preferably less than 125 μm, and preferably has a thickness of more than 10 μm, particularly preferably more than 20 μm. This means that the dimensions of the housing can also be implemented particularly compactly in the stacking direction of the substrates.

[0055] The cover substrate can be provided in the form of a film substrate and welded to the base substrate. Alternatively, a substrate of greater thickness can be thinned by removing material after being connected to the base substrate.

[0056] The cover substrate and the base substrate are at the contact surface A i directly abut each other, so that the laser bonding surface A swept by at least one laser bonding line wThe connection in the housing is free of foreign materials, in particular, free of connection materials such as adhesives, glass frits or absorbent layers. Since no foreign materials are used when sealing the housing, contamination of the functional area, for example due to components of the adhesive, is avoided.

[0057] The functional area can be configured as a cavity. Such a cavity is preferably configured to accommodate a functional element, so that one or more functional elements can be accommodated in the cavity of such a housing. The cavity has a bottom surface and side walls provided by the base substrate and has a top surface provided by the cover substrate. In this embodiment, the thickness of the side wall corresponds to the contact surface width.

[0058] The base substrate can have a flat bottom substrate, which forms the bottom surface of the functional region configured as a cavity, and an intermediate substrate, which forms the side wall of the cavity with the end surface facing the cover substrate. The bottom substrate and the intermediate substrate are preferably connected to each other in a hermetically sealed manner via at least one laser bonding line. In particular, the method described herein can be used similarly to lay out this welding connection, and this welding connection can be laid out similarly to the connection between the cover substrate and the base substrate described herein.

[0059] Alternatively or additionally, the base substrate can be configured as a functional region in the form of a depression with a bottom surface and side walls, which together with the cover substrate as the top surface form a cavity. Such a depression can be formed, for example, by grinding or etching.

[0060] In other examples of the housing, the functional area may be a functionalized area of ​​the base substrate. Such functionalization may be achieved, for example, by applying a coating and / or by surface structuring.

[0061] The cover substrate and / or the base substrate are preferably made of glass, glass ceramic, silicon, sapphire or a combination of the above materials. In particular, borosilicate glass is suitable as the glass material.

[0062] The invention also relates to the use of the proposed housing as a housing for sensor units and / or medical implants. In these applications, the gas-tight seal of the housing and the compact dimensions that can be achieved are particularly advantageous. In the case of a contact surface width of, for example, 500 μm and a very small wall thickness, the housing is only insignificantly larger than the functional element accommodated therein.

[0063] Furthermore, the sensor unit and / or the medical implant accordingly comprises one of the housings described herein. Preferably, the housing has a cavity which surrounds the functional elements of the sensor unit and / or the medical implant.

[0064] One example of a housing comprises a bottom substrate and an intermediate substrate and a cover substrate, the bottom substrate and the intermediate substrate together forming a base substrate. All substrates consist of borosilicate glass, for example available under the name BOROFLOAT® 33. The bottom 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 5 mm respectively. By choosing the contact surface width B to be 500 μm, a cavity with side walls and a top wall having a thickness of 500 μm is provided.

[0065] Example for determining the empirical parameter P: Test specimens were produced in which two substrates were placed one on top of the other, which were made of a float borosilicate flat glass named BOROFLOAT® 33 with a length and width of 5 mm and a thickness of 1.1 mm. In order to verify the assumption that the shear force is linear with the total length of the laser bond line, the total length L was written in the first type 1. ges The total length L is written in the second type Typ 2. ges The total length L is 40 mm for the laser bonding wire and is written in the third type Typ 3. ges A laser bonding wire of 60 mm. The laser bonding wire can be introduced in principle in any desired geometry. In this example, half of the bonding wire length is written in a first direction and the other half is written in a second direction perpendicular thereto, so that a "+" shape is formed. The overlap of the laser bonding wires in the center of this cross is negligible due to its small surface.

[0066] 30 specimens of each of the three types were produced and the shear force at which the connection between the two substrates fails was determined in each case. For this purpose, the following device was used: in this device, two flat plates placed one above the other can be displaced relative to each other with a defined force, i.e. sheared. In each flat plate, a depression is arranged, the shape and depth of which correspond to the dimensions of the substrate, except for small tolerances. The side walls of the depression are therefore in close contact with the side faces of the respective substrate, respectively. In order to determine the shear force at which the connection between the two substrates of one of the specimens fails, the specimen is placed between the two flat plates and the two plates are displaced relative to each other at a rate of 1.5 mm / min, and the force is measured. When the connection fails, the specimen no longer resists displacement, which is known from the sudden drop in the measured force. The shear force at which the connection fails is therefore the highest force obtained when the two flat plates are displaced or sheared.

[0067] The measurement is repeated for all specimens, where the shear force at which the connection between the two substrates of the specimen fails is recorded. The cumulative probability KP is measured in Figure 6 The data are presented in double logarithmic form.

[0068] By adjusting the parameters of the distribution function p(F) of the cumulative failure probability under shear force F, the failure shear force F can be determined. V , where the corresponding specimen type fails at this failure shear force. The distribution function p(F) is given by:

[0069] The parameter z represents the width of the distribution function and can be obtained by adjusting the parameters.

[0070] For the three specimen types, the following values ​​for the failure shear force F were obtained for a 95% confidence interval: V The result is that Figure 7 The total length L of the laser bonding line is also ges The function renders: Type 1: F V =107.9 (101.8 … 114.3) N; Type 2: F V =144.1 (139.6 … 148.8) N; Type 3: F V =219.6 (206.6 … 233.6) N.

[0071] By fitting the affine function, it can be easily seen that the sample has a failure shear force of about 45 N, which is not equal to zero, without laser welding, that is, the length of the laser joint line is 0. This basic contribution to the shear force is attributed to the c It can also be seen that the shear resistance increases by about 2.8N for each mm of laser bond line.

[0072] For both specimen types 1 to 3, the material pairs used resulted in an empirical constant P of 2.8 N / mm.

[0073] Since this involves a linear relationship, it is sufficient to carry out this measurement on a single sample type of the material pair to be analyzed to determine the constant P empirically.

[0074] It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the respectively stated combination but also in other combinations or alone, without departing from the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Preferred exemplary embodiments and implementations of the invention are shown in the drawings and are explained in more detail in the following description, wherein the same reference numerals refer to the same or similar or functionally identical components or elements.

[0076] The accompanying drawings schematically show: Figure 1 A perspective view of two substrates connected by laser bonding wire; Figure 2 A top view of the airtight housing; Figure 3 A sectional view of the side of the airtight housing; Figure 4 is a cross-sectional view through the laser joint line along the welding direction; Figure 5 is a cross-sectional view through the laser joint line perpendicular to the welding direction; Figure 6 is a graph of failure probability of laser welded test specimens versus applied shear force in shear tests conducted on laser weld lines of three different total lengths; Figure 7 is a graph of representative failure force of laser welded specimens versus total length of the laser joint line; Figure 8 A graph of determined empirical constants for joint strength per unit length; Fig. 9 is a microscope photograph of a cross section of two substrates connected to each other by a laser bonding wire; Fig.10 Three examples of fracture patterns for welded joint failure when the failure shear force is exceeded; Fig.11 Three examples of fracture patterns where one or both substrates break apart due to force without premature solder connection failure. DETAILED DESCRIPTION

[0077] Figure 1 A perspective view of two substrates 3 and 4 connected by a laser bonding line 2 is shown. Here, the first substrate 3 is placed on the second substrate 4 so that the two substrates 3 and 4 are directly touching. The surface where the two substrates 3 and 4 touch is called the contact surface A. i .

[0078] If the surfaces of the two substrates 3, 4 are smooth, the surfaces lying one above the other are spaced apart from one another by a distance which can no longer be determined optically. This is usually the case when the distance is less than about 250 nm. With such a small distance, adhesion forces already occur between the two substrates 3, 4 when they are placed. These adhesion forces occur at the so-called contact surface A. c In the area of ​​​​the contact surface A c Smaller than the entire contact surface A i .

[0079] In order to make the two substrates 3 and 4 contact each other at the contact surface A cThe laser welding is performed by introducing a laser joining line 2. Along the laser joining line 2, the material is melted by means of an ultrashort pulse laser and cooled again, so that the two substrates 3, 4 are connected at their contact surface A. c The laser joint surface A produced by laser welding is connected together when they are closely adjacent to each other in the area. w In the embodiment, the two substrates 3, 4 are materially connected to each other so that there is no longer a gap between the substrates 3, 4. The width of the laser bonding line 2 is approximately 20 μm to 75 μm thin, so that Figure 1 In the full-surface connection of the substrates 3 and 4 shown as an example in FIG. 1 , only the contact surface A is welded by laser processing. c Or contact surface A i Very small portion.

[0080] Surprisingly, despite Figure 1 The entire contact surface A in the example shown i and contact surface A c In comparison, the laser bonded surface A w The surface of the two substrates 3 and 4 is very small, but the surface A w The contribution of the connection to the shear resistance is much greater than that of the contact surface A c The contribution of adhesion in the area of ​​laser bonding surface 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 shear forces acting thereon.

[0081] Figure 2 FIG. 1 shows a top view of an embodiment of a gas-tight housing 1. The housing has a length a, a width b and a height c (see FIG. Figure 3 ). A functional region 20 is formed in the housing 1 in the form of a cavity or hollow space 21 , into which a functional element 22 , for example a sensor or a transponder, is encapsulated in a gas-tight manner.

[0082] Typical dimensions of the housing are a=5 mm, b=5 mm, c=2.5 mm, but larger and flatter (eg a=10 mm, b=5 mm, c=0.9 mm) or more compact (a=3 mm, b=4 mm, c=2 mm) dimensions are also possible.

[0083] In order to form the housing 1, the cover substrate 14 is placed on the base substrate 10 (see Figure 3 ) and on contact surface A i The contact surface A touches the base substrate 10. i Corresponding to the end surface 16 of the base substrate 10, see Figure 3 .

[0084] The cover substrate 14 is connected to the base substrate 10 in a hermetically sealed manner via a plurality of laser bonding lines 2. The laser bonding lines 2 run parallel to the side walls of the cavity 21, wherein in the example shown, the cavity 21 is rectangular and has four side walls. In this example, two bonding lines 2 each run parallel to one of the side walls of the cavity, wherein the thickness of the side wall corresponds to the contact surface width B. Only bonding lines 2 that are not separated from each other by a functional region 20 or a cavity 21 are considered to be adjacent to each other. In this example, the laser bonding lines 2 form two closed rectangular paths around the functional region 20.

[0085] Figure 2 The housing shown in FIG. 1 is obtained from a wafer stack, wherein a wafer for a base substrate 10 and a wafer for a cover substrate 14 are placed one above the other and connected to one another. The wafer stack thus obtained comprises a plurality of housings 1 connected to one another. In this case, the laser bonding lines 2 are respectively implemented over the entire width or length of the wafer stack. Figure 2 The single housing 1 shown in FIG. 1 is obtained by dividing a plurality of housings.

[0086] Figure 3 Shown along Figure 2 The section line marked with AA Figure 2 A side sectional view of the airtight housing 1 is shown.

[0087] exist Figure 3 As can be seen from the cross-sectional view of FIG. 1 , the base substrate 10 in this embodiment is composed of a bottom substrate 11 and an intermediate substrate 12. The bottom substrate 11 and the intermediate substrate 12 are hermetically sealed connected via a plurality of laser bonding lines 2 in the same manner as the connection between the cover substrate 14 and the base substrate 10 or the intermediate substrate 11.

[0088] The side walls of the formed cavity 21 are formed here 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 on the bottom substrate 11 in the cavity 21.

[0089] Figure 4 A section through the laser joining line 2 is shown along the welding direction. The welding direction is the direction in which the laser beam is guided on the substrates 11, 12, 14 to be connected, wherein the individual pulses overlap locally several times, so that a weld seam is produced due to the heat accumulation above the focus (32). The cross section of the weld seam is pear-shaped and is referred to as a weld pear 30. The weld pear 30 is a region of the substrates 11, 12, 14 that is processed by the corresponding laser pulses so that the material is heated above the glass transition temperature T Gor melting temperature and adjacent substrates 11 , 12 , 14 can each be connected by material bonding. In this case, the scanning speed is selected in conjunction with the pulse repetition rate of the ultrashort pulse laser so that a continuous laser joining region is produced in the region of the laser joining line 2 .

[0090] The laser beam is focused in such a way that the focus 32 is located at a distance T from the joining plane between the two respective substrates 11 , 12 , 14 . Starting from the focus 32 , a weld pear 30 with a height HL is then formed by the energy transmitted to the respective substrate 11 , 12 , 14 by the laser pulses.

[0091] Figure 5 A sectional view through the laser joining line 2 perpendicular to the welding direction is shown. In this sectional view, it can be seen that the respective laser joining line 2 has a width w with respect to the connection plane between the respective substrates 11, 12, 14 to be connected, in this case between the bottom substrate 11 and the intermediate substrate 12 and between the intermediate substrate 12 and the cover substrate 14. Since the width of the welding pear 30 varies along the height HL of the welding pear 30, the width w of the laser joining line 2 can be set accordingly by selecting the depth T of the focal point 32 with respect to the respective connection plane. The spacing H between two respectively adjacent laser joining lines 2, respectively measured from one center to the other, is preferably selected so that the laser joining lines 2 do not overlap. Accordingly, the spacing H is greater than or equal to the width w. In addition, it is also intended to implement the housing 1 as compactly as possible and accordingly select the contact surface width B to be as small as possible, which corresponds here to the width of the side walls of the cavity 21, see Figure 3 Accordingly, the distance between two laser joining lines 2 is preferably selected to be at most five times the width w.

[0092] Figure 6 A double logarithmic diagram of the cumulative failure probability of laser welded specimens in shear tests with three different total lengths of laser joint lines is shown versus the applied shear force in N. A first curve 101 shows the cumulative failure probability of 30 specimens with a total laser joint line length of 20 mm, a second curve 102 shows the cumulative failure probability of 30 specimens with a total laser joint line length of 40 mm, and a third curve 103 shows the cumulative failure probability of 30 specimens with a total laser joint line length of 60 mm.

[0093] Figure 7 A graph showing the characteristic failure force of a laser welded specimen versus the total length of the laser joint line is shown. An empirical constant P can be determined using a fitted affine function. The slope of the function corresponds to the constant P. The y-intercept corresponds to the contact surface A. c (See Figure 1 ) provides adhesion.

[0094] Figure 8 For three curves 101, 102, 103 (see Figure 6 ) Graph of a specific empirical constant P for the joint strength per unit length. It can be seen that the value of the constant p obtained is independent of the laser joint line length of the corresponding specimen within the error range.

[0095] Fig. 9 The example of substrates 10, 14 made of borosilicate glass shows a microscope image of a cross section of two substrates 10, 14 connected to one another by a laser bonding line 2. The laser bonding line 2 can be clearly seen by the change in the fracture coefficient that occurs during heating and cooling again.

[0096] Fig.10 Three examples a, b and c of fracture patterns of failure of a welded connection between two substrates when the failure shear force is exceeded are shown. It can be easily seen that in this case the two substrates are separated from each other substantially along the weld or laser joint line without further damage.

[0097] Fig.11 Three examples a, b, c of fracture images are shown in which one or both substrates break apart due to force without premature failure of the soldered connection. In each case, it can be easily seen that the fracture line does not extend along the original surface of the substrate here, but that the respective substrate itself is damaged. In this case, parts of the respective substrate are removed.

[0098] Although the present invention has been described based on preferred embodiments, the invention is not limited thereto but can be modified in various ways.

[0099] Reference numerals list A i Contact surface A c Contact surface A w Laser bonding surface 1 Housing 2 Laser bonding wire 3. First substrate 4 Second substrate 10 Base substrate 11 Bottom substrate 12 Intermediate substrate 14 Cover substrate 16 End face 20 Functional Areas 21 Cavity 22 Functional elements 30 welding pear 32 Focus A Section Line A Length of housing B Width of housing C Height of housing B Width of contact surface HL Height of laser bonding line T Depth of laser bond line W Width of laser bonding line H is the distance between two laser bonding lines. 101 First Curve 102 Second Curve 103 The Third Curve KW Cumulative failure probability S Shear force P empirical constant F V Failure shear force L is the length of the laser bond line.

Claims

1. A method for arranging laser welding between a base substrate (10) and a cover substrate (14) of a housing (1), wherein: The base substrate (10) has a functional area (20), and the cover substrate (14) 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 connected to each other in an airtight manner via at least one laser bonding line (2), so that the functional area (20) is airtightly enclosed inside the formed housing (1), characterized in that a minimum shear force F is preset for the connection between the cover substrate (14) and the base substrate (10). min , the laser weld should withstand the minimum shear force, and The sum of the lengths of all laser bonding lines (2) is L ges is selected to be greater than the required minimum length L of all laser bond lines (2) min , where the minimum shear force F is set min Divide by the empirically determined force per unit laser bond line length P to determine L min : L min =F min / P, and The contact surface width B, which is the shortest distance between the functional area (20) and the outer side of the housing (1), measured in the plane of the end surface (16) of the base substrate (10) facing the cover substrate (14), is selected so that the contact surface A i and laser bonding surface A w The composition ratio J=A i / A w In the range of 1 to 10, wherein the contact surface A i The base substrate (10) and the cover substrate (14) can touch each other, and the laser bonding surface A swept by the laser bonding line (2) having a width w w Located at the end surface (16) of the base substrate (10) facing the cover substrate (14).

2. The method according to claim 1, characterized in that: N closed paths of laser joining lines (2) having a width w and a spacing H between the centers of two adjacent laser joining lines (2) of at least width w are arranged around a functional area (20), wherein the number N is determined as a minimum number N for which the total length L of all laser joining lines (2) is obtained by multiplying the number N by the length of a contour line defining the functional area (20). ges Greater than the minimum length L min .

3. The method according to claim 1 or 2, characterized in that: The distance H between the centers of two adjacent laser joining lines ( 2 ) having a width w is selected in the range of 1w to 5w, preferably in the range of 1.01w to 2.5w, particularly preferably in the range of 1.05w to 2w.

4. The method according to any one of claims 1 to 3, characterized in that The contact surface width B is selected within the range of 100 μm to 1000 μm.

5. The method according to any one of claims 1 to 4, characterized in that The width w of the laser bonding line (2) is selected in the range of 20 μm to 75 μm, preferably in the range of 30 μm to 60 μm.

6. The method according to any one of claims 1 to 5, characterized in that The force per unit laser bond line length P is determined empirically by manufacturing a plurality of test pieces, wherein a first substrate (3) made of a cover substrate material is connected to a second substrate (4) made of a base substrate material via a laser bond line (2), wherein the total length L of the laser bond line is ges The shear resistance of the specimens is determined by applying an increased shear force to the connection between the first substrate (3) and the second substrate (4), determining the force at which the connection is broken, and evaluating a failure probability distribution.

7. The method according to any one of claims 1 to 6, characterized in that The minimum shear force F min It is provided that when producing a plurality of test pieces, a first substrate (3) made of a cover substrate material is connected to a second substrate (4) made of a base substrate material via laser welding lines (2), so that these laser welding lines are designed for a minimum shear force F min , and so that the minimum shear force F is applied min When the welding connection fails, more than 50%, preferably more than 75%, particularly preferably more than 90%, and most preferably 95% of the test pieces do not break along the contact surface due to welding connection failure, but break at other locations, especially at the edges of one or more of the substrates (3, 4).

8. A hermetically sealed housing (1), comprising a base substrate (10) and a cover substrate (14), wherein the base substrate has a functional area (20), and the cover substrate 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 connected to each other in an airtight manner via at least one laser bonding line (2), and wherein the functional area (20) is airtightly enclosed inside the formed housing (1), characterized in that By contact surface A i and laser bonding surface A w The composition ratio J=A i / A w In the range of 1 to 10, wherein the contact surface A i The base substrate (10) and the cover substrate (14) can touch each other, and the laser bonding surface A swept by at least one laser bonding line (2) having a width w w Located at a surface of an interface between the base substrate (10) and the cover substrate (14), wherein a contact surface width B as the shortest distance between the functional area (20) and the outer side of the housing (1) measured in a plane of an end surface (16) of the base substrate (10) facing the cover substrate (14) is in a range of 100 μm to 1000 μm.

9. The housing (1) according to claim 8, characterized in that A surface A scanned by at least one laser bonding line (2) w The connection between the cover substrate (10) and the base substrate (14) is selected such that it has a shear failure force in the range of 10N to 1000N, preferably 50N to 500N, particularly preferably in the range of 100N to 400N.

10. The housing (1) according to claim 8 or 9, characterized in that The total length L of the laser bonding line (2) is selected according to the layout method according to any one of claims 1 to 6 ges .

11. The housing (1) according to any one of claims 8 to 10, characterized in that There is one or more laser joining lines (2), which have a width w and the spacing H between the centers of two adjacent laser joining lines (2) is selected in the range of 1w to 5w, preferably in the range of 1.01w to 2.5w, particularly preferably in the range of 1.05w to 2w.

12. The housing (1) according to any one of claims 8 to 11, characterized in that The cover substrate (14) is designed as a transparent film substrate, wherein the cover 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 of more than 10 μm, particularly preferably more than 20 μm.

13. The housing (1) according to any one of claims 8 to 12, characterized in that The cover substrate (14) and the base substrate (10) are disposed at the contact surface A. i directly abut each other at the locations so that the laser bonding surface A swept by at least one laser bonding line (2) w The connections in the embodiment are free of foreign material, in particular free of connection materials such as adhesives, glass frits or absorbent layers.

14. The housing (1) according to any one of claims 8 to 13, characterized in that The base substrate (10) comprises a flat bottom substrate (11) and an intermediate substrate (12), wherein the bottom substrate forms a bottom surface of a functional region (20) configured as a cavity (21), and the intermediate substrate forms a side wall of the cavity (21) having an end surface facing the cover substrate (14), and the bottom substrate (11) and the intermediate substrate (12) are connected to each other in an airtight manner via at least one laser bonding line (2), or a functional region (20) in the form of a recess having a bottom surface and side walls is formed in the base substrate (10), and the bottom surface and the side walls together with the cover substrate (14) as a top surface form the cavity (21).

15. The housing (1) according to any one of claims 8 to 14, characterized in that The cover substrate (14) and / or the base substrate (10) are made of glass, glass ceramics, silicon, sapphire or a combination of the above materials.

16. The housing (1) according to any one of claims 8 to 15, characterized in that The width w of the laser joining lines (2) is in the range of 20 μm to 75 μm, preferably 30 μm to 60 μm, and / or the width w of all laser joining lines (2) is within the total length L of the laser joining lines (2). ges The above variation is at most 30%, particularly preferably at most 20%, most preferably at most 10%.

17. A sensor unit and / or a medical implant, comprising a housing (1) according to at least one of claims 8 to 16 or obtained by arranging according to a method according to any one of claims 1 to 7.

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