METHOD FOR HEATING A MULTIPLE OF ELECTRICALLY CONDUCTIVE STRUCTURES AND DEVICE FOR USE IN THE METHOD

Abstract

Method for heating a plurality of electrically conductive structures (2, 4) by induction, which are arranged on an electrically non-conductive first substrate (1), comprising the steps: - Providing a first inductor (6) with a plurality of inductor elements (30) arranged side by side, each inductor element having at least one first connecting section (31) and at least two legs (32), the first connecting section (31) connecting the two legs (32) of the inductor element (30) together, and the inductor elements (30) being connected together in series by second connecting sections (33), - Arranging the first inductor (6) above or below the first substrate (1) such that ◯ each inductor element (30) overlaps at least partially with an edge (5) of at least one electrically conductive structure (2, 4) and / or ◯ each inductor element runs at least partially parallel to the edge (5) of the electrically conductive structure (2, 4), - Applying an alternating current or voltage to the first inductor (6) and - Inducing eddy currents in the electrically conductive structures (2, 4), - wherein the electrically conductive structures are heated exclusively or at least primarily by the eddy currents induced in the electrically conductive structures, - wherein no electrically conductive elements are arranged between the inductor and the electrically conductive structures to avoid shielding and / or wherein only electrically non-conductive elements are arranged between the inductor and the electrically conductive structures.

Description

[0001] Many novel products in microsystems technology pose a major technological challenge for current bonding and joining processes.

[0002] Today's assembly and interconnection technology (AIT) focuses on increasingly smaller and more complex components and microsystems. For the purposes of this document, "micro" means that the component or microsystem has at least one dimension between 0.1 µm and 10 mm, typically between 1 µm and 1 mm. The aim is to minimize the thermal and mechanical stress on the component during the joining process to avoid damaging sensitive elements. Consequently, joining pressure and temperature input should be distributed homogeneously across the components being joined. Furthermore, some joining processes place high demands on the surface finish of the joining partners. The joint should hermetically seal components with high mechanical strength. Other important requirements include integration density, material diversity, and the accessibility of the joining points (e.g.,3D integration), as well as process and cycle times.

[0003] Established joining processes or wafer bonding methods in microsystems technology, such as anodic bonding, low-temperature silicon direct bonding, glass frit bonding, or eutectic bonding, which result in hermetically sealed connections, do indeed create reliable bonds. However, these processes involve temperatures of up to 400°C for extended periods. These temperatures are applied globally to the entire assembly (substrates, functional elements and layers, contacts, and bonding layer) via heating plugs with integrated heating conductors. An electric current flows through the heating conductors, and their Joule heating is transferred via thermal conduction first to the surface of the heating plug and subsequently to the assembly. These high and relatively prolonged temperatures can damage sensitive components or materials.Furthermore, due to the differences in thermal expansion coefficients, it is complicated to tightly bond various substrates, such as silicon, metals, ceramics or polymers, over large areas.

[0004] On the other hand, it is becoming increasingly difficult to automatically, reliably, and tightly join complex products and their housings. In addition to temperature-sensitive sensors, there are recurring issues with shadowed joints that are not easily accessible with welding and soldering tools.

[0005] For this reason, research in recent years has intensified on technologies that enable selective energy input only at the required joining point on areas measuring just square micrometers.

[0006] Methods have been developed that utilize a local energy source, allowing the energy to act directly at the bond. For example, reactive powders are used that generate a self-propagating reaction, which, however, is difficult to control. Furthermore, reactive multilayer systems exist in the prior art, consisting of numerous thin, alternating layers whose reactive properties enable control of the very high, but short-term, thermal energy released. In such methods, preparation is complex and structuring complicated, which can make them relatively complex and expensive. For example, DE 10 2009 006 822 A1 discloses a method for producing a microstructure with at least one bonding substrate and a reactive multilayer system.Documents US 7,064,004 B2 and US 7,332,411 B2 describe the joining of substrates using metallic solder beads or metallic frame structures. In these documents, eddy currents are induced in the metal by generating a time-varying electromagnetic field using a coil (induction), and the metal's temperature rises due to Joule heating. However, it has been found that the heating of the metal is not sufficiently homogeneous with the methods described therein, which can lead to local overheating.

[0007] German patent application DE 10 2006 034 600 A1 describes a method for producing a soldered joint. Two components are provided for joining at a predetermined joint. A metallic intermediate plate and a soldering device with an inductor are also provided. The inductor generates eddy currents in the intermediate plate, causing it to heat up and melt the solder in thermal contact with it. The heating of the solder and the components is therefore not direct, but indirect, via the intermediate plate heated by the inductor. Consequently, the heat input into the solder through the intermediate plate is achieved via thermal conduction.

[0008] Publication JP 2004-353035 A describes an inductor that achieves uniform heating in a full-surface plate through a zigzag-shaped inductor structure, regardless of the arrangement of the structure to be heated.

[0009] The invention aims to overcome at least one or more problems of the prior art. This objective is achieved by a method for heating a plurality of electrically conductive structures according to the main claim and an apparatus for use in said method according to the dependent claim. Further developments are described in more detail in the following description and the dependent claims.

[0010] The method for heating a plurality of electrically conductive structures arranged on an electrically non-conductive first substrate comprises the following steps: Providing a first inductor with a plurality of inductor elements arranged side by side, each inductor element having at least one first connecting section and at least two legs, the first connecting section connecting the two legs of the inductor element together, and the inductor elements being connected to each other in series by second connecting sections, Arranging the first inductor above or below the first substrate, such that Each inductor element overlaps at least partially with an edge of at least one electrically conductive structure and / or Each inductor element runs at least partially parallel to the edge of the electrically conductive structure, Applying an alternating current and / or an alternating voltage to the first inductor and Inducing eddy currents in electrically conductive structures.

[0011] The inventors have recognized that adapting the inductor shape to the geometry of the electrically conductive structures, as well as arranging the inductor accordingly above and / or below the substrate in accordance with the geometry of the electrically conductive structures, enables particularly homogeneous heating of the electrically conductive structures.

[0012] In addition, further homogenization of the temperature can be achieved by partially raising the inductor elements in the z-direction, i.e. perpendicular to the substrate, and / or by partially using field-carrying elements above the inductor elements.

[0013] The proposed method allows for the homogeneous heating of electrically conductive structures. This homogeneous heating, in turn, reduces local temperature peaks, thereby preventing damage to temperature-sensitive components. The described method can preferably be carried out using the apparatus described below.

[0014] By applying an alternating voltage or current, the inductor typically generates alternating electromagnetic fields that induce eddy currents in the electrically conductive structures. These eddy currents, in turn, cause a temperature increase within the conductive structures. The eddy currents induced in the conductive structures can be induced directly and / or primarily by the magnetic field generated by the inductor.

[0015] Heating the electrically conductive structures allows for the formation of a metallurgical bond between the electrically conductive structures and the first substrate and / or other components (see below). This metallurgical bond can be achieved, for example, by soldering, welding, sintering, and / or diffusion of the material from the electrically conductive structures into the first substrate or the respective other components. In one embodiment, the electrically conductive structures are at least partially melted by the eddy currents induced within them. According to the invention, the electrically conductive structures are heated exclusively or at least primarily by the eddy currents induced within them.

[0016] Furthermore, only non-conductive elements are arranged between the inductor and the electrically conductive structures. Alternatively or additionally, no electrically conductive elements are arranged between the inductor and the electrically conductive structures. Thus, the electrically conductive structures are not shielded, resulting in more effective heating of the electrically conductive structures.

[0017] The terms “electrically conductive” and “electrically non-conductive” as used in this document mean that the first substrate has an electrical conductivity that is at least fifty, one hundred, or one thousand times lower than the electrical conductivity of the electrically conductive structures. The conductivity of the first substrate should be less than 2 × 10 4S / m (corresponding to the conductivity of highly doped silicon), e.g. less than 100 S / m or less than 10 S / m or less than 1 S / m, so that no or only a few eddy currents are induced in the first substrate.

[0018] The material of the first substrate can include, for example, silicon, glass, ceramic, or FR4. FR4 refers to a class of flame-retardant composite materials comprising or consisting of epoxy resin and fiberglass fabric. The first substrate can be made of a semiconductor material. The semiconductor material should be lightly doped so that the conductivity of the first substrate remains low, i.e., significantly lower than the electrical conductivity of the electrically conductive structures.

[0019] The electrically conductive structures can be metallic. Suitable metals include, for example, aluminum, silver, copper, gold, tin, nickel, or an alloy of at least one of these metals. Materials used for solder joints (e.g., tin-silver) are also suitable. The electrically conductive structures typically touch the first substrate and are therefore located directly on it.

[0020] In this advanced training, each inductor element runs parallel to the edge of the electrically conductive structure in the area of ​​overlap. This further contributes to a homogeneous heating of the electrically conductive structure.

[0021] The edge of the structure can be understood as its outer boundary. A dimension of the edge of the electrically conductive structure, for example, a web width, can comprise up to 50%, 40%, 30%, 20%, or 10% of the structure's dimension in that spatial direction. For example, a dimension of a left-hand edge and / or a dimension of a right-hand edge of the structure each comprise at most 50%, 40%, 30%, 20%, or 10% of the structure's dimension in the chosen spatial direction.

[0022] In one embodiment, the first inductor comprises a first group and a second group of inductor elements arranged side by side. The first group and the second group can be connected in parallel.

[0023] In one embodiment, the first inductor comprises a first group. In addition, there exist a number n of further groups of inductor elements arranged side by side. The number n can be a positive integer greater than or equal to one. The first group and the further group(s) can be connected in parallel.

[0024] The inductor elements can together form a conductor loop. The conductor loop encloses an inner region, with an outer region lying outside the loop. Preferably, the first inductor is arranged such that all electrically conductive structures to be heated lie within a projection of the inner region onto the substrate or within a projection of the outer region onto the substrate. This embodiment of the method increases the degree of homogenization of the heating of the electrically conductive structures.

[0025] Typically, the field strength and flux density of the electromagnetic field induced by the first inductor are greater in the inner region of the conductor loop than in the outer region. Therefore, for effective heating of the electrically conductive structures, it is advantageous if the structures to be heated are located within the projection of the inner region onto the substrate.

[0026] Typically, the number of electrically conductive structures on the first substrate can be at least 10, 20, 50, 100, 200, 500, or even more than 1000. The electrically conductive structures are usually arranged at regular intervals on the first substrate.

[0027] The edges of electrically conductive structures can be, for example, circular, rectangular, or cuboid. Furthermore, depending on the application, the electrically conductive structures can be ring-shaped, frame-shaped, plate-shaped, or disc-shaped.

[0028] Each electrically conductive structure may comprise a plurality, e.g., 2, 3, 4, 5, or 6, of interconnected webs. The webs may be arranged in a frame-like configuration. Each web may have a straight or curved path. The aforementioned edge may be formed by the webs.

[0029] To improve the generation of eddy currents and thus the heating, the electrically conductive structures can be connected to each other via electrically conductive connecting bridges. These electrically conductive connecting bridges can, for example, be arranged on the first substrate.

[0030] The electrically conductive structures can each form a closed conductor loop. The eddy currents induced by the first inductor can develop particularly well in such a conductor loop. Furthermore, such a closed conductor loop can be used for encapsulating a structure to be encapsulated (see below). The closed conductor loop can be, for example, frame-shaped or ring-shaped (see above). The aforementioned edge can be formed by the closed conductor loop.

[0031] Functional elements or microsystems can be arranged on the first substrate, the lateral dimensions of which are smaller than those of the electrically conductive structures to be heated. For example, the functional elements can have dimensions that are at most 50%, 40%, 30%, 20%, or 10% of the lateral extent of the electrically conductive structures.

[0032] A turn width typically comprises two leg widths and a leg spacing between two adjacent legs of an inductor element. The turn width can be at most the sum of two lateral extensions of the electrically conductive structures and a lateral spacing between the electrically conductive structures. The functional elements or microsystems can, for example, be arranged within the closed conductor loop on the first substrate. In their lateral dimensions, the functional elements or microsystems are usually smaller than the turn width of the inductor elements. Typically, the functional elements have dimensions that are at most 50%, 40%, 30%, 20%, or 10% of the width of the closed conductor loop.

[0033] In a design, a leg width (width of one leg) is at most as large as the extent of the electrically conductive structures in one spatial direction, e.g., laterally. For example, a leg width corresponds to the width of the webs of the electrically conductive structure.

[0034] The frequency of the alternating current and / or voltage should be selected to generate eddy currents in the electrically conductive structures, thereby generating heat. As the dimensions of the structures to be heated decrease, higher frequencies become increasingly advantageous to ensure effective heating.

[0035] Depending on the dimensions of the electrically conductive structures, the alternating current or voltage can have a frequency of at least 100 kHz, 200 kHz, 500 kHz, or 1000 kHz. Furthermore, the frequency of the alternating current or voltage can be at most 15 GHz, 1 GHz, 500 MHz, 200 MHz, 100 MHz, 50 MHz, 20 MHz, or 10 MHz.

[0036] The current in the inductor can be, for example, greater than 10 A, 20 A, 50 A, or 100 A. It can also be less than, for example, 1000 A, 750 A, 500 A, or 200 A. The voltage applied to the first inductor can be, for example, greater than 10 V, 20 V, 50 V, 100 V, 150 V, 200 V, or 300 V. It can also be less than 1500 V, 1000 V, 800 V, or 600 V.

[0037] The duration of the current flow to the first inductor can be at least 0.01 s, 0.1 s, 0.5 s, or 1 s. The maximum duration of the current flow to the first inductor can be at most 60 s, 45 s, 30 s, or 15 s. In some embodiments, the duration of the current flow is 30 to 60 minutes.

[0038] The inductor elements can be formed by hollow tubes through which a cooling fluid, such as water, flows. The cooling fluid can cool the inductor elements from the inside. Alternatively, the inductor elements can be cooled externally by the cooling medium or passively by heat conduction.

[0039] It may be provided that the first inductor is connected to a power source which operates as an alternating current source and / or an alternating voltage source.

[0040] Typically, the first inductor is arranged such that the inductor elements each extend along the entire longitudinal axis of at least one electrically conductive structure. In other words, each inductor element can run along the entire length of the electrically conductive structure. This allows for more homogeneous and efficient heating of the structures.

[0041] Since the shape of the inductor and its arrangement relative to the substrate are adapted to the geometry of the electrically conductive structures, the inductor should not move relative to the substrate during the application of an alternating current and / or an alternating voltage to the first inductor.

[0042] The procedure may additionally include the following step: Providing a second substrate.

[0043] The first and second substrates can be identical or different. For example, the second substrate can be provided with or without electrically conductive structures. The first and / or second substrates can be configured as wafers or chips. If both substrates are wafers, the method preferably includes the wafer bonding step. If at least one substrate is a chip, the method preferably includes the chip bonding step. The first and / or second substrates can be made predominantly, e.g., at least 80%, or entirely of silicon, glass, ceramics, plastics, FR4, or the like. For the features of the second substrate, reference can be made to the above description of the features of the first substrate.

[0044] The procedure may additionally include the following step: Before positioning the inductor above or below the first substrate: Align the second substrate with respect to the first. For example, the electrically conductive structures of the first and second substrates can be brought into contact. The second substrate can be positioned so that it touches the electrically conductive structures of the first substrate. After alignment, the first and second substrates can be attached, pressed, or clamped together, for example, using clamps or clips.

[0045] The first inductor can then be arranged as described above. Heating the electrically conductive structures allows for a metallurgical bond between the first and second substrates. This bond can be achieved, for example, by soldering, welding, sintering, and / or diffusion of the material from the electrically conductive structures into the second substrate. The eddy currents induced within the electrically conductive structures melt them, at least partially, thus allowing the second and first substrates to be bonded together.

[0046] At least one microsystem to be encapsulated can be enclosed by at least one electrically conductive structure, the first substrate, and the second substrate. Typically, the microsystem is hermetically encapsulated, e.g., airtight or waterproof. The microsystems to be encapsulated can be, for example, integrated circuits (ICs), microelectromechanical systems (MEMS), micro-optoelectromechanical systems (MOEMS), microprocessors, or microcontrollers.

[0047] The process may include further steps: Arranging a second inductor below or above the first substrate, wherein the second inductor is arranged on the opposite side of the first substrate relative to the first inductor, and the second inductor is aligned parallel to the first inductor or rotated by 90° or 180°.

[0048] The process may include further steps: Arranging a second inductor below or above the second substrate, wherein the second inductor is arranged on the opposite side of the second substrate relative to the first inductor, and the second inductor is aligned parallel or rotated by 90° or 180° relative to the first inductor.

[0049] The first and second inductors can be configured differently or identically. For the characteristics of the second inductor, refer to the description of the first inductor above and below.

[0050] The voltages and currents used for the two inductors should be matched or synchronized with each other.

[0051] Furthermore, a device for use in the aforementioned method is proposed. The device comprises at least one first inductor. The first inductor includes a plurality of inductor elements arranged side by side, each inductor element having at least one first connecting section and at least two legs. The first connecting section joins the two legs of the inductor element together. The inductor elements are also connected to each other in series by second connecting sections.

[0052] In one embodiment, the inductor elements are arranged in a meandering shape. The first inductor can therefore have a meandering shape.

[0053] The legs can be arranged in a plane. The legs typically run essentially in a longitudinal direction. A lateral direction is perpendicular to the longitudinal direction. It can be provided that adjacent legs of adjacent inductor elements and / or adjacent legs of an inductor element are essentially parallel to each other in the longitudinal direction. For example, the longitudinal directions of the legs of each inductor element are essentially parallel to each other.

[0054] Typically, a lateral projection of the legs of each inductor element onto the substrate includes at most two electrically conductive structures to be heated, preferably one. For example, a lateral projection of the legs of each inductor element onto the substrate includes at most two rows of electrically conductive structures to be heated, preferably one row. If the inductor element has more than two legs, a lateral projection of the outer legs of the inductor element onto the substrate includes, for example, at most two electrically conductive structures to be heated, preferably one. If the inductor element has more than two legs, a lateral projection of the outer legs of the inductor element onto the substrate includes, for example,The arrangement includes at most two rows of electrically conductive structures to be heated in a lateral direction, preferably one row of electrically conductive structures to be heated. A row of electrically conductive structures to be heated typically comprises an arrangement of at least two electrically conductive structures which are aligned along a line, such as a spatial direction, e.g. in the longitudinal direction, transverse direction, x-direction or y-direction.

[0055] A leg width can be smaller than the extent of an electrically conductive structure to be heated in a spatial direction, e.g., laterally. Depending on the design of the structures to be heated, the leg width can be either constant or variable along the length of the leg.

[0056] In one embodiment, a leg spacing defines a maximum lateral distance between the two legs of an inductor element. The leg spacing between two adjacent legs can be constant. The leg spacing can be constant within each inductor element. Furthermore, the leg spacing can be the same in each inductor element. Alternatively, it can be provided that there are at least two inductor elements that have different leg spacings. The leg spacing within an inductor element can be greater than the leg spacing between two adjacent inductor elements.

[0057] The first and / or second connection section can be designed as arc-shaped sections, e.g., circular arcs or straight sections. This helps prevent voltage flashovers at the high voltage used.

[0058] It may be provided that at least one inductor element has more than two legs which are connected to each other in series by means of several first connecting sections, wherein the number of legs of the inductor element is an even number 2n, and the number of first connecting sections is 2n-1.

[0059] Typically, the legs are essentially straight in the longitudinal direction. A leg cross-section can be round, oval, square, or rectangular.

[0060] The device may include an electrical power source. Furthermore, the device may include an alternating current source for supplying the first inductor with an alternating current or an alternating voltage source for applying an alternating voltage to the first inductor. The alternating current source or the alternating voltage source may be configured such that the alternating current or alternating voltage has a frequency of at least 100 kHz and / or at most 15 GHz. The frequency of the alternating current or alternating voltage may be constant or variable. The first inductor, and if provided, further inductors, may be connected to the alternating current source or the alternating voltage source by means of connecting leads.

[0061] The device may have a second inductor, which is aligned parallel or at an angle of 90° or 180° to the first inductor. The second inductor and the first inductor may be identical or different. For the characteristics of the second inductor, reference is made to the description of the first inductor above. The second inductor may be connected to the aforementioned electrical power source. Alternatively, a second electrical power source may be provided for the second inductor.

[0062] Typically, a control device is provided which controls the electrical energy source or sources.

[0063] A temperature sensor may be provided, configured to measure the temperature of the electrically conductive structures and / or the first substrate and / or the second substrate. The temperature sensor is preferably connected to the control device. The control device may be configured to evaluate the measured values ​​or data provided by the temperature sensor. If the temperature of the aforementioned components, as measured by the temperature sensor, exceeds a limit value, the current to the first inductor and / or the second inductor can be switched off. It is also possible to measure the temperature of different areas of the electrically conductive structures and / or the first substrate and / or the second substrate. If a temperature gradient exceeds a predetermined value, the current to the inductor can be switched off.The control device can also define or determine the current-sensing duration of the first inductor and / or the second inductor. The control device can be, for example, a processor. Furthermore, a storage medium can be provided, which can store, for example, voltage values, current values, AC frequencies, AC voltage frequencies, current-sensing durations, temperature profiles, and / or temperature gradients of known material combinations. The storage medium is preferably connected to the control device.

[0064] The described device can be used in particular in the method described above for heating a large number of electrically conductive structures.

[0065] It should be emphasized at this point that features mentioned only in relation to the device can also be claimed for the method mentioned, and vice versa.

[0066] The invention is explained below with reference to the accompanying figures. The figures show Fig. 1. A top view of a substrate with a variety of electrically conductive structures and functional elements; Fig. 2 Detail X of the Fig. 1; Fig. 3 a view of two different electrically conductive structures; Fig. 4 a part of a side view of the substrate of the Fig. 1; Fig. 5 a side view of a configuration of two substrates connected to each other by means of electrically conductive structures; Fig. 6 Another embodiment of a substrate with frame, electrically conductive structures and electrically conductive connecting bridges in top view; Fig. 7 another embodiment of a substrate with electrically conductive structures and electrically conductive connecting bridges in top view; Fig. 8 a top view of a meandering inductor; Fig. 9 a view of several meandering inductors connected in parallel; Fig. 10 an arrangement of an inductor and a substrate according to an embodiment; Fig. 11 an arrangement of an inductor and a substrate according to a further embodiment; Fig. 12 an arrangement of an inductor and a substrate according to a further embodiment; Fig. 13 an arrangement of an inductor and a substrate according to a further embodiment; Fig. 14 an arrangement of an inductor and a substrate according to a further embodiment; Fig. 15 an arrangement of an inductor and a substrate according to a comparative example; Fig. 16 an arrangement of an inductor and a substrate according to a comparative example; Fig. 17 an arrangement of an inductor and a substrate according to a comparative example; and Fig. 18 an arrangement of an inductor and a substrate according to a comparative example.

[0067] Recurring features in the figures are labelled with the same reference symbols.

[0068] Before discussing the method according to the invention, the structures and devices used in the method will first be explained.

[0069] The Fig. Figure 1 shows a top view of a substrate 1 with a plurality of electrically conductive structures 2, which are arranged at regular intervals 99 on the substrate 1. Fig. Figure 2 shows a section X of the Fig. 1.

[0070] The electrically conductive structures 2, 4 are produced on the substrate 1, for example, by physical vapor deposition (PVD) and photolithographic structuring. Such a process is familiar to those skilled in the art; alternative methods for depositing the electrically conductive structures 2, 4 onto the substrate 1 are also conceivable. The electrically conductive structures 2, 4 (hereinafter also referred to as "structures" 2) are thus metallurgically bonded to the substrate 1.

[0071] In the exemplary embodiment of the Fig. There are 37 structures 2 arranged on the substrate 1. The number of structures can be higher or lower depending on requirements. For example, 10, 100, 200, 500, 1000 or even more structures 2 can be arranged on the substrate 1. The structures 2 comprise four interconnected webs 97, which are arranged in a frame-like shape. The edge 5 of a structure 2 is, for example, square ( Fig. 2) or rectangular ( Fig. 3 left). The square structures 2 have dimensions of 15 mm × 15 mm (y-direction and x-direction, respectively). The webs 97 have a width b of 3 mm and a height h (in the z-direction) of 1.5 µm (see. Fig. 4). In the Fig. Figure 4 is part of a side view of substrate 1 of the Fig. Figure 1 shows the height h of the structures 2 enlarged in the z-direction for better illustration. The width b and height h can be significantly smaller in other embodiments. For example, the webs can have a width b of 0.5 mm or less and a height of 0.2 µm or less.

[0072] The structures 2 are preferably metallic and can be made, for example, of aluminum, silver, copper, gold, tin, lead, or an alloy of at least one of the aforementioned metals. The webs 97 of the structure 2 thus each form a closed electrical conductor loop.

[0073] In the illustrated embodiment, substrate 1 is a wafer made of a semiconductor material, such as silicon. The substrate has an electrical conductivity that is at least fifty times lower than that of the structures 2.

[0074] Furthermore, a multitude of microsystems 3 are located on the substrate 1. These microsystems can be configured as integrated circuits, integrated circuits, microprocessors, microelectromechanical systems (MEMS), microcontrollers, or sensors. Each microsystem 3 is positioned within the frame of the electrically conductive structure 2. The microsystems 3 are encapsulated by the substrate 1, the structures 2, and another substrate 100 in the procedure described below. The microsystems 3 can have a number of different functional elements 22. The dimensions of the functional elements 22 of the microsystems 3 are generally smaller than the width b of the electrically conductive structures 2. For example, the dimensions of the functional elements are at most 10% of the width b of the structures 2.

[0075] The Fig. Figure 5 shows a side view of a configuration of two substrates 1 and 100, which are connected to each other by means of electrically conductive structures 2. The substrates 1, 100 and the structures 2 enclose the microsystems 3. By separating the substrates 1, 100, a multitude of separate encapsulated microsystems 3 can be obtained.

[0076] The Fig. 6 and Fig. Figure 7 shows two further embodiments of substrates 1 on which electrically conductive structures 2 are arranged. The electrically conductive structures 2, 4 of the Fig. 6 and Fig. The 7 components are connected to each other via electrically conductive connecting bridges 23. The electrically conductive connecting bridges 23 are also arranged on the substrate 1.

[0077] The Fig. Figure 3 shows a top view of two alternative electrically conductive structures 2, 4. In contrast to the structures 2 of the Fig. 1, Fig. 2 and Fig. 3 on the left are the electrically conductive structures 4 of the Fig. Structures 3 on the right and 7 are not frame-shaped but flat. They therefore lack a central opening. Structures 4 can, for example, be described as "pads".

[0078] Various inductors 6 for heating the structures 2, 4 are described in more detail below.

[0079] The Fig. Figures 8 to 14 show different embodiments of inductors 6. For better illustration, the following are shown in the Fig. 10, Fig. 11, Fig. 12 and Fig. 14 sections AA of the respective Fig. 10, Fig. 11, Fig. 12 or 14 are shown.

[0080] By applying an alternating voltage or current, the inductors can generate electromagnetic fields, which in turn, with a suitable arrangement of the inductors, generate eddy currents in the electrically conductive structures 2, 4. Various electrically conductive materials (usually metals such as copper, aluminum, silver, or their alloys) can be used as inductor materials.

[0081] The inductor 6 can be manufactured by forming (bending), separating (milling, laser cutting, waterjet cutting, shearing, EDM), primary shaping (3D printing / selective laser sintering, casting), or coating (aerosol jet, screen printing, electroplating). The inductor 6 can be actively cooled, passively cooled, or used without cooling. Cooling of the inductor 6 can be achieved using heat transfer fluids or gases (e.g., cooling water, compressed air). Cooling can be integrated internally (e.g., inductor as a hollow tube) or externally (e.g., inductor surrounded by cooling water).

[0082] The one in the Fig. The inductor 6 shown in Figures 8-14 has a plurality of inductor elements 30 arranged side by side. Each inductor element 30 has at least one (first) connecting section 31 and at least two legs 32, the (first) connecting section 31 connecting the two legs 32 to each other. The inductor elements 30 are connected to each other in series via second connecting sections 33. The inductor elements 30 together form a conductor loop having an inner region 7 and an outer region 8. Typically, the electromagnetic field strength and flux density of the electromagnetic field and flux generated by the inductor 6 are greater in the inner region 7 of the inductor 6 than in the outer region 8 of the inductor 6.

[0083] The legs 32 of the inductor elements 30 are arranged in a plane parallel to the substrate 1 (see below). The legs 32 are essentially straight along a longitudinal direction y and run parallel to each other. A lateral direction x is perpendicular to the longitudinal direction y. The connecting sections 31 and 33 are arc-shaped, so that the inductor 6, or the inductor elements 30 as a whole, has a meandering structure.

[0084] As in sections AA of the Fig. 10, Fig. 11, Fig. 12 and Fig. As can be seen in Figure 14, the legs 32 of the inductor elements 30 have a square cross-section. Alternatively, the cross-section of the legs 32 can also be, for example, oval, round, or rectangular.

[0085] The legs 32 of each individual inductor element 30 of the Fig. 8, Fig. 9, Fig. 10, Fig. 11 and Fig. The 14 have a constant and equal leg spacing 9, 13 in the x-direction / lateral direction x to each other. A coil width 98 typically consists of two leg widths 11, 15 and a leg spacing 9, 13. In the Fig. 10 corresponds to a winding width of 98 approximately to a lateral extent of an electrically conductive structure 2. In the Fig. 11 the winding width 98 is as large as two lateral extensions of the structures 2 and a distance 99 between the structures 2.

[0086] In the Fig. 12 and Fig. 13 is a leg distance ( Fig. 12: Leg spacing 19, 20) within a single inductor element 30 is constant and the same; however, the leg spacing differs between the various inductor elements 30. Therefore, there are at least two inductor elements 30 that have different leg spacings 19, 20.

[0087] In the Fig. 12 There are several inductor elements 30, each of which has more than two legs 32. In this case, in the Fig. Sections 16 and 17 are shown, which, in addition to the outer legs 32 of the inductor elements 30, have two or four further legs 32 in the inner region 7. Furthermore, section 18 shows two additional legs 32 in the outer region 8. The number of legs 32 of each inductor element 30 is an even number 2n, where the number of first connecting sections is 2n-1. This ensures that the current direction in the inductor 6 is not reversed.

[0088] The thighs 32 of the Fig. Legs 8-14 have a constant leg width 11, 15, 21. Alternatively, the leg width 11, 15, 21 can also vary along the longitudinal direction y of the legs 32. The leg width 11, 15, 21 corresponds to a web width b of the webs 97 of the electrically conductive structures 2. The leg width is thus less than half the sum of the dimensions of the structures 2 and the structure spacing 99 in the lateral direction x.

[0089] From the Fig. Evidence from paragraphs 8 to 14 shows that a projection of the legs 32 of each inductor element 31 onto the substrate 1 in the lateral direction x includes at most two electrically conductive structures 2 to be heated.

[0090] A leg spacing or distance between adjacent inductor elements 30 is also constant and in the Fig. 8, Fig. 9, Fig. 10 and Fig. 14 marked with reference numbers 10 and 14.

[0091] The embodiment of the in the Fig. The inductor 6 shown in Figure 13 is a hybrid form of the inductors from the embodiments of the Fig. 10 and Fig. 11. Other hybrid forms are also possible.

[0092] The one in Fig. The inductor 6 shown in Figure 9 differs from those shown in the diagram. Fig. The inductors shown in Figures 8, 10-14 differ from the inductor 6, which has three groups 36, 37, 38 of inductor elements 30, wherein the groups 36, 37, 38 are connected in parallel to each other. Two groups or more than three groups can be provided.

[0093] The inductor 6 from the Fig. 8-14 is connected via leads 34 to an electrical power source 35, which can be an alternating current source or an alternating voltage source. The electrical power source is designed to provide an alternating voltage or an alternating current to the inductor 6. The frequency of the alternating voltage or alternating current depends on the specific application and can be, for example, at least 100 kHz and / or at most 15 MHz. The electrical power source 35 can apply a voltage of approximately 100 to 900 V to the inductor 6. The current flowing through the inductor 6 has a current intensity of approximately 300–500 A.

[0094] A control device (not shown) is provided, configured to control the electrical energy source 35. Optionally, a temperature sensor may be provided, configured to measure the temperature of the electrically conductive structures 2 and / or the first substrate 1 and / or the second substrate 100. The temperature sensor is connected to the control device, which is configured to evaluate measured values ​​or data from the temperature sensor. Furthermore, a storage medium connected to the control device is provided, in which voltage waveforms, current waveforms, AC frequencies, AC voltage frequencies, current durations, and / or temperature waveforms of previously known material combinations are stored.

[0095] The in the Fig. The electrically conductive structures 2 shown in Figures 1-7 can preferably be synthesized using the methods described in the Fig. Heat the inductors 6 shown in 8-14.

[0096] For this purpose, the inductor 6 is first arranged above or below the substrate 1, see. Fig. 10-14. The inductor 6 is arranged such that each inductor element 30 overlaps with an edge of at least one electrically conductive structure 2. Furthermore, the inductor 6 is arranged such that the respective inductor element 30 runs parallel to the edge of the electrically conductive structure 2. In this respect, each inductor element 30, in particular the legs 32, preferably runs parallel to the edge of the respective electrically conductive structure 2 in the area of ​​overlap. The inductor elements 30, in particular the legs 32, can each extend along a complete length in the longitudinal direction y of the electrically conductive structure 2.

[0097] After positioning the inductor 6 above or below the substrate 1, it is supplied with an alternating current via the electrical power source 35. Alternatively or additionally, an alternating voltage is applied to the inductor 6 via the electrical power source 35. This generates eddy currents in the electrically conductive structures 2. The eddy currents are typically induced directly in the electrically conductive structures 2 by the alternating magnetic field of the inductor 6. The eddy currents heat the electrically conductive structures 2 according to Joule's first law. The frequency of the alternating current and / or the alternating voltage is matched to the dimensions of the electrically conductive structures to ensure the most effective and efficient generation of eddy currents.

[0098] Since the electrically conductive structures 2 to be heated can be heated more strongly within the projection of the inner area 7 on the substrate 1 than within the projection of the outer area 8 on the substrate 1, the inductor 6 is arranged such that the electrically conductive structures 2 lie within the projection of the inner area 7 on the substrate 1 (cf. Fig. 10-14).

[0099] Since the shape and spatial arrangement of the inductor 6 with respect to the substrate 1 are adapted to the geometry and arrangement of the electrically conductive structures 2 on the substrate 1, the inductor 6 should not move with respect to the substrate 1 during the induction of eddy currents in the electrically conductive structures 2 and the heating of the electrically conductive structures 2.

[0100] The substrate 1 can be connected to another substrate 100 by heating the electrically conductive structures 2, e.g. Fig. 5. Details of this can be found, for example, in publication US 7 332 411 B2, which is incorporated in its entirety into the present application by reference.

[0101] The first substrate 1 and the second substrate 100 can be identical or different. For example, the second substrate 100 can be provided with or without electrically conductive structures 2. While the first substrate 1 is generally configured as a wafer or printed circuit board, the second substrate 100 can be, for example, a glass sheet, a wafer, or a printed circuit board. The invention is not limited to a specific shape of the substrates 1 and 100. For the features of the second substrate 100, reference can be made to the above description of the features of the first substrate 1.

[0102] Before the step of arranging the inductor 6 above or below the first substrate 1, the second substrate 100 is aligned with respect to the first substrate 1. This is referred to as bond alignment. For example, the electrically conductive structures 2 of the first substrate 1 and the second substrate 100, if present, can be positioned on top of each other. The second substrate 100 can be arranged such that it touches the electrically conductive structures 2 of the first substrate 1. Fig. 5. After the alignment step, the first substrate 1 and the second substrate 100 can be attached, pressed or clamped together, e.g. using clamps.

[0103] The inductor 6 is then arranged as described above. By heating the electrically conductive structures 2, a metallurgical bond between the two substrates 1 and 100 can be established. The electrically conductive structures 2 can be melted by the resulting temperature increase. The metallurgical bond can be achieved, for example, by soldering, welding, sintering, and / or diffusion.

[0104] The method described above is particularly suitable for encapsulating microsystems 3. By connecting the two substrates 1, 100 using the electrically conductive structures 2, the intermediate microsystem 3 is hermetically encapsulated.

[0105] To increase the efficiency or homogeneity of the heating, a second inductor 60 can also be used, see [reference]. Fig. 14. If the first inductor 6 is positioned above the first substrate 1, the second inductor 60 is positioned below the first substrate 1. The second inductor 60 can be oriented, for example, parallel to the first inductor 6 or rotated by 90° or 180°. The first inductor 6 and the second inductor 60 can be of different or identical design. For the characteristics of the second inductor 60, refer to the description of the first inductor 6 above.

[0106] It should be emphasized that the use of two inductors 6, 60 with two substrates 1, 100 is also possible.

[0107] In addition to the above, further homogenization of the temperature of the electrically conductive structures 2, 4 can be achieved by partially raising the inductor elements 30 in the z-direction, i.e. perpendicular to the substrate 1, 100, and / or by partially using field-carrying elements above the inductor elements 30.

[0108] The following is a comparison of application examples 1-4. Fig. Figures 15 to 18 show arrangements of an inductor and a substrate according to application examples 1-4. In the lower graphs of the Fig. Figures 15-18 show spatial temperature profiles during the heating of the electrically conductive structures 2.

[0109] The following parameters were used in comparison examples 1-4: ▪ Cross-section of the inductor legs: Square, 4 mm × 4 mm ▪ Inductor material: Cu-ETP ▪ Manufacturing the inductor: Forming (bending) ▪ Cooling of the inductor: internally cooled with water ▪ Material of the structures to be heated inductively: Aluminum, thickness: 1.5 µm ▪ Geometry of the structures to be heated: Frame, 15 mm × 15 mm, web width: 3 mm ▪ Inductively non-heatable substrate: silicon, Ø 150 mm, thickness: 675 µm, p(100), ρ = 10...20 Ω·cm ▪ Functional elements not to be heated inductively: none present ▪ Connecting bridges: none present ▪ Generator parameter: f Res = 1400 kHz, RF voltage: 436 V, RF current: 151 A ▪ Heating time: 3 seconds

[0110] The comparison examples differ only in the shape of the inductor 6 and the arrangement of the inductor 6 above the substrate 1.

[0111] In the Fig. 15 a meandering inductor according to the embodiment of the Fig. 10 was selected. It can be seen that the shape and arrangement of the inductor are adapted to the specific shape of the electrically conductive structures.

[0112] The one in Fig. The inductor shown in 16 is also meandering. The one in the Fig. 17 and Fig. The 18 inductors shown are ring-shaped or spiral-shaped. The ones in the Fig. The inductor geometries shown in Figures 16 to 18 are not adapted to the specific frame-shaped geometry of the electrically conductive structures.

[0113] Thermography was used to determine the temperature of the arrangements. Fig. 15-18 measured and shown in the lower representations of the Fig. 15-18 visualized.

[0114] The following minimum and maximum temperatures T were used. min or T max Measured in °C: ◯ Fig. 15: T min = 197 °C ; T max = 218 °C (ΔT = 21 K; ± 5%) ◯ Fig. 16: T min= 109 °C ; T max > 300 °C (ΔT > 191 K; ± 34%) ◯ Fig. 17: T min = 162 °C ; T max > 300 °C (ΔT > 138 K; ± 25%) ◯ Fig. 18: T min = 60 °C ; T max = 246 °C (ΔT = 186 K; ± 41%)

[0115] The temperature difference between T max and T min is given here as ΔT in K. While the temperature difference ΔT of the example of the Fig. 15 is only 21 K, the temperature differences ΔT of the examples are Fig. 16-18 significantly larger than 100 K. Consequently, the frame-shaped structures can be induced by the inductor of the Fig. 15 are heated homogeneously (i.e., ΔT is, for example, less than 50 K, 40 K, or 30 K), while the Fig. 16-18 exhibit inhomogeneous temperature profiles of the frame-shaped structures. Reference symbol list: 1 substrate 2 electrically conductive structures 3 Microsystems 4 electrically conductive structures 5 Rand 6 first inductor 7 Indoor area 8 Outdoor area 9 Leg spacing between two legs of an inductor element 10 Leg spacing between two adjacent inductor elements 11 thigh width 12. Extent of an electrically conductive structure in the x-direction 13 Leg spacing between two legs of an inductor element 14 Leg spacing between two adjacent inductor elements 15 thigh width 16 Inductor section 17 Inductor section 18 Inductor section 19 Leg spacing between two legs of an inductor element 20 Leg spacing between two legs of an inductor element 21 thigh width 30 inductor element 31 first connecting section 32 thighs 33 second connecting section 34 Supply line 35 electrical energy source 36 Group of inductor elements 37 Group of inductor elements 38 Group of inductor elements 60 second inductor 97 Bridge 98 coil width 99 structural spacing 100 additional substrate b Width of the electrically conductive structure h Height of the electrically conductive structure x lateral direction y longitudinal direction

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