Packaged optoelectronic module and method for its fabrication

Abstract

Cap (2) for the housing (3) of an optoelectronic component (1), comprising - a frame (5) made of a nitride ceramic, which has an opening (7), as well as - a glass element (8) hermetically sealing the opening (7), which is fused to the nitride ceramic and fixed in contact with the nitride ceramic of the frame (5), wherein along the entire interface (57) between the glass of the glass element (8) and the nitride ceramic of the frame (5) the surfaces of the glass and the nitride ceramic are in contact and have a complementary fine structure, wherein the glass element (8) is fused into the opening (7) of the frame (5) and connected to the inner wall (9) of the opening (7), wherein the complementary fine structures provide a positive fit between the glass element (8) and the frame (5) and the glass element (8) is connected to an inner wall (9) of the opening (7), so that the inner wall (9) of the opening (7) surrounds the glass element (8) on a circumference of the glass element (8) and hermetically seals a transition between the frame (5) and the glass element (8).

Description

[0001] The invention relates generally to optoelectronic modules, such as, in particular, optoelectronic transducers for generating or detecting light or other electromagnetic radiation. In particular, the invention relates to the design of a housing for such modules.

[0002] UV LED modules, especially in the UVB and UVC range, require materials and assembly and connection techniques that are stable against the generated radiation and can withstand demanding environmental conditions.

[0003] Typical LED modules made of polymers or plastic-encapsulated metal components only partially meet these requirements. For example, the materials yellow due to UV radiation. Besides material stability, non-gas-tight housings pose the risk of damaging or destroying the sensitive LED chip due to atmospheric conditions or contaminants. A hermetic housing therefore significantly increases the stability and reliability of the LED module.

[0004] US patent 2019 / 0122945 A1 describes a method for coating aluminum nitride with a glass layer. Similarly, a glass lid is coated with a layer. Both layers are then brought into contact and bonded with a laser, creating a hermetic seal between the two components. This process is initially complex and expensive.

[0005] In JP 2017-73489A, a hermetic housing for UV LEDs is described in which the cap of the LED module is made entirely of glass and partially coated. The connection between the cap and the substrate is achieved by anodic bonding.

[0006] US 2006 / 0180909A1 describes a rectangular cap with curved corners, the frame of which is made of Kovar or another metal.

[0007] US Patent 2019 / 0074416A1 describes a glass element made of quartz glass that has a bonding surface for joining to another element, for example, a ceramic. This bonding surface has a bonding film.

[0008] The compound film contains glass obtained by melting a glass frit, as well as gold powder with an average particle size of less than 3 µm.

[0009] The object of the invention is to construct a stable, hermetically sealed, optically partially transparent cap for use in protecting optoelectronic components, which provides good cooling for the installed circuit elements and is as temperature and UV stable as possible.

[0010] This problem is solved by the subject matter of the independent claims. Advantageous embodiments of the invention are specified in the dependent claims.

[0011] Accordingly, a cap is provided for the housing of an optoelectronic component, comprising - a frame made of a nitride ceramic which has an opening, as well as A glass element hermetically seals the opening, is fused to the nitride ceramic, and fixed in contact with the nitride ceramic of the frame. This creates a direct connection between the glass and the ceramic. The bond formed by the fusion of the glass element to the aluminum nitride ceramic can be easily verified under a microscope. Due to the fusion process, the glass precisely follows the surface microstructure of the nitride ceramic. This applies to the entire interface between the glass and the nitride ceramic because the entire glass element softens. The complementary surface features along the entire interface ensure a tight fit and thus a very strong interlocking of the glass element with the ceramic.

[0012] Particularly secure fixation is achieved by fusing the glass element into the frame opening and bonding it to the inner wall of the opening, so that the inner wall of the frame completely encloses the glass element in a ring-like fashion, or according to the geometry of the frame, i.e., around its circumference, and hermetically seals the transition between the frame and the glass element. In particular, an open cavity can be formed on the inner side of the glass element in the cap to enclose the switching element(s) of an optoelectronic component formed with the cap.

[0013] With this configuration, a hermetic connection between the glass element and a nitride ceramic is possible without intermediate layers or other measures. Since no intermediate layer is required, a direct interface is formed between the glass and the nitride ceramic. The glass at the interface is then identical to the glass in the middle or within the volume of the glass element.

[0014] The frame preferably contains aluminum nitride. This material exhibits high thermal conductivity but is also non-electrically conductive. Nitride ceramics are generally very chemically inert, so it is surprising to achieve a stable bond between glass and ceramic, as chemical bonding is not expected. This is particularly surprising given the associated or expected low wettability of glass and AlN.

[0015] It has been shown that the bond also forms when the contact angle between the ceramic and the glass is greater than 90°. In this case, the ceramic behaves like a superphobic material with respect to the glass of the glass element.

[0016] According to a further aspect of the invention, the optoelectronic component encapsulated by the cap according to this disclosure is also provided. The component comprises a carrier and at least one electronic circuit element attached to the carrier, for example, a light-sensitive or light-emitting structure and / or a structure consisting of light-sensitive and / or light-emitting elements, wherein the cap is placed on the carrier and connected to it, such that the electronic circuit element is enclosed and hermetically encapsulated in the cavity formed between the cap and the carrier. The glass element forms a light-transmitting window to the cavity in order to couple light in or out.

[0017] It is particularly advantageous if the support, like the cap frame, comprises or is made of nitride ceramic. This enables excellent heat dissipation from the component and simultaneously avoids thermal stresses between the frame and the support. This is especially true if the frame and support are made of the same material to achieve matching coefficients of thermal expansion. Preferably, the frame and support comprise aluminum nitride. According to another embodiment, a ceramic-metal structure is suitable for the support. For example, the support can be constructed in two layers, with a nitride ceramic layer on which the electronic circuit element is arranged, and a metal layer. The metal layer can provide further improved heat dissipation.

[0018] The invention will be explained in more detail below with reference to the figures. Fig. 1 and Fig. Figures 2 each show a sectional view of an optoelectronic component. Fig. 3 a view of the optoelectronic component according to Fig. 1, Fig. 4, Fig. 5 and Fig. Figure 6 shows electron micrographs of the area of ​​the interface between the frame and the glass element. Fig. Figure 7 shows the frame of the cap and a glass pre-body with a mold for shaping the glass pre-body before joining. Fig. Figure 8 shows an alternative embodiment of the arrangement. Fig. 7. Fig. Figure 9 shows a continuous furnace for melting the glass element onto the frame.

[0019] Fig. Figure 1 shows a sectional view of an optoelectronic component 1. The component 1 comprises a cap 2 with a frame 5 made of a nitride ceramic, which has an opening 7, and a glass element 8 that hermetically seals the opening 7, is fused to the nitride ceramic, and is fixed in contact with the nitride ceramic of the frame 5. Fig. 2. The frame 5 has a recess 60 on its inner circumference into which the glass element 8 can be inserted, the depth of which can also be less than the thickness of the glass element. Accordingly, in an embodiment without being limited to the specific configuration of the example of Fig. 2 provided that the frame has a step 60 or a step on which the glass element 8 can be placed and which is accordingly in contact with the glass element 8 after melting.

[0020] As in the example shown, Fig. 1 and Fig. 3 It is preferred if an open cavity 11 is formed in the cap 2 on an inner surface 17 of the glass element 8. The electronic circuit element 13 then projects into this cavity 11.

[0021] The component 1 further comprises a carrier 10 and at least one electronic circuit element 13 mounted on the carrier 10, wherein the cap 2 is placed on and connected to the carrier 10, such that the electronic circuit element 13 is enclosed and hermetically encapsulated in a cavity 11 formed between the cap 2 and the carrier 10. According to a preferred embodiment, the electronic circuit element 13 can be a UV light-emitting diode (LED). In this case, the component 1 is accordingly an enclosed LED for emitting UV light. The structure described here is particularly advantageous for UV LEDs, since the efficiency of LEDs is low (typically 1-2%), causing them to become very hot.

[0022] A good connection between frame 5 and glass element 8 is achieved in particular when the glass element 8 is fused into the opening 7 of frame 5 and connected to the inner wall 9 of the opening 7, so that the inner wall 9 of frame 5 surrounds the glass element 8 in an annular manner and hermetically seals the transition between frame 5 and glass element 8. It is also possible, in particular, to create the connection between frame and glass element without intermediate materials. Accordingly, it is provided that a direct interface 57 is formed between the glass of the glass element 8 and the nitride ceramic.

[0023] The Fig. 4, Fig. 5 and Fig. Figure 6 shows electron micrographs of the interface between frame 5 and glass element 8 at various magnifications. As is preferred, frame 5 in this example is made of aluminum nitride. The scale is indicated by the bars below each image. The granular structure of the aluminum nitride ceramic is clearly visible. No transition zone is discernible at interface 57. This indicates that no reaction or mixing occurs at the interface between the nitride ceramic of frame 5 and the glass of glass element 8, resulting in a sharp interface, or rather, a seamless connection between the glass and the aluminum nitride ceramic.Surprisingly, it was found that this can be influenced by the composition of the glass of the glass element 8, and in particular, glasses containing bismuth can be detrimental to a tight interlock at the interface 57 between the glass element 8 and the frame 5. According to one embodiment, it is therefore also provided that the glass of the glass element has a bismuth content of less than 5 wt%, preferably less than 2 wt%, or is even bismuth-free, at least at the interface 57 with the frame 5. The figures also show that the glass and nitride ceramic are in contact along the entire interface due to the melting of the glass element as a result of softening of the entire glass element.Therefore, in one embodiment, it is generally provided that along the entire interface 57 between the glass of the glass element 8 and the nitride ceramic of the frame 5, the surfaces of the glass and the nitride ceramic are in contact and have a complementary fine structure. This also distinguishes the interface from, for example, a laser-joined connection. In the case of such a connection, the material is only melted locally, for example, along a joining line. The nitride ceramic preferably has at least one grain size with a mean grain diameter in the range of 1 to 10 µm. This results in a sufficiently rough surface to firmly anchor the glass element. On the other hand, the grains are still sufficiently small to create a dense structure for a hermetic enclosure of the electronic circuit element(s).

[0024] Generally, without limitation to what is in the Fig. 1 and Fig. The example shown in Figure 3 is a further development of the optoelectronic component described here, in which the support 10 also includes nitride ceramic in order to achieve good heat dissipation from the electronic circuit element 13.

[0025] For a hermetic connection between frame 5 and glass element 8, it is generally particularly advantageous if the frame has a linear coefficient of thermal expansion that is greater than the coefficient of thermal expansion of the glass in glass element 8. This applies especially to the average value of the frame's coefficient of thermal expansion compared to the average value of the glass element's coefficient of thermal expansion over a temperature range from 20°C to the glass transition temperature Tc. g of the glass element. The difference Δα of the coefficients of thermal expansion can easily reach up to Δα = 7 · 10 -6 K -1 The difference Δα is preferably less than 3 · 10 -6 K -1The difference in the coefficients of thermal expansion supports the development of compressive stress during cooling after melting and solidification of the glass element 8 in frame 5. Therefore, it is advantageous if the difference in the coefficients of thermal expansion is at least Δα = 2 · 10 -6 K -1 , preferably at least Δα = 0.5 · 10 -6 K -1 , usually preferably at least Δα = 0.1 · 10 -6 K -1 In a particularly preferred embodiment, it is also provided that the frame 5 then exerts a compressive stress on the glass element 8. Surprisingly, the formation of a hermetic connection is possible even with approximately equal or identical coefficients of thermal expansion, i.e., with a suitable glazing unit. Approximately equal or substantially equal coefficients of thermal expansion α also encompass a range of up to |Δα = 1.0 · 10 -6 K -1|, preferably up to |Δα = 0.1 · 10 -6 K -1 |, i.e., a difference in the absolute value of the coefficients of thermal expansion of the frame and the glass element up to the aforementioned value of 1.0 · 10 -6 K -1 , preferably up to 0.1 · 10 -6 K -1 . In this context, the coefficient of thermal expansion of the glass may be both greater and less than the coefficient of thermal expansion of the frame, even within this absolute difference.

[0026] To ensure that the compressive stress presses the glass and the nitride ceramic together at the interface, it is advantageous not to choose a glass element that is too thin relative to its lateral dimensions. Otherwise, the compressive stress can be reduced by elastic deflection of the glass element. Lateral dimensions in the range of 2 mm to 20 mm are preferred. For rectangular or square glass elements, these dimensions are the longest side lengths. The diagonal dimensions can be correspondingly longer. The mean thickness of the glass element 8 is preferably in the range of 0.2 mm to 2 mm. Taking these dimensions into account, the ratio of the mean thickness of the glass element to its lateral dimensions, i.e., in particular to the diameter or the longest side length, is preferably less than 1 / 20, and preferably less than 1 / 15.Shapes with a ratio greater than 1 are also conceivable, for example, if the glass element is designed as a thick lens or light guide. The frame 5 preferably has a minimum thickness to improve heat transfer. A minimum thickness is also advantageous for generating high compressive stresses. According to one embodiment of the invention, the frame has a thickness, or wall thickness, in the range of 0.5 mm to 2 mm. In general, without limiting itself to the illustrated example, a cap 2 according to this disclosure can have one or more of the aforementioned features with respect to dimensions and dimensional ratios.

[0027] At the in Fig. In the example shown in Figure 3, the opening has a square shape. The hermetic connection between the glass and the nitride ceramic is generally facilitated if the opening 7, in the case of a square or polygonal shape, has rounded corners 14. It is particularly preferred if the radius of the rounded corners is greater than 0.05 mm. Advantageously, the radius is at least 0.2 mm. Without limiting this to the examples shown in Figure 3, the following applies: Fig. The opening 7 can have a square shape shown in Figure 3, but it can also have round, elliptical and / or other non-round shapes, including angular or polygonal shapes, in particular to meet the geometry or geometric requirements of an optoelectronic component 1.

[0028] To connect the cap 2 and the carrier 10 to produce an optoelectronic component 1, soldering the two parts is suitable. Fig. Figure 1 shows the connection between cap 2 and support 10 using a metallic solder 19. The solder bonds well with the nitride ceramic and also exhibits high thermal conductivity, thus creating low thermal resistance at the interface between support 10 and cap 2.

[0029] The cap 2 according to this disclosure can be produced by a process in which a frame 5 made of a nitride ceramic is provided, having an opening 7, and in which a glass part or glass preform is brought together with the frame 5 so that the opening 7 in the frame 5 is closed, and in which the glass preform 6 is isothermally heated together with the frame 5 so that the glass of the glass preform softens and melts onto the frame 5.

[0030] The melting of the glass preform to form the glass element 8 closing the opening 7 is particularly preferably carried out in a continuous furnace. The process steps according to preferred embodiments are explained in more detail below with reference to the purely exemplary drawings. Fig. Figure 7 shows the frame 5 and a glass preform 6, which is to be fused to the frame 5 to form the cap 2. For this purpose, the frame 5 is placed on a mold 20 and the glass preform 6 is inserted into the opening 7 of the frame 5. The top surface of the mold 20 serves as the molding surface for the glass preform 6. In the simplest case, the molding surface is flat in order to form a flat outer surface of the glass element 8.

[0031] Fig. Figure 9 shows an alternative embodiment of the Fig. 8 shown arrangement. Here, the shaped body 20 is designed as a stamp, the stamping surface 22 of which projects into the frame 5 when it is placed on the frame. The glass pre-body 6 is positioned as in the arrangement of the Fig. 8 is inserted into the frame 5. The glass pre-body 6 now rests on the inside of the shaped body 20.

[0032] In a further development of the process, it is provided that the fusing of the glass preform 6 with the frame 5 takes place in a continuous furnace. Fig. Figure 9 shows a continuous furnace 23 with one or more heating elements 25. The molded parts 20 with the applied frames 5 and the glass preforms 6 inserted into the openings 7 of the frames 5, in particular as shown in Fig. 7 or Fig. Figure 8 shows, for example, that the materials are conveyed through the continuous furnace 23 on a conveyor belt 27. The continuous furnace can, in particular, have zones of different temperatures, temperature gradients, velocities and / or furnace atmospheres.

[0033] In order to selectively shape the inner surface 17 of the glass element 8 produced from the glass preform 6, a further preferred embodiment of the method provides that a punch 21 is pressed onto the glass preform 6, so that upon softening, the glass yields to the pressure of the punch 21 and is pressed against the wall of the opening 7. Simultaneously, the surfaces of the glass element 8 are shaped according to the surfaces of the punch 21 and the support 20. This makes it possible not only to form flat, disc-shaped glass elements 8, but also to create the following: Fig.The example shown already exhibits a slightly biconvex shape. Therefore, the process allows for the formation of glass elements during the production of cap 2, which can function as optical elements such as lenses, prisms, or coupling elements like light guides. Furthermore, the application of pressure has an overall positive effect, particularly when the coefficients of thermal expansion of glass element 8 and frame 5 are essentially the same, on the formation of an interlocking relationship between glass element 8 and frame 5.

[0034] If the linear coefficient of thermal expansion of the frame 5 is, as preferably provided, greater than the linear coefficient of thermal expansion of the glass element 8, a compressive stress acting on the glass element 8 is built up during joint cooling after the glass transition temperature of the glass element is reached, since the frame 5 contracts more than the glass element 8. This compressive stress presses the nitride ceramic and the glass together at the interface 57. Particularly through this mechanism, on the one hand, and the surface structures that fit together precisely due to the melting process, a hermetic seal is achieved even with superphobic material pairings. Reference symbol list 1 optoelectronic component 2 caps 5 frames 6 glass forebody 7 openings in 5 8 glass elements 10 carriers 11 Cavity 13 electronic circuit element 14 corners of 7 17 Inside of 8 19 Lot 20 molded part 21 stamps 22 stamping area 23 Continuous oven 25 heating element 27 Conveyor belt 57 Interface between frame 5 and glass element 8 60 paragraph

Claims

[1] Cap (2) for the housing (3) of an optoelectronic component (1), comprising - a frame (5) made of a nitride ceramic, which has an opening (7), as well as - a glass element (8) hermetically sealing the opening (7), which is fused to the nitride ceramic and fixed in contact with the nitride ceramic of the frame (5), wherein along the entire interface (57) between the glass of the glass element (8) and the nitride ceramic of the frame (5) the surfaces of the glass and the nitride ceramic are in contact and have a complementary fine structure, wherein the glass element (8) is fused into the opening (7) of the frame (5) and connected to the inner wall (9) of the opening (7), wherein the complementary fine structures provide a positive fit between the glass element (8) and the frame (5) and the glass element (8) is connected to an inner wall (9) of the opening (7), so that the inner wall (9) of the opening (7) surrounds the glass element (8) on a circumference of the glass element (8) and hermetically seals a transition between the frame (5) and the glass element (8). [2] Cap (2) according to one of the preceding claims wherein an open cavity (11) is formed in the cap (2) on an inner side (17) of the glass element (8). [3] Cap (2) according to any one of the preceding claims, characterized by , that the frame (5) contains aluminium nitride. [4] Cap (2) according to any one of the preceding claims, characterized by , that the contact angle between the glass of the glass element (8) and the nitride ceramic of the frame (5) is more than 90°. [5] Cap (2) according to any one of the preceding claims, characterized by , that the frame has a linear coefficient of thermal expansion which is greater than or equal to the coefficient of thermal expansion of the glass of the glass element (8), in particular wherein the mean value of the coefficient of thermal expansion of the frame in a temperature interval from 20°C to the glass transition temperature T gthe glass is greater than or equal to the mean value of the thermal expansion coefficient of the glass element. [6] Cap (2) according to the preceding claim, characterized by that the difference in the coefficients of thermal expansion is at least Δα = 2 - 10 -6 K -1 , preferably at least Δα = 0.5 · 10 -6 K -1 , usually preferably at least Δα = 0.1 · 10 -6 K -1 amounts. [7] Cap (2) according to any one of the preceding claims, characterized by , that the glass of the glass element (8) has a bismuth content of less than 5 wt%, preferably less than 2 wt%, at least at the interface (57) to the frame (5). [8] Cap (2) according to any one of the preceding claims, characterized by , that the opening (7) has a round, non-round, angular or polygonal shape, wherein in the case of angular or polygonal shapes it preferably has rounded corners (14). [9] Cap (2) according to any one of the preceding claims, characterized by , that the frame (5) exerts a compressive stress on the glass element (8). [10] Cap (2) according to any one of the preceding claims, characterized by at least one of the following characteristics: - the lateral dimension of the glass element (8) is in the range of 2 mm to 20 mm, - the average thickness of the glass element (8) is in the range of 0.2 mm to 2 mm, - the ratio of the mean thickness of the glass element (8) to the lateral dimension is less than 1 / 20, - the frame (5) has a wall thickness in the range of 0.5 mm to 2 mm, - the frame (5) has a step (60) in the opening (7) in contact with the glass element (8), - the nitride ceramic of the frame (5) has a grain size with a mean grain diameter in the range of 1 to 10 µm, -The opening (7) of the frame (5) has rounded corners (14), the radius of which is greater than 0.05 mm. [11] Optoelectronic component (1) with a cap according to one of the preceding claims, wherein the component (1) has a carrier (10) and at least one electronic circuit element (13) attached to the carrier (10), wherein the cap (2) is placed on the carrier (10) and connected to it, so that the electronic circuit element (13) is enclosed and hermetically encapsulated in the cavity (11) formed between the cap (2) and the carrier (10), and the glass element (8) forms a light-transmitting window to the cavity. [12] Optoelectronic component (1) according to the preceding claim, characterized by at least one of the following characteristics: - the support (10) comprises nitride ceramic, - the support (10) is connected to the cap (2) with a plumb line (19), - the electronic circuit element is a UV light-emitting diode (13). [13] Method, wherein a cap (2) is produced according to any one of claims 1 to 12, wherein a frame (5) made of a nitride ceramic is provided, which has an opening (7), and wherein a glass preform (6) is brought together with the frame (5) so that the opening (7) in the frame (5) is closed, and wherein the glass preform (6) is isothermally heated together with the frame (5) so that the glass of the glass preform (6) softens and melts onto the frame (5). [14] Method according to the preceding claim, characterized by , that a stamp (21) is pressed onto the glass preform (6) so that, upon softening, the glass yields to the pressure of the stamp (21) and is pressed against the wall of the opening (7). [15] Method according to one of the two preceding claims, characterized by, that the linear coefficient of thermal expansion of the frame (5) is greater than the linear coefficient of thermal expansion of the glass element (8), wherein when the frame (5) and glass element (8) cool together after the glass transition temperature of the glass element (8) is undershot, a compressive stress acting on the glass element (8) is built up by the frame (5) contracting more than the glass element (8).

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