Arrangement with LED module

Abstract

arrangement, showing a flexible carrier and an LED module - with a thermally conductive substrate (11) made of a multilayer ceramic, - with at least one LED (1,2) on the substrate, with passive SMD components (4,5,6,8,9) arranged on the substrate, - with a passive component (3) integrated into the substrate (11), - with means for dissipating waste heat in the horizontal (17) and vertical (14) direction, wherein - on the underside of the LED module are connections (15) for connection to the flexible carrier, which is a rigid-flex board or a flex board (7), and - the flexible beam has thermal vias (14'') that are guided vertically through the flexible beam.

Description

[0001] The present invention relates to a multi-LED system, particularly designed for generating a flashlight. Such multi-LED systems are particularly needed for mobile applications such as smartphones or digital cameras.

[0002] Multi-LED systems are known, featuring a hybrid structure consisting of a substrate and a mounting of passive components, as well as two light-emitting diodes (LEDs). The LEDs are covered with light conversion layers, producing, for example, a combination of warm white and cool white light. This is intended to provide better illumination and more natural colors in flash photography. One known solution comprises an LED submodule mounted on a metal-core circuit board. This submodule is mounted on a main board together with individual passive components and the driver for the multi-LED system.

[0003] In particular, mobile applications such as digital cameras, smartphones and the like increasingly require more space-saving solutions that cannot be realized with a hybrid structure.

[0004] The object of the present invention is therefore to provide an arrangement with a more highly integrated LED module, which is particularly suitable as an LED flash module.

[0005] This object is achieved by an arrangement with an LED module according to independent claim 1. Advantageous embodiments emerge from dependent claims.

[0006] An LED module is specified that is constructed on a thermally highly conductive substrate made of multilayer ceramic. All components of the module can be mounted or integrated on this substrate. At least one LED and passive SMD components, in particular for implementing a driver circuit for the LED, are arranged on the substrate. At least one passive component is also integrated into the substrate. Furthermore, the module has means for dissipating waste heat in the horizontal and vertical directions.

[0007] With its thermally conductive substrate and means for dissipating waste heat, the module is ideally suited for heat-generating semiconductors, such as LEDs and their associated drivers. A highly thermally conductive substrate is defined as a substrate made of a material with a thermal conductivity of more than 20 W / mK. Existing ceramic materials, which have an even higher heat dissipation value of, for example, more than 100 W / mK, are more advantageous.

[0008] The multilayer ceramic used as a substrate comprises several ceramic layers, between which structured metallization levels are arranged. Structured metallic layers can also be provided on both surfaces. These serve for rewiring and are connected via through-holes or vias, both to each other and to contacts on the top side of the substrate or to terminals on the bottom side.

[0009] The substrate material is selected to provide a functional ceramic for the passive components integrated into the substrate. Components that can be integrated include varistors, capacitors, thermistors, resistors, NTC elements, and coils.

[0010] The means for dissipating the waste heat comprise thermal vias that are passed through the substrate. A thermal via can have a larger cross-section than a via that is optimized solely for the function of an electrical through-hole. The thermal vias are preferably led in a straight line from a contact on the top side of the substrate through the substrate to a connection on the underside of the substrate. Such vias are also referred to as stacked vias because they are usually produced by arranging several vias of individual ceramic layers on top of one another. From the underside of the substrate, the heat can be further dissipated into a circuit environment having a heat sink, into which the module can be installed. In any case, the improved dissipation of the waste heat prevents the module or its components from becoming excessively hot.

[0011] To more quickly dissipate heat loss horizontally from parts or components that generate heat loss, metallic layers can be formed in the substrate as horizontal thermal dissipation layers – heat spreaders. Here, too, these thermal dissipation layers are designed with a larger cross-section or larger surface area than structured metal layers that serve solely for the electrical control of parts or components. Faster horizontal and vertical heat dissipation further reduces the potential heating of the module.

[0012] In one embodiment, an ESD protection component is integrated into the ceramic of the substrate. This can be implemented as a varistor. For this purpose, at least some of the ceramic layers in the multilayer ceramic are formed from a varistor material. Various zinc oxide-based materials are suitable for this purpose, for example, ZnO-Bi, ZnO-Pr, or SrTiO3.

[0013] An ESD protection element designed as a varistor comprises two terminals, each connected to several alternating, overlapping electrode surfaces inside the multilayer ceramic. The varistor voltage can be adjusted, for example, by adjusting the distance between two adjacent, different electrodes.

[0014] In one embodiment, a semiconductor component is mounted on the surface of the substrate. In addition to the LED, this may include an integrated circuit for a driver circuit for the LED.

[0015] The semiconductor component can be implemented as an SMD component. It is also possible to mount the semiconductor component using a flip-chip assembly, or to glue it on and connect it to a contact on the top side of the substrate via a bonding wire. These mounting options can also be optional and, if necessary, different for the other components to be applied to the surface of the substrate.

[0016] However, it is also possible to use the underside of the substrate for mounting components and devices on the module. This provides a larger surface area for mounting components, allowing for a more highly integrated module.

[0017] The underside of the LED module features external contacts that allow the module to be connected to a circuit board. Such a board can be selected from a rigid-flex board or a flex board. A flex or rigid-flex board has the advantage of being able to create a flexible connection to another circuit board or PCB.

[0018] In one embodiment, the substrate comprises several layers of different functional ceramics. Different passive components are integrated into these different materials, with the integrated components then using the functional ceramic as a function-defining layer. Such passive components can be selected from capacitors, inductors, resistors, ESD protection components, or NTC elements. One or more components can be integrated within the module.

[0019] If high quality or high performance are required for the passive elements, mountable discrete components are preferred. However, varistors can be integrated into the substrate without compromising quality or performance.

[0020] The module's substrate can comprise a ceramic selected from aluminum oxide, zinc oxide, or aluminum nitride. While the first two materials have thermal conductivities of more than 20 W / mK, aluminum nitride is considered to be particularly thermally conductive, exhibiting a thermal conductivity of more than 100 W / mK.

[0021] In one embodiment, the module includes a sensor mounted as a component on the substrate. Such sensors serve to optimize the components, or rather, to optimize their usability when this depends on external parameters, such as temperature or brightness. Accordingly, a sensor can be designed as a temperature sensor or a light sensor.

[0022] A simple version of a temperature sensor includes an NTC element. The light sensor can be designed as a photoelectric element, a photodiode, or a solar cell.

[0023] If the LED module is used as an LED flash module, it also includes the discharge capacitors, inductors, and resistors required for operation as a flash module. All of these components can also be mounted as discrete elements on or below the substrate.

[0024] The module presented here has an extremely compact design and, unlike conventional hybrid modules, is virtually a single piece. The module is therefore a so-called SIP (System in Package) module. The higher heat dissipation during operation, which is typically due to the high integration density, is at least compensated for by the provided heat dissipation measures. In certain versions of the module, the higher heat loss is even more than compensated for, so that such modules exhibit a lower temperature increase during operation than conventional LED modules.

[0025] The module is smaller than conventional modules and can therefore be easily integrated into miniaturized or mobile devices, such as smartphones or digital cameras. In addition to being used as a flash module, it can also be designed as a lighting module, as is particularly required for a flashlight function or for background illumination during video recordings.

[0026] The invention is explained in more detail below using exemplary embodiments and the accompanying figures. The figures are only schematic and not to scale, so neither absolute nor relative dimensions can be derived from them. Individual parts may be shown enlarged or reduced in size for clarity. Identical or equivalent parts are designated by the same reference numerals. Fig. 1 shows a schematic cross-section of an LED module according to the invention, Fig. 2 shows a schematic plan view of an embodiment of an arrangement with an LED module on a flexible carrier, Fig. 3 shows another embodiment of an LED module in plan view, Fig. 4 shows a schematic cross-section of an arrangement with an LED module on a flexible carrier, Fig. Figure 5 shows the improved temperature behavior of a module according to the invention using a temperature curve plotted over time.

[0027] Fig. Figure 1 shows a schematic cross-section of an LED module, e.g., an LED flash module with an integrated driver, temperature sensor, light sensor, discharge capacitors, inductance, and resistors. The LED module has a substrate 11 made of a multilayer ceramic. Several ceramic layers 16 are arranged in the substrate between structured metallization levels 17.

[0028] On the top side of the substrate, contacts 10 are provided for electrically connecting the components to be mounted. On the underside of the substrate, terminals 15 are provided for connecting the module to an external circuit environment.

[0029] The structured metallization levels, or the conductor tracks and electrode surfaces produced from them, are connected to each other, to the contacts 10, and / or to the terminals 15 via through-holes or vias 14. Individual, preferably several, or even all of the vias 14 can be designed as thermal vias.

[0030] A passive component is integrated inside the substrate 11, which is shown and designed as a varistor 3 in the figure. This component has several overlapping electrode layers 17, which are alternately connected to different vias. Such a varistor is a non-linear element whose resistance depends on the voltage applied to both electrodes. If an overvoltage occurs, the varistor harmlessly discharges it as a short circuit to the other electrode. It is possible to connect both electrodes of the varistor to two terminals of the component to be protected, in particular the LED. However, it is also possible to connect only one electrode of the varistor to the component and the other electrode of the varistor to a ground connection on the underside of the substrate.

[0031] Various components are mounted on the top side of the substrate, and different fastening options can be provided for assembly. The figure shows, for example, a light sensor 6, which can be designed as an NTC resistor. One electrode of this sensor can be connected directly to a via 14, while the other is connected to an adjacent contact 10 via a bonding wire. 2 and 2' represent two LEDs on the top side of the substrate, which can have the same design and / or the same fastening method. However, it is useful for an LED module to use different LEDs with different light colors or luminosities. A light conversion layer 12, for example a varnish filled with an appropriate conversion material, can be applied over the LEDs 2, 2', which here radiate upwards.Furthermore, ceramic multilayer capacitors (SMD MLCCs) 5 applied in SMD design can be arranged or mounted on the surface. In the . Fig. 1 shows an NTC sensor 4 mounted in SMD assembly and another capacitor 5'.

[0032] Each of the contacts 10 on the top side can be assigned a connection 15 on the underside of the substrate 11. Typically, the multilayer wiring inside the substrate 11 reduces the number of connections 15 compared to the number of contacts 10. If, in addition to the vias that function as electrical connections, thermally active vias used solely for heat dissipation are provided in the substrate 11, these can each be routed to a connection 15 on the underside that is to be connected to ground. However, it is also possible to provide one or more connections with a larger area than other connections for ground, each of which is connected to several thermal vias.

[0033] Fig. 2 shows an embodiment for the Fig.1 shows a schematically illustrated LED module in plan view. Four LEDs 1, 1', 2, 2', which have two different designs, are mounted on the substrate 11 of the module. The temperature sensor can be embodied as an NTC component 4. Capacitors 5, 5', and 5'' can be discharge capacitors or matching capacitors mounted on the surface of the substrate 11. Also shown here are a coil 8 and a driver for the LED 9, each mounted as discrete components on the top side. Another capacitor is designated 5'''. A light-sensitive element is embodied as a light sensor 6.

[0034] In the exemplary embodiment, the substrate 11 is mounted on a carrier board 7, 7'. This can comprise a mechanically more stable central part 7' and a more flexible connection part 7. Like a printed circuit board, the carrier board 7, 7' has contact surfaces that can be connected to the connections 15 of the substrate. Soldering is preferred as the connection method.

[0035] Fig. Figure 3 shows a schematic top view of another embodiment of an LED module. Four LEDs 1, 1', 2, 2' are mounted on the substrate 11. At least one capacitor 5, a temperature sensor 4, and a light sensor 6 are mounted as additional discrete components. Such a module can be designed with minimal dimensions, which in the illustrated embodiment can be, for example, 1.85 × 3.06 mm.

[0036] In the Fig. 2 and Fig.3 not shown are varistors 3, which are integrated into the module substrate 11 and are therefore not visible in the plan view.

[0037] Fig. 4 shows a schematic cross-section of a Fig. 1, which is mounted on a flexible carrier 7. In the illustrated embodiment, the flexible carrier has thermal vias 14'' that are guided vertically through the flexible carrier. On the underside of the carrier 7, these are connected to further connection surfaces. These connection surfaces can be used for further contact with the circuit environment or for mounting additional components, for example, MLCC capacitors 5'' or an inductor 8. Such mounting on the underside of a carrier, shown here as flexible, is particularly suitable for large-area components, as well as for components that generate a particularly high amount of heat and should therefore be arranged away from other components.

[0038] The flexible carrier 7 may comprise integrated metallic layers that can be led out laterally from the carrier and can be attached to a desired location on a motherboard by means of the flexible part of the carrier. Further shown in Fig. 6 a reflective layer 13, which can be applied as a varnish over some of the components. The reflective varnish 13 serves to improve the radiation of the LEDs, or rather, to increase the luminous efficacy of the LED module.

[0039] Fig. Figure 5 shows the temperature behavior of an exemplary LED module according to the invention during operation. It can be seen that the heat loss generated during operation of the module initially leads to a temperature increase, but this is quickly dissipated again, as can be seen from the upper curve. After the flash event with the associated temperature increase, the temperature drops steeply again.

[0040] The lower curve shows the temperature behavior without the LED in use, although in this standby mode, the module's temperature increase is naturally lower. Thanks to the good or improved heat dissipation, the maximum temperature reached during operation remains well below the permissible temperature limit of, for example, 150 °C, which represents a critical temperature for the LED's functionality.

[0041] The LED module can be designed as a so-called CeraPad module. A solder comprising tin, silver, and copper can be used to connect the components on the substrate 11 and to connect the module to a circuit environment. A copper-based heat sink, which has both high conductivity and sufficient specific heat, can be provided in a carrier board.

[0042] The following table shows the thermal conductivities, densities, and specific heats for the module materials used in the exemplary embodiments. The table shows that the metallizations and vias, as well as the inner metallization layers and the heat sink, exhibit the relatively highest thermal conductivities. The thermal conductivity of the ceramic material, on the other hand, is low, but this is compensated for by the high thermal conductivity of the heat-dissipating elements. Ceramics Top and bottom metallizations Via and metallization levels LED copper heat sink Lot Thermal conductivity (W / Km) 22 90 180 35 400 67 Density (kg / m 3 ) 6640 8900 9500 3960 8933 700 0 Specific heat (JKgK) 470 444 235 850 385 230

[0043] The invention has been illustrated using only a few exemplary embodiments and is therefore not limited to them. Arrangements comprising the features recited in claim 1 are considered to be within the scope of the invention. Features and components can be combined or integrated in any number and composition on the LED module. List of reference symbols 1.2 LEDs 3 Varistor / ESD protection component 4 NTC element / temperature sensor 5 SMD MLCC 6 Light sensor 7 circuit board 8 coil 9 drivers 10 Contact 11 Substrat 12 optical conversion layer 13 reflective layer 14 Via 15 Connection 16 ceramic layer 17 Metallization

Claims

[1] Arrangement comprising a flexible carrier and an LED module - with a thermally conductive substrate (11) made of a multilayer ceramic, - with at least one LED (1,2) on the substrate, with passive SMD components (4,5,6,8,9) arranged on the substrate, - with a passive component (3) integrated in the substrate (11), - with means for dissipating heat loss in horizontal (17) and vertical (14) directions, whereby - terminals (15) for connection to the flexible carrier, which is a rigid-flex board or a flex board (7), are arranged on the underside of the LED module and - the flexible carrier has thermal vias (14'') which are guided vertically through the flexible carrier. [2] Arrangement according to claim 1, in which thermal vias (14) are guided through the substrate (11) as a means for dissipating waste heat. [3] Arrangement according to claim 1 or 2, in which structured metallic layers (17) are provided in and / or on the multilayer ceramic and in which at least one of the metallic layers is designed as a horizontal, thermal dissipation layer as a means for dissipating waste heat. [4] Arrangement according to one of the preceding claims, in which an ESD protection component is integrated in the multilayer ceramic of the substrate, which is realized as a varistor (3). [5] Arrangement according to one of the preceding claims, in which an active semiconductor component is mounted on the surface of the substrate (11). [6] Arrangement according to one of the preceding claims, in which passive components selected from capacitor (5), coil (8), resistor and NTC element (4) are mounted on the top or bottom of the substrate (11). [7] Arrangement according to one of the preceding claims, in which wiring levels (17) are provided in the substrate (11) for interconnecting and rewiring all components integrated on and in the multilayer ceramic. [8] Arrangement according to one of the preceding claims, in which the substrate (11) has several layers of different functional ceramics (16) and in which different passive components, selected from capacitor, coil, resistor, ESD protection component (3) and NTC element, are realized in the different layers (16) of functional ceramic. [9] Arrangement according to one of the preceding claims, wherein the substrate (11) comprises a ceramic consisting of AlO x , ZnO and AlN. [10] Arrangement according to one of the preceding claims, wherein a component mounted on the substrate (11) comprises a sensor (4,6) selected from a temperature sensor (4) and a light sensor (6). [11] Arrangement according to one of the preceding claims, in which a driver and discharge capacitors (5) are mounted on the substrate (11).

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