This patent application is a national phase filing under section 371 of PCT/EP20 18/071787, filed Aug. 10, 2018, which claims the priority of German patent application 102017118490.2, filed Aug. 14, 2017, each of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a multi-LED system designed in particular for generating a flashlight. Such multi-LED systems are particularly required for mobile applications such as smartphones or digital cameras.

BACKGROUND

Multi-LED systems having a hybrid construction composed of a substrate and an assembly with passive components as well as with two light-emitting diodes (LEDs) are known. The LEDs are covered with light conversion layers, so that a combination of warm white light and of cold white light is produced, for example. This is to ensure better illumination and more natural colors when using the flash. A known solution comprises an LED submodule which is mounted on a metal core board. This submodule is mounted on a main board together with individual passive components and the driver for the multi-LED system.

However, in particular mobile applications such as digital cameras, smartphones and the like increasingly require space-saving solutions, which cannot be realized using a hybrid configuration.

SUMMARY OF THE INVENTION

Embodiments provide a more highly integrated LED module which is particularly suitable for being used as an LED flash module.

An LED module is specified which is built on a thermally well conducting substrate made of a multilayer ceramic. All components of the module can be mounted and/or integrated on the substrate. At least one LED and passive SMD components, in particular for realizing a driver circuit for the LED, are arranged on the substrate. Also, at least one passive component is integrated in the substrate. Furthermore, the module comprises means for the dissipation of waste heat in horizontal and vertical directions.

Due to the thermally conductive substrate and the means for the dissipation of waste heat, the module is ideally suited for heat-producing semiconductors, like the LED and the associated drivers. A thermally well-conducting substrate is understood to mean a substrate which has a material with a thermal conductivity of more than 20 W/mK. More advantageous are existing ceramic materials having an even higher heat dissipation value of more than 100 W/mK, for example.

The multilayer ceramic used as a substrate comprises several ceramic layers, between which structured metallization layers are arranged. On the two surfaces, too, structured metallic layers can be provided. They are intended for rewiring and, for this purpose, are connected via through-contacts or so-called vias both to each other and to contacts on the top side of the substrate or to terminals on the bottom side of the substrate.

The substrate material is selected such that it constitutes a functional ceramic for the passive components integrated in the substrate. As an example, it is possible to integrate components that are selected from among varistors, capacitors, thermistors, resistors, NTC elements, PTC elements and coils.

The means for the dissipation of waste heat comprise thermal vias, which are routed through the substrate. A thermal via can have a larger cross-section than a via that is optimized solely for functioning as an electrical through-contact. Advantageously, the thermal vias are routed from a contact on the top side of the substrate in a straight line through the substrate as far as a terminal on the bottom side of the substrate. Such vias are also referred to as stacked vias as they are usually produced by arranging several vias of individual ceramic layers on top of each other. From the bottom side of the substrate, the heat can be dissipated further to a circuit environment which comprises a heat sink and into which the module can be incorporated. The improved waste heat dissipation definitely prevents excessive heating of the module or its components.

In order to achieve a quicker horizontal dissipation of waste heat off waste-heat-generating components, metallic layers can be formed in the substrate as horizontal thermal dissipation layers or heatspreaders. Here, again, these thermal dissipation layers are formed with a larger cross-section or a larger surface than those structured metal layers that solely provide for electrical contacting of parts or components. By speeding up horizontal and vertical heat dissipation, possible heating of the module is reduced further.

In one embodiment an ESD protection element is integrated in the ceramic of the substrate. The ESD protection element can be present in the form of a varistor. For this purpose at least some of the ceramic layers in the multilayer ceramic are formed from a varistor material. Suitable materials for this are various materials based on zinc oxide, for example ZnO—Bi, ZnO—BiSb, ZnO—Pr, SiC or SrTiO3and others.

An ESD protection element in the form of a varistor has two terminals, each of which is connected to a plurality of alternately overlapping electrode areas inside the multilayer ceramic. The varistor voltage can be adjusted via the distance of two adjacent different electrodes, for instance.

In one embodiment a semiconductor component is mounted on the surface of the substrate. Besides the LED, the semiconductor component can have an integrated circuit for a driver circuit for the LED and/or a microcontroller.

The semiconductor component can be designed as an SMD component. It is also possible to fix the semiconductor component by means of a flip-chip arrangement, or to glue it and connect it to a contact on the top side of the substrate via a bonding wire. These mounting options can also be used optionally and possibly in different forms for the remaining components to be applied on the surface of the substrate.

It is also possible, however, to use the bottom side of the substrate for mounting parts and components on the module. In this way, the available surface for mounting components is larger so that a more highly integrated module can be obtained.

The bottom side of the LED module exhibits external contacts, by means of which the module can be connected to a circuit board. Such circuit board can be selected from among metal core boards, rigid-flex boards or flex boards. A flex board or a rigid-flex board has the advantage that it can establish a flexible connection to a further circuit board or a PCB.

In one embodiment the substrate has several layers made of different functional ceramics. Into these different materials different passive components are integrated, wherein the integrated components then use the functional ceramic as a function-defining layer. Such passive components can be selected from among capacitor, coil, resistor, ESD protection element or NTC element. One or several components can be integrated within the module.

If the passive elements must fulfil high quality requirements or high performance requirements, preference is given to mountable discrete components. However, varistors can be integrated in the substrate without reducing quality or performance.

The substrate of the module can comprise a ceramic selected from among aluminum oxide, zinc oxide or aluminum nitride. While the first two of these materials have thermal conductivities of more than 20 W/mK, aluminum nitride can be considered as a particularly good heat conductor, having a heat conductivity of more than 100 W/mK.

In a further embodiment the module comprises a ceramic based on manganese and Ni which has an NTC functionality. In this type of ceramic an NTC component can then be integrated as a protection element.

In one embodiment the module comprises a sensor, which is mounted on the substrate as a component. Such sensors serve to optimize the components, or optimize their operational capability, if the capability is dependent on external parameters, like temperature or brightness, for example. A sensor can accordingly be present in the form of a temperature sensor or a light sensor.

A simple type of temperature sensor comprises an NTC element. The light sensor can be a photoelectric element, a photodiode or a solar cell.

If the LED module is used as an LED flash module, it additionally comprises discharge capacitors, microcontrollers, inductances and resistors, which are necessary when the module is to be operated as a flash module. All these components can as well be mounted as discrete elements on or under the substrate.

The proposed ceramic module makes it possible to realize an LED module with improved (reduced) response time, as the ceramic of the module exhibits a very low heat capacity and good thermal coupling of the individual components of the module. This is particularly advantageous for flash light applications, especially those with multiple and/or ultra-short pulses.

The present module has an extremely compact design and is practically a one-piece device in contrast to known hybrid modules. Hence the module constitutes a so-called SIP (System In Package) module. The amount of heat, which is generally higher due to the high density of integration and which must be dissipated during operation of the module, is at least compensated by the provided measures for heat dissipation. In some embodiments of the module the higher amount of waste heat is even overcompensated, so that modules of that type exhibit a lower temperature increase during operation than do known LED modules.

Due to the compact design of the LED module as a ceramic multilayer structure it is also possible to implement an LED matrix used as a flashlight for a camera with very small distances between the individual LEDs. In this way it is possible to also make the optical system at or above the LED matrix very small, so that better optical properties can be obtained at lower manufacturing costs.

Especially for designing the LED module as a flashlight module for a camera, measures for suppressing optical crosstalk between the LED and the camera can be taken. For example, cavities can be formed in the module, the cavities reducing or interrupting the conduction of light within the substrate. These cavities can advantageously be provided all around the LED matrix, preferably in one or more near-surface layers.

Furthermore, electrical or optical components of the camera can be provided in or on the module, for example a CMOS chip, in particular one that can function as an image sensor.

The module is smaller in volume than known modules and can thus be easily incorporated into miniaturized or mobile devices such as smartphones or digital cameras. Apart from being used as a flash module it can also be designed as a lighting module, as required in particular for a torch function or as backlighting for video recordings.

