Method for determining thermal quality metric of sample

Abstract

The invention relates to a method for determining a thermal quality metric of a sample (1) in a spatially resolved manner, in which a surface region (3) of the sample is irradiated with incident light (13, 27), a temperature is measured for each of the one or more sub-regions of the surface region (3), and a quality characteristic value is obtained for each sub-region on the basis of the temperature measured for the respective sub-region and a reference temperature and the optical power of the incident light incident on the respective sub-region.

Description

Technical Field

[0001] The invention relates to a method for determining a thermal mass measure of at least one region of a sample. Background Art

[0002] Thermographic methods for determining the thermal properties of a sample are known in the prior art. For example, the so-called laser flash method can be used for this purpose. This makes it possible to measure the thermal diffusion or thermal conductivity of the sample material and thus determine the quality of the sample, for example a quality relevant to a specific application.

[0003] However, it has been shown that the known methods usually require specific properties of the sample as a prerequisite or can only detect individual influences of the thermal properties of the sample. There are also often limitations in the spatially resolved determination of the thermal properties. Summary of the invention

[0004] It is therefore an object of the present invention to provide a method and a device with which the quality of a sample, in particular with regard to its thermal properties, can be determined reliably and efficiently.

[0005] This object is achieved by the invention according to a first aspect by a method proposed for determining a thermal mass measure of at least one region of a sample, the method comprising: Provide at least one sample; illuminating at least one surface area of ​​the sample with illumination light; measuring a first temperature for each of the one or more sub-regions of the surface region; and A quality characteristic value is obtained for each subregion based on the first temperature measured for the corresponding subregion and the reference temperature of the subregion and the optical power of the incident light incident on the corresponding subregion.

[0006] The present invention is therefore based on the surprising finding that evaluating the local light-induced heat flux density of individual local areas of a sample surface provides a particularly reliable and efficient way of determining a measure of the thermal mass of the sample.

[0007] Information about the local light-induced heat flux density can in turn be obtained, taking into account the incident light power, at least using the respectively locally existing temperature at the individual sub-regions and a reference temperature. A thermal mass measure can thus be determined by an easy-to-implement local temperature measurement of the individual sub-regions. Since the surface is divided into sub-regions, this is even spatially resolved here. Since the method can also work without contact and therefore without destroying the sample, the method can be used particularly effectively.

[0008] Thus, using this method, in particular changes in the heat input and / or heat transport within the sample can be determined from the outside in a spatially resolved manner. A spatially resolved thermal mass measure of the sample can thereby be obtained.

[0009] For example, such a quality measure can indicate thermal hot spots, ie potential or actual overheating locations. This makes it possible to identify anomalies in or on the sample. The hot spots can be present in locally limited surface areas and / or volume regions of the sample.

[0010] Thermal hot spots are particularly critical in luminescent converter components, in which light of a specific wavelength is irradiated and the frequency-converted light is emitted again from the component. In such converter components, thermal hot spots lead to localized excessive and undesirable heating of the sample at the start of irradiation.

[0011] Such a luminescent converter component consists, for example, of a converter material which is applied to a heat diffuser by means of a solder layer or adhesive layer on the back side. In use, the converter material can be illuminated on the front side by light which is partially absorbed by the component, thereby causing heat input into the component.

[0012] In particular, in samples in general and in optical or optoelectronic components which may consist of a plurality of components, local overheating may be caused, for example, by a poor thermal connection of two components or by an increased heat generation in the component.

[0013] The proposed method is therefore particularly suitable for identifying potential "hot spots" of a sample, such as in particular optical or optoelectronic components, which during regular operation of the sample could lead to thermally induced failures of the respective component or parts thereof. The sample can then be classified or repaired.

[0014] The proposed method is actually based on obtaining the so-called photothermal impedance (unit [K m 2 / Watt]), especially completely or at least some of its necessary intermediate steps. This parameter describes the surface of the sample when subjected to a specified irradiation intensity (unit [Watt / m 2 ]) The particularly local temperature rise experienced during irradiation (in [K]).

[0015] The photothermal impedance of components, such as the samples discussed herein, is described in more detail below with the example of an exemplary luminescent converter assembly. The optical thermal impedance of the converter assembly is determined by the heat generation in the converter, the heat transfer through the converter, and the thermal connection of the converter to the heat spreader. Heat generation in the converter is proportional to the absorption of the impinging excitation light minus the light emission resulting from the luminescent conversion. Converter materials that use backscattering with strong diffuse reflection of the impinging light absorb less light and therefore generate less heat. If the other geometric, optical and thermal properties of the component are the same, a luminescent converter component constructed in this way has a lower photothermal impedance than a component with a weakly scattering converter material. The heat transfer through the converter is largely determined by the thermal conductivity and thickness of the converter material. A converter component with a thicker converter material exhibits a higher light-thermal impedance than the same component with a thinner converter material. A converter component with a converter material with poor thermal conductivity exhibits a higher light-thermal impedance than the same component with a converter material with better thermal conductivity. The thermal connection of the converter to the heat spreader is determined by the material used (eg adhesive or solder), but also by the thermal resistance of the interface. Thus, an assembly with a glued luminescence converter has a higher photothermal resistance than an assembly with a soldered luminescence converter. These parameters may in particular have local inhomogeneities: For example, due to defects on the surface or in the volume of the converter material, the heat generation may be increased locally.

[0016] For example, the thermal connection of the converter to the heat spreader may also be disrupted by air bubbles in the adhesive layer or solder layer.

[0017] The first temperature and the reference temperature just make it possible to quantify and / or characterize the relevant temperature increase caused by the irradiation. Here, the required temperature can be measured very easily, very quickly and reliably. For example, the first temperature of all sub-areas can be measured in a short time, for example in a few seconds or even less than a second. This makes the implementation of the process very efficient. Therefore, it can also be used for quality control and quality assurance, because a large number of samples can be tested in a short time. For example, more than 60, more than 360, more than 720, more than 1800, or even more than 3600 samples per hour can be tested using the proposed method, so that a thermal mass measure of each sample can be determined.

[0018] This means that characterization of samples and their quality assessment can be performed particularly easily and reliably, even in a large-scale production environment.

[0019] By taking into account at least the optical power of the illumination light, the illumination light does not have to be incident uniformly on the sample, but can have any spatial profile. The surface of the sample does not have to be illuminated uniformly.

[0020] The light power allocated to each sub-area can be obtained individually for a specific light source. For example, the light power can be calculated from the average irradiance [W / m 2 ] and the size of the sub-region [m 2 ] is calculated by multiplying .

[0021] The proposed method also allows the identification of various different causes of impending local overheating during the test. The method thus makes it possible to obtain a reliable indication of a defective sample. Because at least it depends on the temperature obtained. All causes leading to temperature changes, such as changes in the heat flow due to anomalies in the sample, can thus be determined using the method. However, it is particularly advantageous that not only anomalies due to poor thermal conductivity can be identified, but also anomalies due to increased absorption and therefore increased heat input. Thus, a very comprehensive thermal quality measure can be determined using the proposed method.

[0022] It should be noted that a different heat flow at least locally does not necessarily indicate an abnormality in the sense of damage. It can also be a material property of the sample, so that the heat flow can also be determined as a thermal mass measure, thereby enabling conclusions to be drawn about the material properties.

[0023] By dividing the temperature measurement into a plurality of regions, the temperature changes can be determined in a spatially resolved manner. This makes it particularly easy to assign the temperature changes to specific physical regions of the sample. In this way, the cause of local hot spots can be found particularly easily based on the measurements performed if the structure of the sample is known. For example, the cause of poor heat transfer, gas bubble inclusions and / or regions of increased absorption in the sample material can be discovered.

[0024] Here, the proposed method can be applied to both homogeneous samples and samples with or composite or layered materials. The proposed method can also be easily adapted to samples with thermal interface materials. Therefore, the proposed method overcomes the current limitations of the prior art.

[0025] It is thus no longer necessary to use the conventionally often considered measured variables of thermal impedance (especially transient behavior) or thermal resistance (especially static behavior). This is very advantageous, since these measured variables have not proven to be particularly reliable, since they are used to take into account the entire thermal power when a temperature increase occurs. Conventionally, therefore, the sample to be checked is brought into contact with a hot contact surface and a cold contact surface, and the temperature difference measured between these contact surfaces is divided by the heat flow that is also to be measured, resulting in a single thermal impedance of the sample to be checked. This is very complex to implement and is also inaccurate and does not allow any further differentiated conclusions to be drawn about the location and type of abnormal or different heat flows.

[0026] The proposed method does not require, in particular, the extraction of thermal material data, such as thermal diffusion or thermal conductivity, from the recorded measurement data, as is sometimes necessary in conventional methods in thermography. Instead, only a temperature measurement, which can be performed very easily and reliably, and characteristic data of the optical power are required.

[0027] Advantageously, in one embodiment, the proposed method also makes it possible to determine the quality of the sample related to a specific application of other properties that are not necessarily limited to thermal properties. In luminescent converters, this can be, for example, light diffuse reflection or light conversion efficiency, which together with the thermal properties determine the radiation resistance of the sample.

[0028] In one embodiment, the sample comprises an optical, optoelectronic and / or electronic component. In one embodiment, the sample alternatively or additionally comprises or is at least one electronic component. In one embodiment, the sample alternatively or additionally comprises a plurality of layers consisting of at least partially different materials.

[0029] Determining the thermal mass metric may be done manually or automatically.

[0030] In one embodiment, the thermal mass metric is the heat distribution within the sample.

[0031] For example, the thermal mass metric may be determined explicitly based on the mass characteristic values. Therefore, the method preferably comprises: determining the thermal mass metric based on the obtained mass characteristic values. The thermal mass metric may be applied to the entire sample or to a portion of the sample. For example, the determination of the thermal mass metric may be limited to a central area of ​​the sample.

[0032] Optionally, the method may include characterizing and / or classifying the anomaly or thermal properties of the sample, in particular based on the quality characteristic values. Characterization may, for example, include obtaining the spatial extent of the anomaly, in particular within the sample, and / or obtaining the spatial extent of the anomaly based on the quality characteristic values. Classification may, for example, include obtaining the type of anomaly and / or obtaining a defect in the sample. Classification may preferably also include assigning one or more elements of the real sample to the anomaly sub-region, and in particular determining these elements as defective. For example, the assignment may be based on spatial proximity and / or probability values.

[0033] An abnormal subregion is preferably a subregion for which a quality characteristic value indicating the presence of an abnormality in the subregion is obtained.

[0034] For example, if the abnormal sub-region is spatially close to the bonding transition ), then the anomaly determined for such a sub-region can be assigned to the junction transition. Such anomaly can then be classified as, for example, an anomaly of the junction transition.

[0035] The temperature such as the first temperature or the reference temperature can preferably be an absolute temperature value in Kelvin in the present application. Alternatively or additionally, the temperature can also be a measure of temperature. Optionally, the measure can be converted into an absolute temperature value in Kelvin, for example based on a reference table and / or a conversion rule. If the corresponding temperature is a measure of absolute temperature, the temperature can be obtained in a variety of ways. And measures that do not originally allow temperature measurement are also used. For example, if the absolute temperature value is not important, but several measures are compared and analyzed or evaluated based on them, then one measure is sufficient. For example, the measure of temperature can be a qualitative measure of temperature in Kelvin. For example, the measure of temperature can also be a temperature with an unknown offset. This is particularly suitable for comparison between several temperatures.

[0036] The illumination light can be provided using a laser. The emission area of ​​the laser is preferably circular or rectangular. For example, the laser is emitted from an optical fiber with a circular or rectangular cross section. For example, the illumination light can be shaped and / or directed in the direction of the sample by an optical device. The optical device can have at least one converging lens and / or at least one diverging lens.

[0037] The illumination light can thereby be projected onto the sample, in particular onto a surface area. As a result, a large-area light spot can be arranged on the sample particularly reliably. The light spot can preferably be circular or angular, in particular rectangular or square.

[0038] In this case, a thermal mass measurement can be performed on at least one region of the sample and / or on multiple regions of the sample, respectively. For example, a mass characteristic value of a sub-region apportioned to each region can be used. By determining the mass measurement, anomalies can be determined and / or located.

[0039] The illuminating light preferably has a wavelength or a wavelength range which is in the application area of ​​the sample, in particular the optical component.

[0040] In one embodiment, the light can have a wavelength in the visible spectral range, preferably in the blue spectral range. Alternatively or additionally, the light can also have a wavelength in the invisible spectral range, for example in the UV spectral range, in the X-ray spectral range and / or in the IR range.

[0041] Alternatively or additionally, it may also be provided that: (i) the sample comprises or consists of glass, glass ceramic, fluorescent glass (PIG) ​​and / or ceramic; and / or (ii) the sample comprises or is at least one luminescence converter component or a component thereof, And preferably, the luminescence converter component comprises at least a ceramic luminescence converter, in particular at least a ceramic substrate, for example at least a cerium-doped YAG and / or LuAG ceramic substrate, and / or at least a heat diffuser, preferably made of copper, aluminum and / or ceramic.

[0042] For example, the sample includes a portion exposed to the irradiation intensity and a mount for the portion, typically a luminescence converter and a heat diffuser.

[0043] The entire sample can be transparent (for transmissive applications) or non-transmissive (for reflective applications). Generally speaking, transmissive structures differ from reflective structures in that some or all parts of the transmissive structure are transparent. Therefore, all or part of such a sample does not contain metal solder or Ag layers, etc. In addition, the adhesion layer between the luminescent converter and the heat diffuser is also at least partially transparent. It can use epoxy or silicone adhesives.

[0044] An example of an exemplary reflective structure of a sample as viewed from the light incident side: 1. Optional: one or more optical coatings, such as an anti-reflection (AR) layer and / or an optical smoothing layer, 2. Mandatory: luminescent converter, preferably ceramic converter (single-crystal and polycrystalline), alternatively: phosphor glass (PIG), phosphor ceramic (PIC), 3. Optional: one or more optical layers (e.g. Ag layer or other HR layer, and / or optical smoothing layer), preferably Ag layer, 4. Connecting layer: metallic solder, solder glass and / or filled or unfilled adhesive (layer thickness 5 to 70 μm, preferably 10 to 60 μm, more preferably 15 to 50 μm, particularly preferably 20 to 50 μm). 5. Heat diffuser (in certain embodiments may be sufficiently reflective so that the HR layer can be omitted if necessary, but the connecting layer must be transparent).

[0045] An example of an exemplary transmission structure of a sample as viewed from the light incident side: 1. Optional: one or more optical coatings, such as an anti-reflection (AR) layer and / or an optical smoothing layer, 2. Mandatory: luminescent converter, preferably ceramic converter (single-crystal and polycrystalline), alternatively: phosphor glass (PIG), phosphor ceramic (PIC), bonded phosphor layer, single-crystal converter, 3. Connecting layer: must be transparent, adhesive, solder glass, in the case of side fixing, opaque fasteners can also be used, 4. A transparent heat diffuser, such as sapphire or a non-transparent (eg metal) heat diffuser at the edge of the transparent area.

[0046] The method is particularly suitable for samples in the form of luminescence converter components. Such components are used to convert irradiated light (e.g. blue light) into other wavelength ranges (e.g. yellow and / or green light) by means of photoluminescence. Such components are used, for example, in laser-excited luminescent light sources. In such components, the method can be used to detect unexpected failures of the component and of the light source in advance and thus avoid them.

[0047] The method can be used particularly well in the field of luminescent light sources and / or the production of components thereof.

[0048] In one embodiment, the luminescent converter component has an absorption of the irradiated light of 30% or more, preferably 50% or more.

[0049] The luminescence converter assembly preferably has a ceramic substrate joined to a heat diffuser. In one embodiment, the luminescence converter assembly has, in a stacking direction, in particular directly successively to one another: a ceramic substrate; in particular a coating on the back side of the ceramic substrate; a connecting layer, for example a solder layer and / or an adhesive (optionally a filled adhesive); and / or a heat diffuser. Optionally, the ceramic substrate has an antireflection coating, in particular on a main side facing away from the back side coating, in particular on the front side. The back side coating can be a silver coating, i.e. contains silver.

[0050] The luminescence converter component may comprise further layers having optical and / or thermal and / or mechanical functions, for example silver mirror layers, gold mirror layers, dielectric layers, smoothing layers and / or adhesion-enhancing layers.

[0051] In one embodiment, the luminescent converter component has one or more optical coatings, such as anti-reflection layers, dichroic layers and / or HR layers (high reflection layers) on both sides of the ceramic substrate.

[0052] Preferably, the main side is the largest side surface of the ceramic substrate.The ceramic substrate can have one or more, in particular two, main sides.

[0053] The solder layer preferably has a thickness of (a) at least 5 μm, preferably at least 15 μm, preferably at least 20 μm, (b) at most 100 μm, preferably at most 50 μm, preferably at most 40 μm, preferably at most 35 μm, and / or (c) between 5 μm and 100 μm, preferably between 20 μm and 60 μm, preferably between 20 μm and 55 μm, preferably between 25 μm and 35 μm.

[0054] The coating preferably has a thickness of (a) at least 0.1 μm, preferably at least 1 μm, preferably at least 5 μm, preferably at least 8 μm, (b) at most 30 μm, preferably at most 20 μm, preferably at most 15 μm, preferably at most 10 μm, and / or (c) between 0.1 μm and 30 μm, preferably between 1 μm and 20 μm, preferably between 5 μm and 15 μm, preferably between 8 μm and 12 μm.

[0055] The sample, in particular the luminescence converter component, can have a transparent adhesive. The heat diffuser can also be provided in the form of a reflector. At least some of the individual components of the sample can be glued to one another.

[0056] In luminescent converter components, overheating can be caused by poor heat dissipation and / or thermal bonding of the converter material (i.e. the ceramic substrate) to the heat diffuser (i.e. due to poor thermal impedance), but can also be caused by increased heat generation in the component (i.e. reduced light conversion). In practical use, both factors are highly correlated. Therefore, they can also be used together under the term photothermal impedance. Photothermal impedance describes the combined influence of the two factors here. Thus, for example, thermal hot spots can be caused by a) disturbed heat dissipation within the sample, b) local increase in light absorption within the sample or on the surface of the sample, and c) local disturbance of light conversion within the sample. In all cases, the function of the sample is impaired because local heating occurs in the sample, which can ultimately even lead to its destruction. All these different causes of thermal hot spots can be identified by the proposed method, even combinations of these causes. This is therefore an advantage over conventional thermal imaging techniques, by which only the causes of disturbed heat dissipation mentioned in a) can be identified.

[0057] The method can therefore be used preferably for determining the photothermal impedance of a luminescence converter component in a spatially resolved manner. This variable has been determined to be an extremely reliable variable by which the suitability of a component for use in a laser excitation light source can be assessed.

[0058] If the photothermal impedance is known, it is very advantageously possible to estimate the maximum irradiance intensity that the luminescent converter assembly is allowed to withstand.

[0059] Furthermore, it is even possible to optionally separate the optical and thermal contributions to the photothermal impedance, if this is of particular interest, for example for a more detailed determination of a quality measure and / or for characterizing and / or classifying an anomaly.

[0060] The proposed method is particularly suitable for characterizing so-called static luminescence converter components (sometimes also referred to simply as static converters). These are in particular ceramic luminescence converter components made of cerium-doped YAG or LuAG ceramic substrates (sometimes also referred to as ceramic plates).

[0061] These plates, which are 60 μm to 225 μm thick, for example, are optionally coated at least partially with a silver layer on the back and are preferably arranged on a heat diffuser, for example made of copper, in particular soldered thereto, but can also be glued thereto.

[0062] The luminescent converter preferably comprises at least one luminescent material which is able to at least partially convert incident light of a specific wavelength into light of a different wavelength. In this case, it is in particular a nitride and / or a garnet which contains at least one excitation element, for example europium and / or cerium. It can advantageously be a ceramic luminescent material (hereinafter also referred to as optoelectronic ceramic) or a luminescent material in which luminescent substance particles ("phosphor") are embedded in an inorganic matrix, preferably a "phosphor in glass" (PIG), a "phosphor in ceramic" (PIG), or an "inorganic phosphor" (PII), preferably a ceramic luminescent material.

[0063] Corresponding advantageous materials or luminescence converters are described, for example, in DE 10 2013 100 832 A1, DE 10 2013 100 821 A1 and DE 10 2012 005 654 A1. The luminescence converter assembly is advantageously a static converter assembly or a dynamic converter assembly (hereinafter also referred to as a phosphor wheel). The luminescence converter assembly can be operated transmissively or reflectively. In an advantageous embodiment, the luminescence converter assembly is operated in a reflective manner.

[0064] A heat diffuser may for example be and / or comprise a device, in particular a mechanical device, which promotes and / or causes a heat flow between two elements, which are each connected to the device in a heat-conducting manner.

[0065] The heat diffuser can be transparent or opaque for the emitted light. In particular, in reflective applications, a heat diffuser comprising metal and / or ceramic can be provided. For example, the heat diffuser can have copper, aluminum, sapphire, ceramic, glass ceramic, glass and / or plastic as material. For example, a copper-ceramic sandwich can also be provided as a heat diffuser. The heat diffuser can be a fixedly mounted body (for a static converter) or a body that is movable, for example rotating, during use (for a phosphor wheel), but its photothermal impedance can preferably also be measured in the stationary state.

[0066] The converter is preferably used in a laser-excited luminescent light source, wherein it is irradiated with blue light. Part of the irradiated blue light power is converted into, for example, yellow light and / or green light by photoluminescence. Another part is converted into heat, which is dissipated via the heat diffuser. The heat diffuser is in turn preferably mounted on a heat sink in order to be able to dissipate the input heat.

[0067] More precisely, in particular in one embodiment, (blue) light falls on the surface of the ceramic substrate. A small part of the light is reflected, but a major part of the light penetrates into the substrate. A part of the major part is diffusely reflected, another part is absorbed. A part of the absorbed light (or its power) is converted into emitted cold light, another part generates heat in the substrate material.

[0068] The majority of the heat is usually generated in the converter volume below the excitation point of the emitted light. However, incident (eg blue) light can also be absorbed in the transition region to the heat diffuser and generate heat there.

[0069] The heat is then preferably conducted to the heat sink, for example, via a heat diffuser. For example, a heat conducting paste and / or a heat conducting pad may be arranged between the heat sink and the heat diffuser. Heat transfer by heat radiation or heat convection due to surface cooling is neglected here.

[0070] The specimen preferably has a luminescence converter component in the form of a static luminescence converter component.

[0071] However, the method is not limited to static converters. The method is also equally applicable to so-called dynamic converters. A dynamic converter is understood to be a converter component in which the converter material moves relative to the irradiation light, for example. This occurs, for example, with so-called phosphor wheels, in which, for example, a ring-shaped converter is applied, in particular glued, to a rotating metal disk of a mirror surface. In this case, the ambient air can advantageously be regarded as a heat sink, which, despite its poor thermal conductivity, can dissipate heat well from the phosphor wheel due to the large surface area of ​​the phosphor wheel.

[0072] In samples, in particular in the form of luminescent converter components, for example in the form of static converters, various types of local overheating can be determined using the proposed method. For example, this is caused by poor thermal contact impedance between converter and heat diffuser. But it can also be caused by poor local thermal conductivity or increased absorption of the irradiated light. Conventional methods do not allow the assessment of the cause of overheating by simple measurements.

[0073] The main side of the ceramic substrate has, for example, at least one side length between 0.5 mm and 50 mm, preferably between 0.5 mm and 40 mm, preferably between 2 mm and 30 mm, preferably between 2 mm and 20 mm, preferably between 2 mm and 10 mm, preferably between 2 mm and 7 mm, preferably between 3 mm and 5 mm.

[0074] The main side of the ceramic substrate has at least one side length of, for example, at least 0.5 mm, preferably at least 1 mm, preferably at least 2 mm, preferably at least 5 mm, preferably at least 7 mm, preferably at least 10 mm, preferably at least 15 mm, preferably at least 20 mm, preferably at least 25 mm, preferably at least 30 mm, preferably at least 40 mm, preferably at least 50 mm, preferably at least 60 mm, preferably at least 70 mm, preferably at least 80 mm.

[0075] The main side of the ceramic substrate alternatively or additionally has, for example, at most 100 mm, preferably at most 90 mm, preferably at most 80 mm, preferably at most 70 mm, preferably at most 60 mm, preferably at most 50 mm, preferably at most 40 mm, preferably at most 30 mm, preferably at most 20 mm, preferably at most 10 mm, preferably at most 7 mm, preferably at most 5 mm, preferably at most 4 mm, preferably at most 3 mm, preferably at most 1 mm.

[0076] The ceramic substrate preferably has square or rectangular main sides.

[0077] For example, the main side of the heat diffuser has at least one side length between 1 mm and 100 mm, preferably between 5 mm and 80 mm, preferably between 15 mm and 60 mm, preferably between 15 mm and 50 mm, preferably between 15 mm and 450 mm, preferably between 20 mm and 40 mm.

[0078] The main side of the heat diffuser has, for example, at least one side length of at least 1 mm, preferably at least 10 mm, preferably at least 20 mm, preferably at least 30 mm, preferably at least 40 mm, preferably at least 50 mm, preferably at least 60 mm, preferably at least 70 mm, preferably at least 80 mm.

[0079] Alternatively or additionally, the main side of the heat diffuser has, for example, at most 100 mm, preferably at most 90 mm, preferably at most 80 mm, preferably at most 70 mm, preferably at most 60 mm, preferably at most 50 mm, preferably at most 40 mm, preferably at most 30 mm, preferably at most 20 mm, preferably at most 10 mm, preferably at most 7 mm, preferably at most 5 mm, preferably at most 4 mm, preferably at most 3 mm, preferably at most 2 mm.

[0080] The thickness of the heat diffuser may be between 2 mm and 30 mm, preferably between 2 mm and 10 mm. For example, the thickness may be 3.2 mm or 4 mm.

[0081] The heat diffuser preferably has square or rectangular main sides. Preferably, a main side is the side surface of the heat diffuser with the largest area. The heat diffuser can have one or more, in particular two, main sides.

[0082] In one embodiment, the heat diffuser may be circular. Thus, the heat diffuser may have a diameter, for example, between 2 mm and 30 mm, preferably between 4 mm and 20 mm, preferably between 5 mm and 15 mm. Alternatively or additionally, the heat diffuser may have a thickness, for example, between 0.5 mm and 10 mm, preferably between 1 mm and 4 mm.

[0083] In one embodiment, the heat diffuser can be a wheel made of aluminum or ceramic. In this case, the heat diffuser can have a diameter of, for example, between 20 mm and 200 mm, preferably between 25 mm and 120 mm, preferably between 30 mm and 100 mm.

[0084] In the present application, if a range of values ​​is specified as "between X and Y", in a preferred embodiment, the boundary values ​​X and Y are included in the range of values. In other words, the range of values ​​includes the boundaries.

[0085] Alternatively or additionally, it may also be provided that: (i) the thickness of the ceramic substrate is (a) at least 30 μm, preferably at least 80 μm, preferably at least 100 μm, (b) at most 400 μm, preferably at most 300 μm, preferably at most 250 μm, preferably at most 225 μm, preferably at most 200 μm, and / or (c) between 30 μm and 400 μm, preferably between 60 μm and 300 μm, preferably between 80 μm and 225 μm; (ii) the ceramic substrate is at least partially coated, in particular with a silver coating, at least on one main side; and / or (iii) Arranging the ceramic substrate, in particular the coated side, on the heat diffuser, in particular soldering it thereto, preferably forming a solder layer between the heat diffuser and the ceramic substrate.

[0086] The solder layer preferably establishes a mechanical and thermal connection between the heat diffuser and the (possibly coated) ceramic substrate.

[0087] Optionally, the silver layer is applied to the entire surface of the ceramic substrate. Optionally, the solder layer is applied to the entire surface of the coated main side of the ceramic substrate.

[0088] As an alternative to the solder layer, another connection mechanism may be provided between the ceramic substrate and the heat diffuser to fasten the two together, such as an adhesive layer.

[0089] Alternatively or additionally, it can also be provided that, at least based on the quality characteristic values ​​obtained for the individual sub-regions, (a) the photothermal impedance of these sub-regions is obtained or represented by the quality characteristic values, (b) characteristics of the sample are determined as thermal mass metrics and / or (c) local anomalies of the sample, such as thermal hot spots of the sample, are determined as thermal mass metrics.

[0090] Thermal hot spots are particularly important for static converters, so determining whether they exist is particularly preferred.

[0091] Alternatively or additionally, it may also be provided that the method further comprises: respectively measuring and / or obtaining a second temperature for each corresponding sub-area in which the first temperature has been measured, The second temperature is a reference temperature of the corresponding subregion or the reference temperature is obtainable and / or is obtained with the aid of the second temperature.

[0092] By measuring the second temperature of the preferably non-irradiated sample, a measure of the temperature increase upon irradiation can be obtained particularly reliably by using the temperature difference between the first temperature and the second temperature.

[0093] The second temperature can preferably be measured independently of the first temperature. As a result, the method can be used particularly flexibly and efficiently.

[0094] It is even advantageous that the same second temperature can be used as reference temperature for a plurality of samples. This can reduce the workload in the method and increase its efficiency. For example, the same second temperature can be used to determine a thermal mass measure for the samples involved in a specific time period.

[0095] Preferably, the first temperature and the second temperature are each expressed as an absolute temperature value in Kelvin or in particular as a qualitative or quantitative measure of the temperature.

[0096] An absolute temperature value in Kelvin is, for example, 300 K. A qualitative measure of temperature is, for example, a value on a scale, for example between 1 (cold) and 10 (hot), where the value may be, for example, 3. A temperature measure with an "8" on the scale would lead to the conclusion that the location where the measure "8" was obtained is hotter than the location where the measure "3" was obtained.

[0097] Alternatively or additionally, provision can also be made for the first temperature of the individual sub-regions to be measured at a corresponding, preferably common, first time point. In which, the first time point is preferably (a) at least 0.01 seconds, preferably at least 0.03 seconds, preferably at least 0.05 seconds, preferably at least 0.07 seconds, preferably at least 0.1 seconds, preferably at least 1 second, preferably at least 2 seconds, preferably at least 3 seconds, preferably at least 5 seconds after the start, during and / or before the end of irradiation of the surface area of ​​the sample with the irradiation light, (b) at most 10 seconds, preferably at most 7 seconds, preferably at most 5 seconds, preferably at most 3 seconds, preferably at most 1 second, preferably at most 0.7 seconds, preferably at most 0.5 seconds, preferably at most 0.3 seconds, preferably at most 0.1 seconds, preferably at most 0.07 seconds, preferably at most 0.05 seconds, preferably at most 0.03 seconds, and / or (c) between 0.01 seconds and 10 seconds, preferably between 0.1 seconds and 10 seconds, preferably between 0.1 seconds and 1 second.

[0098] In this context, it has surprisingly been found that samples with different components can each have different heat capacities and / or thermal conductivities and that based on this, particularly reliable knowledge can be derived using the method. Therefore, the individual components require different times to heat up when irradiated with irradiation light.

[0099] For example, in a rough approximation, the converter can be considered as a body with uniform heat input connected to a heat diffuser. The initial temperature rise can then be estimated by ΔT / Δt=P / Q. The typical time constant before reaching the equilibrium temperature is Δt=d 2 / a. This can usually be done in a few milliseconds. If the heat diffuser is not connected to a heat sink, it heats up slowly according to ΔT / Δt=P / Q. Since the heat capacity of the exemplary heat diffuser is about 800 times higher than that of a typical converter, the heating patterns of the two components can be well distinguished from each other and therefore separated from each other. This is also shown in the thermal characterization data of the exemplary converter and heat diffuser presented later.

[0100] If the first point in time is therefore after the start of irradiation of the surface area, the consideration can be restricted to the components relevant for the evaluation of the thermal mass measure by correspondingly selecting the time offset between the start of irradiation and the point in time at which the first temperature is measured. The method is particularly suitable for determining thermal mass measures, in particular thermal mass measures of converter components such as static converters, if the first point in time is preferably selected shortly after the start of irradiation (or alternatively shortly before the end of irradiation, respectively), wherein values ​​between 0.01 seconds and 10 seconds have proven to be particularly preferred here.

[0101] The reason is that in the exemplary assembly, the thermal capacities of the thin converter chip (i.e. the ceramic substrate) and the large heat diffuser (e.g. made of copper) are different. Thermal modeling of the exemplary converter assembly shows that the heating of the ceramic substrate can be accomplished on a time scale that is up to three or four orders of magnitude smaller than the time scale associated with heating the heat diffuser. For example, under irradiation with irradiating light, the ceramic substrate can be heated within a few milliseconds to subseconds, while a copper heat diffuser requires several seconds for this. In the case of a relatively poor connection of the heat diffuser (e.g. made of copper) to the sample holder acting as a heat sink, a continuous temperature increase can even occur over a longer period of time. However, the proposed method is also characterized in that even in such rather unfavorable circumstances, thermal values, such as the photothermal impedance, can always be well determined.

[0102] These circumstances can be particularly well exploited in static converter measurements. The thermal time constant of the converter including the connecting layer differs significantly from the thermal time constant of the heat spreader.

[0103] In other words, if the specific irradiance (E[W / mm 2 ]) to measure and / or determine the photothermal impedance of a static converter component by measuring the temperature increment (Delta T [K]) under a certain temperature condition, a time-dependent curve is obtained, which, over a measurement duration of a few seconds, usually shows a temperature increase on two time scales: The temperature measured on the sample surface increases suddenly immediately after the laser incident light is switched on (e.g. 5-6 K in 0.1 seconds). Thereafter, the temperature increase still occurs, but significantly slows down.

[0104] All first temperatures are preferably measured at the same first point in time. All first temperatures measured at this first point in time are then present under the same conditions of the sample. This enables particularly reliable conclusions to be drawn about the individual quality characteristic values ​​and the thermal quality measure.

[0105] The first point in time is preferably between 0.01 seconds and 0.3 seconds, in particular between 0.03 seconds and 0.3 seconds, in particular between 0.05 seconds and 0.3 seconds after the start.

[0106] Alternatively or additionally, provision can also be made for the second temperature of the individual subregions to be measured at a second, preferably common, time. Wherein, preferably, the second time point is before the start of irradiation of the surface area of ​​the sample with the irradiation light and / or after the end of the irradiation, in particular before and / or after the start (a) at least 0.01 second, preferably at least 0.03 second, preferably at least 0.5 second, preferably at least 0.1 second, preferably at least 1 second, preferably at least 2 seconds, preferably at least 3 seconds, preferably at least 5 seconds, (b) at most 10 seconds, preferably at most 7 seconds, preferably at most 5 seconds, preferably at most 3 seconds, preferably at most 1 second, preferably at most 0.5 seconds, preferably at most 0.1 second, preferably at most 0.05 seconds, preferably at most 0.03 seconds, and / or (c) between 0.01 second and 10 seconds, preferably between 0.1 second and 10 seconds, preferably between 0.1 second and 5 seconds.

[0107] By preferably selecting the second time point before the start of irradiation and the first time point shortly after the start (i.e. between approximately 0.01 and 10 seconds after the start), the influence of the heat diffuser can be eliminated particularly simply and reliably for the sample, in particular for a converter assembly, such as a static converter assembly, and the consideration can be limited to the ceramic substrate including the connecting layer. In other words, the thermal impedance or photothermal impedance of the ceramic substrate and the connecting layer (in particular the silver coating and / or the solder layer) can be easily extracted from the impedance curve of the entire system.

[0108] This has the particular advantage that the influence of the heat spreader in such a system can be eliminated very easily and reliably and that no elaborate connection of the heat spreader to the heat sink is required.

[0109] Preferably, all second temperatures are measured at the same second point in time. All second temperatures measured at this second point in time are then under the same conditions of the sample. This enables particularly reliable conclusions to be drawn about the individual quality characteristic values ​​and the thermal quality measure.

[0110] The second point in time is preferably between 0.01 seconds and 0.3 seconds, in particular between 0.03 seconds and 0.3 seconds, and in particular between 0.05 seconds and 0.3 seconds before the start of irradiation of the surface area of ​​the sample with the irradiation light.

[0111] Alternatively or additionally, it may also be provided that each first temperature is a surface temperature of the sample; and / or Each second temperature is a surface temperature of the sample.

[0112] The surface temperature can be measured on a sample particularly easily, contactlessly and non-destructively and is therefore advantageous.

[0113] Alternatively or additionally, it may also be provided that the measurement of the first temperature comprises: Preferably, at least one first image of the sample is recorded by at least one first thermal imaging camera at a first point in time and a first temperature of each sub-region is obtained from the image information of the at least one first image, Wherein, preferably (i) the recorded first image has multiple pixels, and each sub-area is at least partially covered by at least one pixel, and the first temperature is obtained using image information of each pixel provided by the camera, such as a temperature value, and / or (ii) the first temperature is calculated from multiple first images, preferably by extrapolating the temperature curve of each pixel at the time point when the illumination light is turned on or off.

[0114] The first temperatures can be measured particularly reliably with a thermal imaging camera. In particular, the use of a thermal imaging camera makes it possible to measure all first temperatures simultaneously or substantially simultaneously.

[0115] "Substantially simultaneously" here preferably means that the latest and oldest image information related to the first temperature recorded and stored by the thermal imaging camera are within a very short time period, for example less than 1 second, preferably less than 0.1 second, preferably less than 0.05 second, preferably less than 0.01 second.

[0116] Using thermal imaging cameras, it is even possible to achieve time resolutions in the millisecond range or even in the sub-millisecond range. Preferably, therefore, the first thermal imaging camera has a time resolution in the millisecond range or in the sub-millisecond range, for example between 0.1 ms and 100 ms, preferably between 0.1 ms and 70 ms, preferably between 1 ms and 50 ms, preferably between 5 ms and 50 ms, preferably between 5 ms and 40 ms. Thus, for certain applications of the invention, even rapid temperature changes can be resolved sufficiently well in a timely manner. This preferred time resolution is preferably achieved with an actively cooled thermal imaging camera.

[0117] Alternatively, the first thermal imaging camera can also be a bolometer chip camera. This usually has a lower time resolution than the above-mentioned actively cooled thermal imaging cameras. For example, the time constant of the response time of the camera can be 10 ms. However, bolometer chip cameras have proven to be particularly preferred for determining thermal mass measures of converter components. On the one hand, cameras of this type are cheap to purchase and maintain (for example, no cooling is required). On the other hand, bolometer chip cameras also make it possible, in particular in converter arrangements, to clearly distinguish between the thermal time constant of the converter including the connection layer and the thermal time constant of the heat diffuser.

[0118] The first image may have a plurality of pixels and the thermal imaging camera provides different image information for each pixel. Based on this image information, a first temperature may then preferably be obtained for each pixel or the first temperature may be obtained directly from the image information. The latter is particularly advantageous when the thermal imaging camera provides an absolute temperature value or a measure of such a temperature for each pixel. This is very efficient and reliable.

[0119] Alternatively or additionally, the temperature can also be measured using one or more non-spatially resolved temperature sensors. In this case, the number of sub-areas that can be measured in one measurement cycle can be given by the number of temperature sensors.

[0120] The sub-region of the surface area can be covered by one or more pixels. Preferably, each sub-region is covered by more than one pixel, for example, at least 5, preferably at least 9, preferably at least 25, preferably at least 49 pixels. If each region is just covered by one pixel, then the best spatial resolution can be achieved. Optionally, each sub-region is covered by a maximum of 10000 pixels, preferably a maximum of 1000 pixels, preferably a maximum of 100 pixels, preferably a maximum of 20 pixels, preferably a maximum of 10 pixels. For example, each sub-region is covered by a pixel between 2 and 10000, preferably a pixel between 2 and 5000, preferably a pixel between 2 and 3000, preferably a pixel between 2 and 1000, preferably a pixel between 2 and 500, preferably a pixel between 2 and 300, preferably a pixel between 2 and 1000, preferably a pixel between 2 to 50, preferably a pixel between 2 to 25.

[0121] The first camera preferably has at least 10,000 pixels, preferably at least 50,000 pixels, preferably at least 100,000 pixels, preferably at least 300,000 pixels, preferably at least 500,000 pixels, preferably at least 1,000,000 pixels.

[0122] The first camera preferably has at most 5,000,000 pixels, preferably at most 3,000,000 pixels, preferably at most 2,000,000 pixels, preferably at most 1,000,000 pixels, preferably at most 500,000 pixels, preferably at most 300,000 pixels, preferably at most 100,000 pixels.

[0123] The first camera preferably has between 100,000 and 5,000,000 pixels, preferably between 100,000 and 2,000,000 pixels, preferably between 300,000 and 1,000,000 pixels, preferably between 300,000 and 800,000 pixels, preferably between 300,000 and 700,000 pixels, preferably between 500,000 and 700,000 pixels.

[0124] If a sub-region is covered by more than one pixel, the first temperature of the sub-region can optionally be obtained by the average value of all temperatures of the pixels allocated to the sub-region. For example, a single sub-region can be covered by four pixels. The thermal imaging camera provides the temperatures of T1 to T4 for each pixel. Then the average value of all four temperatures T1 to T4 obtained according to (T1+T2+T3+T4) / 4 can be used as the first temperature of the sub-region. This can improve the measurement result. If a pixel is only partially located in a sub-region, it is preferably processed in the same way as a pixel completely located in the sub-region. This makes the process very efficient and reliable.

[0125] Preferably, the maximum side length of a pixel of a thermal imaging camera, in particular one with a macro lens, is (a) at least 1 μm, preferably at least 3 μm, preferably at least 5 μm, preferably at least 10 μm, preferably at least 20 μm, preferably at least 25 μm, preferably at least 30 μm, preferably at least 35 μm, preferably at least 40 μm, preferably at least 45 μm, preferably at least 50 μm, (b) at most 100 μm, preferably at most 80 μm, preferably at most 50 μm, preferably at most 45 μm m, preferably at most 40 μm, preferably at most 35 μm, preferably at most 30 μm, preferably at most 25 μm, preferably at most 20 μm, preferably at most 10 μm, preferably at most 5 μm, preferably at most 1 μm, and / or (c) between 1 μm and 100 μm, preferably between 1 μm and 50 μm, preferably between 1 μm and 40 μm, preferably between 10 μm and 40 μm, preferably between 20 μm and 40 μm, preferably between 30 μm and 40 μm. Optionally, the pixels are square and / or all pixels have the same size.

[0126] In a preferred embodiment, the side length of the square pixel is 35 μm. This is the lower limit of the spatial resolution of the photothermal impedance. This pixel size has proven to be particularly advantageous in terms of cost and efficiency.

[0127] When referring to "pixel size" or "side length of a pixel" here, this preferably means the corresponding size of the part of the real sample that is imaged on one pixel of the thermal imaging camera. I.e., this is the size of the sample part that is captured by the pixel of the recorded image. By using modified optics, the pixel sizes mentioned here can easily be matched to the respective requirements.

[0128] In one embodiment, the first image is taken from a main viewing direction. Optionally, the illumination light is incident on the sample along a main propagation direction. Preferably, it can be provided that the main propagation direction of the illumination light incident on the sample and the main viewing direction of the first thermal imaging camera are at an angle to each other.

[0129] The angle is preferably at least 1 degree, preferably at least 10 degrees, preferably at least 20 degrees, preferably at least 30 degrees, preferably at least 40 degrees, preferably at least 50 degrees, preferably at least 60 degrees, preferably at least 70 degrees, and preferably at least 80 degrees.

[0130] The angle is preferably at most 90 degrees, preferably at most 80 degrees, preferably at most 70 degrees, preferably at most 60 degrees, preferably at most 50 degrees, preferably at most 40 degrees, preferably at most 40 degrees, preferably at most 20 degrees.

[0131] The angle is preferably between 1 degree and 90 degrees, preferably between 5 degrees and 80 degrees, preferably between 10 degrees and 60 degrees, preferably between 15 degrees and 45 degrees, preferably between 20 degrees and 40 degrees.

[0132] Alternatively or additionally, provision may also be made for the measurement of the second temperature to include: Preferably, at a second time point, at least one second image of the sample is recorded by at least one second thermal imaging camera and / or the first thermal imaging camera, and a second temperature of each sub-area is obtained from the image information of the at least one second image, Preferably, (i) the recorded second image has multiple pixels and each sub-area is at least partially covered by at least one pixel, and the second temperature is obtained using image information of each pixel provided by the camera, such as a temperature value, and / or (ii) the second temperature is calculated from multiple second images, preferably by extrapolating the temperature curve of each pixel at the time point when the illumination light is turned on or off.

[0133] The second temperatures can be measured particularly reliably using a thermal imaging camera. In particular, the use of a thermal imaging camera makes it possible to measure all second temperatures simultaneously or substantially simultaneously.

[0134] Since the embodiments corresponding to the measurement of the second temperature also apply to the measurement of the first temperature, reference can be made to the above statements. The same applies to the second thermal imaging camera.

[0135] If the same thermal imaging camera is used to record the first image and the second image, it is particularly easy to assign the same pixels or groups of pixels to the same sub-region. Or in other words, the same pixels in both images provide temperature information for the same sub-region. This makes the method efficient, since, for example, the pixels in row X and column Y cover the same at least one sub-region in both images. If different cameras are used, it is optionally necessary to assign ("map") the pixels of one camera to the pixels of the other camera. However, this can also be implemented very simply based on a calibration record.

[0136] Preferably, the first and / or second thermal imaging camera is calibrated by means of a calibration standard.

[0137] If two different thermal imaging cameras are used as the first thermal imaging camera and the second thermal imaging camera, the cameras are preferably calibrated using the same calibration standard, thereby ensuring that the values ​​of the two cameras can be combined with one another.

[0138] Alternatively or additionally, it may also be provided that the acquisition of the quality characteristic value of the sub-region comprises: calculating a quality characteristic value of the sub-region based at least on a temperature difference formed between a first temperature of the sub-region and a reference temperature of the sub-region, Preferably, in order to calculate the quality characteristic value, (i) the temperature difference divided by the light power incident on the corresponding sub-area, (ii) the temperature difference divided by the quotient of the light power incident on the corresponding sub-area and its area, and / or (iii) the light power of the irradiation light incident on the corresponding sub-area, in particular the temperature difference divided by the light power.

[0139] By calculating the temperature differences respectively, the temperature increase of each sub-region of the surface area of ​​the sample due to the irradiation with the illumination light can be easily and reliably determined, for example as an absolute value in Kelvin or as a measure.

[0140] In one embodiment, a larger temperature difference between the sub-regions leads to a larger quality characteristic value of the corresponding sub-region.

[0141] Optionally in an embodiment, a calibration measurement of the irradiance intensity is performed by measuring the beam profile of the excitation light irradiating the homogeneous sample with a camera. The camera can even be at least one thermal imaging camera. Optionally, normalization is performed based on the total light power distributed over the surface area. Thus, at least for each subarea, a power distribution in watts per square millimeter (W / mm 2 ]) as the unit of radiation intensity.

[0142] The photothermal impedance can then advantageously be obtained as the temperature response divided by the normalized power density distribution. Or in other words, the photothermal impedance corresponds to the temperature rise of each sub-area due to the illumination divided by the normalized irradiation intensity of this sub-area.

[0143] Optionally, obtaining the quality characteristic value of the sub-region may include: The quality characteristic value of the sub-region is also calculated based on the irradiance intensity of the illumination light incident on the corresponding sub-region, in particular, subtracting the irradiance intensity of the emitted light from the irradiance intensity of the illumination light incident on the corresponding sub-region.

[0144] In other words, the measured temperature rise is independent of the total irradiation intensity, but only of the actual absorbed power of the irradiated light in the respective sub-area. This is calculated by subtracting the emission intensity from the irradiation intensity.

[0145] The emitted light irradiance is preferably composed of Fresnel reflection of the (blue) incident light, diffuse reflection of the (e.g. blue) incident light by backscattering in the converter material, and emission of converted light generated by photoluminescence. These parameters can be measured directly or indirectly by measurement techniques known to those skilled in the art. For example, in a separate experiment, the reflectivity can be obtained as the quotient of the emitted light irradiance and the irradiation light irradiance, and the emission current density can then be obtained from the measured irradiance intensity by means of this quotient.

[0146] Alternatively or additionally, it may also be provided that the method further comprises: determining an abnormality of the sample, preferably a local abnormality, based on the obtained quality characteristic value of the sub-region, Wherein, determining the abnormality of the sample preferably includes: A subregion whose quality characteristic value is above a limit value, below a limit value and / or within a defined or definable limit is determined as an abnormal subregion, and The anomaly sub-regions are preferably assigned to one or more surface and / or volume regions of the sample and / or are characterized and / or classified with respect to the type of anomaly, such as in particular delamination, bubble inclusions, particles and / or contaminants on the surface, and / or inclusions or contaminants in the volume.

[0147] In particular, the determination of an anomaly in the sub-area may include processing at least the first temperature and the reference temperature and the evaluation result of the incident light power by a filter, and determining an anomaly based on at least one processing result. The filter may be, for example, a filter from the field of image processing and may have, for example, an edge detector.

[0148] As a further filter in the field of image processing, a threshold filter with dynamic threshold adjustment can be provided. This makes it possible, for example, to identify pixels or sub-areas whose values ​​are above the mean or median value of the evaluation area by a certain factor. If the number of consecutive pixels or the sum of the pixel values ​​of consecutive pixels exceeds a certain value, a local anomaly is present.

[0149] However, for example, the distribution density of the pixel values ​​can also be determined and the value of a certain percentile can be determined. If this value is above a limit value, the presence of an anomaly can be detected from this.

[0150] More than one abnormal sub-region may include a single abnormality. For example, several sub-regions may have elevated temperatures due to an abnormality. A single abnormal sub-region may include more than one abnormality. For example, two abnormalities in the same sub-region may result in increased heat.

[0151] Alternatively or additionally, provision may also be made that: (i) the surface area of ​​the sample is irradiated uniformly with the irradiation light, in particular the irradiation intensity at two different locations of the surface area differs by at most 20%, preferably at most 10%, preferably at most 5%, preferably at most 1%; (ii) The irradiance at each location on the surface area of ​​the sample is: (a) at least 0.1 Watt / mm 2 , preferably at least 1 Watt / mm 2 , preferably at least 3Watt / mm 2 , preferably at least 5 Watt / mm 2 , preferably at least 10Watt / mm 2 , preferably at least 30Watt / mm 2 , preferably at least 50 Watt / mm 2 , preferably at least 70Watt / mm 2 , (b) up to 100Watt / mm 2 , preferably up to 50Watt / mm 2 , preferably at most 10Watt / mm 2 , preferably at most 5Watt / mm 2 , preferably at most 3Watt / mm 2 , preferably at most 1Watt / mm 2 , and / or (c) at 0.1 Watt / mm 2 With 100Watt / mm 2 between 1Watt / mm 2 and 50Watt / mm 2 between 1Watt / mm 2 and 30Watt / mm 2 between 1Watt / mm 2 and 10Watt / mm 2 between 1Watt / mm 2 and 5Watt / mm 2 between; and / or (iii) The irradiating light comprises light in the visible wavelength range, in particular light in the wavelength range of 430 nm to 490 nm, preferably light in the wavelength range of 445 nm to 465 nm, and / or is from a laser.

[0152] By uniformly irradiating the surface area, a thermal mass measure of the sample can be determined particularly reliably.

[0153] With the described irradiation intensity, a large part of the structure of the sample can also be heated sufficiently within a short time window.

[0154] If the illuminating light comes from this wavelength range, it corresponds exactly to the light that is also used in preferred application scenarios in real use. It is thereby possible to determine a practical and reasonable thermal mass measure for the actual application case and, in particular, to determine anomalies that are relevant to the actual application case.

[0155] The specific advantages and special embodiments of the present invention have been described above and will be described below in whole or in part based on a sample in the form of a converter assembly. However, these advantages and embodiments are of course also applicable to samples of different forms. The advantages of the present invention can be particularly well applied, especially in samples in which different elements with different heat capacities are present.

[0156] Alternatively or additionally, it can also be provided that: (i) when obtaining a measure of the temperature distribution of the individual sub-regions, the temperature drop of the irradiated sub-region after the end of irradiation is taken into account and / or (ii) the temperature curves of the individual sub-regions before, during and / or after the incident light is switched on are averaged and / or extrapolated and taken into account when obtaining a measure of the temperature distribution of the individual sub-regions.

[0157] The good connection of the heat spreader to the heat sink allows good measurements of the photothermal impedance of the converter even with a small heat spreader.

[0158] Averaging or extrapolating the temperature profile before, during and / or after switching on the light makes it possible to reduce the noise of the thermal imaging. This can also be used optionally to determine the irradiance.

[0159] According to a second aspect, the object is achieved by the invention in that a device is provided, comprising a light source (e.g., in particular a laser) for emitting illumination light and at least one measuring device (e.g., in particular at least one thermal imaging camera), wherein the device is configured to (i) implement the method according to the first aspect of the invention and / or (ii) implement at least the following operations: illuminating at least one surface area of ​​the sample with illumination light from a light source; measuring a first temperature of each of the one or more sub-regions of the surface region using a measuring device; and / or Based on the first temperature measured for the corresponding subregion and the reference temperature of the subregion and the optical power of the illumination light incident on the corresponding subregion, a quality characteristic value for each subregion is obtained, in particular by a calculation unit also included in the device.

[0160] The device is therefore particularly suitable for carrying out the method according to the invention or parts thereof.

[0161] The thermal imaging camera can be the first thermal imaging camera according to the first aspect of the present invention. The second temperature can be measured using the second thermal imaging camera according to the first aspect of the present invention. Therefore, the device can also optionally have another thermal imaging camera.

[0162] The thermal mass measure and / or the determination of anomalies of the sample may preferably be determined by means of a computing unit.The computing unit may be or comprise a computer.

[0163] Thermal characterization data for converters and heat spreaders

[0164] The following two-part table shows an overview of the thermal characterization data for an exemplary converter and heat spreader.

[0165] Calculation Example

[0166] Thermal resistance R th Defined as the heat flow from the heat source through the body to the heat sink.

[0167] If the body is a plate with area A and thickness d and thermal conductivity λ, R should be calculated from these data th :

[0168] By convention, if the definition is generalized to the heat flux dP th / dA, we are discussing thermal impedance here. In this case it applies:

[0169] For a ceramic converter with a thickness of d = 100 μm and a thermal conductivity of λ = 6 W / mK, the resulting thermal impedance is 16.7 K mm 2 / W. When the input thermal power density is 1W / mm 2 When the temperature of the converter increases by 16.7K.

[0170] For static converters, the thermal power is not input directly but as optical power input. Therefore the thermal power input needs to be determined from the optical power input.

[0171] If the optical power impinging on the converter is considered, the following observations can be made for the exemplary converter: - Fresnel reflection occurs on the surface of the converter (typical value: η Fresnel = 3% of input power); - Diffuse reflection occurs within the converter volume (typical value: η R_diffus=7% of input power); - emits cold light (typical value: η emission = 60% of input power); - Thermal power loss occurs (typical value: η thermisch =30%).

[0172] In order to be able to differentiate between thermal and optical power, the unit Watt is now indexed with W_therm or W_opt.

[0173] Similar to thermal impedance, photothermal impedance can now be defined, which represents the increase in surface temperature of a sample in response to the irradiated optical power.

[0174] The same applies to photothermal impedance Z o-th =η thermisch Z th .

[0175] Thus, for the above example, the thermal impedance of 16.7K and the thermal power component of 30% give 5Kmm 2 / W_opt's light-thermal impedance is lower than 16.7Kmm 2 / W_therm thermal impedance, since only a portion of the introduced optical power results in a temperature increase.

[0176] Previously it was assumed that the conversion of optical power into thermal power and the pure thermal impedance were constant in space. However, this is not necessarily the case, since there may be local absorption centers that lead to increased heat input. The thermal impedance may also deteriorate locally, for example due to bubbles in the solder layer or due to local separation at the converter-solder interface.

[0177] For a given irradiation intensity, this results in a local increase in temperature compared to locations on the sample surface that are irradiated with the same irradiation intensity. BRIEF DESCRIPTION OF THE DRAWINGS

[0178] Further features and advantages of the invention emerge from the following description in which preferred embodiments of the invention are explained with reference to schematic drawings.

[0179] Here it is shown:

[0180] Figure 1a shows a perspective view of a luminescent converter assembly of a first embodiment;

[0181] Figure 1b Shows Figure 1a A cross-sectional view of a luminescent converter assembly in FIG.

[0182] Figure 1cshows a cross-sectional view of a luminescent converter assembly of a second embodiment;

[0183] Figure 2a Shows Figure 1a-1b A perspective view of an intended application of a luminescence converter assembly in FIG.

[0184] Figure 2b The cross-sectional view shows Figure 2a Illustrations and other details in the;

[0185] Figure 3 shows a cross-sectional view of a luminescent converter assembly having an anomaly;

[0186] Figure 4 A structure for implementing the method according to the invention is shown;

[0187] Figure 5 shows a diagram of a camera image recorded during the method;

[0188] Figure 6 a graph showing the temperature of a sub-region of the sample as a function of time;

[0189] Figure 7a-Figure 7b a diagram showing the results of the evaluation of the temperature of a sub-region of a sample;

[0190] Figure 8a-8b A diagram showing the results of evaluating the temperature of a sub-region of a sample with and without taking into account the light power incident on the sub-region, respectively;

[0191] Figure 9a-9b A diagram showing the results of evaluating the temperature of a sub-region of a sample with and without taking into account the light power incident on the sub-region, respectively;

[0192] Fig.10 shows the quality characteristic values ​​obtained for two uniform samples of different thicknesses; and

[0193] Fig.11 Spatially resolved measurements of the quality characteristic values ​​of a sample and its X-ray radiograph are shown. DETAILED DESCRIPTION

[0194] Figure 1a A perspective view of a luminescent converter assembly 1 of a first embodiment is shown. Figure 1b A cross-section of the assembly 1 is shown. The luminescent converter assembly 1 is sometimes also referred to below as converter assembly 1 or just assembly 1 for short.

[0195] The luminescence converter component 1 is a ceramic luminescence converter for a laser-excited photoluminescent light source. The component 1 therefore has a ceramic substrate 3. The ceramic substrate 3 is coated with a silver coating 7 ( Figure 1a The ceramic substrate 3 is formed by ( Figure 1a A solder connection 9 (also not shown) is arranged on a heat diffuser 5 made of copper. Optionally, the ceramic substrate 3 has an antireflection coating on the other main side.

[0196] exist Figure 1b The silver coating 7 and the solder connection 9 can be seen.

[0197] The size of the ceramic substrate 3 is 4×4×0.150 mm 3 The size of the heat diffuser 5 is 20×20×4 mm. 3 The thickness of the silver layer is 12 μm. The thickness of the solder layer is 30 μm. The figure is not drawn to scale.

[0198] Figure 1c A cross-sectional view of a converter assembly 1 of a second embodiment is shown. For simplicity, identical features are provided with identical reference numerals here. The ceramic substrate 3 is arranged via a transparent adhesive layer 10 on a heat diffuser 5 made of aluminum, which is provided with a mirror layer 8. This variant of the converter assembly is advantageous for a converter wheel whose heat diffuser is made of a circular aluminum sheet with a central hole. An example is a converter wheel heat diffuser with a thickness of 1 mm and a diameter of 65 mm.

[0199] Figure 2a Shows Figure 1a-1b Perspective view of the use of the luminescence converter component 1. Figure 2b A sectional view with an illustration of further optional details of the assembly 1 is shown.

[0200] When the assembly 1 is used, the ceramic substrate 3 is illuminated with a laser beam 11 in the blue wavelength range. Part of the incident light beam 11 is converted by photoluminescence into yellow light 13, which is emitted by the ceramic substrate 3. The emitted light 13 passes through an optical device 15 in the form of a lens. Other assemblies convert the incident laser beam, for example, into green or red light. Other geometries for using the assembly are also possible, in which, for example, the incident light 11 is also guided through an optical device.

[0201] At least part of the irradiation light power is used to generate yellow light by photoluminescence. Since the photons of the irradiated light 15 generated by photoluminescence have lower energy than the photons of the incident light 11, heat is generated in the ceramic substrate 3 or below the irradiated surface area of ​​the component 1, especially in this area of ​​the ceramic substrate 3.

[0202] The heat generated in the ceramic substrate 3 is dissipated through the heat diffuser 5. Optionally, the heat diffuser 5 can also be connected to (such as Figure 2b A heat diffuser 6 is provided to further dissipate heat.

[0203] Figure 3 A schematic cross-sectional view of a luminescent converter assembly 1 with an anomaly is shown. Figure 3 Components and Figure 1a-Figure 1c and / or Figure 2a-2b The components are different from those already mentioned Figure 1a-Figure 1c and Figure 2a-2b Like features are described using like reference numerals.

[0204] Figure 3 An anomaly 17 of the component 1 is shown in the form of a cavity in the solder layer 9. The cavity may be an air pocket, whereby the solder layer 9 is not continuous and uniform.

[0205] Figure 3 A further anomaly 19 of the component 1 is shown in the form of local delamination of the silver coating 7 from the lower main side of the ceramic substrate 3 .

[0206] The two anomalies 17 and 19 have in common that they affect the heat transfer from the heat generated by the incident light in the ceramic substrate 3 to the heat diffuser 5. This effect can lead to a local temperature increase within the component 1, which can eventually also lead to overheating of the relevant area. Such a local temperature increase is also often referred to as a thermal hot spot.

[0207] Figure 3 Other anomalies 20 of the component 1 are shown in the form of local absorption centers on the surface or in the volume of the ceramic substrate 3. This anomaly on the surface can be a contaminant or an adhering particle. Inclusions or contaminants may be present in the volume. Even if there are no anomalies in the heat transfer to the heat diffuser 5, the anomaly 20 increases the heat input by increasing the light absorption and thus also creates a thermal hot spot.

[0208] Thermal hot spots may lead to reduced power or even damage to the component 1, depending on their characteristics. These anomalies are therefore undesirable and the affected components should be identified and isolated as early as possible, e.g. Figure 3 Component 1 in.

[0209] The method according to the invention can be used to determine such anomalies, since the method can be used to determine a thermal mass measure of a sample in the form of component 1 and, based thereon, conclusions can be drawn as to whether an anomaly is present. Figure 4 The structure for carrying out the method according to the invention is shown.

[0210] exist Figure 4 Only the component 1 with its ceramic substrate 3 and the heat diffuser 5 is shown. Again, the same features are used as already described. Figure 1a-Figure 1c , Figure 2a-2b and Figure 3 The same reference numerals are used in the drawings.

[0211] With the aid of the laser 21, blue illumination light 27 is emitted via the optical waveguide 23 at the coupling-out element 25 having a rectangular cross section and directed to the component 1 with the aid of an optical device 29 in the form of a lens. Thus, a surface area of ​​the component 1 is illuminated by the illumination light 27. Advantageously, the illumination light 27 is selected in such a way that its wavelength corresponds to the laser light also used when the component 1 is actually used.

[0212] The component 1, in particular the illuminated surface area, is detected by the recording area of ​​the thermal imaging camera 31. The main viewing direction of the camera 31 is at an angle of, for example, 30 degrees to the main propagation direction of the incident light 27.

[0213] The image portion detected by the thermal imaging camera from the component 1 can be obtained in particular by Figure 4 The optical device not shown in the figure can be adjusted, in particular reduced (zoomed out) or enlarged (zoomed in). The thermal imaging camera 31 can take an image of the component 1 at a specific time point.

[0214] Figure 5 A diagram of a camera image of the component 1 recorded with a thermal imaging camera 31 during the process is shown.

[0215] The optics of the thermal imaging camera 31 are selected such that the entire ceramic substrate 3 and a portion of the heat diffuser 5 can be seen on the camera image. The camera image consists of a plurality of pixels 33. Due to the selected optics and the selected relative positioning of the camera 31 and the component 1 to one another, the ceramic substrate 3 is covered by nine pixels 33 in the present case. The remaining 35 pixels 33 cover the detected portion of the heat diffuser 5. For the sake of clarity, the number of pixels in the figure has been greatly reduced. For example, a typical camera image may consist of 640 x 480 or 640 x 120 pixels.

[0216] In the present case, each pixel covers only a sub-area of ​​the surface area of ​​the component 1. However, it is also possible that some or all sub-areas are respectively covered by a plurality of pixels.

[0217] Generally, it is advantageous to define a quality zone for the ceramic substrate within which the optical thermal impedance must not exceed certain limit values, ie within which a certain minimum thermal mass must exist and / or within which no local anomalies must exist.

[0218] The thermal imaging camera provides a temperature value for each pixel 33. Thus, a temperature value can be assigned to each sub-area of ​​the surface area of ​​the component 1 which is currently covered by a pixel 33 based on the image recorded from the component 1.

[0219] Figure 6 The diagram shows the time curve of the temperature of a sub-area of ​​the sample. More precisely, the diagram shows the temperature curve of the central pixel 33 of the ceramic substrate 3 (see Figure 5 ).

[0220] At a certain point in time, the laser 21 is switched on, thereby starting to irradiate the component 1 with the irradiation light 27 .

[0221] After the start of the irradiation, the temperature value rises from a value "T2" of approximately 23.3° C. to a value "T1" of approximately 28.0° C. at the time "X1" within a time of approximately 0.1 seconds. The temperature value then continues to rise, although this rise is significantly slower and tends towards a limit value, which is no longer of interest here. The irradiation can therefore be ended after the time X1 and a number of consecutive measurements can be carried out at very short time intervals.

[0222] Before being switched on, the thermal imaging camera 31 provides a temperature value “ T2 ” of approximately 23.3° C. for the central pixel 33 at the time point “ X2 ”.

[0223] It must be pointed out that the temperature value provided by the thermal imaging camera 31 can also represent only a measure of the temperature, so an absolute temperature value is not absolutely necessary. In the present case, the temperature difference (T1-T2) obtained is 4.7 K. That is, due to the irradiation of the irradiation light 27, the sub-area of ​​the surface area of ​​the ceramic substrate 3 covered by the central pixel 33 is heated by 4.7 K.

[0224] Instead of measuring the first temperature T1 and the second temperature T2 at the first time point X1 and the second time point X2 near the start of irradiation, it is also possible to measure the temperature T3 at the first time point X3 and the temperature T4 at the second time point X4. In this case, the time points X3 and X4 are near the end of irradiation.

[0225] Since the converter cools with the same time constant as the heating, the temperature profile when the irradiation light is switched off can also be used to determine the temperature difference ΔT=T3-T4. For theoretical reasons, the temperature difference should be equal to the temperature difference ΔT=T1-T2. Alternatively, measurements can even be made at all four points in time (T1, T2, T3, T4) and two values ​​of ΔT can be determined and based on this an average value can be determined from the two temperature differences obtained. This minimizes the measurement error. An average value can also be obtained from an entire series of radiation pulses in rapid succession.

[0226] The method according to the invention now provides for dividing the surface area of ​​the component 1 into sub-areas. A first temperature of each sub-area is then measured at a first time point (corresponding to time point "X1"), for example, after the start of the irradiation of the component 1 and during the irradiation.

[0227] In addition, a second temperature of each sub-area is measured at a second time point (eg corresponding to time point "X2"), which is before the start of irradiation of component 1. This second temperature is a reference temperature of the corresponding sub-area.

[0228] For this purpose, a first image is recorded at a first point in time using a thermal imaging camera 31. As described above, the individual sub-regions are identified here by pixels 33. Thus, there are 5x7=35 first temperatures for the first point in time, since each pixel 33 of the thermal imaging camera 31 supplies a temperature value which is a first temperature value since it was measured for the corresponding sub-region at the first point in time.

[0229] Previously, a second image was recorded at a second point in time with the thermal imaging camera 31. The second point in time is before the start of the irradiation of the component 1. Accordingly, the thermal imaging camera 31 also provides a temperature value for each pixel 33, which is the second temperature value because it is measured for the corresponding sub-area (i.e. pixel) at the second point in time.

[0230] The measured first and second temperatures are then evaluated, in this case a total of 2 x 35 = 70. This is done in such a way that the difference between the two temperatures is obtained by subtracting the second temperature from the first temperature.

[0231] In order to obtain a quality characteristic value for a sub-region, the temperature difference is correlated with the optical power of the incident light incident on the sub-region. This takes into account a possible inhomogeneous illumination of the component 1 by the incident light 27. Thus, first of all, it is considered that surface regions of an ideal (homogeneous) sample with less incident optical power will generally heat up to a lesser extent than sub-regions with greater incident optical power.

[0232] Of course, the respective values ​​of the optical power may be different for the individual sub-areas, ie the individual pixels 33. The individual values ​​of the optical power may have been obtained, for example, by previously measuring the incident light 27 in the plane of the sample.

[0233] Based on the evaluation of the temperature and the optical power of the individual sub-regions, a quality characteristic value of the sub-region and thus a spatially resolved thermal mass metric of the sample can then be determined. The thermal mass metric can then be used to determine anomalies of the component 1, such as cavities 17 or delaminations 19.

[0234] For example, for this purpose, the quality characteristic values ​​can be evaluated by using suitable filters, for example filters from the field of image processing, in particular in the form of edge detectors, and anomalies can thus be determined.

[0235] In an alternative embodiment, the first temperature T1 and the second temperature T2 are not measured directly, but obtained by extrapolation. To this end, a linear or more complex function is used to interpolate the temperature curve in the region before and after the laser is turned on. These functions are then preferably extrapolated at the time point between the measurement of T1 and T2, preferably at the time point when the laser is turned on. The first temperature T1 and the second temperature T2 and the temperature difference are thus obtained. This process can also be used similarly for the temperature drop when the irradiation is turned off. The advantage of this alternative is a better signal-to-noise ratio. In addition, the effect of the slow temperature rise can be reduced by heating the thermal diffuser. This can also reduce the measurement error when measuring the sample using a smaller thermal diffuser.

[0236] Figure 7a A diagram showing the result of evaluating the quality characteristic values ​​of sub-regions of a real sample is shown. It can be seen that the sample is gridded into sub-regions, wherein each sub-region has a value corresponding to the temperature difference obtained in relation to the optical power of the corresponding sub-region. For visualization purposes, the value is displayed as a pattern and sub-regions with the same value have the same pattern. This form of display is similar to the display of a "heat map" in order to visualize the values ​​of a two-dimensional definition set.

[0237] Figure 7a The mesh in is so fine that the individual sub-regions cannot be distinguished from each other. In other words, Figure 7a The recording thermal imaging camera is able to achieve a very detailed spatial resolution of the sample due to its very high pixel count.

[0238] Figure 7a The samples and Figure 3 The component 1 shown is comparable and has a cavity as an anomaly in the solder layer. The cavity is visible in the figure as a circular area 35 with an elevated temperature.

[0239] exist Figure 7b In Figure 7a Another sample diagram is shown in the same manner. Figure 7b The samples and Figure 3 The component 1 shown in FIG. 1 is comparable and shows delamination of the silver coating as an anomaly. The delamination can be identified in the figure as a large surface area 37 where the temperature is increased.

[0240] In both cases, the temperature increase is due to anomalies in the sample. The reason is that the anomalies reduce the loss of heat introduced into the ceramic substrate by the incident light in the direction of the heat diffuser. This in turn leads to local hot spots 35 and 37.

[0241] For example, by using a threshold detector and / or an edge detector Figure 7a or Figure 7bBy filtering the image shown in FIG. 3 , these anomalies can be automatically determined. This allows detection of regions with increased quality characteristic values, such as regions 35 and 37. The corresponding samples can then be selected in an automated process.

[0242] exist Figure 7a and 7b In the figure, the same reference numerals are used for components 1 ( Figure 3 ) so that they can be easily matched even for separate samples.

[0243] It is of interest here to consider the influence of the light power respectively allocated to the sub-areas when using light sources with an inhomogeneous illumination profile.

[0244] in this regard, Figure 8a and 8b The results of the temperature evaluation of a sub-area of ​​the sample before and after taking the optical power into account are shown.

[0245] In the upper figures, each graph shows the evaluation result of the temperature of a sub-area of ​​a real sample, where the optical power has not yet been taken into account. The lower figure shows the result graph taking the optical power into account.

[0246] exist Figure 8a In the figure above, it can be clearly seen that the central area of ​​the sample (see component 1) has an increased temperature difference due to the illumination of the illumination light. This is due to the higher optical power of the illumination light in this area. However, if this uneven intensity distribution is taken into account by amortizing the optical power to the sub-areas, see Figure 8a In the lower figure, in this case, areas of different heat conduction caused by the sample, such as the corners of the ceramic substrate, become apparent.

[0247] Figure 8b It is also shown that, by taking into account the distribution of the optical power to the sub-areas, the heating caused by the sample is only visible in the left edge region of the ceramic substrate.

[0248] Figure 9a and Figure 9b The quality characteristic values ​​are determined from the temperature differences and the light powers of a sample (eg component 1) measured spatially resolved, ie for individual sub-regions, and compared with Figure 8a-8b Similarly, different data for sub-regions of the sample are shown.

[0249] Here Figure 9a The case of illumination with illumination light having a circular Gaussian beam profile is shown. Figure 9b The case of illumination with illumination light having a square beam profile that is almost uniform within the square is shown.

[0250] exist Figure 9a and 9bThe measured temperature difference is shown in the first row of . Since the sub-areas are very small, they cannot be resolved individually. The power distribution of the irradiation light that causes this temperature difference is shown in the second row.

[0251] When determining the quality characteristic values, the influence of the power distribution is subtracted.

[0252] Fig.10 The quality characteristic values ​​of sub-regions existing in the sample center region of two homogeneous samples (converter components) of different thicknesses obtained according to the method of the present invention are shown.

[0253] This clearly shows that it is possible to measure the quality characteristic values ​​of homogeneous samples. This makes it possible to show the dependence of the quality characteristic values ​​on the thickness.

[0254] Fig.11 The spatially resolved measurement of the quality characteristic values ​​of a sample with a local anomaly is shown on the right. The contrast X-ray image of the sample on the left shows that this local anomaly is associated with a defect site in the solder layer of the luminescence converter component. In the X-ray image, the gray value scale is inverted for better visualization of the defect. Dark areas indicate higher X-ray transmittance.

[0255] The features disclosed in the above description, the claims and the drawings can be essential for various embodiments of the invention both individually and in combination. Reference numerals list 1 Luminescence converter assembly 3 Ceramic Substrate 5. Thermal Diffuser 6 Thermal Diffuser 7 Silver coating 8 Mirror layer 9 Welding connection 10 Adhesive layer 11 Laser Beam 13 Light 15 Optics 17 Abnormal 19 Abnormal 20 Abnormal 21 Laser 23 Photoconductor 25. Coupling element 27 Illuminating light 29 Optical Devices 31 Thermal Imaging Camera 33 pixels 35 Area 37 Area X1 Time Point X2 time point X3 Time Point X4 Time Point T1 Temperature T2 Temperature T3 Temperature T4 temperature.

Claims

1. A method for determining a thermal mass metric of at least one region of a sample, the method comprising: Provide at least one sample; illuminating at least one surface area of ​​the sample with illumination light; measuring a first temperature for each of the one or more sub-regions of the surface region; and A quality characteristic value of each sub-region is obtained based on the first temperature measured in the corresponding sub-region, the reference temperature of the sub-region, and the optical power of the illumination light incident on the corresponding sub-region.

2. The method according to claim 1, in, (i) the sample comprises or consists of glass, glass ceramic, fluorescent glass PIG and / or ceramic; and / or (ii) the sample comprises or is at least one luminescence converter component or a component thereof, And preferably, the luminescence converter component comprises at least a ceramic luminescence converter, in particular at least a ceramic substrate, for example at least a cerium-doped YAG and / or LuAG ceramic substrate, and / or at least a heat diffuser, preferably made of copper, aluminum and / or ceramic.

3. The method according to any one of the preceding claims, in, At least based on the quality characteristic values ​​obtained for each sub-area, (a) obtaining the photothermal impedance of the sub-region or representing the photothermal impedance by a quality characteristic value, (b) determining a thermal mass metric as a characteristic of the sample; and / or (c) determining a thermal mass metric as a local anomaly of the sample, such as a thermal hot spot of the sample.

4. The method according to any one of the preceding claims, in, The method further comprises: respectively measuring and / or obtaining a second temperature for each sub-area for which the first temperature has been measured, Therein, the second temperature represents a reference temperature of the corresponding sub-region or the reference temperature is obtainable and / or is obtained with the aid of the second temperature.

5. The method according to any one of the preceding claims, in, measuring a first temperature of each sub-region at a first, preferably common, point in time, Wherein, preferably, the first time point is (a) at least 0.01 seconds, preferably at least 0.03 seconds, preferably at least 0.05 seconds, preferably at least 0.07 seconds, preferably at least 0.1 seconds, preferably at least 1 second, preferably at least 2 seconds, preferably at least 3 seconds, preferably at least 5 seconds after the start, during and / or before the end of irradiation of the surface area of ​​the sample with the irradiation light, (b) at most 10 seconds, preferably at most 7 seconds, preferably at most 5 seconds, preferably at most 3 seconds, preferably at most 1 second, preferably at most 0.7 seconds, preferably at most 0.5 seconds, preferably at most 0.3 seconds, preferably at most 0.1 seconds, preferably at most 0.07 seconds, preferably at most 0.05 seconds, preferably at most 0.03 seconds, and / or (c) between 0.01 seconds and 10 seconds, preferably between 0.1 seconds and 10 seconds, preferably between 0.1 seconds and 1 second.

6. The method according to any one of the preceding claims, in, measuring a second temperature of the individual subregions at a second, preferably common, point in time, Wherein, preferably, the second time point is before the start of irradiation of the surface area of ​​the sample with incident light and / or after the end of irradiation, in particular before and / or after the start (a) at least 0.01 second, preferably at least 0.03 second, preferably at least 0.5 second, preferably at least 0.1 second, preferably at least 1 second, preferably at least 2 seconds, preferably at least 3 seconds, preferably at least 5 seconds, (b) at most 10 seconds, preferably at most 7 seconds, preferably at most 5 seconds, preferably at most 3 seconds, preferably at most 1 second, preferably at most 0.5 seconds, preferably at most 0.1 second, preferably at most 0.05 seconds, preferably at most 0.03 seconds, and / or (c) between 0.01 second and 10 seconds, preferably between 0.1 second and 10 seconds, preferably between 0.1 second and 5 seconds.

7. The method according to any one of the preceding claims, in, Each first temperature is a surface temperature of the sample; and / or Wherein, each second temperature is the surface temperature of the sample.

8. The method according to any one of the preceding claims, in, The measurement of the first temperature includes: Preferably, at a first time point, at least one first image of the sample is recorded by at least one first thermal imaging camera and a first temperature of each sub-region is obtained from the image information of the at least one first image, Wherein, preferably (i) the recorded first image includes multiple pixels, and each sub-area is at least partially covered by at least one pixel, and the first temperature is obtained using image information of each pixel provided by the camera, such as a temperature value, and / or (ii) the first temperature is calculated from multiple first images, preferably by extrapolating the temperature curve of each pixel at the time point when the illumination light is turned on or off.

9. The method according to any one of the preceding claims, in, The measurement of the second temperature includes: Preferably, at a second time point, at least one second image of the sample is recorded by at least one second thermal imaging camera and / or the first thermal imaging camera, and a second temperature of each sub-area is obtained from the image information of the at least one second image, Wherein, preferably (i) the recorded second image includes multiple pixels, and each sub-area is at least partially covered by at least one pixel, and the second temperature is obtained using image information of each pixel provided by the camera, such as a temperature value, and / or (ii) the second temperature is calculated from multiple second images, preferably by extrapolating the temperature curve of each pixel at the time point when the illumination light is turned on or off.

10. The method according to any one of the preceding claims, in, The quality characteristic value of the sub-region is obtained by: calculating a quality characteristic value of the sub-region based at least on a temperature difference formed between a first temperature of the sub-region and a reference temperature of the sub-region, Preferably, in order to calculate the quality characteristic value, (i) the temperature difference is also taken into account divided by the light power incident on the corresponding sub-area, (ii) the temperature difference is divided by the quotient of the light power incident on the corresponding sub-area and its area, and / or (iii) the light power of the illumination light incident on the corresponding sub-area, in particular the temperature difference is divided by the light power.

11. The method according to any one of the preceding claims, in, The method further comprises: determining an abnormality of the sample, preferably a local abnormality, based on the obtained quality characteristic value of the sub-region, Wherein, the determination of the abnormality of the sample preferably includes: A subregion whose quality characteristic value is above a limit value, below a limit value and / or within a defined or definable limit is determined as an abnormal subregion, and The anomaly sub-regions are preferably assigned to one or more surface and / or volume regions of the sample and / or are characterized and / or classified with respect to the type of anomaly, such as in particular delamination, bubble inclusions, particles and / or contaminants on the surface, and / or inclusions or contaminants in the volume.

12. The method according to any one of the preceding claims, in, (i) irradiating the surface area of ​​the sample uniformly with irradiation light, in particular the irradiation intensity at two different locations of the surface area differs by at most 20%, preferably at most 10%, preferably at most 5%, preferably at most 1%; (ii) the irradiance at each location on the surface area of ​​the sample is: (a) at least 0.1 Watt / mm 2 , preferably at least 1 Watt / mm 2 , preferably at least 3Watt / mm 2 , preferably at least 5 Watt / mm 2 , preferably at least 10Watt / mm 2 , preferably at least 30Watt / mm 2 , preferably at least 50Watt / mm 2 , preferably at least 70Watt / mm 2 , (b) up to 100Watt / mm 2 , preferably up to 50Watt / mm 2 , preferably at most 10Watt / mm 2 , preferably at most 5Watt / mm 2 , preferably at most 3Watt / mm 2 , preferably at most 1Watt / mm 2 , and / or (c) at 0.1 Watt / mm 2 With 100Watt / mm 2 between 1Watt / mm 2 and 50Watt / mm 2 between 1Watt / mm 2 and 30Watt / mm 2 between 1Watt / mm 2 and 10Watt / mm 2 between 1Watt / mm 2 and 5Watt / mm 2 between; and / or (iii) The irradiation light comprises light in the visible wavelength range, in particular light in the wavelength range of 430 nm to 490 nm, preferably light in the wavelength range of 445 nm to 465 nm, and / or is from a laser.

13. The method according to any one of the preceding claims, in, (i) the thickness of the ceramic substrate is (a) at least 30 μm, preferably at least 80 μm, preferably at least 100 μm, (b) at most 400 μm, preferably at most 300 μm, preferably at most 250 μm, preferably at most 225 μm, preferably at most 200 μm, and / or (c) between 30 μm and 400 μm, preferably between 60 μm and 300 μm, preferably between 80 μm and 225 μm; (ii) the ceramic substrate is at least partially coated, in particular with a silver coating, at least on one main side; and / or (iii) arranging the ceramic substrate, in particular the coated side, on the heat diffuser, in particular soldering it thereto, preferably forming a solder layer between the heat diffuser and the ceramic substrate.

14. The method according to any one of the preceding claims, in, (i) taking into account the temperature drop of the irradiated sub-area after the end of irradiation when obtaining a measure of the temperature distribution of the individual sub-areas and / or (ii) averaging and / or extrapolating the temperature curves of the individual sub-areas before, during and / or after switching on the irradiation light and taking this into account when obtaining a measure of the temperature distribution of the individual sub-areas.

15. A device comprising a light source for emitting illumination light, such as in particular a laser, and at least one measuring device, such as in particular at least one thermal imaging camera, wherein: The apparatus is configured to (i) implement the method according to any one of claims 1 to 14, and / or (ii) implement at least the following operations: illuminating at least one surface area of ​​the sample with illumination light from the light source; measuring a first temperature of each of the one or more sub-regions of the surface region using a measuring device; and / or Based on the first temperature measured for the corresponding subregion and the reference temperature of the subregion and the optical power of the illumination light incident on the respective subregion, a quality characteristic value for each subregion is obtained, in particular by a calculation unit also included in the device.

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