DE102017203765A1 - Method for the determination of mechanical stresses in substrates or circuit carriers, which are formed with a ceramic material - Google Patents

Abstract

For the determination of mechanical stresses in substrates or circuit carriers (3), which are formed with a ceramic material, a laser beam is directed onto a surface region of a substrate to be examined and reflected and scattered from the irradiated surface with a detector (1a) designed for spatially resolved detection detected electromagnetic radiation in the form of a speckle pattern. The detection of speckle patterns occurs at a first and at least a second subsequent time. Static detection of an image of a detected speckle pattern of at least one area which is illuminated by electromagnetic radiation is checked for its properties and is characterized and parameterized when the evaluation has a correlation function with a gray-scale transmission matrix. The data recorded with the optical detector (1) are fed to an electronic evaluation unit and in the electronic evaluation unit a comparison is made with speckle patterns stored in an electronic memory obtained by calibration and with the comparison the respective mechanical stress of the ceramic material of the substrate certainly.

Description

The invention relates to a method for the determination of mechanical stresses in substrates or circuit carriers, which are formed with a ceramic material.

Power electronic modules are usually implemented on the basis of ceramic circuit carriers. The usually flat formed circuit carriers are provided with structured metallic interconnects and contact pads to connect the electronic components together electrically or thermally and mechanically. Due to the compounds formed with different materials, mechanical stresses occur in the substrates or carriers formed from ceramic materials, which lead to cracks when overstressed. Overuse occurs as a result of the manufacturing process in the ceramic-metal composites, in the manufacture of power modules, or in operating loads during use. The cracks run i.d.R. in the ceramic and essentially separate the metallizations from the ceramic. As a result, either directly or at a later time, defects that can result in the functional failure of the module result. In the context of a test of internal mechanical stresses on the one hand to avoid the malfunction in the operation of the assembly and on the other hand costs are saved if early in the value-added process of production, the critical ceramic substrates or circuit boards can be identified and sorted out.

The circuit carriers are typically composites of at least one ceramic substrate (e.g., Al 2 O 3, AlN, Si 3 N 4, etc.) and metal layers formed on surfaces (e.g., Cu, Al, Ni, etc.) which form electrical traces and electrical connection contacts. The layer structure is sintered under pressure and very high temperatures and then cooled. The different physical coefficients of thermal expansion of the partner ceramic and the metal lead to mechanical layer stresses that occur in particular in the joining or interface area. Other constructions, e.g. Electronic components, heat sink connections or housings that are mounted lead to changes in residual stress states in the joint areas.

Typical circuit board types are: DCB - Direct Copper Bonding, AMB - Aluminum Metal Brazing, DAB - Direct Aluminum Bonding.

In order to obtain information on the reliability of the composite layer between metal and ceramic, very time-consuming and costly tests are currently being carried out. With passive cycles and ultrasound measurements one is able to detect already formed cracks and to follow the further development of cracks. In this case, circuit carriers are exposed to cyclic temperature fluctuations in temperature change furnaces for several days to weeks. After certain time intervals are taken withdrawals of the circuit board and an ultrasonic test. The circuit carriers located in the water bath are tested by means of a sequentially scanning ultrasound measuring head. In this case, ultrasonic waves are coupled into the object and detected at interfaces of the layer structure ultrasonic waves detected and evaluated. Additional echoes of the reflected ultrasonic waves appear when cracks or delaminations have occurred. So it is a destructive process, because you have to generate the cracks in order to detect increased mechanical stresses.

A well-known measuring method for the optical determination of distortions is the grayscale analysis by means of digital image correlation (Digital Image Correlation). In the process, the deformations are captured using patterns that the test object has to offer. An evaluation of an occurring distortion of the respective pattern leads to a deformation field with the help of which mechanical strains can be detected. The main disadvantage of the method is that basically a pattern must be present and it may change only slightly within the distortion of the object. There is a risk that the pattern recognition fails and no deformation field determination can be made. Representatives here are MicroDac or the ARAMIS system. The ARAMIS relies on additional surface coloration of the test object.

Moire interferometry is known as another highly sensitive optical method for determining voltage variations. The measurement method is based on a two-beam speckle interferometry. For the calculation of the voltages high-resolution interferometric lattice patterns (fringes) are used. The method calculates the displacement / strain field factor used to convert to the stress values. For this purpose, the method compares the surface condition in an unloaded and a loaded condition. Thus, forces must be exerted on an object to be examined, which can lead to deformation and thus possible damage to the object being examined.

It is therefore an object of the invention, possibilities for the non-destructive determination of mechanical voltages to circuit carriers, the specify from a substrate having formed on surfaces layers which form electrical conductors and / or electrical connection contacts for electrical or electronic components, which can be easily performed in a short time, with sufficient accuracy and low cost.

According to the invention, this object is achieved by a method having the features of claim 1. Advantageous embodiments and further developments of the invention can be realized with features specified in the subordinate claims.

In the method according to the invention, a laser beam emitted by a laser source is directed onto a surface region of a substrate to be examined and with a detector designed for spatially resolved detection from the irradiated surface reflected and scattered electromagnetic radiation in the form of a speckle pattern to a first and be detected at least a second subsequent time. The data acquired with the optical detector are supplied to an electronic evaluation unit and in the electronic evaluation unit, a comparison is carried out with speckle patterns stored in an electronic memory and obtained by a calibration. With the comparison, the respective mechanical stress of the ceramic material is then determined at least in the region of the irradiated surface of the substrate.

If the evaluation is carried out with a correlation function or with a gray value transition matrix (GLCM), a static detection of an image of a detected speckle pattern of at least one area which is illuminated by electromagnetic radiation is possible and thus checked for its properties and thereby characterized and parameterized. The parameter calculated with one of the equations (2) to (7) is compared by means of a previously determined calibration function and the value of the respective mechanical stress is determined from the comparison. With static detection, no time-resolved detection is required and detection is sufficient at a single time.

The stored speckle patterns obtained by a calibration should be those speckle patterns which have been determined under the same conditions, in parallel with which the respective mechanical residual stresses have been determined with another measurement method and the respective ones recorded during the calibration Speckle patterns have been assigned. Thus, in the case of a recognized sufficient match of speckle patterns detected by the method according to the invention with speckle patterns detected correspondingly in a calibration on a sample of the same or a comparable material, the respective mechanical properties of the sample investigated with the invention can be in the form of a substrate or Circuit carrier are assigned.

When calibrating, the same materials or composite materials, identical energy inputs and speckle patterns, which have been detected and stored at the same time after energy input, should be taken into account when determining the mechanical residual stresses of the respective sample (substrate, circuit carrier). It should also be the same lighting conditions and the same settings on the trained for spatially resolved detection detector met.

Of course, more than two speckle patterns sequentially detected at a time interval may be taken into account in a time-resolved detection. This can be done up to a history, that is, detection of a plurality of speckle patterns detected at small time intervals in succession, so that a quasi-detection similar to that of a film can be performed. When evaluating with GLCM, one single detection is sufficient at a time.

The energy input can occur before or during the detection of speckle patterns in the material of the respective substrate. An energy input can be achieved, in particular, by an elastic deformation on the substrate and / or a thermal excitation, which is carried out, for example, by irradiation with electromagnetic radiation, which is preferably pulse-shaped.

The energy input can preferably take place by the action of mechanical stress or by a focused laser beam, with whose radiation reflected from the respective surface and impinging on the optical detector, the speckle patterns are also detected. During the time in which the energy input takes place, a power density in the focal spot which is greater than in times in which detection of speckle patterns is carried out with the optical detector should be observed. This can be done with a corresponding beam shaping, in which the size of the surface of the focal spot during the time of energy input is smaller, than during the times in which speckle patterns are detected and used for the determination of the mechanical residual stresses. This can be achieved by simply changing the focal length by a translatory movement of at least one optical lens, which is arranged in the beam path of the laser beam. The laser power can be kept constant.

As an optical detector, a CCD or a CMOS camera can be used.

In the invention, substrates which have on their surface metallic layers, with which preferably electrical interconnects or electrical connection pads are formed, can be examined in a region of the surface of the substrate. In this case, the examination may preferably be carried out in a region in which a metallic layer is formed and / or in a region which is arranged directly next to a metallic layer. In this case, an area immediately adjacent to a metallic layer may have a distance of up to 2 mm.

The determination of internal mechanical stresses in the metal-ceramic circuit carriers or pure ceramic substrates takes place by means of laser speckle photometry. This is a laser-optical, non-contact and fast measuring method that can detect geometric distortions of surfaces without contact and non-destructive. A useful geometric distortion on the surface can be initiated by an energy input, which can be caused in particular by mechanical deformation or by heating. A locally limited heating can be achieved with a laser beam emitted by a radiation source and preferably focused on a surface of the circuit carrier. By reflection of the laser radiation and the specific surface roughness, a changing speckle pattern is formed. It is then a single-jet speckle process without interferometric pattern generation (fringes). The scattered and reflected from the irradiated surface laser radiation with the trained speckle pattern is spatially resolved with a CCD camera as a suitable optical detector and detected and digitized at certain times. In contrast to the Digital Image Correlation, no particular speckle pattern is observed on the surface or its deformation is observed, but a comparison of at least two completely different stochastic speckle patterns caused by external state changes is performed based on the spatial relationship of one point to neighboring points. Or the quality of the speckle pattern is taken from the image processing logarithms from a static image of the detected surface area.

1. a) Histogramm -Anisotropie, Entropie
2. b) Grauwertübergangsmatrix - Energie zweiter Ordnung, Kontrast, Homogenität, Korrelation
3. c) Bildintensität - Mittelwert, Standardabweichung
4. d) Differenz-Korrelationsfunktion (Aussagen über den zeitlichen Zusammenhang der stochastischen Intensitätssignale)

With the detected speckle patterns and their change by external state changes systematic conclusions can be made on the mechanical residual stresses at least in the material of the circuit substrate. For this purpose, calibrations are required which take into account a correlation between the respective mechanical residual stress and the spatially resolved detected laser speckle signals. The spatially resolved and digitized speckle pattern signals can be evaluated by means of various image processing algorithms. Suitable image processing logarithms are:

1. a) histogram anisotropy, entropy
2. b) Gray value transition matrix - second order energy, contrast, homogeneity, correlation
3. c) image intensity - mean, standard deviation
4. d) Difference correlation function (statements about the temporal relationship of the stochastic intensity signals)

Below, the four mentioned image processing algorithms suitable for this purpose will be explained in more detail.

wobei nmax die maximale Anzahl von mit dem zur ortsaufgelösten Erfassung ausgebildeten Detektor, τ die Zeitverschiebung oder die Anzahl der Rahmenintervalle, S (n, x, y) die Intensität eines jeweiligen Bildpunktes (Pixels), dessen Position durch die Koordinaten x und y im n-ten Rahmen ist. Diese Korrelationsfunktion ergibt sich aus dem sogenannten Semivariogramm, bei dem es sich um ein geostatistisches Werkzeug handelt, mit dem die Beziehung zwischen ortsaufgelöst detektierten Intensitäten in Abhängigkeit von Abstand/Verschiebung zu einem Zeit- und/oder Raumpunkt untersucht werden kann. Das Ergebnis dieser Korrelationsfunktion bei den Zeitpunkten zeigt die Akkumulation der Intensitätsdifferenz von Intensitätspaaren einer zeitlichen Folge. Bei der Erfassung mechanischer Spannungen konzentriert sich die Korrelationsfunktion jedoch auf den Unterschied zwischen der ersten und anderen detektierten Abbildungen eines beleuchteten Oberflächenbereichs in Abhängigkeit von der Zeitverschiebung. Daher wurde eine geringfügige Änderung der Gl. (8) vorgenommen, wobei n zu einem festen Wert n = 1 festgelegt wird. Der Exponent wurde als 1 gesetzt, um die Richtungsänderungen von mechanischer Spannung zu verfolgen. Die neue Korrelationsfunktion ist gegeben durch: $$C\left(\tau \right)=\frac{1}{N\langle I\rangle }\langle I\left(1+\tau ,x,y\right)-I\left(\mathrm{1,}x,y\right)\rangle$$

wobei N der Anzahl der detektierten einzelnen Abbildungen und I (n, x, y) die Intensität eines jeweiligen Bildpunktes (Pixels) entspricht.The dynamic evaluation may be performed based on the evaluation of surface area images of an illuminated surface area successively detected at multiple times. The intensity detected in time resolution can be examined by the correlation function (1) for its statistical properties. $$C\left(\tau \right)={{\displaystyle \underset{n=1}{\overset{n_{max}}{\Sigma }}\left(S\left(n+\tau .x.y\right)-S\left(n.x.y\right)\right)}}^2,$$

where nmax is the maximum number of detectors designed for spatially resolved detection, τ the time shift or the number of frame intervals, S (n, x, y) the intensity of a respective pixel whose position is determined by the coordinates x and y in n -th frame is. This correlation function results from the so-called semivariogram, which is a geostatistical tool with which the relationship between spatially resolved detected intensities can be examined as a function of distance / displacement to a time and / or point in space. The result of this correlation function at the time points shows the accumulation of the intensity difference of intensity pairs of a temporal sequence. However, in the detection of mechanical stresses, the correlation function focuses on the difference between the first and other detected images of an illuminated surface area as a function of the time shift. Therefore, a slight change in Eq. (8), where n is set to a fixed value n = 1. The exponent was set as 1 to the direction changes of mechanical stress to pursue. The new correlation function is given by: $$C\left(\tau \right)=\frac{1}{N<I>}<I\left(1+\tau .x.y\right)-I\left(\mathrm{1,}x.y\right)>$$

where N is the number of detected individual images and I (n, x, y) corresponds to the intensity of a respective pixel (pixel).

• Energie:
  
• Homogenität:
  
• Kontrast:
  
• Korrelation: $$Correlation=\frac{{\displaystyle {\sum }_{i,j=0}^{width}\left(i-u_x\right)\left(j-u_y\right)c_{ij}}}{s_x{s}_y}$$
  
  mit $$-1\le \mathrm{<figure-callout\; id="1"\; label="R\; \le "\; filenames="DE102017203765A1\_0016.png,DE102017203765A1\_0017.png"\; state="\{\{state\}\}">R</figure-callout>}\le 1$$
  

In addition to the evaluation of the correlation function of the time signal of the stochastic signal, the detection of speckle patterns of the respective sample can be characterized using image processing methods for texture analysis (cooccurrence matrix) and used to evaluate the respective mechanical stress state of the respective substrate. These include the following characteristics:

• Energy:
  
• Homogeneity:
  
• Contrast:
  
• Correlation: $$COrrelatiOn=\frac{{\displaystyle {\Sigma }_{i.j=0}^{widtH}\left(i-u_x\right)\left(j-u_y\right)c_{ij}}}{s_x{s}_y}$$
  
  With $$-1\le R\le 1$$
  

wobei h(i) die Häufigkeit und g der Grauwert sind.In addition, the entropy of the histogram of a static map can be evaluated according to equation (10):

where h (i) is the frequency and g is the gray value.

The spatially resolved signals, which represent the respective detected speckle pattern, can be brought in conjunction with mechanical quantities that occur at a substrate or circuit substrate under investigation at the irradiated and detected surface area. Mechanical quantities can be forces, moments and deformations. By means of numerical calculations, in which the knowledge about the mechanical material properties of the ceramic to be tested are introduced, secondary mechanical quantities, in particular mechanical stresses and strains, can be determined. For a final calibration function, the respective mechanical stresses and one of the og. Bring signal quantities into a mathematical context. This makes it possible to determine the mechanical residual stresses on any circuit carriers, which consist of a metal-ceramic composite. The respective ceramic material of the respective substrate or circuit substrate investigated should be the same or a material of the same type of ceramic as was taken into account in the calibration function.

The invention is a nondestructive, non-contact optical method and an application and evaluation methodology with which occurred residual mechanical stresses in a substrate or circuit carrier, which is formed with a ceramic material, can be determined. As a result, it is possible to carry out tests in every process step and at every point in the processing of the ceramic circuit carriers with regard to residual stresses. It can therefore be recognized immediately during the manufacturing process errors and defects in a short time. In particular, non-or only slightly processed circuit carriers, in which no or only part of the components have already been mounted, can be sorted out, which can significantly reduce costs. There is even the possibility to detect errors in the manufacturing process and to counteract these by adapting process parameters, for example a change in the temperature profile. Metal-ceramic circuit carriers or ceramic substrates can be determined after their production and after each subsequent process step with their respective mechanical residual stress state.

Since metal-ceramic substrates or other ceramic substrates can be inspected non-destructively with regard to their mechanical residual stress, a tested circuit carrier can be returned to the manufacturing process. So it can be avoided committee as a result of an audit.

The optical measurement comes without aids, such as a water bath in the Ultrasound microscopy or surface staining on ARAMIS. Thus, the respective tested circuit carrier remains contamination-free. In addition, mechanical stresses and residual stresses in the material can be determined without causing damage, for example in the form of a crack. Thus, an evaluation of the state of a substrate or of a circuit carrier can take place, with which a preventive recognition of possible failures or, if appropriate, defects that later develop can be achieved with sufficient certainty.

The method can be performed with a measurement in a very short time with sufficient accuracy. Thus, a measurement and inspection of a circuit substrate or substrate can be carried out in a time period <15 s, which is conducive to use directly during the production process.

Using a similar construction, other speckle pattern parameters can be calculated to establish the calibration function.

The measurement setup for the mechanical voltage determination may differ by the type of activation / excitation. In this case, forces can act at a distance from the irradiated surface area on the substrate or the circuit carrier. As a result of a mechanical force (load) or a temperature change, there are changes to the surface. The speckle parameters, calculated according to equations (2-7), capture these changes over time.

Over time, the position and brightness (intensity) of the speckles change as a result of changes in the surface's expansion fields during the propagation of locally introduced energy (deformation energy, heat). The surface state and thus the specific detected speckle images are functions of the strain fields εi, j (t, R) (t - the time, R the location of the measurement and i, j - respectively the coordinate axes x, y in the detected and influenced by energy input surface area). These are in turn connected to the equation (8) of the thermal expansion with the temperature T (t, R) and via the elastic laws to the mechanical stresses σi, j (t, R): $${\epsilon }_{x.y}\left(t.R\right)=\frac{{\sigma }_{k.l}\left(t.R\right)}{e_{x.y.k.l}}+{\alpha }_{x.y}\left(T\left(t.R\right)-T_0\right),$$

The mechanical strain is governed by Hooke's law with mechanical stresses σi, j (t, R) and the elastic modulus E and the relative change in length of the respective sample (substrate, circuit carrier) by thermal expansion over the temperature range (T (t, R) -T0 ) given with known thermal expansion coefficient α.

For the preparation of the calibration function, the equation (8) can be summarized as follows: $$Paramete{r}_{LSP}\left(t\right)=a\cdot \frac{\sigma \left(t\right)}{e}+b\cdot \alpha \cdot \Delta T+c$$

und durch Definition der Parameter P1- P3: $$P_1=\frac{E}{a}$$

$$P_2=-b$$

$$P_3=-c$$

zu Gleichung (11) vereinfacht. $$\sigma \left(t\right)=P_1\left(Paramete{r}_{LSP}\left(t\right)+P_2\alpha \Delta T+P_3\right)$$

For the stress change calculation, the equation (9) was converted into a suitable form: $$\sigma \left(t\right)=\left(Paramete{r}_{LSP}\left(t\right)-b*\alpha *\Delta T-c\right)*\frac{e}{a}$$

and by defining the parameters P1-P3: $${\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="DE102017203765A1\_0016.png,DE102017203765A1\_0017.png"\; state="\{\{state\}\}">P</figure-callout>}}_1=\frac{e}{a}$$

$${\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="DE102017203765A1\_0016.png,DE102017203765A1\_0017.png"\; state="\{\{state\}\}">P</figure-callout>}}_2=-b$$

$${\mathrm{<figure-callout\; id="3"\; label="P"\; filenames="DE102017203765A1\_0016.png,DE102017203765A1\_0017.png"\; state="\{\{state\}\}">P</figure-callout>}}_3=-c$$

simplified to equation (11). $$\sigma \left(t\right)=P_1\left(Paramete{r}_{LSP}\left(t\right)+{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="DE102017203765A1\_0016.png,DE102017203765A1\_0017.png"\; state="\{\{state\}\}">P</figure-callout>}}_2\alpha \Delta T+P_3\right)$$

The quantities P1, P2 and P3 are initially unknown and must be determined using a suitable calibration method.

The invention can thus be used in the determination of residual stress in metal-ceramic substrates of electronics (hybrid electronics, power electronics), but also in the determination of inherent voltage in monoceramic layers (for example membranes, covering shells).

The invention will be explained in more detail by way of example in the following.

• 1 in schematischer Form beispielhaft einen Aufbau mit dem eine Laser-Speckle-Photometrie (LSP) während einer Messung an einem Schaltungsträger DCB durchführbar ist;
• 2a eine Darstellung zur Realisierung einer Kalibrierung unter Anwendung der Laser-Speckle-Photometrie-Technik und einer Biegevorrichtung zur elastischen Verformung;
• 2b eine Datenverarbeitung, in dem die detektierten LSP-Signale parametrisiert und die mechanische Belastungsangaben für die Durchführung von FEM-Berechnungen zur Eigenspannungsbestimmung an der Messposition verwendet werden.
• 2c eine Aufstellung von Kalibrierungsfunktionen anhand der ermittelten Parameter bzw. Eigenspannungswerte aus einer FEM-Berechnung.
• 3a ein Beispiel der umgerechneten Spannung aus der LSP-Messtechnik, entnommen aus dem Biegeversuch an Aluminiumoxid, im Zusammenhang mit der ermittelten Eigenspannung aus FEM-Berechnung und
• 3b eine Darstellung der ermittelten relativen Fehler in % zwischen der mechanischen Eigenspannung aus FEM-Berechnung und der ermittelten Eigenspannung aus LSP.

Showing:

• 1 in schematic form by way of example a construction with which a laser speckle photometry (LSP) during a measurement on a circuit carrier DCB is feasible;
• 2a a representation for the realization of a calibration using the laser speckle photometry technique and a bending device for elastic deformation;
• 2 B a data processing in which the detected LSP signals are parameterized and the mechanical load information used to perform FEM calculations for residual stress determination at the measuring position.
• 2c a list of calibration functions based on the determined parameters or residual stress values from a FEM calculation.
• 3a an example of the converted voltage from the LSP measuring technique, taken from the bending test of aluminum oxide, in connection with the determined residual stress from FEM calculation and
• 3b a representation of the determined relative errors in% between the mechanical residual stress from FEM calculation and the determined residual stress from LSP.

Here is a circuit carrier 3 , here a conventional DCB ceramic by means of the laser diode as a radiation source 2 illuminated. A CCD camera as a detector designed for spatially resolved detection 1 with detector 1a picks up the speckle pattern at the measuring position in an irradiated surface area and is connected to an electronic evaluation unit, in this case a personal computer.

With the radiation source 2 becomes an area of the surface of the circuit substrate 3 illuminated and reflected therefrom and / or scattered electromagnetic radiation with the detector 1a recorded in a spatially resolved manner. As 2 B As can be seen, individual detected speckles change as to their position and intensity, the reflected and / or scattered electromagnetic radiation. From these changes and also from the change in direction of the individual positions of speckles after energy input into the material of the respective circuit substrate 3 can make statements about the mechanical residual stresses on a circuit carrier 3 , as a particularly interesting example of a ceramic substrate.

For the calibration attempt, the circuit carrier 3 on a trailer 5 placed and with a moving fin 4 loaded and thereby elastically deformed. The change of speckle pattern is using the camera as a detector 1a detected. Subsequently, the spatially resolved intensities from the force device and the LSP technique are used to calculate the parameters P1, P2 and P3 according to equation (11). The determined parameters P1 to P3 are used in the recalculation of the same materials for the determination of mechanical residual stress at the examined measuring position within the illuminated surface area of the circuit substrate 3 ,

Claims (6)

Method for determining mechanical stresses in substrates or circuit carriers (3) formed with a ceramic material, in which a laser beam emitted from a laser source (2) is directed onto a surface area of a substrate to be examined and detected by a detector (1a) designed for spatially resolved detection from the irradiated surface reflected and scattered electromagnetic radiation in the form of a speckle pattern; wherein the detection of speckle patterns are detected at a first and at least a second subsequent time, or a static detection of an image of a detected speckle pattern of at least one area which is illuminated by electromagnetic radiation, checked for its properties and thereby characterized and parameterized when the evaluation is performed with a correlation function with a gray scale transmission matrix, and the data detected by the optical detector (1) are supplied to an electronic evaluation unit and in the electronic evaluation unit, a comparison is carried out with speckle patterns stored in an electronic memory obtained by a calibration, and with the comparison the respective mechanical stress of the ceramic material is determined at least in the area of the irradiated surface of the substrate. Method according to Claim 1 , characterized in that before or during the detection of speckle patterns, an energy input into the material of the respective substrate, in particular by an elastic deformation of the substrate or on the substrate (4, 5) or by irradiation with electromagnetic radiation is achieved. Method according to one of the preceding claims, characterized in that a CCD or CMOS camera (1) is used as the optical detector. Method according to one of the preceding claims, characterized in that a substrate (3) having on its surface metallic layers with which preferably electrical conductor tracks or electrical connection pads are formed, are examined in a region of the surface of the substrate, the investigation preferred in an area where one metallic layer is formed and / or in a region which is disposed immediately adjacent to a metallic layer is performed. Method according to one of the preceding claims, characterized in that in the electronic evaluation unit an image processing logarithm is performed, which is selected from an image intensity, histogram, a grayscale matrix evaluation, an image intensity analysis and / or a difference correlation function. Method according to one of the preceding claims, characterized in that the same materials or material composites, same energy inputs and speckle patterns, which have been detected and stored at the same time after the energy input, as well as the same illumination conditions and the same settings on the detector for spatially resolved detection (1a) are taken into account and adhered to in the determination of the mechanical residual stresses of the particular substrate or circuit substrate (3) investigated and the calibration.

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