Systems and methods for visualizing and modeling thermomechanical stress using photoluminescence

Abstract

The present disclosure relates to systems and methods for visualizing and modeling thermomechanical stress using photoluminescence. An electronic system may include a substrate, an electronic device bonded to the substrate, a plurality of photoluminescent particles disposed on the electronic device, an illuminator, a sensor, and a control module. The illuminator may illuminate the electronic device. The sensor may capture a first set of positions of the photoluminescent particles on the electronic device when the electronic device is not operating under a load and a second set of positions of the photoluminescent particles when the electronic device is operating under a load. The control module may determine the thermomechanical stress on the electronic device based at least in part on the difference between the first set of positions and the second set of positions.

Description

Technical Field

[0001] The present description relates generally to systems and methods for detecting thermomechanical stress on semiconductor chips, and more particularly, to systems and methods for visualizing and modeling thermomechanical stress on semiconductor chips using photoluminescence. Background Art

[0002] The operation of semiconductors in power electronics components in electric vehicles and other high-heat environments can generate large heat fluxes. Due to differences in thermal expansion coefficients between layers of a power electronics component, one or more layers of the component may flex due to thermomechanical stresses. This movement can cause the semiconductor chip to crack or otherwise become damaged.

[0003] Therefore, there is a need for alternative systems and methods for measuring thermomechanical stresses generated during operation of semiconductors in power electronic components. Summary of the Invention

[0004] In one embodiment, an electronic system includes a substrate, an electronic device bonded to the substrate, a plurality of photoluminescent particles disposed on the electronic device, an illuminator, a sensor, and a control module. The illuminator illuminates the electronic device. The sensor captures a first set of positions of the photoluminescent particles on the electronic device when the electronic device is not operating under a load and a second set of positions of the photoluminescent particles when the electronic device is operating under a load. The control module determines thermomechanical stress on the electronic device based at least in part on a difference between the first set of positions and the second set of positions.

[0005] In another embodiment, a method includes depositing a plurality of photoluminescent particles on a surface of an electronic device bonded to a substrate; illuminating the surface of the electronic device with light of a first wavelength and determining a first set of locations of the photoluminescent particles on the electronic device when the electronic device is not operating under a load; illuminating the surface of the electronic device with light of the first wavelength and determining a second set of locations of the photoluminescent particles on the electronic device when the electronic device is operating under a load; and determining thermomechanical stress on the electronic device based at least in part on a difference between the first set of locations and the second set of locations.

[0006] These and additional features provided by the embodiments described herein will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The embodiments illustrated in the accompanying drawings are illustrative and exemplary in nature and are not intended to limit the subject matter defined by the claims. The following detailed description of the illustrative embodiments may be understood when read in conjunction with the following drawings, in which like structures are designated by like reference numerals, and in which:

[0008] Figure 1 schematically depicts a diagram of an example electronic system according to one or more embodiments shown or described herein;

[0009] Figure 2A schematically depicts a diagram of another example electronic system according to one or more embodiments shown or described herein;

[0010] Figure 2B Shown Figure 2A a perspective view of a portion of an electronic system;

[0011] Figure 2C Shown Figure 2A a perspective view of a portion of an electronic system;

[0012] Figure 2D Shows the Figure 2C Example images captured by the substrate;

[0013] Figure 3A Shown Figure 1 Example arrangement of photoluminescent particles on a substrate in an electronic system;

[0014] Figure 3B Shown Figure 1 Example movement of photoluminescent particles on a substrate in an electronic system;

[0015] Figure 4 Schematically depicts Figure 1 the arrangement of layers in an electronic system;

[0016] Figure 5 Shown Figure 1 Example strain map of a semiconductor chip in an electronic system. DETAILED DESCRIPTION

[0017] Figure 1 One embodiment of an electronic system is generally described. Figure 1 An electronic system includes an electronic device coupled to a substrate, an illuminator, a sensor, and a control module. A plurality of photoluminescent particles are disposed on the electronic device. The illuminator can illuminate the electronic device to illuminate the photoluminescent particles, allowing the sensor to capture the location of the photoluminescent particles. During operation of the electronic system, thermomechanical stresses can cause fatigue in the electronic device and ultimately failure due to cracking and / or delamination of the solder bond between the electronic device and the substrate.

[0018] The systems and methods disclosed herein allow for real-time visualization of stress on electronic devices, which allows for detection of cracks in the electronic device and / or delamination between the electronic device and the substrate while the electronic device is in operation. By detecting these problems in real time, corrective action can be taken before the problem becomes too severe.

[0019] As described herein, the presence of photoluminescent particles on an electronic device allows for real-time monitoring of thermomechanical stress on the electronic device. When the electronic device is operating under load, an illuminator illuminates the photoluminescent particles, causing them to emit light and allowing a sensor to track their movement. The movement of the particles can then be used to monitor the thermomechanical load on the electronic device, allowing corrective action to be taken, if necessary, before significant damage occurs.

[0020] Now refer to Figure 1 , illustrates one embodiment of an electronic system 100. The electronic system 100 generally includes a substrate 102, an electronic device 104 coupled to the substrate 102, an illuminator 106, a sensor 108, and a control module 110.

[0021] Substrate 102 is the base onto which electronic device 104 is bonded and can be any suitable substrate. Non-limiting examples include copper, directly bonded copper, a metal-inverse opal layer, and the like. In some embodiments, electronic device 104 is a semiconductor that is part of a power control unit in an electrified vehicle, switching on and off to convert DC voltage to AC voltage. In other embodiments, electronic device 104 can be an electronic component other than a semiconductor and can be used in other environments and for other purposes as part of other electronic systems.

[0022] refer to Figure 2A , another example electronic system 200 is illustrated. Figure 2A In a non-limiting example, the electronic system 200 includes Figure 1 The substrate 102 and two Figure 1 1. The electronic device 104 is bonded to the substrate 102. The device 104 is bonded to the substrate 102 using a solder layer 103. The device 104 can be connected to a bus bar 105 via a wire 107. The bus bar 105 electrically couples the device 104 to other components in the power electronics assembly. In addition, the electronic system 200 includes a base plate 112 and a heat sink 114. The base plate 112 can form the base of the substrate 102 and can be any suitable material, such as copper, aluminum, etc. The heat sink 114 can be used to cool the substrate 102 and the electronic device 104. The electronic system 200 is enclosed in a housing 116.

[0023] Figure 2B A perspective view of a substrate 102 and an electronic device 104 bonded to the substrate 102 is shown. When the electronic device 104 operates under load, a large amount of heat is generated. The difference between the thermal expansion coefficient of the substrate 102 and the thermal expansion coefficient of the electronic device 104 may cause thermomechanical stress to be applied to the electronic device 104. This may cause portions of the electronic device 104 to be deformed. Figure 2B1. The electronic device 104 may expand or contract (eg, flex) in the x-direction and / or y-direction shown in FIG. As described above, this may cause damage to the electronic device 104.

[0024] In order to visualize the expansion or contraction of the electronic device 104, a plurality of photoluminescent particles 300 are deposited on the surface of the electronic device 104, such as Figure 2C The particles 300 have a photoluminescent property such that when they are illuminated with light of a specific wavelength (excitation wavelength), they emit light of another wavelength (emission wavelength).

[0025] In some embodiments, the photoluminescent particles 300 are phosphors that emit visible light when illuminated with ultraviolet light (i.e., the excitation wavelength of the particles 300 is in the ultraviolet portion of the electromagnetic spectrum, and the emission wavelength of the particles 300 is in the visible portion of the electromagnetic spectrum). More particularly, in some embodiments, the photoluminescent particles 300 have an excitation wavelength between approximately 345-350 nm and an emission wavelength between approximately 530-540 nm. It should be understood that the particles 300 can have other excitation and emission wavelengths in other parts of the electromagnetic spectrum.

[0026] Phosphors are particularly desirable for use with electronic systems 100 as described herein because they are stable at high temperatures. However, in other embodiments, particles 300 may include other materials, such as polymerized quantum dots or other photochromic materials, so long as the material has appropriate photoluminescent properties.

[0027] The particle size (e.g., particle diameter) of the photoluminescent particles 300 can range from 220 nm (approximately the limit of human vision) to 20 microns. In a non-limiting example, the particle size of the photoluminescent particles 300 is between 5-15 microns. In some embodiments, the particles 300 are deposited on the surface of the electronic device 104 using a sprayable transparent coating. In other embodiments, other methods can be used to deposit the particles 300 on the surface of the electronic device 104. Figure 4 In some embodiments, the photoluminescent particles 300 are provided in a particle layer 400 that is adhered to the electronic device 104 by an adhesive layer 402 .

[0028] Now refer to Figure 3A , the surface of the electronic device 104 has a plurality of photoluminescent particles 300 disposed on the surface thereof. In some embodiments, the photoluminescent particles 300 are arranged in a predetermined pattern on the surface of the substrate 102. In other embodiments, the photoluminescent particles 300 are arranged in a random pattern on the surface of the substrate 102.

[0029] When the electronic device 104 operates under load and heats up, the electronic device 104 is subjected to thermomechanical stresses that cause the electronic device 104 to flex. The photoluminescent particles 300 on the surface of the electronic device 104 will move as the electronic device 104 flexes. Figure 3B shows a structure in which the photoluminescent particles 300 have been removed from the Figure 3A Their initial starting positions (in Figure 3B By monitoring the movement of the photoluminescent particles 300 while the electronic device 104 is operating under load, the thermomechanical stress on the electronic device 104 can be monitored in real time.

[0030] Reference again Figure 1 , illuminator 106 is positioned above electronic device 104. Illuminator 106 illuminates the surface of electronic device 104 with light at the excitation wavelength of photoluminescent particles 300. This triggers the particles 300 to emit light, making the particles 300 visible to sensor 108. Illuminator 106 may include a light emitting diode, a laser, or any other light source capable of illuminating the surface of electronic device 104 with light at the excitation wavelength of photoluminescent particles 300.

[0031] Still refer to Figure 1 , sensor 108 is positioned above electronic device 104. Sensor 108 captures an image of photoluminescent particle 300 when photoluminescent particle 300 emits light. That is, sensor 108 captures light emitted by photoluminescent particle 300 at its emission wavelength. In some embodiments, sensor 108 is a color camera. In other embodiments, sensor 108 is a black and white camera. In still other embodiments, sensor 108 may be another device configured to capture an image of photoluminescent particle 300 when photoluminescent particle 300 emits light at its emission wavelength.

[0032] like Figure 1 As shown, the illuminator 106 and sensor 108 are slightly offset in the horizontal direction from the electronic device 104. In some embodiments, the illuminator 106 or sensor 108 can be positioned directly above the electronic device 104. If the illuminator 106 or sensor 108 is offset from the electronic device 104, the illuminator 106 or sensor 108 can be angled so that they are directed toward the surface of the electronic device 104.

[0033] In some embodiments, illuminator 106 and sensor 108 comprise a single device that both illuminates photoluminescent particle 300 with light at its excitation wavelength and captures an image of particle 300 as it emits light at its emission wavelength. Figure 2CAn example device 210 is shown positioned directly above the electronic device 104, operating as both an illuminator and a sensor. Figure 2D An example image 220 of photoluminescent particles 300 present on the surface of the electronic device 104 and captured by the sensor 108 is shown. Figure 2D In the example shown, the particle size of the particles 300 is 300 microns.

[0034] Reference again Figure 1 , control module 110 controls the operation of illuminator 106 and sensor 108 and determines thermomechanical stress on electronic device 104 based on images captured by sensor 108, as explained in more detail herein. Control module 110 may include a computer. In some embodiments, control module 110 determines thermomechanical stress on electronic device 104 by monitoring the movement of photoluminescent particles 300 on the surface of electronic device 104 while electronic device 104 is operating under load.

[0035] In operation, when the electronic system 100 is not operating under a load, the photoluminescent particles 300 are deposited on the surface of the electronic device 104. The illuminator 106 then illuminates the surface of the electronic device 104, and the sensor 108 captures an image of the surface of the electronic device 104. This image will show the initial position of the photoluminescent particles 300 on the surface of the electronic device 104. This can be used as a baseline for comparison with images taken of the surface of the electronic device 104 when the electronic device 104 is operating under a load, as described in further detail below.

[0036] Once the sensor 108 captures an image of the electronic device 104 showing the initial positions of the photoluminescent particles 300 on the surface of the electronic device 104, the control module 110 stores the image and / or the initial positions. The electronic device 104 is then operated under load. While the electronic device 104 is operating under load, the system 100 monitors the movement of the particles 300 by continuously or periodically illuminating the surface of the electronic device 104 with the illuminator 106 and capturing images of the electronic device 104 with the sensor 108 (e.g., periodically capturing images with a set time interval between each image capture).

[0037] When the electronic device 104 expands or contracts due to thermomechanical stress, the photoluminescent particles 300 will move from their initial positions, as described above and Figure 3B. In particular, particles 300 at locations on the surface of electronic device 104 that expand or contract will move with that portion of electronic device 104. Thus, the movement of a particular particle 300 corresponds to the expansion or contraction of a particular portion of electronic device 104. By visualizing the movement of particles 300 on the surface of electronic device 104, the stress on electronic device 104 can be visualized. The greater the displacement of any particle 300 from its initial position, the greater the stress on electronic device 104 at the location of those particles. Thus, by visualizing the initial positions of particles 300 when electronic device 104 is not operating under load (e.g., Figure 3A ) and the position of the particle 300 when the electronic device 104 is operated under load (e.g., Figure 3B ), the control module 110 can create a strain map, such as Figure 5 An example strain map 500 is shown in FIG. Strain map 500 is a heat map that plots the amount of displacement of each particle 300 along the surface of electronic device 104. Thus, strain map 500 shows the amount of strain at each location on electronic device 104.

[0038] Once a strain map has been created for the electronic device 104, the control module 110 converts the strain map into a stress map, which displays the amount of stress at each location on the electronic device 104. In a non-limiting example, the control module 110 converts the strain map into a stress map using a linear elastic model of the surface of the electronic device 104. The linear elastic model of the surface of the electronic device 104 determines the expected dislocation of the particles 300 on the surface of the electronic device 104 when the electronic device 104 is operated under load. The expected dislocation of the particles 300 can be used as a reference data set. If the actual dislocation of the particles 300 is greater than the expected amount from the reference data, this indicates poor adhesion between the electronic device 104 and the substrate 102, for example, due to damage to the solder layer between the substrate 102 and the electronic device 104. When subjected to high temperatures, poor adhesion can cause the solder to expand more than the substrate 102. Therefore, the dislocation of the particles 300 on the surface of the electronic device 104 can be correlated with damage to the surface of the electronic device 104.

[0039] Various open source software can be used to perform the above analysis to convert the strain map into a stress map, such as, for example, NI-CORR and Open FTM. In some embodiments, the control module 110 converts the strain map into a stress map without comparing the actual displacement of the particle 300 with a reference data set. In these embodiments, the control module 110 uses the well-known properties of the materials comprising the substrate 102 and the electronic device 104 to determine the expected displacement of the particle 300 during operation of the electronic device 104. These known material properties allow the control module 110 to determine a certain expected behavior of the particle 300 assuming uniform adhesion between the substrate 102 and the electronic device 104. A stress map is then created based on the difference between this expected behavior and the actual measured dislocations of the particle 300 when the electronic device 104 is operated under load.

[0040] In some embodiments, in addition to being photoluminescent, particles 300 also have thermoluminescent properties, such that the intensity of light emitted by particles 300 at their emission wavelength when illuminated by light changes in response to the temperature of particles 300. In these embodiments, if the solder layer between substrate 102 and electronic device 104 is damaged, there will not be efficient heat transfer from electronic device 104 to substrate 102 and to cooling surfaces below substrate 102 (such as heat sink 114) in the area where the damage exists. This can lead to pockets of high temperature areas forming on electronic device 104. In embodiments where particles 300 are thermoluminescent, particles 300 will emit light more brightly in areas where there is a significant temperature difference between substrate 102 and electronic device 104.

[0041] In embodiments where particles 300 exhibit thermoluminescence, as described above, when electronic device 104 is not operating under load, illuminator 106 illuminates the surface of electronic device 104, and sensor 108 measures the luminescence intensity of particles 300. This can serve as a baseline luminescence intensity for particles 300. Subsequently, when electronic device 104 is operating under load, illuminator 106 illuminates the surface of electronic device 104 again, and sensor 108 measures the luminescence intensity of particles 300. Control module 110 then compares the measured intensity of photoluminescent particles 300 when electronic device 104 is operating under load with the baseline luminescence intensity to create a strain map based on the differences at each location on the surface of electronic device 104. The strain map can be converted into a stress map using the techniques described above. In some embodiments, control module 110 uses the above-described method of monitoring the displacement of particles 300 in conjunction with the method of monitoring the photoluminescence intensity of particles 300 to determine damage to electronic device 104.

[0042] In some embodiments, when particle 300 is subjected to a temperature change, the wavelength of the photoluminescent emission of particle 300 changes. In these embodiments, sensor 108 detects the wavelength change of the luminescent emission of particle 300 (e.g., the sensor can be a color camera), and control module 110 creates a strain map of electronic device 104 based at least in part on the wavelength change. The strain map can then be converted into a stress map using the techniques described above.

[0043] It should now be appreciated that the embodiments described herein allow for real-time visualization and monitoring of thermomechanical stresses on electronic devices by tracking the movement of photoluminescent particles on the surface of electronic devices in power electronics assemblies. By monitoring these stresses on electronic devices while operating under load, corrective action can be taken before significant damage to the devices occurs.

[0044] It is noted that the terms "substantially" and "approximately" may be used herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. These terms are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.

[0045] While specific embodiments have been illustrated and described herein, it will be appreciated that various other changes and modifications may be made without departing from the spirit and scope of the claimed subject matter. Furthermore, while various aspects of the claimed subject matter have been described herein, these aspects need not be used in combination. It is therefore intended that the appended claims cover all such changes and modifications within the scope of the claimed subject matter.

Claims

1. An electronic system for determining thermomechanical stress using photoluminescence, comprising: substrate; an electronic device bonded to the substrate; a plurality of photoluminescent particles disposed on the electronic device; an illuminator, the illuminator being used to illuminate the electronic device; a sensor for capturing a first set of positions of photoluminescent particles on the electronic device when the electronic device is not operating under a load and a second set of positions of photoluminescent particles when the electronic device is operating under a load; as well as A control module is configured to determine a thermomechanical stress on the electronic device based on an amount of displacement between the first set of positions and the second set of positions.

2. The electronic system of claim 1, wherein when the photoluminescent particles are irradiated with ultraviolet light by the irradiator, the photoluminescent particles emit visible light.

3. The electronic system of claim 1, wherein the photoluminescent particles comprise phosphor particles. The electronic system of claim 1 , wherein the substrate is bonded to a backplane.

5. The electronic system of claim 1, wherein the photoluminescent particles are arranged in a predetermined pattern.

6. The electronic system of claim 1, wherein the photoluminescent particles are arranged in a random pattern.

7. The electronic system of claim 1, wherein the control module determines delamination between the substrate and the electronic device based at least in part on a difference between the first set of locations and the second set of locations.

8. The electronic system of claim 1, wherein the control module determines a strain map of the electronic device based at least in part on a difference between the first set of positions and the second set of positions.

9. The electronic system of claim 8, wherein the control module converts the strain map into a stress map of the electronic device. 10 . The electronic system of claim 9 , wherein the control module converts the strain map into a stress map based on a linear elastic model of the surface of the electronic device.

11. The electronic system of claim 1, wherein the sensor detects an intensity of luminescence of the plurality of photoluminescent particles, and the control module determines the thermomechanical stress on the electronic device based at least in part on the detected intensity.

12. The electronic system of claim 1, wherein the sensor detects wavelengths of photoluminescent emissions of a plurality of photoluminescent particles, and the control module determines the thermomechanical stress on the electronic device based at least in part on the detected wavelengths of the photoluminescent emissions.

13. A method for determining thermomechanical stress using photoluminescence, comprising: depositing a plurality of photoluminescent particles on a surface of an electronic device bonded to a substrate; illuminating a surface of the electronic device with light of a first wavelength when the electronic device is not operating under a load, and determining a first set of locations of photoluminescent particles on the electronic device; illuminating a surface of the electronic device with light of the first wavelength while the electronic device is operating under load, and determining a second set of locations of photoluminescent particles on the electronic device; as well as A thermomechanical stress on the electronic device is determined based on an amount of displacement between the first set of positions and the second set of positions.

14. The method of claim 13, wherein determining the location of the photoluminescent particles when the surface of the electronic device is illuminated with light of the first wavelength comprises capturing an image of the electronic device with a sensor capable of detecting light of a second wavelength, wherein the photoluminescent particles emit light of the second wavelength when illuminated with light of the first wavelength.

15. The method of claim 13, wherein the plurality of photoluminescent particles are deposited on the surface of the electronic device in a predetermined pattern.

16. The method of claim 13, further comprising determining a strain map of the electronic device based at least in part on a difference between the first set of positions and the second set of positions.

17. The method of claim 16, further comprising converting the strain map into a stress map of the electronic device.

18. The method of claim 17, further comprising converting the strain map into a stress map based on a linear elastic model of the surface of the electronic device.

19. The method of claim 13, further comprising: determining a first set of intensities of luminescence of the photoluminescent particles when the particles are illuminated with light of the first wavelength and the electronic device is not operating under a load; determining a second set of intensities of luminescence of the photoluminescent particles when the particles are illuminated with light of the first wavelength and the electronic device is operated under a load; as well as Thermomechanical stress on the electronic device is determined based at least in part on a difference between the first set of intensities and the second set of intensities.

20. The method of claim 13, further comprising: determining a first set of wavelengths of light emission from the photoluminescent particles when the particles are illuminated with light of the first wavelength and the electronic device is not operating under a load; determining a second set of wavelengths of light emitted by the photoluminescent particles when the particles are illuminated with light of the first wavelength and the electronic device is operated under a load; as well as Thermomechanical stress on the electronic device is determined based at least in part on a difference between the first set of wavelengths and the second set of wavelengths.

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