MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) module junction temperature monitoring structure based on embedded fiber grating sensor and preparation and application thereof

Abstract

The invention discloses an MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) module junction temperature monitoring structure based on an embedded fiber grating sensor as well as a preparation method and application of the MOSFET module junction temperature monitoring structure. Comprising a general assembly MOSFET and at least one fiber grating sensor. The general assembly MOSFET comprises at least one MOSFET chip and a slotted DBC board, at least one groove is formed in the slotted DBC board, each groove penetrates through the slotted DBC board in the horizontal direction, and at least one MOSFET chip is arranged above each fiber grating sensor; the fiber bragg grating sensors are fixed in the corresponding grooves through metal ink, and gaps between the fiber bragg grating sensors and the groove walls of the grooves are filled with the metal ink; each fiber grating sensor comprises a bare fiber and a composite coating, and the composite coating sequentially comprises a chromium layer, an inner silver layer and an outer silver layer from inside to outside. The device has the advantages of high-precision temperature measurement, real-time response, high temperature resistance, long-term stability, packaging compatibility, mechanical reliability and the like.

Description

Technical Field

[0001] This invention relates to the field of junction temperature monitoring technology, specifically to a junction temperature monitoring structure for a MOSFET module based on an embedded fiber Bragg grating sensor, its fabrication method, and its application. Background Technology

[0002] In modern power electronic systems, MOSFET modules, with their high-efficiency power conversion capabilities, have become core components in the drive and control stages. As systems evolve towards higher frequencies and higher power densities, the junction temperature of MOSFET modules can rise rapidly under high-frequency switching and high-current conditions. When the junction temperature exceeds the material's tolerance threshold, it can not only lead to performance degradation but also potentially cause thermal runaway or even permanent damage, seriously threatening the stability and reliability of the system. Therefore, accurate real-time monitoring of MOSFET module junction temperature has become a critical technical requirement for ensuring the safe operation of power electronic systems.

[0003] Currently, methods for measuring junction temperature in MOSFET modules have significant limitations. Traditional thermocouple measurements require damaging the device structure, introducing additional thermal resistance and resulting in significant measurement errors; infrared thermometry is greatly affected by environmental interference and struggles to penetrate the package to obtain the internal junction temperature; while electrical parameter methods are non-invasive, they rely on complex calibration models and are difficult to adapt to dynamic operating conditions. In contrast, fiber optic sensors, with their advantages of good insulation, strong resistance to electromagnetic interference, and small size, have become a highly regarded new monitoring method in recent years. They can not only achieve in-situ measurements of MOSFET modules but also directly contact critical heat-generating areas of the chip, effectively overcoming the shortcomings of traditional methods.

[0004] However, existing MOSFET junction temperature monitoring technologies based on fiber Bragg grating sensors still face many challenges. In terms of installation processes, the commonly used adhesive fixing method easily leads to glue overflow, contaminating the chip surface and affecting heat dissipation efficiency and device performance. If the optical fiber is placed around the chip, it cannot accurately capture the highest junction temperature at the chip center, resulting in measurement deviations. Furthermore, optical fibers operating in high-temperature environments for extended periods are prone to aging and increased loss, and current packaging methods cannot guarantee long-term measurement requirements.

[0005] Therefore, there is an urgent need for a fiber Bragg grating sensor packaging and monitoring solution that balances measurement accuracy, reliability, and integration to meet the application requirements of MOSFET modules in high-performance power electronic systems. Summary of the Invention

[0006] To address the problems existing in the background art, this invention provides a MOSFET module junction temperature monitoring structure based on an embedded fiber Bragg grating sensor, its fabrication method, and its application. This invention aims to improve the sensitivity and reliability of the fiber Bragg grating sensor by optimizing its packaging structure, thereby further improving the accuracy of junction temperature measurement; simultaneously, by optimizing the embedding method of the fiber Bragg grating sensor in the MOSFET module, it meets the technical objective of real-time monitoring requirements.

[0007] The technical solution adopted in this invention is: I. A MOSFET module junction temperature monitoring structure based on an embedded fiber Bragg grating sensor: The MOSFET module junction temperature monitoring structure includes an assembled MOSFET and at least one fiber Bragg grating sensor. The assembled MOSFET includes at least one MOSFET chip, a slotted DBC board, and a base plate. The MOSFET chip is connected to the top surface of the slotted DBC board, and the bottom surface of the slotted DBC board is connected to the top surface of the base plate via a solder layer. The slotted DBC board has at least one groove, each groove penetrating the slotted DBC board horizontally. At least one MOSFET chip is arranged above each fiber Bragg grating sensor, and each MOSFET chip is correspondingly arranged on the fiber Bragg grating sensor. The fiber Bragg grating sensor is positioned directly above a grating and vertically aligned with the central axis of the fiber Bragg grating sensor. The number of gratings etched on each grating corresponds to the number of MOSFET chips above it, and the central reflection wavelengths of different gratings are different. The grating sensor is fixed in the corresponding groove by metallic ink, and the gap between the grating sensor and the groove wall is filled with metallic ink. Each grating sensor includes a bare optical fiber and a composite coating, which consists of a chromium layer, an inner silver layer, and an outer silver layer from the inside out.

[0008] The grooved DBC board has a thickness of 0.35~1.0mm, and the groove has an etching depth of 0.2~0.8mm and a width of 0.2~0.8mm.

[0009] In the composite coating, the chromium layer and the inner silver layer are both processed by magnetron sputtering, and their thickness is in the nanometer range. The outer silver layer is processed by electroplating, and its thickness is in the micrometer range.

[0010] The diameter of the bare optical fiber is 0.1~0.35mm; the magnetron sputtering particle size of the chromium layer is 1~10nm and the sputtering thickness is 50~1000nm; the magnetron sputtering particle size of the inner silver layer is 1~10nm and the sputtering thickness is 100~800nm; the electroplating thickness of the outer silver layer is 10~200μm.

[0011] The solder layer uses nano-silver solder paste; the metal ink is copper ink or silver ink.

[0012] II. A method for fabricating a MOSFET module junction temperature monitoring structure based on an embedded fiber Bragg grating sensor The preparation method includes the following steps: Step S1) According to the preset layout of the MOSFET chip, a groove is etched on the DBC substrate using an ultraviolet laser to obtain a slotted DBC board; Step S2) A composite coating is processed on the surface of the bare optical fiber to obtain a fiber grating sensor; Step S3) Place a fiber Bragg grating sensor in each groove of the slotted DBC board, fix it with metallic ink and fill the gaps; Step S4) Apply nano silver solder paste to the top surface of the slotted DBC board and adhere the MOSFET chip to the top surface of the slotted DBC board according to the preset layout. Nano-silver solder paste is coated on the bottom surface of the slotted DBC board, and the slotted DBC board is adhered to the top surface of the base plate to obtain the junction temperature monitoring structure of the MOSFET module.

[0013] Step S2 includes: Step S2.1) Clean and plasma activate the surface of the bare optical fiber to remove the surface coating layer; Step S2.2) A chromium layer and an inner silver layer are sequentially fabricated using magnetron sputtering. The conditions for magnetron sputtering are: sputtering power of 2kW, gas pressure of 0.5Pa, and substrate temperature of 150℃. Step S2.3) The outer silver layer is formed by electroplating. The electroplating method uses a plating solution containing 100 g / L potassium silver cyanide and 150 g / L potassium cyanide, at a temperature of 35°C and a current density of 2 A / dm³. 2 .

[0014] In step S3, the metallic ink is copper ink or silver ink, and the curing temperature of the metallic ink is 100~160℃, and the curing time is 10~40min.

[0015] In step S4, the nano-silver solder paste is sintered without pressure at a temperature of 180~250℃ and a holding time of 20~60min.

[0016] III. A junction temperature monitoring method for a MOSFET module using a junction temperature monitoring structure based on an embedded fiber Bragg grating sensor. The junction temperature monitoring method includes the following steps: First, gradually increase the temperature and record the grating reflection wavelength of each fiber Bragg grating sensor corresponding to each temperature point, and obtain the wavelength-temperature relationship by linear fitting, that is, the temperature calibration curve corresponding to each chip; then, collect the reflection wavelength of each fiber Bragg grating sensor in real time, and combine it with the pre-constructed temperature calibration curve of each chip to obtain the real-time junction temperature of each MOSFET chip above the fiber Bragg grating sensor.

[0017] The temperature-wavelength relationship model can be a fitted curve of temperature-wavelength.

[0018] The beneficial effects of this invention are: High-precision temperature measurement and real-time response: This invention achieves direct measurement of junction temperature by directly embedding a fiber optic grating sensor into a groove on the DBC substrate and aligning it with the center of the bottom surface of the chip. The temperature measurement error is ≤ ±0.5℃ and the response time is ≤10ms, which is significantly better than the accuracy (error is usually ±2℃ or more) and response speed of traditional indirect temperature measurement methods (such as thermistors and infrared thermometry), and achieves the purpose of real-time monitoring.

[0019] 2. High temperature resistance and long-term stability: The present invention prepares a fiber grating sensor with a chromium-silver composite coating, which enables the fiber grating sensor to withstand a long-term working environment of about 300°C. After 1000 hours of continuous operation, the performance degradation is less than 5%, which solves the problem of traditional adhesive sensors being easy to fall off or age at high temperatures.

[0020] 3. Packaging compatibility and mechanical reliability: Through the innovative slotted DBC structure design, this invention not only ensures the thermal coupling between the sensor and the chip, but also achieves integrated packaging through metal ink filling. The shear strength of the solder joint reaches more than 30 MPa, and the vibration and shock resistance is significantly better than the traditional surface mount method.

[0021] 4. Process integration and cost advantages: This invention organically combines processes such as laser grooving, magnetron sputtering, electroplating, and nano-silver sintering to form an integrated manufacturing solution that can be mass-produced, avoiding complex micro-machining processes and high equipment costs. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the monitoring structure provided by the present invention; Figure 2 This is a schematic diagram of the fiber Bragg grating sensor provided by the present invention; Figure 3 This is a schematic diagram of the layout of the MOSFET chip and the groove provided by the present invention.

[0023] In the diagram: 1. Assembly MOSFET, 1-1. MOSFET chip, 1-2. Solder layer, 1-3. Slotted DBC board, 1-4. Base plate; 2. Fiber Bragg grating sensor, 2-1. Bare optical fiber, 2-2. Composite coating. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] This invention provides a junction temperature monitoring structure for a MOSFET module based on an embedded fiber Bragg grating sensor.

[0026] like Figure 1 As shown, the MOSFET module junction temperature monitoring structure includes an assembled MOSFET 1 and at least one fiber Bragg grating sensor 2. The assembled MOSFET 1 includes at least one MOSFET chip 1-1, a slotted DBC board 1-3, and a base plate 1-4. The MOSFET chip 1-1 is connected to the top surface of the slotted DBC board 1-3, and the bottom surface of the slotted DBC board 1-3 is connected to the top surface of the base plate 1-4 through a solder layer 1-2.

[0027] like Figure 2 As shown, each fiber grating sensor 2 includes a bare optical fiber 2-1 and a composite coating 2-2 formed on the surface of the bare optical fiber 2-1. The composite coating 2-2 includes a chromium layer, an inner silver layer and an outer silver layer from the inside to the outside.

[0028] like Figure 3 As shown, at least one groove is formed on the slotted DBC board 1-3. Each groove extends horizontally through the side of the slotted DBC board 1-3. At least one MOSFET chip 1-1 is arranged above each groove along the extension direction. Each MOSFET chip 1-1 is arranged directly above a grating of a fiber Bragg grating sensor 2 and is aligned vertically with the central axis of the fiber Bragg grating sensor 2. The number of fiber Bragg grating sensors 2 and the number of grooves in the slotted DBC board 1-3 are the same and correspond one-to-one. The number of gratings etched in the fiber Bragg grating sensor 2 is the same and corresponds one-to-one with the number of MOSFET chips 1-1, and the reflection wavelengths at the center of different gratings are different. The fiber Bragg grating sensor 2 is fixed in the corresponding groove by metallic ink, and the gap between the fiber Bragg grating sensor 2 and the groove wall is filled by metallic ink.

[0029] Optionally, on the slotted DBC boards 1-3, the slotting direction extends in the transverse, longitudinal, or cross directions and penetrates the entire DBC substrate.

[0030] Preferably, the thickness of the slotted DBC board 1-3 is 0.35~1.0mm, the etching depth of the groove is 0.2~0.8mm, and the width is 0.2~0.8mm, so as to meet the embedding requirements of the fiber Bragg grating sensor 2.

[0031] Furthermore, after etching is completed, the groove walls are polished to control the roughness Ra≤0.8μm.

[0032] Preferably, in the composite coating 2-2, the chromium layer and the inner silver layer are both processed by magnetron sputtering, and their thicknesses are both in the nanometer range, while the outer silver layer is processed by electroplating, and its thickness is in the micrometer range.

[0033] Preferably, the diameter of the bare optical fiber 2-1 is 0.1~0.35mm; the magnetron sputtering particle size of the chromium layer is 1~10nm and the sputtering thickness is 50~1000nm; the magnetron sputtering particle size of the inner silver layer is 1~10nm and the sputtering thickness is 100~800nm; and the electroplating thickness of the outer silver layer is 10~200μm.

[0034] Preferably, solder layers 1-2 are made of nano-silver solder paste.

[0035] Preferably, the metallic ink is copper ink or silver ink.

[0036] Preferably, the base plate 1-4 is made of copper or aluminum alloy.

[0037] This invention also provides a method for fabricating the above-mentioned MOSFET module junction temperature monitoring structure based on an embedded fiber Bragg grating sensor, specifically including the following steps: Step S1) According to the preset layout of MOSFET chip 1-1, use ultraviolet laser to etch grooves on DBC substrate to obtain slotted DBC board 1-3.

[0038] Step S2) A composite coating 2-2 is fabricated on the surface of the bare optical fiber 2-1 to obtain the fiber grating sensor 2. Step S2 includes: Step S2.1) Clean and plasma activate the surface of the bare optical fiber 2-1 to remove the surface coating layer; Step S2.2) A chromium layer and an inner silver layer are sequentially fabricated using magnetron sputtering. The conditions for magnetron sputtering are: sputtering power of 2kW, gas pressure of 0.5Pa, and substrate temperature of 150℃. Step S2.3) The outer silver layer is formed by electroplating. The electroplating method uses a plating solution containing 100 g / L potassium silver cyanide and 150 g / L potassium cyanide, at a temperature of 35°C and a current density of 2 A / dm³. 2 .

[0039] Step S3) Place a fiber Bragg grating sensor 2 in each groove of the slotted DBC board 1-3, fix it with metallic ink and fill the gaps to obtain the slotted DBC board 1-3 with the fiber Bragg grating sensor 2 installed.

[0040] In step S3, the metallic ink is copper ink or silver ink, and the curing temperature of the metallic ink is 100~160℃, and the curing time is 10~40min.

[0041] Step S4) Apply nano-silver solder paste to the top surface of the slotted DBC board 1-3 on which the fiber Bragg grating sensor 2 is installed, and attach the MOSFET chip 1-1 to the top surface of the slotted DBC board 1-3 on which the fiber Bragg grating sensor 2 is installed according to the preset layout, so as to obtain the slotted DBC board 1-3 on which the fiber Bragg grating sensor 2 and the MOSFET chip 1-1 are installed. Nano-silver solder paste is applied to the bottom surface of the slotted DBC board 1-3, on which the fiber optic grating sensor 2 and MOSFET chip 1-1 are installed. The slotted DBC board 1-3 is then adhered to the top surface of the base plate 1-4 to obtain the MOSFET module junction temperature monitoring structure.

[0042] In step S4, the nano-silver solder paste is sintered without pressure at a temperature of 180~250℃ and a holding time of 20~60min.

[0043] The present invention also provides an application of the above-mentioned MOSFET module junction temperature monitoring structure based on an embedded fiber optic grating sensor, specifically: for monitoring the junction temperature of the assembled MOSFET1.

[0044] The present invention also provides a junction temperature monitoring method using the above-mentioned junction temperature monitoring structure of a MOSFET module based on an embedded fiber Bragg grating sensor, specifically including the following steps: connecting a demodulation device, acquiring the real-time reflected light wavelength output by each fiber Bragg grating sensor 2 in real time, inputting it into a pre-built temperature-wavelength relationship model, and obtaining the real-time junction temperature of each MOSFET chip 1-1 above the fiber Bragg grating sensor 2.

[0045] The temperature-wavelength relationship model can be a fitted curve of temperature-wavelength.

[0046] In practice, the temperature-wavelength relationship model can be constructed through the following process: gradually increase the temperature, record the grating reflection wavelength of each fiber optic sensor 2 corresponding to each temperature point, and obtain the wavelength-temperature relationship by linear fitting, that is, the temperature calibration curve corresponding to each chip.

[0047] In practice, the real-time junction temperature of each MOSFET chip 1-1 can be detected through the following process: the reflected wavelength of each fiber optic grating sensor 2 is acquired in real time, and combined with the pre-constructed temperature calibration curve of each chip, the real-time junction temperature of each MOSFET chip 1-1 above the fiber optic grating sensor 2 is obtained.

[0048] Specific embodiments of the present invention are as follows: Example 1 This embodiment fabricates a MOSFET module junction temperature monitoring structure based on an embedded fiber Bragg grating sensor, and uses it for junction temperature detection. The specific process is as follows: 1. Prepare grooved DBC plates 1-3 A DBC substrate with a thickness of 0.85mm, consisting of an upper copper layer, a ceramic layer, and a lower copper layer, was selected. A groove with a depth of 0.65mm and a width of 0.65mm was etched on the upper surface of the DBC using an ultraviolet laser. The groove was cut longitudinally through the entire DBC substrate. After etching, the groove walls were polished.

[0049] 2. Fabrication of a fiber optic grating sensor The bare optical fiber 2-1 was cleaned and plasma-activated to remove the surface coating. Then, a chromium-silver composite coating 2-2 was fabricated on the surface of the bare optical fiber 2-1 using magnetron sputtering and electroplating techniques. The specific process was as follows: First, the 0.3 mm diameter bare optical fiber 2-1 was cleaned and plasma-activated. Then, a chromium layer and an inner silver layer were sequentially deposited on the surface of the bare optical fiber 2-1 using magnetron sputtering. The chromium layer had a sputtering particle size of 10 nm and a thickness of 1 μm, with a sputtering power of 2 kW, a gas pressure of 0.5 Pa, and a substrate temperature of 150 °C. The inner silver layer had a sputtering particle size of 10 nm and a thickness of 600 nm, with process parameters matching those of the chromium layer. Finally, an outer silver layer was deposited on the surface of the inner silver layer using electroplating. The electroplated silver grains had a particle size of 2 μm and a thickness of 150 μm. The plating solution contained 100 g / L potassium silver cyanide and 150 g / L potassium cyanide, the temperature was 35 °C, and the current density was 2 A / dm³. 2 .

[0050] 3. Use metallic ink to fix the sensor to the filling groove. The fiber grating sensor 2 is fixed in the groove of the slotted DBC board 1-3 using copper ink or silver ink and the gaps are filled: After placing the fiber grating sensor 2 into the corresponding groove, the fiber grating sensor is fixed and the gaps are filled with silver ink. The curing temperature is 150℃ and the curing time is 15min.

[0051] 4. Silver solder paste sintering and module assembly The connection between MOSFET chip 1-1 and slotted DBC board 1-3, and between slotted DBC board 1-3 and base plate 1-4 is completed using silver solder paste: Nano silver solder paste is coated on the upper surface of slotted DBC board 1-3, and MOSFET chip 1-1 is adhered to the solder paste. Pressureless sintering technology is used, the sintering temperature is 230℃, and the holding time is 35min. At the same time, the bottom surface of the lower copper layer of slotted DBC board 1-3 is adhered to copper base plate 1-4 using nano silver solder paste, and the sintering process is the same as above.

[0052] 5. Demodulation system connection and temperature monitoring Before the experiment, the temperature-wavelength curve of the fabricated fiber Bragg grating sensor 2 was calibrated, and the goodness of fit R was determined. 2 =0.992. After the experiment began, fiber Bragg grating sensor 2 was connected to the fiber demodulation device to build a junction temperature monitoring system: fiber Bragg grating sensor 2 was connected to the wavelength demodulator via fiber optic patch cord, and the MOSFET module was driven to work to collect reflected light signals in real time. A temperature-wavelength calibration curve was established in the host computer, and finally, the real-time temperature change of the chip was observed through the host computer monitor based on the real-time reflected light signals.

[0053] Example 2 This embodiment fabricates a MOSFET module junction temperature monitoring structure based on an embedded fiber Bragg grating sensor, and uses it for junction temperature detection. The specific process is as follows: 1. Prepare grooved DBC plates 1-3 A DBC substrate with a thickness of 0.6mm, consisting of an upper copper layer, a ceramic layer, and a lower copper layer, was selected. A groove with a depth of 0.45mm and a width of 0.45mm was etched on the upper surface of the DBC using an ultraviolet laser. The groove was cut horizontally and penetrated the entire DBC substrate. After etching, the groove walls were polished.

[0054] 2. Fabrication of a fiber optic grating sensor The bare optical fiber 2-1 was cleaned and plasma activated to remove the surface coating. Then, a chromium-silver composite coating 2-2 was fabricated on the surface of the bare optical fiber using magnetron sputtering and electroplating techniques. The specific process was as follows: First, the 0.2 mm diameter bare optical fiber 2-1 was cleaned and plasma activated. Then, a chromium layer and an inner silver layer were sequentially deposited on the surface of the bare optical fiber 2-1 using magnetron sputtering. The sputtering particle size of the chromium layer was 10 nm, the thickness was 800 nm, the sputtering power was 2 kW, the gas pressure was 0.5 Pa, and the substrate temperature was 150 °C. The sputtering particle size of the inner silver layer was 10 nm, the thickness was 300 nm, and the process parameters were the same as for the chromium layer. Finally, an outer silver layer was deposited on the surface of the inner silver layer using electroplating. The electroplated silver grain size was 2 μm, the thickness was 100 μm, the plating solution contained 100 g / L potassium silver cyanide and 150 g / L potassium cyanide, the temperature was 35 °C, and the current density was 2 A / dm³. 2 .

[0055] 3. Use metallic ink to fix the sensor to the filling groove. The fiber grating sensor 2 is fixed in the groove of the slotted DBC board 1-3 using copper ink and the gaps are filled: After the fiber grating sensor 2 is placed in the corresponding groove, the fiber grating sensor is fixed and the gaps are filled by copper ink. The curing temperature is 135℃ and the curing time is 30min.

[0056] 4. Silver solder paste sintering and module assembly The connection between MOSFET chip 1-1 and slotted DBC board 1-3, and between slotted DBC board 1-3 and base plate 1-4 is completed using silver solder paste: Nano silver solder paste is coated on the upper surface of slotted DBC board 1-3, and MOSFET chip 1-1 is adhered to the solder paste. Pressureless sintering technology is used, the sintering temperature is 200℃, and the holding time is 45min. At the same time, the bottom surface of the lower copper layer of slotted DBC board 1-3 is adhered to copper base plate 1-4 using nano silver solder paste, and the sintering process is the same as above.

[0057] 5. Demodulation system connection and temperature monitoring Before the experiment, the temperature-wavelength curve of the prepared fiber Bragg grating sensor sample was calibrated, and the goodness of fit R was determined. 2 =0.995. After the experiment began, the fiber Bragg grating sensor was connected to the fiber demodulation equipment to build a junction temperature monitoring system: the fiber Bragg grating sensor was connected to the wavelength demodulator via fiber optic patch cords, driving the MOSFET module to operate and acquiring the reflected light signal in real time. A temperature-wavelength calibration curve was established in the host computer, and finally, the real-time temperature change of the chip was observed through the host computer monitor based on the real-time reflected light signal.

[0058] Example 3 This embodiment fabricates a MOSFET module junction temperature monitoring structure based on an embedded fiber Bragg grating sensor, and uses it for junction temperature detection. The specific process is as follows: 1. Prepare grooved DBC plates 1-3 A DBC substrate consisting of an upper copper layer, a ceramic layer, and a lower copper layer with a thickness of 0.35 mm was selected. A groove with a depth of 0.3 mm and a width of 0.3 mm was etched on the upper surface of the DBC using an ultraviolet laser. The grooves were cut along the intersecting direction and penetrated the entire DBC substrate. After etching, the groove walls were polished.

[0059] 2. Fabrication of a fiber optic grating sensor The bare optical fiber 2-1 was cleaned and plasma activated to remove the surface coating. Then, a chromium-silver composite coating 2-2 was fabricated on the surface of the bare optical fiber 2-1 using magnetron sputtering and electroplating techniques. The specific process was as follows: First, the 0.15mm diameter bare optical fiber 2-1 was cleaned and plasma activated. Then, a chromium layer and an inner silver layer were sequentially deposited on the surface of the bare optical fiber using magnetron sputtering. The sputtering parameters for the chromium layer were 5nm, 2kW, 0.5Pa, and 150℃. The sputtering parameters for the inner silver layer were 5nm and 500nm, matching those for the chromium layer. Finally, an outer silver layer was deposited on the surface of the inner silver layer using electroplating. The electroplated silver grains had a diameter of 2.5μm and a thickness of 50μm. The plating solution contained 100g / L potassium silver cyanide and 150g / L potassium cyanide, the temperature was 35℃, and the current density was 2A / dm³. 2 .

[0060] 3. Use metallic ink to fix the sensor to the filling groove. The fiber grating sensor 2 is fixed in the groove of the slotted DBC board 1-3 using copper ink or silver ink and the gaps are filled: After the fiber grating sensor 2 is placed in the corresponding groove, the fiber grating sensor 2 is fixed in place with copper ink and the gaps are filled. The curing temperature is 120℃ and the curing time is 35min.

[0061] 4. Silver solder paste sintering and module assembly The connection between the chip and the slotted DBC board 1-3, and between the slotted DBC board 1-3 and the base plate is completed using silver solder paste: Nano silver solder paste is coated on the upper surface of the slotted DBC board 1-3, and the MOSFET chip is adhered to the solder paste. Pressureless sintering technology is used, the sintering temperature is 180℃, and the holding time is 60min. At the same time, the bottom surface of the lower copper layer of the slotted DBC board 1-3 is adhered to the copper base plate 1-4 using silver solder paste, and the sintering process is the same as above.

[0062] 5. Demodulation system connection and temperature monitoring Before the experiment, the temperature-wavelength curve of the fabricated fiber Bragg grating sensor 2 was calibrated, and the goodness of fit R was determined. 2 =0.997. After the experiment began, fiber Bragg grating sensor 2 was connected to the fiber demodulation device to build a junction temperature monitoring system: fiber Bragg grating sensor 2 was connected to the wavelength demodulator via fiber optic patch cords, driving the MOSFET module to operate and acquiring the reflected light signal in real time. A temperature-wavelength calibration curve was established in the host computer, and finally, the real-time temperature change of the chip was observed through the host computer monitor based on the real-time reflected light signal.

[0063] Tests showed that the fiber Bragg grating sensors 2 prepared in Examples 1 to 3 all had a temperature measurement range of -40℃ to 350℃, a temperature sensitivity greater than 20 pm / ℃, a response time less than 10 ms, and a performance degradation of less than 5% after continuous operation at 300℃ for 1000 hours.

[0064] Furthermore, in Examples 1 to 3, the shear strength of the silver solder paste joints all reached over 30 MPa, and the thermal resistance was less than 0.1℃ / W. Therefore, it can be ensured that a complete heat conduction path is formed between the fiber optic grating sensor 2 and the bottom surface of the MOSFET chip 1-1, ultimately achieving an efficient connection of the heat conduction path.

[0065] During junction temperature monitoring, in Examples 1 to 3, the temperature-wavelength curve calibration fitting degree of fiber Bragg grating sensor 2 all met R. 2 ≥0.98, the temperature measurement error can be below ±0.5℃.

[0066] Comparative Example 1 To compare and verify the effect of the embedded monitoring of the present invention, the same MOSFET chip and DBC substrate as in Example 1 were selected, and the traditional surface adhesive mounting method was used for comparison.

[0067] The specific method is as follows: On an ungrooved DBC substrate, a fiber Bragg grating sensor is placed next to a MOSFET chip and adhered and fixed using high-temperature epoxy adhesive, with an adhesive layer thickness of approximately 150~250μm. After the adhesive cures, a junction temperature test environment is set up, and the temperature measurement performance is compared with that of Examples 1 to 3 under the same conditions.

[0068] The results are as follows: In the comparative sample, when the chip steady-state temperature is 150℃, the temperature measurement error of the comparative sample is ±3.5℃, which is significantly higher than ±0.5℃ in the embedded structure of Example 1; the temperature response time of the comparative sample is about 30~90ms, while the response time in Example 1 is only 5~10ms; after the comparative sample has been working continuously at 200℃ for 300 hours, the adhesive layer shows obvious aging and cracking, and the reflection peak intensity of the optical fiber decreases by more than 10%; while the embedded silver-coated optical fiber in the example still shows less than 5% performance degradation after working under the same conditions for 1000 hours.

[0069] In summary, the adhesive mounting method is significantly inferior to the slotted embedded fiber Bragg grating sensor structure of this invention in terms of temperature measurement accuracy, response speed, and high-temperature reliability, and is unable to meet the requirements of high-power-density MOSFET modules for real-time and accurate junction temperature monitoring.

[0070] Comparative Example 2 To verify the performance of the fiber Bragg grating sensor composite coating in this invention, a comparative experiment was conducted between the chromium-silver composite coating and a commonly used polyimide-encapsulated fiber Bragg grating sensor. Both types of fiber Bragg grating sensors used the same grating writing process and were tested for temperature resistance, temperature stability, and long-term reliability under the same high-temperature environment and thermal cycling conditions. The test results are as follows: When the ambient temperature exceeds 280°C, the coating of the polyimide-encapsulated fiber Bragg grating sensor begins to soften, carbonize, and even peel off, leading to a sharp decrease in the intensity of the grating's reflection peak. After 100 hours of continuous operation at 280°C, the polyimide coating exhibits obvious cracks and peeling, and the grating's reflection peak attenuation exceeds 20%. In contrast, the chromium-silver composite-coated fiber Bragg grating sensor of this invention can operate continuously for 1000 hours at 300°C with a reflection peak attenuation of less than 5%, indicating that it possesses significantly superior high-temperature resistance and long-term stability compared to polyimide-coated optical fibers.

[0071] Experiments have shown that the temperature response time of polyimide-encapsulated fiber optic grating sensors is typically 20-60 ms, while the response time of the chromium-silver composite-coated fiber optic grating sensor of this invention can be maintained at 5-10 ms, which is significantly faster than the traditional polyimide encapsulation method.

[0072] In summary, the metallized fiber Bragg grating sensor of the present invention is significantly superior to traditional polyimide-encapsulated optical fibers in terms of high temperature resistance, thermal response speed, and reliability, and is more suitable for long-term junction temperature monitoring applications inside high power density MOSFET modules.

[0073] The above specific embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

[0074] The above description is only a preferred embodiment of the present invention. Therefore, all equivalent changes or modifications made to the structure, features and principles described in the claims of this patent application are included in the scope of this patent application.

Claims

1. A MOSFET module junction temperature monitoring structure based on an embedded fiber Bragg grating sensor, characterized in that: The junction temperature monitoring structure of the MOSFET module includes an assembled MOSFET (1) and at least one fiber Bragg grating sensor (2); the assembled MOSFET (1) includes at least one MOSFET chip (1-1), a slotted DBC board (1-3) and a base plate (1-4); at least one groove is provided on the slotted DBC board (1-3), each groove penetrates the slotted DBC board (1-3) in the horizontal direction, and at least one MOSFET chip (1-1) is arranged above each fiber Bragg grating sensor (2); The fiber grating sensor (2) corresponds one-to-one with the grooves of the slotted DBC board (1-3). The number of gratings etched by the fiber grating sensor (2) corresponds one-to-one with the MOSFET chip (1-1) above, and the center reflection wavelengths of different gratings are different. The fiber grating sensor (2) is fixed in the corresponding groove by metal ink, and the gap between the fiber grating sensor (2) and the groove wall is filled by metal ink. Each fiber grating sensor (2) includes a bare optical fiber (2-1) and a composite coating (2-2), wherein the composite coating (2-2) consists of a chromium layer, an inner silver layer and an outer silver layer from the inside out.

2. The MOSFET module junction temperature monitoring structure based on an embedded fiber Bragg grating sensor according to claim 1, characterized in that: The thickness of the slotted DBC board (1-3) is 0.35~1.0mm, the etching depth of the groove is 0.2~0.8mm, and the width is 0.2~0.8mm.

3. The MOSFET module junction temperature monitoring structure based on an embedded fiber Bragg grating sensor according to claim 1, characterized in that: In the composite coating (2-2), the chromium layer and the inner silver layer are both processed by magnetron sputtering and have a thickness in the nanometer range, while the outer silver layer is processed by electroplating and has a thickness in the micrometer range.

4. The MOSFET module junction temperature monitoring structure based on an embedded fiber Bragg grating sensor according to claim 3, characterized in that: The diameter of the bare optical fiber (2-1) is 0.1~0.35mm; the magnetron sputtering particle size of the chromium layer is 1~10nm and the sputtering thickness is 50~1000nm; the magnetron sputtering particle size of the inner silver layer is 1~10nm and the sputtering thickness is 100~800nm; the electroplating thickness of the outer silver layer is 10~200μm.

5. The MOSFET module junction temperature monitoring structure based on an embedded fiber Bragg grating sensor according to claim 1, characterized in that: The MOSFET chip (1-1) is connected to the top surface of the slotted DBC board (1-3), and the bottom surface of the slotted DBC board (1-3) is connected to the top surface of the base plate (1-4) by a solder layer (1-2). The solder layer (1-2) is made of nano silver solder paste. The metal ink is copper ink or silver ink.

6. A method for fabricating a MOSFET module junction temperature monitoring structure based on an embedded fiber Bragg grating sensor as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Step S1) According to the preset layout of the MOSFET chip (1-1), a groove is etched on the DBC substrate using an ultraviolet laser to obtain a slotted DBC board (1-3). Step S2) A composite coating (2-2) is processed on the surface of the bare optical fiber (2-1) to obtain the fiber grating sensor (2). Step S3) Place a fiber Bragg grating sensor (2) in each groove of the slotted DBC board (1-3), fix it with metallic ink and fill the gaps; Step S4) Apply nano silver solder paste to the top surface of the slotted DBC board (1-3) and attach the MOSFET chip (1-1) to the top surface of the slotted DBC board (1-3) according to the preset layout; Nano-silver solder paste is coated on the bottom surface of the slotted DBC board (1-3), and the slotted DBC board (1-3) is adhered to the top surface of the base plate (1-4) to obtain the junction temperature monitoring structure of the MOSFET module.

7. The fabrication method of the MOSFET module junction temperature monitoring structure based on an embedded fiber Bragg grating sensor according to claim 6, characterized in that: Step S2 includes: Step S2.1) The surface of the bare optical fiber (2-1) is cleaned and plasma activated to remove the surface coating layer; Step S2.2) A chromium layer and an inner silver layer are sequentially fabricated using magnetron sputtering. The conditions for magnetron sputtering are: sputtering power of 2kW, gas pressure of 0.5Pa, and substrate temperature of 150℃. Step S2.3) The outer silver layer is formed by electroplating. The electroplating method uses a plating solution containing 100 g / L potassium silver cyanide and 150 g / L potassium cyanide, at a temperature of 35°C and a current density of 2 A / dm³. 2 .

8. The method for fabricating a MOSFET module junction temperature monitoring structure based on an embedded fiber Bragg grating sensor according to claim 6, characterized in that: In step S3, the metallic ink is copper ink or silver ink, and the curing temperature of the metallic ink is 100~160℃, and the curing time is 10~40min.

9. The method for fabricating a MOSFET module junction temperature monitoring structure based on an embedded fiber Bragg grating sensor according to claim 6, characterized in that: In step S4, the nano-silver solder paste is sintered without pressure at a temperature of 180~250℃ and a holding time of 20~60min.

10. A junction temperature monitoring method employing a MOSFET module junction temperature monitoring structure based on an embedded fiber Bragg grating sensor as described in any one of claims 1 to 5, characterized in that, The process includes the following steps: First, gradually increase the temperature and record the grating reflection wavelength of each fiber optic sensor (2) at each temperature point to obtain the wavelength-temperature relationship through linear fitting, i.e., the temperature calibration curve corresponding to each chip; then, collect the reflection wavelength of each fiber optic sensor (2) in real time, and combine it with the pre-constructed temperature calibration curve of each chip to obtain the real-time junction temperature of each MOSFET chip (1-1) above the fiber optic sensor (2).

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