Power module including PCB with deformation sensing element for monitoring mechanical fatigue of power
By embedding strain gauge and Wheatstone bridge in the PCB, the mechanical stress problem caused by the difference in the thermal expansion coefficient of the material is solved, and the self-monitoring and life prediction of the power module are realized, which improves reliability and production commissioning capabilities.
Patent Information
- Application Number
- CN202380091759.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-01-23
- Filing Date
- 2023-08-30
- Publication Date
- 2025-08-26
AI Technical Summary
In the prior art, the difference in thermal expansion coefficients of different materials in the PCB stack leads to mechanical stress, resulting in PCB deformation and aging, affecting the reliability and life of the power module.
Embed deformation sensing elements, such as strain gauge, are used to monitor mechanical stress and deformation, and combine Wheatstone bridge with controller chip to achieve self-monitoring and life prediction.
By monitoring PCB deformation and stress in real time, it provides accurate life prediction and adaptive control, improving the reliability and production commissioning capabilities of power modules.
Smart Images
Figure CN120548451A_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to the field of monitoring degradation of electronic power modules using integrated power board (IPB) technology subjected to thermal stress, and in particular to the field of monitoring mechanical fatigue of power module packages. Background Art
[0002] For power modules using integrated power board technology, where the PCB is embedded in the components, one of the challenges to be addressed is the compatibility between each material used in the PCB stackup. Copper, epoxy, silicon, and more generally all the constituent elements have different coefficients of thermal expansion (CTE), which creates mechanical stresses under thermal cycling.
[0003] From PCB manufacturing to end-of-life, embedded power modules are subject to thermal shock, thermal stress during cycling, and mechanical constraints. PCB deformation and flexibility due to its mechanical properties are among the primary causes of PCB power module degradation, leading to PCB delamination and other defects such as die shorts, cracks in conductive paths, and other defects. Summary of the Invention
[0004] In view of this problem, the present disclosure aims to address the lack of monitoring capabilities during the operational life of PCB embedded power modules and proposes to incorporate one or more strain gauges in such PCB to provide self-monitoring, end-of-life prediction and production debugging capabilities of such PCB.
[0005] More precisely, the present disclosure proposes a power module comprising a PCB comprising at least two outer layers provided with metal traces and comprising a core layer (16) in which one or more power semiconductor dies are embedded, wherein the power module comprises one or more deformation sensing elements embedded in the PCB to sense mechanical stress in at least one axis of a three-dimensional coordinate system attached to the PCB.
[0006] The deformation sensing element provides a means of calculating the results of the deformation cycles of the PCB and providing an estimate of the time before failure of such PCB.
[0007] The power module may include at least one of the sensing elements proximate the one or more power dies to detect mechanical deformation due to temperature cycling of the dies.
[0008] This gives an accurate detection of the deformation of the PCB at the die location.
[0009] The power module may include at least one of the sensing elements in a corner region of the PCB, the sensing element being adapted to provide a measure of mechanical flatness defects of the PCB when the PCB is mounted on a heat sink.
[0010] This provides a measure of the stress on the PCB when mounted on the heat sink.
[0011] At least one of the sensing elements may be designed as a frame in the PCB and adapted to provide a measure of mechanical flatness defects of the PCB when the PCB is mounted on a heat sink.
[0012] At least one of the sensing elements may be made from a metal trace constructed in a copper layer on a top or bottom surface of the core layer of the PCB.
[0013] The one or more sensing elements may be made of additional parts glued on the top or bottom surface of the core layer in a copper-free area of the top or bottom surface of the core layer.
[0014] A power module may include two or more power semiconductor dies and may include a sensing element for each of the power semiconductor dies.
[0015] At least one of the sensing elements may comprise a strain gauge device including a resistive pattern designed to form an indicator of mechanical forces in the vicinity of the strain gauge device, regardless of the direction of such mechanical forces in the three-dimensional coordinate system attached to the PCB.
[0016] The one or more sensing elements may have connections made from vias and traces on the PCB.
[0017] The one or more sensing elements may be strain gauges incorporated in a Wheatstone bridge having a differential output V connected to a controller chip through an amplifier and an analog-to-digital converter. CH .
[0018] The present disclosure also relates to a process for measuring stress on a power module PCB according to the present disclosure, and the process comprises:
[0019] (a) an initial measurement of the deformation D0 of the PCB used during a calibration period, wherein the strain gauge provides a calibration of the initial deformation range of the PCB,
[0020] (b) in-use measurement of the deformation cycles Cy of the PCB and counting of said deformation cycles,
[0021] (c) repeating the in-use measurement during operation of the power module.
[0022] The process may include measuring plastic deformation of the PCB by comparing minimum and maximum deformations of the PCB during operation of the power module to an initial deformation range.
[0023] For a power module comprising two or more power semiconductors (wherein the power module comprises a strain gauge for each die of the power semiconductors), the process may include comparing the deformation at a location of each of the die and generating a feedback signal to a controller of a gate driver driving the power semiconductors to provide adaptive gate control or counting of abnormal imbalance conditions in the event of uneven deformation of the PCB at the location.
[0024] The process may further include providing the deformation measurement data to a life model of the PCB to provide a life model prediction for predictive maintenance.
[0025] Additional features, details, and advantages will be shown in the following detailed description and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] [ Figure 1 ]
[0027] Figure 1 A perspective view showing thermal deformation of a PCB around a power semiconductor die.
[0028] [ Figure 2 ]
[0029] Figure 2 A portion of a power module with an embedded die is shown.
[0030] [ Figure 3 ]
[0031] Figure 3 A portion of a power module with an embedded die including a strain gauge according to a first embodiment is shown.
[0032] [ Figure 4 ]
[0033] Figure 4 A first example of a power module with an embedded die including strain gauges is shown.
[0034] [ Figure 5 ]
[0035] Figure 5 A second example of a power module with an embedded die including strain gauges is shown.
[0036] [ Figure 6 ]
[0037] Figure 6 A simplified schematic diagram of a PCB deformation detector with strain gauges is shown.
[0038] [ Figure 7 ]
[0039] Figure 7 A portion of a power module with an embedded die including a strain gauge according to a second embodiment is shown.
[0040] [ Figure 8 ]
[0041] Figure 8 A flow chart showing the steps of the process of the present disclosure is shown.
[0042] [ Figure 9 ]
[0043] Figure 9 A simplified schematic diagram showing the multi-strain gauge testing process.
[0044] [ Figure 10 ]
[0045] Figure 10 A possible strain gauge arrangement is shown. DETAILED DESCRIPTION
[0046] A power module package based on integrated power board technology includes a PCB with at least one power die embedded therein. Different power dies typically have varying inherent characteristics, leading to differences in switching and thermal behavior. Furthermore, the die's position within the package can affect the thermal behavior of both die and package, causing PCB deformation that can lead to delamination cracks in solder joints or vias and ultimately module failure.
[0047] Figure 1 The deformation of a 20×20 mm sample is shown, with 4 layers of vias between each copper layer and a die 17 in the center. In the simulation, each corner was constrained as if the sample were screwed to a support. A water cooling system was applied at 8000 W.m / °C on the bottom, with insulation on the edges and natural convection at 15 W.m / °C on the top of the sample. At 200 W / cm 2 For a realistic power loss density, the median expected deformation reaches 46 microns. This demonstrates the feasibility of implementing deformation-sensing elements (such as strain gauges with a practical copper design) in PCBs to sense global deformation or deformation near individual dies. Similar deformation patterns emerge for other examples of PCBs with different sizes and different numbers of layers.
[0048] The sensing element to be implemented in the case of Z-axis extension may be a bending type strain gauge.
[0049] Other types of sensing elements are also contemplated, such as piezoelectric elements if compatible with the embedding process.
[0050] In the present disclosure, at least one sensing element 20, 21, 22 made of a strain gauge is embedded in a PCB to measure the deformation of the PCB during its lifetime in order to monitor its health.
[0051] Different sensing elements can be located in the package depending on the area of the stress that can be monitored. Strain gauges can be embedded near the die as Figure 3 、 Figure 4 、 Figure 5 The strain gauge 21 in the PCB or embedded on one side as Figure 4 Strain gauge 20, Figure 5 Strain gauge 22 or Figure 7 The strain gauge 20a in FIG.
[0052] Figure 2 A perspective cross-sectional view of a power module is shown comprising a PCB comprising at least two outer layers, an upper layer 11 and a lower layer 12 provided with metal traces 13 , 14 , 15 and comprising a core layer 16 embedding one or more power semiconductor dies 17 .
[0053] The connections between the contact areas on the die 17 and the traces 13, 14, 15 on the outer layers are made by drilling vias 18 into the outer layers and traces and filling them with a conductive material such as copper or a copper alloy.
[0054] exist Figure 3 In the embodiment, strain gauges 21a are embedded in the PCB to sense mechanical stress in at least one axis of a three-dimensional coordinate system attached to the PCB. The strain gauges 21a near the die 17 detect mechanical deformation caused by temperature cycling of the die.
[0055] In such an example, the strain gauges are made of metal traces 210 constructed in the copper layer 16a on the top surface of the core layer 16 of the PCB. The contact pads 211, 212 of the strain gauges can be connected to the detection circuit with vias 19 and traces 23. However, in this case, the resistance of copper varies a lot with temperature, requiring significant temperature compensation. In addition, the chemical etching spacing is limited by the copper thickness, and typically power applications require thick copper, which is not compatible with the thin spacing required for sensitive strain gauges. For example, for a base copper thickness of 17 microns, the minimum space between traces is set to 75 microns for our PCB manufacturer. This can be a significant limitation for fine sensitive sensors. In view of this limitation, the preferred design is to have strain gauges made of additional components 20a, such as Figure 7 These parts can then be glued onto the top or bottom surface of the core layer 16, in the copper-free area 16c of said top or bottom surface of said core layer, during the lamination process of the PCB in which one or more power dies are embedded. In this case, the connectors of the strain gauge connection pads are connected to the Figure 3 This is done in the same way as in the example embodiment, where the vias and traces have the same manufacturing process as the connections to one or more dies.
[0056] In this example, the strain gauges are located close to the die 17, but in other designs, at least one of the strain gauges 20 may be located at a corner region of the PCB 10, such as at Figure 4 In this case, providing strain gauges at all corners of the PCB allows providing a measure of mechanical flatness defects of the PCB when the PCB is mounted on the heat sink 30 .
[0057] Another possibility is to design at least one of the strain gauges 22 as a frame in the PCB, such as Figure 5 Such strain gauges in the peripheral area also provide a measure of mechanical flatness defects of the PCB when the PCB is mounted on a heat sink.
[0058] In some cases, the strain gauge may include a resistor made from a pattern designed to form an indicator of mechanical forces in the vicinity of the strain gauge, regardless of the direction of such mechanical forces in the three-dimensional coordinate system attached to the PCB.
[0059] Figure 5 Also shown is a design in which there are two power semiconductor dies 17 and each die includes a closed strain gauge 21. This design allows a power module including two or more power semiconductors (where the module includes a strain gauge 21a, 21b for each die of a power semiconductor) to provide a comparison 50 of deformation at a location of each of said dies and to provide generation 51 of a feedback signal to a controller 52 of a gate driver driving said power semiconductors to provide adaptive gate control or counting of abnormal imbalance conditions in the event of uneven deformation of the PCB at said locations, such as Figure 9 shown.
[0060] One or more strain gauges 20, 21, 22 may be incorporated into a Wheatstone bridge 200, such as Figure 6 The strain gauge is described in the design of a quarter bridge strain gauge, where the strain gauge is the resistor R4 and the temperature compensation resistor R L The bridge has a voltage input V that can come from the power module 10 or from the control module 40. EX , and has a differential output V connected to the controller chip 43 through an amplifier 41 and an analog-to-digital converter 42 CH .
[0061] The bridge can be located on the power module PCB, such as Figure 6 As shown, it is possible to locate the strain gauges in the controller board, and the connection of the strain gauges can be done via the flexible circuit board of the cable between the power module and the controller board.
[0062] exist Figure 10In the invention, a strain gauge arrangement is disclosed comprising two resistive patterns 22a, 22b oriented at 90° allowing to form an indicator of mechanical forces in the vicinity of the strain gauge, whatever the direction of such mechanical forces in said three-dimensional coordinate system attached to the PCB.
[0063] In this case, the resistance pattern 22a may be incorporated into the layer 16a, and the resistance pattern 22b may be incorporated into the layer 16a. Figure 3 Layer 16b, wherein the copper layer is removed at the location where the strain gauge is incorporated.
[0064] A process for measuring stress on a power module PCB according to the present disclosure may include:
[0065] (a) an initial measurement of the deformation D0 of the PCB used during a calibration period 100, wherein the strain gauge provides a calibration of the initial deformation range of the PCB,
[0066] (b) in-use measurement 110 of the deformation cycles Cy of the PCB and counting 120 of the deformation cycles,
[0067] (c) Repeating 150 the in-use measurement during operation of the power module.
[0068] The measurements may be repeated on a time basis (such as daily, weekly) or on an operating time basis (such as every hour or tenth of an hour of operation of the module), may be continuous or may be repeated after a defined number of deformation cycles.
[0069] The process may further comprise measuring the plastic deformation of the PCB by comparing the minimum and maximum deformation of the PCB during operation of the power module with an initial deformation range 130. This may comprise selecting minimum and maximum values of the deformation to obtain the deformation range and its evolution in real time.
[0070] The process may include providing deformation measurement data to a life model 140 of the PCB to provide life model predictions for predictive maintenance 150 .
[0071] {Industrial Applicability}
[0072] Applications of deformation sensing elements can include manufacturing and production debugging: the sensing elements help identify abnormal mechanical stresses maintained during this first life cycle of the product. The sensing elements can also help check the overall deformation of the PCB after manufacturing and the good mechanical fastening during production when the PCB is assembled in the final product (for example, on a cooling device).
[0073] Over the life of a PCB-embedded power module, sensing elements track the amount and magnitude of thermal stresses in the PCB. These values track abnormal stresses and feed an end-of-life prediction model to a microcontroller via a communication line. The maximum number of stress cycles is calculated, and a predictive maintenance program can be planned accordingly before failure occurs.
[0074] To achieve homogeneous behavior and thus improve the global reliability of power modules for converters or other applications with embedded power dies, deformation sensing elements can be used in a closed-loop system that can track zero variation between the dies of such power modules. This can be achieved through gate drivers that adjust control for each die. This technique, known as mechanical stress equalization, improves reliability by redistributing stress evenly within the package. By providing a sensing element embedded near the die within the PCB package, stress can be monitored with greater accuracy and fitted to the stress map.
[0075] This solution provides a key means for monitoring the health of the package during manufacturing steps, production steps (such as mechanical assembly), during the use of the power module (power cycling, stress cycle counting), and for self-diagnosis and end-of-life prediction (stress end-of-life rules related to delamination aging processes).
[0076] The present disclosure is not limited to the examples described, and the invention defined in the claims may encompass any alternative that a person skilled in the art would conceive of upon reading this specification. In an example, one or more Wheatstone bridges may be configured as a half-bridge with temperature-compensated strain gauges or a full Wheatstone bridge with four strain gauges to measure torsion in various locations of a power module PCB.
Claims
1. A power module comprising a PCB, the PCB comprising at least two outer layers, the at least two outer layers being provided with metal traces and comprising a core layer in which one or more power semiconductor dies are embedded, characterized in that The power module includes one or more deformation sensing elements embedded in the PCB to sense mechanical stress in at least one axis in a three-dimensional coordinate system attached to the PCB. 2 . The power module of claim 1 , comprising at least one of the sensing elements proximate the one or more power semiconductor dies to detect mechanical deformation due to temperature cycling of the dies.
3. The power module according to claim 1 or 2, comprising at least one of the sensing elements in a corner region of the PCB, the sensing element being adapted to provide a measure of mechanical flatness defects of the PCB when the PCB is mounted on a heat sink.
4. The power module according to claim 1 or 2, comprising at least one of the sensing elements designed as a frame in the PCB, the frame being adapted to provide a measure of mechanical flatness defects of the PCB when the PCB is mounted on a heat sink.
5. The power module according to any one of claims 1 to 4, wherein: At least one of the sensing elements is made of a metal trace constructed in a copper layer on a top surface or a bottom surface of the core layer of the PCB.
6. The power module according to any one of claims 1 to 4, wherein: The one or more deformation sensing elements are additional parts glued on the top surface or the bottom surface of the core layer in a copper-free area of the top surface or the bottom surface of the core layer.
7. The power module according to any one of claims 1 to 6, comprising two or more power semiconductor dies, wherein: The power module includes a sensing element for each of the power semiconductor dies.
8. The power module according to any one of claims 1 to 7, wherein: At least one of the sensing elements comprises a strain gauge device including a resistive pattern designed to form an indicator of mechanical forces in the vicinity of the strain gauge device, regardless of the direction of such mechanical forces in the three-dimensional coordinate system attached to the PCB.
9. The power module according to any one of claims 1 to 8, wherein: The one or more sensing elements have connections made from vias and traces on the PCB.
10. The power module according to any one of claims 1 to 9, wherein: The one or more sensing elements are strain gauges incorporated in a Wheatstone bridge having a differential output V connected to a controller chip through an amplifier and an analog-to-digital converter. CH .
11. A process for measuring stress on a power module PCB according to any one of claims 1 to 10, the process comprising: - an initial measurement of the deformation D0 of the PCB used during a calibration period, wherein the strain gauge provides a calibration of the initial deformation range of the PCB, - in-use measurement of deformation cycles Cy of said PCB and counting of said deformation cycles, - repeating said in-use measurement during operation of said power module.
12. The process of claim 11, comprising measuring the plastic deformation of the PCB by comparing a minimum deformation and a maximum deformation of the PCB during operation of the power module with the initial deformation range.
13. The process according to claim 11 or 12, wherein the process is used for a power module comprising two or more power semiconductors, The power module comprises a strain gauge for each die of the power semiconductor, wherein the process comprises comparing deformation at a location of each of the die and comprising generating a feedback signal to a controller of a gate driver driving the power semiconductor to provide adaptive gate control or counting of abnormal imbalance conditions in the event of uneven deformation of the PCB at said location.
14. The process of any one of claims 11 to 13, comprising providing deformation measurement data to a life model of the PCB to provide life model predictions for predictive maintenance.