Power module with PCB having deformation sensing elements for monitoring mechanical fatigue of power module packaging - Patents.com

Abstract

The power module comprises a PCB having at least two outer layers provided with metal tracks and a core layer incorporating one or more power semiconductor dies, and one or more deformation sensing elements incorporated in the PCB for sensing mechanical stress in at least one axis of a three-dimensional coordinate system associated with the PCB. A process for measuring stress in the PCB of such a power module includes using strain gauges to perform an initial measurement of the deformation D0 of the PCB during use during a calibration period to calibrate the initial deformation range of the PCB, measuring and counting the deformation cycles Cy while the PCB is in use, and repeating the measurement during use while the power module is in operation.

Description

[Technical Field]

[0001] The present disclosure relates to the field of monitoring the degradation of electronic power modules using integrated power board (IPB) technology that are subjected to thermal stress, and in particular to the field of monitoring the mechanical fatigue of the power module packaging. [Background technology]

[0002] For power modules using integrated power board technology, where components are embedded in a PCB, one of the challenges to be addressed is the compatibility between the materials used in the laminated PCB: copper, epoxy resin, silicone, and more generally all components have different coefficients of thermal expansion (CTE), which result in mechanical stresses under thermal cycling.

[0003] From PCB manufacturing to end-of-life, embedded power modules face thermal shock, thermal stress and mechanical constraints during cycling. PCB deformation and flexibility due to the mechanical properties of PCBs are one of the main causes of PCB power module aging, which mainly leads to PCB delamination, among other defects such as die shorts and cracks on conductive paths. Summary of the Invention [Problem to be solved by the invention]

[0004] In view of this problem, the present disclosure aims to solve the lack of operational monitoring capabilities of power modules incorporated into PCBs, and proposes incorporating one or more strain gauges into such PCBs to provide self-monitoring capabilities, end-of-life prediction capabilities, and manufacturing debug capabilities for the PCBs. [Means for solving the problem]

[0005] More precisely, the present disclosure proposes a power module comprising a PCB having at least two outer layers provided with metal tracks and a core layer 16 in which one or more power semiconductor dies are embedded, the power module comprising one or more deformation sensing elements integrated into the PCB for sensing mechanical stress in at least one axis of a three-dimensional coordinate system associated with the PCB.

[0006] The deformation sensing element provides a means to calculate the results of deformation cycles of a PCB and provide an estimate of the time to failure of such a PCB.

[0007] The power module may include at least one of the sensing elements in proximity to one or more power dies to detect mechanical deformation due to temperature cycling of the dies.

[0008] This allows for accurate detection of PCB deformation at the die location.

[0009] The power module includes at least one of the sensing elements in a corner region of the PCB, the sensing element adapted to provide a measurement of mechanical flatness imperfections of the PCB when the PCB is mounted on a heat sink.

[0010] This provides a measure of the stress on the PCB when attached to the heat sink.

[0011] At least one of the sensing elements can be designed as a frame on the PCB and adapted to provide a measurement of mechanical flatness defects of the PCB when the PCB is mounted on a heat sink.

[0012] At least one of the sensing elements can be made using metal tracks structured in a copper layer on the top or bottom side of the core layer of the PCB.

[0013] One or more sensing elements can be made from additional portions bonded to the top or bottom side of the core layer in copper-free areas of the top or bottom side of the core layer.

[0014] The power module may include two or more power semiconductor dies, each of which may include a sensing element.

[0015] At least one of the sensing elements can be a strain gauge arrangement comprising a resistive pattern designed to provide an indicator of a mechanical force, regardless of the direction of the mechanical force in a three-dimensional coordinate system associated with the PCB, in the vicinity of the strain gauge arrangement.

[0016] One or more sensing elements may have connections made by vias and tracks on the PCB.

[0017] One or more sensing elements provide a differential output V that is connected to the controller chip via an amplifier and an analog-to-digital converter. CH The strain gauge may be incorporated into a Wheatstone bridge having a

[0018] The present disclosure also provides a process for measuring stress in a PCB of a power module according to the present disclosure, comprising: (a) during a calibration period, using strain gauges to perform an initial measurement of the deformation value D0 of the PCB in use to calibrate the initial deformation range of the PCB; (b) measuring and counting the deformation cycles Cy of the PCB during use of the PCB; (c) repeating the in-use measurements while the power module is in operation; and The present invention relates to a process including:

[0019] The process may include 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.

[0020] For a power module with two or more power semiconductors, the power module includes a strain gauge for each power semiconductor die, and the process includes comparing the deformation at each location on the die and generating a feedback signal to a controller that drives the gate drivers of the power semiconductors, providing adaptive gate control or counting of abnormal imbalance cases when the PCB deformation at that location is not flat.

[0021] The process also includes providing the deformation measurement data to a life model of the PCB to generate life model predictions for predictive maintenance.

[0022] Other features, details and advantages are set forth in the following detailed description and figures. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a perspective view of thermal deformation of a PCB around a power semiconductor die. [Figure 2] FIG. 1 illustrates a portion of a power module with an embedded die. [Figure 3] 1 shows a part of a power module having an embedded die with strain gauges according to a first embodiment; [Figure 4] FIG. 1 shows a first example of a power module having an embedded die with strain gauges. [Figure 5] FIG. 10 shows a second example of a power module having an embedded die with strain gauges. [Figure 6] 1 is a simplified diagram of a PCB deformation detector with strain gauges. [Figure 7] 10 shows a part of a power module having an embedded die with strain gauges according to a second embodiment. [Figure 8] 1 is a flowchart of the steps of a process of the present disclosure. [Figure 9] FIG. 1 is a simplified diagram of a multiple gauge detection process. [Figure 10] FIG. 10 is a diagram showing an example of arrangement of strain gauges. DETAILED DESCRIPTION OF THE INVENTION

[0024] Power module packages are based on integrated power board technology, which includes at least a PCB with a power die embedded in it. Different power dies often have differences in terms of their inherent characteristics, resulting in different switching and thermal behavior. Different die positions in the package also affect the thermal behavior of the die and package, which can lead to PCB deformation and delamination cracks in solder joints or vias, resulting in module failure.

[0025] Figure 1 shows the deformation of a 20 mm x 20 mm sample with four levels of vias between each copper layer and a single die 17 at the center. In the simulation, the sample is clamped at each corner as if it were screwed onto a support. A water cooling system of 8000 W·m / °C is applied to the bottom of the sample, the edges are thermally insulated, and natural convection of 15 W·m / °C is applied to the top of the sample. For a realistic power dissipation density of 200 W / cm2, the expected deformation at the center reaches 46 μm. This confirms the feasibility of implementing deformation-sensing elements, such as strain gauges, in realistic copper designs on PCBs to detect global deformation or deformation in the vicinity of a single die. Similar deformation patterns occur for other PCB examples with different sizes and different numbers of levels.

[0026] The sensing element implemented when expanded in the z-axis direction can be a bending type strain gauge.

[0027] Other types of sensing elements, such as piezoelectric elements, may also be considered if they are compatible with the implantation process.

[0028] In the present disclosure, in order to monitor the health of a PCB, at least one sensing element 20, 21, 22 made using strain gauges is incorporated into the PCB to measure the deformation of the PCB during its operation.

[0029] The package can have various sensing elements positioned in areas depending on the stresses that can be monitored. The strain gauges can be integrated near the die as strain gauge 21a in Figure 3, strain gauge 21 in Figures 4 and 5, or they can be integrated on the side of the PCB as strain gauge 20 in Figure 4, strain gauge 22 in Figure 5, or strain gauge 20a in Figure 7.

[0030] FIG. 2 shows a perspective cross-sectional view of a power module with a PCB including at least two outer layers, namely an upper layer 11 and a lower layer 12 provided with metal tracks 13, 14, 15, and a core layer 16 incorporating one or more power semiconductor dies 17.

[0031] The connections between the contact areas of the die 17 and the tracks 13, 14, 15 on the outer layers are made using vias 18 drilled through the outer layers and inside the tracks and filled with a conductive material such as copper or a copper alloy.

[0032] 3, strain gauges 21a are embedded in the PCB to sense mechanical stress in at least one axis in a three-dimensional coordinate system associated with the PCB, and are located adjacent to die 17 to detect mechanical deformations due to temperature cycling of the die.

[0033] In this example, the strain gauge is fabricated using metal tracks 210 structured on the copper layer 16a on the top side of the PCB's core layer 16. The strain gauge's contact pads 211 and 212 can be connected to the sensing circuitry using vias 19 and tracks 23. However, in this case, significant temperature compensation is required because the resistance of copper varies significantly with temperature. In addition, the pitch of the chemical etching is limited by the copper thickness. Power applications typically require thick copper, which is incompatible with the fine pitch required for high-sensitivity strain gauges. For example, if the base copper thickness is 17 μm, our PCB manufacturer sets the minimum spacing between tracks at 75 μm. This is a clear limitation for fine, high-sensitivity sensors. Considering these limitations, a preferred design is to fabricate the strain gauge with an additional section 20a, as shown in Figure 7. In that case, these additional portions can be bonded to the top or bottom side of the core layer during the lamination process of the PCB incorporating the power die, in the copper-free areas 16c on the top or bottom side of the core layer 16. In such a case, the connection of the gauge connection pads is made in the same manner as in Figure 3, using vias and tracks in the same manufacturing process as the connection of the die.

[0034] In this example, the strain gauge is adjacent to the die 17, but in other designs, at least one strain gauge 20 can be placed in a corner region of the PCB 10, as in Figure 4. In such a case, placing strain gauges at all corners of the PCB can provide a measure of mechanical flatness defects of the PCB when mounted on the heat sink 30.

[0035] Another possibility is to design at least one of the strain gauges 22 as a frame for the PCB, as shown in Figure 5. Such strain gauges in the peripheral area also provide a measure of the mechanical flatness defects of the PCB when it is mounted on a heat sink.

[0036] In some cases, the strain gauge may comprise a resistor comprised of a pattern designed to form an indicator of a mechanical force in a three-dimensional coordinate system associated with the PCB, regardless of the direction of such force in the vicinity of the strain gauge.

[0037] 5 also shows a design in which there are two power semiconductor dies 17, each with a nearby strain gauge 21. With this design, in a power module having two or more power semiconductors and each with a strain gauge 21a, 21b for each power semiconductor die, it is possible to compare (50) the deformation at each position of the die, generate (51) a feedback signal to a controller 52 that drives the gate drivers of the power semiconductors, and provide adaptive gate control or counting of abnormal imbalance cases when the deformation at the PCB position is not flat, as shown in FIG.

[0038] One or more strain gauges 20, 21, 22 are connected to resistor R4 and temperature compensation resistor R5 as shown in FIG. L The bridge can be incorporated into a Wheatstone bridge 200 of quarter-bridge strain gauge design, which is a voltage input V issued from the power module 10 or the control module 40. EX and a differential output V that is connected to a controller chip 43 via an amplifier 41 and an analog-to-digital converter 42. CH There is.

[0039] The bridge can be located on the PCB of the power module, as shown in Figure 6, but it can also be located on the controller board. The strain gauge connection can also be made via a flexible circuit board in the cable between the power module and the controller board.

[0040] 10 discloses a strain gauge arrangement with two resistive patterns 22a, 22b oriented at 90 degrees to form an indicator of a mechanical force regardless of the direction of that force in the vicinity of the strain gauge in a three-dimensional coordinate system associated with the PCB.

[0041] In such a case, resistor pattern 22a can be incorporated into layer 16a of FIG. 3, and resistor pattern 22b can be incorporated into layer 16b of FIG. 3, with the copper layer removed where the strain gauges are incorporated.

[0042] The process for measuring stress on a PCB of a power module according to the present disclosure comprises: (a) performing an initial measurement of the deformation D0 of the PCB during use during a calibration period 100 using a strain gauge to calibrate the initial deformation range of the PCB; (b) measuring 110 the deformation cycles Cy during use of the PCB and counting the deformation cycles 120; (c) repeating the in-use measurements (150) while the power module is in operation; may include:

[0043] Measurements can be repeated on an hourly basis, such as daily or weekly, or on an operating time basis, such as every hour or 0.1 hour while the module is in operation, or can be performed continuously, or can be repeated after a set number of deformation cycles.

[0044] The process may also include measuring 130 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, which may include selecting the minimum and maximum deformation values ​​and obtaining the deformation range and its evolution in real time.

[0045] This process may include providing deformation measurement data to a PCB life model 140 to generate life model predictions for predictive maintenance 160 . [Industrial Applicability]

[0046] Applications for deformation sensing elements include manufacturing and production debug: they help identify abnormal mechanical stresses experienced during this first operational step of the product. They also help verify the overall deformation of the PCB after manufacturing and a good mechanical fastening during manufacturing when the PCB is assembled in the final product (e.g., onto a cooling device).

[0047] During operation of the power module incorporating the PCB, the sensing element keeps track of the number and amplitude of thermal stresses on the PCB. These values ​​track the progression of abnormal stresses and provide a life prediction model to the microcontroller via communication lines. The maximum number of stress cycles is calculated and predictive maintenance can be planned accordingly before failure.

[0048] To achieve uniform operation and improve overall reliability in power modules for converters or other applications in which the power die is incorporated, deformation sensing elements can be used in a closed-loop system to track the null difference between the dies in such power modules. This can be achieved by gate drivers that adapt control to each of the dies. This technique, called mechanical stress equalization, improves reliability by uniformly redistributing stress within the package. By incorporating sensing elements near the die incorporated into the PCB package, stress can be monitored and adapted for stress mapping with greater precision.

[0049] The above solutions provide the key to monitoring the package health during manufacturing steps, production steps (e.g., mechanical assembly), during power module usage (power cycles, stress cycle counts), and for self-diagnosis and life prediction (stress life rules related to delamination aging process).

[0050] The present disclosure is not limited to the described examples, and the invention defined in the claims can encompass any alternatives that a person skilled in the art would imagine upon reading this description. For example, one or more Wheatstone bridges can be configured as a half bridge with temperature-compensated strain gauges or as a full Wheatstone bridge with four strain gauges to measure torsion at multiple locations on the PCB of the power module.

Claims

1. 1. A power module comprising a PCB having at least two outer layers provided with metal tracks and a core layer incorporating one or more power semiconductor dies, one or more deformation sensing elements integrated into the PCB that sense mechanical stress in at least one axis of a three-dimensional coordinate system associated with the PCB; Power module.

2. The power module according to claim 1 , further comprising: at least one of the deformation sensing elements disposed near the one or more power semiconductor dies, the deformation sensing elements detecting mechanical deformations caused by temperature cycling of the power semiconductor dies.

3. 3. The power module according to claim 1, further comprising at least one of the deformation sensing elements in a corner region of the PCB, the deformation sensing element being adapted to measure defects in mechanical flatness of the PCB when the PCB is mounted on a heat sink.

4. 3. The power module according to claim 1 or 2, comprising at least one of the deformation sensing elements designed as a frame on the PCB, the deformation sensing element being adapted to measure defects in mechanical flatness of the PCB when the PCB is mounted on a heat sink.

5. 5. The power module according to claim 1, wherein at least one of the deformation sensing elements is made using metal tracks structured in a copper layer on the top side or bottom side of the core layer of the PCB.

6. 5. The power module according to claim 1, wherein the one or more deformation sensing elements are additional parts bonded to the top side or the bottom side of the core layer in a copper-free region of the top side or the bottom side of the core layer.

7. The power module according to any one of claims 1 to 6, comprising two or more power semiconductor dies, and the power module is provided with the deformation sensing element in each of the power semiconductor dies.

8. 8. A power module according to claim 1, wherein at least one of the deformation sensing elements is a strain gauge arrangement, the strain gauge arrangement comprising a resistive pattern designed to form an indicator of a mechanical force acting thereon, regardless of the direction of the mechanical force in the vicinity of the strain gauge arrangement, in a three-dimensional coordinate system associated with the PCB.

9. A power module according to any one of claims 1 to 8, wherein the one or more deformation sensing elements have connections made from vias and tracks on the PCB.

10. The one or more deformation sensing elements have a differential output V that is connected to a controller chip via an amplifier and an analog-to-digital converter. ＣＨ 10. The power module according to claim 1, wherein the strain gauges are incorporated into a Wheatstone bridge having:

11. A process for measuring stress in the PCB of a power module according to any one of claims 1 to 10, comprising the steps of: During the calibration period, strain gauges are used to measure the deformation value D of the PCB during use. ０ performing an initial measurement to calibrate an initial deformation range of the PCB; measuring and counting deformation cycles Cy of the PCB during use of the PCB; repeating in-use measurements during operation of said power module; The process includes:

12. 12. The process of claim 11, comprising measuring plastic deformation of the PCB by comparing minimum and maximum deformation of the PCB during operation of the power module with the initial deformation range.

13. 13. The process of claim 11 or 12, for a power module comprising two or more power semiconductors, wherein the power module comprises a strain gauge for each die of the power semiconductor, and the process comprises comparing deformations at each position of the dies and generating a feedback signal to a controller that drives gate drivers of the power semiconductors, and providing adaptive gating or counting of abnormal unbalance cases when deformations of the PCB at the each position are not flat.

14. The process of any one of claims 11 to 13, comprising providing deformation measurement data to a life model of the PCB to make life model predictions for predictive maintenance.

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