Strain threshold detection method for automotive-grade chip components

Abstract

This invention relates to the field of chip reliability testing technology, and provides a method for detecting the strain threshold of automotive-grade chip components. The method includes: determining a corresponding stress profile based on the stress type experienced by the chip component in actual applications; loading the chip component using a corresponding simulation test based on the determined stress profile, and monitoring the strain value in the area near the chip component's pin solder joints in real time during the test using strain gauges arranged on a printed circuit board; after completing the simulation test, slicing the solder joints of the chip component and determining the cracking ratio of the solder joints through microscopic observation; establishing a correspondence between the cracking ratio of the solder joints and the monitored strain values; and determining the safe strain threshold of the chip component under the corresponding stress profile based on a preset failure criterion. This invention can accurately assess the damage degree of automotive-grade chip component solder joints under different stress environments, determine the safe strain threshold, and improve the safety and reliability of the entire vehicle.

Description

Technical Field

[0001] This invention relates to the field of chip reliability testing technology, and in particular to a method for detecting the strain threshold of automotive-grade chip components. Background Technology

[0002] With the rapid development of new energy vehicles towards intelligence, connectivity, and electrification, the application of automotive-grade chips is becoming increasingly widespread and critical. As core components realizing various functions and controls of the entire vehicle, their reliability directly affects the vehicle's safety and performance. Therefore, how to accurately and effectively evaluate the reliability of automotive-grade chips has become a research hotspot in the industry. Among them, the solder joint interconnection structure between chip components and printed circuit boards (PCBs) is a key link in mechanical and electrical connections. During vehicle assembly, operation, and long-term use, it will be subjected to various complex stresses such as mechanical overstress, temperature cycling, and thermo-mechanical coupling. Quantitatively evaluating the degree of strain damage to solder joints under these stress conditions, and then determining their strain threshold for safe operation, is crucial for evaluating the reliability of chip components and even the performance and quality of the entire vehicle.

[0003] Currently, there are several technical solutions for strain threshold testing. For example, the publicly available technical document "Method and Procedure for Determining Sea State Thresholds of Strain Damage to Submarine Suspended Cables" provides a method for assessing strain damage to submarine cables. This method mainly involves acquiring cable physical parameters, determining the test scale, dividing the operating conditions, conducting simulation experiments in a wave tank, monitoring cable strain using strain gauges, and finally determining the critical sea state threshold by combining preset damage rules. However, this solution focuses on the strain response of submarine cables under specific marine environmental loads. Its application scenarios, failure mechanisms, and test conditions are fundamentally different from those of automotive electronic components, and it cannot be directly applied to strain threshold testing of solder joints in automotive-grade chip components.

[0004] In the field of electronic assembly, the industry typically refers to the standard IPC / JEDEC-9704, "Guideline for Strain Testing of Printed Circuit Boards." This standard details the strain testing process for circuit board assemblies under general mechanical loads (such as assembly stress), including steps such as strain gauge placement, data acquisition, and report analysis. While this guideline provides basic testing methods, it does not offer specific steps and criteria for strain threshold testing of automotive-grade chip components under the harsh application environments specific to vehicles (such as high and low temperature cycling, mechanical vibration, and their coupling effects). It cannot quantify the actual damage caused to solder joints of automotive-grade chip components by specific strain levels, nor does it establish a quantitative relationship between strain values ​​and solder joint reliability under different stress profiles such as mechanical overstress, temperature stress, and long-term thermo-mechanical coupling stress.

[0005] In summary, existing technical solutions have significant limitations: methods for submarine cables are incompatible with automotive electronics scenarios; and existing strain testing standards for electronic components lack specific testing methods and threshold standards for automotive-grade applications. This results in the industry lacking a systematic and clear method to evaluate the strain thresholds of solder joints in automotive-grade chip components under various real-world operating conditions. Consequently, it fails to provide direct regulatory basis for chip component assembly process control, vehicle environmental adaptability design, and reliability assessment, potentially leading to device malfunctions due to premature solder joint failure, which could negatively impact the safety and reliable operation of the entire vehicle.

[0006] Therefore, it is necessary to provide a strain threshold detection method for automotive-grade chip components to solve the above-mentioned technical problems. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a strain threshold detection method for automotive-grade chip components. By selecting corresponding simulation tests for different stress profiles, a correlation between the solder joint cracking ratio and strain value is established, thereby determining the safe strain threshold and achieving an accurate quantitative assessment of the solder joint reliability of automotive-grade chip components.

[0008] This invention provides a strain threshold detection method for automotive-grade chip components, the detection method comprising the following steps: S1. Determine the corresponding stress profile for the type of stress that the chip component is subjected to in actual application, wherein the stress profile includes mechanical overstress, temperature stress and thermomechanical coupling stress. S2. Based on the determined stress profile, select the corresponding simulation test to load the chip assembly, and monitor the strain value of the pin solder joints of the chip assembly within a predetermined distance range in real time during the simulation test. S3. After completing the simulation test, the solder joints of the chip assembly are sliced ​​to determine the cracking ratio of the pin solder joints. S4. Establish the correspondence between the cracking ratio of the pin solder joints and the strain value. Based on a preset failure criterion, determine the safe strain threshold of the chip assembly under the corresponding stress profile, wherein: When the stress profile is mechanically overstressed, the corresponding simulation test is a three-point bending test; When the stress profile is temperature stress, the corresponding simulation test is a temperature cycling test or a temperature shock test; When the stress profile is thermomechanical coupled stress, the corresponding simulation test is a combined temperature cycling and mechanical vibration test.

[0009] Preferably, in step S2, the predetermined distance range is the printed circuit board position within 3mm of the pin solder joint, and the strain value is monitored in real time by a strain gauge attached to the printed circuit board position.

[0010] Preferably, in step S3, the cracking ratio is determined by metallographic microscopic observation of the weld points after slicing.

[0011] Preferably, in step S4, the failure criterion is that the cracking ratio is greater than 20%, and the safe strain threshold is the maximum strain value corresponding to when the cracking ratio does not exceed 20%.

[0012] Preferably, when performing the three-point bending test, the top of the chip assembly is pressured by the test machine pusher at a preset pressing rate, which includes 5 mm / min and 20 mm / min.

[0013] Preferably, when conducting the temperature cycling test, the test conditions are: temperature range -40℃ to 85℃, high and low temperature points held for 30 minutes, temperature change rate 10℃ / min, and 500 cycles.

[0014] Preferably, when conducting the temperature shock test, the test conditions are: temperature range -40℃ to 85℃, high and low temperature points maintained for 30 minutes, temperature transition time less than 10 seconds, and 500 shocks.

[0015] Preferably, during temperature stress testing, the chip assembly is mounted using a test fixture, and different initial pre-strain levels are applied to the chip assembly by adjusting the tightness of the fixture.

[0016] Preferably, when conducting the combined temperature cycling and mechanical vibration test, the test conditions include: a temperature cycling range of -40℃ to 125℃, with each cycle lasting 8 hours; mechanical vibration consisting of applying random vibrations sequentially to the X, Y, and Z axes within a frequency range of 10Hz to 1000Hz, with each axis lasting 8 hours; and a total test duration of 72 hours.

[0017] Preferably, the power spectral density parameter of the random vibration is as follows: 20 (m / s) at 10 Hz. 2 ) 2 / Hz, 6.5 (m / s) at 55Hz. 2 ) 2 / Hz, 0.25 (m / s) at 180Hz. 2 ) 2 / Hz, 0.25 (m / s) at 300Hz. 2 ) 2 / Hz, 0.14 (m / s) at 360Hz. 2 ) 2 / Hz, 0.14 (m / s) at 1000Hz. 2 ) 2 / Hz.

[0018] Compared with related technologies, the strain threshold detection method for automotive-grade chip components provided by this invention has the following advantages: This invention addresses three typical stress profiles: mechanical overstress, temperature stress, and thermomechanical coupling stress. Three-point bending tests, temperature cycling / impact tests, and combined temperature cycling and mechanical vibration tests were designed for each. By placing strain gauges at specific locations on the printed circuit board to monitor strain values ​​in real time, and combining this with microscopic observation of solder joint sections after the tests, a quantitative correlation between the solder joint cracking rate and strain values ​​was established. This method can accurately and effectively assess the damage degree of automotive-grade chip component solder joints under different environments, determine the safe strain threshold, and thus provide a scientific basis for the installation and use of automotive-grade chip components, contributing to improved vehicle safety and reliability. Attached Figure Description

[0019] Figure 1 This is a schematic flowchart of the strain threshold detection method according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a three-point bending test according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the test fixture according to an embodiment of the present invention; Figure 4 This is a schematic diagram illustrating the application of different strain levels according to an embodiment of the present invention. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the drawings, not all structures. Moreover, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0021] It should also be noted that, for ease of description, the accompanying drawings show only the parts relevant to the invention and not all of them. Before discussing exemplary embodiments in more detail, it should be mentioned that some exemplary embodiments are described as processes or methods depicted as flowcharts. Although the flowcharts describe the operations (or steps) as sequential processes, many of the operations can be performed in parallel, concurrently, or simultaneously. Furthermore, the order of the operations can be rearranged. The process can be terminated when its operation is completed, but it may also have additional steps not included in the drawings. The process may correspond to a method, function, procedure, subroutine, subroutine, etc. Example 1

[0022] like Figure 1As shown, this embodiment provides a strain threshold detection method for automotive-grade chip components. This method addresses the reliability assessment needs of automotive-grade chips under actual vehicle operating conditions, constructing a complete detection architecture from stress scenario identification to quantification threshold determination. The method includes the following steps: Step S1: Determine the corresponding stress profile for the type of stress that the chip component experiences in actual applications. The stress profile includes mechanical overstress, temperature stress, and thermomechanical coupling stress.

[0023] Specifically, this step involves summarizing and classifying the stress environment throughout the entire lifecycle of chip components. For automotive-grade chip components, their failure modes are strongly correlated with the stress environment they experience. This embodiment deconstructs the complex vehicle operating conditions into three typical stress profiles: mechanical overstress mainly simulates the instantaneous or continuous mechanical external forces experienced by the chip component during vehicle assembly (such as bolt tightening, PCB board separation, and plug-in installation); temperature stress mainly simulates the periodic temperature changes in the vehicle operating environment (such as engine compartment, chassis, and external environment) caused by diurnal temperature differences, seasonal changes, or operating heating; and thermomechanical coupling stress simulates the complex operating conditions of a vehicle simultaneously experiencing temperature fluctuations and mechanical vibrations while driving on bumpy roads. These three stress profiles cover the main failure causes of automotive-grade chip components from production and installation to end-use applications, providing a clear physical model basis for subsequent simulation tests.

[0024] Step S2: Based on the stress profile determined in step S1, select the corresponding simulation test to load the chip assembly, and monitor the strain value in the area near the pin solder joints of the chip assembly in real time by strain gauges arranged on the printed circuit board during the test.

[0025] Specifically, this step aims to reproduce the aforementioned stress profile in a laboratory environment. Different testing equipment is required for precise loading depending on the stress profile. When the stress profile is determined to be mechanically overstressed, a universal testing machine or push-pull testing machine is typically used to induce bending deformation of the PCB board through mechanical loading. When the stress profile is determined to be thermally overstressed, a high-low temperature environmental test chamber is required to provide precise temperature cycling or shock environments. When the stress profile is determined to be thermomechanically coupled, a three-dimensional environmental test chamber is needed, coupling the vibration table and the temperature chamber to achieve synchronous excitation of temperature and vibration. During the test, the acquisition of strain data is crucial for evaluating the stress on the solder joints. Strain gauges are typically attached to the printed circuit board near the solder joints of the chip components. This is because solder joints are weak points in the interconnection between the chip and the PCB board, and the surrounding PCB area experiences significant stress concentration under stress. The strain value at this location most directly reflects the stress level borne by the solder joint. It should be understood that the placement of the strain gauges needs to be optimized according to the chip package and pin distribution to ensure that the captured strain signals are representative.

[0026] Step S3: After completing the simulation test, the solder joints of the chip assembly are sliced ​​and the cracking ratio of the solder joints is determined by microscopic observation.

[0027] Specifically, this step falls under the category of destructive physical analysis (DPA). Since solder joint cracks often originate at internal interfaces or within the solder joint itself, early microcracks are difficult to detect through visual inspection; therefore, cross-sectioning is necessary. Cross-sectioning typically involves epoxy resin mounting, grinding, and polishing to expose the metallographic cross-section of the solder joint. Subsequently, a metallographic microscope or scanning electron microscope (SEM) is used to observe the solder joint cross-section to identify the presence and direction of cracks. The cracking percentage is usually calculated based on the percentage of crack length to the effective weld joint length, or the percentage of crack area to the effective weld joint area. Statistical analysis of multiple solder joints can yield quantitative data on the degree of damage under the experimental conditions.

[0028] Step S4: Establish the correspondence between the cracking ratio of the solder joint and the strain value obtained in step S2, and determine the safe strain threshold of the chip assembly under the corresponding stress profile based on the preset failure criteria.

[0029] Specifically, this step is the core logic of the entire testing method. Through the aforementioned steps, cracking ratio data of multiple sets of test samples under different strain levels were obtained. Plotting this data on a coordinate system allows for the fitting of a "strain-damage" relationship curve. The failure criterion is a quantitative standard for determining solder joint failure; for example, a solder joint cracking ratio reaching a certain value (e.g., 20%) is considered a failure. Based on this criterion, the corresponding strain value is found on the relationship curve; this value is the safe strain threshold. The physical meaning of the safe strain threshold is that under a specific stress profile, as long as the strain value borne by the chip component is lower than this threshold, the probability of its solder joint failing (cracking ratio exceeding the criterion) is extremely low. This provides clear data support for automakers in structural design, process formulation, and reliability acceptance, achieving a leap from qualitative assessment to quantitative control.

[0030] Wherein: when the stress profile is mechanical overstress, the corresponding simulation test in step S2 is a three-point bending test, in which pressure is applied to the top of the chip assembly by the pusher of the testing machine at a preset downward pressing rate; when the stress profile is temperature stress, the corresponding simulation test in step S2 is a temperature cycling test or a temperature shock test, in which alternating temperature loads are applied to the chip assembly mounted on the test fixture by an environmental test chamber; when the stress profile is thermomechanical coupling stress, the corresponding simulation test in step S2 is a combined temperature cycling and mechanical vibration test, in which alternating temperature loads and random vibration loads are simultaneously applied to the chip assembly mounted on the vibration table by a three-dimensional environmental test chamber.

[0031] Specifically, the three test paths described above correspond to different failure mechanisms. The three-point bending test, by controlling the compression rate and span, can accurately simulate the bending state of the PCB board during assembly, inducing overstress cracking of the solder joints; the temperature cycling test focuses on examining low-cycle fatigue failure caused by mismatch in the coefficient of thermal expansion (CTE) of the material, while the temperature shock test focuses on examining the resistance to thermal shock under extreme temperature differences; the three-combination test is the most stringent, simulating the synergistic effect of vibration stress and thermal stress, accelerating the early failure of solder joints under complex working conditions. Through this categorized test design, it can be ensured that the measured strain threshold has clear engineering relevance and physical failure context. Example 2

[0032] This embodiment is a more specific implementation scheme based on Embodiment 1, focusing on the stress profile of mechanical overstress, and elaborating in detail the specific simulation test implementation process and parameter setting logic.

[0033] When the stress profile is mechanically overstressed, the corresponding simulation test in step S2 is a three-point bending test, in which pressure is applied to the top of the chip assembly by the testing machine pusher at a preset downward pressing rate. Specifically, in conjunction with Figure 2 As shown, the three-point bending test is a classic method for evaluating the reliability of solder joints when a printed circuit board (PCB) is subjected to bending deformation under external force during assembly. During the test, the PCB board with the chip assembly is placed on a three-point bending fixture. The fixture has two lower support points, and the span is typically set to 90mm, but this is not a limiting requirement. Those skilled in the art can adjust the span according to the size and material stiffness of the PCB board, as long as the expected bending deformation is ensured under force. The pusher of the testing machine is located directly above the two support points, acting directly on the top center of the chip assembly. The downward pressure of the pusher forces the PCB board to bend, thereby generating tensile or compressive stress in the pin solder joint area of ​​the chip assembly. This stress state highly replicates the real-world working conditions of the PCB board under mechanical external forces during vehicle assembly (such as bolt tightening, board separation, and component installation).

[0034] During the three-point bending test, the preset compression rates include 5 mm / min and 20 mm / min. It should be understood that different compression rates directly correspond to different failure mechanisms and engineering scenarios. Setting a slow compression rate of 5 mm / min aims to simulate the slow, continuous stress loading process during vehicle assembly, such as the slow tightening of a radiator or the gradual assembly of structural components. In this process, the stress loading time is relatively long, and the solder joints mainly exhibit a static overstress response. Conversely, setting a fast compression rate of 20 mm / min aims to simulate the instantaneous impact loads that may be encountered during vehicle manufacturing or transportation, such as tool drop impacts, rapid insertion and removal operations, or instantaneous bumps of the vehicle under harsh road conditions. In this process, the stress loading rate is fast, and the solder joint material may exhibit a certain strain rate effect, making it more prone to brittle fracture. Through comparative testing of these two typical rates, the main failure modes of automotive-grade chip components under mechanical overstress scenarios can be comprehensively covered, ensuring that the measured strain thresholds have broad engineering guidance significance.

[0035] Accurate acquisition of strain data is crucial during the experiment. In step S2, the strain gauge is attached to the printed circuit board within a 3mm range of the solder joint of the chip component pin. This location is the optimal monitoring point verified by extensive engineering practice. If the strain gauge is attached too far from the solder joint, the monitored strain value cannot accurately reflect the high stress concentration at the root of the solder joint, resulting in data distortion. If the attachment position is too close to the solder joint or even directly covers it, the strain gauge substrate will not be able to accurately sense the local deformation of the PCB board due to the unevenness of the solder joint surface and the deformation interference of the solder body, and it is also prone to damage during the experiment. The 3mm distance range avoids the geometric interference zone of the solder joint body and the solder wetting angle, and is located in the high stress gradient region extending from the solder joint pin, which can most sensitively capture the maximum principal strain signal that the solder joint is subjected to when the PCB is bent, laying a data foundation for establishing an accurate strain-damage relationship.

[0036] After completing the simulation test, the solder joints of the chip assembly are sliced, and the cracking ratio of the solder joints is determined by microscopic observation. Specifically, in step S3, the failure criterion is that the cracking ratio of the solder joint is greater than 20%, and the safe strain threshold determined in step S4 is the maximum strain value corresponding to the solder joint cracking ratio not exceeding 20%. The slicing process typically involves embedding and curing the PCB board after the test with epoxy resin, followed by grinding and polishing along the centerline of the solder joint to expose its metallographic cross-section. The cross-sectional morphology is observed using a high-magnification metallographic microscope, and the length of the crack extending along the solder joint interface or inside the solder joint is measured. The cracking ratio is defined as the ratio of the crack length to the effective connection length of the solder joint. Setting 20% ​​as the failure criterion is based on safety margin considerations in solder joint fracture mechanics: when the crack ratio exceeds 20%, the effective conductive cross-sectional area and mechanical connection strength of the solder joint will significantly decrease, and the crack tip is highly prone to propagation during subsequent use, leading to sudden device failure. Defining the maximum strain value corresponding to a crack ratio not exceeding 20% ​​as the safety threshold provides sufficient safety redundancy for engineering applications, ensuring that the solder joints will not suffer irreversible fatal damage when the chip assembly is assembled and used below this strain value. Through the above steps, this embodiment successfully constructs a complete closed-loop detection process under mechanical overstress profiles, from experimental loading and data monitoring to failure determination. Example 3

[0037] This embodiment is another specific scheme based on Embodiment 1, focusing on the stress profile of temperature stress, and elaborating in detail the specific implementation path and pre-strain application mechanism of its simulation test.

[0038] When the stress profile is temperature stress, the corresponding simulation test in step S2 is a temperature cycling test or a temperature shock test, in which an alternating temperature load is applied to the chip assembly mounted on the test fixture using an environmental test chamber. Specifically, in conjunction with Figure 3 As shown, the test fixture plays a crucial role in temperature stress testing. In actual vehicle electronic control units (ECUs), chip components are typically fixed to the radiator or chassis structure using screws or clips. This mounting method generates initial deformation and installation stress on the PCB board. To realistically reproduce this state in a laboratory environment, this embodiment uses a dedicated test fixture to simulate the actual installation boundary conditions of the chip components. The fixture is typically made of a material similar to that of the actual radiator (such as aluminum alloy) and has screw holes corresponding to the mounting holes of the chip components. By fixing the chip components to the fixture, the bending state of the PCB board under clamping force can be replicated, thereby ensuring that the stress state of the solder joints is consistent with the actual vehicle operating conditions when subsequent temperature loads are applied.

[0039] The temperature cycling test conditions included: a temperature range of -40℃ to 85℃, a holding time of 30 minutes between high and low temperatures, a temperature change rate of 10℃ / min, and 500 cycles. This test condition was designed with a clear physical purpose. The -40℃ to 85℃ range covers the full operating temperature range of automotive-grade chips from winter parking in extremely cold regions to high-temperature operation in the engine compartment. The 10℃ / min temperature change rate simulates the gradual temperature change process caused by diurnal temperature variations or vehicle start-stop cycles in natural environments. During this process, due to the significant difference in the coefficient of thermal expansion (CTE) between the chip package (usually plastic) and the PCB board (FR-4 material), the solder joints are subjected to alternating shear stresses with periodic temperature changes. After 500 cycles, cracks will form inside the solder joints due to accumulated fatigue damage. This test path primarily targets the low-cycle fatigue failure mechanism of the solder joints.

[0040] As another harsh operating condition of temperature stress, the conditions for temperature shock testing include: a temperature range of -40°C to 85°C, a holding time of 30 minutes between high and low temperatures, a temperature transition time of less than 10 seconds, and 500 shock cycles. Unlike temperature cycling, temperature shock testing emphasizes extremely rapid temperature transitions. The transition time of less than 10 seconds simulates a scenario where a vehicle suddenly enters a high-temperature workshop from an extremely cold environment or experiences extreme thermal shock. This drastic temperature change can cause huge transient thermal mismatch stresses between different materials within the chip component, especially for large-size packages or solder joints with internal defects, which can easily induce brittle fracture. Therefore, this test path is mainly used to evaluate the resistance of solder joints to brittle fracture under extreme thermal shock environments.

[0041] When simulating temperature stress or thermomechanical coupling stress, different initial pre-strain levels are applied to the chip assembly by adjusting the tightness of the test fixture on the chip assembly. Specifically, this step is the key means to achieve "multi-stress level testing" in this embodiment. In actual operation, the clamping degree of the fixture on the PCB board can be adjusted by controlling the torque of the fastening screws. For example, three torque levels—low, medium, and high—can be set, each corresponding to different installation stress levels. When the screw torque increases, the bending deformation of the PCB board on the fixture intensifies, and the initial strain value (i.e., pre-strain) near the solder joints of the chip assembly pins also increases accordingly. By recording the initial strain values ​​under different torques before the test and detecting the solder joint cracking ratio after subsequent temperature cycling or impact tests, a three-dimensional correspondence between "initial installation stress - temperature stress - solder joint damage" can be established. This design can help automakers identify the safest installation torque range, avoid premature solder joint failure due to over-tightening, and thus more comprehensively determine the safe strain threshold.

[0042] After completing the temperature stress test described above, the slice analysis in step S3 and the threshold determination logic in step S4 are performed in the same way. The failure criteria and data processing methods are consistent with those in Example 1, and will not be repeated here. The method of this embodiment can accurately separate the single influencing factor of temperature stress on solder joint reliability, providing data support for the thermal design optimization of automotive-grade chip components. Example 4

[0043] This embodiment is another specific scheme based on Embodiment 1. It focuses on the most complex stress profile, thermomechanical coupling stress, and elaborates in detail the specific implementation path and key parameter setting logic of the temperature cycling and mechanical vibration composite test.

[0044] When the stress profile is thermomechanically coupled stress, the corresponding simulation test in step S2 is a combined temperature cycling and mechanical vibration test, in which alternating temperature loads and random vibration loads are simultaneously applied to the chip assembly mounted on the vibration table using a three-dimensional environmental test chamber. Specifically, combined with Figure 4 As shown, the thermomechanical coupling stress profile aims to simulate the harsh operating conditions of an electronic control unit (ECU) under the simultaneous stress of drastic changes in ambient temperature, road bumps, engine vibration, and other multi-physical field excitations during vehicle operation. The three-dimensional environmental test chamber integrates a temperature test chamber and an electric vibration table, enabling the chip components to withstand mechanical vibration excitation from the base while experiencing alternating high and low temperatures. This "synchronous application" method is not a simple superposition of single stresses, but rather utilizes the coupling effect of temperature and vibration: at high temperatures, the modulus of the solder joint material decreases, weakening its resistance to vibration fatigue, making it more susceptible to inducing solder joint cracks when vibration is applied; at low temperatures, the material becomes brittle, and vibration stress easily leads to brittle fracture. Through this coupled loading, the potential failure modes of the solder joints under real-vehicle conditions can be more efficiently stimulated, thereby obtaining a strain threshold with a greater safety margin.

[0045] When conducting combined temperature cycling and mechanical vibration tests, the temperature cycling conditions included a temperature range of -40℃ to 125℃, with high and low temperature holding times of 2 hours each, and heating and cooling times of 2 hours each. The mechanical vibration conditions involved applying random vibration sequentially along the X, Y, and Z axes within a frequency range of 10Hz to 1000Hz, with each axis lasting 8 hours, for a total test duration of 72 hours. It should be understood that the above parameters were set with strict reference to the stringent levels of reliability testing standards for automotive-grade electronic products (such as AEC-Q100). The temperature range was extended to 125℃ to cover the high-temperature operating environment near the engine compartment or motor controller. This temperature is close to the recrystallization temperature of solder joint materials (such as SAC305 tin-silver-copper solder), which can significantly accelerate creep fatigue damage to the solder joints. The high and low temperature holding time was set to 2 hours to ensure internal thermal balance of the chip components, allowing the solder joints to undergo sufficient thermal expansion deformation. The mechanical vibration was applied sequentially along the three axes for a total duration of 72 hours, aiming to simulate the cumulative vibration fatigue damage experienced by a vehicle throughout its entire lifespan.

[0046] For mechanical vibration conditions, the power spectral density parameter of the random vibration is: 20 (m / s²) at 10 Hz. 2 ) 2 / Hz, which is 6.5 (m / s) at 55Hz. 2 ) 2 / Hz, which is 0.25 (m / s) at 180Hz. 2 ) 2 / Hz, which is 0.25 (m / s) at 300Hz. 2 ) 2 / Hz, which is 0.14 (m / s) at 360Hz. 2 ) 2 / Hz, which is 0.14 (m / s) at 1000Hz. 2 ) 2 / Hz. This power spectral density (PSD) spectrum is a typical operating condition spectrum obtained by fitting a large amount of real vehicle road spectrum collection data.

[0047] Specifically, the 10Hz to 55Hz frequency band has higher energy and mainly simulates the low-frequency, large-amplitude impact generated by the suspension system when a vehicle is driving on rough roads. This low-frequency vibration can easily cause the PCB board to bend and deform, resulting in significant stress and strain on the solder joints. The 180Hz to 1000Hz frequency band has relatively lower energy and mainly simulates the high-frequency vibrations transmitted from engine operation and road texture to the vehicle body. This high-frequency vibration can easily excite local modal resonances on the PCB board, leading to high-frequency fatigue damage to solder joints in specific locations. This wide-bandwidth, multi-energy-gradient random vibration excitation comprehensively covers various vibration frequency components that automotive-grade chip components may encounter in actual use, ensuring the comprehensiveness and representativeness of the test results.

[0048] In this embodiment, the pre-strain application mechanism described in Embodiment 3 is also applied. When simulating thermomechanical coupling stress, different initial pre-strain levels are applied to the chip assembly by adjusting the tightness of the test fixture on the chip assembly. By comparing the cracking ratio of solder joints after the coupling stress test under different pre-strain levels, the influence weight of installation stress on solder joint reliability can be evaluated, thereby providing more accurate data support for setting screw torque in the vehicle assembly process. After the test, the slice analysis in step S3 and the threshold determination logic in step S4 are also executed to finally determine the safe strain threshold of the chip assembly under the thermomechanical coupling stress profile. Example 5

[0049] This embodiment uses a specific automotive-grade microcontroller unit (MCU) as the testing object to illustrate in detail the application process of the strain threshold detection method described in this invention in actual engineering. This MCU adopts a BGA (Ball Grid Array) package, has a large number of I / O pins and a large package size, and is widely used in vehicle controllers. The reliability of its solder joints is directly related to the safety of vehicle control.

[0050] Step S1: Determine the corresponding stress profile based on the type of stress the chip assembly experiences in practical applications.

[0051] Specifically, in practical applications, this MCU is installed inside the power control unit (PCU) of new energy vehicles. It not only needs to withstand the high-temperature environment generated by the engine compartment or motor controller, but also the road bumps and motor vibrations during vehicle operation. Therefore, this embodiment determines its corresponding stress profile as thermomechanical coupling stress, which can most realistically reproduce the complex stress state of the chip component under real vehicle operating conditions.

[0052] Step S2: Based on the stress profile determined in step S1, select the corresponding simulation test to load the chip assembly, and monitor the strain value in the area near the pin solder joints of the chip assembly in real time by strain gauges arranged on the printed circuit board during the test.

[0053] Specifically, this embodiment uses a combined temperature cycling and mechanical vibration test for loading. In the test preparation stage, strain gauges are first arranged. The strain gauges are attached to the printed circuit board within a 3mm range of the chip assembly's pin solder joints. For BGA packages, the solder joints at the four corners are typically stress concentration points; therefore, the pin solder joints near the four corners of the chip are preferentially selected as monitoring targets. The strain gauges are precisely attached within a 1mm to 3mm range from the edge of the solder joint to ensure that the captured strain signal can reflect the stress at the root of the solder joint to the greatest extent possible.

[0054] Subsequently, pre-strain is applied. Different initial pre-strain levels are applied to the chip assembly by adjusting the tightness of the test fixture during the simulation of thermomechanical coupling stress.

[0055] This embodiment simulates different installation stresses by controlling the torque of the mounting screws. Three pre-strain levels are set: low pre-strain level (installation torque 0.5 N·m, measured initial strain approximately 200 με), medium pre-strain level (installation torque 1.0 N·m, measured initial strain approximately 500 με), and high pre-strain level (installation torque 1.5 N·m, measured initial strain approximately 800 με). In this way, the initial state of the chip assembly under different assembly processes is simulated.

[0056] Next, samples with different pre-strain levels were installed in a three-dimensional environmental test chamber for testing. The combined temperature cycling and mechanical vibration test included the following temperature cycling conditions: a temperature range of -40℃ to 125℃, a high and low temperature holding time of 2 hours, and a heating and cooling time of 2 hours each; the mechanical vibration conditions involved applying random vibration sequentially to the X, Y, and Z axes within a frequency range of 10Hz to 1000Hz, with each axis lasting 8 hours, for a total test duration of 72 hours.

[0057] Specifically, the power spectral density parameters of the random vibration are set as follows: 20 (m / s²)² / Hz at 10 Hz, 6.5 (m / s²)² / Hz at 55 Hz, 0.25 (m / s²)² / Hz at 180 Hz, 0.25 (m / s²)² / Hz at 300 Hz, 0.14 (m / s²)² / Hz at 360 Hz, and 0.14 (m / s²)² / Hz at 1000 Hz. This vibration spectrum simulates the typical vibration excitation of a vehicle traveling on a rough road surface. Combined with a wide temperature range of -40℃ to 125℃ cycling, it can effectively induce fatigue failure of the weld joint under the coupled action of thermal stress and vibration stress.

[0058] Step S3: After completing the simulation test, the solder joints of the chip assembly are sliced ​​and the cracking ratio of the solder joints is determined by microscopic observation.

[0059] Specifically, after the experiment, the PCB board was removed, and key solder joints located diagonally opposite the chip were selected for cross-sectional analysis. Metallurgical microscopy revealed varying degrees of crack propagation at the solder joints under different pre-strain levels. For example, in samples with low pre-strain levels, only micro-cracks were observed at the interface; while in samples with high pre-strain levels, the cracks had penetrated part of the interface. Based on the observations, the cracking rate of the solder joints for each sample was calculated.

[0060] Step S4: Establish the correspondence between the cracking ratio of the solder joint and the strain value obtained in step S2, and determine the safe strain threshold of the chip assembly under the corresponding stress profile based on the preset failure criteria.

[0061] Specifically, this embodiment collected data from multiple samples and established a correspondence between "strain value - cracking ratio". The specific data are as follows: the maximum principal strain value monitored was 600... 900 1200 1500 At that time, the corresponding weld cracking rates were 5%, 12%, 25%, and 45%, respectively. In step S3, the failure criterion is that the weld cracking rate is greater than 20%, and the safety strain threshold determined in step S4 is the maximum strain value corresponding to when the weld cracking rate does not exceed 20%.

[0062] Based on the above data, the critical strain value corresponding to a cracking rate of 20% can be determined using linear interpolation or curve fitting. For example, a cracking rate of 12% corresponds to a critical strain value of 900... A cracking rate of 25% corresponds to 1200. In this case, the strain value corresponding to a cracking ratio of 20% is calculated to be approximately 1100 by interpolation. Therefore, the safe strain threshold for this type of automotive-grade MCU under thermomechanical coupling stress profile is determined to be 1100. This means that during actual vehicle assembly and use, the strain value near the solder joints of the chip component pins should be controlled to not exceed 1100. This ensures the reliability of the solder joints. The demonstration in this embodiment verifies that the method provided by this invention can accurately and quantitatively determine the safe strain threshold of a specific chip component under specific operating conditions, providing a scientific basis for the reliability design of automotive-grade chips.

[0063] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0064] Those skilled in the art will understand that all or part of the steps in the various methods of the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, including read-only memory (ROM), random access memory (RAM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), one-time programmable read-only memory (OTPROM), electrically erasable programmable read-only memory (EEPROM), compact disc read-only memory (CD-ROM) or other optical disc storage, disk storage, magnetic tape storage, or any other computer-readable medium capable of carrying or storing data.

[0065] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

Claims

1. A method for detecting the strain threshold of an automotive-grade chip component, characterized in that, The detection method includes the following steps: S1. Determine the corresponding stress profile for the type of stress that the chip component is subjected to in actual application, wherein the stress profile includes mechanical overstress, temperature stress and thermomechanical coupling stress. S2. Based on the determined stress profile, select the corresponding simulation test to load the chip assembly, and monitor the strain value of the pin solder joints of the chip assembly within a predetermined distance range in real time during the simulation test. S3. After completing the simulation test, the solder joints of the chip assembly are sliced ​​to determine the cracking ratio of the pin solder joints. S4. Establish the correspondence between the cracking ratio of the pin solder joints and the strain value. Based on a preset failure criterion, determine the safe strain threshold of the chip assembly under the corresponding stress profile, wherein: When the stress profile is mechanically overstressed, the corresponding simulation test is a three-point bending test; When the stress profile is temperature stress, the corresponding simulation test is a temperature cycling test or a temperature shock test; When the stress profile is thermomechanical coupled stress, the corresponding simulation test is a combined temperature cycling and mechanical vibration test.

2. The method for detecting the strain threshold of an automotive-grade chip assembly according to claim 1, characterized in that, In step S2, the predetermined distance range is the printed circuit board position within 3mm of the pin solder joint, and the strain value is monitored in real time by a strain gauge attached to the printed circuit board position.

3. The strain threshold detection method for automotive-grade chip components according to claim 1 or 2, characterized in that, In step S3, the cracking ratio is determined by metallographic microscopic observation of the weld points after slicing.

4. The strain threshold detection method for automotive-grade chip components according to claim 1 or 2, characterized in that, In step S4, the failure criterion is that the cracking ratio is greater than 20%, and the safe strain threshold is the maximum strain value corresponding to the cracking ratio not exceeding 20%.

5. The strain threshold detection method for automotive-grade chip components according to claim 1, characterized in that, When performing the three-point bending test, pressure is applied to the top of the chip assembly by the test machine pusher at a preset pressing rate, which includes 5 mm / min and 20 mm / min.

6. The method for detecting the strain threshold of an automotive-grade chip assembly according to claim 1, characterized in that, When conducting the temperature cycling test, the test conditions are: temperature range -40℃ to 85℃, high and low temperature points held for 30 minutes, temperature change rate 10℃ / min, and 500 cycles.

7. The strain threshold detection method for automotive-grade chip components according to claim 1, characterized in that, When conducting the temperature shock test, the test conditions are: temperature range -40℃ to 85℃, high and low temperature points are maintained for 30 minutes, temperature transition time is less than 10 seconds, and the shock is repeated 500 times.

8. A strain threshold detection method for automotive-grade chip components according to claim 1, 6, or 7, characterized in that, During temperature stress testing, the chip assembly is mounted using a test fixture, and different initial pre-strain levels are applied to the chip assembly by adjusting the tightness of the fixture.

9. The strain threshold detection method for automotive-grade chip components according to claim 1, characterized in that, When conducting the combined temperature cycling and mechanical vibration test, the test conditions include: temperature cycling range of -40℃ to 125℃, 8 hours per cycle; mechanical vibration is applied to the X, Y, and Z axes in sequence within the frequency range of 10Hz-1000Hz, 8 hours per axis; the total test duration is 72 hours.

10. The strain threshold detection method for an automotive-grade chip assembly according to claim 9, characterized in that, The power spectral density parameters of the random vibration are as follows: 20 (m / s) at 10 Hz. 2 ) 2 / Hz, 6.5 (m / s) at 55Hz. 2 ) 2 / Hz, 0.25 (m / s) at 180Hz. 2 ) 2 / Hz, 0.25 (m / s) at 300Hz. 2 ) 2 / Hz, 0.14 (m / s) at 360Hz. 2 ) 2 / Hz, 0.14 (m / s) at 1000Hz. 2 ) 2 / Hz.

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