Test device and method for hard polymer package stress under non-restricted constraint structure

Abstract

The application discloses a device and method for testing hard polymer packaging stress under non-restricted constraint structure, which is characterized in that a hard polymer packaging material is wrapped around a thin-walled side wall cylinder for solidification, a three-dimensional non-restricted constraint structure is constructed in combination with the characteristics of small rigidity and easy deformation of the side wall cylinder, and the deformation of the hard polymer packaging material is reflected on the deformation of the thin-walled side wall cylinder; strain sensors are arranged on the inner wall of the side wall cylinder in advance, so that the hard polymer packaging stress (including solidification residual stress and thermal stress) can be tested without direct contact between the sensors and the hard polymer packaging material in a flowing state; the device and method realize in-situ real-time measurement of the non-restricted constraint packaging stress, can effectively eliminate temperature interference in the measurement, and accurately reflect the packaging stress mechanism of the non-restricted constraint structure with low stress level in a high-elastic state, and are suitable for three-dimensional non-restricted constraint electronic packaging working conditions such as coating, encapsulation, molding and the like, and have wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of electronic packaging technology, and particularly relates to a testing device and method for stress in rigid polymer packaging under unconstrained structures. Background Technology

[0002] Rigid polymers such as epoxy resin, polyurethane, and polyamide are widely used in electronic device packaging through processes such as potting, encapsulation, coating, and injection molding, serving functions such as structural fixation, impact damping, moisture protection, and high-voltage insulation. However, rigid polymer encapsulation is prone to generating significant residual stress during material curing and use in high and low temperature environments, leading to problems such as cracking of the encapsulation material, solder joint detachment, and device damage. Therefore, it is necessary to test the stress of rigid polymer encapsulation in electronic packaging process design and reliability analysis to assess and minimize encapsulation stress as much as possible.

[0003] Encapsulation stress in rigid polymers includes residual curing stress and thermally induced stress. Residual curing stress is mechanical stress caused by chemical shrinkage and temperature changes during the curing process, while thermally induced stress is mechanical stress caused by the difference in thermal expansion coefficients between the rigid polymer and the encapsulated object under temperature changes. During the curing reaction of thermosetting polymers and the heating molding process of thermoplastic polymers, the materials typically undergo irreversible chemical changes from a viscous flow state to a highly elastic state. During the recovery to room temperature after the complete curing reaction of thermosetting polymers and under external temperature changes, the materials typically undergo reversible physical changes from a highly elastic state to a glassy state. Highly elastic polymers exhibit near-incompressible volumetric properties similar to rubber, with elastic mechanical parameters showing a Poisson's ratio close to 0.5 and a Young's modulus much lower than the bulk modulus. Derivation from elasticity theory shows that encapsulation stress in one-dimensional and two-dimensional constrained structures is determined by the Young's modulus, while in three-dimensional constrained structures, it is mainly determined by the bulk modulus. Due to the difference between the Young's modulus and the bulk modulus in the highly elastic state, the rate of stress formation and the moment when stress begins to form (stress "zero point") vary significantly in different constrained structures.

[0004] When a rigid polymer with a high coefficient of thermal expansion surrounds an electronic device with a low coefficient of thermal expansion, the constraint exerted by the electronic device structure on the packaging material is approximately two-dimensional or weakly three-dimensional; this is collectively referred to as an unconstrained structure. Typical unconstrained structures include printed circuit board surface coating, solder joint encapsulation, and chip molding. In unconstrained structures, when the temperature changes or the packaging material cures and shrinks, the rigid polymer can deform freely to the surrounding surfaces, experiencing less constraint from the electronic device structure. Its packaging stress is mainly affected by Young's modulus, with a relatively low proportion of bulk modulus. Therefore, its curing residual stress is low, and the proportion of elastic stress is small. Stress failure typically occurs under low-temperature conditions.

[0005] Strain measurement based on resistance strain gauges or fiber optic gratings (FBGs) is currently the most commonly used method for stress testing of polymer packages. The resistance strain gauge method involves pre-attaching a resistance strain gauge to the surface of the device or structure under test (DUT), and detecting changes in the strain gauge's resistance to reflect the strain on that surface. The FBG method involves pre-embedding an FBG optical fiber within the polymer package or pre-attaching it to the surface of the DUT, and detecting changes in characteristic wavelengths to reflect the strain at that location.

[0006] Currently, both domestically and internationally, the following shortcomings are commonly found in the use of resistance strain gauges and FBGs for encapsulation stress measurement: 1) The measurement methods do not analyze and differentiate the degree of constraint of the testing device, leading to inconsistent or even contradictory conclusions about the encapsulation stress obtained when using different devices. For example, in a common resistance strain gauge measurement, the strain gauge is attached to the surface of a metal tube, and the polymer is placed inside the tube. The metal tube restricts the free expansion of the polymer, which is a structure with strong constraint. The stress formation and evolution laws obtained based on this structure are not applicable to scenarios with weaker constraints. 2) The measurement methods do not eliminate the influence of temperature, or the methods for eliminating the influence of temperature introduce large measurement errors. The strain signal measured by resistance strain gauges and FBGs is not only related to the strain at the measuring point, but also to the temperature at the measuring point. The strain at the measuring point includes both thermal expansion strain caused by the temperature change of the measured material and mechanical strain. Only mechanical strain is related to residual stress, thermal stress, etc. Therefore, it is necessary to subtract the thermal expansion strain and the spurious strain (collectively referred to as thermal output) caused by temperature changes in the strain gauge and FBG themselves from the measured strain signal. Most existing measurement methods fail to account for the influence of temperature at the measurement point and / or the thermal expansion strain of the measured material, resulting in measurement results that do not reflect the true stress at the measurement point. Furthermore, a common method to eliminate temperature influence is to attach a sensor to the surface of a material with a known coefficient of thermal expansion and measure the compensation strain signal. The compensation sensor and the working sensor placed at the measurement point perform strain measurements simultaneously, and the thermal output is calculated based on the known coefficient of thermal expansion and the compensation strain signal. However, due to potential individual differences in manufacturing and bonding processes between the working and compensation sensors, the difference in thermal output between the two sensors can be as high as 200 με or more. In contrast, the residual stress at the measurement point under unconstrained structures can be as low as 100–500 με. Therefore, this method of eliminating temperature influence introduces significant errors into the mechanical strain analysis results. Furthermore, the larger the temperature range covered by the test, the greater the absolute error of the mechanical strain; and the smaller the stress at the measurement point, the greater the relative error of the mechanical strain.

[0007] Therefore, for electronic packaging applications with weak three-dimensional constraints such as coating, encapsulation, and molding, it is necessary to develop stress measurement devices and methods for rigid polymer packaging that have unconstrained structural features and effectively eliminate the influence of temperature, suitable for the curing process and temperature changes. Summary of the Invention

[0008] In view of this, this invention addresses a class of applications in rigid polymer electronic packaging with weak three-dimensional constraints, such as coating, encapsulation, and molding. It proposes a testing device and method for measuring the residual stress and thermally induced stress (collectively referred to as: packaging stress) of rigid polymers under unconstrained structures. Under weak three-dimensional constraints, the stress caused by curing shrinkage and temperature changes in the highly elastic state of the rigid polymer is relatively small, resulting in a lower monitored stress level. Therefore, it is necessary to construct an unconstrained structure to simulate the weak three-dimensional constraints for testing.

[0009] This stress measurement device consists of a rigid polymer encapsulation material encapsulating and curing a sidewall cylinder. Strain sensors are placed within the sidewall cylinder. Utilizing the low stiffness and easy deformation of the sidewall cylinder, the deformation of the rigid polymer is reflected in the deformation of the metal sidewall cylinder, enabling in-situ real-time testing of the residual stress and thermally induced stress of the cured rigid polymer. By designing the rigid polymer-encapsulated sidewall cylinder structure, it effectively reflects the characteristics of unconstrained structures and the corresponding encapsulation stress formation patterns. Through reasonable design, size, and material selection of the sidewall cylinder structure, the inner wall of the sidewall cylinder can develop a sufficient magnitude of mechanical strain after the rigid polymer cures and undergoes temperature changes, reducing the influence of sensor measurement errors and ensuring the required strain measurement accuracy.

[0010] This stress measurement method obtains the thermal output data of the strain sensor through temperature change experiments on a blank sample in an unfilled rigid polymer state. This thermal output data is then subtracted from the strain readings of the strain sensor during the curing process and under high and low temperature environments. This yields the mechanical strain at the measurement point of the rigid polymer encapsulation material, excluding the influence of temperature factors, thus eliminating the mechanical strain analysis error introduced by the introduction of compensation sensor thermal output testing. Stress testing experiments conducted based on the device and method designed in this invention typically yield strain levels in the range of hundreds to thousands of με, with a testing error on the order of 10 με.

[0011] To achieve this objective, the first aspect of the present invention provides a testing device for the stress of rigid polymer encapsulation under an unconstrained structure. The device uses a rigid polymer encapsulation material to encapsulate a sidewall cylinder and cure it. It utilizes the chemical shrinkage deformation characteristics of the rigid polymer during the curing process, the mismatch in the coefficients of thermal expansion between the rigid polymer and the metal material, and the characteristics of the sidewall cylinder having low stiffness and being easily deformed to construct a three-dimensional unconstrained structure. By utilizing the force transmission between the rigid polymer and the sidewall cylinder, combined with the relationship between mechanical strain and stress, the device monitors the change in mechanical strain of the sidewall cylinder after it is subjected to force, reflecting the formation process of encapsulation stress under the three-dimensional unconstrained structure.

[0012] The device includes a base, an outer cylinder, a support shaft, a lower sleeve, a side wall cylinder, an upper sleeve, a strain sensor, and a temperature sensor.

[0013] The base is located at the bottom of the testing device and has a central hole;

[0014] The lower end of the outer cylinder is mounted on the base and is located on the outermost layer of the testing device;

[0015] One end of the support shaft is installed in the center hole of the base;

[0016] The lower sleeve, side wall sleeve, and upper sleeve are connected in order from bottom to top and then mounted on the support shaft via the lower sleeve; a cavity for filling with rigid polymer encapsulation material is formed between the outer side of the lower sleeve, side wall sleeve, and upper sleeve and the inner side of the outer cylinder.

[0017] The sidewall cylinder is made of metal material, and the wall thickness design of the sidewall cylinder ensures that the deformation of the sidewall cylinder during the curing process of the rigid polymer encapsulation material can be measured and meets the minimum wall thickness that can be processed.

[0018] The upper sleeve has a central hole, through which a lead wire is installed via a shaft.

[0019] The strain sensor and temperature sensor are arranged on the inner surface of the side wall cylinder, and the signal lines of the strain sensor and temperature sensor are led out through the shaft via leads.

[0020] Preferably, the strain sensor and temperature sensor are arranged in adjacent pairs, and the testing device is arranged in one or more pairs.

[0021] Preferably, the strain sensor and temperature sensor are arranged in the middle of the sidewall cylinder.

[0022] Preferably, the outer cylindrical body is composed of a detachable left lobe mold and a right lobe mold.

[0023] Preferably, the wall thickness of the sidewall cylinder is 0.5mm to 1.0mm.

[0024] Preferably, the upper end face of the lead wire is at least 15 mm above the highest liquid level of the filled rigid polymer encapsulation material.

[0025] Preferably, both the upper surface of the base and the inner surface of the outer cylinder are coated with a release agent.

[0026] The second aspect of this application provides a method for testing the stress of rigid polymer encapsulation under unconstrained structures. The method is based on the above-mentioned testing apparatus and includes testing the residual stress of the rigid polymer encapsulation material after curing and testing the thermally induced stress of the rigid polymer encapsulation material.

[0027] (a) The test results for residual stress after curing of rigid polymer encapsulation materials are as follows:

[0028] S1-1: Attach strain sensors and temperature sensors to the inner wall of the sidewall cylinder, and assemble the sidewall cylinder, lower sleeve, upper sleeve, support shaft, and lead wire through the shaft to form the inner cavity;

[0029] S1-2: Place the inner cavity in the environmental test chamber and zero the strain sensor at room temperature T0; start the environmental test chamber temperature control, first cooling and then heating. Throughout the process, use the strain sensor and temperature sensor to collect data on the sidewall cylinder at different times t. i strain ε i,rsc (t i ) and temperature data T i (t i ); utilizing strain ε i,rsc (t i ) and temperature data T i (t i The strain ε of the sidewall cylinder was obtained by fitting. i,rsc (t i ) and temperature T i (t i The functional relationship between ε i,rsc (T i ), and with the x-axis as T i (t i ), with the ordinate being ε i,rsc (t i Plot the heat output temperature curve;

[0030] S1-3: Assemble the inner cavity in S1-1 with the outer cylinder and base, and fill the space between the inner cavity and the outer cylinder with rigid polymer encapsulation material;

[0031] S1-4: Start the environmental test chamber temperature control to carry out the curing process of the rigid polymer encapsulation material, and collect data at different times (t) of the sidewall cylinder during the curing process of the rigid polymer encapsulation material. j Indicated strain and temperature data

[0032] S1-5: Using interpolation, obtain different temperature data from the heat output temperature curve obtained in S1-2. Strain of the lower sidewall cylinder

[0033] S1-6: Calculate the residual stress after curing of the rigid polymer encapsulation material:

[0034] (II) The potting thermal stress of rigid polymer encapsulation materials was tested as follows:

[0035] First, obtain the thermal output temperature curve and fill the rigid polymer encapsulation material to be tested. The operation steps are the same as those in S1-1 to S1-3 of the test of the curing residual stress of the rigid polymer encapsulation material.

[0036] Next, high and low temperature cycling conditions were set, the environmental test chamber temperature control was activated, and temperature cycling loading was performed on the rigid polymer encapsulation material. Data were collected at different times (t) of the sidewall cylinder of the rigid polymer encapsulation material under test during the high and low temperature cycling test. j Indicated strain and temperature data

[0037] Then, using interpolation, different temperature data are obtained from the heat output temperature curve obtained in S1-2. Strain of the lower sidewall cylinder

[0038] Finally, the thermally induced stress of the rigid polymer encapsulation under test was calculated:

[0039] Preferably, step S1-2 further includes eliminating zero-point drift caused by the strain sensor during its first exposure to high and low temperatures, specifically including:

[0040] First, multiple heating and cooling cycles were set up, and strain and temperature data were collected during the heating and cooling processes. The start and end times of the last heating cycle were recorded as t1 and t2, respectively. k and t l ;

[0041] Next, after the heating and cooling cycle is completed, the temperature is restored to room temperature T0 and held at that temperature. The end time of the holding period is recorded as t. n ;

[0042] Then, using the time period t k ~t l Strain ε collected internally i,rsc (t i ) and temperature data T i (t i The strain ε was calculated. i,rsc (t i ) and temperature T i (t i The functional relationship between ε i,rsc (T i );

[0043] Finally, the end time of heat preservation is t. n The strain is taken as the zero strain point ε n,rsc (t n ), for the functional relation ε i,rsc (T iThe strain ε is then corrected to obtain the corrected strain. i,rsc (t i ) and temperature T i (t i The functional relationship between ε and ε: i ′ ,rsc (T i )=ε i,rsc (T i )-ε n,rsc (t n The heat output temperature curve was plotted using the corrected functional relationship.

[0044] The beneficial effects of the present invention are as follows: The test device and method for the stress of rigid polymer encapsulation under unconstrained structure disclosed in the present invention are as follows: (1) The structure of a thin-walled sidewall tube wrapped with rigid polymer encapsulation material is adopted. Under this structure, the deformation of the encapsulation material is suppressed on only one side, simulating the scenario where the deformation of the polymer encapsulation material is weakly suppressed due to high temperature expansion and low temperature contraction, thus forming the characteristics of a three-dimensional unconstrained structure; (2) By utilizing the chemical shrinkage deformation characteristics of the rigid polymer during the curing process, the mismatch of the thermal expansion coefficients between the rigid polymer and the metal material, and the characteristics of the sidewall tube having low stiffness and being easily deformed, the deformation of the rigid polymer is reflected on the deformation of the metal cavity. The deformation of the sidewall tube is measured by a sensor to realize the measurement of the residual stress and thermal stress caused by the curing of the rigid polymer. The device is constructed to simulate the three-dimensional unconstrained load situation; (3) The device and method of the present invention use the side wall cylinder as the medium layer to ensure that the sensor does not directly contact the rigid polymer in the flow state, realize the monitoring of the solidification strain evolution process, and solve the problem that the rigid polymer cannot directly attach the strain sensor for measurement due to the phase change during the solidification process; (4) The method disclosed in this application is designed according to the test principle of the strain sensor, takes into account the influence of the thermal output of the strain sensor, first obtains the thermal output data of the strain sensor in the unencapsulated state, then fills and solidifies the encapsulation material, and finally deducts the thermal output data of the strain sensor from the indicated strain in the solidification process of the rigid polymer encapsulation material and the high and low temperature environment, eliminates the contribution of temperature to the strain signal, and obtains the true strain (mechanical strain) reflecting the residual stress.

[0045] The testing device and method proposed in this patent have the following uses: (1) for the comparison of rigid polymer encapsulation materials. Using the method described in this application, the encapsulation stress of different encapsulation materials under unconstrained structures can be obtained. For the selection of encapsulation materials with the aim of reducing encapsulation stress, quantitative analysis basis can be directly provided without carrying out tedious performance parameter characterization analysis such as thermal expansion coefficient, elastic modulus, and glass transition temperature of encapsulation materials; (2) for the design and optimization of rigid polymer encapsulation curing process parameters. Using the method described in this application, the curing residual stress is diagnosed, and the influence of different curing process parameters such as curing time, curing temperature, and heating / cooling rate on the curing residual stress is compared, thereby optimizing the curing process and reducing the curing residual stress; (3) for the analysis of the stress formation mechanism of rigid polymer encapsulation. Using the method described in this application, the process data of the formation of curing residual stress and thermal stress in unconstrained structures can be obtained. The magnitude and trend of stress formed by rigid polymer at various times and temperature ranges can be quantitatively obtained, and the stress mechanism can be quantitatively guided. Analysis; (4) Used for setting temperature cycling test conditions for rigid polymer packaging. Using the method described in this application, the evolution of packaging stress and stress failure assessment data during temperature cycling can be obtained, and quantitative analysis results including high and low temperature conditions of temperature cycling, high and low temperature holding time, temperature change rate, and number of cycles can be given, supporting the setting of temperature cycling test conditions; (5) Used for evaluating the evolution of rigid polymer packaging stress during storage or accelerated storage. Using the method described in this application, the evolution data of packaging stress during long-term storage or accelerated storage can be obtained, and quantitative assessment results of storage stress under different storage conditions such as long-term, high temperature, and low temperature can be obtained; (6) Used for verification of rigid polymer packaging stress simulation model. Using the method described in this application, the stress data formed by rigid polymer at various times and temperature ranges can be quantitatively obtained. This data can provide reference data for the simulation model and verify the accuracy of the simulation model; (7) Used for packaging mold design. Using the method described in this application, the influence of different packaging mold materials and structures on rigid polymer packaging stress can be quantitatively obtained, guiding the design of packaging molds. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the structure of the testing device for residual stress and thermally induced stress of hard polymers in an embodiment of the present invention.

[0047] Figure 2 This is a top view of the testing device for residual stress and thermally induced stress of hard polymers in an embodiment of the present invention;

[0048] Figure 3 yes Figure 2 A cross-sectional view of the test apparatus for testing the residual stress and thermally induced stress of the hard polymer after curing, shown in section AA;

[0049] The components include: 1. Base; 2. Left lobe mold; 3. Right lobe mold; 4. Support shaft; 5. Lower sleeve; 6. Side wall sleeve; 7. Upper sleeve; 8. Lead wire through shaft; 9. Rigid polymer encapsulation material; 10. Strain sensor; 11. Temperature sensor; 12. Wire harness.

[0050] Figure 4 These are typical test results from the measurement of residual stress during the curing of rigid polymers under an unconstrained structure in this embodiment of the invention.

[0051] Figure 5 These are typical test results from the thermal stress measurement of a rigid polymer under an unconstrained structure in this embodiment of the invention. Detailed Implementation

[0052] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

[0053] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0054] A testing device for rigid polymer encapsulation stress under unconstrained structures is proposed. This device utilizes the chemical shrinkage deformation characteristics of rigid polymers during curing, the mismatch in thermal expansion coefficients between rigid polymers and metal materials, and the low stiffness and easy deformation of the sidewall cylinder. The device is designed with a rigid polymer encapsulating the sidewall cylinder cavity, reflecting the deformation of the rigid polymer in the deformation of the metal cavity. During the curing process of the rigid polymer encapsulation material and at low temperatures, the rigid polymer undergoes chemical and thermal shrinkage, compressing the sidewall cylinder and generating compressive strain on the inner wall of the sidewall cylinder. At high temperatures, the rigid polymer thermally expands relative to the metal sidewall cylinder, generating tensile strain on the inner wall of the sidewall cylinder. The strain of the rigid polymer is then measured by measuring the strain of the sidewall cylinder.

[0055] As an example, its structure is as follows Figures 1-3As shown, the device includes a base 1, an outer cylinder, a support shaft 4, a lower sleeve 5, a side wall cylinder 6, an upper sleeve 7, a strain sensor 10, and a temperature sensor 11. The base 1 is located at the bottom of the device and has a central hole. The lower end of the outer cylinder is mounted on the base 1 and is located on the outermost layer of the device. One end of the support shaft 4 is installed in the central hole of the base 1. The lower sleeve 5, side wall cylinder 6, and upper sleeve 7 are connected in a bottom-to-top order and are mounted on the support shaft 4 via the lower sleeve 5. A cavity is formed between the outer side of the sleeve 7 and the inner side of the outer cylinder, which is filled with rigid polymer encapsulation material 9 during testing. The upper sleeve 7 has a central hole through which a lead wire is mounted, passing through a shaft 8, to lead out the signal harness 12 of the strain sensor 10 and temperature sensor 11. The support shaft 4, lower sleeve 5, sidewall cylinder 6, upper sleeve 7, and lead wire passing through shaft 8 form a closed inner cavity. Space is provided on the inner wall of the sidewall cylinder 6 for attaching the strain sensor 10 and temperature sensor 11. This inner cavity isolates the rigid polymer encapsulation material under test from the sensors, avoiding signal interference and difficulties in signal interpretation caused by direct contact between the encapsulation material and the sensors. Furthermore, the inner cavity provides a deformable sidewall cylinder 6 to ensure that the strain signal remains within the measurable range. The strain sensor 10 and temperature sensor 11 are mounted on the inner surface of the sidewall cylinder 6. The sensing device monitors in real time the residual stress of the rigid polymer encapsulation material after curing to room temperature and its formation process, as well as the thermal stress under high and low temperature environmental loads.

[0056] The design of the sidewall tube 6 is crucial for stress testing. Made of a rigid material, its wall thickness is designed to ensure that the deformation of the sidewall tube during the curing process of the rigid polymer encapsulation material can be measured, while simultaneously ensuring that the sidewall tube is not too thin. Generally, it should be feasible to manufacture. If the sidewall tube is made of a high-modulus metal, the wall thickness should be appropriately reduced; conversely, the wall thickness can be appropriately increased to reduce manufacturing difficulty. For example, when the sidewall tube is made of aluminum alloy, its wall thickness is designed to be 0.5mm to 1.0mm. This thickness ensures both the feasibility of manufacturing the sidewall tube and meets the testing requirements.

[0057] As an example, strain sensor 10 and temperature sensor 11 are arranged in pairs adjacent to each other to ensure that the temperature at their locations is consistent. Typically, one or more pairs are used to measure the mechanical strain of the rigid polymer encapsulation material. The type of sensing device can be selected according to actual needs. For example, the temperature sensor can be a thermocouple; the strain sensor can be a strain gauge or fiber Bragg grating sensor, or it can be a strain rose, multiple strain gauges, or multiple fiber Bragg grating sensors.

[0058] As an example, in order to achieve better measurement results, the strain sensor 10 and the temperature sensor 11 are arranged in the middle of the side wall cylinder. The temperature sensor can be fixed by using high and low temperature resistant polyimide tape, and the strain sensor can be fixed by high and low temperature resistant glue.

[0059] As an example, to facilitate disassembly and assembly, the outer cylindrical body is composed of a detachable left lobe mold 2 and a right lobe mold 3. The left lobe mold 2 and the right lobe mold 3 are made of metal materials and are not easily deformed, such as aluminum alloy. At the same time, to facilitate separation from the hard polymer material after testing, a release agent is applied to the upper surface of the base and the inner surface of the outer cylinder.

[0060] As an example, the upper surface of the lead through shaft 8 is at least 15mm higher than the highest liquid level of the filled rigid polymer encapsulation material to ensure that the rigid polymer does not overflow into the central through hole of the lead through shaft 8 during the vacuum degassing process. The diameter of the central through hole of the lead through shaft 8 should be ≥8mm to ensure that the lead wires of the sensing device have sufficient space to pass through.

[0061] (a) The method for testing the residual stress of hard polymers after curing using the above-mentioned testing device is as follows:

[0062] S1: Attach strain sensor 10 and temperature sensor 11 to the inner wall of sidewall cylinder 6, and assemble sidewall cylinder 6, lower sleeve 5, upper sleeve 7, support shaft 4 and lead wire through shaft 8 to form inner cavity;

[0063] S2: Place the inner cavity in an environmental test chamber and zero the strain sensor 10 at temperature T0. Then, start the temperature sensor 11 and the strain sensor 10 to collect data on the side wall cylinder 6 at different times t. i strain ε i,rsc (t i ) and temperature data T i (t i During the data collection process, the temperature was first reduced from T0 to T11 at a rate of 1℃ / m11. L Then the temperature was changed from T L Heat up to T H Then, using the collected strain ε i,rsc (t i ) and temperature data T i (t i The strain ε of the sidewall cylinder was obtained by fitting. i,rsc (t i ) and temperature T i (t i The functional relationship between ε i,rsc (T i ), and with the x-axis as T i (t i ), with the ordinate being ε i,rsc (t i Plot the heat output temperature curve;

[0064] As another embodiment, this step can also consider eliminating the zero-point drift of the strain sensor when it first experiences high and low temperatures. The process differs from the one described above, specifically including:

[0065] Temperature T L To temperature T H Set up multiple heating and cooling cycles, and record the last cycle starting from temperature T. L To temperature T H The start and end times of the heating cycle are t and t, respectively. k and t l Return the temperature to room temperature T0 and maintain this temperature for a period of time until time t. n The time ends; then, the heating time period t is used. k ~t l Strain ε collected internally i,rsc (t i ) and temperature data T i (t i The strain ε was obtained by fitting. i,rsc (t i ) and temperature T i (t i The functional relationship between them...; finally, at the endpoint time t... n The strain is taken as the zero strain point ε n,rsc (t n ), for the functional relation ε i,rsc (T i The corrected ε is obtained by making corrections. i ′ ,rsc (T i )=ε i,rsc (T i )-ε n,rsc (t n The heat output temperature curve, plotted using the corrected functional relationship, serves as a reference for calculating the sidewall cylinder temperature strain of the cured residual stress of the rigid polymer encapsulation material.

[0066] S3: Assemble the inner cavity in S1 with the outer cylinder and base, and fill the space between the inner cavity and the outer cylinder with rigid polymer encapsulation material;

[0067] S4: Start the external temperature control system to perform the curing process of the rigid polymer encapsulation material, and collect data at different times t on the sidewall cylinder during the curing process. j Indicated strain and temperature data

[0068] S5: Using interpolation, obtain the heat output temperature curves from S2 for different temperatures. Strain of the lower sidewall cylinder

[0069]

[0070] S6: Calculate the residual stress after curing of the rigid polymer encapsulation material. or (Consider eliminating the zero-point drift caused by the strain sensor when it first experiences high and low temperatures).

[0071] (II) The method for measuring the thermally induced stress of rigid polymers using the above-mentioned testing device is as follows:

[0072] The procedure for obtaining the thermal output temperature curve and filling the rigid polymer encapsulation material to be tested is the same as S1-1 to S1-3 in the test of the curing residual stress of the rigid polymer encapsulation material.

[0073] Next, high and low temperature cycling conditions were set, the external temperature control system was started, and temperature cycling loading was performed on the rigid polymer encapsulation material. The indicated strain of the sidewall cylinder at the strain sensor location was collected during the high and low temperature cycling test of the rigid polymer encapsulation material. Temperature of the sidewall cylinder at the location of the temperature sensor

[0074] Then, using interpolation, different temperatures are obtained from the heat output temperature curve in S2. Strain of the lower sidewall cylinder

[0075]

[0076] Finally, using indicated strain and temperature Calculate the thermal stress induced by the encapsulation of the rigid polymer encapsulation material under test.

[0077] Using the unconstrained structure disclosed in this invention, residual stress measurements of hard polymer curing were performed, and the results were as follows: Figure 4 Typical results are shown; thermally induced stress measurements of rigid polymers during temperature cycling were performed using the unconstrained structure disclosed in this invention, yielding results as follows: Figure 5 The typical test results are shown.

Claims

1. A testing device for the stress of rigid polymer encapsulation under unconstrained structures, characterized in that, The testing device includes a base, an outer cylinder, a support shaft, a lower sleeve, a side wall cylinder, an upper sleeve, a strain sensor, and a temperature sensor. The base is located at the bottom of the testing device and has a central hole; The lower end of the outer cylinder is mounted on the base and is located on the outermost layer of the testing device; One end of the support shaft is installed in the center hole of the base; The lower sleeve, side wall sleeve, and upper sleeve are connected in order from bottom to top and then mounted on the support shaft via the lower sleeve; a cavity for filling with rigid polymer encapsulation material is formed between the outer side of the lower sleeve, side wall sleeve, and upper sleeve and the inner side of the outer cylinder. The sidewall cylinder is made of metal material, and the wall thickness design of the sidewall cylinder ensures that the deformation of the sidewall cylinder during the curing process of the rigid polymer encapsulation material can be measured and meets the minimum wall thickness that can be processed. The upper sleeve has a central hole, through which a lead wire is installed via a shaft. The strain sensor and temperature sensor are arranged on the inner surface of the side wall cylinder, and the signal lines of the strain sensor and temperature sensor are led out through the shaft via leads.

2. The testing device for the stress of rigid polymer encapsulation under unconstrained structures according to claim 1, characterized in that, The strain sensor and temperature sensor are arranged in adjacent pairs, and the testing device is arranged in one or more pairs.

3. The testing device for the stress of rigid polymer encapsulation under unconstrained structures according to claim 1, characterized in that, The strain sensor and temperature sensor are arranged in the middle of the sidewall cylinder.

4. The testing device for the stress of rigid polymer encapsulation under unconstrained structures according to claim 1, characterized in that, The outer cylinder is composed of a detachable left and right lobe mold.

5. The testing device for the stress of rigid polymer encapsulation under unconstrained structures according to claim 1, characterized in that, The wall thickness of the sidewall cylinder is 0.5mm to 1.0mm.

6. The testing device for the stress of rigid polymer encapsulation under unconstrained structures according to claim 1, characterized in that, The lead wire passes through the upper end face of the shaft, which is at least 15 mm above the highest liquid level of the filled rigid polymer encapsulation material.

7. The testing apparatus for the stress of rigid polymer encapsulation under unconstrained structures according to claim 1, characterized in that, Both the upper surface of the base and the inner surface of the outer cylinder are coated with a release agent.

8. A method for testing the stress of rigid polymer encapsulation under unconstrained structures, characterized in that, The method is performed based on the testing apparatus according to any one of claims 1 to 7, and the method includes testing the residual stress of the hard polymer encapsulation material after curing and testing the thermal stress caused by the hard polymer encapsulation material. (a) The test results for residual stress after curing of rigid polymer encapsulation materials are as follows: S1-1: Attach strain sensors and temperature sensors to the inner wall of the sidewall cylinder, and assemble the sidewall cylinder, lower sleeve, upper sleeve, support shaft, and lead wire through the shaft to form the inner cavity; S1-2: Place the inner cavity in an environmental test chamber and zero the strain sensor at room temperature; start the environmental test chamber temperature control, first cooling and then heating. Throughout the process, use the strain sensor and temperature sensor to collect data on the sidewall cylinder at different times (t). i strain ε i,rsc (t i ) and temperature data T i (t i According to strain ε i,rsc (t i ) and temperature T i (t i The time synchronization relationship can be used to obtain the strain ε. i,rsc (t i ) and temperature T i (t i The curve ε between ) i,rsc (T i ), i.e., the heat output temperature curve T i (t i )-ε i,rsc (t i ); S1-3: Assemble the inner cavity in S1-1 with the outer cylinder and base, and fill the space between the inner cavity and the outer cylinder with rigid polymer encapsulation material; S1-4: Start the environmental test chamber temperature control to carry out the curing process of the rigid polymer encapsulation material, and collect data at different times (t) of the sidewall cylinder during the curing process of the rigid polymer encapsulation material. j Indicated strain and temperature data S1-5: Using interpolation, obtain different temperature data from the heat output temperature curve obtained in S1-2. Strain of the lower sidewall cylinder S1-6: Calculate the residual stress after curing of the rigid polymer encapsulation material: (II) The test results for the thermal stress induced by the encapsulation of rigid polymer encapsulation materials are as follows: First, obtain the thermal output temperature curve and fill the rigid polymer encapsulation material to be tested. The operation steps are the same as those in S1-1 to S1-3 of the test of the curing residual stress of the rigid polymer encapsulation material. Next, high and low temperature cycling conditions were set, the environmental test chamber temperature control was activated, and temperature cycling loading was performed on the rigid polymer encapsulation material. Data were collected at different times (t) of the sidewall cylinder of the rigid polymer encapsulation material under test during the high and low temperature cycling test. j Indicated strain and temperature data Then, using interpolation, different temperature data are obtained from the heat output temperature curve obtained in S1-2. Strain of the lower sidewall cylinder Finally, the thermally induced stress of the rigid polymer encapsulation under test was calculated:

9. The method for testing the stress of rigid polymer encapsulation under unconstrained structures according to claim 8, characterized in that, S1-2 also includes eliminating zero-point drift caused by the strain sensor during its first exposure to high and low temperatures, specifically including: First, multiple heating and cooling cycles were set up, and strain and temperature data were collected during the heating and cooling processes. The start and end times of the last heating cycle were recorded as t1 and t2, respectively. k and t l ; Next, after the heating and cooling cycle is completed, the temperature is restored to room temperature T0 and held at that temperature. The end time of the holding period is recorded as t. n ; Then, using the time period t k ~t l Strain ε collected internally i,rsc (t i ) and temperature data T i (t i The strain ε was calculated. i,rsc (t i ) and temperature T i (t i The functional relationship between ε i,rsc (T i ); Finally, the end time of heat preservation is t. n The strain is taken as the zero strain point ε n,rsc (t n ), for the functional relation ε i,rsc (T i The strain ε is then corrected to obtain the corrected strain. i,rsc (t i ) and temperature T i (t i The functional relationship between ε and ε: i ′ ,rsc (T i )=ε i,rsc (T i )-ε n,rsc (t n The heat output temperature curve was plotted using the corrected functional relationship.

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