A reliability evaluation method of conductive thermal interface material

Abstract

This invention discloses a reliability evaluation method for conductive thermal interface materials, comprising: fabricating substitute samples based on the adhesive layer structure and sintering process of the conductive thermal interface material of the actual device; gradually increasing the ambient temperature to test the actual device, and using the increase in interface thermal resistance when the device performance fails to meet the requirements as the failure threshold; conducting thermoelectric stress tests on all substitute samples according to the set temperature stress and current stress conditions, stopping the test after a certain period of time, and then conducting interface thermal resistance tests; when the increase in interface thermal resistance of the substitute sample exceeds the failure threshold, stopping the thermoelectric stress test of the substitute sample and recording the failure lifetime, until the increase in interface thermal resistance of all substitute samples exceeds the failure threshold; obtaining the failure lifetime of the conductive thermal interface material based on the failure lifetime data of all substitute samples, thereby achieving reliability evaluation of the conductive thermal interface material. This invention can effectively evaluate the reliability of interface thermal resistance degradation caused by electromigration effects.

Description

Technical Field

[0001] This invention belongs to the field of thermal interface materials, and specifically relates to a reliability evaluation method for conductive thermal interface materials. Background Technology

[0002] Thermal interface materials are mainly used for bonding and heat dissipation at the packaging interfaces of high-power integrated circuits and electronic components. With the continuous increase in power density of microelectronic devices, device overheating failures are becoming more frequent, leading to increased industry attention on thermal interface materials. In recent years, to meet the interconnection requirements of high-temperature, high-power electronic devices, the industry has invested heavily in research and development of high-performance, highly reliable conductive thermal interface materials. For example, conductive thermal interface materials with excellent mechanical and thermal transfer properties, such as micro / nano silver and nano copper paste, are gradually entering the market. Reliability evaluation of such conductive thermal interface materials is also being carried out gradually.

[0003] Existing technologies evaluate the reliability of adhesive interfaces from different mechanisms, such as high-temperature degradation and electromigration degradation, based on the actual application scenarios of conductive thermal interface materials. This is a common and traditional method for evaluating the reliability of adhesive interfaces. However, when electromigration degradation occurs at the adhesive interface, the thermal resistance of the interface will also degrade simultaneously. Interface thermal resistance is an important parameter of adhesive performance, but research on interface thermal resistance degradation caused by electromigration effects is still lacking in the industry. Existing technologies cannot conduct reliability evaluations of interface thermal resistance degradation caused by electromigration effects. Summary of the Invention

[0004] The purpose of this invention is to provide a reliability evaluation method for conductive thermal interface materials, which can effectively evaluate the reliability of interface thermal resistance degradation caused by electromigration effects.

[0005] To achieve the above objectives, one aspect of the present invention provides a reliability evaluation method for conductive thermal interface materials, comprising:

[0006] Step S1: Prepare alternative samples based on the actual device's conductive and thermal interface material bonding layer structure and sintering process.

[0007] Step S2: Gradually increase the ambient temperature to test the actual device. The increase in interface thermal resistance when the device performance fails to meet the requirements is taken as the failure threshold of interface thermal resistance. The interface thermal resistance is the sum of the bulk thermal resistance of the thermal interface material and the contact thermal resistance between the thermal interface material and the upper and lower interfaces.

[0008] Step S3: Determine the thermoelectric stress test conditions for the substitute sample, set the temperature to the normal operating temperature of the device, determine the current stress based on the current density of the adhesive layer or the voltage difference between the upper and lower interfaces under the actual working conditions of the device, determine the number of substitute samples and test the initial interfacial thermal resistance of the substitute samples.

[0009] Step S4: Apply thermoelectric stress to all substitute samples according to the set temperature stress and current stress conditions, carry out thermoelectric stress test, stop the test after a period of time, and perform interface thermal resistance test on the substitute samples.

[0010] Step S5: When the increase in the interfacial thermal resistance of the substitute sample does not exceed the failure threshold, continue to perform the thermoelectric stress test; when the increase in the interfacial thermal resistance of the substitute sample exceeds the failure threshold, stop the thermoelectric stress test of the substitute sample and record its test time as the failure life, until the increase in the interfacial thermal resistance of all substitute samples exceeds the failure threshold, then stop the test of all substitute samples.

[0011] Step S6: Based on the failure lifetime data of all alternative samples, obtain the failure lifetime of the conductive thermal interface material to achieve the reliability evaluation of the conductive thermal interface material.

[0012] According to the reliability evaluation method for conductive thermal interface materials of the present invention described above, it is possible to effectively evaluate the reliability of interfacial thermal resistance degradation caused by electromigration effects. Attached Figure Description

[0013] To more clearly illustrate the technical solutions of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort:

[0014] Figure 1 This is a flowchart of a reliability evaluation method for conductive thermal interface materials according to an embodiment of the present invention;

[0015] Figure 2 This is a schematic diagram of the structure of an alternative sample according to an embodiment of the present invention. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0017] One embodiment of the present invention provides a reliability evaluation method for conductive thermal interface materials, such as... Figure 1 As shown, the reliability evaluation method for conductive thermal interface materials in this embodiment of the invention includes steps S1 to S6.

[0018] Step S1: Preparation of substitute samples

[0019] This study analyzes the real-world application scenarios of conductive thermal interface materials in actual devices to determine the structure of the adhesive layer and sintering process parameters. For example, a certain device uses nano-silver paste conductive thermal interface material to bond a silicon chip to a copper base (copper substrate). The sintering process parameters are: slowly increasing the temperature from room temperature to 150°C at 10°C / min and holding for 20 min, then slowly increasing the temperature to 180°C at 5°C / min and curing for 60 min, followed by natural cooling to room temperature to complete sintering. Extensive research has shown that the composition of the actual adhesive material, the structure of the adhesive interface, and the sintering process of the conductive thermal interface material all affect the initial and degradation properties of the interface thermal resistance. Therefore, it is necessary to strictly refer to the actual composition and structure of the adhesive material and the sintering process of the conductive thermal interface material to prepare alternative samples. An example of the sample structure of the alternative sample is shown below. Figure 2 As shown, from top to bottom, the structure includes a silicon chip 1, a silicon chip surface plating layer 2, a conductive and thermal interface material adhesive layer (e.g., a nano-silver paste adhesive layer) 3, a copper substrate surface plating layer 4, and a copper substrate 5. Electrodes 6 are welded to the sides of the silicon chip 1 and the copper substrate 5 for interface thermal resistance testing and current stress loading. The silicon chip surface plating layer 2 and the copper substrate surface plating layer 4 above and below the conductive and thermal interface material adhesive layer 3 are, for example, gold-plated layers, to facilitate adhesion or conductivity.

[0020] Step S2: Failure Threshold Calculation

[0021] Analyzing the actual operating scenarios of the device, the interfacial thermal resistance failure threshold of the substitute sample was determined. Interfacial thermal resistance mainly includes the sum of the bulk thermal resistance of the thermal interface material and the contact thermal resistance between the thermal interface material and the upper and lower interfaces; that is, the region in the thermal interface material bonding structure prone to thermal resistance changes. The bulk thermal resistance is mainly related to parameters such as the thermal conductivity and thickness of the conductive thermal interface material, while the contact thermal resistance of the upper and lower interfaces is mainly related to the surface roughness and contact conditions of the bonding. Figure 1 In the figure, the bulk thermal resistance of the material corresponds to the bulk thermal resistance of the conductive thermal interface material adhesive layer 3, the upper interface contact thermal resistance corresponds to the contact thermal resistance of the interface between the conductive thermal interface material adhesive layer 3 and the silicon chip surface plating layer 2, and the lower interface contact thermal resistance corresponds to the contact thermal resistance of the interface between the conductive thermal interface material adhesive layer 3 and the copper substrate surface plating layer 4.

[0022] An example of how to determine the failure threshold is as follows: A certain type of device uses nano-silver paste conductive thermal interface material to bond the chip to the bottom copper metal base. Under normal operating conditions at room temperature, the device's power is P. During operation, due to the device's own heat generation, the actual internal temperature is T1. Under temperature T1, the device functions normally and its parameters meet technical requirements. As the ambient temperature is gradually increased from room temperature, the actual internal temperature of the device is simultaneously monitored. When the actual internal temperature reaches T2, the device's function and performance parameters fail to meet requirements.

[0023] As is well known, the actual internal temperature of a device is related to parameters such as its heat generation power and heat dissipation capacity. Degradation of the thermal resistance at the interface between the conductive and thermally conductive materials leads to a decrease in the device's heat dissipation capacity, which in turn causes an increase in the actual internal temperature. When the interface thermal resistance degrades to a certain threshold, the actual internal temperature of the device will increase from T1 to T2. The failure threshold of the interface thermal resistance can be calculated as follows:

[0024] (1)

[0025] That is, the increase in interfacial thermal resistance compared to the initial state before the test reached [amount missing]. If the ambient temperature is gradually increased, the device is considered to have failed due to its inability to function properly. For example, if a device has a working power of 20W and an actual internal temperature of 100℃ at room temperature, and the ambient temperature is gradually increased during testing, it is found that when the internal working temperature of the device increases to 120℃, the device's functional performance indicators do not meet the requirements. According to the formula, the failure threshold of the interface thermal resistance is 1℃ / W, that is, if the interface thermal resistance of the conductive thermal interface material increases by 1℃ / W compared to the initial state before the test, it can be considered as interface failure.

[0026] Step S3: Determine the thermoelectric stress test conditions

[0027] The actual working scenario of the device is analyzed to determine the thermoelectric stress test conditions for the substitute sample, mainly including the applied current and operating temperature. The temperature setting is the same as the actual operating temperature T1 of the device, and the current applied can be selected based on parameters such as the current density borne by the adhesive layer under actual device operation or the voltage difference between the upper and lower interfaces. In one embodiment, if the actual internal temperature of a device at room temperature is 100°C, then the temperature is set to 100°C; the current density borne by the conductive thermal interface material during operation is 40 A / cm. 2 The calculated current applied to the substitute sample was approximately 10A.

[0028] Determine the number of substitute samples based on actual needs, and test and record the initial interfacial thermal resistance of the substitute samples to be tested (the sum of the bulk thermal resistance of the thermal interface material and the contact thermal resistance between the thermal interface material and the upper and lower interfaces). For example, select 10 substitute samples for testing.

[0029] Step S4: Conduct thermoelectric stress test

[0030] Thermoelectric stress tests were conducted on the substitute specimens according to the determined current density and operating temperature stress:

[0031] (1) Temperature stress loading in thermoelectric stress test includes, but is not limited to, loading temperature stress by placing a substitute sample in a high-temperature chamber or on a heating plate;

[0032] (2) In thermoelectric stress tests, current stress loading is mainly achieved by using a constant DC power supply to replace the sample electrodes.

[0033] (3) Apply thermoelectric stress to all substitute samples according to the obtained temperature stress and current stress conditions, conduct thermoelectric stress tests, and stop the test after a period of time according to actual needs. Perform interface thermal resistance tests on the tested substitute samples and record the results. Interface thermal resistance test methods include, but are not limited to: steady-state heat flow method, laser flash method, time-domain thermal reflection method, frequency-domain thermal reflection method, etc.

[0034] In one embodiment, the test specimen is subjected to thermoelectric stress test under coupling conditions of 100°C and 10A current, and the thermoelectric stress test is stopped after a certain period of time to test the interfacial thermal resistance of the substitute specimen.

[0035] The thermal resistance test interval can be determined as follows: In the initial stage of the test, the test can be conducted every 15 or 20 days depending on the condition of the sample. When the increase in interface thermal resistance reaches 60% of the failure threshold, the test interval can be reduced to once every 3 or 5 days as appropriate. When the increase in interface thermal resistance reaches 90%, the test interval can be reduced to once every 1 day or 0.5 days as appropriate.

[0036] Step S5: Obtain the failure lifetime

[0037] During the interfacial thermal resistance test of the substitute test specimens, if the increase in the interfacial thermal resistance of the substitute test specimens does not exceed the threshold, the thermoelectric stress test continues under the original conditions; if the increase in the interfacial thermal resistance of the substitute test specimens exceeds the threshold, the thermoelectric stress test of the substitute test specimens is stopped, and the test time is recorded as the failure life. All tests are stopped when the increase in the interfacial thermal resistance of all substitute test specimens exceeds the threshold.

[0038] Step S6: Conduct a reliability assessment

[0039] Organize and analyze all failure lifetime data to obtain the failure lifetime of the conductive thermal interface material. Specific methods include, but are not limited to, the following:

[0040] Average lifetime, for example: the average failure lifetime of 10 substitute samples;

[0041] Quantitative lifetime, for example: to obtain the 0.2 quantile lifetime, sort the failure lifetimes of 10 substitute samples from smallest to largest, and take the second lifetime data as the 0.2 quantile lifetime;

[0042] Distributional statistical lifetime, for example: fitting the failure lifetime data of 10 substitute samples into a distribution. Users can choose statistical methods, including but not limited to normal distribution and Weibull distribution, according to the actual situation, and confirm the failure lifetime of the substitute samples based on the statistical distribution.

[0043] The following example provides a more detailed description of the reliability evaluation method for conductive thermal interface materials according to an embodiment of the present invention.

[0044] In step S1, a certain type of device uses nano-silver paste conductive thermal interface material to bond the chip to the bottom copper metal base. The bonding process parameters are: slowly raise the temperature from room temperature to 150℃ at 10℃ / min and hold for 20min, then slowly raise the temperature to 180℃ at 5℃ / min and cure for 60min, and then naturally cool to room temperature to complete the sintering. Ten alternative samples are made with reference to the actual composition and structure of the device and the sintering process of the conductive thermal interface material.

[0045] In step S2, the device operates at a power of 20W, and the actual internal temperature of the device is 100℃ at room temperature. The testers gradually increased the ambient temperature and found that when the internal operating temperature of the device increased to 120℃, the device's functional performance indicators did not meet the requirements. According to the formula, the failure threshold of the interface thermal resistance is 1℃ / W, that is, the interface thermal resistance of the conductive thermal interface material increases by 1℃ / W compared with the initial state before the test, which can be considered as interface failure.

[0046] In step S3, the current density that the conductive thermal interface material of the device withstands during operation is 40 A / cm². 2 The calculated current applied to the substitute sample is approximately 10A.

[0047] In step S4, the test sample is subjected to thermoelectric stress test under high temperature of 100°C and current of 10A coupling conditions, and the thermoelectric stress test is stopped after a certain period of time to test the interface thermal resistance of the substitute sample.

[0048] In step S5, the failure lifetime data of all substitute samples are obtained. The initial interfacial thermal resistance data and failure lifetime data of all substitute samples are shown in the table below:

[0049] Test data table

[0050]

[0051] In step S6, based on the above test data, we can obtain the following: the average lifespan is 6310h, the 0.2 quantile lifespan is 6200h, the average value is 6310h and the standard deviation is about 120h according to the normal distribution. We can calculate that there is a 75% probability that the test lifespan is greater than 6400h.

[0052] In summary, the reliability evaluation method for conductive thermal interface materials in this invention involves: analyzing the structure of actual devices to prepare alternative samples for the bonding interface of conductive thermal interface materials; determining the failure threshold of the alternative samples based on the degradation of interface thermal resistance by analyzing the actual operating conditions of the devices; monitoring the degradation of interface thermal resistance at intervals by conducting high-temperature and current stress coupling tests on the samples; and determining the failure life of the samples by analyzing the interface thermal resistance degradation data.

[0053] The reliability evaluation method for conductive thermal interface materials in this invention assesses the reliability of the bonding interface from the perspective of the degradation of interfacial thermal resistance caused by electromigration effects, and then determines the failure lifetime of the bonding interface. This effectively fills the technical gap in this field in traditional solutions and provides a new solution for the reliability evaluation of conductive thermal interface materials. In recent years, the industry has invested a great deal of time and economic resources in developing high-performance, high-reliability conductive thermal interface materials such as micro / nano silver and nano copper paste. This invention can accurately evaluate the reliability of such conductive thermal interface materials, which is conducive to accelerating their rapid market application. Therefore, this invention has significant economic and social benefits.

[0054] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A reliability evaluation method for conductive thermal interface materials, characterized in that, include: Step S1: Prepare a substitute sample based on the actual device’s conductive thermal interface material bonding layer structure and sintering process. The sample structure of the prepared substitute sample, from top to bottom, includes a silicon chip, a silicon chip surface coating, a conductive thermal interface material bonding layer, a copper substrate surface coating, and a copper substrate. Electrodes are welded to the sides of the silicon chip and the copper substrate for interface thermal resistance testing and current stress loading. Step S2: Gradually increase the ambient temperature to test the actual device. The increase in interface thermal resistance when the device performance fails to meet the requirements is taken as the failure threshold of interface thermal resistance. The interface thermal resistance is the sum of the bulk thermal resistance of the thermal interface material and the contact thermal resistance between the thermal interface material and the upper and lower interfaces. The bulk thermal resistance of the thermal interface material corresponds to the bulk thermal resistance of the conductive thermal interface material adhesive layer. The upper interface contact thermal resistance corresponds to the contact thermal resistance between the conductive thermal interface material adhesive layer and the silicon chip surface plating layer. The lower interface contact thermal resistance corresponds to the contact thermal resistance between the conductive thermal interface material adhesive layer and the copper substrate surface plating layer. Step S3: Determine the thermoelectric stress test conditions for the substitute sample, set the temperature to the normal operating temperature of the device, determine the current stress based on the current density of the adhesive layer or the voltage difference between the upper and lower interfaces under the actual working conditions of the device, determine the number of substitute samples and test the initial interfacial thermal resistance of the substitute samples. Step S4: Apply thermoelectric stress to all substitute samples according to the set temperature stress and current stress conditions, carry out thermoelectric stress test, stop the test after a period of time, and perform interface thermal resistance test on the substitute samples. Step S5: When the increase in the interfacial thermal resistance of the substitute sample does not exceed the failure threshold, continue to perform the thermoelectric stress test; when the increase in the interfacial thermal resistance of the substitute sample exceeds the failure threshold, stop the thermoelectric stress test of the substitute sample and record its test time as the failure life, until the increase in the interfacial thermal resistance of all substitute samples exceeds the failure threshold, then stop the test of all substitute samples. Step S6: Based on the failure lifetime data of all substitute samples, obtain the failure lifetime of the conductive thermal interface material to achieve the reliability evaluation of the conductive thermal interface material. In step S6, obtaining the failure lifetime of the conductive thermal interface material includes averaging the failure lifetimes of all substitute samples; sorting the failure lifetimes of all substitute samples from smallest to largest to obtain the 0.2 quantile lifetime; fitting the failure lifetime data of all substitute samples and obtaining the failure lifetime of the conductive thermal interface material according to the statistical distribution, which includes the normal distribution and the Weibull distribution.

2. The method as described in claim 1, characterized in that, In step S2, the failure threshold is calculated as follows: ， Where ΔR is the failure threshold of the interface thermal resistance, P is the normal operating power of the device, T1 is the normal operating temperature of the device, and T2 is the temperature at which the device performance cannot meet the requirements.

3. The method as described in claim 1, characterized in that, In step S4, the temperature stress loading in the thermoelectric stress test includes placing the substitute sample in a high-temperature chamber or on a heating plate, and the current stress loading is achieved by connecting a constant DC power supply to the electrodes of the substitute sample.

4. The method as described in claim 1, characterized in that, Methods for testing interfacial thermal resistance include steady-state heat flow method, laser flare method, time-domain thermal reflection method, and frequency-domain thermal reflection method.

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