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User Benefits Application News Fig. 2 Test Fixture Fatigue testing machine : EHF-LV Load cell : 5 kN Test fixture : SiC chip fixture with fine-adjustment stage (prototype) Controller : Servo Controller 4830 Software : Windows software for 4830 X-ray CT instrument : inspeXio SMX-225CT FPD HR Plus Fig. 1 Dimensions of Test Specimen (SiC Chip Thickness: 0.35 mm) Fig. 1 shows a schematic diagram of the test specimen. A SiC chip with a one-side length of 3 mm and thickness of approximately 0.35 mm was bonded to the center of a copper substrate with a one-side length of 24 mm. Fig. 2 shows the test fixture. Since the deformation of the bond during the test is extremely small, in addition to the stroke of the testing machine, displacement was also measured using a laser displacement sensor. The target SiC chip is also very brittle, and cracking will occur, originating from the loading point, if the load is concentrated on one point. Since this would make it impossible to evaluate the bond surface, the fixture was equipped with a fine-adjustment stage so that compression could be applied uniformly to the entire surface on the SiC chip, and the indenter contact angle and test position were adjusted while observing the specimen on a monitor. Fig. 3 shows the condition of specimen position adjustment, and Table 1 shows the instrument configuration. After the endurance test, the specimen was observed by X-ray CT. Specimen Information and Measurement System Table 1 Instrument Configuration Fig. 3 Condition of Specimen Position Adjustment Silver (Ag) sinter joining is a technique in which particles are bonded together by heating/compression of a paste containing silver particles. In recent years, attention has focused on EVs (electric vehicles) as a key technology for realizing a decarbonized society, and wide bandgap power semiconductors such as SiC, which are expected to reduce energy loss and provide excellent heat conduction/heat resistance, have become indispensable for improving EV performance. In particular, with the use of large current/high density power semiconductors, performance under high temperature environments is now required. To achieve this, Ag sinter joining has attracted interest, as Ag sintered bonds can maintain good mechanical properties under higher temperature environments than conventional solder bonds. In this article, a shear fatigue test of the bond between a SiC chip and a copper substrate formed by silver sinter joining was conducted using a Servopulser dynamic and fatigue testing system, and the fracture mode of the SiC chip after an endurance test was observed using X-ray CT. Introduction Shear fatigue testing of SiC chips mounted by silver sintering is possible by using a SiC chip fixture with a fine-adjustment stage. High-accuracy dynamic control can be achieved by using the Servo Controller 4830. X-ray CT allows nondestructive observation of the internal condition of SiC chips and Ag sintered bonds. Durability Evaluation of Bond Between SiC Chip and Copper Substrate Joined with Silver Sintering Die Attach Material Fumiaki Yano, Satoshi Iguchi Servopulser EHF-L Series Tabletop Dynamic and Fatigue Testing System inspeXio SMX -225CT FPD HR Plus Microfocus X-Ray CT System 24 3 SiC chip Cu substrate Indenter Laser displacement sensor Chip fixture with fine- adjustment stage Specimen Check of SiC chip position by monitor Adjustment of parallelism of SiC chip and indenter Adjustment of distance between SiC chip and indenter SiC chip Indenter Indenter SiC chip
Application News Fig. 4 Test Force-Displacement Diagram Static Shear Test To set the conditions for the fatigue test, first, a static shear test was carried out. Table 2 shows the test conditions of the static shear test, Fig. 4 shows the test force-displacement diagram of respective test specimens, and Fig. 5 shows examples of the test specimens after the test. In Fig. 5 (a), the SiC chip has fractured, and in Fig. 5 (b), shear fracture has occurred. Table 3 summarizes the test results. The results in Table 3 are the results excluding fracture of the SiC chip. Test speed : 0.1 mm/min Origin point of elongation : 5N Number of tests : n = 3 Table 2 Test Conditions Test force [N] Displacement [mm] (a) Fig. 5 Examples of Test Specimens after Test (a) Fracture of SiC chip (b) Shear fracture Test No. Max. test force [N] Max. stroke [mm] Max. displacement [mm] 1 310.39 0.0569 0.0527 2 316.98 0.0477 0.0446 43 317.97 0.0510 0.0496 Average 315.11 0.0519 0.0489 Standard deviation 4.12 0.0047 0.0041 Coefficient of variation 1.31 8.99 8.36 Table 3 Instrument Configuration Endurance Test An endurance test was conducted with specimens A and B. The condition of the endurance test was set to a displacement- control maximum stroke of 0.03 mm for the average maximum stroke of 0.0519 mm in the static shear test. Table 4 summarizes the conditions of the endurance test. Fig. 6 shows the waveform at 10000 cycles for specimen A. From Fig. 6 (a), it can be understood that the stroke could be controlled to approximately a sine wave, as targeted. Fig. 6 (b) shows the test force-stroke diagram. As the results of the endurance test, Fig. 7 shows graphs of the characteristic values of the peak values of specimens A and B. From Fig. 7, the peak values of the test force during the test show approximately constant values, and brittle fracture occurred instantaneously on reaching the number of cycles to fracture. The number of cycles to fracture was 17988 for specimen A and 19262 for specimen B. Control method : Stroke control Maximum stroke : 0.03 mm Frequency : 1 Hz Number of tests : 2 (specimen A, specimen B) Table 4 Conditions of Endurance Test Fig. 6 Waveform of Specimen A at 10000 Cycles (a) Time-Test Force-Stroke Diagram, (b) Test Force-Stroke Diagram Fig. 7 Results of Endurance Test (a) Graph of Characteristic Values of Peak Values for Specimen A (b) Graph of Characteristic Values of Peak Values for Specimen B Table 1 Instrument Configuration (b) (a) Time (sec) (b) Cycles Cycles (a) (b)
Application News Fig. 10 X-Ray CT Images of Specimen B (a) Cross-Sectional Image of Ag Sintered Bond Layer from Above SiC Chip Surface (b) Cross-Sectional Image from Side of SiC Chip (Horizontal) (c) Cross-Sectional Image from Side of SiC Chip (Vertical) Fig. 8 Appearance of Specimens after Endurance Test (a) Specimen A (b) Specimen B Fracture Observation by X-Ray CT Fig. 8 shows photographs of the specimens after the endurance test. In specimen A, a crack has occurred in part of the upper right area of the chip, and some of the sintered die attach material on the underside of the chip has delaminated. In specimen B, the entire chip is heavily damaged. Nondestructive observation of the respective specimens was carried out by X- ray CT. Fig. 9 shows X-ray CT images of specimen A. From Fig. 9 (a), it was found that damage had occurred in the Ag sintered bond layer directly under the damage of the SiC chip observed by visual inspection. From Fig. 9 (b), it can be understood that the crack in the Ag sintered bond layer reached the Cu substrate. In Fig. 9 (c), although the Ag sintered bond layer is damaged, the SiC chip itself is almost undamaged, but delamination of the Ag sintered bond layer under the SiC chip was observed. (a) (b) Partial damage of SiC chip Partial delamination of sintered material Heavy damage of SiC chip (a) Loading direction Crack of Ag sintered bond material Ag sintered bond layer Cu substrate Fracture of Ag sintered bond layer SiC chip Ag sintered bond layer Cu substrate (b) Fracture of Ag sintered bond layer Delamination of Ag sintered bond layer (c) Loading direction (a) Crack of Ag sintered bond material Fracture of Ag sintered bond layer (b) Fracture of Ag sintered bond layer (c) (b) (c) (b) (c) Fig. 9 X-Ray CT Images of Specimen A (a) Cross-Sectional Image of Ag Sintered Bond Layer from Above SiC Chip Surface (b) Cross-Sectional Image from Side of SiC Chip (Horizontal) (c) Cross-Sectional Image from Side of SiC Chip (Vertical) Fig. 10 shows X-ray CT images of specimen B. In Fig. 10 (a), a crack was observed in the lower left part of the Ag sintered bond layer. In Fig. 10 (b) and (c), fracture was observed in the Ag sintered bond layer, but delamination was not observed under the SiC chip. It is thought that delamination did not occur in specimen B because the SiC chip fractured over a wide range. Fig. 11 (a) shows an X-ray CT image of the crack in the SiC chip of specimen B. In this image, part of the crack in Fig. 8 (b) was observed. From Fig. 11 (b) and (c), it was found that this crack in the SiC chip did not reach the Ag sintered bond layer.
Application News www.shimadzu.com/an/ Shimadzu Corporation © Shimadzu Corporation, 2025 For Research Use Only. Not for use in diagnostic procedures. This publication may contain references to products that are not available in your country. Please contact us to check the availability of these products in your country. The content of this publication shall not be reproduced, altered or sold for any commercial purpose without the written approval of Shimadzu. See https://www.shimadzu.com/about/trademarks/index.html for details. Third party trademarks and trade names may be used in this publication to refer to either the entities or their products/services, whether or not they are used with trademark symbol “TM” or “”. Shimadzu disclaims any proprietary interest in trademarks and trade names other than its own. The information contained herein is provided to you "as is" without warranty of any kind including without limitation warranties as to its accuracy or completeness. Shimadzu does not assume any responsibility or liability for any damage, whether direct or indirect, relating to the use of this publication. This publication is based upon the information available to Shimadzu on or before the date of publication, and subject to change without notice. First Edition: Dec. 2025 01-01049-EN Conclusion Servopulser, inspeXio, and SMX are trademarks of Shimadzu Corporation or its affiliated companies in Japan and/or other countries. An endurance test of SiC chips was conducted using the Servopulser dynamic and fatigue testing system. Satisfactory testing was possible by using a SiC chip fixture with a fine- adjustment mechanism. Use of X-ray CT allowed detailed observation of the fracture of SiC chips. <Related Applications> 1. Cross-Sectional Analysis of Power Semiconductor and Silver Sintering Die Attach Material, Application News No. 01-00989 Fig. 11 X-Ray CT Images of Specimen B (a) Cross-Sectional Image of SiC Chip from Above SiC Chip Surface (b) Cross-Sectional Image from Side of SiC Chip (Horizontal) (c) Cross-Sectional Image from Side of SiC Chip (Vertical) (a) Loading direction Crack of SiC chip SiC chip Cu substrate (b) Crack of SiC chip (c) Crack of SiC chip Cu substrate Ag sintered bond layer (b) (c)
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