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In this work, an acoustic emission (AE) technique was applied to online condition monitoring (CM) of solder fatigue in a clip-bonding SiC mosfet power assembly during short and long power cycling tests (PCTs). Solder fatigue caused by PCTs was identified in the clip-bonding assembly via scanning acoustic tomography and scanning electron microscopy and successfully diagnosed via the AE-based online CM. By analyzing AE signals, junction temperature, and junction-to-case thermal resistance, it can be confirmed that the AE signal shows a superior sensitivity in initial fatigue diagnosis to the thermal or electrical signals. Meanwhile, two solder fatigue processes, cracking initiation and cracking acceleration, were identified based on the cumulative AE counts and AE energy during the long PCT. An abrupt increase in AE energy happened at the end stage of the long PCT due to a severe cracking process, which can be regarded as a prewarning of a failure point of the power assembly. In addition, the relationship between transitional thermal resistance and accumulative AE energy was investigated and shows a linear relationship. These results suggest that the AE technique can be a promising online CM approach to diagnose and predict solder fatigue in power assemblies during operation. [ABSTRACT FROM AUTHOR]

In this article, an SiC die was directly attached on a bare DBA (Al/AlN/Al) substrate via micron-sized Ag sintering at 250 °C without pressure. The micron-sized structure of the Ag–Al joint revealed robust bonding (33.6 MPa), which was attributed to the excellent sinterability of the Ag paste. A high-temperature storage test was conducted for 1000 h at 250 °C, and the thermal shock test was conducted from −50 to 250 °C for 2000 cycles. The shear strength was >30 MPa even after 1000 h of high-temperature storage. Furthermore, the online thermal resistance (Rth) of the direct bonding of SiC–DBA was measured during the power cycling test employing an n-doped 4 H-SiC thermal engineering group (TEG) chip. The SiC–TEG chip exhibited ultra-high power density (1200 W/cm2) and ensured that the junction temperature reached 200 °C. The total Rth increased from 0.58 to 0.7 K/W after 10 000 power cycles at a swing temperature, ΔTj, of 175 °C, indicating that the increase in the Rth was 20.7% at such a large power density. The results revealed that the SiC–DBA power module structure exhibited very good bonding and thermal-resistance reliability, which can be employed as a new structure for next-generation SiC power modules. [ABSTRACT FROM AUTHOR]

Despite the rapid progression of silicon carbide (SiC) power devices, the thermal characteristic evaluation during power cycling at high temperature (>200 °C) is an issue. In this article, a fast and miniaturized evaluation system with online thermal characteristic measurement function was introduced by an n-doped 4H SiC thermal engineering group (TEG) chip. Online thermal resistance measurement of a power module structure by Ag sinter joining with micron/submicron Ag particles paste in low temperature, low pressure, and cooling system by a thermal interface material bonding was performed. High-temperature reliability was systemically investigated by power cycling tests by switching on/off the power source which is connected to the SiC-TEG chip by Au wires. The total thermal resistance of the power module from the SiC-TEG chip to the cooling system increased from 0.5 to 0.53 K/W with the enhanced power source, and remained almost same after 20 000 power cycling at a swing temperature ΔTj of 150 °C. Furthermore, the SiC-TEG power module structure with the die attached with Pb and Pb-free solders, alongwith the same power source as sinter Ag paste was also measured. The Ag sinter joint possesses the lowest thermal resistance and highest high temperature reliability during power cycling compared with Pb and Pb-free die-attach materials. [ABSTRACT FROM AUTHOR]

In the article, acoustic emission (AE) was applied to monitor the wear-out failure in discrete SiC Schottky barrier diodes devices with a Ag sinter die attach to successfully monitor the real-time progress of failure of Al ribbons for the first time. After eliminating background AE noise including the power on–off switch and the ambient noise via a noise filtering process, AE signals were successfully collected for the SiC devices during a power cycling test. Furthermore, AE monitoring was compared to the traditional failure monitoring method using forward voltage. Physics-of-failure analysis was performed, and fatigue cracks, and lift-off in Al ribbons were confirmed as the dominant failure modes for the discrete devices. Specifically, AE counts that correspond to one of the time-domain parameters of AE signals increased with power cycling, thereby corresponding to the observed fatigue cracks in Al ribbons leading to lift-off failure. Additionally, the AE count rate was highly correlated with the crack growth rate. Based on the relationship between an AE count rate and fatigue crack growth rate, the results indicate that AE monitoring can be used to understand the fatigue propagation in Al ribbons (i.e., failure mechanism) and also as an early warning before catastrophic lift-off fracture for power electronic devices. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) power modules with Ag sinter-bonding die attach were designed on the basis of thermal stress analysis for reliable high-temperature operations. Both the finite-element analysis (FEA) simulations and preliminary experiments confirmed that inserting the direct-bonded-copper (DBC) substrates can effectively reduce the maximum thermal stress in the module. A prototype SiC power module using sintered Ag die attach with a DBC substrate was designed and fabricated. The modules exhibited excellent durability in power cycling between 65 °C and 250 °C up to 20 000 cycles. FEA calculations of cumulative thermal strain and stress distributions adequately predicted the initial cracking position in the specimens after prolonged power cycles, observed by scanning electron microscopy. [ABSTRACT FROM AUTHOR]