Abstract
This paper investigates the degradation mechanism of pressure-sintered silver (s-Ag) film for silicon carbide (SiC) chip assembly with a 2-millimeter-thick copper substrate by means of thermal shock test (TST). Two different types of silver paste, nano-sized silver paste (NP) and nano-micron-sized paste (NMP), were used to sinter the silver film at 300 °C under a pressure of 60 MPa. The mean porosity (p) of the NP and MNP s-Ag films was 2.4% and 8%, respectively. The pore shape of the NP s-Ag was almost spherical, whereas the NMP s-Ag had an irregular shape resembling a peanut shell. After performing the TST at temperatures ranging from −40 to 150 °C, the scanning acoustic tomography (SAT) results suggested that delamination occurs from the edge of the assembly, and the delamination of the NMP s-Ag assembly was faster than that of the NM s-Ag assembly. The NMP s-Ag assembly showed a random delamination, indicating that the delamination speed varies from place to place. The difference in fracture mechanism is discussed based on cross-sectional scanning electron microscope (SEM) observation results after TST and plastic strain distribution results estimated by finite element analysis (FEA) considering pore configuration.
Highlights
Reducing CO2 emissions has become one of the most pressing issues worldwide for safe ecology
The two representative scanning electron microscope (SEM) images show that the nano-sized silver paste (NP) s-Ag has almost spherical pores, whereas the nano-micronsized paste (NMP) s-Ag has irregular pore shapes resembling peanut shells
The fracture area of the NMP assemblies showed a random delamination pattern indicating that degradation speed varied from place to place
Summary
Reducing CO2 emissions has become one of the most pressing issues worldwide for safe ecology. The replacement of fuel vehicles with electric vehicles (EVs) is progressing. EVs demand high power density systems to miniaturize the car body and expand interior living spaces. Power modules with high power density and that are small have been one of the main trends in EV power conversion [1]. Wide bandgap (WBG) semiconductor devices, such as SiC and GaN, contribute significantly because WBG devices possess excellent performance of low resistance loss and switching loss [2]. To draw out device properties and apply them for power modules, new thermal management is essential, because the increase in device thermal density with chip size reduction becomes a more decisive problem than the reduction in heat generation loss
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