Various types of epoxy/BN composites were prepared to optimize material conditions for high thermal conductivity and high breakdown strength. The best composite was found to be epoxy/conglomerated h-BN/ nano silica nano micro composite with thermal conductivity 12 W/m·K and BD strength 15 kV peak /0.2 mm. One of the most important factors to obtain high values of the two performances is to reduce void content. Surface treatment of fillers and nano filler addition are also useful.
Various types of epoxy/BN composites were prepared to optimize material conditions for high thermal conductivity and high breakdown strength. The best composite was found to be epoxy/conglomerated h-BN/nano silica nano micro composite with thermal conductivity 12 W/m·K and BD strength 15 kV peak /0.2 mm. One of the most important factors to obtain high values of the two performances is to reduce void content. Surface treatment of fillers and nano filler addition are also useful.
Recently, SiC (silicon carbide) has attracted attention as a new material to replace silicon power semiconductors. Since SiC is a wide-bandgap semiconductor and has high heat resistance, it can be operated in a high temperature environment. However, the conventional power module package is mainly joined by a low melting point material such as lead-free solder, and interconnection does not have enough heat resistance. Therefore, we have been proposing and experimenting with Nickel Micro-Plating Bonding (NMPB) using Ni (nickel), which has excellent heat resistance and strong bonding strength, as a new bonding method. Although various researches have been conducted on the bonding reliability of NMPB, long-term reliability evaluated from the aspect of metal fatigue has not been much discussed. In this study, a test has been conducted using a resonant type fatigue testing machine and examined whether acceleration of fatigue evaluation time and long-term reliability of NMPB were confirmed.
The improvement of interconnection technology is becoming a top priority for the operation of high power devices such as SiC at higher temperatures. We proposed a interconnection method using Nickel Nano-particles direct bonding to form bonds between the chip electrodes and substrates. SiC devices assembled with the Ni bonding interconnection were confirmed to be operated successfully in a high temperature environment over 300 °C.
Oxidative degradation of polypropylene (PP) is accelerated by not only sunlight but also temperature. Here we propose how the degradation behavior of PP under ultraviolet light irradiation conditions at elevated temperatures, which are more severe than the standards set by the Japanese Industrial Standards (JIS), can be examined. Fourier-transform infrared spectroscopy in conjunction with gel permeation chromatography revealed that the combination of light and heat definitely accelerated the chain scission, or oxidative degradation, of PP, resulting in deterioration of mechanical properties for PP.
Infancy trees, i.e. trees in their early stage, in neat epoxy and epoxy/silica nanocomposite were investigated in terms of their generation time and morphology. Generation time represented by V-t characteristics obeys a formula V oc t −n . It is to be noted that similar effects are imposed not only on mm order long trees but also on several tens µm order short infancy trees. Infancy tree generation time is increased by nano filler 5 wt% addition and by surface treatment of nano filler. The same thing can be said to a value "n". As for morphology of the infancy trees, it was clarified from optical microscope observation that there is no significant difference either in epoxy or in nanocomposite, as far as their lengths are almost the same. An infancy tree seems to grow at first between neighboring nano filler particles and to extend by contacting nano filler particles in their growing path. Since the infancy tree is thin in the beginning and becomes thick afterwards, chance of the tree to meet with nano filler is considered to be increase.
Aiming for application to the inverter system of HEV and EV, we have developed a novel packaging technique for SiC power devices based on Nickel Micro Plating Bonding (NMPB) technique. We implemented heat resistant mounting of SiC schottky barrier diode (SBD) on the TO247 type package and confirmed the rectifying behavior even after the high temperature storage for 500hr at 250°C without any significant degradations. We also fabricated one-leg inverter modules mounting SBDs and MOSFETs using newly designed lead frames for NMPB process. The module showed normal rectifying and switching behavior even at high temperature such as about 250°C.
In this investigation, four kinds of epoxy/silica nanocomposites with different sizes of nano-fillers were experimentally investigated on treeing breakdown lifetime. The nanocomposite specimens used included 3 wt% nano-fillers of 12, 40, 90 and 300 nm in size, and were prepared with and without silane-coupling agents for evaluation. According to SEM observation, nano-fillers were considered to be well dispersed in all the specimens used. As a result, it was found that the nanocomposite specimens with 12 nm size fillers own much longer tree breakdown time than neat epoxy and other epoxy nanocomposite specimens under applied voltage of 10 to 30 kVrms. Difference in lifetime between neat epoxy and nanocomposites with 12 nm size fillers tends to be enlarged, as applied voltage is lowered. Furthermore, it was confirmed that the addition of coupling agents would help increase lifetime. The coupling in the interfaces is considered to suppress tree propagation in this process.
The improvement of interconnection technology is becoming a top priority for the operation of SiC devices at high temperatures. We proposed a new interconnection method using nickel electroplating to form bonds between chip electrodes and substrate leads. We also newly proposed low-temperature nickel nanoparticle sintering to form die bonding connections. SiC devices assembled with these new connection methods operated successfully in a high-temperature environment of about 300°C. We confirmed that these methods had adequate potential as an advanced heat resistant package in comparison with conventional interconnections.
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