Hideki Mizuhara

Development of a laser processing technology for high thermal radiation multilayer module

We developed a laser drilling technique using UV laser (lambda=355nm) for epoxy resin that includes aluminum oxide filler at high density to realize a high thermal radiation multilayer module. By studying the laser condition to see what conditions enable the via hole to make good contact with the metal layer, it was found that both laser fluence and a beam diameter had threshold. Here threshold fluence was lower than threshold diameter, so when the diameter was smaller than the threshold, unprocessed aluminum oxide filler remained in the via hole. Hence, when the resin with high density filler was irradiated with a UV laser, while the resin evaporated the aluminum filler with high melting point was hardly processed but rather discharged from the via hole with the gaseous resin. It follows from this that high speed drilling by low laser fluence is possible when the filler size is smaller than the via hole diameter, and we realized a high thermal radiation multilayer substrate at low cost. Applying the developed laser drilling technique, we made inverter modules. Measuring the temperature distribution using IR camera, heat from the power device was diffused to the metal substrate through thermal via holes

Improvement of the spin-on-glass process by ion implantation for highly reliable MOS devices

We have developed a novel process for intermetal dielectrics (IMD) using ion-implanted organic spin-on glass (SOG). Ion implantation into the SOG films improves the hot carrier (HC) reliability, which deteriorates from the use of organic SOG films. The content of mobile water-related species in the organic SOG films, which was examined by thermal desorption spectrometry (TDS), is reduced by Art-ion implantation under the conditions of 140 keV, 1 x 10 15 ions/cm 2 ; while on the contrary, the content of mobile hydrogen in SOG is increased by ion implantation. The change in the mechanical stress due to ion implantation is small, because ion implantation shrinks SOG only in the direction vertical to the wafer surface. Thus the change in stress due to ion implantation scarcely affect the electrical characteristics of the underlying MOS-FET. Therefore the deterioration of HC reliability for the MOS devices with SOG as IMD is well explained by a water diffusion model rather than by a hydrogen diffusion and mechanical stress model.

Development of Material and Processing Technology for High Thermal Conductive Multilayer Module

We have developed a multilayer substrate that is formed from a high thermal conductive resin including ceramic fillers at high density in order to realize a module that is more miniaturized and has lower thermal resistance. First, we realized a resin with a very high filler filling rate of 75% by mixing two kinds of spherical fillers different in particle size. The thermal conductivity of the insulation resin films we developed is 4.4 W/mK. And we were able to make resin films with a thickness from 35 mum-120 mum. Additionally, with the improvement of adhesion between Cu and resin affected by control of the resin fluidity and filler diameter, a high thermal conductive multilayer substrate could be realized. The reliability of the high thermal conductive multilayer substrate formed from the developed resin was then investigated. Even after 1000 cycles of HC test (heat cycle test: 233 K-398 K, 30 minutes at each temperature), the resistance of the daisy chain pattern did not change. The THB test results (temperature, humidity, and bias test: 358 K, 85% RH, 50 V), showed that an insulation layer of more than 60 mum thickness gives enough dielectric reliability. Finally, we made a high voltage (350 V) drive inverter power supply circuit module for automobile applications including the high thermal conductive multilayer substrate we developed. Applying a multilayer substrate enabled the inverter module to be downsized to 85% of the one with a conventional monolayer substrate. Further, the thermal resistance of the miniaturized module was the same as the conventional module. In addition, the results of HC test and THB test indicated that the reliability of the developed module is sufficient for automobile applications.