Kiyoshi Hasegawa

Rearrangeable and exchangeable optical module with system-on-chip for wearable functional near-infrared spectroscopy system

Abstract. We developed a system-on-chip (SoC)-incorporated light-emitting diode (LED) and avalanche photodiode (APD) modules to improve the usability and flexibility of a fiberless wearable functional near-infrared spectroscopy (fNIRS) system. The SoC has a microprocessing unit and programmable circuits. The time division method and the lock-in method were used for separately detecting signals from different positions and signals of different wavelengths, respectively. Each module autonomously works for this time-divided-lock-in measurement with a high sensitivity for haired regions. By supplying +3.3  V of power and base and data clocks, the LED module emits both 730- and 855-nm wavelengths of light, amplitudes of which are modulated in each lock-in frequency generated from the base clock, and the APD module provides the lock-in detected signals synchronizing with the data clock. The SoC provided many functions, including automatic-power-control of the LED, automatic judgment of detected power level, and automatic-gain-control of the programmable gain amplifier. The number and the arrangement of modules can be adaptively changed by connecting this exchangeable modules in a daisy chain and setting the parameters dependent on the probing position. Therefore, users can configure a variety of arrangements (single- or multidistance combinations) of them with this module-based system.

Electroless Ni/Pd/Au plating for semiconductor package substrates-effect of gold plating combinations on gold wire bonding reliability

In order to investigate the root causes of the good wire bonding reliability in electroless Ni/Pd/Au plating (ENEPIGEG), the wire bonding reliability of the combinations with electrolytic and electroless processes were evaluated. The reliability of ENEPIGEG and electrolytic Ni (SB-Watt)/IGEG were equivalent to that of the conventional electrolytic Ni (SB-Watt)/electrolytic Au and were excellent. The reliability of electrolytic Ni (SB-Watt)/IGEG was higher than that of EN/Electrolytic Au after heat treatment. We found that the grain size of the gold deposit coordinated with the grain size of the underplated Ni deposit with the epitaxial crystal growth. The large grain size of the gold deposit decreased the grain boundary of the gold deposit and reduced the grain boundary diffusion from the underplated metals onto the gold plating. We concluded that the wire bonding reliability after heat treatment depended on the diffusion behavior of the underplated metals and the grain size of the gold deposit.