Takao Higashimachi

Microjoining of LSI chips on poly(ethylene naphthalate) using compliant bump

We show that microjoining of LSI chips on a film made of poly(ethylene naphthalate) (PEN), whose glass transition temperature is 155 °C, can be realized by using a cone-shaped compliant bump for flexible electronics. A 20-µm-pitch area array of cone-shaped Au bumps was fabricated on a Si wafer by photolithography and electroplating. The counter electrode on the PEN film was composed of a Au (top)/Ni/Al (bottom) layered structure, where Ni and Au layers were deposited by electroless plating on patterned Al. The bonding was carried out at 150 °C. More than 10,000 connections with 108 mΩ/bump were achieved. Mechanical analysis using finite element method indicates that the joining is due to deformation of the cone-shaped Au bumps.

Compliant bump technology for back-side illuminated CMOS image sensor

We have developed a compliant bump technology for 3D chip stacking with the same number of inter-chip connections as that in a VGA (video graphic array, 640 × 480). Using this technology together with a through-Si via (TSV) technology, we demonstrate a prototype of back-side illuminated CMOS image sensor, in which a very-thin rear-illuminated photodiode array is electrically connected to the CMOS readout circuit at a pixel level.

Finite Element Analysis of External, Middle and Inner Ear under Loads through Temporomandibular Joint

A structural analysis model including the temporomandibular joint (TMJ), external auditory canal, tympanic membrane, auditory ossicles and cochlea was made. Loads through the TMJ were applied to this model in three-dimensional finite element analysis. It became clear that stress concentration occurred at the lower portion of the external auditory canal, superior tympanic portion (attic), incus long crus, stapes crus and inlet of cochlea. The lower portion of the external auditory canal and attic are favourite sites of cholesteatoma (pearl tumour). Incus long crus and stapes crus are favourite sites of auditory ossicular defects, which are the cause of otitis media. Damage of the cochlea entrance causes high-frequency hearing loss which is age-related.