Masao Tomikawa

Novel high refractive index positive-tone photosensitive polyimide for microlens of image sensors

A novel high refractive index positive-tone photosensitive polyimide (posi-PSPI) has been successfully developed. The posi-PSPI has a refractive index of 1.78 at 633 nm and good transparency (> 80% at 400 nm). It is prepared from an alkali—soluble transparent polyimide precursor, a diazo-naphthoquinone-type photoactive compound, a surface-modified high refractive index nanosol, and a UV absorbent. The posi-PSPI has a round shape because of the UV absorbent. Further, it displays good sensitivity as well as a good round pattern profile after thermal curing. In addition, the 1% weight loss temperature of the posi-PSPI is 407 °C, which indicates that the posi-PSPI has excellent thermal stability.

Effect of Photo-active Compound Structure on Photosensitivity of Positive Photosensitive Polyimide

The photo-active compound (PAC) in positive tone photosensitive polyimide (posi PSPI) was investigated in order to obtain good photo lithographic performance (small development loss and good photosensitivity). When the PAC structure was changed posi PSPI showed different levels of photosensitivity and development loss. The development loss and photosensitivity showed a good correlation. The lower development loss posi PSPI showed lower photosensitivity. From the molecular orbital calculation, the PAC in the lower development loss posi PSPI had a lower dipole moment than that in the larger development loss posi PSPI. In addition, dissolution rate measurement (DRM) results suggest that posi PSPI may have two layers from the point of dissolution. The dissolution rate of the surface layer in posi PSPI was shown to be lower than that of a bottom layer. This suggests that PAC using the lower development loss posi PSPI may exist mainly on its surface. These results are quite important for the design of good posi PSPI.

Photosensitive polyimide adhesive sheet

Positive tone Photosensitive Polyimide B-stage sheet which was composed of transparent soluble polyimide, naphthoquinone diazide compound, thermal cross linker and solvent, was developed. We designed new polyimide structure and cross linker suitable for photosensitive polyimide sheet. The photosensitive sheet shows fine pattern formation capability as well as good thermal stability and mechanical properties. It is quite easy to obtain flat surface on topological surface to laminate the photosensitive sheet.

New Non Conductive Film for high productivity process

Novel Non Conductive Film (NCF) was developed for high productivity process. To meet high productivity, we add viscosity stability on a hot stage and snap cure property at higher than 140C. In addition, the NCF is transparent for optical alignment process.

Extreme low interfacial thermal resistance heat conductive sheet

High thermal conductive adhesive is important to cool power devices. Recently thermal conductivity reaches more than 10W/mK by efficient addition of thermal conductive filler(1). However, high loading of filler makes the thermal conductive sheet poor adhesion. In order to have high thermal conductivity and good adhesion, we tried to use AlN whisker developed by Nagoya university(2) to orient Z-direction. One volume percent of the AlN whisker improved the thermal conductivity drastically (3). Furthermore, we focused on reducing an interfacial heat resistance between high thermal conductive sheet composed of resin and heat conductive filler and metal such as Cu or Al. The interfacial heat resistance was determined by dispersion of high heat conductive filler and interfacial residual stress. The good dispersed sheet shows lower interfacial resistance than poor dispersed sheet, The interfacial residual stress causes an poor contact to metal to make void in the interface. To consider the effect of those facts, we successfully developed the high thermal conductive sheet with extremely low interfacial resistance. Bulk heat conductivity of the sheet is higher than 13W/mK. The interface heat resistance is below 0,009W/C.

Development of thermal conductive sheet with low interfacial heat resistance

Abstract In order to reduce total heat resistance, we focused on reducing an interfacial heat resistance between high thermal conductive sheet composed of resin and heat conductive filler and metal such as Cu or Al. The interfacial heat resistance was determined by dispersion of high heat conductive filler and interfacial residual stress. The good dispersed sheet shows lower interfacial resistance than poor dispersed sheet, The interfacial residual stress causes an poor contact to metal to make void in the interface. To consider the effect of those facts, we successfully developed the high thermal conductive sheet with extremely low interfacial resistance. The interface heat resistance is below 0,009W/C.

Improvement of chemical resistance of positive-tone photosensitive polyimide coatings in the electroless plating process

We found that positive-tone photosensitive polyimide (posi-PSPI) shows not to be compatible for electroless Ni/Au plating process which are used for Au micro bumping. In order to meet compatibility for the process, we improved chemical resistance of positive-tone photosensitive polyimide especially for electroless plating process. Changing of polyimide polymer structure is most effective to obtain chemical resistant for the electroless plating process. The obtained PSPI are useful for saving bumping process and reliable in forming pattern.