Daisuke Makino

Low Thermal Expansion Polyimides and their Applications

Thermal expansion coefficients (TECs) for polyimides differ very much depending on their chemical structures. Polyimdes with a rod-like structure as their backbone chains have lower TEC values. This is attributed to restraining of thermal expansion by rod-like molecules within intermolecular spaces, analogous to glass fibers in FRPs. The development of new polyimides which can closely match TECs of inorganic materials, such as metal or Si, can eliminate problems produced by thermal stress including warping, cracking or delamination. A new multilevel interconnection system using multilayered dielectrics consisting of low thermal expansion polyimide and inorganic materials has been proposed as one future technology for submicron VLSIs. Consequently, adhesiveless, high quality flexible printed circuit boards have been developed using a polyimide with the same TEC as copper foil. Their most significant property is a high dimensional stability after heat treatments, such as in a soldering process. Furthermore, they have very high adhesion strength at elevated temperatures.

Photosensitive polyimide for IC devices

Photosensitive polyimide has potential applications for interlayer insulation, alpha-ray shielding, and buffer coating of IC and LSI devices because it offers reduction in processing time. There are two main methods used to photosensitize polyimide. One is based on ion bonding and the other on covalent bonding between polyamic acid and photosensitive groups. The sensitivity, resolution, and mechanical properties such as tensile strength, elongation, and adhesion strength of the photosensitive polyimides have been investigated. The studies indicate that the covalent-bonding type is better than the ion-bonding type in terms of optical properties; the physical properties of the ion-bonding type, however, are much better. In terms of the physical properties conventional nonphotosensitive polyimides still have superior properties compared to photosensitive polyimides.<<ETX>>

New polyimide for multi-chip module application

P-terphenyltetracarboxylic dianhydride (p-TPDA), which has a rodlike structure, has been developed as a raw material for polyimides in order to reduce the propagation delay time associated with polyimide packaging for multichip modules. The coefficient of thermal expansion (CTE) of the polyimides derived from p-TPDA is approximately 2*10/sup -6/. This is much lower than that of conventional polyimides derived from bisphenyltetracarboxylic dianhydride (BPDA), which have a CTE of 8*10/sup -6/ K/sup -1/. Another attribute that these polyimides have is low dielectric constant, with a typical value of about 2.9. As a result, this polyimide can give improved performance when used in multichip module applications.<<ETX>>

A Series Of Azide-Phenolic Resin Resists For The Range Of Deep UV To Visible Light

A series of new type of negative photoresists composed of a phenolic resin and azide sensitizers has been developed. RD-2000N is sensitive in the deep UV region, RU-1000N in the mid UV region and RG-3000N in the mid UV to visible region. These resists are non-swelling aqueous developable, and give higher resolution compared to conventional cyclic rubber based negative resists. Resolution in less than 1 μm can be obtained by 1 : 1 projection or 10 : 1 reduction projection aligning method. Adequate exposure doses to define submicron patterns are 50 mJ/cm4(at 254nm),70 mJ/cm° (at 365 nm) and 180 mJ/cm2(at 436nm) for RD-2000N, RU-1000N and RG-3000N, respectively. The resistance to dry etch gases is also superior to conventional negative resists, and comparable with novolak resin based positive resists. Intense absorption of irradiating light by these resists makes them insensitive to reflected light from the substrate, resulting in a high resolution on stepped substrates without any antireflective layers which are necessary in positive resist applications.