Polyimides for Electronic Applications

This chapter deals with the synthesis, characterization, and applications of advanced polyimide materials for electronic applications. Aromatic polyimides have been extensively used in microelectronics manufacturing and packaging, especially as passivation layers, dielectrics, or insulator layers in multilayer structures and alpha-particle barriers. In addition, aromatic polyimides have been employed as the alignment layer for aligning the liquid crystal (LC) molecules in TFT-LCD devices and as the substrate films for the flexible optoelectric displays. Photosensitive polyimides (PSPI), including negative tone and positive tone, are first introduced. PSPIs are primarily used as the passivation layers on the IC chip surface and as the multilayer dielectrics in the bumping process of BGA, CSP, and WLP, etc. The polyimide alignment layers in LCD devices are then discussed in detail, including the mechanical rubbing alignment materials and photoinduced alignment materials. Although mechanical rubbing alignment polyimides have been extensively used in industry, there are still some shortcomings, such as dust generation and electrostatic problems, etc. Thus, photoinduced alignment polyimides have been developed, which retain all of the advantageous properties of the mechanical rubbing alignment polyimides. Furthermore, polyimides used as the flexible substrates for flexible displays such as organic light emitting diode (OLED) are also discussed.In the last section, the recent emerging area, polyimide materials as electret layers for memory devices, is introduced.