TABLE OF CONTENTS Polyimides, noted for their high thermal stabilities and chemical and radiation resistance, were first developed by DuPont and introduced on the market in 1961. Subsequently other manufacturers entered the market, notably Ciba Geigy and Hitachi. In 1997, Hitachi and DuPont created a joint venture called HD MicroSystems to produce polyimides for the microelectronics industry. Meanwhile, Ciba Geigy's polyimide technology, developed in the 1970s, was augmented in the 1980s by their licensing the photosensitive polyimide technology from Siemens. Then, in 1990, Ciba Geigy and Olin formed a joint venture which later transitioned to Olin Microelectronics and has now passed on to Arch Chemicals who markets polyimide coatings under the Durimide tradename.
Besides the changes in the companies that developed them, the applications for polyimides have also undergone considerable changes. Whereas early applications were for varnishes, wire coatings, and impregnants for magnetic parts, now polyimide coatings are also used as stress buffers and passivation in the processing of ICs and as interlayer dielectrics to fabricate very high density multilayer substrates. In addition, polyimides are used in processes to redistribute bond pads on integrated circuit chips and wafers, rendering them amenable to flip-chip bonding. They are also used as plating resists in the fabrication of micromachined parts (See Ch. 4 on "Applications").
Like other polymer classes, there are hundreds of polyimide formulations on the market, but only a few meet all the requirements for use on ICs and microelectronic assemblies. Of the many engineering properties desired of a dielectric, three are...
