ABSTRACT
When the first commercial polyimide was brought to market as Kapton* film in the early 1960s [1] the electronics industry was comparatively still in its infancy. At that time most dielectrics in applications ranging from device insulation to electronic packages consisted of inorganic materials such as A12O3, SiO2, and other metal oxides or nitrides. Chip carriers in high-performance applications such as mainframe computers and components for space and military applications were all based on multilayer ceramic packages [2–4]. The ceramic used was mostly based on alumina, which has a relatively high dielectric constant of 9. In the late 1970s it became obvious that the goal of ever faster computers was strongly hampered by the delays an electrical signal incurs while it travels from one chip to another by way of the package. These signal delays caused by the interaction of the electrical signal with the dielectric medium of the package are aptly called package delays. As we will see below, a material with a lower dielectric constant decreases the signal delays. To that end polyimides were introduced into electronics packages in the early 1980. Polyimides were chosen primarily because of their suitable combination of properties, which include higher thermal stability, good mechanical properties, and a comparatively low dielectric constant [5–7].
