ABSTRACT
Polyimides are commonly used in the semiconductor and electronic packaging industry because of their high thermal stability, good insulation properties with a low dielectric constant (about 3.5), good adhesion to commonly used substrates, and superior chemical stability. Polyimide based on pyromellitic dianhydride-oxydianiline (PMDA-ODA) poly(amic acid) is one of the most commonly used polyimides. In this chapter we will concentrate on this particular polyimide. Because of its insolubility in most solvents, the poly(amic acid) is usually dissolved in N-methyl-2-pyrrolidone to form a viscous solution with a concentration of 10-20%. This solution can be coated onto various substrates by spin coating, spray coating, or high-speed roller coating. During the drying operation, much of the solvent is removed, and less than 20% imidization will occur if the temperature remains below 110°C [1]. In Figure 1, a typical imidization (cure) reaction is illustrated: the poly(amic acid) (I) formed from pyromellitic dianhydride (PMDA) and oxydianiline (ODA), is transformed to (PMDA-ODA) polyimide, poly-[N,N′-4,4′-oxydiphenylene]-pyromellitimide (II), by application of heat and elimination of water.
