RAMP RATE EFFECT ON POLYIMIDE FILM PROPERTIES AND MORPHOLOGY

The stress in films of semirigid and rigid polyimides (PIs) on silicon (Si) substrate has been measured in situ during curing using a newly modified bending beam apparatus. By using the apparatus, the onset of residual stress in the initially solvent-rich films has also been inve stigated. The stress characteristics of the PI films are strongly ramp rate dependent. Different ramp rates result in markedly different str ess patterns, thermo-mechanical properties, and film morphologies. The residual stress at room temperature after curing is seat tered around 23-31 MPa for the films of pyromellitic dianhydride-4,4'-oxydianiline (PMDA-ODA). For pyromellitic dianhydride-p-phenylenediamine (PMDA-PDA ), it systematically increases from -6 to 28 MPa for ramp rate increas ing from 0.5 to 10 degrees C/min. The residual stress is very low in t he slowly cured PMDA-PDA films. However, these films have gone through a very high-stress transient state during curing. The maximum transie nt stress is comparatively higher in the films of PMDA-PDA than in PMD A-ODA. Slowly cured PMDA-PDA films exhibit high structural ordering, h igh in-plane anisotropy, and low coefficient of thermal expansion. (C) 1995 John Wiley and Sons, Inc.