A Universal Study on the Effect Thermal Imidization Has on the Physico-Chemical, Mechanical, Thermal and Electrical Properties of Polyimide for Integrated Electronics Applications

Abstract

Polyimides (PI) are a class of dielectric polymer used in a wide range of electronics and electrical engineering applications from low-voltage microelectronics to high voltage isolation. They are well appreciated because of their excellent thermal, electrical, and mechanical properties, each of which need to be optimized uniquely depending on the end application. For example, for high-voltage applications, the final polymer breakdown field and dielectric properties must be optimized, both of which are dependent on the curing process and the final physico-chemical properties of PI. The majority of studies to date have focused on a limited set of properties of the polymer and have analyzed the effect of curing from a physicochemical-, mechanical- or electrical-centric viewpoint. This paper seeks to overcome this, unifying all of these characterizations in the same study to accurately describe the universal effect of the cure temperature on the properties of PI and at an industrial processing scale. This paper reports the widest-ranging study of its kind on the effect that cure temperature has on the physico-chemical, mechanical, thermal and electrical properties of polyimide, specifically poly (pyromellitic dianhydride-co-4, 4′-oxydianiline) (PMDA/ODA). The optimization of the cure temperature is accurately studied not only regarding the degree of imidization (DOI), but also considering the entire physical properties. Particularly, the analysis elucidates the key role of the charge–transfer complex (CTC) on these properties. The results show that while the thermal and mechanical properties improve with both DOI and CTC formation, the electrical properties, particularly at high field conditions, show an antagonistic behavior enhancing with increasing DOI while degrading at higher temperatures as the CTC formation increases. The electrical characterization at low field presents an enhancement of the final PI properties likely due to the DOI. On the contrary, at high electric field, the conductivity results show an improvement at an intermediate temperature emphasizing an ideal compromise between a high DOI and PI chain packing when the thermal imidization process is performed over this equilibrium. This balance enables maximum performance to be obtained for the PI film with optimized electrical properties and, overall, optimal thermal and mechanical properties are achieved.

Intrinsic AC Dielectric Breakdown Strength of Polyimide Films at the Extreme: New Breakthrough Insights on Thickness Dependence

“…The spin‐coating speed was adjusted to give a final, post cure PI film thickness within the range from 5 µm to 60 µm using a multilayer coating process, as previously reported. [ 29 ] The deposited film stack was subsequently metallized with another TiW/Au bilayer. Test structures were lithography patterned to obtain circular PI capacitors ( Figure a).…”

Study on the Diffusion Coefficients of Molecules in Precursor Varnishes and Solid Polyimides for Understanding the Polyimide Curing Process

“…The varnish is cast and dried via subsequent high-temperature treatments to remove the solvent by evaporation and is imidized (Scheme ). The imidization reaction and the resultant polyimide have been investigated well. − The solvent molecules like NMP hydrogen-bonded with carboxylic and amide groups of PAA need to be released from the proton donor sites prior to the imidization reaction. ,, Moreover, imidization is rate-limited by the mobility of PAA and can therefore be accelerated with solvent molecules via plasticization. − Thus, the diffusion of DMAc and PAA in the varnish is crucial to comprehend imidization.…”