  A new approach for fabricating open and closed porous structures based on
laser processing is presented. Liquid polyimide (PI) was mixed with
azodicarbonamide (ADC, ADA) which is a chemical blowing agent (CBA) and mixture
was pre-cured in order to fabricate solid PI film. Porous PI was prepared by
irradiating PI film mixed with azodicarbonamide. The PI film with
azodicarbonamide was etched by laser ablation, and the CBA was decomposed by
heat induced by the absorbed laser energy. The higher the laser beam
irradiation, the more pores were fabricated due to the resulting increase in
CBA decomposition from 27 mJ/cm2 to 40 mJ/cm2 per single pulse. Higher fluence
at about 50 mJ/cm2 resulted in fewer and larger open pores, which were formed
by the coalescence of small pores. In contrast, a closed porous structure was
fabricated at a fluence of less than 1 mJ/cm2 because PI was barely etched. The
proposed method can be sued to create open and closed micro porous structures
selectively, and is not limited to thermosetting polymers, but is also
effective with thermoplastic polymers.

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