Evaluation of the surface free energy of spin-coated photodefinable epoxy

Markus P.K. Turunen, Tomi Laurila, Jorma K. Kivilahti*

*Corresponding author for this work

    Research output: Contribution to journalArticleScientificpeer-review

    20 Citations (Scopus)

    Abstract

    The surface free energy of crosslinked photodefinable epoxy (PDE) was evaluated from the advancing contact angles measured by the sessile drop method. Poly(tetrafluoroethylene) (PTFE) was used as a reference material in the evaluation of the surface free energies by various models. Pure water, diiodomethane, formamide, ethylene glycol, diethylene glycol, glycerol, 1-bromonaphthalene, decane, and tetradecane were used as the probing liquids. The surface free energies for PDE and PTFE were calculated to be 43.6 and 21.2 mJ/m2, respectively. The contact-angle measurements indicated the isotropy of the PDE surface with respect to the surface free energy. The PDE coating was further characterized with scanning electron microscopy and atomic force microscopy. The PDE surface was treated chemically and by reactive ion etching (RIE) to determine their impact on the wettability and adhesion. The treatments resulted in decreased contact angles between the crosslinked PDE surface and water as the polarity of the surface increased from about 9% to 18 and 43% by the chemical and RIE treatments, respectively. On the contrary, the surface free energy of the treated PDEs, as calculated by the geometric mean model, did not change markedly (to 47.4 and 41.8 mJ/m2 by the chemical and RIE treatments, respectively). Consequently, the contact angles of diiodomethane and the PDE solution on the treated surfaces did not decrease noticeably. The stud-pull test showed improved adhesion strength for PDE that was left less crosslinked and, therefore, had residual affinity against the sequential PDE layer.

    Original languageEnglish
    Pages (from-to)2137-2149
    Number of pages13
    JournalJournal of Polymer Science Part B: Polymer Physics
    Volume40
    Issue number18
    DOIs
    Publication statusPublished - 15 Sep 2002
    MoE publication typeA1 Journal article-refereed

    Keywords

    • Adhesion
    • Photoresists
    • Printed wiring board
    • Sessile drop
    • Surfaces

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