Photolithography of polytetrafluoroethylene for adhesion

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Abstract
Irradiation of polytetrafluoroethylene (PTFE) with Mg(Kα) X‐rays is shown to protect the surface against the chemical etching steps used to prepare PTFE for adhesion. Preirradiated etched samples of PTFE have adhesion strengths to epoxies of less than 3% of that for nonirradiated etched samples. The major portion of this decrease in adhesion strength occurs for X‐ray exposures of less than 10 min and failure in every case occurs in PTFE and not in the bonded transition region. XPS measurements (20 Å sampling depth) show little difference in F content between irradiated and nonirradiated samples, but thermal desorption shows increasing short chain fluorocarbon desorption with irradiation time. These results are consistent with previous studies showing that irradiation produces free radicals that lead to branching and/or crosslinking, and a surface rich in low molecular weight fluorocarbons. The crosslinked surface is resistant to deep (10,000 Å) chemical attack and rich in short chain fluorocarbons; both effects are expected to lead to weak adhesive bonding.

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