Abstract
This study examined dry removal of CO2 laser via bottom residue using 60 Hz nonequilibrium atmospheric pressure plasma with trifluoromethyl trifluorovinyl ether (C3F6O) mixing gas. (‘Removal of residue’ is defined as ‘de-smear’ in this paper.) Existing wet de-smear processing with KMnO4 will have a technical limitation for fine via that diameter is 50 μm or less. A dry process technology that allows fine via de-smearing is necessary for fine-pitch printed circuit board manufacturing. Results show that via bottom residue was de-smeared successfully using the plasma treatment with 2.0% of C3F6O mixing to argon gas. For tetrafluoromethane (CF4), 10.0% mixing was necessary for the plasma dry de-smearing. The global warming potential of C3F6O is close to zero as 4.57 × 10−4, so the result of de-smearing with 2.0% of C3F6O mixing ratio (the mixing ratio is 1/5 of CF4) gives us high expectations of conducting a low environmental impact practical manufacturing process. The optical emission spectra of the plasma were measured, and found that the intensity of CF2 radical and CF3 radical correspond to the result of the via bottom residual ratio. It reveals that CF2 radical and CF3 radical are active species to volatilize SiO2 filler residue. The gas molecule of C3F6O, which includes the fluoroalkyl ether group, is easily dissociated with low energy electrons. The 60 Hz nonequilibrium atmospheric pressure plasma has high density of low-temperature (energy) electrons. Therefore, the via bottom residue was de-smeared successfully using the atmospheric pressure plasma with a low mixing ratio of C3F6O.
