Novel method for plasma etching of printed circuit boards as alternative for fluorocarbon gases
Wolfram Kintzel1, *, Marvin Schmid1, Achim Rentschler2, Jorg Eisenlohr1, Volker Bucher1
* The author to whom correspondence should be addressed.
1 Hochschule Furtwangen, Institute for Microsystems Technology (iMST),
Jakob-Kienzle-Str. 17, 78054 Villingen-Schwenningen, Germany
2 Plasma technology GmbH, Marie-Curie-Strase 8, 71083 Herrenberg-Gultstein, Germany
Abstract
This paper describes a novel method for plasma etching of printed circuit boards (PCBs), replacing climate-damaging perfluorinated Hydrocarbons (HFCs) such as tetrafluoromethane (CF4). In our alternative process, reactive fluorine would be generated from an inert precursor like commercial PTFE (polytetrafluoroethylene) by means of low-pressure oxygen plasmas. The released fluorine would further be applied to PCB as etchant. Excess fluorine could be chemically absorbed and re-used as recycled precursor later in order to gain a process free of fluorine emissions. Diverse tests were carried out in a lab-scale RF plasma device. We considered different precursor types and examined the plasma composition by means of real-time mass spectrometry. We also determined etch rates on epoxy resin samples by means of mass loss measurements. Process gas composition, precursor type and plasma power were varied, including comparative tests applying state-of-the-art CF4-O2-plasma. The efficiency of the etching process was proven. The environmental impact of the novel method was discussed and evaluated regarding PTFE production and greenhouse gas emissions.
Keywords - Printed circuit board, plasma etching, fluorocarbon, PCB, HFC, PTFE.