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Cleaning the Walls of Drilled Throughholes in Printed Circuit Boards and Cards by Plasma Etching

IP.com Disclosure Number: IPCOM000042892D
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Cziep, W: AUTHOR [+3]

Abstract

For the complete and fast removal of an epoxy resin/glass particle/copper drilling smear layer, occurring during the drilling of throughholes in printed circuit boards and cards on the hole walls of the copper planes, it is proposed that the previous O2/CF4 plasma etch process be followed by a further plasma process, using activated gases, such as methyl chloride, bromide or iodide. During a plasma etch process with a gas mixture of O2 and CF4 and an operating pressure of about 0.4 mbar, substantially only epoxy resin is removed which together with glass particles and copper drillings forms the smear layer on the hole walls of drilled copper conductor planes.

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Cleaning the Walls of Drilled Throughholes in Printed Circuit Boards and Cards by Plasma Etching

For the complete and fast removal of an epoxy resin/glass particle/copper drilling smear layer, occurring during the drilling of throughholes in printed circuit boards and cards on the hole walls of the copper planes, it is proposed that the previous O2/CF4 plasma etch process be followed by a further plasma process, using activated gases, such as methyl chloride, bromide or iodide. During a plasma etch process with a gas mixture of O2 and CF4 and an operating pressure of about 0.4 mbar, substantially only epoxy resin is removed which together with glass particles and copper drillings forms the smear layer on the hole walls of drilled copper conductor planes. As the bared glass particles and the copper drillings serve as a mask for the epoxy resin positioned below them in the smear layer, even long etching times fail to remove thick smear layers completely. By additionally removing several micrometers of copper from the hole walls of drilled copper conductor planes, the glass particles, sticking to the copper wall, are subetched, thus dropping off. For removing the copper, activated methyl compounds, such as methyl chloride, bromide or iodide, are used. These can be directly added to the O2/CF4 gas mixture in an appropriate quantity, so that the epoxy resin and the copper are simultaneously etched. The plasma etch process may also be effected such that initially the e...