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Electrode Arrangement for Plasma Etching

IP.com Disclosure Number: IPCOM000045479D
Original Publication Date: 1983-Mar-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 24K

Publishing Venue

IBM

Related People

Ruh, D: AUTHOR

Abstract

An electrode arrangement is described for plasma etching via holes, which ensures uniform etch rates across the entire board.

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Electrode Arrangement for Plasma Etching

An electrode arrangement is described for plasma etching via holes, which ensures uniform etch rates across the entire board.

After the via holes have been drilled in printed circuit boards or cards, their walls must be cleaned from smearing matter by plasma etching. For plasma etching, an O(2) + CF(4) gas mixture is used at an operating pressure of about
0.3 Torr. During this process, the boards or cards are positioned between two plate electrodes, the anode and the cathode. Using a high-frequency electric field, a plasma is generated containing ions, atoms and radicals, by means of which epoxy or polymers can be etched at high rates.

With large-area boards, etch gradients are encountered, i.e., the etch rates along the board edges are higher than in the centers. If the holes are thoroughly cleaned in the center, these different etch rates lead to undesirable undercutting of the holes along the edges. The etch gradient is mainly attributable to 1. surface effects on boards and electrodes, which are caused by high-frequency fields applied (e.g., skin effect) and 2. impaired gas exchange between board edge and center (supply of etch species and discharge of etched gaseous products).

To achieve a uniform etch rate across the board, the etch rate in the holes of the board center is increased and that along the edges is reduced. For this purpose, the electrodes are convexly shaped (see diagrammatic plan and side views), so tha...