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Board-Cleaning Technique Using Hollow Cathode Plasma Discharge

IP.com Disclosure Number: IPCOM000061837D
Original Publication Date: 1986-Sep-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 3 page(s) / 51K

Publishing Venue

IBM

Related People

Cuomo, JJ: AUTHOR [+2]

Abstract

Due to the increasing complexity of circuit board construction for use in electronic devices, there has been a trend away from wet or acid cleaning of these boards. In various stages of the manufacturing process, either after a deposition, exposure, or strip, or else following a mechanical step, such as drilling through the boards for the mounting of pins or other interconnects, there is a need to clean the surface and the drilled hole prior to the next manufacturing step. Dry processing such as plasma etching or reactive ion etching, has been successfully used in the past to prevent some of the inherent problems associated with the wet processing of complex, multilayer patterns. These techniques have been used in commercial systems and are in current usage in some manufacturing applications.

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Board-Cleaning Technique Using Hollow Cathode Plasma Discharge

Due to the increasing complexity of circuit board construction for use in electronic devices, there has been a trend away from wet or acid cleaning of these boards. In various stages of the manufacturing process, either after a deposition, exposure, or strip, or else following a mechanical step, such as drilling through the boards for the mounting of pins or other interconnects, there is a need to clean the surface and the drilled hole prior to the next manufacturing step. Dry processing such as plasma etching or reactive ion etching, has been successfully used in the past to prevent some of the inherent problems associated with the wet processing of complex, multilayer patterns. These techniques have been used in commercial systems and are in current usage in some manufacturing applications. The techniques suffer from some basic inefficiencies which limit the speed and scope of operation. The present board- cleaning technique differs only slightly in physical design from known board- cleaning techniques. The operation of the plasma, however, is significantly different. A preferred embodiment is shown in the figure. The board-electrodes 33-41 are powered together, such that they are all connected directly to the same power supply 16. The electrodes are driven by a 13.6 megahertz supply 15 through a standard matching network 16. The electrodes are located in a vacuum chamber 20 which is grounded. The chamber is pumped by standard high vacuum pump and operates at gas pressures in the millitorr range. A means of introduction of gases 21 is shown, which consists of one or many leak valves, connected to respective gas or vapor sources. For purposes of this discussion, no specific means of directing the gas to any particular area of the chamber is specified. This is often done, however, particularly in systems that operate at higher pressures. A high voltage RF potential is applied to the electrodes 33-41 with respect to ground. The chamber 20 functions as a counter electrode for the plasma. The high voltage difference, in a sufficient background pressure of the desired gas, causes the gas to form a plasma. The ions from the plasma, as well as other excited or reactive species from the plasma, can then impact the circuit boards and cause the desired etching or cleaning process. The circuit boards form hollow cathode electrode...