Browse Prior Art Database

Etch Rate Uniformity Enhancement for Plasma Drill Smear Removal

IP.com Disclosure Number: IPCOM000039528D
Original Publication Date: 1987-Jun-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 59K

Publishing Venue

IBM

Related People

Egitto, FD: AUTHOR [+2]

Abstract

RF plasmas of oxygen and fluorine are commonly used to remove epoxy drill smear from through holes on printed circuit boards. Achieving uniform plasma etch rates, especially for large boards or multiple standard size panels in close proximity, can be difficult. A method for achieving uniform etch rates is described in the following. The primary etch species used are atomic oxygen and atomic fluorine. For a given amount of atomic oxygen in the plasma, there is an optimum amount of atomic fluorine required to achieve a maximum etch rate. Fluorine atoms in small concentrations enhance etch rates through reactions which generate radical surface sites. Fluorine present in excess, however, inhibits etching through competition with O atoms for sites leading to the formation of fluorocarbon compounds on the surface.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 52% of the total text.

Page 1 of 2

Etch Rate Uniformity Enhancement for Plasma Drill Smear Removal

RF plasmas of oxygen and fluorine are commonly used to remove epoxy drill smear from through holes on printed circuit boards. Achieving uniform plasma etch rates, especially for large boards or multiple standard size panels in close proximity, can be difficult. A method for achieving uniform etch rates is described in the following. The primary etch species used are atomic oxygen and atomic fluorine. For a given amount of atomic oxygen in the plasma, there is an optimum amount of atomic fluorine required to achieve a maximum etch rate. Fluorine atoms in small concentrations enhance etch rates through reactions which generate radical surface sites. Fluorine present in excess, however, inhibits etching through competition with O atoms for sites leading to the formation of fluorocarbon compounds on the surface. Hence, the concept of optimum ratio of atomic concentrations of O and F ([O]/[F]) is fundamental to uniform etching. In addition, the etching process consumes relatively more fluorine than oxygen, resulting in an increase in O/F. Achieving uniform etch rates in the through holes across a panel is a major concern. Typically, nonuniform etching is characterized by positions near the perimeter of the board etching at higher rates than positions near the center of the board. This is due to consumption of etching species resulting in a concentration gradient across the board. One means of compensating for this depletion of species is to use a feed gas composition that is rich in fluorine. The excessive atomic fluorine concentration produces a fluorine rich mixture at the edge of the board (low
[O]/[F]). As etchant is consumed toward the center of the board, O/F increases toward a more optimum value. Hence...