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Improvement of Uniformity of Through-Hole Coverage

IP.com Disclosure Number: IPCOM000040121D
Original Publication Date: 1987-Sep-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 47K

Publishing Venue

IBM

Related People

Blackwell, KJ: AUTHOR [+4]

Abstract

A mechanism to improve the copper coverage of through-holes with a sputtering technique is accomplished using a shield to more accurately direct the sputtered particles. The process is as follows. The material to be sputtered is the cathode plate 1 (Fig. 1). With a magnetic field surrounding cathode plate 1 and the North Pole at the center, the positive particles are accelerated toward the cathode 1. When these particles collide with the plate 1, electrons and neutral atoms are sputtered out from the cathode 1 (the motion of the sputtered electrons is affected by electric and magnetic fields). Part of the electrons will fall back due to Larmor Motion. The sputtered neutral atoms or atoms that are not affected by either the electric or magnetic fields will travel out in a straight line and arrive at the anode, i.e.

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Improvement of Uniformity of Through-Hole Coverage

A mechanism to improve the copper coverage of through-holes with a sputtering technique is accomplished using a shield to more accurately direct the sputtered particles. The process is as follows. The material to be sputtered is the cathode plate 1 (Fig.
1). With a magnetic field surrounding cathode plate 1 and the North Pole at the center, the positive particles are accelerated toward the cathode 1. When these particles collide with the plate 1, electrons and neutral atoms are sputtered out from the cathode 1 (the motion of the sputtered electrons is affected by electric and magnetic fields).

Part of the electrons will fall back due to Larmor Motion. The sputtered neutral atoms or atoms that are not affected by either the electric or magnetic fields will travel out in a straight line and arrive at the anode, i.e., through-holes. Assuming that the particles emitting from the cathode have a distribution f(d), the flux at x (from the surface) in the hole (Fig. 2) is

(Image Omitted)

I(X)= f(d) cos d pd dp... (1)

R

3 when x JJ r I(x) V 2r (2) and independent of f(d) because the x variation of d is very small. If x is the length of the hole, then x is the aspect ratio. 2r If both sides of the printed circuit board are to be sputtered, 3 then the center of the hole has a flux 4r , where L is the length L of the hole and r is the radius of the hole. If a hole has an aspect ratio of 10, the flux is .008 of the surface flux. This relation makes it very difficult for the center of the hole to obtain the desired flux. This...