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Monitoring Coupon for Plasma Etching Drilled Holes

IP.com Disclosure Number: IPCOM000062728D
Original Publication Date: 1986-Nov-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Frisbie, WG: AUTHOR [+3]

Abstract

The drilling of a printed circuit board (PCB), i.e., through copper planes and epoxy-glass layers, results in drill smearing of the interplane copper which must be removed. Plasma etching is an effective means of drill smear removal. A simple, nondestructive technique of measuring the performance of the pl etching process for various hole geometries is conducted using a process monitor coupon.

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Monitoring Coupon for Plasma Etching Drilled Holes

The drilling of a printed circuit board (PCB), i.e., through copper planes and epoxy-glass layers, results in drill smearing of the interplane copper which must be removed. Plasma etching is an effective means of drill smear removal. A simple, nondestructive technique of measuring the performance of the pl etching process for various hole geometries is conducted using a process monitor coupon.

The coupon 1 is seen in Fig. 1 from a side view. It is constructed of two parallel pieces of epoxy-based resin coated silicon chips 2, 3 which are separated from each other by some suitable non-etchable spacer 4. Epoxy- coated sides of chips 2, 3 face the inside of cavity. The bottom silicon chip 3 is mounted on a PCB (not shown), thus sensing the board temperature, and is selectively covered with a patterned non-etchable material 5 (Fig. 2) which simulates the shape of the drilled hole cross section. Fig. 2 shows a top view of the coupon 1 with the spacers 4 and top silicon chip 2 removed.

An empirical model defining the coupon geometry can be derived from the hydraulic radius(D), D=(cross section area filled with fluid)/(length of a wetted perimeter). For a square pipe or duct, D=(side length/4).

The geometric requirements for the coupon were found to be defined by D=(4/3) a, where D is the hydraulic radius and a is the thickness of the spacer separating the two silicon chips. The distance b (Fig. 1) is each repeating uni...