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Hole Cleaning of High Aspect Ratio Through Holes in Printed Circuit Boards

IP.com Disclosure Number: IPCOM000087317D
Original Publication Date: 1977-Jan-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Alpaugh, WA: AUTHOR [+3]

Abstract

Through-holes in a printed-circuit board having a high length-to-diameter aspect ratio (greater than 5 to 1) are difficult to clean prior to the subsequent plating of the through-holes. These high aspect ratio holes generally do not permit good circulation of chemical cleaning solutions using conventional dip methods or do not provide adequate channels for vapor-blasting with air.

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Hole Cleaning of High Aspect Ratio Through Holes in Printed Circuit Boards

Through-holes in a printed-circuit board having a high length-to-diameter aspect ratio (greater than 5 to 1) are difficult to clean prior to the subsequent plating of the through-holes. These high aspect ratio holes generally do not permit good circulation of chemical cleaning solutions using conventional dip methods or do not provide adequate channels for vapor-blasting with air.

To overcome these cleaning problems, the holes are first vapor-blasted at approximately right angles to the board surfaces, removing loose drill hole debris and opening holes that may have been plugged. Next, the holes are treated with a suitable solvent to loosen the fibers, and the epoxy is smeared on to make it easier for the subsequent cleaning solution to reach and remove the debris. Any excess solvent is removed by immersing the board, for example, in methylchloroform, and the board is air-blown dry. Next, a gravity feed of a cleaning solution such as chrome/sulfuric acid is allowed to flow unilaterally through the holes of the board at a rate of about 40 gallons per minute. This results in a uniform attack of smear and etch back of innerplanes at all depths in the board. Following this, the panels can be vapor-blasted again to remove any minor particles that may remain.

In some instances, it may not be necessary to subject the through holes first to a solvent, but rather one can proceed directly with the c...