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Coating of Through Hole Dielectric Substrates

IP.com Disclosure Number: IPCOM000094244D
Original Publication Date: 1966-Aug-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Haddad, MM: AUTHOR [+2]

Abstract

Thick, uniform coatings of photoresist materials are deposited onto dielectric substrates having through-holes in printed circuit technology. Current methods, such as spraying and dip-coating, do not provide the uniformity of coating desired. This is because of surface tension effects of the coating around the hole edges.

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Coating of Through Hole Dielectric Substrates

Thick, uniform coatings of photoresist materials are deposited onto dielectric substrates having through-holes in printed circuit technology. Current methods, such as spraying and dip-coating, do not provide the uniformity of coating desired. This is because of surface tension effects of the coating around the hole edges.

The following techniques are effective in solving this coating problem. A first technique is to fill the holes in the dielectric substrate with a water-soluble powder, such as a mixture of sodium bicarbonate and citric acid. Then the substrate is coated with the photoresist coating using the standard doctor blade technique. Finally, the powder is dissolved using ultrasonically agitated water.

A second technique is to immerse the substrate in water, dry the water from the surface of the substrate while allowing the holes to remain wetted. Then the substrate is coated with hydrophobic photoresist material.

The photoresist coating covers the substrate except in the area of the holes which remain wetted with water. The water is then evaporated from the holes.

A third procedure consists of silk-screening the photoresist material through a patternless screen onto the substrate. A photoresist forced through the screen adheres to the substrate in all areas except above the hole areas. Here surface phenomena causes the photoresist to be retained on the screen.

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