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Making Multilayer Circuit Boards

IP.com Disclosure Number: IPCOM000061872D
Original Publication Date: 1986-Jul-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Fuller, JW: AUTHOR [+2]

Abstract

Multilayer circuit boards can be made by using a CBS process for the internal planes. The CBS process involves laminating copper to the surface of an epoxy laminate and etching it away so that you have a surface that can then be additively plated.

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Making Multilayer Circuit Boards

Multilayer circuit boards can be made by using a CBS process for the internal planes. The CBS process involves laminating copper to the surface of an epoxy laminate and etching it away so that you have a surface that can then be additively plated.

Normally, the external planes on such a multilayer circuit board are made by a peel-a-part process where peel-a-part copper is bonded to the external epoxy.

The CBS process is not used on the externals because: 1) If you drill before you etch the externals, when you etch off the sacrificial layer, you will also etch inside the drilled holes. 2) If you etch before you drill, you would have to desmear the drilled holes after the etch and this would destroy the epoxy on the outside surface.

The epoxy can be covered during the desmear operation but there are disadvantages to doing this operation.

An alternative process is as follows: Make a CBS signal core where all the sacrificial copper has been removed, but no copper lines have been additively plated onto the epoxy. It is noted that epoxy in the CBS blank is cured when the sacrificial copper is bonded to the surface.

Normally, a composite is formed by bonding the signal planes together by laminating with sticker sheets of uncured prepreg. In the process described here, a sheet of copper is put on the top and bottom of the outside composites without any sticker sheets between it and the cured epoxy. The final composite will be held in one...