International Business Machines Corporation

Ku Ho Chong

Charles H Crockett, Jr

Karl G Hoebener

Michael G McMaster

Julian P Partridge

Bhavyen S Sanghavi

Stephen Alan Dunn, Deceased

A method of manufacturing a multiple layer circuit board with stacked vias of fine dimension and pitch. A base laminate with conductive pattern is coated with a dielectric which is photolithographically processed to create holes exposing selected regions of the underlying conductive pattern. The holes through the dielectric are plated to form via connections between the surface and the conductive pattern on the base laminate. The recess created by the via is filled with a conductive and plateable polymer which upon curing forms a conductive plug. A second dielectric layer is deposited on the board structure and in succession photolithographically processed to expose the underlying plated via and plug. The hole in the second dielectric is plated and filled with conductive polymer so as to create a second via vertically aligned with and electrically connected to the underlying first via. The ability to form fine pitch stacked vias is particularly important for printed circuit board structures such as carriers of flip chip die, in that the fine pitch of the solder ball array of the flip chip needs to be expanded and/or disbursed through multiple board layers with minimum area and electrical degradation.

Method of manufacturing a multiple layer circuit board die carrier with

Fine dimension stacked vias for a multiple layer circuit board structure

A method, and product created thereby, by which low melting point solder suitable for reflow connection of components is formed on select fine pitch contacts of a printed circuit board. The method is particularly suited to the attachment of flip-chip die to printed circuit boards which also include coarse pitch surface mount components. Controlled volumes of solder are formed onto fine pitch contacts of the printed circuit board through selective holes in a mask formed onto the board. The deposit is accomplished by molten solder immersion preferably using conventional hot air solder level manufacturing equipment. The volume of solder is related to the thickness of the mask. The mask is then removed, the deposited low temperature solder is flattened, and the coarse pitch contacts are covered with solder paste in a conventional screening process. Flux is applied to the fine pitch contacts. After component placement, the solder reflow connects in one operation both the fine and coarse pitch components to their respective printed circuit board contacts.

Fine pitch solder formation on printed circuit board process and product

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Arlington Heights, IL, United States of America

Ku Ho Chong