Proposal of Very High Performance and High Density Printed Wiring Board and Its Very High Productivity Manufacturing Processes

Copper sputter-deposition by a newly developed technique called rotation magnetron sputtering is introduced for copper seed layer formation on printed wiring boards (PWBs) as an alternative to the electroless copper plating, which requires many complicated process steps as well as an intentional roughness-induced process to obtain practical adhesion capability between the copper and the resin. A rough copper surface degrades high-speed signal propagation due to an increase in conductive loss, and makes difficult the realization of further miniaturization of copper wirings. Thus, a very smooth surface layer of cycloolefin resin with a low dielectric constant and a low dielectric loss is introduced for realizing high-speed signal propagation, low electrical power consumption, and very high density packaging by introducing PWBs with a new structure, which are characterized by: 1) high characteristic impedance of 100 Ω instead of the current characteristic impedance of 50 Ω, which decreases the electrical power consumption down by one-half and increases the packaging density up to about four times by decreasing the copper wiring width down to one-fourth of the current characteristic impedance of 50 Ω, and 2) multi-resin step copper wiring to simultaneously establish very high density packaging by introducing 10-μm width copper wiring with 40 μm resin thickness and very high speed signal propagation with 80- and/or 120-μm resin thickness copper wiring. By introducing the plasma process steps, such as radio frequency bias Ar/H₂ plasma cleaning of the resin surface as well as the exposed inner copper surface, plasma nitridation of the resin surface, deposition of copper nitride, and deposition of the copper seed layer, a copper seed layer with a very smooth surface having very strong adhesion with the resin can be obtained. This technology greatly contributes to next-generation PWBs with very high performance and - ery high productivity.