Integrated metallization system for high density interconnects and modified semi additive processing

Printed circuit designers continually increase the technological complexity of their products. This includes more utilization of microvias and higher population densities via decreases in pitch. Many of these products will also require the application of thinner copper foils (<; 17 microns) to resolve tighter lines and spaces. Building these more complex products often pushes the limits of capability in existing production processes and controls. Fabricators must investigate alternative methods to produce these highly functional devices while maintaining quality and low cost. This paper will detail a simple, highly automated metallization system that can enable the fabricator to consistently produce high quality, high density interconnect packages with high yields. This integrated metallization system combines a horizontal desmear process, with a horizontal carbon technology, and a vertical continuous plating system. The production proven carbon system is well suited for modified semi additive processes (MSAP) when coupled with a newly developed copper etching technology. This innovative copper cleaning system completely removes carbon from the copper surfaces with a 0.2μm-0.3μm etch rate, eliminating negative etch back and wedge voids due to excessive nail heading, while maintaining a highly conductive coating on the dielectric substrate. In this paper, we will describe this integrated metallization system that produces HDI technology with the same or better performance as electroless copper while providing the added benefits of reduced costs, simpler process controls, and with a smaller equipment foot print than conventional horizontal electroless copper processes. Additionally, we compare this new copper cleaning process to the traditional sulfuric acid/persulfate microetch cleaning as it pertains to copper cleanliness, through hole integrity and microvia reliability. The low etch copper cleaning is adaptable to existing equipment sets with m- nimal or no modification.