Copper Electroplating Processes for Advanced HDI Applications

The design requirements of circuitry for 5G communications technology is requiring new manufacturing techniques to be implemented. These techniques, such as high density interconnects (HDI) for printed circuit boards (PCBs) make the devices less expensive and allow for more functionality to be packed into ever decreasing dimensions. The advantages of HDI PCBs are numerous and include finer copper traces, thinner and more flexible base materials and laser drilled via holes. HDI PCBs have played a crucial role in creating miniature smartphones and other embedded subsystems and the demands of 5G technology are pushing the limits of HDI technology even further. Researchers in the electronics manufacturing space are highly motivated to formulate solutions for the HDI market, especially acid copper via fill solutions to meet the market demands.Two innovative DC acid copper micro-via fill plating electrolytes are discussed in this paper. One is for an advanced tenting process and the other is for modified semi additive process (mSAP), with VCP (Vertical Continues Plating) applications. These two acid copper via fill processes can provide fine line resolution from the range of 35 μm to 20 μm, which enables makers of 5G smartphones and other demanding gadgets to achieve unprecedented densities while offering superior geometries with exacting impedance control for their high frequency operation. The electrolyte for advanced tenting process has distinctly rapid filling performance, which allows this electrolyte to plate very thin copper on the surface while filling the vias. For example, 125×75 μm vias are seamlessly filled with only 10 μm of Cu on the surface. The advantage with such thin plated copper is to eliminate copper reduction process, thus eliminating the issue of V-pitting which originates in the half-etch step. Advanced advanced tenting process is still a subtractive process, which allows the fabricators to use current equipment and a similar process to manufacture advanced HDI PCBs. The electrolyte for mSAP can fill blind micro-vias and plate through holes simultaneously. This feature resolves the copper plating challenge having to fill micro-vias or to plate through holes using separate processes. The “additive” nature of mSAP is such that copper plated on a much thinner base copper layer, with the thin base copper layer then etched away in what is called the flash etch step. This process offers copper traces that can be prepared with much greater precision, in straight vertical lines, yielding a rectangular-shaped lines that better maximize circuit density and enable accurate impedance control with lower signal loss. This paper discusses the capabilities from these two plating processes.