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OCTOBER 2020 I PCB007 MAGAZINE 63 Figure 6: Peel strength of SAP copper plated on multiple ABF substrates. Figure 7: RDL features created with two-in-one via filling and fine-feature plating enable organic substrate buildup. erogeneous designs to other components, for high-density pitch and interposer routing in fan-out packaging and more. At the leading edge of the technology are electroplating chemistries that can fill the ver- tical via connections while also plating the subsequent layer's fine line traces in a sin- gle step [1] . These processes build electrolytic copper to precise dimensions on both SAP buildup substrates and the ultra-thin foil sub- strates used in mSAP and advanced tenting processes (ATP) and are a tremendous enabler for advanced packaging. Figure 7 shows the location of the RDL plating in a chip package diagram. RDL copper via filling baths have high con- centrations of copper (up to 250 g/L), lower concentrations of sulfuric acid (50 g/L), and a combination of a wetter (or carrier), bright- ener, and leveler to promote rapid filling. The additives work together to control the plating rate, the flatness of the deposit, and overall physical properties of the copper. The bright- ener acts to accelerate the plating deposit. The wetter is a high molecular weight polyoxy- alkyl compound that suppresses the plating by