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48 PCB007 MAGAZINE I MAY 2023 assume that without additives, the copper deposit would not be able to withstand the high temperature and mechanical stresses subjected to the board during assembly and service in harsh use environments. What functions do these additives perform? Are they simple? e short answer is "no." As stated earlier, the complexity of circuit board designs today, and certainly in the future, requires new and improved plating additives, as well as methods to con- trol them. Traditional through-hole via (direct current) plating parame- ters and chemistries are not optimal for these more complex structures. Worse yet, metallization of boards with blind and through-hole vias require trade- offs in plating conditions and chemistries to achieve acceptable results on through-holes and in the blind vias. e additives, which are sometimes referred to as brighteners (for the cosmetic effect on the copper), are formulated with multiple compo- nents that can be blended into a single con- tainer or added individually as needed. (e latter is recommended for tighter control of the process.) So, what are these components, and what functions do they perform? In the absence of these organic additives, copper grains grow preferentially on surface defect sites. e copper then grows along pre- ferred copper crystal planes. e plated cop- per does not exhibit the fine-grained equiaxed structure that is beneficial in providing ductil- ity and tensile strength to the deposit. Under these conditions, the plated copper is dull (matte) and brittle or non-ductile. is causes the plated copper to fracture when stressed, due to the deposit's poor ductility. In gen- eral, additive-free or low-additive plating solutions typically produce deposits with columnar structure, which can lead to cracking in solder float tests (Figure 1). Copper grows faster on protrud- ing topographies (high spots on the surface), as well as high spots in the via caused by poor drilling. ese high spots typically form because of higher primary current density (Fig- ure 2). e primary current distribu- tion is mostly dependent on the board Figure 1: Barrel cracking and corner crack due to brittle cop- per deposit. Also, note the rough nodular deposits in the via. Figure 2: Rough spots due to poor leveling of the copper.