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66 PCB007 MAGAZINE I MARCH 2025 rel of the hole is the result of this fatigue. e deposit must have sufficient tensile strength to be able to withstand fatigue cracking. It is well understood that the organic addition agents utilized in acid copper plating processes influ- ence the deposit's physical properties. One can think of tensile strength as the ability to withstand shock, vibration, and flexing. is is where tensile strength comes in. Certainly, you may surmise, there is a symbiotic relation- ship between tensile strength and elongation. ese two properties greatly influence the per- formance of the copper plating especially under thermal stress and mechanical stress condi- tions. Essentially, it is not possible to achieve extremely high tensile strength and very high elongation values. ere is a trade-off. As ten- sile strength increases, ductility declines, and vice versa. However, that is a good thing. ere is the sweet spot as shown in Figure 1. ese organic addition agents influence the physical properties of the copper deposit. is includes grain refinement, and leveling of the deposit through the surface, and vias. When controlled properly, the addition agents add strength to the deposit. is added strength or robustness permits the deposit to with- stand the thermal and mechanical excursions that the circuit board will be subjected to. is allows the deposit to achieve the sweet spot for reliability (Figure 1). Let's take a closer look at the functions of the various addition agents that make up most commercial addition agents' systems. Construction of the Acid Copper Addition Agent Acid copper additives contain at least one material described as a brightener and a sec- ond material that is described as a high molec- ular weight polymeric compound. Option- ally, the additive package also contains a level- ing agent. Each of these materials will now be described in some detail: Brightener e brightener is classed as nitrogen or sul- fur containing compound that by coulombic Figure 1: Interaction between tensile strength and elongation. (Image credit: Wu, Jian & Chen, L & Li, H & Su, B & Wang, Y. 2018) 20.0 17.5 15.0 12.5 10.0 20 40 60 80 100