Investigation into the Influence of Alkyl Thioureas with Varying Steric Hindrance on the Tensile Strength of Electrolytic Copper Foil

Abstract

Abstract Thiourea derivatives are typical additives that exert different steric hindrance effects on the tensile strength of electrolytic copper foil (ECF). However, the underlying mechanisms remain unclear. Herein, thioureas with methyl, isopropyl, tertbutyl substituents, and unsubstituted thiourea were selected. The influence mechanism of alkyl thiourea compounds with varying steric hindrance effects on the tensile strength of ECF was systematically investigated through electroplating experiments combined with density functional theory (DFT) calculations. The results indicate that larger substituents lead to greater steric hindrance effects, likely due to their increased volume and enhanced contact area with copper ions in the electroplating solution. Additionally, as steric hindrance increases, the energy gap between HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) decreases, thereby enhancing the binding affinity with copper. For tertbutyl thiourea, the tensile strength of ECF reached 650.56 MPa. The findings reveal that in tertbutyl thiourea, the substituent not only exhibits a larger volume and stronger adsorption behavior, effectively inhibiting the deposition rate of copper ions and promoting denser structure's formation, but also enhances the stability of the C═S double bond in alkyl thiourea, reduces residual sulfur (S) content caused by additives, improves purity, and simultaneously increases the tensile strength of ECF.

Keywords

• alkyl thiourea
• density functional theory (DFT)
• electrolytic copper foil (ECF)
• steric hindrance
• tensile strength