Reactions of high lead solders with BIOACT EC-7R semi-aqueous cleaning reagents

Due to environmental concerns, terpene-based cleaning fluids have replaced Freon in cleaning baths at several AT&T manufacturing sites. The terpene fluids are employed in a semi-aqueous process and, typically, are used to deflux circuit boards where most of the interconnections are formed using 60Pb/40Sn solder. Recently, the use of terpene cleaning BIOACT EC-7R was extended to thin film ceramic substrates where high lead solder (95Pb/5Sn) forms the interconnection. In the presence of high lead solder, EC-7R quickly changes from colorless to bright yellow. In addition, the cleaning process deteriorates and residues are found on the circuits. The goal of the work discussed below is to elucidate the reactions between the circuit metallurgy and the EC-7R chemical composition. A matrix experiment was performed where EC-7R and its component chemicals were reacted with pure lead, tin, copper, and two high lead solders (98Pb/2Sn and 95Pb/5Sn) for three months. In a second experimental group, 95Pb/5Sn solder was reacted with EC-7R containing varying amounts of water. Precipitates were observed in many reaction vessels, especially when water and high lead content were present. The precipitates could be responsible for the residues found in the production baths. Finally, we studied the reaction mixtures and determined some of the EC-7R bath oxidation mechanisms using UV-visible spectroscopy, and gas chromatography/mass spectroscopy (GC/MS). These results were used to formulate a high performance EC-7R, to monitor the EC-7R bath, and maintain longer lasting baths.