Small chamber study of lead exposures from manual soldering of microelectronics

Abstract

Airborne and surface Pb concentrations were measured inside a glovebox chamber with controlled inflow rate at 1.0 L/min of ultrapure air over a 4-hour period while an operator completed 1,680 solder connections using Sn63:Pb37 solder with rosin flux core. Chamber atmosphere showed released mean Pb mass of 0.0238 ± 0.011 μg and mean airborne concentration of 0.176 ± 0.085 μg/m³. Of the total solder mass used in two trials, on average 4.65% was recovered from the tip cleaning sponge and 0.14% dropped onto the work surface, with a surface loading rate of 0.30–0.45 μg/cm². The estimated fingertip surface area in contact with solder wire was 14.7 cm², with a measured average Pb mass of 14.9 μg, and a corresponding dermal loading rate of 1.01 μg/cm². The waste solder dross surface area determined from digital micrographs in each trial were 1.65 and 2.43 cm², with corresponding Pb density of 714 and 610 mg/cm² and >90% of the detected dross mass comprising particles >100 μm in the widest dimension. Corresponding increases in blood Pb levels estimated using physiologically-based pharmacokinetic modeling were negligible compared with background. These findings demonstrate very low Pb emissions to air and surfaces during intensive manual microelectronic soldering activities.

Keywords:

• lead soldering
• airborne lead emissions
• dermal contact
• fine metal particulates

Acknowledgements

Costs for the design and implementation of this study were funded by a microelectronics manufacturing company that became a defendant in a personal injury litigation in part pertaining to claims of occupational exposures to lead in the 1980s while performing manual soldering of high reliability switches under military specifications. Permission was given to publish the study data, but the authors received no additional funding or assistance outside of their respective employers to develop and submit this manuscript.

Conflict of interest

Three of the authors (BDK, AEL, MJG) are employees of Exponent, Inc., an engineering and scientific consulting firm that performs research for private sector and governmental clients. One author (RG) is an employee of Brooks Applied Labs, an analytical laboratory that also provides consulting assistance for private sector and governmental clients. One of the authors (BDK) has served as an expert witness in litigation pertaining to lead. No parties outside of the authors participated in the design, implementation, and interpretation of the study findings or in the creation and submission of this manuscript.