Journal of SMT Article

IMPACT OF HIGHER MELTING LEAD-FREE SOLDERS ON THE RELIABILITY OF PRINTED WIRING ASSEMBLIES

Author: Dr. Laura J. Turbini
Company: University of Toronto (CMAP)
Date Published: 10/1/2000   Volume: 13-4

Abstract: The move toward lead-free electronics has become a rapidly emerging issue for concern and evaluation. The movement has been triggered by the European Union’s (EU) proposal for a Directive on Waste from Electrical and Electronic Equipment (WEEE) and by the Japanese focus on environmental marketing. The candidate solder alloys that have been identified as substitutes require high soldering temperatures since these alloys have typical melting temperatures between 198 degrees Celsius and 227 degrees Celsius. Concern has been raised that the higher processing temperatures required for wave and reflow soldering with these alloys will create increased drop out due to printed wiring board (PWB) warpage and component failures, since most components are not qualified in terms of reliability for these higher processing temperatures.

In this paper, we present evidence for an additional reliability concern for lead-free soldered electronic product. Conductive anodic filament (CAF) formation is a failure mode associated with boards, which either operate or are stored in a humid environment. This paper compares the number of CAF formed on boards reflowed at 201 degrees Celsius vs. 241 degrees Celsius after aging under 100V bias at 85 degrees Celsium/85% RH for 28 days. The incidence of CAF under the higher reflow conditions was typically 1-2 orders of magnitude greater than at the lower reflow conditions. The data provide additional reliability concerns for lead-free soldering.



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