WHITE RESIDUE FORMATION ON PRINTED CIRCUIT BOARD ASSEMBLIES

摘要

Experimental and analytical approach was undertaken to investigate and correct white residue and corrosion failures found on multiple PCBAs. SEM and EDX evaluation of the failure sites reveled the presence of Chloride, Sodium and Carbon. Ion Chromatography test of residue found on the failure sites also revealed the presence of 0.01-0.75 μg/in{sup}2 Chloride and 0.35 μg/in{sup}2 Bromide. The result of Fourier Transform Infrared Spectroscopy (FTIR) analysis identified the contaminant as flux residue coming from both aqueous and No-Clean Flux used in the assembly process. The field failure was successfully duplicated at the factory. Further more, response of both aqueous and no-clean flux to white residue formation was evaluated. Experimental results revealed that solder joints of active devices tend to produce white residue independent of ionic contamination level when both moisture and bias are applied to the site. The combination of experimental results and duplication of the failure at the manufacturing site, indicated that device power up during PCB testing combined with inadequate moisture control were found to be the primary cause of the failure. New testing and device power up schemes were developed and implemented.