Electro-Chemical Migration Paper Published at APEX February 2016

Test Method Development for Detecting Pitting / Crevice Corrosion Formation on Electronic Assemblies

 

Abstract

 

Pitting/Crevice corrosion on printed circuit boards has not been well studied in the industry.  This mechanism has been seen at small solder mask openings near circuit traces on printed circuit boards when stored or shipped in a humid environment with no-clean soldering fluxes that passed all standard tests.  Failure modes are theorized to be driven by openings or defects in solder masks and humidity levels that mobilized surface contamination.  Harsh environments, which can bring in outside contaminants, can be one of the factors that causes pitting corrosion to initiate and grow.

In many of the applications employing high density assemblies processed with mixed technology, the quality of the laminate construction, the assembly process and quality of design are critical.  Solder mask type (glossy or matte,) curing and application process have been known to cause corrosion issues.  Often the soldermask employed (manufacturer, chemical structure, Tg, filler type and thickness) can be factors that lead to pitting corrosion and should be understood.  In some cases, the thickness, quality and roughness of the copper at the surface can contribute to corrosion.

The High Density Packaging User Group Consortium (HDP User Group) Electro-Chemical Migration (ECM) team is investigating pitting / crevice corrosion failure mechanism and the factors that cause the defect to occur.  The purpose of the research is to report current findings and the experimental description for qualifying soldering materials and to determine conditions needed to mitigate this failure mechanism.

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