THE EFFECTS OF IMMERSION SILVER CIRCUIT BOARD SURFACE FINISH ON ELECTROCHEMICAL MIGRATIONAuthor: Donald P. Cullen
Company: MacDermid, Inc.
Date Published: 9/26/2004 Conference: SMTA International
UL’s concern with the use of silver revolved around historical accounts of dendrite formation, a type of defect caused by electrochemical migration. The UL restriction began to hinder widespread use of immersion silver by OEM’s who had conducted extensive reliability studies. Upon review, it was determined that the UL electrochemical migration test method needed to be updated to reflect changes in PCB technology. Further investigation proved that all surface finishes could fail the UL test method, even if there was no evidence of dendrite formation.
A group of companies from the electronics supply chain formed a task group to work with UL in updating their specifications. Later, this group became the IPC 3-11g Metal Finishes Data Acquisition Group. This article describes the testing, demonstrations, revisions, and ongoing work of IPC 3-11g in coordination with Underwriters Laboratories. More specifically, this article will present data from a team project to identify the important parameters affecting electrochemical migration from the viewpoint of UL. This article will augment previously published project updates with physical analysis of experimental samples.
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