SMTA International Conference Proceedings


THE EFFECTS OF IMMERSION SILVER CIRCUIT BOARD SURFACE FINISH ON ELECTROCHEMICAL MIGRATION

Author: Donald P. Cullen
Company: MacDermid, Inc.
Date Published: 9/26/2004   Conference: SMTA International


Abstract: At times, the electronics industry changes faster than the testing and regulatory groups serving the industry. In this case, the electronics supply chain thoroughly evaluated the new printed circuit board (PCB) surface finish Immersion Silver. The silver finish was subjected to comprehensive testing and received product specifications throughout all industry sectors between 1995-2003. Specifications within Underwriters Laboratories (UL), however, were not current with the industry testing. UL maintained concerns over the use of silver metal in electronic packages, and implemented special testing for PCB devices using silver in their construction if the device was intended to operate at higher voltage/energy levels.

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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