Characterization of Soldered Plated Through Holes (PTHs) and Gold Embrittlement Conditions
Authors: David Hillman and Daphne Gates Company: Rockwell Collins Date Published: 7/30/2019
Abstract: The implementation of the Restriction of Hazardous Substances (RoHS) European Union Directive in 2005 resulted in an increased use of gold plating as a surface finish for component terminations. The industry has long understood the issues of creating unacceptable solder joint integrity due to excessive gold content in the solder joint composition. Gold and tin combine to form a brittle intermetallic compound (IMC) when the gold content of the solder joint exceeds 3 weight percent. Controlling the component gold plating thickness, the soldering process temperature and soldering process time can insure that a gold embrittlement situation is avoided. The industry rule of thumb for avoiding solder joint integrity loss due to gold embrittlement for plated through holes (PTHs) was not allowing the component gold plating thickness to exceed 100 microinches. Recent changes in the IPC-JSTD-001 specification called into question the 100 microinch gold plating thickness maximum value when manually soldering PTHs. A series of soldering trials were conducted to characterize the solder joint microstructure and formation of the gold/tin IMC when manually soldering PTHs. This paper documents the investigation and results for those soldering trials.