Lead Tinning Requirements for the 21St Century

ABSTRACT The solderability of components in the process of manufacturing printed circuit assemblies is key to the longevity and reliability of the finished product. Hot solder lead tinning is the most dependable method to mitigate tin whiskers and prevent their growth when changing from a RoHS finish to a tin-lead finish for high reliability parts; or when changing to a RoHS-compatible finish when a leadfree finish is required; and hot solder lead tinning is also used to remove oxidized or contaminated solder surfaces in the instance of legacy components. Molten solder tinning is also used for prevention of gold embrittlement. Successful solder attachment of components to a circuit assembly relies largely on the solderability of surfaces to be joined, establishing optimum thickness of intermetallics for a strong, yet compliant joint. Achieving this requires complimentary chemistries with the appropriate temperatures and dwell times. Many factors necessary for a successful, repeatable and reliable process must be understood and controlled, and the end product finally tested to show that the end result meets or exceeds a customer’s requirements. This paper examines the need for a two pot, molten solder lead tinning process, what it achieves, and how it is successfully implemented and proven from a solderability proof perspective, including results obtained from XRF analysis, wetting balance measurements and ionic cleanliness testing, in conjunction and in compliance with IPC/EIA JSTD-002 and ANSI/GEIA STD-0006 standards.