SEM - EDS

A scanning electron microscope is used to determine the topographical image or make-up of a sample. It has a greater depth of field, higher resolution and higher magnification than an ordinary optical microscope. It is relatively easy to use and is widely-used in almost all research areas. The SEM only produces high-resolution images of the sample surface.  Hence, the internal structures of the sample cannot be determined unless cross-section is performed.

Energy Dispersive Spectroscopy (EDS) is a standard method of identifying and quantifying elemental composition of sample surfaces. The characteristic x-rays are produced when the sample is bombarded with electrons in an electron beam instrument, such as a scanning electron microscope. Detection of these x-rays and discrimination of the x-ray energies can be accomplished by an energy dispersive spectrometer.

Suspect Pure Tin on the surface of your part?  EDS can validate your suspicion.

Applicable Specifications & Standards:

ASTM E1829, Standard Guide for Handling Specimens Prior to Surface Analysis
ASTM E1508, Standard Guide for Quantitative Analysis by Energy-Dispersive Spectroscopy