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Electron microscopy is a natural extension of optical microscopy in failure analysis. The use of electrons instead of a light source provides much higher magnification (up to 100,000x) and much better depth of field, unique imaging, and the opportunity to perform elemental analysis and phase identification.
CALCE houses a state-of-the-art FEI Quanta Environmental Scanning Electron Microscope (ESEM) with advanced Energy Dispersive Spectroscopy (EDS), Digital Imaging, and in-situ Heating/Cooling capabilities. The ESEM can be operated in a high vacuum-high accelerating voltage mode (standard SEM mode) very high magnification (>100KX) and high resolution or low vacuum high accelerating voltage mode. If it is used in the standard SEM mode then non-conductive samples generally require sputter coating of the sample with a very thin layer of conductive material. This material is generally gold (Au) platinum (Pt) or carbon (C) The ESEM can be operated in two imaging modes, secondary electron and backscatter imaging.
The secondary electron imaging mode provides high-magnification and resolution imaging of sample surface structures morphology details. This mode also used for analysis that require EDX elemental analysis.
The backscattered electron imaging mode provides relatively good range of magnification and resolution imaging that show in grey scale sample elemental composition variation, as well as surface structure and topography detail. In this mode the sample may do not need to be coated.
In the ESEM mode, the specimen pressure chamber is pumped to pressures that are ten thousand times higher than that of the traditional scanning electron microscope (SEM), without contaminating the microscope. An ESEM is able to work with pressure and without surface charging because the detector is designed based on the principle of gas ionization. As the secondary electrons are emitted from the specimen surface and accelerated towards the detector, they collide with the gas molecules, liberating more free electrons and thereby providing a greater number of signals. Proper operating pressure prevents any surface charging. Depending upon the environmental requirements, the pressure source can be water-vapor, air, argon, nitrogen or other gases.
These three modes (high-vacuum, low-vacuum and ESEM) accommodate the widest range of samples and allow CALCE researchers to examine unprepared, uncoated specimens in their natural environment. CALCE also possesses the added capability to conduct dynamic characterization like wetting, drying, absorption, melting, corrosion, and crystallization using the ESEM.
E-SEM image of a BGA solder ball showing crack on the board side
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