Analytical Capacity
High-vacuum surface analysis technique utilizing monochromatic X-rays to measure the elemental composition and chemical state of the top few atomic layers of a material represents a primary diagnostic tool for circuit board finishes. This spectroscopic method, known as X-ray photoelectron spectroscopy, identifies both the elements present and their chemical bonding states. It is widely used to inspect electronic finishes for thin contaminants and oxidation layers.
Chemical State
Distinguishing between metallic elements and their oxides allows analysts to identify the root causes of solderability failures on the board pads. For example, during an investigation of poor solder wetting, X-ray photoelectron spectroscopy can determine if the outer gold layer of the finish contains oxidized nickel that has migrated to the surface. This chemical information is invaluable for diagnosing plating bath problems and optimizing the storage conditions of finished boards.
Depth Evaluation
Combining this analytical technique with continuous ion sputtering enables the reconstruction of the element concentration profiles down to a depth of several hundred nanometers. Although this process is destructive, it provides a highly detailed map of the individual layers within multi-layer board finishes. Maintaining a low-energy sputter beam during the depth profile minimizes atomic mixing and helps preserve the chemical state of the underlying layers.
These profiles allow for the direct measurement of transition zones and intermetallic compound layers, giving manufacturers the data needed to adjust chemical plating lines or trace sources of contamination in the production process.
