The use of scanning electron microscopy (SEM) in the analysis of defects
The abbreviation of scanning electron microscope is scanning electron microscope, abbreviated as SEM. It uses a finely focused electron beam to bombard the surface of the sample, and observes and analyzes the surface or fracture morphology of the sample through secondary electrons, backscattered electrons, etc. generated by the interaction between electrons and the sample.
In failure analysis, SEM has a wide range of application scenarios, playing a crucial role in determining failure analysis modes and identifying the causes of failure.
The main application scenarios of SEM in failure analysis are:
Q: What is failure analysis?
A: The so-called failure analysis is based on failure phenomena, through information collection, visual inspection, and electrical performance testing, to determine the failure location and possible failure modes, that is, failure localization;
Then, a series of analysis methods are adopted to conduct root cause analysis and root cause verification for the failure mode;
Finally, based on the test data obtained from the analysis process, prepare an analysis report and propose improvement suggestions.
Practical analysis and application cases
1. Observation and measurement of intermetallic compound IMC
Welding relies on the alloy layer generated on the joint surface, namely the IMC layer, to achieve the required connection strength. The IMC formed by diffusion has a variety of growth forms, which have a unique impact on the physical and chemical properties, especially mechanical and corrosion resistance, of the junction. Moreover, both too thick and too thin IMC can affect the strength of welding.
2. Observation and measurement of phosphorus rich layer
After being treated with chemical nickel gold (ENIG), the solder pads will accumulate excess phosphorus at the edge of the alloy layer after Ni participates in alloying, forming a phosphorus rich layer. If the rich phosphorus layer is thick enough, the reliability of the solder joints will be greatly reduced.
3. Metal fracture analysis
Analyze some basic issues of fracture through the morphology of the fracture surface, such as the cause of fracture, fracture properties, fracture mode, fracture mechanism, fracture toughness, stress state during the fracture process, and crack propagation rate. Fracture analysis has become an important means of failure analysis for metal components.
4. Observation of nickel corrosion (black plate) phenomenon
Observation of corrosion cracks (mud cracks) from the fracture surface and the presence of numerous black spots and cracks on the surface of the nickel layer after gold stripping indicate nickel corrosion. Observing the morphology of the nickel layer cross-section, continuous nickel corrosion can be observed, further confirming the existence of nickel corrosion phenomenon in the poorly solderable plate, and the abnormal growth of IMC at the nickel corrosion area, resulting in poor weldability.
