EPMA, XMA
Electron Probe X-ray MicroAnalyzer
Electron Probe X-ray Micro Analysis system irradiates finely focused electric beam on solid-state specimen to detect characteristic
X-ray generated from the area electron beams reaches (of about 1µm). Elements in the target area of secondary electron image
or in foreign material can be analyzed to identify their description, amount and distribution. This Analysis method is well-known
for its excellent quantitative feature, compared to other solid-state surface analysis method.
There are 2 types of X-ray spectrometer; Wave length dispersion system (WDS) and Energy dispersion system (EDS). The former
features high energy resolution and excellent quantitative analysis. In general, "EPMA" refers to the system applying
WDS. With the latter, EDS, rapid Qualitative analysis is available. Typically, it is used by mounting on SEM.
Equipment
JXA-8800RL
JXA-8800RL with EPMA LaB6 electron probe attached allow us to obtain fine electro beam with wich more microscopic area can
be observed and analyzed.
In addition, with the higher performance of X-ray detector, sensitivity to trace of light element (C, O, N) has been greatly
improved.
Analysis Example
Foreign material in ditch bottom of PCB trace
SEM image
X-ray mapping of Carbon
(Red and Yellow show the area with high density of Carbon)
Short defect due to corrosion in lead of IC component mounted on Substrate
After removing the component, foreign material (FM) is found in lead area in the substrate
Conduct color mapping analysis by means of EPMA
Foreign material like the trace of liquid dry-out was identified as residual flux (Chlorine (Cl), Sn of solder).
Foreign material segregated like form of branch was identified as corrosion / segregation of solder constituent.
Root cause
Solvent containing flux penetrated into gap between substrate and component, causing solder corrosion after voltage application on lead. Solder constitution was segregated in gaps between adjacent leads and electric short occurred.
Short circuit due to migration of solder constituent
Metal is segregated (migrated) in form of dendrite between adjacent conductive traces on PCB, from conductive trace with lower potential to that with higher potential.
Conduct Mono chrome mapping (characteristic X-ray) analysis by means of EPMA
Chorine (Cl) is observed in addition to Sn and Pb (Solder constituent) in Migration area
Root cause
Electrolytic reaction has been accelerated between Water condensation and Cl in residual flux caused migration, and resulting electric short
Two dimensional density mapping analysis on solder junction cross section
Color mapping by means of EPMA
In junction area of Cu pattern and Solder, Cu and solder may generate intermetallic compound that results in decreased junction force. Below EPMA image illustrates the statue of intermetallic compound generation in cross section of the junction area.
