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Ionic contamination is a frequent cause of reliability
problems in electronic devices and equipment. Ion chromatography
provides an ideal method to pinpoint the source of contamination,
understand the mechanism of failure and so avoid future problems…
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Ionic contamination can initiate and accelerate a range
of corrosion processes as well as reducing electrical
surface insulation and increasing the likelihood of
electro-migration of metals. Indeed, in many corrosion
and migration phenomena even very low levels of certain
ions are known to have a significant detrimental effect.
Identification of specific ionic contaminants
Extraction procedures, where the increase in conductivity
of a wash solution is measured, are commonly used to
estimate total ionic contamination but these provide
only crude information. The role played by contamination
depends critically on the ion species, where they are
found and in what local concentrations.
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Figure 1. What caused these gold
plated contacts to corrode? |
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Ion chromatography provides the best approach to diagnosing
this information. Common inorganic anions such as chloride,
bromide and sulphate can be separated and quantified
at the low parts per million range in just a few minutes
with a sample size of just a few microlitres. The small
sample size and high sensitivity allows for small parts
of boards, individual components or even parts of components
to be investigated. Where non-destructive analysis is
required, or to understand the ingress of environmental
contaminants in closed systems, small area swab samples
can be collected.
Ion chromatography allows this detailed information
to be discovered. This can represent a type of fingerprint
connecting the contamination to a particular source.
Pinpointing this source and understanding the mechanism
of failure is essential in avoiding future problems.
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Case study - corrosion of connector
Figure 1 shows corrosion on the contacts of an edge
connector from a piece of consumer electronics. The
contacts are gold over nickel on brass. The green areas
indicate that corrosion of the underlying nickel has
occurred.
A wash solution from this corroded area was subjected
to IC. The results are shown in Figure 2. The two main
ionic contaminants are clearly chloride and bromide.
Possible sources of these contaminants include flame
retardants from the connector body (for bromide) and
residues from HASL or other fluxes (for chloride).
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Figure 2. IC spectrum of contaminants found on contacts |
The level of contamination was be quantified by IC - giving
an indication of the threat posed by the individual ions.
Localisation of the source is determined by individual IC
analysis of the components in the system (e.g. bare board,
connector, fluxes etc.).
How we can help
ERA's Reliability and Failure Analysis group has bought a
state-of-the-art ion chromatography system to add to its battery
of analysis tools used in forensic investigation. To find
out how this might benefit you call us on +44 (0)1372 367444
or email.
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Identifying contaminants using ion chromatography
