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Frequently Asked Questions: General
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Q. How much does ion chromatography (IC) testing cost to set up?
b. Figure about 85 - 100K in equipment and
hiring a trained chemist as an analyst.
Q. How much does ion chromatography cost as a service, and is it
available as such?
A. Several independent test laboratories offer IC as a service,
along with some major corporations. Costs vary between sites. As
far as we know, only Foresite offers interpretation of the data included
in the test
price.
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Q. How do the facilities rate in terms of cost?
A. This is not something we can objectively cover here. You will
probably find Foresite more expensive than other labs due to the
interpretation we include. We do not offer a data-only option as
the raw data
can often lead the customer down the wrong path.
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Q. What is meant by co-elusion?
A. Ion chromatography, like any chromatographic method, is used
to separate a solution into its various components for individual
analysis. Separation is attained by passing the solution through
a column of specially
charged resin. Different materials move through the resin at different
rates, eventually resulting in separation of most materials. Some
materials, though,
pass through the resin at the same rate, even though they are different
materials. The two materials come out at the same point in the
spectrum and so are said to co-elute.
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Q. How do I know when I should be concerned about polyglycol? Can't
I just look at what chemicals I am using in my process?
A. Looking at the MSDS sheets will often tell you if a polyglycol
material is present as a material element. Unfortunately, there
is not a good way to tell if you have adequately removed the polyglycol
residues
from the substrate. We often suspect polyglycol residues when we
see electrical leakage failures on hardware in humid environments,
but no corrosion or
metal migration.
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Q. What are the factors that can collectively cause corrosion?
A. Electrochemical failures consist of three elements: electrical
potential, ionic contaminants, and moisture. The relative amounts
of each factor determines what failure mechanism predominates,
and at what speeds.
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Q. My Omegameter: How do I know when to change the columns?
A. When it starts taking you a very long time to clean up the solution
and return to the machine starting point. The columns are weak
and need to be replaced.
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Q. SIR Testing: How does it work?
A. The concept is simple. Take a substrate designed for SIR testing,
solder wires to the test pattern, put it in a temperature-humidity
chamber and apply an electrical potential. Measure the insulation
resistance periodically
and watch how it changes. Knowing how to run the test repeatably
and knowing how to interpret the numbers are the hard parts.
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Q. What is ionic contamination?
A. Ionic contamination refers to any electrically conductive residue
remaining on an assembly. Not all ionic materials, as measured
in some ionics tests, are detrimental to circuit reliability.
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Q. Can my BIC (bulk ion contamination) tester be used to analyze
non-rosin flux technology assemblies?
A. The use of a BIC tester is not recommended as a process evaluation
tool, but can be successfully used as a process control tool. The
BICs were all developed based on rosin fluxes and all of the materials
properties of rosins. Newer flux technologies are based on very
low levels of rosin,
or resin, the solubilities are different, the chemicals are different.
Many of the newer flux technologies have electrically conductive
elements
which
are not harmful to the long-term reliability of the assembly. A
BIC tester cannot distinguish between harmful and non-harmful residues.
A BIC tester
can be used as a process control tool to determine changes in contamination
levels, but it is important to understand what the BIC response
means.
Note: An excellent report, published by the Electronics Manufacturing
Productivity Facility (Report number RR0013, phone 317-226-5634)
discusses many of the relevant issues regarding BIC testers and
their applicability to various technologies.
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Q. What is the correlation between the response of a BIC (bulk
ion contamination) tester and ion chromatography (IC)?
A. Good question! At present the correlation is very general at
best. An increase in BIC response will generally correspond to
increases in ionic species as measured by IC, but not always. IC
is more repeatable
and precise than a BIC. There are extraneous factors in a BIC,
the most predominant one being the mixing of carbon dioxide from
the air which alters
the conductivity of the solution.
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Q. What is ion chromatography?
A. Ion chromatography is an analytical test method which takes
a solution containing multiple contaminants and separates, identifies,
and quantifies each individual contaminant species. By species,
we refer to
basic elements, such as chloride or bromide, or molecular compounds,
such as sulfates or weak organic acids. By knowing the specific
conductive species,
we can make a better estimation of which residues are harmful,
and how much of a harmful material equates to poor assembly performance.
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Q. What does ion chromatography (IC) tell me that my bulk ionic
contamination tester will not?
A. A BIC (bulk ion contamination) tester will only indicate how
conductive a solution is, not what elements are present which make
the solution conductive. IC testing will determine which specific
ionic materials are
present and in what amounts. It is much like comparing an auto
mechanic's big screwdriver to a jeweler's screwdriver. Which one
would you use to fix
a precision watch?
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Q. What kind of residue does ion chromatography (IC) detect?
A. As useful a tool as IC is, it will not detect all possible residues.
To our knowledge, no single analytical equipment or test method
will detect all residues. Maybe NASA has something, but they haven't
told us! IC wll
detect residues which: 1) can be brought into solution by an extraction
method; and 2) are electrically conductive to some degree. If a
residue simply cannot be dissolved by a reasonable solvent (one
which does not destroy
the assembly itself), then there would be no contaminants in the
solution to detect. Also, if the residue was an insulative material,
and conducted
no electricity, it could not be detected by the precision conductivity
meter that is part of the IC equipment. Other test methods, such
as high pressure
liquid chromatography or mass spectroscopy can be used to detect
such non-conductive residues.
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Q. Are there accepted pass/fail limits for ion chromatography in
military or commercial specifications?
A. At present, the answer is no. IC testing in the printed wiring
assembly industry is still relatively new and has not made it's
way into many specifications yet. The only specifications where
IC is referenced is J-STD-004 and MIL-F-14256, which allow the
use of IC as an acceptable
method of determining the halide concentration in fluxes. We are
presently
involved with several national specification efforts, and are working
on the incorporation of IC as an accepted process evaluation tool.
We have our own set of recommended pass/fail limits, depending
on the flux chemistry
involved, but these limits are not (yet) nationally accepted.
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Q. Is ion chromatography (IC) a destructive test?
A. That depends. The destructiveness of IC testing is dependent
on the extraction technique used. For most tests which we do, the
extraction solution is iospropanol and water (75/25), the same
as in BIC testers, but
the temperature is 80C and the extraction time is 60 minutes. While
this does not exactly destroy the assembly, many of the materials
involved may
be sufficiently altered such that the reliability of the assembly
would be in question. However, by modifying the extraction technique,
either using
alternative solvents such as pure water, or by using lower temperatures
and longer extraction times, the IC analysis can be non-destructive.
This becomes particularly attractive when analyzing expensive assemblies.
If
an assembly contains components or material which are susceptible
to either isopropanol or water, then the IC method would be considered
destructive, regardless of the time or temperature used in the
extraction method.
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Q. Where is the electronics manufacturing industry transitioning?
A. A good answer to this would be to review the IPC Technology
Roadmap. It does address fabrication issues and assembly issues,
as well as the coming technologies. From our perspective, most
manufacturers are
transitioning away from rosin fluxes and alternative cleaning.
Of those who are transitioning, we would estimate that about half
are going to a
low solids flux, some with cleaning, some without. The other half
is going to a water soluble flux with aqueous cleaning, but with
a goal of eventually
transitioning to no clean. The jump to no clean is often easier
to make in two small steps rather than as one big leap.
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Q. Your test reports show recommended levels for various anions
found. How do you arrive at these values?
A. These values come from the failure analysis projects we do with
customers. Let us say we do an evaluation of an assembly that is
experiencing corrosion or metal migration problems. Anion levels
are measured at Level
X. Cleaning up the residues to Level Y seems to cure the problem.
Therefore, the threshold (Z) of the problem lies somewhere between
levels X and Y. Over
time, that threshold becomes more statistically valid with the
execution of similar projects. In general, chloride levels over
Z1 can cause problems.
Bromide levels over Z2 can cause problems. There are no guarantees
because every assembly has its own sensitivity.
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Q. Do you have an MSDS for the C3 Extraction
Solution that I could download?
A. Yes.
Click here to be taken to our C3 Extraction
Solution MSDS.
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