Residue Testing FAQs
Residue testing is a complicated process, and you’re likely to have questions. If none of these FAQs address your specific question, please contact us.
Q. What is ion chromatography?
A. Ion chromatography is an analytical test method which separates, identifies, and quantifies each individual contaminant species present in a sample solution. 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 determination of which residues are harmful, how much of a harmful material equates to poor assembly performance and, usually, the likely source.
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.
Q. What kind of residue does ion chromatography (IC) detect?
A. As useful as IC is, it will not detect all 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 will detect residues which: 1) can be brought into solution by an extraction method; 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.
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 electronics industry is still relatively new and has not made its way into many specifications yet. The only specifications where IC is referenced are 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.
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 we do, the extraction solution is iospropanol and water (75/25), the same as in BIC testers, but the temperature is 80°C 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 could be compromised. 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 materials 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.
Q. How much does ion chromatography cost as a service?
A. Several independent test laboratories offer IC as a service, along with some major corporations. The difference at Foresite is that we also interpret the data (included in the project price) and work with our customers to determine root cause and correct the underlying issue. For a price quote, contact us.
Other residue testing questions
Q. What is ionic contamination?
A. Ionic contamination refers to any electrically conductive residue remaining on an electronics assembly. Not all ionic materials, as measured in some ionics tests, are detrimental to circuit reliability.
Q. How do the residue testing facilities rate in terms of cost?
A. This is not something we can objectively cover here. You will probably find Foresite to be more expensive than other labs due to the interpretation we include. We do not offer a data-only option because the raw data can often lead the customer down the wrong path.
Q. What is meant by co-elution?
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.
Q. How do I know when to be concerned about polyglycol? Can 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.
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.
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 consistently run the test, for repeatable results, and how to interpret the data are the hard parts.
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 the 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 electronics. 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.
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.
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 clients. 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.
Q. Do you have an MSDS for the C3 Extraction Solution that I could download?
A. Yes, you can download the MSDS from the C3 page.