Authored By:
Terry Munson,
Foresite, Inc.
IN USA
Summary
Since the 1980s the electronics industry has utilized ion chromatography (IC) analysis to understand the relationship of ions, and some organics, to product reliability. From component and board fabrication to complete electronic assemblies and their end-use environment, IC analysis has been the de facto method for evaluating ionic cleanliness of electronic hardware. Typical ions accounted for include chloride, bromide, nitrate, sulfate, weak-organic acid (WOA), sodium and ammonium. Environmental and other concerns have driven the industry to adopt myriad flux formulations, which has created a need to further differentiate weak-organic acids beyond what a typical IC system using conductivity can provide.
By utilizing an Ion Chromatography/Mass Spectroscopy (IC/MS) system optimized for organic separation, we can use the same IC column technology for the typical suite of anion/organic species, then run the sample through a quad-pole mass spectrometer which provides the molecular weight assessment of organics for over two dozen channels. This capability is critical to our failure analysis work at Foresite, as it allows for identification of specific organic acids and flux activators. This information can aid in identifying specific residue sources (e.g. board fabrication, SMT paste flux, waver solder liquid flux, hand solder flux or a completely different, possibly unauthorized, source.
Conclusions
Due to all the changes in electronic design, size, sensitivity, application and expected reliability, it is vital to understand the variables of cleanliness (residues from key critical steps) on the hardware pad to pad, hole to hole and lead to ground. Using traditional ROSE testing allows for a gross understanding of some small percentage of an average of conductive soluble residues (not NaCl but a scale using a salt standard of gross conductivity) over the entire board/component surfaces with room temperature extractions.
Similar to this, Ion Chromatography utilizing total board bag extractions gives a better understanding of the average species detectable by the heated (80 °C for one hour IPA/DI water) extraction, but again this is an average over the entire board and only uses conductivity detection. Using tools that isolate the residue and specific area (with a heated DI water extraction) where failures are occurring (lead to ground under the QFN), then utilizing both IC and IC/MS analysis to detect which residues are present in these areas allows us to gain a better understanding of failures and whether they are unique or if they originate from manufacturing processes. Or, is it an environmental impact or both? Understanding electronic cleanliness (both when things are working well and when they fail) is critical to identifying how to predict the reliability needs of your specific electronic hardware in your application, it starts with tools that allow you to understand the different chemicals being left on the assembly or in the system that will impact performance.
Initially Published in the SMTA Proceedings
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