Applications of Dispersive Raman Microscopy to Failure AnalysisSpring 2004 European Seminar Series

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AcknowledgementsRaman spectra and images supplied byJohn Wolfgong, Ph.D., Raytheon, McKinney, TexasCollected on a Nicolet Almega with 532 and 785 nm lasers

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The Role of Raman in Failure AnalysisRaman fills an important gap in the failure analysis labProvides molecular information on very small spotsSmall particles becoming increasingly more importantSEMProvides good image analysis and elemental informationOften this is not enough to identify small organic particles or to diagnose failure modes in organic materialsFT-IRProvides good molecular informationLimited to about 10 m in sizeRaman extends the limit for molecular materials to 1 m

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Nondestructive Plus SamplingRaman allows samples to be analyzed as isOften you do not want to damage sample or the substrateNondestructive PlusCan even measure directly through glass or plastic packaging

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Real Life ExamplesFailure analysis encompasses a wide range of samples and information needs. We will examine a few specific real-life examples to see how Raman was applied to solve the problem.

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Braze Joint Crack AnalysisProblem statement: Determine at what point in the process the crack appeared. Crack was easily confirmed by visual inspection. Then further analyzed by embedding it in epoxy and cross sectioning it to determine the extent of the crack by visual inspection. The part goes through a processing step where it is coated with at Silicone conformal coating. If the crack had appeared before the coating it should be filled with Silicone conformal material, otherwise it would be expected to be empty. This could not be established with certainty by visual inspection.

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Braze Joint Crack AnalysisRaman was used to analyze the contents of the crack.532 nm laser was used no fluorescence.A reference spectrum of the epoxy potting compound was also collected to insure that it was not confused. Potting Compound Reference Conformal Coating Reference Spectrum Obtained from within Area 2 Spectrum Obtained from within Area 1 500 1000 1500 2000 2500 3000 Raman shift (cm-1)

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Braze Joint Crack Analysis Potting Compound Reference Conformal Coating Reference Spectrum Obtained from within Area 2 Spectrum Obtained from within Area 1 400 600 800 1000 1200 1400 1600 1800 Raman shift (cm-1) Raman easily confirmed that the crack occurred before the coating step.

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Troubleshooting Magnetically Actuated ClutchesProblem statement: Clutches passed all inspection tests and were found to be inoperable after 6 months of storage. Clutches could be freed up by pulling the clutches loose with pressure. What is causing the problem with the clutches?

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Troubleshooting Magnetically Actuated ClutchesInitial investigation applied FT-IR microscopy to the lubricantTurned up spectra of particles exhibiting a strong carbohydrate spectrum.First course of investigation pointed to possible sources of cotton fiber contamination

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 Absorbance 1000 1500 2000 2500 3000 3500 Wavenumbers-1)

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Troubleshooting Magnetically Actuated ClutchesContinued investigation revealed distinctly crystalline imagesFT-IR spectrum diagnosed as sucrose at this pointDiagnoses was met with considerable skepticism as there was no known means for sucrose to be introduced into the product.

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Troubleshooting Magnetically Actuated ClutchesRaman spectroscopy utilized to support FT-IR diagnosisRaman spectrum is less sensitive to the -OH end groups in carbohydrates and readily identified the material as sucrose

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Troubleshooting Magnetically Actuated Clutches

Clear Crystal on Spring (2868) - [Analysis using 532 nm laser]

Crystal on Gray Outer Ring After Removal of Clutch (2868) - [Analysis using 532 nm laser]

Solid crystal (2868) - [Analysis using 785 nm laser]

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Raman shift (cm-1)

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Troubleshooting Magnetically Actuated ClutchesConclusion: Armed with a confirmed diagnosis, further inquires as to the source of the sucrose with the vendor uncovered that production crews were allowed to drink coffee on the line and that they had a sugar dispenser nearby. Slow crystallization of the sugar caused the failures.

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Analysis of Residual Contaminant Problem statement: A small residue measuring about 1x4 m was discovered in a cavity formed between various stackup layers during manufacture of a semiconductor device on 6 Silicon wafers. Investigators were asked to determine what the residue was without disturbing the residue or the wafer in any way.

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Analysis of Residual ContaminantInitially tried FT-IR Failed to produce results due to the small spot size and interference from specular reflection off of the Si substrateRaman pursued next Failed initially with a 532 nm excitation because of overwhelming fluorescence from the sample Switching to a 785 nm laser yielded an excellent spectrum

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Analysis of Residual ContaminantConclusion: Searching against a reference library revealed the residue was a polyimide Residue Polyimide Reference Spectrum 500 1000 1500 2000 2500 3000 Raman shift (cm-1)

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SummaryRaman has a lot to offer to the failure analysis lab todayTraditionally Raman systems tended to be rather difficult to use and required lots of maintenanceModern Raman systems such as the Almega XR are part of a new generation designed to be productive tools requiring very little training or maintenanceIt is likely that they will quickly take their place as one of the primary analysis techniques for failure analysis due to theirApplicability to small particlesInsensitivity to substratesApplicability to nondestructive plus analysis

Note: These were not Raytheon parts. These were bought in from an outside vendor.