ADVANCED MATERIALS & PROCESSES | OCTOBER 2025 27 In the initial design phase of adhesive validation, the team observed robustness in bonding strength through various environmental tests. The adhesive joint consisted of an aluminum alloy with a chromate coating and a brass lens barrel. For about eight months, the manufacturing process did not encounter any issues with adhesive alignment and curing in the oven. However, concerns later arose when cured lens mount assemblies were found with detached adhesive. An intensive investigation revealed that surface contaminants on the aluminum lens mount reduced adhesive strength, causing some assemblies to detach easily when handled. Further analysis identified organic silicone as the root cause of the adhesive bond detachment. The likely source of contamination was the operator using the same gloves to handle both the thermal pad and the lens mounts. Engineering design of experiments showed that the thermal pad could cause the lens mount to detach. These samples were used as a baseline for Raman spectroscopy. The baseline was then compared to samples returned from the field and samples that failed at the manu- facturing plants. FAILURE ANALYSIS USING RAMAN SPECTROSCOPY The Raman spectroscopy technique measures the inelastic scattering of light to identify molecular vibrations, rotations, and other low-frequency modes. It is particularly effective for detecting organic compounds and DETECTION CHALLENGES: ADAS SMART CAMERA Silicone contamination is challenging to detect because it can be present in very thin layers that are not visible to the naked eye. Advanced analytical techniques, such as x-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and Fourier transform infrared spectroscopy (FTIR) are often required to identify silicone residues.[1,2] These methods are often expensive, time-consuming, and not readily available in most manufacturing environments. Moreover, FTIR struggles to detect low-frequency vibrational modes, which are critical for identifying certain organic compounds. This limitation led to the exploration of alternative analytical techniques. (b) (a) Fig. 3 — (a) Raman spectrum obtained from thermal pad. (b) Raman spectrum obtained from epoxy flake from “good” control sample. (b) (a) Fig. 4 — (a) Comparison between averaged Raman spectrum obtained on failed lens mount (red peak) and that acquired for the thermal pad. Note: these Raman spectra have been normalized to the peak maximum for permitting greater ease of visualizing differences between the spectra. (b) Comparison between averaged Raman spectrum obtained from the failed lens mount and that acquired for the epoxy flaked off “good” control sample.
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