Case Study: Failure Analysis to Determine Cause of Chrome Plating Problems
PROBLEM: Automotive supplier needed to understand why chrome plated ABS substrates were exhibiting a visual "streak" or "worm track" blister that had resulted in warranty claims
SOLUTION: Impact Analytical performed failure analysis services to determine cause of chrome plating problems
TECHNIQUES: Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM) and Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS)
Impact Analytical, a leader in analytical testing and problem solving services, was contacted to perform failure analysis for an automotive supplier that was having problems with returns for chrome-plated parts. The parts were being returned due to poor adhesion of the chrome plate to the ABS substrate. These parts contained a “streak” area or “worm track” blister which was visible to the eye.
FT-IR analysis was used to evaluate the defect plastic surface for evidence of chemical contamination and compare it to a good area that did not exhibit the adhesion problem. FT-IR is a common technique used to identify and provide a base fingerprint of a material. With this project, the FT-IR spectrum bands were consistent with the presence of polystyrene (PS) as the main component of the substrate. Weak bands also observed indicated the presence of a hydrated sulfate salt.
SEM analysis was employed to image the defect area for surface morphology evaluation and to visualize the degree of surface etch. Portions of the streaked area of the samples were observed in direct comparison with good proper plating areas. A key finding with the SEM analysis was that the expected etch appearance at the streaked area was absent. Instead, many voids were observed, but the surface did not appear as expected for one that had been etched. The surface of the good area as examined by SEM had a definite cellular appearance from an etching process. The good area also did not display such large voids (etch) pits as was observed in the streak area. An edge of the streak is shown in the attached figure with the streaked area on the left half of the image, and the good area on the right showing a clear difference in appearance.
X-ray spectra of the streaked and good regions of the samples were acquired to determine if elemental differences were present. The spectra of both good and bad regions were similar expect for the presence of copper found in the streaked region. Copper was observed in the streak region of each sample, but not in the good areas.
SOLUTION & RESULTS
SEM and EDS analysis of the streak areas compared to the good areas indicated a difference in the surface etching and roughness where the streak occurs, suggesting the streak area was improperly etched and/or had etchant residue remaining on the surface. Copper was also present in the streaked region, but not the good region.
Scanning electron micrograph at edge of streaked region. Streaked region is on the left where you can see the large voids (etch) pits and the non-cellular appearance expected of an etched surface. The good region is on the right. Notice the definite cellular appearance from the etch process. Scale bar is 20 microns.