Program Information
Gamma-Ray Induced Growth of Metal Whiskers
M Killefer1 , V Borra1 , A Al-Bayati1 , E Parsai2 , D Georgiev1 , V Karpov1 , D Shvydka2*, (1) University of Toledo, Toledo, OH, (2) University of Toledo Health Science Campus, Toledo, OH
Presentations
SU-I-GPD-T-17 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: Metal whiskers (MWs) are thin metallic protrusions, growing on surfaces of many technologically important metals, including soldering compounds, have been identified as a cause of catastrophic failures in devices ranging from satellites to pacemakers. Despite decades of research MWs growth cannot be reliably predicted or mitigated. Recently developed electrostatic theory of MWs growth points towards electric field as the main culprit. We demonstrate that such fields may be generated under HDR irradiation conditions, thus raising concerns for related treatment devices.
Methods: We have irradiated samples of thin (<1 micron) zinc and tin metal layers, deposited on glass substrates, with an Ir-192 source of a clinical HDR afterloader with a line-source irradiation pattern, delivering the highest dose to central regions. After receiving doses up to 20kGy through multiple irradiation sessions, samples were assessed with scanning electron microscopy, allowing for quantitative assessment of whisker growth.
Results: Samples were evaluated in two rounds after receiving doses of up to 10 and 20kGy. After the first round the central regions of sample receiving the highest dose were found to develop whisker infestation, while the reference sample remained in its pristine as-deposited condition. The second round of irradiation generated more and longer whiskers. The observed phenomenon can be explained by radiation-induced charge accumulation in the glass substrate, generating an electric field that promotes whisker growth. The observed concomitant substrate glass darkening confirms development of color centers related to charge trapping.
Conclusion: Whisker growth on thin metal samples was unambiguously correlated with the radiation dose received by the glass substrate directly below the metal. The observed phenomenon points to unexplored potential reliability issue with HDR-related equipment, including the afterloader parts, and insertable devices with metal components and soldered junctions. Similar investigations for linac photon beams are underway.
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