Growth of tin whiskers for lead-free plated leadframe packages in high humid environments and during thermal cycling

Abstract

Growth behavior of tin whiskers from pure tin and tin-bismuth plated leadframe (LF) packages for elevated temperature and high humidity storages and during thermal cycling was observed. In the storage at 60°C/93% relative humidity (RH) and 85°C/85%RH the galvanic corrosion occurred at the outer lead toes and shoulders where the base LF material is exposed, forming tin oxide layers of SnO 2 . The corroded layers spread inside the film and formed whiskers around the corroded islands. Many whiskers were observed to grow from grain boundaries for the Fe-42Ni alloy (alloy42) LF packages. It was confirmed that the corrosion tends to occur on the side surfaces of outer leads adjacent to the mold flash. The contribution of ionic contaminants in epoxy mold compound (EMC) to the corrosion was not identified. During thermal cycling between À65°C and +150°C whiskers grew out of as-deposited grains for pure tin plated alloy42 LF packages and they grew linearly with an increase of number of cycle. Growth mechanisms of the whiskers from grain boundaries and asdeposited grains were discussed from the deformation mechanism map for tin and mathematical calculation with a steady-state diffusion model.

Whisker-Like Formations in Sn-3.0Ag-Pb Alloys

“…2 shows one of the experimental results. The whisker-like formation (Sample 4) is compared with an image from the literature [12]. The shape of both formation is nodule, which type appears when the oxide layer is relatively thick (because of slow cooling rate in normal atmosphere).…”

Localized Surface Plasmon Resonance Dew Sensor for Use Under Low Humidity Conditions

“…Dew condensation can cause these devices to short circuit, leading to corrosion or to whisker and dendrite growth. 3) Furthermore, the size of a condensed dew particle that can damage a circuit is now on the order of just the wavelength of visible light. However, detection of these so-called micro-dew particles using a conventional chilled mirror hygrometer is difficult because of the diffraction limit of light.…”