Mixed flowing gas studies of creep corrosion on plastic encapsulated microcircuit packages with noble metal pre-plated leadframes

This paper describes tests and analysis of creep corrosion on plastic encapsulated electronic components with Ni/Pd or Ni/Pd/Au plated copper leadframes. Samples were subjected to three standard mixed flowing gas (MFG) tests to simulate corrosion effects in an accelerated manner, which included Telcordia Outdoor, and Battelle Class III Telcordia Indoor MFG environments. With an MFG exposure of 10 days, creep corrosion was observed over the plastic molding compound surface in the first two of the test environments. The formation and thickness of creep corrosion products on molding compound surface were characterized by microscopic observation. A four-decade drop in insulation resistance was measured between adjacent leads with visible bridging of corrosion products. Energy dispersive spectroscopy (EDS) was used to assess the elemental composition of corrosion products on both the component leads and the molding compound surfaces, and corrosion products were found to be copper salts. Sample pre-conditions, including surface cleaning, mold compound surface roughness, additional lead scratches, and applied voltage biases, were evaluated, and found to have no significant effects on the creep corrosion process. Conformal coating of the components was found to be an effective mitigation strategy to eliminate creep corrosion on packages with noble metal pre-plated leadframes.

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