Corrosion characteristics of passivated and unpassivated Al-to-PtAg wire bonds under accelerated temperature — Humidity conditions

This paper describes the effects of an 85°C/ 85% RH environment on the bond strength of passivated and unpassivated aluminum wire bonds in contact with thick film platinum-silver metallization in a non-hermetic package. An RTV silicone junction coating material and a ceramic cover coated with a single component epoxy resin powder were used singly and in combination to protect the wire bonds. Test samples were exposed to the 85°C/85%RH environment for a total period of 168 hours. Bonds were destructively pull tested at the end of 24, 96 and 168 hours. Selected samples were also examined with an optical microscope and a scanning electron microscope (SEM). It was observed that the unencapsulated wire bonds suffered extensive galvanic corrosion at the Al-to-PtAg interface after 24 hours of exposure. The encapsulated bonds had no visible corrosion at the bond sites and retained more than 80% of the initial bond strength even after 168 hours of exposure.