Purple plague

Device life time There are several factors that determine the lifetime of the implant, such as (a) the internal battery lifetime, (b) hermaticity (the time it takes water to leak in and create a bubble drop), (c) time for corrosion to destroy the ceramic case, (d) time for corrosion to damage the metal leads and/or electrodes, and (e) other potential failure modes such as purple plague, (a degradation of wire bonding between aluminium and gold). 

The compound interface is the type of interface found in reactive systems such as oxygen-active metal films on oxide substrates, where a mixed oxide interphase material is formed, or in intermetallic-forming metal-on-metal systems such as Au-Al and Al-U. In the case of Au-Al the interdiffusion and reaction form both Kirkendall voids and a brittle intermetallic phase termed purple plague , which allows easy bond failure. When materials react, the reaction can be exothermic, where energy in the form of heat is released, or endothermic, where energy is taken up. Table 10.2 lists some heats of formation of various materials in forming compounds. An exothermic reaction is indicated by a negative heat of formation and an endothermic reaction is indicated by a positive heat of reaction. 

The interfacial material is most often characterized by fracture analysis, where failure occurs in the interfacial material and, after failure, the fracture surfaces are examined. The purple plague failure discussed in Sec. 10.3.3 is an example. 

Purple plague (adhesion) The color of the fracture surface in an Au-Al interface when the... 

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