The ageing behaviour of aluminium wire bonds (Al‐1%Si wire, 25 µm diameter) on five different gold thick film inks from three different manufacturers has been investigated. A new mechanism, the oxidation of the gold‐aluminium intermetallics, is proposed to explain the degradation of contact resistance for this system. With this theory the degradation of bond resistance, as well as the ‘healing effect’, can be explained. The oxidation can be proven by ageing in a vacuum. Surface analytical methods have shown the compound Au4Al to be responsible for the oxidation.
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