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70 PCB007 MAGAZINE I NOVEMBER 2019 the newly introduced rules governed this eval- uation. The key difference was not the type of immersion gold but the type of nickel. Please note that the cyanide-containing gold is dedi- cated to specific nickel types. Performance Benchmarking The general performance characteristics in- dicate that the CNF Au bath is a potentially viable immersion gold bath. The performance of the CNF Au bath is predictable, and the sta- bility is as good as or better than production- qualified cyanide alternatives. In the field, im- mersion gold can be realistically expected to have a lifetime of over 10 MTOs, not less than 10 MTOs, as is the case for CNF Au. However, "the proof of the pudding is the eating." In this section, the CNF Au will be compared using quality indicators that cover wire bonding, sol- dering, and corrosion. Aluminum Wire Bonding Aluminum wire bonding is an expected per- formance criterion for any electroless nickel immersion gold (ENIG) process. Wire bonding is generally regarded as a reflection of the com- patibility of the gold and nickel in the system. Whether this is true or not, it is definitely an analog representation of functionality. Bonding performance is measured by the force required to break the wire and the location of the break (fracture mode). The ideal pulling mechanics are described in Figure 9. Aluminum wire bonding utilizes wedge-to- wedge bonding as opposed to ball bonding. This is important for understanding the frac- ture mode as described in Figure 10 but re- quires no further discussion in the context of this article. Heraeus 25-μm gauge aluminum wire was used in this exercise. This has a breaking load of 14.9–15.2 g (according to the supplier). And according to DVS 2811, the average pull strength should exceed 50% of the breaking load [2] . Therefore, the pass criterion is approxi- mately 7.5 g. Figure 11 represents the pull strength for all the immersion gold types that were tested. Figure 9: ANOVA, wetting balance force after two seconds by ageing. Figure 10: Corrosion by internal evaluation techniques. Figure 11: The pulling conditions applied to test wire bonding in this article.