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76 PCB007 MAGAZINE I NOVEMBER 2019 The result for the CNF Au gold bath is worse than that for the cyanide-containing baths. The determining decision factor is the type 4 and type 5 fracture modes as these types of fracture modes indicate brittleness. However, the popu- lation size may have influenced the outcome. It is worth considering that the total percent- ages for fracture mode 4 and the percentages in Table 3 are below 1%. Ultimately, the ductile types fracture mode 2 represent over 97% of the results. To complete the circle, the impact of the nickel was evaluated. The shear strength can be seen in Figure 24. The shear strength for the nickel types is comparable and a statistical difference be- tween the averages that cannot be identified. In Table 4, as with Table 3, differences are ob- servable but are once again, the resolution is too low to show the actual numerical classi- fications. Both nickel baths generally display high ductility. The brittle fracture modes for both the nickel types are below 1%. Solderability Solderability is the reflection of the function- ality of a final finish in assembly as opposed to after assembly. Solder flow or wettability is required to secure components and potential- ly saving money by minimizing the volume of solder paste. This article will address two of these evalu- ation methods; although these are proprietary, they remain topical for this article. The tests are the solder indicator (SI) test and the solder spread (SS) test. These are described in Figure 26 and Figure 27. In both test methods, solder paste is applied in a specific pattern, or loca- tion, from where it can flow during reflow. In the case of the SI test, the solder is expect- ed to close the gap in the solder and is scored accordingly, depending on how far it flows, and, of course, in which direction. Less than 2 is poor, indicating dewetting, while 10 is excel- lent but rarely achieved. In the case of the SS test, a limited volume of solder paste is applied, and the coupon is reflowed. After reflow, the angle will be mea- sured to assess flow potential. The lower the angle, the better, but around 20° is regarded as the critical value. Figure 24: ANOVA, a comparison of the shear strength for the gold types. Table 4: The fracture mode data for the nickel baths. Figure 25: A comparison of the ball shear fracture modes for the gold types.