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62 PCB007 MAGAZINE I AUGUST 2018 creased and was limited to 1.2 µin (0.032 µm) , when the thickness of the EP was 5.6 µin (0.14 µm) or greater. The explanation is that the gold ions, at the lower palladium thickness, had ac- cess to the underlying nickel and proceeded to deposit at an accelerated rate, producing nick- el corrosion. In absence of availability of the underlying nickel the immersion gold reaction with non-phos palladium, becomes self-limit- ing to 1.2 µin (0.03 µm). Figures 7, 8 and 9 are SEM micrographs de- picting the level and type of corrosion at dif- ferent levels of non-phos palladium thick- ness. Figure 7 shows extensive very shallow corrosion and a thicker gold deposit, 3.2 µin (0.08 µm); Figure 8 shows intermittent deep corrosion spikes and a gold thickness of 2.0 µin (0.05 µm); and Figure 9 has no corrosion spikes, however, the gold thickness was limit- ed to 1.2 µin (0.03 µm). Under the conditions of the test (the 30 min- utes extended dwell time in the gold bath) the data from the non-phos palladium shows sim- ilar trends as the phos-palladium data. At the lower thickness corrosion of the nickel will oc- cur, and at a thickness greater than 6.0 µin (0.15 µm) no corrosion occurs and the gold thickness is limited to 1.2 µin (0.03 µm). Figure 10 is a graphic presentation of the data from Table 5. The data shows that the gold thickness of the reduction-assisted or mixed-reaction immersion gold was virtually independent of the phos-palladium thickness. Gold continued to deposit at a high rate when Figure 6: Chart of non-phos palladium and gold thicknesses vs. time in the palladium bath. Figure 7: Non-phos palladium at 1.6 µin (0.04 µm). Corrosion was extensive and shallow. Figure 8: Non-phos palladium at 3.6 µin (0.09 µm). Very intermittent deep corrosion. Figure 9: Non-phos palladium at 7.6 µin (0.19 µm). No corrosion.