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JUNE 2018 I PCB007 MAGAZINE 49 cro-distribution is defined as the ratio of the average copper deposit thickness in the center of the through-hole to the average copper de- posit thickness at the surface. According to the data shown in Figure 8, greater than 65% mi- cro-distribution was obtained even in an elec- trolyte designed for via fill, that is, a high cop- per and low acid electrolyte. The cross-sec- tion evaluation of the through-holes showed no thin corners; however, a sloping was ob- served from the bulk surface to the through- hole edge. Further, a solder float test was performed to evaluate thermal characteristics of the depos- it in accordance with IPC TM-650 2.6.8. Solder shock (SS) conditions were 10 seconds float at 288°C for three times on the same side of the test coupon. Results are shown in Figure 9. Af- ter 3X SS testing, no cracks, or via bottom sep- aration was observed. Structural Analysis, Hardness and Impurities X-ray diffraction (XRD) study was performed for the plated deposits to identify the crystal phase and different planes. A typical diffrac- tion pattern (Figure 10) was obtained as the standard reported in the literature with reflec- tions from planes (111), (200), (220), and (311) were observed [8] . Narrow sharp peaks in the XRD pattern were observed which indicates highly ordered copper crystals in the deposit. Table 2 and 3 show no significant change in the major peaks, lattice constant or density of the plated copper after aging. This is an indi- cation that the crystal phase of the deposit is similar even after bath aging up to 150 Ah/L. Figure 7: Propagation results for direct metallization applications. Figure 9: Solder float results. Figure 8: Throwing power for 1.6 mm board thickness. Corresponding micro-distribution shown in graph above.