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characteristics of epig deposits for fine-line applications continues Figure 4: HSS results with M705 as the solder ball; EPIG (Pd 0.05–0.2 µm, Au 0.1 µm) and ENEPIG (Ni-P 6 µm, Pd 0.05–0.2 µm, Au 0.1 µm). than that of EPIG. The broken energy of EPIG film after heat treatment became poorer, compared with as-plated sample. On the other hand, if using ENEPIG process, the broken energy of HSS was kept even if there was heat treatment. The cross-section image of the IMC was observed to consider the cause of HSS results. When using EPIG film or ENEPIG film with Pd thickness of 0.1 µm and with Au thickness of 0.1 µm, the observation of IMC and the analysis of IMC composition by EDS were shown in Fig. 5. From the results of EDS, when using EPIG film, Cu6Sn5 was formed as layer 1 and Cu3Sn was formed near Cu layer as layer 2. On the other hand, when using ENEPIG film, (Cu, Ni)6Sn5 was formed as layer 1 and Ni+Ni3P was formed near Ni-P layer as layer 2[2,3,4]. It was considered that HSS results of ENEPIG were better for As16 The PCB Magazine • January 2014 plated because layer 1 of ENEPIG film was more uniform than that of EPIG film. When comparing the film of 300hrs HT, layer 2 of EPIG became thicker significantly because Sn was supplied from the solder phase more and more by heat treatment. And layer 1 became thicker also. It was considered that these thicker IMC will cause poor broken energy of HSS. On the other hand, the thickness of layer 1 and 2 was not changed for ENEPIG film. It was considered that Ni+Ni3P was thinner as layer 2 because (Cu, Ni)6Sn5 was formed by the existence of Cu in the solder ball of M705 and this IMC inhibited the growth of layer 2. Moreover, because layer 1 will be dissolved into the solder phase gradually, thinner layer 1 was kept[2]. Therefore, the broken energies of ENEPIG film were better even if there was heat treatment.