Preventing Void Growth Between Ni3Sn4 and Solder

Electrodeposition Complexity and the Root Cause of Interfacial Voiding in Solder Joints with Plated Nickel

“…The consistent presence of bubbles, entrapped in the solder after reflow, provides direct evidence of the previously hypothesized thermal gasification of Ni impurities, incorporated during the plating process. 10 These findings help us build a solid foundation for anticipating and justifying the presence of Ni(OH) 2 and NiOOH compounds formed and incorporated during the Ni electroplating process. Subsequently, during the reflow and annealing processes, it is plausible that these inclusions outgas and, thus, create void-nucleation centers.…”

“…10 Notably, despite the extensive variations of the plating bath composition in an attempt to associate the voiding with a specific chemistry, the resultant cross-sections kept exhibiting a substantial presence of voids after accelerated aging at 200 °C for different times. 10 The cross-sections presented in Figures 3a and S1a set the starting point of directed experimental variations in the Ni deposition chemistry followed by a critical analysis of the plating environment's impact on the voiding propensity. An effort to expand this approach directed us toward a sulfamate bath, an alternative medium for Ni deposition, as demonstrated in Figures 3b and S1b.…”

“…Given the acidic nature of both of these baths, we have hypothesized that the void formation may stem from the outgassing of HERgenerated H 2 gas. To investigate this new hypothesis further, 10 we evaluated the effect of higher solution pH on the voiding propensity of Ni−Sn joints by depositing Ni in an alkaline bath with pH ≥ 8, which substantially limits the impact of H 2 evolution. However, as shown in Figures 3c, d and S1c,d, the voiding propensity increased, rather than being reduced in comparison with the acidic plating baths (Figure 3a,b).…”

“…Additional details about the formation and further development of this void structure can be found through our group's earlier work. 10 Coarse Estimate of the Oxidized Ni Incorporation. To further assess our hypothesis of Ni oxo-hydroxide species prompting the voiding process, we aim to conduct an estimate of the quantity of such species that may be entrapped within the electrodeposited Ni.…”

“…While we successfully influenced void growth in most experiments, our results yielded inconclusive findings regarding both the actual impurities responsible for bubble formation and the mechanism of their incorporation into the plated Ni. 10 Therefore, the primary objective of our activity is to address these two key goals and provide concrete evidence of the presence of such impurities within the Ni-deposited layers. Our investigation centers on evaluating the potential incorporation of either H 2 gas, which forms concurrently with Ni deposition, or Ni hydroxide and Ni oxohydroxide (Ni(OH) 2 and NiOOH, respectively) clusters whose formation and entrapment are likely facilitated by the inherent alkalization of the vicinity near the electrode, a phenomenon well-documented during Ni electrodeposition.…”