EFFECT OF PROCESS VARIATIONS ON SOLDER JOINT RELIABILITY FOR NICKEL-BASED SURFACE FINISHESAuthors: Hugh Roberts and Sven Lamprecht, et al.
Company: Atotech Inc.
Date Published: 4/8/2008 Conference: SMTA China
This paper summarizes the results of recent investigations to examine the effect of electroless nickel process variations with respect to Pb-free (Sn-3.0Ag-0.5Cu) solder connections. These investigations included both ENIG and NiPd as surface finishes intended for second level interconnects in BGA applications. Process variations that are suspected to weaken solder joint reliability, including treatment time and pH, were used to achieve differences in nickel layer composition. Immersion gold deposits were also varied, but were directly dependent upon the plated nickel characteristics. In contrast to gold, different electroless palladium thicknesses were independently achieved by treatment time adjustments.
Results of investigations include: (1) Cold ball pull testing to evaluate solder joint integrity, (2) SEM examinations of the underlying nickel surface and (3) IMC examinations to quantify nickel thickness degradation after multiple solder reflow cycles. The paper discusses the relatively simple approach that, if proven effective in large-scale fabrication, may significantly reduce or eliminate many of the well-known reliability concerns associated with nickel-based intermetallics in a Pb-free assembly environment.
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