Elemental Characterization for Electroless Cu Interface Layer of Stacked Micro-via in Substrate by STEM and ToF-SIMS

We investigated the electroless Cu interface layer of stacked micro-via in the substrate, prepared by two methods; a Ni-added electroless Cu plating and a Ni-free (OPC-FLET) one. We found nanovoids existed in the electroless Cu interface layer in an as-made state and grew or occurred during the thermal cycle test. Hydrogen concentration is less in the Ni-free electroless Cu layer, which means the OPC-FLET process is less susceptible to hydrogen embrittlement.