Effect of W content in Co-W-P metallization on both oxidation resistance and resin adhesion

The application of Co-W-P plating technology in high-temperature package structure is advantageous from a point of structural reliability because Co-W-P metallization is known to deliver strong bonding to both high-temperature-compatible Ag-sintered joining and high-temperature-compatible encapsulation resins. However, Co-W-P, unlike a noble metal, has a potential risk of surface oxidation in the module fabrication process. This surface oxidation can result in a decrease in resin adhesion. In this paper, the effects of W content (7 wt%, 11 wt%, 21 wt%) in Co-W-P metallization on both the oxidation resistance and the resin adhesion were studied. The resin adhesion on the annealed Co-W-P metallization with a high W content (21 wt%) was found to be sufficiently strong even after 250 °C anneal for 1 h. This resin adhesion strength was not present in other Co-W-P metallization tests. SEM–EDS analysis revealed that the oxidization of the Co-W-P-metallized surface during the anneal process proceeded more slowly in the case of the Co-W-P metallization with a doping 21 wt% W. XPS analysis revealed that Co(OH)₂, necessary for a chemical reaction with the resin, exists mainly on the Co-W-P-metallized surface in the case of doping 21 wt% W, even after 250 °C anneal. XRD analysis revealed its structure to be a characteristic Co-W solid solution, unlike the structures found in other Co-W-P metallization. The findings in this study are significant for the promotion of Co-W-P metallization in the module fabrication process, as well as to the fundamental understanding of oxidation resistance and adhesion behavior on Co-W-P metallization.