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We discuss the possible existence a spin singlet excitation with charge$\pm2$ ($\eta$-mode) originating the $A_{1g}$ Raman resonance in cupratesuperconductors. This $\eta$-mode relates the $d$-wave superconducting singletpairing channel to a $d$-wave charge channel. We show that the $\eta$ bosonforms a particle-particle bound state below the $2\Delta$ threshold of theparticle-hole continuum where $\Delta$ is the maximum $d$-wave gap. Within ageneralized random phase approximation and Bethe-Salpether approximation study,we find that this mode has energies similar to the resonance observed byInelastic Neutron Scattering (INS) below the superconducting (SC) coherent peakat $2\Delta$ in various SC cuprates compounds. We show that it is a very goodcandidate for the resonance observed in Raman scattering below the $2\Delta$peak in the $A_{1g}$ symmetry. Since the $\eta$-mode sits in the $S=0$ channel,it may be observable via Raman, X -ray or Electron Energy Loss Spectroscopyprobes.

$\eta$ collective mode as A$_{1g}$ Raman resonance in cuprate superconductors