  A previous analysis of the charge (Z) correlations in the $\Delta Z-<Z>$
plane for Xe+Sn central collisions at 32 MeV/u has shown an enhancement in the
production of equally sized fragments (low $\Delta Z$) which was interpreted as
an evidence for spinodal decomposition. However the signal is weak and rises
the question of the estimation of the uncorrelated yield. After a critical
analysis of its robustness, we propose in this paper a new technique to build
the uncorrelated yield in the charge correlation function. The application of
this method to Xe+Sn central collision data at 32, 39, 45 and 50 MeV/u does not
show any particular enhancement of the correlation function in any $\Delta Z$
bin.
