The neutron rich isotopes with Z<20, in particular those with neutron numbers around N=28,have been at the focus of a lot experimental and theoretical scrutiny during the last few years.Shell model calculations using the effective interaction SDPF-NR, were able to predictor to explain most of the properties featured by these nuclei. Prominent among them is the disappearance of the N=28 shell closure for Z<=16. We have incorporated to SDPF-NR some modifications, either on purely theoretical grounds or guided by new experimental information. The proposed interaction, SDPF-U, contains USD as its sd-shell part and KB3G as its pf-shell-part. Its range of applicability is enlarged and its reliability enhanced with respect to the earlier version.