Beginning in 2002, a new Solar X-ray Imager (SXI) will become part of the instrument complement on NOAA's GOES N and O spacecraft. The SXI is being developed under a NASA contract by the Lockheed Martin Solar and Astrophysics Laboratory (LMSAL) within the LM Advanced Technology Center. The SXI will provide full disk images of the Sun from 0.2 to 2 keV through a combination of a grazing incidence telescope, bandpass filters, and a back-illuminated CCD. The CCDs are begin fabricated by EEV Ltd., screened by the Mullard Space Science Laboratory, and tested in x-rays by LMSAL. Early evaluation of test devices will be crucial in selecting the optimum backside treatment process for the flight CCDs, specifically with regard to quantum efficiency, spatial resolution, and the high dose of solar x-rays that the detector will experience over the course of SXI's 5 year mission life. In this paper, we describe results from an initial series of such test and the implications for the SXI mission.