The phase diagram of DNA linker mediated nanoparticle assemblies was experimentally investigated and constructed. Using small angle x-ray scattering we studied the dependence of the internal structure of assembly on two main system parameters: DNA linker length and the number of linkers per particle. The formation of a crystalline bcc phase was observed for a limited range of linker lengths, while the number of linkers per particle controlled the onset of system crystallization. The influence of linkage defects on crystalline structure was also examined.