In this work, the thermo-mechanical behaviour, the evolution of phases of thin films consisting of the immiscible system Molybdenum-Silver (Mo-Ag) were investigated. The 40 nm to 770 nm thick films were deposited via a dc magnetron sputtering process on rigid (Silicon) and flexible (Polyimide) substrates. The compositions ranged from 9 at.% to pure silver films, with a focus on the Mo-rich films. It was observed that differences in terms of composition and film thickness in the rigid system led to differences in thermo-mechanical behaviour. These differences were evaluated using different annealing treatments in a wafer curvature system and then they were used to interpret the behaviour of the flexible counterparts. Via X-Ray diffraction it was observed that phases ranged from metastable phases before annealing and after annealing to segregated Mo-rich and Ag-rich phases. The surface evolution was found to evolve with increasing silver content and with both time and temperature.