the optical substrate 304 differ in their thermal expansion coefficients tecs for example preferably the mux substrate 310 is formed of sapphire and the optical substrate is a silicon structure due to the differences in the properties of the materials used including the mismatch of their tecs thermal stresses are created in the cooling process as a consequence in plane forces which strain the bumps laterally as well as out of plane forces which strain and compress the interconnect bumps vertically may be generated moreover since the bumps on one side to the surface of the optically sensitive material the in plane and out of plane forces are also transmitted to the optically sensitive material thus degrading the quality of the material and causing a potentially significant decline in the performance of the fpa repeated cool down of the fpa may aggravate the damage to improve fpa reliability the mux 310 is preferably mounted on a core layer 314 using an appropriate epoxy 312 the core layer is preferably formed of a rigid material such as stainless steel which has a higher modulus of elasticity and tec than the mux the core layer 314 is coupled to a balancing layer 318 using another layer of epoxy 316.