Techniques of assembly, packaging and reliability of infrared focal plane array(IRFPA) were systematically studied. Some theoretic and technical problems were solved, such as the simulation of assembly conformation, high precision allocation of the modules, the design of flat leading wire, low leakage rate of laser welding, the way to decrease outgassing of Dewar inner surface. For the IRFPA detector the tests of assembly reliability, high-energy particle and laser irradiations were carried out. A batch of practical infrared focal plane Dewar assembly and flat leading wire were obtained. These techniques have been implemented in project. The experimental results show that the thermal load of micro-Dewar is less than 250mW and the vacuum life of Dewar is more than 18 months.