With the development of wafer process nodes, the package integration is increasingly higher. As a result, the linewidth and spacing of the packaged organic substrate gradually decrease, the number of micropore increases, and its pore diameter decreases. The micropore failure of organic substrate in ball grid array (BGA) packaging has always been a major problem affecting the reliability of high performance and high density chip packaging. Aiming at the micropore failure in organic substrate, the failure modes of flip welding under 500 times of temperature cycle loading at -65 ℃ - 150 ℃ and -55 ℃ - 125 ℃ were studied systematically by means of temperature cycle reliability test, finite element analysis, focused ion beam, scanning electron microscope and energy spectrometer. The results show that the micropores of organic substrates are delaminated due to temperature cyclic fatigue stress under the condition of temperature cycle from-65 ℃ to 150 ℃. The simulation results show that the average equivalent stress of the substrate increases by about 8 MPa. Subsequently, the structure of the heat dissipation cover is improved. After the improvement, the equivalent stress is reduced by 21.4%, and it can pass the reliability verification of 500 times thermal cycling from -65 ℃ to 150 ℃, which meets the requirements of high reliability.