Abstract: Aiming at the problem of pseudo soldering defects in the electronic products that cannot be effectively detected by the existing welding quality detection technology, the virtual joint process of infrared thermal image detection is analyzed by using numerical simulation method, and the transient heat transmission was detailed discussed, and the relationship between the solder surface temperature and the factors, such as pseudo soldering degree, heat flux density, solder volume and heat stimulation position on the detectable signals, are analyzed. The simulation results showed that the difference of the heat amplitude of the welding spot with the virtual welding degree below 40% is small, which is difficult to identify; the higher the heat flux density is, the higher the SNR is, and the higher the reliability of spot virtual welding detection is; the temperature difference of virtual welding defects at different excitation positions reached 0.36 ℃, which had a great influence. The solder joint size has little influence on the temperature difference of virtual welding.