It is essential for electronics reliability to develop effective methodologies to detect hidden solder joint defects. Active infrared thermography is an alternative to X-ray detection methodologies. The limits of active infrared thermography to detect solder ball defects on plastic ball grid arrays (PBGA) components (missing, open, cracked, and head on pillow defects) are investigated here. A FEM was used to simulate the thermal phenomena during the infrared thermography inspection of a PBGA component. The FEM was proven to be temporal and spatial grids size independent. The average temperature difference (ΔT) amid regions with and without defects was used as a detectability indicator. Defects detectability was found to decrease as the number of blocking objects increases. Missing solder balls were barely detected when blocked by the substrate and moulding compound with detectability numbers close to 1 °C. Head on pillow and cracked defects were impossible to detect with a maximum ΔT = 0.6 °C. Open solder balls were not detected below two objects with a maximum ΔT = 0.3 °C. These results clearly suggest that infrared thermography can be effectively used to detect hidden missing and open solder ball defects on PBGA components composed by a substrate and a die.