When PCBs in electronics assemblies absorb moisture in humid environments, a swelling hygroscopic stress is developed in the PCB. The induced swelling stresses cause the PCB to deform and expand in volume, and may adversely affect the connected solder joints, and limit their lifetime. We developed a non-linear finite element analysis to investigate the effect of PCB moisture absorption and swelling on damage accumulation in BGA solder joints of a ceramic component. For this purpose, moisture diffusion in PCB was modelled by Fick's law, which enables calculation of moisture concentration and the resulting deformation in PCB. The solder joints attaching the component to the PCB are affected by PCB deformation, and may develop inelastic stresses and strains. A viscoplastic material model was used to represent solder inelastic behaviour, and capture its damage evolution. The effect of PCB thickness on the solder maximum stress was also studied. The simulation results provide a framework to investigate the effect of humid environments on solder joints reliability