Some through hole pads of printed circuit board connected to ground layer. Large heat dissipation in ground layer would lead to low solder tin-permeability rate during the manual welding process. To solve the problem, temperature distribution of common and low tin-permeability rate pads was calculated by ABAQUS software. And the influence of whole board preheating on the peak temperature and permeability rate was analyzed. The results show that without preheating printed circuit board, the heat dissipation in ground layer is 4 times as that of the common through hole pads. The peak temperature of non-welded surface of low tin-permeability rate pads is 125~126 ℃, which was far lower than the melting point of the tin-lead eutectic solder (183 ℃). When printed circuit board is preheated to 85,100 and 115 ℃, the peak temperature of non-welded surface of low tin-permeability rate pads is increased to 171.5,179 and 187.5 ℃, respectively. Simulation and experimental results indicate that preheating Printed Circuit Board at 85~115 ℃ is beneficial to improve the permeability rate and solder-joint reliability of Sn-Pb eutectic solder.