In this paper, we study the effect of mechanical compliance on the impact force of human-robot interactions, more specifically the maximum impact force during a collision. Here we consider two methods of introducing compliance to industrial manipulators: joint compliance and link compliance. To compare their effect on the maximum impact force, we study two designs of a 2D robot link: a rigid link with torsion spring at the joint and a uniform compliant link. The dynamic impact model is based on the Hertz contact model. The results show that the compliant joint solution could produce a larger impact force than that of the compliant link solution if the arm mass is larger than that of the end mass, given the same lateral stiffness and all other inertial parameters (e.g. mass). Simulations and experiment have been done and verified this conclusion. The research demonstrates that the compliant link solution could be a promising approach for addressing safety concerns of human robot interactions.