In this paper, the use of a two-sensing-fingers gripper for grasping planar microparts (smaller than 0.1 mm$^3$) is being investigated and the force range during a microassembly sequence is estimated between 0 to 3 mN. An analytical model of their gripping forces in the presence of a lateral contact force is proposed and is compared to Finite Element Analysis. An experimental validation is performed by a proposed setup for a lateral contact force in the range of a few tens to hundreds of micronewtons. Effects of the variation of parameters like the distance of contact, the thickness of the finger, the compliance of the finger, and the preload are investigated. Design statements of microgripper and the applied force range are given in order to achieve automated microassembly tasks.