In the assembly process of printed circuit board components， some problems (misalignment of solder paste， little tin and cracking) caused product quality degradation. It is of great significance to improve the yield rate through high-precision solder paste inspection， and this method has attracted widespread attention in the industry. The phase profile measurement method needs to project the grating fringes on the PCBA， and detect the defects of the circuit board by detecting the deformation of the fringes. The accuracy of the fringe projection determines the detection accuracy of the system. Therefore， a high-quality projection objective is necessary to complete this type of inspection. A laser diode as the illumination source is used. The lens structure adopts the classic double Gaussian form and is optimized by Zemax software. The design results show that the performance of the objective lens is close to the diffraction limit. The modulation transfer function is above 0.4 at 30lp/mm， and the maximum distortion is less than 0.3%. The objective lens realizes high-precision projection of grating fringes， and the design results and methods can provide references for the design of optical instruments in the electronic equipment manufacturing industry.