In manufacturing industry, bonding wires are used to interconnect the pads of a semiconductor chip to terminals of a package containing the chip. With increasing demand of tiny wires, current detection apparatus encounters some limitations. In this paper, a method to detect breakage of tiny bonding wires using diffraction of light is proposed. A laser head generates the light beam, and a slit is introduced in the path of light source, so the slot generates diffraction pattern, and light irradiance loss at the receiver due to the presence of a wire could be observed. Simulation results show that the proposed method with a slit design renders satisfactory detection sensitivity for tiny wires.