At the solder ball mounting process on the CSP (chip size package) package, must have inspection of excess solder on the inhaling tool. This study is how to detect excess solder during inhaling tool moving when using laser through-beam sensor. First, in order to remove the influence of the sensor output value by the normal solder ball and to extract only the sensor output value by the excess solder ball, the gobo was attached to the inhaling tool and the effect was checked. Next, create a slit on the laser receiver that increasing sensitivity of laser through-beam sensor and confirmed the improvement. The slit is created to increase sensor output value that compares result of excess solder on the inhaling tool with or without excess solder ball. Furthermore, we supposition production line study the inhaling tool movement error. Therefore then inhaling tool movement error is occur then measure sensor output value. Then we attempt to use difference value. It turns out that the detection method developed by this research can apply to manufacture line, because the excess solder ball of φ 0.30 mm, φ 0.25 mm and φ.0.18 mm can be detected certainly, without being influenced of the movement error of inhaling tool.