エネルギーサブトラクション法を用いたCSPはんだ接続部の抽出

抄録

X-ray images have been used as a way of inspecting solder joints of BGA packages and CSP. But, in X-ray images, other parts are piled up, besides the solder joints which are being subject to inspection. We propose a new method for extracting the solder joints using energy subtraction method. The technique employs the fact that photon energy characteristic of attenuation coefficient is specific to the materials. Concretely, the X-ray spectrum is made to change by appropriately controlling the voltage of the X-ray tube, and two images are taken. Next we conduct contrast correction so that the gray level of the region where X-ray does not permeate solder joints may become equal. Lastly, by subtracting the images, the lead, which is the main constituent of the solder, is extracted. This technique has been verified through both the simulation studies and the prototype system. A good result where solder joints are clearly extracted is provided. By using this technique, it becomes easy to extract automatically the region of the solder joints from X-ray images.