Patent ID: 8358735

Claim:
A method of testing whether a foreign material including an Fe element or an Al element is adhered to a substrate for a liquid crystal display device in order to select the substrate having the foreign material adhered thereto and remove the substrate during a substrate manufacturing process, the method comprising: a first test step of detecting size and position of a foreign material adhered to substrates; and further steps of excluding a substrate from which the foreign material with a sufficient size to damage an opposite substrate is detected among the substrates having the foreign materials adhered thereto, which are detected in the first test step, adjusting position of a test head of a test device to match the position of the foreign material detected in the first step, for the substrates remaining after excluding the substrate, and testing only whether the foreign material includes an Fe element or an Al element wherein, the adjusting the position of the test head to match the position of the foreign material is performed based on information of coordinates of the position in the first test step, a camera unit is used to capture an image of position where there is the foreign material, detailed coordinates of the foreign material are determined from the image, and adjusting the position of the test head to match the position of the foreign material is performed based on the detailed coordinates, and when the foreign material includes the Fe element or the Al element, the test device determines that the substrate is defective.