Contrapose data line and common line invisible short(DCS Invisible) in production of copper process array substrate, a new method based on cutting for locating the position of DCS Invisible is presented. Based on the result of data and failure analysis, an observation experiment of layer section with different ashing process time is designed to explore the mechanism. In ashing process, reaction gas SF6 below the photoresist which looks like the shape of roof will corrode copper metal of common line. Under the condition of high humidity, the corrosion will be aggravated. Corrosion products grow up and can’t be covered by thin film of GI/Active. After thin film process of SD(Source & Drain), the data line will connect with corrosion products and finally cause DCS which is invisible on the front side of array substrate. Based on the research, the experiment of reaction gas consumption of SF6 in ashing process, relative humidity, waiting time from Ashing to 2nd Gate Wet Etch and design improvement is proceeded. Finally, DCS Invisible is solved by reducing reaction gas consumption of SF6, decreasing relative humidity, controlling waiting time from Ashing to 2nd Gate Wet Etch and insuring space H of slotting design larger.