ATS SmartVision™ Software Quality in Solar Panels Success Story
Our client wanted to reduce scrapped parts caused by improper screen printing of solar cells. Operators had to watch the cells as they left the screen printers. If they observed a problem, they would E-stop the machine to correct it. This was a time-consuming and tiring task that our client wanted us to address.
Solar cells are manufactured by screen printing a conductive ink in a series of lines on the surface of a silicon wafer. Power is collected along these lines and collected at wires bonded to the edges of the cell. The screen printing process can result in lines that are damaged or missing due to contamination on the screen print surface, low ink levels, cracked or damaged wafers, etc. Damaged ink lines cause a reduction of the maximum power that can be produced by the cell. Once these cells are screen printed, they are immediately baked in an oven to harden the ink. Once the ink is hardened, the cells cannot be reworked to repair any damaged lines.
A vision system was placed at three positions on the dial used for screen printing. The first system checked the cells for cracks and chips before any ink was applied to the surface. This allowed those cells to be removed and laser cut into smaller cells in an offline process. The other two vision systems were designed to immediately inspect each cell as it left one of the two screen printers on the dial (one was a spare).
Every line on the surface of the cell was checked from damage and any damage would immediately stop the dial before the parts were able to reach the oven. This inspection task was accomplished within the machine cycle time of two seconds.
Three 4-megapixel cameras were used to acquire high resolution images of the cells. A custom lighting hood was also designed and manufactured by ATS to evenly illuminate the solar cells with red light. The cells are violet in color and red light gets absorbed by the cell and appears black to the camera. The ink is highly reflective in red light so the lines appear with high contrast in the image. This also eliminates the “crystalline” appearance of the cells as they appear in the white light.
ATS SmartVision software was used to develop the inspection system. A series of Dispense Tools were used to analyze every pixel of each row of ink for gaps, thick regions, and think regions. This tool is unique to SmartVision.
Our customer significantly reduced their scrap rate due to screen printing problems. As well, the operators were able to spend time more productively since they no longer had to monitor the screen printing process so closely.