High Speed Solar Cell Printing Line
A large international conglomerate in the solar cell business needed a high-throughput line to print, inspect, and cure solar cells. Because thin substrates are cut from a large ingot, the silicon material is stressed and tends to break very easily. The dynamics of wafer handling was very important.
Robots pick and place in up/down stacking magazines of wafers. The top-most wafer floats on a cushion of air to allow the robots to vacuum pick without damaging the wafer beneath. In a two-up configuration, wafers are moved to upward-looking cameras for grip position refinement. The wafers are then placed on a large rotary dial by the two load robots. After indexing through screen printing, the wafers are inspected for print defects. The cells are then edge-gripped and placed on linear conveyors. After passing through a cure oven in a four-up configuration, the cells transition to a back-light conveyor. The vision system acquires substrate positions. The cells are tracked into the reference space of two robots. Wafers are picked up on-the-fly and their gripped positions are refined by using upward-looking cameras. The cured product is placed in down-stacking magazines.
outcomes and benefits
• Fast precise handling of large, fragile wafers
• 0.003” dial placement accuracy
• Five robots, four machine vision applications, and all process I/O on one robot controller
• Line-scan machine vision (2k x 2k) inspection for 0.005” defects on a six-inch wafer
• Three different product sizes and form factors
• Cycle rate of 2,800 cells per hour
Five Robots Use Vacuums to Pick Delicate Silicon Wafers