The system enables probing and hence testing of chips with large arrays of 40µm-pitch micro-bumps, on 300mm wafers. Its importance to the industry is highlighted by the recent winning of the 2017 National Instruments Engineering Impact Award at a ceremony in Austin, Texas
Pre-bond testing is important to increase the yield of 3D stacked chips, an emerging technology that still has many open options and technical challenges. One of these challenges is probing of the individual chips, before being stacked, to ensure a good yield of the 3D stacked ICs. The inter-chip connections of 3D stacked ICs are made by large arrays of fine-pitch micro-bumps which makes probing these bumps a challenge. Until today, the probing solution is to add dedicated pre-bond probe pads to the to-be-stacked dies, but this requires extra space and design effort and increases test time.
Imec and Cascade Microtech have now developed a fully automatic test cell that can provide test access by probing large arrays of fine-pitch micro-bumps. The system is based on a Cascade Microtech CM300 probe station and National Instruments PXI test instrumentation, complemented by in-house developed software for automatic test generation, data analysis, and visualization. The system allows testing of wafers up to 300mm diameter, including thinned wafers on tape frame with exposed through-silicon vias. After several years of intense collaboration between imec and Cascade Microtech, partly supported by the EU-funded FP7 SEA4KET project, good results were achieved with Cascade Microtech’s Pyramid Probe® prototype RBI probe cards on imec’s 300mm wafers with 40µm-pitch micro-bumped chips.