Test-Cost Reduction for 2.5D ICs Using Microspring Technology for Die Attachment and Rework

Interposer-based 2.5D integrated circuits (ICs) are being increasingly adopted in the semiconductor industry for FPGAs and GPUs. However, the cost of testing is still a major concern for 2.5D ICs because if a faulty die is detected after it is bonded to the interposer, the entire 2.5D assembly has to be discarded. We consider 2.5D integration based on the use of microsprings for attaching dies to the interposer. A key advantage of microsprings is that they allow the 2.5D assembly to be reworkable. If a faulty die is detected during post-bond testing, we can replace the faulty die with a fault-free one. In order to quantify the benefit of the reworkable 2.5D assembly, we present a test-flow selection method for 2.5D ICs with microsprings. We compare the test cost of microspring-based integration with a baseline of test flows for microbump-only integration, with respect to some key parameters such as pre-bond test cost, fault coverage of tests, and microspring cost. For a large number of dies and a relatively low die yield, microsprings provide significant benefits over the baseline.