Process development and characterization of 3D multi-die stacking

In this paper the stacking process development and the characterizations of multi-die stacks N=16, which contain 15 thinned top dies on a bottom die, are described. A comparison study between sequential and vertical collective bonding, to see the impact on their characteristics is examined in detail. Also, an in-situ temperature measurement during stacking is performed and a simulation is done to find the proper thermo compression bonding (TCB) profile to stack a large number of dies with good soldering connection also on the bottom die. Multi-die stacks with high alignment accuracy and good electrical yield (e-yield) are made and characterized by cross-section SEM, SAM and X-RAY analysis.