Design and assembly of a double-sided 3D package with a controller and a DRAM stack

The microelectronic packaging field is moving into the third dimension for miniaturization, low power consumption, and better performance. In this paper, we present a double-sided flip-chip organic substrate with a memory controller on one side of the package, and 3D stacked disaggregated memory chips on the other side of the package. This design allows the controller to interface with the DRAM stack directly through the substrate providing the shortest possible interconnect path, and thus achieving the fastest signaling speed. However, this double-sided flip chip on organic substrate also causes yield, assembly, test, and reliability challenges. In order to optimize the assembly process, a sequential 3D finite-element model was developed to simulate the package assembly process. In these simulations, various assembly process sequences were simulated with different conditions and materials. In addition, a probing test model was also built to study the connectivity of the Land Grid Array (LGA) pin array with the PCB sockets. Results show that the careful selection of assembly steps and package materials are crucial for the successful package assembly and also important for the probing test.