A Simple Low-Cost Electric-Contact-Assisted Alignment Method for Die Stacking on an Interposer or a Printed Circuit Board

We propose a new simple and low-cost alignment method utilizing electric contact for die stacking on an interposer or a printed circuit board. Without any expensive aligning/bonding equipment assisted by microscopy, we successfully stacked and bonded two silicon dies on a printed circuit board achieving alignment accuracy of 20~\mu \text{m} by utilizing only cheap equipment: manual micropositioners, a stage, a stand, a heat gun, a hot plate, and a power supply. In the proposed method, conductive alignment marks are fabricated on the bonding surfaces, and the electric contact between them are used to characterize misalignment. Therefore, the proposed method does not require any expensive complex microscopy equipment for alignment. In addition, alignment can be quickly and simply examined in situ by detecting electrical conduction during bonding. In experiment, alignment accuracy better than 20~\mu \text{m} and 100% bonding yield was measured in testing of 1800 bonds connecting two silicon interposer dies which were stacked on a printed circuit board by the proposed method.