Modeling of self-alignment mechanism in flip-chip soldering. II. Multichip solder joints

A mathematical model to study the self-alignment behavior between a chip and a substrate connected by multiple solder joints is established. This dynamic model is capable of providing the oscillation frequency and amplitude of the chip motion, and characterizing the effects of different joint sizes. This model calculates the dynamics balance between the restoring force for self-alignment, viscous damping force resulting from friction of molten solder, and chip inertia. The developed model is capable of simulating the chip movement, and changing profiles of solder joints and misalignment levels at each time step during the reflow. This model has been used to understand two challenging applications: optical alignment demanding a 1 μm accuracy and low-cost flip-chip soldering with alignment joints