On the Design of the World's Smallest Flow Sensor Package

In this letter, a miniature flow sensing system has been designed, simulated, manufactured, and tested. The system is comprised of a thermal flow sensing die, a package body, a lid, and leveling epoxy. The lid design is crucial to the system performance, and a reference design was shown to create vortices within the flow channel, resulting in nonlinear and nonrepeatable sensor response. Two novel lid designs were investigated that showed increased sensitivity and repeatability, while minimizing the effect of vortices disrupting the sensor response. These structures were named “vortex guides.” The first design provided a double increase in the signal sensitivity, while the second design isolated the vortices away from the sensors functional area, providing predictable flow response over a wider flow range. This enables high-sensitivity, large-range, low-cost miniature flow sensing for mass-market production.