Response of Long Sculpted Wire Bonds to Vibrational Excitation

摘要

The pitch of wire bond connections is decreasing to meet the need for higher interconnect densities, while at the sametime, the ratio of wire length to diameter is increasing, which lowers the mechanical resonant frequency of the wire. Inmany applications in which MEMS sensors are coupled with ASIC front end electronics, the bonded wires can besubjected to a wide frequency spectrum of mechanical vibrations. One potential consequence is that the parasiticcapacitances of the sensor could vary dynamically at a magnitude comparable to that of the sensor signal. In extreme cases,intermittent shorts or fatigue failures of the wire bonds could occur. A recent paper by Barber et. al, showed that wirebonds carrying alternating currents in a strong magnetic field could suffer fatigue failure.[1] Their analysis andexperiments focused on simple loop geometries. In many applications, more complex wire bond geometries are used tominimize loop height and obtain dense wiring in stacked chip configurations. These geometries give rise to many morevibration modes with unique resonant frequencies and displaced shapes. We have used simple analytical beam models inconjunction with finite element models (FEM) to study various wire bond configurations subject to mechanical vibratoryexcitation. We focused on the effects of overall wire length and geometric shape on resonant modes. The finite elementmodels were also used to calculate the capacitance between adjacent wires subject to mechanical excitation at one or moreof their resonant frequencies. We show that there is an apparent shift in the time averaged capacitive coupling thatincreases with increasing vibration amplitude.