Open ended microwave oven for flip-chip assembly

A novel open-ended microwave oven in the form of a waveguide cavity partially filled with dielectric is proposed for the microwave curing of bumps, underfills and encapsulants during flip-chip assembly. By adjusting the dimensions and the dielectric permittivity, a well defined resonance can be confined in the dielectric part with non-radiating evanescent decaying fields in the remaining of the cavity. Curing occurs by virtue of the energy stored in localized evanescent field maxima. The dielectric to air interface enhances the longitudinal electric field and therefore the cavity is designed to operate at a TM mode. Careful selection of the resonance order can control the locations of the electric field maxima (hot-spots) allowing for spatially selective heating. The open end design offers enhanced flexibilities for the simultaneous curing and alignment of devices for fast flip-chip assembly, direct chip attach (DCA) or wafer- scale level packaging (WSLP). Low power tests using heat sensitive film demonstrate clearly that selective heating in multiple locations in the open end of the oven is achievable.