3D rectangular waveguide integrated in embedded Wafer Level Ball Grid Array (eWLB) package

Abstract

In this paper, we present for the first time the realization of a 3D rectangular waveguide in the fan-out area of an embedded Wafer Level Ball Grid Array (eWLB) Package using laminate inserts. To obtain the waveguide side walls in eWLB, a RF laminate with micro-vias is inserted in the fan-out area. The classical redistribution layer (RDL) on the one surface and an additional back side metallization on the other surface of the package are used to realize the top and bottom walls of the waveguide. Furthermore, we focus on a single-ended coplanar waveguide (CPW) to rectangular waveguide transition. We investigate and compare two concepts for the transformation of the transverse electromagnetic (TEM) mode of a CPW to the transverse electric (TE) mode of a rectangular waveguide. The first concept is using a via in the waveguide structure to excite the waveguide TE mode. The second concept is a planar realization using a modified shape of the RDL to realize the mode transformation. We show by the means of measurements the characteristics of each version. We show that the mode change is done with almost no additional losses to those related to physical length of the transmission line. Furthermore we present several on-wafer measurements which agree very well with the RF behavior predicted by the simulations. This 3D waveguide integration in eWLB enables the realization of many new RF features in chip embedding technologies in the future.