Embedded inductors incorporated in the design of SAW module SMT packaging

As SAW modules are moving to higher frequencies and their form factor continues to decline in size, the need for incorporating impedance matching components into the package design has become critical to ensure size and cost targets. The impedance matching components discussed here take the form of imbedded spiral inductors. These inductors do not increase the area of the package significantly and impact only the package height slightly. Since surface mount technology (SMT) tooling can be quite significant, errors in the inductor design can be costly. Accurate modeling of the inductor characteristics becomes quite important. Initial attempts for the modeling used closed-form solutions for printed spiral inductors and the results were not very accurate or satisfying. Improvements came after modeling the inductors using an electromagnetic simulator. The inductors were then designed and the packages tooled. This paper compares early model calculations with electromagnetic (EM) simulations, and measured results. Variables such as ground plane proximity, conductivity of the SMT package traces, etc. are discussed.