RF System in Packages (SiP) using Integrated Passive Devices

Abstract

Passive components are indispensible parts used in System in Packages (SiP) for various functions, such as decoupling, biasing, resonating, filtering, matching, transforming, etc. Making passive components embedded inside laminate substrates is limited on passive density. SMD solutions are by far the most popular approaches in the industry, and may still be dominant for some times. As high integration and high performance have become a trend in the packaging solutions, integrated passive device (IPD) technology shows some unique features, which helps to achieve these goals, especially for RF packages. In the IPD process, low-loss substrate material is used, and therefore high-Q inductors can be built. In addition, thin-film IPD process has finer pitch feature and better tolerance control than other commonly available ones, such as PCB and LTCC technologies, which may yield very repeatable electrical performance, and provide packages of high integration. Several cases of study will be presented and here are some highlights of them. In case one, a most straightforward SiP approach is presented using QFN package, where several dies (including IPD dies) are implemented side-by-side. This approach may give fast developing cycle times. But importantly, wire-bonding models have big impact on performance from RF packaging, and should be obtained accurately for designs. Another case of study is a stack-die package, where inter-die coupling/cross talk could be a big issue as far as electrical performance is concerned. Placement of some critical parts, such as coils in IPD and in VCO, should be investigated very carefully in design phases. This leads to a concept of ‘IC/IPD/package’ co-design. Finally, a hybrid SiP package solution, where an IPD die is embedded in a mold compound along side with a RF power amplifier die, is presented. This approach (so called ‘eWLB’ packaging), results in the shortest interconnection between dies to dies and dies to balls. With the benefit from both the IPD process and the eWLB process (where low-loss mold materials are used), this approach may lead to high electrical performance and small form-factor at the same time.