Three-dimensional RF SoP technologies: LTCC versus LCP

The system on package (SoP) is an emerging platform, introduced to provide enhanced functionality, and immense miniaturization through vertically integrated passive components in a multilayer process. This way the package is not a mere holder or cover but is a functional part of the system. The leading multilayer packaging technologies for SoP designs: low temperature co-fired ceramic (LTCC) and liquid crystal polymer (LCP) are compared in this work for the first time. Passive components and filters have been implemented in both technologies to show the advantages of the three-dimensional nature of these technologies. The comparison results show that parallel plate capacitors implemented in the ultra-thin LCP provides the highest capacitance density. For spiral inductors, conversely, LTCC inductors have the highest inductances while LCP inductors offer the highest self-resonant frequencies and the highest quality factors (Q). In a circuit level, simulated and measured results of a bandpass filter at 1.5 GHz show that both LCP and LTCC can provide similar performances with an incredible size reduction for the case of ultra-thin LCP. Also, the thin LCP filter exhibits a large degree of mechanical flexibility which makes this technology suitable for future flexible modules.