An Investigation of the Process Stability of RF SiP Made of DuPont 943 and 9K7

RF packaging is one of the most challenging topics in LTCC technology. Today LTCC is particularly capable for advanced packages and systems-in-package because of its electrical, functional, thermomechanical properties as well as its excellent long-term stability and reliability. LTCC combines the potential for miniaturization, low loss handling of high frequencies up to 110 GHz and offers the opportunity to integrate additional features. Therefore it has to go through various manufacturing steps and several refirings without any performance degradation or loss of dimensional accuracy. This paper discusses the impact of thermal post processing on RF characteristics and geometrical properties of LTCC. Ceramic substrates with radar front ends, calibration structures and other test vehicles made of Du Pont Green Tape® 943 and 9k7 were cofired following the recommended conditions and refired several times in order to investigate and compare the influence of the postfiring. The flatness, dimensions and RF performance of the ceramics up to 110 GHz were evaluated and compared.

An Investigation of the Process Stability of RF SiP Made of DuPont 943 and 9K7

RF packaging is one of the most challenging but also the fastest growing topic in low temperature cofired ceramic (LTCC) technology. Today LTCC is particularly useful for advanced packages and systems-in-package because of its electrical, functional, and thermomechanical properties as well as its excellent long-term stability and reliability. LTCC combines the potential for miniaturization and low loss handling of high frequencies up to 110 GHz and it also offers the opportunity to integrate additional features. Therefore it has to go through various manufacturing steps and several refirings without any performance degradation or loss of dimensional accuracy. This article discusses the impact of thermal postprocessing on RF characteristics and geometric properties of LTCC. Ceramic substrates with radar front ends, calibration structures, and other test vehicles made of DuPont Green Tape® 943 and 9K7 were cofired following the recommended conditions and refired several times in order to investigate and compare the influence of the postfiring. The flatness, dimensions, and RF performance of the ceramics up to 110 GHz were evaluated and compared.

RF System-in-Packages: History and Trend

In the last decade, people have seen tremendous increasing of data transmission speed and data storage capacity, which is mainly attributed to the Moore's law. However, this has little to do with RF devices and RF packages that are often used in the front-ends of wireless communication systems. Making components (e.g., width and spacing) smaller or closer does not necessarily help from RF perspectives, and as a result SoC (System on Chip) products for RF system do not really take off. The things that eventually make RF system evolution are from the concepts of System in Package, which may also include baseband chips and memory chips along with RF chips in a package. Substrate loss and metal loss are the key specifications to be considered for RF packaging. Several substrate technologies (e.g., laminate, LTCC, GaAs, glass, high-resistivity silicon, etc) that are typically used for RF packaging in the industry will be introduced. Some design challenges (e.g., impedance matching, minimizing coupling/cross-talk for high integration packages, etc) will be addressed. A trend for future RF packaging is drawn, based on successful examples of RF packaging in the industry.

RF System in Packages (SiP) using Integrated Passive Devices

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.