Nanjing University of Posts and Telecommunications

Students Design Novel Broadband Substrate Interconnection Structure

 

Company Profile

Nanjing University of Posts and Telecommunications (NUPT) has made remarkable contributions to the establishment and development of the People’s Republic of China. NUPT has developed into a university focusing on engineering, characterized by information technology integrating such disciplines as science, engineering, economics, management, literature, education, art and law, and combining the educational programs leading to bachelor’s, master’s and doctor’s degrees. The university is located in Nanjing, a historical and cultural city, and owns four campuses: Xianlin campus, Sanpailou campus, Suojincun campus, and Jiangning campus.

The Design Challenge

Conventionally, substrate-to-substrate interconnection is established using bond wires and are used extensively in monolithic microwave integrated circuits (MMICs) and multi-chip modules (MCMs) for signal transmission in substrates with different heights. However, a bond wire adds a low-pass element to the microwave system and limits its operating bandwidth. Approaches using multiple bond wires or compensated microstrip stubs can broaden the bandwidth of such interconnections, but none of them exceed 20 GHz frequencies. It is more important that compensated open stubs are used to broaden the bandwidth of bond wire interconnections, but in most cases the required compensated open stubs must be narrower than 0.1 mm, which is impossible to fabricate based on current printed circuit board (PCB) substrate or low temperature co-fired ceramic (LTCC) fabrication processes. 

To solve these challenges, engineers at NUPT wanted to design a novel broadband substrate-to-substrate interconnection structure.

The Solution

The designers developed a broadband interconnection using double bond wires with square-shaped defected ground structure (DGS) under open stubs. The square-shaped DGS etched under compensated microstrip open stubs not only expanded its operating bandwidth, but also increased the characteristic impedance of the microstrip line without narrowing its width, which overcame the PCB fabrication limitation of narrow stubs.

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