Design, Fabrication, and Characterization of Novel Vertical Coaxial Transitions for Flip-Chip Interconnects

Abstract

Abstract-In this paper, a novel transition design using vertical "coaxial transition" for coplanar waveguide (CPW-to-CPW) flip-chip interconnect is proposed and presented for the first time. The signal continuity is greatly improved since the coaxial-type transition provides more return current paths compared to the conventional transition in the flip-chip structure. The proposed coaxial transition structure shows a real coaxial property from the 3-D electromagnetic wave simulation results. The design rules for the coaxial transition are presented in detail with the key parameters of the coaxial transition structure discussed. For demonstration, the back-to-back flip-chip interconnect structures with the vertical coaxial transitions have been successfully fabricated and characterized. The demonstrated interconnect structure using the coaxial transition exhibits the return loss below 25 dB and the insertion loss within 0.4 dB from dc to 40 GHz. Furthermore, the measurement and simulation results show good agreement. The novel coaxial transition demonstrates excellent interconnect performance for flip-chip interconnects and shows great potential for flip-chip packaging applications at millimeter waves.

Development of a through wafer 3D vertical micro-coaxial probe

“…The measured results of the micro-coaxial probes are shown in the figure above. When measuring the reflection coefficient, most of the probes seem to demonstrate good results compared to simulations with more than −10 dB loss difference at high frequencies from approximately 15 to 57 GHz, increasing the operating frequency range achieved in previous work for packaging applications by approximately 30 GHz [21,32,33]. At lower frequencies (dc-to-10 GHz) however, majority of the signal received from port 1 was reflected back and passed the −10 dB mark, which reveals a device short and/or poor signal transmission.…”

Electrical Characterization of Through-Silicon-via-Based Coaxial Line for High-Frequency 3D Integration (Invited Paper)

“…Coaxial transmission line is a typical and widely used high-frequency structure for electromagnetic field transmission, due to its advantage of being able to efficiently transmit transverse electromagnetic waves and having low loss. Therefore, coaxial shield TSVs have been designed for high-speed signal transmission [9] and used as an efficient vertical transition in flip-chip structures [10]. The basic configuration of a coaxial shield TSV has a central signal conductor surrounded by an outside concentric ground shell, which can consequently suppress undesirable substrate crosstalk [11] and effectively reduce the losses caused by radiation and coupling when it is used for transmitting microwave signals [12,13].…”

Through Wafer 3D Vertical Micro-Coaxial Probe for High Frequency Material Characterization and Millimeter Wave Packaging Systems

“…Additionally, previous researchers have also used a novel flip chip approach to develop a vertical coaxial probe [42]. Figure 3.3 shows the flip-chip probe design which was used to integrate with packaging systems as interconnects.…”