Design, fabrication, and characterization of novel vertical coaxial transitions for flip-chip interconnects

Wei Cheng Wu*, Edward Yi Chang, Ruey-Bing Hwang, Li Han Hsu, Chen Hua Huang, Camilla Kärnfelt, Herbert Zirath

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


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.

Original languageAmerican English
Article number10667154
Pages (from-to)362-371
Number of pages10
JournalIEEE Transactions on Advanced Packaging
Issue number2
StatePublished - 16 Mar 2009


  • Coaxial
  • Conductors
  • Coplanar waveguide (CPW)
  • Coplanar waveguides
  • Fabrication
  • Flip-chip
  • Gold
  • Interconnect
  • Resists
  • Simulation
  • Substrates
  • Transition

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