Characterization and Performance Improvement of Bondwire Interconnects in QFN Packages for Bandpass mm-Wave Applications

In this article, the input and output impedances of the bondwire interconnects in quad flat no-lead (QFN) packages are extracted and analyzed over the wide frequency range of dc-100 GHz. It is shown that knowing the impedance parameters of a transition makes it simpler and faster to optimize the structure for a desired operating frequency. Using extracted impedance properties, a compensation bondwire interconnections method based on only one quarter-wavelength impedance transformer line on the printed circuit board (PCB) side is proposed. It is shown that this technique can easily improve the bandpass impedance matching of the bondwire at any desired frequency up to 50 GHz. The bondwire transition is found to be interchangeably capacitive and inductive for frequencies above 50 GHz. Therefore, another simple and effective method based on the defected ground structure (DGS) concept are proposed to improve the bandpass performance of the QFN packaging for frequencies up to 80 GHz. At each step of this work, commercial three-dimensional (3-D) electromagnetic (EM) field software is used to analyze and verify the microwave characteristics of the proposed methods. Both matching network topologies are implemented on the PCB side, without any on-die compensation circuit, which reduces the cost, time, and complexity of the design process and implementation.