Novel PCB and wire bond architecture to accommodate microwave frequencies

Extends the use of wire bonding on PCB’s to address needs in the high-frequency range

Communications Electronics

Wire bonds are often used to connect an integrated circuit (IC) to a printed circuit board (PCB). Sometimes, these wire bonds are used to route direct current in order to control the operation of the chip. During low-frequency operations, the negative effects of utilizing a wire bond are not an issue. However, for high-speed/frequency RF microwave signals, any discontinuity in the signal path caused by wire bonding can significantly degrade the quality of the signal. This is because a wire bond is inductive in nature, and at high frequencies, an inductor acts as an open circuit leading to signal loss.

Various methods can be used to mitigate wire bond losses at high frequency. One method is to lower the inductance by using two or three wire bonds in parallel. Ribbon bonds, which are wider than wire bonds and lower in inductance, can also be utilized. Compensation techniques are also popular. Compensation methods usually implement additional capacitors and inductors (network components) directly on the PCB so that the PCB inductance matches the IC impedance. Such compensation techniques have their own limitations.

To address the above, a Navy engineer developed a device and method for connecting an IC to a PCB using a single wire bond in a manner that allows for high-frequency operation with low-loss. The method takes advantage of a wire bond and a defect (opening) in the ground plane in order to achieve broadband performance. The opening minimizes inductance losses at high frequencies.  The system avoids the use of matching network components or multiple wire bonds or wire ribbons.

The geometry of the defect is generally a rectangle when viewed from above but the size, number, and orientation of the rectangular slot can be chosen according to the desired operating frequency of the device.

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