Wedge bonding is a process of joining patch cords between electronic components and a printed circuit board using ultrasonic or thermosonic energy and pressure. The process involves bonding a wire connector to a terminal on the component and a PCB with a flat wedge-shaped component. It is slower than ball bonding but produces a smaller bonding footprint and is suitable for closely spaced terminals.
Wedge bonding is an automated process for joining patch cords between electronic components and a printed circuit board (PCB). The process involves bonding a wire connector to a terminal on the component and a PCB with a combination of ultrasonic (U/S) or thermosonic (T/S) energy and pressure. The device used to feed the connector wire and transfer pressure and energy to the bonds is a flat wedge-shaped component that gives the bonds their characteristic shape, and the process gets its name. Wedge bonding typically uses aluminum or gold alloy wire, and can bond room temperature aluminum wire with U/S energy or gold alloy wire with T/S energy. Compared to other processes such as ball bonding, wedge bonding has the disadvantages of slower production speeds and limitations in the angular flex range between component and PCB bonds.
One of the most important stages of PCB construction is bonding the plethora of component terminals to the corresponding circuit points on the PCB substrate. The connections must be well made to ensure the integrity of the circuit; even the wires of the physical connector must be positioned in such a way as to occupy the minimum space. All of this is typically done on an almost microscopic scale by highly sophisticated and precise automated machines. Wedge bonding is one of the two most common processes for making these connections; the other is ball bonding.
The glue head in wedge-gluing machines is a flat plate having a feed hole in its lower rear surface and a wedge-shaped pressure pad at the lower front edge. The connecting wire passes through the hole in the back of the plate and is compressed and joined by the wedge. The bond is created by a combination of pressure applied by the wedge shoe and ultrasonic or thermosonic energy. U/S energy is a localized concentration of high-frequency acoustic vibrations that causes a permanent bond and is mainly used for aluminum patch cords. T/S energy is a combination of ultrasonic and conventional heat energy that binds the gold alloy wires.
The wedge bonding process is a multi-step process that begins with the wedge descending onto the component terminal. Once in contact with terminal pressure, U/S or T/S energy is applied to bind the wire. The wedge then rises to a predetermined height and returns to the PCB terminal position. This simultaneous up and back motion pulls enough wire through the wedge to form a suitable wire loop or arc between the component and the PCB. The wedge then comes down and connects the connector to the PCB.
Once the PCB connection is complete, the wedge lifts up and simultaneously cuts the wire before moving on to the next set of terminals. Wedge bonding is a little slower than the alternative ball bonding process and can generally only bond connectors that travel in a straight line between the component and PCB terminals. However, it produces a smaller bonding “footprint” and is therefore suitable for bonding closely spaced terminals.
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