The company says this combines the advantages of ultrasonic bonding and laser welding, and is ideal for package interconnects in power modules and battery pack assemblies. To increase the functionality of typical laser welding, F&K DELVOTEC developed a system it calls Laserbonder. “For example, if you have a battery module with 120 batteries, then you need 240 clamped parts.” “With increasing numbers of parts to bond, this clamping machinery is more expensive, less flexible, and larger,” said von Ribbeck.
However, this adds to the complexity in automation. To prevent this, laser welds must be complemented by a clamping system that ensures a zero gap. If there’s a gap between the components, the laser weld will be unstable and ineffective. For one, laser welding requires that there’s zero gap between the components to be connected, such as a ribbon and battery. Laser-welded bonds can withstand higher currents than ultrasonic bonds, but the technique isn’t without its tradeoffs.
“And this is controlled with epicycloid or hypocycloid movements of the laser beam, which are very fast and overlap the overall geometry of the weld.” “For cylindrical cells, you don’t want to weld too deep into the material because you don’t want to damage or puncture the battery cans,” said von Ribbeck. This is a specific method of laser welding called keyhole welding, and by oscillating the laser just so, the width and depth of the weld can be tightly controlled. In this technique, a ribbon is irradiated from above by a powerful laser that melts some of the ribbon metal in such a way as to create a kind of tunnel through to the substrate. F&K DELVOTEC recommends that ultrasonic wire bonds be used only for applications in which currents will not exceed about 30 A.įor higher-current applications, von Ribbeck says laser welding is better suited. Ultrasonic wire bonding is also limited to lower-current connections.
If there’s grease, dust, or other contaminants in the way, the bonding will not succeed. However, ultrasonic bonding requires an extremely flat and clean bonding surface in order to work properly. For this reason, ultrasonic bonding is also well suited to automation. Ultrasonic bonds produce a very reliable connection quality, and they’re flexible in that they can accommodate different lengths of wire, different directions, and different heights between connected cells. “So it’s a kind of cold welding of the metals – there is never a melted phase.” “The temperature never gets higher than 80 or 100 degrees Celsius,” explained von Ribbeck. Typically, the wire or ribbon is then formed into a loop by the movement of the bonding tool and a second bond is made on another substrate. This causes the metal atoms in the wire to mix in with the metal atoms in the substrate, and after a few hundred milliseconds, the materials are fused together. Then the wire is vibrated at ultrasonic frequencies of around 100 kHz. The process begins with pressing a wire or ribbon onto the substrate to which it will be bonded, such as a cylindrical cell battery canister. Ultrasonic wire bonding is an advanced friction welding process that’s been widely used in the microelectronics and power electronics industries since the 1970s.