Redesigning an ultrasonic wire-bonding machine with a ready-to-install linear module guarantees alignment of the miniature recirculating ball slide and Acme leadscrew drive. The prealigned miniature ball rail and leadscrew are simply bolted to the machine. The device allows eliminating alignment steps and reportedly saves about $500 per unit in assembly costs.
Orthodyne Electronics of Irvine, Calif., used the miniature recirculating ball slide and Acme leadscrew drive from Rexroth Star, on two robotic wire bonders to provide a compact feeder. The low-profile leadscrew and rail increases productivity and reduces the footprint of the automated wire bonder. To further reduce cost and improve reliability, Orthodyne adopted a fully assembled motion-control module in place of individual components.
The bonder, used in the automobile industry, has a four-axis rotary head that attaches aluminum wire leads to electronic devices for interconnects. When semiconductor manufacturers expressed interest in a high-volume production machine, Orthodyne engineers looked for a space-saving mechanism to feed leadframe magazines. "Floor space in electronic assembly areas is expensive," says Bob Babayan, vice president of engineering at Orthodyne. "So there's a lot of work creating a small footprint for assembly machines."
Semiconductor chips from 1 to 10-mm square are commonly bonded on leadframes packed in standard magazines. The automated-feeder concept called for loading magazines at the machine's load station. Leadframes are fed out of the magazine to the bond area. Wire-bonded leadframes are fed into empty magazines on the output side.
To minimize the impact on the machine design, Orthodyne engineers looked for a simple linear-motion system readily integrated with the existing wire bonder. They also wanted an affordable package that could reduce the overall footprint of the machine.
Engineers at Rexroth Star developed a linear-guide feed mechanism with what's called LOSTPED criteria: load, orientation, speed, travel, precision, environment, and duty cycle. A loaded magazine weighs about 7 lb.
With leadframes positioned for welding by the four-axis bonding head, the magazine feeder does not need high positioning accuracy. However, accurate alignment is critical to ensure smooth feeds without jamming. A stainless-steel leadscrew with 0.2-in. lead/rev provides the driving force for the recirculating ball slide. The Acme leadscrew has ±0.0001-in. deviation per inch of travel and less than 0.005-in. backlash. A stepper motor turns the screw at about 10 rps to drive the carrier block at 2 ips. Electronic assembly environments are typically clean, so factory-sealed actuators need neither bellows nor special auxiliary seals. With relatively short strokes and assembly operations typically running 24 hr/day, the feeder mechanism must reliably withstand long duty cycles.
Traditional linear bearings would require a large, costly baseplate to anchor the rail. However, using the end plates as mounting points allows eliminating the baseplate and cutting total system cost by about 25%. The package measures 1.25-in. high × 3-in. wide and requires about 20% less overhead space than comparable recirculating ball-and-rail actuators.
This information provided by Rexroth Star, Charlotte, NC.