Odd form assembly challenges: improve productivity by increasing an application's MTBA and decreasing the MTTR.

Problem

An odd form application had an unacceptable mean time between assists (MTBA) and mean time to repair (MTTR). The net result was excessive handling and labor and poor yields. The application had a large electrolytic capacitor that was packaged in Bandoleer tape with approximately 1,500 parts per reel. The MTBA was just over an hour, and the MTTR was three minutes for full exhaust and one minute when splicing was used. The goal was to quadruple the MTBA to four hours. The number of parts on the machine and per feeder would heavily influence the final result.

Problem Solved

Because the tact time per component was 2.7 seconds, the machine would need an inventory of 6,480 components to achieve the target. The first option was to add four additional tape feeders, but the cost would be too great and the necessary feeder space was not available.

After some other possibilities were investigated, the company finally devised a solution using a bulk bowl feeder. The feeder could be sized to accommodate nearly any quantity of devices because the lane that delivered the components remained relatively small. In this case, the delivery lane occupied two spaces or feeder slots, and the on-line inventory increased to 10,000 components. Since bent leads were a concern, the leads on the electrolytic capacitor were trimmed to roughly 2.54 mm (0.100 in.), and subsequent tests showed very few bent lead occurrences--none of which were attributed to the bowl feeding process.

The bowl feeder increased the on-line inventory without sacrificing too many feeder spaces but left one open issue--polarity. Adding a color sensor at the output of the bowl feeder solved this issue. The sensor looked at the presence of the white polarity stripe on the electrolytic body portion of the device. The sensor was also integrated with the assembly cell. The system was designed to transmit the polarity information to the machine prior to picking up the component. The assembly cell would then make the appropriate orientation correction before insertion. Several other options were considered to solve the problem, but the integrated sensor was a simple solution because the method did not impact cycle time or require any major engineering or customization effort.

The final result was an assembly tool capable of a 99.98% insertion reliability with a repeatability of 0.0102 mm (0.0004 in.), a mean time between assists of four hours and a mean time to repair of one minute with splicing. The equipment supplier and the customer worked together to modify the tooling and to change the feeding approach to achieve these results.

Richard Boulanger ([e-mail]) is vice president of the Advanced Semiconductor Assembly Division and Stan Earley (earleys@uic. com) is sales manager for the Odd Form and Final Assembly Division, both with Universal Instruments Corp., Binghamton, NY.