Case Study: Converting Debug Tools into Manufacturing Fixtures

Optimum Design Associates manufactures high-density circuit boards, some of which are installed into higher-level assemblies. A major step in the assembly process is board-level functional test. Typically, functional testing is designed by the OEM customer, and the fixtures and procedures are then passed to the contract manufacturer.

Last year, facing a customer request for higher unit volumes, a functional test fixture provided by the customer proved inadequate, causing a throughput bottleneck. In this case, the “fixture” was actually a complex cable harness with multiple connectors terminated by hand solder and no strain relief. It supported three unique boards, which are assembled together for insertion into the higher-level assembly. Like many functional tests, this harness was originally put together to support debug, and no resources had been devoted to converting it into a true manufacturing tool. “It was a slow process,” said one of the floor managers. “Multiple boards were going through one station, failures were harder to find, and the wiring on the fixtures was getting worn out do to too much handling.” When encountering a failure, the operator often had to determine whether it was the DUT or the cable that was failing.

Board-level testing is complicated, requiring a test specific for each board, as well as a systems test for the boards' cooperative function. To ensure support for a ramp-up, Optimum concluded that the inadequate fixture was an unacceptable risk. More testing channels and sturdier fixtures were required.

To evaluate the best possible fixture design, Derek Emmett, Optimum’s Director of Engineering, interviewed each staff member of the board-level testing process. He devoted considerable time to understanding the schematics and reviewing past test results. This gave him insight into the best way to design new fixtures to increase throughput and meet the needs of the operators.

“I talked to all of them and asked what would be ideal,” Emmett said. “I took the best of their wish list and then created a platform that fit that wish list—of what would be predicable, what would be comfortable, if it was portable—and channeled them into an idea.”

Although Emmett’s first design was only a prototype, the new fixture was well received by the testing operators. “They loved it, because it met their requirements,” Emmett says. “I was expecting to do other versions.”

Using the first design as a model, Emmett went on to design fixtures for the other two boards in the set. One board in particular posed a challenge due to a mating connector with an unusually high insertion force. Ultimately, he designed a lever system to ensure even distribution of insertion force. The new fixture also mechanically isolated the connectors themselves, thus protecting the soldered terminations.

The fixtures proved sturdy enough for the high-volume throughput to which Optimum needed to quickly adapt. What’s more, the fixtures allowed for a more “modular” setup in the testing process. Because the three-board set could now be tested in parallel, throughput more than tripled. Moreover, the parallel flow enabled the test station to fit into the redesigned lean manufacturing flow, which would not have been possible with a single unreliable cable to test all three boards.

Even though Optimum solved the immediate fixture issue, the company still works to refine its testing processes. The ultimate goal is predictability, which not only improves test results, but the manufacturing process as a whole. The goal of testing should not be to discover defects, but to improve process and as a result, eliminate defects.

“You have to learn the board’s personality, and tailor your testing to its personality,” Emmett says. “What we would like to see is to take out the personality and make the boards more compliant, sort that out before it gets to the tester. It’s a more sophisticated way of testing.”

“The challenge is creating a matrix that’ll vet out more predictable results,” Emmett adds. “It takes problem-solving from everyone—everyone has to throw into the pot—to find the one refined golden child.”

Executive Summary

Issue: Due to a customer request for higher unit volumes, Optimum Design Associates experienced bottlenecked throughput in the board-level functional testing process.

Solution: Optimum’s Director of Engineering worked with schematics, data, and test operators to convert a debug tool into robust production fixtures better suited to high-volume throughput. All work was performed in-house; no customer personnel’s time was requested.

Results:

- Modified test fixtures created a sturdier and more simplified testing process, as well as opened throughput channels of testing.

-Optimum met customer volume requirements.

-Optimum’s throughput tripled.