GETTING LEAN
Utilizing Lean Manufacturing Principles to Cut Time and Cost in Test
Building functional test fixtures in-house mitigates several of the “seven wastes.”
The mantra of the electronics manufacturing services (EMS) industry has been faster, better, cheaper for four decades, given that outsourcing isn’t justifiable without a speed, quality or cost improvement over in-house processes. Continually delivering those benefits requires a focus on working smarter that relentlessly asks, “Where can we improve?”

Taiichi Ohno’s concept of the seven wastes (muda) in manufacturing as part of the Toyota Production System (TPS) provides a good thought process for evaluating any process. To recap, those seven wastes are:

  1. Waste of overproducing (no immediate need for product being produced)
  2. Waste of waiting (idle time between operations)
  3. Waste of transport (product moving more than necessary)
  4. Waste of processing (doing more than what is necessary)
  5. Waste of inventory (excess above what was required)
  6. Waste of motion (any motion not necessary outside of production)
  7. Waste of defects (producing defects requiring rework).

SigmaTron’s Elk Grove Village, IL, facility continually focuses on improving efficiency in inspection and test. Recently, its test engineering team found that building functional test fixtures in-house drove improvements that mitigated several of the seven wastes.

An initial benefit was eliminating the waste of waiting. Ordering parts and building a fixture in-house reduced fixture development lead-time to three weeks from an average of six-to-eight weeks. Given supply and demand imbalances in many markets are driving original equipment manufacturers (OEMs) to speed new product introduction (NPI) processes wherever possible, reducing test fixture lead-time offers significant benefits.

While it will vary from fixture to fixture, in-house fixture design can also reduce test time. For example, in one recent case, the test engineering team designed a two-tiered fixture capable of testing a printed circuit board assembly (PCBA) and a higher-level assembly (HLA). The PBCA was placed on a bed-of-nails with a cable that plugs into the HLA. This combined fixture design cut PCBA test time in half and reduced the HLA test time to 30 seconds from 3.5 minutes. Typically, an outside vendor would have designed this as two fixtures, but in-house personnel were able to consider all product characteristics and anticipated production volumes when optimizing the design.

This design also eliminates the wastes of transport and processing that a two-fixture strategy would have represented. This improves quality outcomes by minimizing the defect opportunities that excess handling can create and adds cost benefits of faster test times and lowered nonrecurring costs.

Building fixtures in-house also shortens the test team’s learning curve and enables them to tailor fixtures to project requirements more closely than may have been possible with an outside vendor.

The team also applied these concepts when determining how best to use flying probe test capabilities. A major driver for adding flying probe test capability is the convenience of a fixtureless test resource for NPI and pre-production builds while functional test fixtures were in development. A secondary benefit is the ability of flying probe test equipment to minimize troubleshooting time on functional test failures by exploiting its electrical test capabilities. Both benefits mitigate the waste of waiting.

For example, a flying probe tester’s ability to detect device voltages helps it determine if the device has issues based on the voltage detected. This works for analog and digital components, as well as bipolar transistors. A higher voltage measurement is used for MOSFET devices. The voltage of interior transistors is measured on CMOS or logic gate devices. With BGAs, the capacitance value of the logic array can be measured and compared to the standard. This particular tester was selected because of an integrated automated optical inspection (AOI) feature, which enables visual inspection of SMT and through-hole component placements, in addition to electrical test.

Using flying probe in NPI and preproduction validation activities helps mitigate the waste of defects when the data are used to fine-tune the process. Combining test and inspection features minimizes the wastes of transport and processing. Using it as a troubleshooting tool helps minimize the waste of waiting by reducing technician time spent identifying the issue.

While the argument can be made that inspection and test activities are non-value-added processing, the reality is they are necessary non-value-added activities. Even when processes are kept within control limits, some components will fail. In the case of NPI and preproduction activities, inspection and test activities help quickly identify issues in the new process, which can lead to corrective actions that eliminate defect opportunities. Finally, finding ways to reduce test and troubleshooting time has more than just a cost benefit. In today’s environment of supply not keeping up with demand, the ability to reduce lead-time or processing time is critical toward meeting OEM schedules in multiple industries.

Anita Tucker headshot
Anita Tucker
is general manager, Elk Grove Village facility, of SigmaTron International (sigmatronintl.com); anita.tucker@sigmatronintl.com.