APQP techniques for identifying and eliminating bottlenecks.

As electronics content grows in automotive products, one of the biggest challenges electronics manufacturing services (EMS) providers face is ensuring that customer requirements for quality and efficiency are met from new product introduction (NPI) through the ramp to high volume. SigmaTron International’s facility in Tijuana, Mexico, utilizes Lean manufacturing principles to address this, and a recent program launch illustrates the efficiencies that can be achieved through careful planning.

The product was a printed circuit board assembly (PCBA) and wire harness assembly that required conformal coating, and wire prep and attach in addition to SMT placement. Given the projected volumes, automation of the post-SMT processes was required.

The project used advanced product quality planning (APQP) techniques. From a planning standpoint, there were six phases:

  • Pre-planning, where inputs are defined.
  • Plan and Define, which focuses on customer expectations, wants needs and desire, as related to requirements.
  • Product Design and Development, which includes design for manufacturability reviews and failure analysis.
  • Process Design and Development, which looks at the manufacturing techniques and measurement methods that will be used.
  • Product and Process Validation, which validates process quality and volume assumptions.
  • Feedback Assessment and Corrective Action, which explores lessons learned.

The tools used during APQP helped the team identify bottlenecks and implement corrective action prior to ramping production. In particular, the run-at-rate testing done during the Product Design and Development phase helped the team optimize the harness prep and assembly automation. Production Part Approval Processes (PPAPs) were performed for each new product type.

A dedicated SMT line with inline PCBA handling equipment, reflow, wash and wave solder equipment was used to minimize transport and manual handling while maximizing throughput. The associated wire harness assembly process was automated with a crimping unit that cuts and strips wire, plus tins and crimps harness terminals. This minimizes variation. The harness was soldered to the PCBA during the wave-solder process, minimizing handling and thermal cycles. Automated conformal coating and curing is also an inline process, minimizing transport.

Test throughput was enhanced by placing electrical test prior to depanelization and testing full panels instead of individual PCBAs. The AQPQ process also identified that specialized tooling was needed to achieve optimum quality during depanelization. The PCB was extremely thin and required tooling that utilized a thinner, sharper blade more aligned with the PCB’s unique design characteristics. Following depanelization, the products go through 100% visual inspection to relevant IPC workmanship standards under a magnifying unit, as well as hourly sampling under a microscope. The harnesses are also subject to SAE USCAR21 requirements. Third-party reliability testing was done to initially validate the process. The Tijuana facility has added pull test equipment and does hourly sampling pull tests and cross-sections of crimps to determine alignment to ensure the equipment is remaining within process limits.

In the packaging area, paced conveyors are used to minimize handling and ensure the project is hitting its throughput requirements.

The project will ramp to full volumes in the first quarter 2018. A second crimp unit and conformal coating system have been added for redundancy. Since the Tijuana facility operates multiple shifts, additional upside beyond projected volumes can be accommodated without the need for additional equipment.

SigmaTron’s systems also play a role in helping monitor product quality. A barcode is laser-etched at the beginning of the process to ensure each assembly can be easily tracked through all process steps. Quality and traceability data are collected in real-time and include yields and component lot data.

The result of incorporating an AQPQ approach to the project has been early identification of bottlenecks and defect opportunities, which have been addressed during the project ramp-up phase. The project is running at the required rate; yields have been 100% during the past four consecutive months, and SigmaTron’s team has real-time access to project status, yield and traceability data.

Fernando Ruiz is quality manager at SigmaTron International’s Tijuana, Mexico, facility (;

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