Getting Lean

Automating inspection in secondary assembly operations.

One of the first lessons in quality management is the difference between quality assurance and quality control. Quality assurance focuses on eliminating defect opportunities before they occur, while quality control focuses on inspection strategies that eliminate defects before they escape the factory. There is universal agreement that quality assurance is more cost effective than quality control. Lean manufacturing principles are based on a quality assurance focus. That said, use of automated inspection equipment has been growing dramatically in recent years because increasing density and complexity in printed circuit board assemblies (PCBAs) is driving the need for a blended quality assurance/quality control approach that includes mass inspection.

Over the past 18 months, SigmaTron International's facility in Tijuana, Mexico, has been exploring the best way to automate inspection and integrate the captured data into real-time corrective action throughout its entire PCBA assembly process. A July 2022 PCD&F/CIRCUITS ASSEMBLY column, "An Industry 4.0 Approach to Employing 3-D AOI on an SMT Line," discussed the journey of integrating Industry 4.0 capabilities in a Lean Six Sigma framework in this facility's SMT area. Once that phase was completed, implementation of 3-D AOI capability began in secondary assembly work cells. Typical secondary assembly operations include soldering cables and components such as switches which can't be reflowed, adding rubber caps and placing QR labels.

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MES upgrades capture kanban inventory levels, allowing electronic replenishment pulls.

The visual factory has come a long way since the concept was introduced, moving from production status viewable by walking the factory floor to a comprehensive collection of real-time data viewable from any interconnected computer. That evolution isn't seamless for many electronics manufacturing services (EMS) providers, however. While newer equipment platforms are designed to integrate with manufacturing execution systems (MES) easily, legacy equipment platforms may require specialized programming or other workarounds to achieve desired interoperability. Equipment communication incompatibilities often lead to multiple shop floor control systems being utilized among work areas, which is inherently inefficient.

SigmaTron International's Chihuahua, Mexico, facility recently dealt with these issues when the facility began transitioning to the company's proprietary Tango MES. The company's corporate IT and operations teams have worked together to define enhanced shop floor capabilities in production and are upgrading system capabilities across facilities. The challenge for facilities implementing the latest enhancements is creating efficient equipment interfaces and integrating or replacing legacy processes.

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A DoE reveals the packaging type matters less than the process used.

The need for electrostatic discharge (ESD) protection is drilled into production workers from day one in most electronics manufacturing facilities. Most facilities have multiple layers of protection including floor tiles or conductive coating, smocks, individual grounding devices, ESD mats on workstations, and ionizing blowers throughout the production process. There are also multiple layers of protection from conductive totes to metalized bags for product as it ships out. There is a tendency to believe more protection is always better. Given that the seven wastes include both defects and overprocessing, however, from a Lean manufacturing standpoint there is value in analyzing how much protection is required for shipped products. Considering whether multiple layers of protection create a false sense of security with operators involved in pack/unpack operations also has value.

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Identify the areas of variance in stencil design and adjust SPI programming accordingly.

Automated inline solder process inspection (SPI) has the potential to deliver some of the highest value among all inspection steps because defects caught at this point in the process require minimal rework. It is simply a matter of cleaning solder paste off the printed circuit board (PCB). Additionally, good printing performance typically represents 80% of a successful SMT assembly process. As the bulk of workmanship-related defects tend to track back to deficiencies in solder paste deposition, closely monitoring control limits in this area has a substantial impact on eliminating defect opportunities.
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Deep dives on defect resolution, one at a time.

Jorge PenaMost medium-to-high volume electronics manufacturing services (EMS) providers design their new product introduction (NPI) process to identify issues in printed circuit board (PCB) layout, overall product design or process flow that create defect opportunities. Unfortunately, a key challenge in the EMS industry is convincing customers to adopt those recommendations. Additionally, some design or process issues escape NPI or pilot production, not becoming evident until a product is running at full volume. SigmaTron International’s team in its Acuña, Mexico, facility is working to change those dynamics one customer at a time.

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Improving problem identification and resolution speed through dual disciplines.

Teams at multiple SigmaTron International facilities have been trained in Lean Six Sigma philosophy. However, some companies work from a pure Lean manufacturing philosophy without Six Sigma tools. This month, we look at the benefits of integrating these disciplines.

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