A process for addressing RMA for multi-factory production.

In a normal business environment, the electronics manufacturing services (EMS) industry has more variation than that of a Lean original equipment manufacturer (OEM). This doesn’t mean EMS providers are disorganized. It simply highlights the challenges of an environment where customer inputs dictate supply-chain choices, processes and validation methodologies that would normally be optimized to minimize variation at a Lean OEM. Pandemic restrictions, supply-chain shortages, logistics constraints and demand spikes of 2021 have caused further variation at EMS providers and customers. However, those challenges serve as incentive to increase Lean discipline.

Past columns have highlighted Lean Six Sigma core tools such Gemba and the DMAIC process that help identify and correct quality issues that develop in manufacturing operations as project assumptions change. Lean Six Sigma is helping create an empowered, educated workforce at SigmaTron, capable of rapidly addressing unanticipated challenges found in today’s production environments. That said, defects can escape the factory or be induced by activities once product leaves the factory. Focusing on this area can have a long-term impact on eliminating another set of defect opportunities: muda (waste) and cost.

In SigmaTron’s model, field-service engineers work with customers that have higher volume or more technically sophisticated products to determine the root cause of field returns. While the company is achieving industry-standard low defect rates on some of its highest volume programs, even that low percentage generates monthly returns when the printed circuit board assembly (PCBA) count is in the millions.

Initially, this model focused on customers in the consumer products sector. In 2021, however, it was expanded to include industrial sector customers meeting the volume and/or complexity criteria.

In most cases, customers have multiple factories. Regular field engineer visits are scheduled with the factories receiving SigmaTron-manufactured product. In the consumer products area, manual functional test sets that mirror those used for final pack validation audits prior to shipment from SigmaTron are located at each customer factory. This process will likely be replicated with industrial customers where appropriate. When the engineers visit, all line-rejected products are 100% tested on those functional testers. Normally these would become products subject to return material authorization (RMA) processing and returned to the proper SigmaTron factory for processing and analysis. Having the field engineers check these before they are returned saves time and cost for both SigmaTron and the customer. Reason: The return analysis shows that more than 50% of the failures are caused by something other than component and workmanship failures in the SigmaTron process. Instead, these types of failures are no trouble found, unintentional customer-induced damages, shipping or customer handling problems, ESD or electrostatic damage, design or design for manufacturability related issues, and testing capability or testing technical limitation issues.

In short, over 50% of RMA product is best addressed at the customer, saving two legs of shipping cost. In this example, the field engineers work with the customer to either reclassify the no-fault-found product as good or correct the root cause issue at the customer assembly location so they can be immediately addressed. This contributes to fewer overall failures going forward.  

Typical issues that drive these types of RMAs include:

• Improper cabling at complete end-product assembly
• Test errors in volume testing
• Improper voltages applied during assembly or testing
• Shipping-related damage
• Handling or ESD damage issues during higher-level assembly at the customer
• Inclusion of components not robust enough for the design.

Once a root cause has been identified, the field engineering team works with the customer to eliminate the condition that caused it.

In the case of no-fault-found units, the team will send it back to the customer’s line for another test. If the unit continues to test bad on the line and good in the manual functional test, the line’s testers are evaluated for software or fixture issues.

If no production handling or component issues are identified in PCBAs that tested good prior to leaving SigmaTron’s factory but now fail all tests at the customer’s factory, shipment, packaging or design may be evaluated.

In the case of design issues, the team may suggest a short-term fix while an engineering change is in development.   

Should the issue be component- or EMS-production-related, the team works with suppliers or the associated SigmaTron factory to correct that root cause, and Lean Six Sigma teams within purchasing or the factory may be involved in the corrective action process.

The result is both improvement in quality and cost. While the actual PCBA RMA numbers are relatively small, the analysis process corrects otherwise hard-to-identify issues that would likely continue to cause defects. Most important, this collaborative approach helps the EMS and customer teams develop closer working relationships that can contribute to a focus on eliminating inefficiencies in the product realization process. 

Allen Abell is corporate director of quality and compliance at SigmaTron International (sigmatronintl.com); allen.abell@sigmatronintl.com.