Quality Assurance

Rightsizing Continuous Improvement Focus

Match the resources that make sense in the scale of your operation.
by Matt Cline

In the early 1990s, some observers were predicting that the EMS market would consolidate and shrink to a handful of large players building the bulk of the world’s electronics products. But outsourced electronics manufacturing isn’t a one-size-fits-all equation. Even large OEMs often have higher mix, lower volume or variable demand segments of business that fit best in a regional EMS provider. Consequently, regional EMS providers continue to thrive.

That said, just as different types of manufacturing projects are often best served by different tiers in the EMS industry, regional EMS companies often need to right-size internal processes to match the resources that make sense in that scale of business. One area that can benefit from this rightsizing approach is quality management and continuous improvement.

While similar ISO quality management system frameworks make sense regardless of company size, the types of metrics collected, the size of the dedicated quality staff and the methodologies in place to drive corrective action do benefit from a more tailored approach.

Key questions that can help right-size the approach include:

  • What factors drive the bulk of defects found in our manufactured products?
  • Based on project volumes, should defects be measured at the solder joint level, the part level or the product level?
  • Does the cost of the defects likely to be caught offset the cost of inline automated inspection systems?
  • Do metrics measure actionable improvement needs?
  • Would process improvements outside of the production line do more to improve quality than more detailed inspections on the line?
  • What range of tools is most effective for identifying issues, root causes and appropriate corrective action?

When the team at Electronics Design & Manufacturing (EDM) started asking those questions, not all answers tracked back to industry norms.

One key difference is that the company is employee owned. In an employee-owned stock plan (ESOP) arrangement, employees receive briefings on company financial results and distributions based on company profitability. The result is that employees see the financial connection between bad quality and quarterly operating results, which in our experience drives a higher level of attention to detail than may be found in companies where employees are compensated on hours worked alone.

The frequency of workmanship-related defects is low. Yields are typically over 99% and, on average, returned material authorizations (RMAs) number fewer than six per month. Typically, defects are caused by one-off mistakes, broker parts, customer test fixture issues and issues at the customer.

Quality assurance focus starts in new product introduction (NPI). The NPI coordinator works with the quality team to perform a risk analysis on process failure modes and then the team addresses the gaps.

While first-pass yield is measured for customer reporting purposes, in many cases it isn’t the best tool to drive down to defect root causes. This is because most customers utilize custom functional tests and test fixture wear or narrow test parameters can cause a spike in defects that has nothing to do with workmanship. To drive corrective action, the quality team monitors defects per thousand parts, which are more applicable to a business its size. The team counts one defect per part regardless of the number of opportunities on that part. Yields are tracked using a real-time dashboard so no defect goes without visibility for more than a week. Typically, the root cause is identified in hours or days depending on whether the issue is resident at the contract manufacturer or OEM.

Figure 1. A focus on actionable metrics and root-cause analysis followed by rapid corrective action works better at this facility.

The team’s root cause analysis utilizes an 8-D methodology for failure analysis and corrective action, evaluating trends related to job number, part number and reference designator. In one recent issue that involved a wrong part, the part was used multiple times per board and not all placements were incorrect. The SMT machine was placing from two different reels. Root cause analysis identified a bad splice as the source of the issue, and the checks and balances on the process associated with splicing one reel to another to avoid downtime was strengthened with a barcode scanning step.

Use of third-party broker parts due to material constraints is one of the biggest drivers of quality issues. Often the brokers selling the parts have not had control over how the parts were handled or whether the parts have been tampered with. When broker parts must be ordered, the customer is notified and a validation plan is developed. Validation steps can range from third-party testing to internal inspection and lot sampling. Incoming inspection looks for changes to part markings, such as ink that wipes off with a solvent. Electrical test or x-ray inspection may be performed on parts designated high risk for issues. Sampling takes parts from several areas of a reel because counterfeiters will normally place the counterfeits in the middle of the reel so that the ends will test good.

Another area of concern is handling of moisture-sensitive parts. Broker-sourced moisture-sensitive parts come in a sealed bag with new desiccant and a humidity indicator card. In those cases, the card is measuring the bag’s humidity content, not the amount of moisture in an older, poorly stored part. To address that, parts with MSL3 or higher ratings are automatically baked to ensure appropriate moisture levels prior to soldering.

Quality metrics are tracked throughout the production process via automated inspection and test processes. Automated inspection includes 3-D solder paste inspection (SPI) and a 3-D AOI. Given the strength of process control, however, defect spikes in test or at the customer often require some detective work.

For example, use of broker parts can increase failure rates in tests with overly narrow parameters. In one case, changes in the weather changed failure rates. In those cases, the test engineering team works with the OEM to adjust test parameters to better align with the faults they are inspecting for.

In other cases, the issue is at the customer. The contract manufacturer’s quality team works closely with customer quality managers to review customer internal processes and may even visit as part of root-cause analysis. In one project, a customer’s facility was inserting USB cables at a bad angle due to housing design and in the process breaking the USB connectors on the PCBAs. The contract manufacturer’s engineering team recommended an engineering change that added epoxy to give the connector additional mechanical strength and solved the issue. In another project, a customer’s final assembly functional test had no ESD protection and PCBAs were getting damaged during test. The customer’s manufacturing operations were predominantly focused on mechanical assembly where ESD protection wasn’t a factor. The contract manufacturer’s quality team worked with the customer to implement an ESD protection program.

As these examples illustrate, often the root cause of a defect spike at this contract manufacturer isn’t workmanship related. The challenge for regional contract manufacturers whose project volumes typically run in the tens of thousands rather than the millions is focusing attention on the right things: having procedures that prevent defect opportunities and rapidly responding to any spikes in defects. While automated inspection equipment and first-pass yield metrics play a role, these tools tend to be deployed to a lesser extent than found in facilities running project volumes in the millions. A focus on actionable metrics and root-cause analysis followed by rapid corrective action works better at this facility. Article ending bug

Matt Cline is quality manager at Electronics Design & Manufacturing (EDM); mcline@edmva.com.