Lean and Quality within the Supply Chain

Outside suppliers can also affect a facility’s quality levels.

Use of Lean manufacturing philosophy and Lean Six Sigma tools have contributed to SigmaTron International’s quality and production teams achieving superior levels of quality, particularly within assembly operations. That said, even with outstanding process control, incoming material can impact achievement of Six Sigma quality levels. As a result, quality management needs to have a strategy for both ensuring supplier quality and identifying and correcting issues when that quality drops.

In this EMS provider’s model, suppliers are asked to complete a self-audit and provide applicable document examples and a copy of a Development Manual, Control Plan, PFMEA, Internal and External PPM data, Quality Reliability and Test equipment list and other documentation, if required, as part of the qualification process. If the subsequent score indicates a need for improvement, the EMS provider assigns a supplier quality engineer (SQE) who works with the supplier’s assigned stakeholders to meet the agreed-on improvement goal.

In cases where results of the self-audit or quality issues drive the need for additional scrutiny, a virtual or onsite audit may be conducted by the EMS provider. Audits for suppliers in North America are conducted by a US team and audits for suppliers in Asia are conducted by a team from the EMS provider’s international purchasing office (IPO) in Taiwan.

While an OEM can rationalize its supply base to a select few and upgrade technology to eliminate problem classes of parts via its design strategy, EMS providers must manage a larger supply base defined by their customers, which may include legacy technologies and suppliers whose performance requires improvement. EMS providers either need to put resources in place to address these situations or inform the customer that poor quality is the tradeoff for maintaining the problem supplier.

In this EMS provider’s case, relays are an example of a chronic issue with a legacy, yet necessary technology. Relays are often the only mechanical device on a printed circuit assembly (PCBA). While design trends are eliminating relays in favor of solid-state components in most applications, mechanical relays remain a choice in situations where overcurrent could damage a solid-state part.

This EMS provider began working with its relay suppliers over a decade ago to improve quality. At that point, failure rates were running at 1000ppm predominantly due to debris getting into relays during the assembly process. A supplier development team worked with the relay suppliers to improve cleanliness in their factory assembly process. They also identified issues in the plastic injection molding process that were corrected by optimizing molds to reduce the need for secondary processing of parts following molding. Improvements to test and introduction of reliability testing for sample lots were also recommended. The result was that failure rates were reduced to 25ppm. That said, given that many of this EMS provider’s customers require zero to 50ppm failure rates for finished products, a 25ppm supplier quality rate is still too high, and the supplier development process is continuing.

In other cases, supplier quality may trend negatively unexpectedly. Six Sigma tools such as the Eight Disciplines (8D) problem-solving methodology or the 5 Whys methodology can be helpful in determining root causes and corrective action.

The 8D methodology was originally developed by the US government in World War II. It was refined by Ford Motor Co. in the 1980s and grew in popularity. The 8Ds are:

• Discipline 1: Define and Describe the Problem
• Discipline 2: Form a Team to Plan a Corrective Action
• Discipline 3: Develop an Interim Containment Plan
• Discipline 4: Determine, Identify and Verify Root Causes and Escape Points
• Discipline 5: Choose and Verify Permanent Corrections for Problem/Non-Conformity
• Discipline 6: Implement and Validate Corrective Actions
• Discipline 7: Take Preventive Measures
• Discipline 8: Recognize the Team.

The 5 Whys methodology determines root causes by looking in detail at possible root causes. For example, if the root cause is identified as a design issue in a portion of the PCBA, the first why might identify the specific area of the PCBA causing the issue, the second why would look at the documentation that drove that design choice, the third why might identify errors in specification, the fourth why might identify what the revision should be and the fifth why might look at checks and balances that would have otherwise prevented the error from occurring. This would drive an action that addresses all elements identified in the 5 Whys process.

For example, in the case of an electronic membrane switch supplier, use of an 8D and 5 Whys approach resulted in the supplier changing its assembly process and improving its test process to enhance assembly process control and provide 100% testing of CTQ elements.

The results of this approach build better relationships with both suppliers and OEM customers because it creates an environment where quality issues are corrected through a collaborative process that quantitatively identifies what drove the issue to both the supplier and the customer. In this EMS provider’s case, this approach has also positively impacted its scorecards with its major customers, delivering quality results from 0-49ppm across multiple high-volume programs.

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