Design for Excellence in Electronics Manufacturing. Cheryl Tulkoff
Design for Manufacturability (DfM) and Design for Reliability (DfR) and involve the actual manufacturers in the DfM process.
Perform root cause analysis (RCA) on test failures and field returns to initiate a full feedback loop.
Best‐in‐class companies have a strong understanding of critical components. Component engineering typically starts the process through the qualification of suppliers and their parts. They only allow bill of materials (BOM) development using an approved vendor list (AVL). Most small to mid‐size (and even large) companies do not have the resources to assess every part and part supplier. Those who are best in class focus resources on those components critical to the design. Component engineering, often in partnership with design engineers, also perform tasks to ensure the success of critical components. This includes design of experiments, test to failure, modeling, supplier assessments, etc. Typical critical component drivers are:
Complexity of the component
Number of components within the circuit
Past experiences with component
Sensitivity of the circuit to component performance
Potential wearout during the desired lifetime
Industry‐wide experiences
Custom design
Single supplier source
From the component perspective, reliability assurance requires the identification of reliability‐critical components and drives the need to develop internal knowledge on margins and wearout behaviors. RCA requires the true identification of drivers for field issues combined with an aggressive feedback loop to reliability and engineering teams and suppliers.
Best in class companies provide strong financial motivation for suppliers to perform well by creating agreements with the supply chain to accept financial incentives and penalties based on field reliability. These practices allow companies to implement aggressive development cycles, proactively respond to change, and optimize field performance.
Establishing a successful, comprehensive reliability program requires planning and commitment. Requisite priorities include:
1 Focus: Reliability must be the goal of the entire organization and must be implemented early in the product development cycle. Separate reliability from regulatory‐required verification and validation activities and mindset.
2 Dedicated staffing: Assignment of responsibilities without assigning resources risks failure.
3 Clearly define reliability goals and the use environment: these drive the rest of the reliability program.
4 Identify critical components, especially those at risk of wearout. Initiate test‐to‐failure and design‐ruggedization activities.
5 Implement step‐stress testing at both sub‐assembly and assembly levels.
6 Perform RCA. Focus on the top three field issues, and repeat; drive to quality assurance as appropriate.
2.3 Elements of a Reliability Program
Elements of a comprehensive reliability program include:
Organization: Develop a system that rewards teams for effective reliability engineering focus. Reliability must be the goal of the entire organization and must be implemented early in the process apart from verification and validation (V and V).
Reliability goals: Consider an availability goal as well.
Reliability resources: Resources need to be assigned to reliability characterization and committed in program staffing. Characterization infrastructure needs building.
Software reliability: Frequently overlooked but critical to today's products and systems
Defined use environments: Engage field service to obtain knowledge of relevant stresses (loads, contaminants, electrostatic discharge [ESD], etc.) in use environment, and then exercise these during reliability characterization.
Thermal analyses.
Circuit and component stress analyses.
Derating: Employ systematic derating by computational and/or experimental analysis.
Critical components identification: Identify and prioritize components and subassemblies for extended reliability analysis and test activity during early development. Use supplier life data where possible; create the expectation of minimum supplier reliability competency.
Failure mode and effects analysis (FMEA).
Critical to quality (CTQs) and tolerance identification.
Comprehensive control plans with suppliers.
Design for excellence practices.– Design for Manufacturability (DfM), Design for Testing (DfT), Design for Reliability (DfR), Design for Excellence (DfE), and Design for Sustainability (DfS).– Manufacturing involvement in DfM and DfT.
Step‐stress tests to define design margins (HALT).
Simulation for end‐of‐life prediction
Relevant product qualification tests
Accelerated life test (ALT) to validate the life‐prediction model
RCA on failures and field returns with a feedback loop (design, measure, analyze, improve, control [DMAIC])
These elements will be explored in more detail in the upcoming sections and chapters.
2.3.1 Reliability Goals
Desired lifetime and product performance metrics must be identified and documented. The desired lifetime may be defined as the warranty period or by the expectations of the customer. Some companies set reliability goals based on survivability, which is often bounded by confidence levels such as 95% reliability with 90% confidence over 15 years. The advantages of using survivability are that it helps set bounds on test time and sample size, and it does not assume a failure rate behavior (decreasing, increasing, steady‐state).
Reliability goals and requirements address the product or system itself and include test and assessment requirements and associated tasks and documentation. These are included in appropriate system/subsystem requirements and specifications, test plans, and contract statements.
Examples of reliability goals and metrics:
Minimum required field service life under defined conditions: 10 years of environmental exposure and 150,000 miles (or 1 million operating hours)
Maximum allowable quality defect rates– Field infant mortality quality defect rates at 3‐6‐9‐12 months– Dead on arrival (DOA) defect rate– Required minimum field reliability at one year or the end of the warranty period– Six Sigma first‐pass quality yield– Non‐repairable or failure to replicate (no trouble found, NTF) rates
2.3.2 Defined Use Environments
Meaningful reliability prediction must consider the environment in which the product is used. There are several commonly used approaches to identifying the environment. One approach involves the use of industry/military specifications such as MIL‐STD‐810, MIL‐HDBK‐310, SAE J1211, IPC‐SM‐785, Telcordia GR3108, and IEC 60721‐3. The advantages of this approach include the low/no cost of the standards, their comprehensive nature, and acceptance throughout the industry. If key information is missing from a given industry standard, simply consider standards from other industries. Disadvantages include the advanced age of the standards (some are more than 20 years old) and the lack of validation against current design usage. Depending upon the product and environment,