Product test plans are critical to the success of a new product or technology, provided the tests are stressful enough to identify defects and correlate to a realistic environment so they are ultimately acceptable to management and customers.
Optimizing test plans to this level requires using Physics of Failure (PoF) to understand failure mechanisms and evaluate useful life under actual operating conditions.
Premature, gradual or erratic failure of a physical device or structure, such as hardware, can be attributed to the degradation of device materials in response to individual or combined thermal, electrical, chemical, moisture, vibration, shock and mechanical stresses.
These types of failures can happen at any point in the process. Therefore, being able to apply PoF beginning at the design stage and throughout the product lifecycle is a distinct advantage over test plans that start at the point of failure. Further, it ensures the accuracy of accelerated life test design, performance and results.
Industry Testing Challenges
Optimal results are gained by combining standard industry specifications with PoF to tailor test strategies for the individual product design, materials, use environment and reliability needs.
Industry testing alone falls short in two important ways:
- A limited degree of mechanism-appropriate testing
- Testing is performed only at transition to new technology nodes
- Mechanism-specific coupons are tested instead of real devices
- Test data is hidden from end users
- Questionable JEDEC tests are promoted to OEMs
- Limited duration testing of up to a total of 1,000 hours hides wear out behaviors
- Simple activation energy is used with the incorrect assumption that all mechanisms are thermally activated, often leading to FIT overestimation by 100x or more
Developing Test Plans with PoF
Successful test plans with PoF are built using specific steps:
- Clearly define objectives. Delineating outcomes – comparison, qualification/validation, research, compliance, regulatory or failure analysis – has a significant bearing on test components and parameters
- Identify and document specific test elements. All robust test plans include:
- Reliability goals:
- Desired lifetime, as defined by the customer
- Product performance including returns during the warranty period, lifetime survivability at a set confidence level, and MTBF if required by the customer (MTBF is traditionally a better fit for logistics and procurement, not failure avoidance)
- Design and materials
- Use environment:
- Encompasses use, shipping and storage environments
- Summarizes customer use of product
- Outlines product protection during shipping
- Identifies factors to which the product will be subjected, including humidity, thermal and mechanical cycling, ambient and operating temperatures, salt, sulfur, dust, and fluids
- Schedule and sample availability
- Practicality and risk
- Reliability goals:
- Testing and Protocols. Once objectives and elements have been determined and documented, appropriate tests and protocols can be initiated. To ensure consistently accurate results, make sure the boards and components being tested have been:
- Assembled at optimum conditions
- Visually and electrically tested
- C-SAM and X-ray inspected