Product test plans are critical to the success of a new product or technology. Preparing a viable test plan involves several steps to properly identify the requirements for the tests. While many test parameters will vary from product to product, there are elements of the methodology for a test plan approach that remain consistent. These include the necessity for a BOM review to determine part limitations, assessing the field environmental conditions so they can be properly mapped to the tests implemented, and the impact of failure history, should it exist. The objective is to develop a test plan that does not stress the assembly to a level where a failure might not be experienced in the field.
REVIEWING THE BILL OF MATERIALS
When formulating a test plan structure for a product, the blueprint for testing should be based upon the product’s field experiences over its life expectancy. A good first step in developing a plan is determining which potential failure mechanisms the product may encounter based on the limitations of its parts. In order to establish possible failure triggers, reliability personnel should consider the bill of materials for a design to get a sense of the different parts that have been chosen for assembly. Upon reviewing the bill of materials, engineers and designers may have the experience to identify parts with a history of being a weak link.
Consider the example of a lithium ion battery. Lithium ion batteries typically have a maximum operating temperature of 60 degrees Celsius. If a design team has assembled a product with a lithium ion battery, testing parameters should utilize the knowledge of its maximum operating temperature. Tests for heat stresses should not exceed 60 degrees Celsius so as to not induce a failure that would not be seen in the field.
It is not always feasible for design teams to tear down a product before developing test protocols. However, doing so provides valuable information that could determine part limitations before ever engaging in costly testing.
IDENTIFYING FIELD CONDITIONS & USE ENVIRONMENTS
It is vital that you have a good understanding of the shipping and use environment for a product. Do you really understand the customer and how they use your product (even the corner cases)? How well is the product protected during shipping (truck, ship, plane, parachute, storage, etc.)? Do you have data or are you guessing?
The most critical element in constructing a test plan is identifying the range of field conditions that the assembly will encounter. Often, products are delivered all over the globe, so field conditions for a single product could exist at opposite extremes. In such a scenario, testing for the product could include worst-case high temperature conditions that mimic the environments of areas like Death Valley, California or Phoenix, Arizona and worst-case low temperature conditions representative of environments like Alaska or Canada. However, it is important that testing is as accurate and reflective as possible – narrowing the range of temperature experiences produces more efficient testing. A test plan that induces failure is not insightful if the parameters of the test do not correspond with field conditions. Remember the importance of ensuring that testing and applied stresses are reflective of the potential experiences of the assembly.
All of the following should be considered when identifying field conditions: temperature cycling, humidity, corrosion, power cycling, electrical loads, electrical noise, mechanical bending, random vibration, harmonic vibration and mechanical shock.
ASSESSING FAILURE HISTORY
Unfortunately, information and data on failure history is not always available to design teams. However, when it is known, failure history data can expedite testing.
While assessing the failure history of parts of an assembly may seem obvious to most, it is an extremely valuable and insightful endeavor, nonetheless. If designers are aware of failure history, than testing will be better equipped to provide more meaningful results. When failure history is documented, test parameters can be installed more accurately, producing more efficient testing.
To learn more about effective test preparation techniques, download our white paper on 6 Steps to Successful Board Level Reliability Testing.
At DfR Solutions, we have extensive experience in developing, implementing and executing test planning for assembled boards, performing hundreds of tests per year. If you would like a consultation on your test plan methodology, contact us today.