Derating Analysis / Component Selection (including developing Derating Guidelines)
DEFINITION
Derating is the practice of operating at a lower stress condition than a part’s rating. The more a part is derated, the lower its failure rate is. The less it is derated, the higher its failure rate is. The amount the derating affects the failure rate is technology-dependent.
As part of derating, we must select the appropriate components for the particular application and environment.
SITUATION
As the demand for reliability continues to increase and the cost continues to be driven down, there is an increasing need for proper derating and proper component selection to match customer end environments.
OBJECTIVE
We can assure that the most cost-effective components are used with the appropriate reliability goals in mind.
VALUE TO YOUR ORGANIZATION
The benefits of performing a derating analysis are to optimize the component size and cost vs. reliability.
The benefits of selecting the appropriate components for the particular application and environment are to optimize cost vs. reliability in the given end environment.
RELIABILITY INTEGRATION
An example of Reliability Integration during Component Selection is as follows:
Component Selection can enhance HALT
In HALT, we often find weak components. Root cause analysis of these components usually reveals that the failure was caused by an overstress condition due to the environment being harsher harsh than what the component can withstand. Proper component selection is very important, including the type of packaging for the specific application.
METHODOLOGY
Derating Analysis
There are numerous derating guidelines already in existence. We will help choose the appropriate guideline for your product or create a guideline specially for your product, and then, by applying these guidelines, we shall determine if there are any components that fall outside of these guidelines. This information can then be fed directly into the reliability prediction to determine the effect of these situations.
Component Selection
When selecting components, we first must understand the environment that the end-product is going into and the overall reliability goal. Then we choose the appropriate standard(s) from which to select components (commercial, screened, MIL).
Even in the commercial world, there are several different levels of components and component reliability and we need to make sure we select the appropriate level. We must also check to assure that the component manufacturer is reputable with a proven track record.
Four common parameters that we typically check for are:
- Part qualification parameters
- Manufacturing stress parameters
- On-going reliability tests for the product
- Manufacturer qualification (Mil house, ISO certified, etc.)
As part of the component selection process, we will help you develop a reliability critical item list. This is a list of components that require special attention and reduction of this list is a key goal early in a program. Components are put on this list for a variety of reasons, but the major reasons are:
- Low reliability
- High criticality
- Long-lead
- Approaching obsolescence
- High cost
- Improper derating
- Possible tolerance issues
- Does not meet (or only marginally meets) field environment
CASE STUDIES/OPTIONS
The following case studies and options provide example approaches. We shall tailor our approach to meet your specific situation.
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Standard Derating Analysis
A military subcontractor came to us for a derating analysis, and chose Mil-HDBK-1547. The handbook outlines most part families and gives a good estimate of derating in the military environment.
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Customized Derating Guidelines
A power supply manufacturer needed a derating analysis performed but the existing derating standards were not suitable for the product. For this, we took 3-4 well known derating guidelines and merge them together to create a Derating Guideline specific to our customer, assuring that the major families of parts used by our customer are addressed and treated appropriately. It came with instructions and examples on how to use and interpret the results.
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Derating Guideline Implementation and Training
A medical manufacturer had several design teams, and each team had knowledge of derating but came from different backgrounds. Therefore, this customer needed more than a guideline – they also needed Derating Awareness Training on why derating is important and how to use properly. Our training consisted of awareness, implementation, follow-up, and on-going support.
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Customized Derating Guidelines Tied to Failure Rates
A cell phone manufacturer needed a good derating guideline, but space on the board was critical, so there were times that they were going to have to choose a smaller component with less derating and therefore higher failure rate. Most derating guidelines only provide single points at which to derate to, but for this customer, we developed a derating guideline that had derating curves for each part family so that their designers had the ability to optimize their design by performing reliability vs. size and cost tradeoffs.
