Cennamo Electronics, LLC
-Reliability Program Planning and Execution
-Electrical and Mechanical Design
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This is a sample Reliability Program Plan (RPP). It should be tailored to the specific application based on company history, experience, cost of units, projected sales, reliability expectations, criticality of performance, etc. This plan is a fairly basic version for complex electronic subsystems with reasonable unit cost and relatively low volume. Some tasks not included in this sample, but may be applicable, are Accelerated Reliability Testing and Design of Experiments (DOE).
Tasks included in the sample are the following:
- Concept Evaluation
- Continuous Design Review
- Reliability Prediction
- Failure Mode and Effects Analysis (FMEA)
- Highly Accelerated Life Test (HALT)
- Highly Accelerated Stress Screening (HASS)
| Responsibility: | Reliability, Maintainability, and Supportability (RMS) Department. |
|---|---|
| Resources Required: | Proposed design concepts and system requirements for reliability. |
| Scheduling: | Prior to concept acceptance and resource scheduling. |
| Outputs to Others: | Feasibility and risk assessments for each concept (Engineering and Business Development). |
Concept evaluation is an essential part of the reliability process. The Reliability, Maintainability, and Supportability (RMS) Department is responsible to coordinate with Engineering regarding the design concepts proposed to meet the requirements of the program. For concepts based on external proposals, this task must be conducted during the proposal process and completed with enough time to develop the proposal for the most appropriate design concept. For internal concept evaluation, this task must be conducted before the engineering schedule and resources are projected for the project. Failure to incorporate this portion of the program can result in a design concept that will take significant effort and cost to meet the reliability requirements or possibly have no chance of meeting them. One example is a design that has extremely high Dispatch Reliability requirements, but the prevailing concept has single points of failure that would prevent dispatch. Internal redundancy may be needed to meet the requirement on essential equipment so a concept with single point failures may not the correct choice in this scenario.
| Responsibility: | RMS Department and Engineering. |
|---|---|
| Resources Required: | Bill of Materials (BOM), schematics (optional, but desired), and drawings (optional, but desired). |
| Scheduling: | Initial: First BOM is available. Update: Continuous as BOM changes. |
| Outputs to Others: | Component suggestions with reliability impact and cost of change (Engineering). |
Design and all components are reviewed and evaluated for their reliability impact. This includes the component type and associated risks, applied stress versus rated stress, placement (vibration and thermal considerations), potential failure effects, and failure modes. Prediction methodologies, online failure mode documentation, and experience are used to trade-off the selected components versus potential alternatives along with any other necessary design considerations such as component size constraints. Suggestions, accompanied by thorough explanation of the suggestion’s benefits, are supplied to the design team for consideration and documented.
As the Bill of Materials (BOM) becomes available it is reviewed by the RMS Department for reliability input. Selection of alternate component compositions and higher ratings are two of the most common items that will be recommended to the design team after review. Consider all information available at the time of review such as the projected physical location in the system design (thermal and vibration) and electrical configuration of the components based on schematics or Engineering consultation (electrical stress for de-rating and composition of components). Standard de-rating and experience are major resources of this step along with preliminary evaluation with MIL-HDBK-217 (latest revision).
This task should be performed continuously as the design matures. After the initial evaluation, each design change should be reviewed for the same criteria as the initial review. If schematics or physical location were not available for the original review then those components should be reviewed for those parameters when available.
| Responsibility: | RMS Department. |
|---|---|
| Resources Required: | Initial: BOM. Update: BOM, schematics, and drawings. |
| Scheduling: | Initial: First prototype is built and BOM is released. Update: Design is fairly stable and schematics are available. Also evaluate/update with final design. |
| Outputs to Others: | Design suggestions with reliability impact and cost of change (Engineering). Reliability Prediction Report (Safety, Engineering, Business Development, and Customers). |
Initial reliability predictions are developed when the prototype BOM is available. The initial reliability prediction will be a parts count type analysis using MIL-HDBK-217 (latest revision) for electronic components. The results of the reliability prediction will be used to provide feedback to the design team as soon as insights are available. The results will also be documented in the initial version of the Reliability Prediction Report along with any suggestions provided or insight gained from the analysis. An assessment of the overall risk for meeting reliability requirements will be made after the results of the initial reliability prediction are available.
The updated reliability prediction will be a parts stress analysis using MIL-HDBK-217 (latest revision) for electronic components. The reliability predictions are updated when the design is fairly stable, the electrical schematics are available, and drawings are available. The BOM is updated in the reliability prediction as a first step. The next step is to look at the schematic and analyze the actual stresses experienced by the components. This is used to verify the de-rating has been followed and provide insights gained to the design team.
A final evaluation/update of the reliability prediction is performed at the end of the design cycle to evaluate the design once again. This is also used to verify the de-rating has been followed and provide insights gained to the design team. Please note that the reliability impacts of design changes are continuously evaluated using the continuous design review task.
| Responsibility: | RMS Department. |
|---|---|
| Resources Required: | Initial: Design overview and subassembly interfaces. Update: Design overview, subassembly interfaces, reliability values, schematics, and drawings. |
| Scheduling: | Initial: Design overview is available. Update: Design is fairly stable, schematics are available. Also evaluate/update with final design. |
| Outputs to Others: | Circuitry or functional suggestions with failure effect and failure frequency impact (Engineering). FMEA Report (Safety, Engineering, and Customers). |
The initial FMEA is developed when a design overview and subassembly interfaces are available. The initial FMEA will be developed using the functional approach of MIL-STD-1629, Task 101 (latest revision). The FMEA detail will cover the system level design including the interfaces between the internal Shop Replaceable Units (SRU). The results of the FMEA will be used to provide feedback to the design team as soon as insights are available. The results will also be documented in the initial version of the report along with any suggestions provided or insight gained from the analysis. An assessment of the overall risk of the design failure mode criticalities will be made after the results of the initial FMEA are available.
The updated FMEA will be developed using the functional approach of MIL-STD-1629, Tasks 101 and 102 (latest revision) adding a Criticality Analysis (CA) to the document. This can also be referred to as a Failure Mode, Effects, and Criticality Analysis (FMECA). The analysis is performed to the internal functions of the SRUs which is a step lower than the previous analysis. The FMEA is updated when the design is fairly stable, the electrical schematics are available, and drawings are available. This is accomplished by looking at the schematic and analyzing the functional areas on the SRUs.
A final evaluation/update of the FMEA is performed at the end of the design cycle to evaluate the design once again. This is also used to provide insights gained to the design team.
| Responsibility: | RMS Department and Engineering. |
|---|---|
| Resources Required: | Unit for testing, test fixtures, test equipment, data capture equipment, and documentation tools. |
| Scheduling: | Initial: First prototypes are available for testing and failures can be detected. Update: Significant design change has occurred. |
| Outputs to Others: | Design suggestions with reliability impact and cost of change (Engineering). HALT Test Report (Safety, Engineering, Business Development, and Customers). |
The HALT process is used to identify potential areas of design improvement for consideration by the design team. HALT is a destructive test that attempts to expose the weakest points in the design to increase the robustness and expected life of the final product. This is accomplished using a short duration test that exceeds expected operating conditions in order to accelerate failure modes. HALT failures are analyzed using trade study techniques to determine if potential corrective actions are appropriate. The resulting final design will be more robust after the weakest points in the design have been identified and corrective actions put in place.
The initial HALT testing is performed on prototype or early designs to determine the failure modes that may require design modifications to prolong the life of the product. At this stage in design, the primary objective is to steer the design while change is more easily accomplished and has less impact on schedule and cost. The testing consists of temperature step, temperature shock, and vibration tests to find the limits of the product and attempt to extend those limits.
HALT pushes the product beyond the design limits to expose inherent design limitations at an accelerated rate. The discovery of these design opportunities enables root cause investigation on the accelerated failure. If the failure is determined to be accelerated then corrective action identification gives an opportunity to make the higher frequency failure modes more robust. This process will increase the robustness of the design and prolong the expected life of the product.
HALT is also performed after major design changes during development. The subsequent HALT testing results will also be evaluated to determine their applicability to the design and may result in design changes to increase the robustness.
| Responsibility: | RMS Department and Production. |
|---|---|
| Resources Required: | HALT test results, data capture ability for system monitoring during test, data capture ability for test failures tied to serial number, and data capture ability for field failures tied to serial number. |
| Scheduling: | Create plan: HALT Test Report has been released and reviewed. Perform testing: First production unit and then ongoing for all production units. |
| Outputs to Others: | Failures logged into tracking (Production), unit for additional study (Production), and analysis of failures (Engineering or RMS Department). |
HASS techniques reduce infant mortality rates (early life failures in excess of random failure distribution) in fielded product by accelerating early life failure modes due to manufacturing and process variations. HASS is a screening process that is performed on all production units after the product is assembled, but before it is delivered to the customer. Highly Accelerated Stress Audit (HASA) is HASS that is performed on a sampling basis and is not recommended for newly fielded designs.
HALT performed will be used to generate the initial HASS profile. Careful monitoring of the HASS profile effectiveness will be continuous throughout the life cycle of the product. The HASS profile will be adjusted as necessary based on the internal analysis of the testing and field performance. Factors that will be considered for HASS profile adjustment are the following.
- Testing failure analysis indicating that experienced failures are due to overstressing components and not due to manufacturing and process defects that cause infant mortality
- Low testing fallout rates combined with significant infant mortality in the field (Weibull analysis will be used to assist in infant mortality classification)
- Experienced life of units below expected values (may be reducing life through testing)
- Significant design changes (determined through analysis)
- Testing equipment changes
The HASS testing is intended for each Line Replaceable Unit (LRU) that is produced and implemented prior to delivery.
HASS tests will be performed based on standard techniques with in-house equipment and will be developed and monitored by the RMS Department. These tests will push the product environmental stresses based on the learning in the HALT test about product limits. The HASS test will be a reduced stress compared to the HALT test, but will provide significant stress to accelerate infant mortality failure modes.
HASS profiles will be developed from HALT results and then proven on the initial products developed. The RMS Department will continue to monitor the performance of products to ensure that the test are both effective and do not reduce the expected life of the product. Pushing the unit beyond the design limits should help to expose manufacturing defects and process variations potentially contained within the unit without significantly reducing the life of the product. These defects and variations range from component defects to assembling errors and will reduce the infant mortality of the product which are independent from the inherent design.
Please e-mail info@cennamoelectronics.com or call (614) 600-7634 for more information.
Cennamo Electronics, LLC is a limited liability company formed in the state of Ohio.