Since product selection, procurement and testing require such strict processes, many designers have considered a more commercial solution when it comes to parts not readily available,
The dictionary defines “off-the-shelf” as not designed or made to order but taken from existing stock or supplies.
According to the Society of Automotive Engineers (SAE), COTS is defined as “An electronic component developed by a supplier for multiple customers, whose design and configuration are controlled by the supplier’s or an industry specification.”
COTS parts tend to be cost-saving and are immediately available, making them a convenient option when you don’t want to pay or wait for customization.
In many cases, these parts have benefited mil/aero design engineers by providing them with the ability to use lower-cost alternatives to full mil-spec parts. In these sectors, especially, COTS is seen as a positive alternative to in-house, government-funded developments.
The benefits of using COTS parts include improved perforance on an acclerated schedule, reduced lead times, lower costs, and ability to implement open-source operating systems and applications.
However, the use of COTS parts is risky due to the lack confidence in the traceability, the long-term performance, and new concerns affecting these types of parts, including temperature and electrical paramaters, Restriction of Hazardous Substances (RoHS) compliance, counterfeiting, long-term reliability, quality, and others.
According to NASA, specific precautions should be implemented to minimize risk. The primary concerns
1. Part life cycle and obsolescence monitoring, particularly for standard product lines
2. Use of historical performance data, long-term performance, and repeatable results
3. Lessons learned for a particular part type, part number, or manufacturer
4. Part-specific temperature constraints
5. Lot homogeneity
6. Procurement technique, i.e., a controlled manufacturer’s specification
7. Counterfeit avoidance
8. Material identification (RoHS) and risk analysis
9. Radiation tolerance (specifically in the case of NASA-specific use case)Source: Commercial Off-The-Shelf (COTS) Parts Risk & Reliability User & Application Guide/ NASA
Even NASA has used commercial parts successfully in spacecraft, including mission-critical applications. In the past, this was achieved through careful selection, screening
And while we see the increasing reliance on these parts, engineers have longed for COTS parts designed to combat harsher conditions.
Weighing the Options
As is always the case, there are pros and cons to every seemingly beneficial solution. There tends to be risks associated with COTS components such as lack of confidence when it comes to traceability and long-term performance.
When using COTS parts, one needs to consider quality and reliability, as well as technical knowledge and support on the part of the manufacturer. Designers also need to consider factors such as RoHS, counterfeiting, and long-term reliability.
The challenge comes in finding the right off-the-shelf part for your specific design. It is recommended that procurement teams always have insight into the design process so that they can understand the details of COTS parts.
COTS: Not Always What it Seems
Let’s also remember that COTS does not always mean plug-and-play. Sometimes, modifications are needed for a particular design. This costs money, time and resources.
A COTS part, though not customized upon purchase, may need to be altered at a later time. However, a small design change can change things so drastically that it no longer works in the original design.
Engineers will face challenges if this happens, and so may the surrounding parts in a system. It is helpful to understand exactly what it will to take to incorporate a COTS part into your assembly, as well as have a back-up plan.
When designing with COTS parts, it’s also important to consider software, which will likely be required at some point due to the connectivity of “everything.” You cannot use the same software in all of your designs so this adjustment negates the term COTS.
Ultimately, COTS is not always the answer, but there are still a broad range of possibilities.