How do I replace old, legacy, or out-of-production parts in my design?

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From a hobbyist point of view, sometimes it feels like certain parts have been available forever. 555 timers, 8-pin DIP packaged op-amps, 80’s era microcontrollers, etc. However, upon further inspection, it’s easy to see that these ubiquitous components have evolved over time and many other components have come and gone, sometimes in less than a decade. And as a professional who needs to worry about the logistics of finding and replacing these parts en masse, the magnitude of applicable changes skyrockets. So, why do parts go away and what can I do about it?

First, a quick note about obsolescence. This is basically where, for one reason or another, a part will no longer be manufactured or supported by its original manufacturer. There are many reasons that obsolescence occurs. Flaws in the design are identified and corrected, manufacturing processes improve enough that a change is warranted or required, or there simply isn’t enough demand for a part and the supplier just isn’t making money off of it anymore. The key result is that the part isn’t available anymore. The way you approach the replacement of those parts in a design varies drastically on the part and the reason the part was discontinued. The problems associated with this obsolescence can be overcome in several ways that generally fall into one of two categories - Finding the part some other way or replacing the part in your design.

While this will focus on replacing obsolete parts, a lot of the concepts can be applied to when a part consistently has too long of lead time or if the parts become too expensive to continue their use in an end product.

Find the Part Some Other Way

Option #1

Look at other distributors. Are they really gone? And can you find them from some other distributor that may have them stockpiled? If you’ve become accustomed to using your “go-to” distributor, it can be easy to forget that there are many other distributors available. Besides standard distributors, there are certain distributors that specialize in warehousing parts that have gone obsolete, either recently or decades ago.

Option #2

Find a drop-in replacement. Not all the time, but often, the manufacturer replaces a part with an improved version that can be used as a direct replacement. Other times, there are some minor changes. Other times, it’s completely different. You may be lucky enough for the direct replacement - it’s worth looking into! Depending on the application, if it needs to be tested for medical, automotive, military standards, it likely doesn’t matter if it’s a drop-in replacement, you will still need to have your product go through thorough testing. Either way, it’ll be less work than a product redesign.

Option #3

Work with a specialist or specialist distributor for help. Part brokers sometimes have a bad reputation in the electronics industry due to an increased likelihood of coming across counterfeit parts. On the other hand, some distributors, even if they don’t have a stockpile of soon-to-be obsolescent parts on hand, are willing to make the upfront purchase of the parts before they go EOL. One of our Friends of CircuitBread, Onlinecomponents.com, has a specific EOL program that, among other possibilities, will purchase soon-to-be obsolete parts in a larger quantity and then warehouse them for future use. But in these scenarios, you will need to work with the distributor directly.

Option #4

Look at riskier options. How many do you need? And what for? Buying parts from non-authorized distributors or from auction sites like eBay can be very sketchy but if you only need one or two for a personal project, it may be the only way. You are opening yourself up to an increased risk of counterfeit parts so you definitely would not want to do this with anything outside of hobby personal projects. Note that this is the most desperate option in finding the parts and we highly recommend against it in most situations.

Adapt to a New Part

In general, the more complicated or custom a part is (FPGA, MCU, PLC versus resistor, capacitor) the harder it will be to replace. A resistor or capacitor is very fungible but specialized chips can cause significant redesigns. However, the reason why a part was discontinued is important because it changes the way a supplier will treat it. Some parts are extremely popular but their manufacturing lines are being upgraded, so they make some improvements to the parts in the process. If that’s the case, they’ll almost always create pin-for-pin replacements that have similar properties but perhaps are slightly more power efficient and with tighter tolerances. On the other end of the spectrum, if a part isn’t popular enough to warrant its continued production, that may mean a complete design overhaul.

Option #5

Minor changes to the circuit/programming. While changes will have to be made, if you’re fortunate, it may be as minimal as removing a single trace to the PCB (removing is almost always easier than adding!) or modifying code to have a different interface that doesn’t affect the core functionality. Perhaps a new temperature sensor has a standard SOT-23-5 footprint but communicates via UART instead of I2C - the footprint is the same, the end data is the same, just the communication protocol needs to change.

Even if the physical and code changes are minimal, a lot of factors can affect the complexity of the replacement that have nothing to do with engineering. Larger corporations or anything related to a government contract will almost always have a more invasive view of making changes while small companies may tend to “wing it” more. But, when making a change to either your hardware or software, make sure you’re checking the bureaucratic boxes to make sure the end result still meets safety and functional standards.

Option #6

Extensive overhauls. On one hand, this is basically the previous option but scaled up. If the part needs to be replaced by something with a completely new form factor and protocols, that will likely have a cascade effect on your hardware and firmware design. Sometimes this yields the need for an extensive redesign or can even cause a complete redesign of your product from the ground up. This may be considered the nuclear option where you just start from scratch. As a bonus, hopefully there are lessons learned from the previous iteration of the product and perhaps other areas that can be improved during this complete redesign. While unfortunate, it’s important to find the silver lining in a situation like this.

Finally, and it’s probably too late to hear this, try to avoid the problem in the first place.

While nothing is guaranteed, often a part will be given a projected lifetime when it’s created. During part selection, check to see if a part is already nearing its product life and perhaps choose something else if that’s the case. Distributors will also send out notices when component manufacturers are planning on discontinuing production (referred to as End of Life or EOL), which should provide some, though perhaps not sufficient, time to prepare for the change in parts.

Transitioning to a new component can create many benefits to your end product but it is always more work and often a great deal of work. We hope that these tips will help you as you face the challenge of legacy or out-of-production parts.

Authored By

Josh Bishop

Interested in embedded systems, hiking, cooking, and reading, Josh got his bachelor's degree in Electrical Engineering from Boise State University. After a few years as a CEC Officer (Seabee) in the US Navy, Josh separated and eventually started working on CircuitBread with a bunch of awesome people. Josh currently lives in southern Idaho with his wife and four kids.

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