During the COVID era electronics manufacturing supply chain crunch, I spent a lot of my time finding alternate components for our customers. This included resistors, capacitors, diodes, transistors, connectors, integrated circuits and more. After umpteen times performing this research, it has become second nature, which inspired me to share with others the process. You do not need to know much about electronics for most of this – just to be able to match up parameters. Some electronics knowledge will help with the harder with more challenging parts.
A quick way to show you how to do this is to walk through an example. Capacitors are relatively easy alternatives to find, so let’s start there. The tools I use for selecting alternatives are free and widely known in the industry. For this example, I will walk you through finding an alternate capacitor with Mouser.com. Their parametric search tools are amazing.
The basic concept is to check all the parameters, looking for an equivalent or better part. Some parameters are critical; some may be important, and some may be not important at all. You do not need to know the circuit at all if you can find an equivalent or better part. If compromises need to be made, then it is important to evaluate them. As an engineer, I can tell you that there are so many options that sometimes we just pick what looks like the best one for the best value, which could be overkill.
For an alternate capacitor:
- Must have matches – capacitance and size
- Probably important matches – voltage rating, tolerance and temperature coefficient
- Possibly important matches – operating temperature, ESR (equivalent series resistance)
- The rest are parameters that may or may not be needed; If you can find a match, go with it, but if not, check to see if it was really needed
Always have someone double-check your choice as a sanity check. For me, this is the customer. We will suggest possible alternatives, but always submit them to the customer for approval. If the alternate you find has differences, summarize what you know to whoever is double-checking your alternate. If the suggested alternate is rejected, get a reason so that you can consider the reason in a new search.
Parameter Reference
Parts of this section get a little technical. Skim it, then come back to it if you are selecting a capacitor that you may need to understand if changes to some of the parameters will be acceptable.
Capacitance
This is the value of the part and should not be changed. If the specified part has a wide tolerance, you may be able to get away with a different value with a tighter tolerance, but this is usually not necessary.
Size
For the alternate to be a drop-in replacement., the size must match. For chip capacitors, they come in standard sizes like 0402, 0603, 0805, etc. For electrolytic capacitors, the main size is the diameter and height but check if there are other important measurements.
Voltage Rating
This is the voltage that can be applied safely to a capacitor without damaging it. There are some standard values such as 6.3V, 16V, 25V, 50V and others. For this parameter, higher voltages are better.
Tolerance
This is a value that the capacitance is guaranteed to be within at room temperature. Older capacitors were lucky to have a tolerance of 20%. Newer capacitors easily have tolerances of 10% or better. For this parameter, smaller values are better.
Temperature Coefficient (Dielectric)
This is a code that shows how stable the capacitor is over temperature. Following is a brief summary of how the codes define their temperature coefficient.
- The first letter is the low temperature that the capacitor is rated: some common ones are X (-55C), Y (-30C) and Z (+10C).
- The second number is the high temperature that the capacitor is rated. The higher number the better. Some common ones are: 5 (+85C) and 7 (+125C).
- The last letter is how much the capacitance changes over that range. The lower letter the better. Some common ones are R (+/- 15%) and S (+/- 22%).
Some examples of capacitor codes are as follows:
- X7S is 22% over the temperature range -55C to +125C
- Y5R is 15% over the temperature range -30C to +85C
- COG is a Class 1 rating that is better than any of the above but is not always available, especially in smaller packages
When selecting alternates for this, try to match exactly, but if it is not available, consider each digit separately.
If needed, do an internet search for “capacitor temperature coefficient” for a more complete description.
Example:
To show the process, let’s find an alternate for a Yageo CC0805MRX5R7BB226
- Launch mouser.com and type in CC0805MRX5R7BB226 in the search field, then press enter. Open a second window and repeat this. Why do this? So you have one window to find an alternate capacitor and the other to refer back to the parameters of the original to match them. If you have two monitors it will make this process easier, but if not, you can just switch tabs.
Mouser will serve the page about the capacitor. The important parts of this page are:
Part-type links: This is a very useful link. In this example, the capacitor is a multilayer ceramic capacitor (MLCC) SMD/SMT. Most likely the best alternate will also be this part type. When you click that link to go back a level, all capacitors of that type will show, and you will start your search there.
Description and Datasheet: Double-check the part number and the description to make sure you have the right part. You may need the datasheet to check parameters not summarized by Mouser.
Specification: This section has a summary of all the parameters that you will be trying to match.
The first thing to do is to click back a level on the part-type links. In this case, “Multilayer Ceramic Capacitors (MLCC) SMD/SMT. This will take you to a parametric search page of all parts in that category. Note that there are 436,735 possible parts, but of course, not all of them will work.
The next step is to go to the page with the original capacitor specifications and start narrowing these parameters to match that one.
Select the critical parameters that must match and apply filters. Also, click the “In Stock” box. If this combination shows 0 results, unclick the “In stock” box – you may need to find an alternate part that will be in stock sooner than the specified part.
- Capacitance 22uF
- Size 0805
This has narrowed the search to 139 possible parts. Also, note that some of the fields may no longer be available because there are no remaining matching parts.
Looking at the remaining parameters, there are four (4) more to narrow down. Select these one at a time making sure there is still some availability before moving on to the next. Also, while selecting these, select multiple choices that are equal to or better than the specified part.
- Tolerance: specified part is 20%, select 10% and 20% (138 results left)
- Voltage rating: specified part is 16 VDC, select all voltages 16 VDC and higher (32 results left)
- Dielectric (temperature coefficient): specified part is X5R. Select it because the remaining options are not as good. (27 results left)
- Temperature range: Specified part is -55C to +85F. This matches all remaining parts.
Since there are plenty of options left, also click the “Active” box. This will result in an alternate that will likely be available for a while without having to do this exercise again. (25 results remaining)
Final Selection:
Sort by price and check the availability. Choose one or two alternates that can be added to the bill of materials (BOM) or used for a one-time build.
The following shows some of the parts that are acceptable alternates after all parameters have been narrowed down. Note that the 25 VDC capacitor is cheaper than the 16 VDC capacitor. This happens often and is likely due to the efficiency of mass production.
This same approach can be applied to any part, including resistors, diodes, transistors, integrated circuits, connectors and more. Most of those will require verifying the parameters with the datasheets.
NOTE: Using the Mouser summary page is usually sufficient for resistors and capacitors. For other types of components, always check the datasheets to confirm the parameters match.
IMPORTANT: Unless you are the engineer who understands how these components are used in the circuit AND are the design authority, always submit the alternates you find for approval.
Bob DiDonato
Engineering Program Manager