How to Decode Alternative Parts Data

Take a look around at your favorite electronic component search engine and click on one of the results. You might see several suggested alternative parts on the parts data page. Sometimes, these alternative parts are from the same part number group, or they may be from a totally different manufacturer. If you look on the bigger distributor websites, you may see similar suggestions for some components, both when shopping for parts or creating a parts order.

How are these suggestions determined, and are they actually worth following in your new build? As with many things in electronics design, it all depends, and there are several factors to qualify when attempting to choose an alternative part. Here's what you should look for when selecting an alternative part based on these suggestions. Depending on where you look, the usability of the alternative may not be so clear.

How Alternative Parts Suggestions Are Determined

Component search engines and distributors have many ways they can determine appropriate alternative parts. For example, they might use statistical data based on customer purchases through their sites. In other instances, the website might use machine learning or similarity metrics between part descriptions to determine when a replacement candidate. Each website has their own secret sauce that they use to determine these potential alternates, and they will almost never reveal that particular information.

I think it's important to understand these nuances because alternate part suggestions are usually based on a small number of pieces of data. Some of that data is manually tagged, some is just based on purchase history, and some might rely on actual extractions from data sheets. The latter is still a tough problem that AI is trying to solve, but it is more difficult given the fact that there is no standard for classifying component specifications and thus easily determining alternate parts.

So before you start using those alternate part suggestions without qualifying them, let's decode what the suggestions mean and what level of manual evaluation might be needed.

Direct Substitution

This is probably the most obvious and yet least common part suggestion. The part is meant to be a direct replacement for another part, right down to the specifications and package size/footprint. This type of substitution most commonly arises within the same manufacturer's part number groups, but it can also happen across multiple manufacturers.

These parts have some common characteristics:

1. They use standard JEDEC packaging
2. They assume standard voltage levels being applied
3. The pin naming is usually identical
4. The function these parts perform is very common
5. The granular specifications are similar enough to not matter in 99% of designs

The most common type of component where you will see this type of direct substitution is in passives. However, many ASICs have been designed specifically as direct substitutions for other ASICs. The qualification process is usually quick: check the package drawing and pin naming, and there's a very high chance the parts are substitutable.

Similar Substitution

A similar substitution designation is by far the most common alternate part designation, and yet it comes with ambiguity. These part designations are the most difficult to decode, because the word “similar” could mean many different things. Similarity among parts could refer to basic functionality, main interfaces, signal and power levels, or anything else. It all depends on the type of part and what features are on it. It could even be something as simple as packaging: packaging might match, but nothing else might match including the pins.

These designations are helpful, but they leave some specificity to be desired. It may not be best to rely on these parts as drop-in replacements, rather as an alternative part that can be used in a design variant.

Before You Use Suggested Alternates

If you're a buyer looking for parts on a search engine, and you see a recommended alternate, there's a temptation to just immediately swap the alternate into the BOM. This can be a risky course of action. Instead, the group of possible substitutes should be sent back to the engineering team for evaluation and approval. While it is true that passives are generally low-risk substitutes, something like an ASIC could be very high risk as it could be the biggest value-creating component in a design.

For engineers, substitute parts designations can be a useful guide for selecting alternates. While it is true the accuracy can vary by specification, it's usually quite easy to pick through a small group of possible alternates and zero in on an appropriate substitute. The best path forward is to select an alternate from the same part number group, then look to direct and similar substitutes to complete a BOM for a design.

When you’re looking for distributor options for parts in your BOM, you can find substitute parts with the advanced search and filtration features in Octopart. You will also find suggested alternates on Octopart’s component pages and up-to-date distributor pricing data, parts inventory, and parts specifications.

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