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I am faced with two types of packaging:

  • SOT 23
  • SOT 23-3

Is there some difference between them?

Based an article in Wikipedia it seems like there are no differences.

psmears
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KMM
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3 Answers3

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In the beginning of the surface mount era was SOT 23, which had three pins. It was used mainly to replace the very popular TO-18 and TO-92 3 pin leaded transistor packages, the name means Small Outline Transistor. As such, three pins in a triangular configuration was easy to read, as it echoed the three pin leaded package.

As densities increased, it was noticed that the SOT 23 had 'missing leads', and the package could be increased to up to 6 leads without increasing significantly the area it consumed. 5 leads was an especially useful package, as it permitted a single op-amp or single 2-input logic gate to be implemented. So SOT 23-5 and SOT 23-6 were born.

Where a manufacturer's data sheet covers only single transistors, they tend to use only the original SOT 23 designation. Where a manufacturer is providing (let's say) diodes, diode pairs and diode triples in 3 and 6 pin versions of the SOT 23 package, they'll sometimes refer to the 3 pin version as SOT 23-3 to distinguish it from the SOT 23-6, but sometimes just call it SOT 23. It's up to the manufacturer.

Note that SOT 23 and SOT 23-3 are just names, they don't have any definition. They have just entered the language through use and custom. JEDEC formally standardises dimensions, its TO-236AB package outline is the JEDEC title for what is known as SOT 23 and SOT 23-3.

Neil_UK
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    This answer reads like Genesis. "In the beginning of the surface mount era was SOT 23, which had three pins. The Engineer saw that it was good. Then He created the SOT 23-5 and SOT 23-6. The Engineer saw that they were good." – Samuel Feb 26 '18 at 20:41
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    So essentially "SOT 23-3" is a retronym for what would once have simply called "SOT 23", much like "acoustic guitar" is a retronym for what used to be simply called a "guitar"? – supercat Feb 26 '18 at 22:33
  • And what is the difference to SOT323? As it seems, SOT323 is just a SOT23-3 but slightly smaller. Does SOT323 have fewer parasitics and is preferable? Or why would I pick SOT23-3 over SOT323 and vice versa? – divB Aug 12 '20 at 20:31
  • @divB SOT-323 is a different standard not directly related to SOT-23, though it's fairly similar to a scaled-down SOT-23. SOT-323 is preferable when smaller area is a consideration without sacrificing hand-solderability (if you don't intend to hand-solder, you can get quite a bit smaller with micro-DFN style packages). SOT-23 is preferable when your die is physically too large to fit in a SOT-323, or when you want something to be easier to solder by hand. – Hearth Oct 08 '22 at 03:41
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SOT23-3 is the 3 pin variant of SOT23. This is the most common variant.

Jasen Слава Україні
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3

Despite the upvotes, the previous answers are not 100% correct.

SOT23 and SOT23-3 look almost identical, and usually fit on the same footprint, but overall the SOT23-X packages are slightly larger than the plain SOT23. This is because the SOT23-X were intended for simple ICs like LDOs, although these days they are also often packaged in SOT23.

For example compare SOT23 and SOT23-3 versions of the AP2127 LDO made by Diodes Inc. Notably the body of the SOT23-3 (and other SOT23-X packages) is wider (1.6mm instead of 1.3mm) and taller (1.45mm vs. 1.1mm max). For many applications this doesn't matter, but if you are working on a tight layout with minimal pad size and component spacing or height restrictions it can cause issues.

Be aware that not all manufactures follow this convention. On top of that even if the base dimensions match the name, the tolerances and overall height can vary. I've seen heights anywhere from 1.0 and 1.5mm.

nqtronix
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    Do you have a source for the difference? I've never seen any indication that they're different. – Hearth Oct 07 '22 at 22:52
  • I've rewritten the hastil typed answer and added a sample datasheet as proof for my claims. If you want an industry overview, I'm afraid you have to compare dozens of datasheets yourself, which you can find easily on sites like digikey. – nqtronix Oct 08 '22 at 14:01
  • There are a few variations of SOT23-alikes in common use; here again the designation is just whatever the manufacturer happened to call it. The datasheet doesn't make reference to any standards so one shouldn't put any stock in what they're called; they could just as well be some gibberish. Which might be less confusing as one wouldn't then be tempted to plop in a standard "SOT23" but has to check the dimensions to be sure. – Tim Williams Oct 08 '22 at 14:25
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    @nqtronix Do any of them disagree with the definition of TO-236 (SOT-23) in JEDEC publication 95? – Hearth Oct 08 '22 at 14:28
  • Standards are often locked behind a paywall and thus meaningless to me. In my personal library I list components with a size code based on their physical dimensions, and optionally annotate them with their de-facto industry standard name. – nqtronix Oct 08 '22 at 14:57
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    I have seldom found two companies with exactly the same mechanical spec on packages that should be the same. SOT-23 variants are no exception. This is why every part on my board gets its own footprint, designed to the manufacturer's specification sheet. – gnuarm Oct 08 '22 at 16:23
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    @gnuarm same for me. And the more I do it, the quicker it’s made. – RemyHx Oct 08 '22 at 17:07
  • For generic parts such as transistors it is extremely helpful to use footprints that fit multiple manufacturers. That way purchasing can swap between manufactures if there are availability issues, if engineering marks a part generic. I use the same policy for my personal projects as well. This also benefits other makers if they choose to copy my design with generic parts they already have on hand. Its more effort upfront, but worth it for common packages such as SOP TSSOP SOT23 SOT323 SOD123 SOD323 – nqtronix Oct 09 '22 at 07:48
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    @nqtronix JEDEC publication 95 is freely available to anyone who signs up for an account on the JEDEC website, I believe. No paywall involved. – Hearth Oct 11 '22 at 05:03
  • @Hearth just confirming you can get Publication 95 from JEDEC after free signup, tried just now. – jonathanjo Aug 30 '23 at 18:17