Why do most transistor packages come with "23"

The encapsulation password of diodes: the ubiquitous mystery of "-23"
 
 In the vast universe of electronic components, diodes, as fundamental and critical components, have a wide variety of packaging forms. An interesting phenomenon is that a large number of micro diode package names are embedded with the number "-23": SOT-23, SOT5-23, SOT3-23, SOT1-23... This is not a coincidence, but behind it lies a clear development of semiconductor packaging technology and a profound standardization logic. Understanding the origin of "-23" is a key to interpreting the evolution of miniaturized electronic design.
 
 Tracing the Origins of SOT-23: The Founder's Status
 
To unravel the mystery of '23', we must return to the source - SOT-23 (Small Outline Transitor-23) encapsulation. This seemingly simple name actually carries profound historical and technological connotations:
 
 1. Standardization origin: SOT-23 is not an exclusive design of a single manufacturer, but an industry standard package developed by the Electronics Industry Council (JEDEC). The "-23" in its name is essentially a specific model identifier of the standard in the JEDEC specification system. It identifies the unique three pin (commonly used for diodes or transistors) Small Outline design of this package.
 
2. Miniaturization milestone: Prior to the establishment of the SOT-23 standard (mainly developed and popularized in the 1960s), the packaging of discrete devices was generally larger (such as TO92). The emergence of SOT-23 represents a significant leap in miniaturization. Its compact size (typical dimensions of approximately 3mm x 1.75mm x 1.3mm) makes it ideal for high-density installation on increasingly compact printed circuit boards (PCBs), greatly saving valuable space.
3. Design paradigm: SOT-23 defines an extremely successful and practical physical structure: the "Gull Wing" shaped pins on both sides are easy to surface mount (SMT), the middle plastic body provides protection and insulation, and there are usually heat dissipation pads at the bottom (especially important for slightly high-power diodes). This structure achieves an excellent balance between cost, manufacturability, reliability, and space efficiency.
 
The Magic of "23": Family Reproduction and Brand Effect
 
 The tremendous success of SOT-23 has made it the benchmark and de facto 'mother' of micro discrete device packaging. When technology continues to advance and smaller packaging sizes are needed, engineers and standard setters naturally choose to evolve on the basis of SOT-23 while retaining the key "-23" logo. This brings multiple significant advantages:
 
 1. Clear technical lineage: Add numbers indicating size changes (such as 5, 3, 1) before or after the original name to form new packaging names (such as SOT3-23, SOT5-23, SOT1-23). '-23' plays the role of 'family surname' here. When engineers see the package name with "-23", even if the specific size is different (such as SOT5-23 being smaller than SOT-23), they can immediately understand that this is a small package developed based on the SOT-23 concept, with similar pin arrangement logic (usually compatible or easy to convert) and basic structural features (plastic body, gull wing pins).
2. Lowering cognitive barriers: Electronic design involves a massive number of components. Retaining the core identifier "23" significantly reduces the learning cost for engineers to identify, remember, and select new packaging. They don't need to learn a brand new, unrelated naming system for every tiny size variant.
3. Compatibility and design continuity: Although the size is reduced, many SOTxyz packages try to maintain consistency or provide clear mapping relationships with SOT-23 in terms of pin function definitions (such as 1-pin cathode, 2-pin anode, and sometimes 3-pin for heat dissipation or NC). This makes it relatively easy to evaluate or switch circuit boards based on SOT-23 design to smaller members of the "23 family" (and vice versa) within space constraints, providing valuable design flexibility and continuity.
 
4. Brand Effect and Market Recognition: "SOT-23" has established a high level of recognition and trust in the industry due to its widespread success. The newly launched micro package uses the "-23" logo, which can naturally leverage this brand effect and be more easily accepted and adopted by the market (engineers, procurement, manufacturers), accelerating its promotion and popularization.
 
The journey of miniaturization: SOTyz's size password
 
 With the continuous development of electronic products towards thin, light, and small sizes, the size requirements for discrete devices such as diodes are becoming increasingly stringent. The SOT-23 family continues to evolve into smaller members, and the prefix numbers in their names often reveal the degree of size reduction:
 
 SOT3-23: It can be understood as a "scaled down version" of SOT-23 (approximately 2.2mm x 1.35mm), and the number "3" may represent a certain proportion of its size that is approximately SOT-23 (not a precise mathematical relationship, more of a sequence identifier). It maintains a 3-pin structure and has slightly lower power processing capability than SOT-23.
 
SOT5-23 (SC89): With further miniaturization in size (approximately 1.6mm x 0.9mm), it is currently a widely used ultra small package. '5' represents that it belongs to a smaller level than SOT3-23. It usually only has 2 valid pins (for diodes), sometimes there are also 3-pin versions.