I have a BC107 transistor, and am so curious to know what those first letters means or what they indicate about the transistor and what the 3 last digits mean. What I only know is that this numbers helps us to find the datasheet of this transistor giving us all information we want to know but my curiosity is in knowing the reason behind those numbers there.
Generally, the number is simply a model number, and the link between the number and any specific properties/parameters is weak at best. For example, even among transistors called BC??8, not every transistor with that name pattern is part of the same family.
However, the first few characters of the part are sometimes more useful for quickly figuring out some basic details.
For example, the actual letters
BC appear to follow the Pro Electron naming scheme identifying it as a silicon transistor for small-signal use.
You may also encounter names like 1N4148 (diode) or 2N3904 (transistor) - the prefix 1N and 2N mean diode and transistor respectively in the JEDEC naming convention which itself evolved from an old naming convention for vacuum tubes. Even then, this doesn't tell you much about the part; for example, a 2N???? part could be a JFET (e.g. 2N3819), MOSFET (e.g. 2n7000), BJT (e.g. 2n3904), or something more obscure like a unijunction transsitor, and it could be P-type or N-type.
Likewise, there is a Japanese identification scheme although I don't know part examples within it offhand.
In an old National Semiconductor data book, transistors are grouped in a few different ways:
- same chip encapsulated in a different package, using unique prefix (MMBTxxx versus 2Nxxx)
- same chip more (or less) rigorously measured to meet various specs. "JEDEC" versus "Consumer-grade"
- application grouping: "high-speed switch" versus "small signal amplifier".
National Semi also grouped chips by "Process number". Each process has different size, shape, and contact pad regions. For example, PROCESS #63 is a square PNP chip 0.483mm x 0.483mm. It is a PNP bipolar meant for medium-power applications. It's process is non-overlay, double-diffused silicon epitaxial. It has similar complementary specs to an NPN process #19. It lists principle device type for:
TO-5 EBC: 2N2905 TO-18 EBC: 2N2907A TO-237 EBC: TN2905 TO-92 EBC: PN2907A, 2N4403 TO-116: MPQ2907 TO-236: MMBT2907 16-SOIC: MMPQ2907
Non-principle devices that also use this PROCESS #63 include:
2N2904, 2n2904A 2N2906, 2N2906A 2N3638, 2N3638A 2N3644 2N3645 2N3702 2N3703 2N4142 2N4143 2N4290 2N4291 2N4402 2N4971 2N4972 2N5142 2N5143 2N5221 2N5226 2N5354 2N5355 2N5365 2N5366 2N5447 2N5817 MPS3638, PN3638 MPS3638A,PN3638A MPS3644, PN3644 MPS3645 PN3645 MPS3702 MPS3703 MPS6533 MPS6534 MPS6535 TIS91 TIS92 TIS93 TN2904A TN2905, TN2905A