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SN74AHCT1G14: Difference between SN74* and 74* parts? Proper part number specification for PCB assembly?

Daniel Ka
Intellectual 627 points
Part Number: SN74AHCT1G14

Hi all,

for a PCB assembly, one element that I specified in the BOM is  TI's  74AHCT1G14DBV. Now, the PCB assembly service is asking me my to specify the device more precisely. Basically, they are correct as it's not a fully specified manufacturer part number.

Looking at the datasheet, there are 4 variants of this device available according to the manufacturer part numbers:

a) There are parts with the additional suffix T and R that indicate package quantity (250 and 3000, respectively). That does not make any difference to me as the required quantity is well below both numbers. 

b)  There are parts with the additional prefix "SN". As I understand it, the only difference is the material finish options:

- 74* = NIPDAU 

- SN74 = NIPDAU | SN

Does that make any difference regarding the soldering process?

All in all, I think adding anything to this part number would not be helpful and rather over-specify the device. 

When I buy from a distributor, I usually pick the article that costs less. Here, it's SN74AHCT1G14DBVR which costs half  as much as the other variants.

Does that make sense?

  • 0
    Guru 317310 points

    The SN prefix has nothing to do with the lead finish; it identifies that the manufacturer is Texas Instruments ("Semiconductor Network"). All TI logic devices should have the SN prefix, but it is omitted from some orderable part numbers if they would become too long otherwise (apparently, some database field would have overflowed).

    All lead finishes will solder properly. (And for "Sn | NiPdAu", you don't know which one you'll get.)

    The G4 suffix means nothing (see [FAQ] Why does a logic device's part number have an E4/G4 suffix?), and exists only for backwards compatibility with old BOMs.

    You can choose whichever one is cheapest, but the assembly service wants a complete number, so you should specify something like SN74AHCT1G14DCKR.

  • 0 in reply to Clemens Ladisch
    Intellectual 627 points

    Thanks Clemens for clarifying the SN prefix.

    I was under the impression that the SN prefix indicated TI as manufacturer. Maybe the datasheet was just misleading me as all part numbers without the "SN" prefix  also dropped the "SN" from the lead finish:

  • 0 in reply to Daniel Ka
    TI__Guru* 97046 points

    Hey Daniel,

    Looking at that materials list, I probably would have come to the same conclusion.

    Clemens is right though - SN is just an indicator for TI parts and doesn't really mean anything regarding functionality or materials.  We also have "CD74" parts that were acquired from Harris and "CY74" parts that came from Cypress.

    The top few parts are different primarily because they had the E4/G4 suffix added, and then had to have the SN removed from the start to meet the 16 character limit. There are even some parts out there where the whole first part "SN74LVC" is removed and replaced with something like "1P" to shorten it.

    If you'd like to learn more about our part numbering scheme for logic, there's a short video that describes it here: Anatomy of a logic part number

  • 0 in reply to Emrys Maier
    TI__Intellectual 1801 points

    Hi Maier,

    As these devices are totally the same besides orderable part number, why the prices are quite different? Thanks. 

    Regards,

    Jiandong

  • 0 in reply to Jiandong Liu
    Guru 317310 points

    Supply and demand. In particular, very few customers want the "legacy" part number, and those customers are less price sensitive.