Confusion over SOT23-6 and SOT26 (package size vs supplier package size) - Page 1
Forum section: electronics / beginners

author: newtekuser
author_rank: Frequent Contributor
timestamp: January 28, 2024, 06:15:25 am
content: My understanding is the number 23 and 26 represent different sizes, but what I'm not clear about is if these sizes are different, then why does the datasheet for the SOT23-6 diode below say it comes in a SOT26 supplier package size?Which is which, is the datasheet incorrect, or do vendors have different ways of representing the package size vs the standard?https://www.digikey.com/en/products/detail/diodes-incorporated/ZHCS2000TA/385999

author: ataradov
author_rank: Super Contributor
timestamp: January 28, 2024, 06:38:47 am
content: Yes, all vendors use random names. SOT26 is how Diodes Inc labels SOT23-6. Usually vendor will have package drawings that corresponds to that name. Those drawings are how the actual device is manufactured, they will in most cases match the standard. But this allows vendors to deviate without causing confusion, since the name that is used is not the standard one, but the company internal one.And the names from different vendors still may clash. So, if not sure and you think it might matter, check with the vendor's drawing, not the standard one.

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: January 28, 2024, 09:06:15 am
content: Another "got ya" with SMD packages and data sheets, is that the pad dimensions shown in the data sheets (and maybe the dimensions in PCB design software) are based on commercial assembly. For anyone hand soldering SMD parts, you may need to extend the pads by 0.5mm (or slightly more) to give an area to place the tip of your iron when soldering... if the pad and component leg are exactly the same size, it is hard to hand solder. Been there, found out the hard way. Measure the actual component and the software displayed pad size for yourself.SJ

author: HwAoRrDk
author_rank: Super Contributor
timestamp: January 28, 2024, 03:47:40 pm
content: The Wikipedia article on SOT packages has a good overview:https://en.wikipedia.org/wiki/Small-outline_transistorIt also lists a lot the common alternate names for things like SOT23-5, SOT23-6, etc. Like for example NXP/Nexperia call it a SOT457, or others call it SC-74.

author: wraper
author_rank: Unknown
timestamp: January 28, 2024, 04:04:39 pm
content: Quote from: Solder_Junkie on January 28, 2024, 09:06:15 amPad size given in datasheets for non QFN/LGA/BGA parts is completely random. Varying from small to huge. If you use exactly those sizes with no second thought, you can end up with 10 vastly different pad dimensions just for 0603 resistors.

author: newtekuser
author_rank: Frequent Contributor
timestamp: January 28, 2024, 06:25:14 pm
content: Thanks for chiming in on this! I typically hand solder SMD components with hot air, so pad accessibility is not a big issue, otherwise I'm using a reflow oven.At the moment I'm using diode sizes of SOT323 which I can place by hand using a microscope, but I'd like to not have to place any components myself once I get a PnP machine (looking at the liteplacer)

author: Siwastaja
author_rank: Super Contributor
timestamp: January 28, 2024, 08:02:06 pm
content: There is only one process which is safe and free of confusion:1) pick part based on availability and technical suitability (datasheet)2) order the exact part number for your design3) following the datasheetfootprintpackage drawing, create footprint for that part in your CAD.No assumptions, no confusion; no reuse, no mistakes related to reuse. Footprint name is only used to match between multiple drawings within one datasheet, nothing else.

author: wraper
author_rank: Unknown
timestamp: January 28, 2024, 11:26:38 pm
content: Quote from: Siwastaja on January 28, 2024, 08:02:06 pmI don't agree with that. Use package dimensions, look on footprint only as guidance. Often they are far from the best and there is no point creating several different footprints for parts with same dimensions. There is no absolute truth in that single recommended footprint in datasheet, sometimes they even come with multiple different footprints (small/medium/large). Not to say footprint may be incompatible with particular stencil thickness or soldering process you use. For example you don't want to use SOT23-6 footprint with tiny pads combined with 0.15mm stencil as you'll have paste application problems. And you don't want too large pads with a thin stencil either.

author: Siwastaja
author_rank: Super Contributor
timestamp: January 29, 2024, 06:51:10 am
content: Quote from: wraper on January 28, 2024, 11:26:38 pmYes. This is actually what I was thinking. Fixed to above post. I tend to use package dimensions plugged in the Altium's wizard, then compare between the Altium's generated footprint vs. manufacturer's recommended footprint, and if differences are large, try to figure out why, and which one would be more correct.