PCB Land pattern is not true to the component...why not?

[treez]

Hello , The DFN5X6 Land pattern has a sideways copper protrusion on each of its sides which is not seen in the land pattern. Why is this?

**broken link removed**

 

[Mattylad]

How are we supposed to know why not?
Perhaps they thought that given that its soldered with the big pad that its stable enough with some little pads too.

Have you tried asking the manufacturers of the component?

 

[treez]

thanks I will ask them now ...and will get back for those that are interested in this...that's if they reply.

perhaps the reason to put it there is so that people looking to replace with a different manuf package part are deterred from so doing as the footprint wont look the same, cuzz it probably wont have those protrusions....with the sheer amount of different types of these DFN type packages you have gotta suspect manufacturer shananigans.....ahhh the good old days of DPAK, D2PAK standardisation

 

[FvM]

Sounds like a replay of your previous thread https://www.edaboard.com/threads/325529/
(And should be appended there according to forum rules.) Can it be that you have already forgotten what you posted four days ago?

I'm under the impression that the question has been exhaustively answered by the PCB experts. There's absolutely no reason to reproduce the small "protrusions" of the thermal pad in the PCB footprint. But if you love over-engineering, then edit the suggested footprint and feel good.

 

[treez]

...yes in that post there are similar protrusions, and sunnyskyguy came up with the updated footprint which did have land pattern adjustment for the lateral protrusions of the sbrt25u80slp diode.

I must admit these super low vf schottkys have me gulping when you see the leakage at high temp...

 

[FvM]

You'll probably noticed that both components have essentially the same DFN5x6 (or however you call it) package and can well use the same footprint. The differences are more or less arbitrary.

A layouter who's not terribly underemployed would take advantage from this fact and use the same footprint (without any silly protrusions) for all similar parts unless specific reasons stand against it. A good layouter has a profound knowledge of PCB manufacturing and assembly processes and knows which footprint details matter and which don't.

 

[marce]

Read my previous answer to the other thread you started.
To be honest these are pretty mundane questions for someone who is supposed to be a PCB designer. Look at the ipc-7351, read my other reply, it is the same problem and the same answers.....