When trying to create a device I need for a circuit in my EAGLE personal parts library, I came across a weird footprint confusion. The part I need to create is this:
The retailer gives "TO-252-2(DPAK)" as the footprint information.
Now, the ref-packages library in EAGLE gives lists these options for DPAK:
It also features a TO-252 package, which in turn seems to be identical in size to a TS-003 package.
Neither of these packages match the drawing of the footprint in the manufacturers datasheet though.
So my question is: What's the deal here? Is there any difference between all the motorola DPAK "styles"? And how do they map to the different TO-252 styles?
Here's the picture I get when selecting the TO-252 (identical to the TS-003 one):
Here's what the DPAK_X looks like (depending on the number, the only thing that changes is the letter in the middle changes, some also have letters at the lower leads):
Here's what the "DPAK" looks like:
My question (maybe not phrased clearly enough), however, was: What is the reason for this many variations of this footprint? I haven't seen anything like that with other footprints, where there was maybe 2 versions (one for reflow and a second for wave soldering).
And why would a manufacturer give a package size and then have solder pad dimensions in the datasheet which don't match the size of any of all these footsprints shown above?
Well the first thing is the red rectangle or rectangles. These are the keep out regions that the layout program can flag up violations. That is places where you can’t route tracks.
The central pad dimension is also used as a heat sink, so it could be that this changes slightly to accommodate different manufacturers chip to package thermal resistances.
These variations could have been built up over the years from different users with specific requirements and then gathered together later.
I know when I worked in a mass consumer electronics we had an engineer who’s job it was to curate PCB footprints.
Grumpy_Mike:
I was always told to live up to expectations.
Rock solid principle!
Grumpy_Mike:
These variations could have been built up over the years from different users with specific requirements and then gathered together later.
I see, thank you for your explanation - that definitely shed some light on the matter for me. I have absolutely no insights into the professional world of electronics.
westfw:
Many of the “standard” eagle packages are very old, and not very trustworthy.
Duly noted, I'll make sure to double-check the dimensions when using them in the future.
(For example, the stock EAGLE TO220H "horizontal" package has the pads too close to the mounting hole for any modern part I've used. I adjusted it, and Sparkfun has adjusted it even further (depending on where we want to bend the leads, I guess.) (OTOH, I'm also back at v7.x of EAGLE...))
Thanks for the input.
