SparkFun Forums

[merelda]

Hi all,

I'm super new to PCB design, and I'm using Eagle to make my first PCB.

I couldn't find the package I need in the library, so I read up on the tutorials to make my own custom device but ran into a problem.
The device has an "exposed backside pad" as Ground, and none of the tutorials explain how to make that..
I'm not even sure what it really means since I haven't used the IC before and only prototyped with a similar IC without the pad.. (I know, bad idea)

If someone has experience or know a library that has this made already, please help!

Thanks in adcance!

The device datasheet:
http://www.micrel.com/_PDF/mic44F18-19-20.pdf

[Kamiquasi]

You would basically treat the exposed pad as a relatively big SMD pad. So in your package design, add an SMD pad as you would for any of the pins, then change its dimensions to those desired. Give it an appropriate name ('EPAD' is pretty common*), and off you go.

* If you have a bunch of libraries installed, searching for 'EPAD' when adding a component will yield some results. There's also a few components with exposed pads in the SparkFun libraries, e.g. the 'QFN-44' package in SparkFun's DigitalIC library.

There are a few tutorials about as well, just google 'eagle exposed pad', but in general it's little more than just a big SMD pad. However, if the component needs some additional thermal management, you may also have to look into via-in-pad options (the vias would 'transport' the heat from the exposed pad through the board to another copper area on the other side and/or to internal layers) and the pitfalls that brings when fabbing.

[Kamiquasi]

And just to add to that.. looks like SparkFun's libraries have an MSOP-8 with exposed pad. See AnalogIC/POWER-SOP8

[merelda]

Hi Kamiquasi,

Thanks so much for the super comprehensive reply!
Found an example in the SparkFun PowerIC, and will look into the tutorials.
Thanks a lot