EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Blitzschnitzel on May 02, 2019, 03:14:49 pm
-
Hi, I’m new here. I want to make a PCB for a Keyboard and want to use the AT90USB1286-MU. The heat gun is already ordered. ;D
Other chips specify in the documentation what to do with the thermal pad but I can’t find it with this chip. Also, can I connect the ground pins to the thermal pad if it should be connected to ground and do I need to connect all ground pins or is one enough?
For some reason Kicad doesn’t want to connect to the thermal pad when I pour the ground plane.
-
It says right in the datasheet under the package drawing:
The large center pad underneath the MLF packages is made of metal and internally connected to GND. It should be soldered or glued to the board to ensure good mechanical stability. If the center pad is left unconnected, the package might loosen from the board.
-
Yep. And you do need to connect all ground pins. It may not be as critical for mega, but it is a good thing to get used to, since more powerful chips will need as much grounding as possible.
-
Thank you very much. With so many pages you have to know where to look. One follow up question: on the backside of the PCB I would leave a bare thermal pad. Would I leave thermal relieves between the ground plane and the thermal pad? As I understand it the thermal reliefs are there so that the copper plane doesn't suck up all the heat when soldering but on the other hand for a thermal dissipation pad you would want as much copper attached as possible.
P.S. I ran a reaction diffusion algorithm over the back of the PCB. I think that will be the backside silk screen. :D
-
Don't worry, AVRs can't dissipate enough heat to be even noticeable. The pad is there purely for mechanical reasons.
-
Thank you. You helped me a lot! :D
-
One of the first microcontrollers I ever programmed was a Teensy++ 2.0 (https://www.pjrc.com/store/teensypp.html) with an Atmel AT90USB1286-MU. They are still manufactured by PJRC, and widely used. The HalfKay boot loader used in the Teensy++ 2.0 is proprietary (allows uploading a new firmware via a HID connection, thus needs no special drivers installed), and I don't think the gerbers are open either; but the schematic is here (https://www.pjrc.com/teensy/schematic.html).
I have not created my own AT90USB1286 board, nor programmed one, except as a Teensy++ 2.0 using the HalfKay boot loader. I basically programmed my Teensy++ 2.0 in Linux, using avr-gcc, avr-libc, and TeensyLoader (for uploading via HalfKay).
I do recommend using a Teensy++ 2.0 for prototyping, even if you end up doing your own board, due to the large amount of existing code and examples for your use case.