7x7mm QFN32 package with 9 vias in EAGLE.

Community PCB Design
1

I am just getting started with electronics and I want to make a breakout board for a ti cc1020 transceiver chip which is a 7x7 mm QFN32 package. I am using the Eagle library editor to create the package and the documentation for the chip contains a good description of the footprint, but I have run into a bit of a problem.

There is a large pad under the chip 5.08x5.08mm which is to contain 9 uniformly spaced 0.254mm vias and this pad is to be attached to analog ground (AGND). I can use the “hole” command to add holes to this large pad, but EAGLE help describes these holes as having no electrical connection between layers. I was thinking of adding a matching pad to the package definition on layer 16 Bottom so that I can attach this large pad to AGND, but I am concerned about connecting the bottom layer pad to the matching top layer pad.

Is this a reasonable approach? Is there a standard method for routing a signal path to the pad under a QFN package?

I have done most of the SparkFun embedded programming tutorial and I am working on a car alarm for my son’s Cub Scout pine-wood derby car. I hope to use the CC1020 chip to implement a remote control and want to do the breakout board to get some experience with batchPCB. I apologize for the newb question.

2

use vias?

3

I think all you can do is, when you route the board, add a couple of vias in the board editor. It will throw up some errors though.

Vias at the bottom for QFN packages are often only for heat sinking, with a GND connection to one of the surrounding pins.

4

You can’t add vias when you are drawing a component, but you can add them later when you put the component on a board. Adding a via to a pad is considered an error, but you can simply ignore it (or, in eagle 5 add it to the “approved list”)

5

Thanks inventore123. I will just leave the “holes” out of the package definition and add the 9 vias when I create a board.

6

Hanson:
“Thanks inventore123.”

But it was me who suggested it… :cry:

7

Thank you FartingMonkey92; you are a very good and special monkey, good monkey.

The last thing any man needs is a unhappy flatulent monkey on his back!