Thanks for that, the layout was as I thought but wanted to confirm, I assume that the 4 mounting lands under the device as indicated in the parallax doc can be connected to vcc?
Thanks for that, the layout was as I thought but wanted to confirm, I assume that the 4 mounting lands under the device as indicated in the parallax doc can be connected to vcc?
Cheers
As I understand it, the pad is not connected and can be used for VDD, ground, or any other purpose.
My device has the center mounting pad connected to ground.
You can change it in the Eagle Library editor as you probably already know.
The purpose of the pad is to help dissipate heat since "the chip" is literally attached to it.
It is connected to ground on most other devices. Anyway, connecting it to ground can make routing to ground pads easier. For a prototype it can be useful to put a large via in the pad, so that the device can be hand-soldered and the pad attached by heating the via and feeding solder into it. It helps to have something like a Metcal soldering station, which can deliver plenty of heat.
The Propstick layout was what I was going to suggest to use as a guide as it is a well proven layout. I also use the QFN and made just a few light changes. Mainly, I lengthened the pads so they extend past the body of the part so that you can reflow the solder connection with an iron. Since a QFN is not designed to have solder on the perimeter, this is the only method to make minor rework possible with an iron. Otherwise, you have to use rework machine (hot air or IR) to rework the device properly.
I connect the large pad to ground. I also used a windowed aperture on the large pad as the spec sheet recommends. This is an industry standard. The main purpose is to reduce the overall volue of paste at the center pad, so that it doesn't prevent the part from settling down on each land, which would leave opens. You can see more details on the thread where I started discussions about my M44D40+ module. It is in production now and I started selling them at UPEW. I have pictures of each step of the build process and will eventually post them up on the forums. There was also a thread just like this one started a while back that has more details on the QFN44 land patterns specifically. I posted a zip file there that might be helpful.
Batang
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I use the LQFP version with 8 mil (IO pins). So far, no problems for me.
Check the layout that Parallax uses for the PropStick:
http://www.parallax.com/Store/Microcontrollers/PropellerChips/tabid/142/ProductID/411/List/0/Default.aspx?SortField=ProductName,ProductName
It is Open Source, and the DipTrace file is available for download on that page.
Attached is my eagle library file. Use at your own risk.
Thanks for that, the layout was as I thought but wanted to confirm, I assume that the 4 mounting lands under the device as indicated in the parallax doc can be connected to vcc?
Cheers
Space is an issue so hence QFN part although I have used the LQFP in the past.
Cheers.
My device has the center mounting pad connected to ground.
You can change it in the Eagle Library editor as you probably already know.
The purpose of the pad is to help dissipate heat since "the chip" is literally attached to it.
I connect the large pad to ground. I also used a windowed aperture on the large pad as the spec sheet recommends. This is an industry standard. The main purpose is to reduce the overall volue of paste at the center pad, so that it doesn't prevent the part from settling down on each land, which would leave opens. You can see more details on the thread where I started discussions about my M44D40+ module. It is in production now and I started selling them at UPEW. I have pictures of each step of the build process and will eventually post them up on the forums. There was also a thread just like this one started a while back that has more details on the QFN44 land patterns specifically. I posted a zip file there that might be helpful.
Enjoy:)
I will be posting it in full on the semiconductor forum later along with a product description.