Which package to use for a Mega328

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I'm planning on using a Mega328 for my next project, but the datasheet is a little unclear on land patterns. There seems to be some vagueness about MLFs and QFNs, with the datasheet saying that the chip comes in both packages (and the one I found on Farnell is a QFN - so I'm running with it) but only has a pattern for a 28QFN and not the 32 that the pinout says.

I emailed Atmel who just directed me to the same datasheet without much explanation.

Somewhere I read that they use QFN/MLF interchangably, but from the chips i've seen visually they're normally different (qfn = square, mlf = rounded square with tapering sides). The Eagle packages I've found so far = including SparkFun's - (I was going to make my own based on actually looking at the chip I get sent in the post if this doesn't get sorted out :)) don't have a centre ground pad which is a little odd too.

Anyway, figured before I bought some chips I might see if anyone else has used the QFN/MLF and which pattern they used?

http://uk.farnell.com/atmel/atme...

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As far as I can see the square package is 4mm x 4mm
and the chamfered corner package is 5mm x 5mm.

The smaller 28pin package has a smaller 2.4 x 2.4mm heat pad, and of course does not have ADC6 and ADC7 pins.

Only you know whether you need 4x4 or 5x5 board space. I doubt that many people would choose the 4x4.

David.

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Quote:

There seems to be some vagueness about MLFs and QFNs, with the datasheet saying that the chip comes in both packages

Let's start there. I went to Atmel's site and pulled up the latest "summary" and "full" datasheet, April-2010. I went to Ordering Information. That indicates that a '328/'328P is available in 32A (TQFP), 32M1-A (32-lead "QFN/MLF" with 0.5mm pitch), and 28P3 (0.3" PDIP).

If you look at the other family members, some are available in the 28M1 package.

So I don't see the great confusion, especially for a '328. The Ordering Information tells you which suffix you want/order/obtain. The Packaging Information gives the layout for that package.

Quote:

with the datasheet saying that the chip comes in both packages

For a Mega328? What datasheet version is that?

Quote:

but only has a pattern for a 28QFN and not the 32 that the pinout says.

No 32M1-A section? What datasheet version is that?

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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I'm using the same datasheet version as you, doc8271.

I just assumed that the 32QFN would be square, not with the chamfered corners - given that the 28QFN doesn't have them.

Guess that clears that up, but still doesn't explain why none of the current libraries have the centre pad - meh, I'll add one in.

The confusion was from this line:
"28-pin PDIP, 32-lead TQFP, 28-pad QFN/MLF and 32-pad QFN/MLF"

But on the pinout configs and the package information they're only captioned MLF - I just wanted to check what I'm buying.