I just saw that zefir was posting something about "sample" chips that get sent by the factory in May before the final chips. First I heard about this.
He said that he would distribute them to buyers in proportion to their order qty. I don't think he knows yet what qty of samples may be due.
So if anyone interested in my board has large chip orders with him you may be able to get some sample qty. in May. If so, it would be very, very, very helpful to try and arrange for those samples to be sent on to me for early board testing so that I can debug and once we know the board works, we can order a large batch in time for final chip deliveries.
BTW I'm moving the power connector down to the end and turning it so that a right angle connector could be used. A little better for those who want to stack boards.
Could you get something that 'emulates' the function of the Avalon chips, populate a PCB or two with all the other components, just to see that everything else works first? Then you know it there's problems its because of the avalon chip and not something else
I see now you're already doing that, nice!
Couple other thoughts offhand..
* good ole fashioned 63/37 lead solder is going to be the easiest to work with and reflow at the lowest temp. do you see any reason NOT to get that? (Maybe the default cheap deals from boardhouses use RoHS HASL now..)
* I'm guessing your OP pic was when you were trying for a 2 layer board (plane fill on top layer) - aye, forget that. you can also get somewhat better heatsinking by tieing all the thermal vias on the ground pad of the QFN to the ground plane with no thermal relief. I will have to check, i once saw an appnote about SMT heatsinking with copper planes (both internal and external) and they calculated the degrees C/W of various configuratins of plane size, plane thickness (e.g. 1oz copper up to 10oz copper, etc). May prove useful for these little QFN buggers. Who knows, maybe it could keep the heat down and allow for a little OC headroom.
* what are your overall dimensions roughly? it looks like this will panalize very nicely. i'm assuming 0.062" FR4.* what board house were you looking to get this from?
I have a few tweaks and ideas i'd like to try, i plan to mill out some initial test pcbs (only 2 layer but just to confirm some thermodynamics and mechanical fit) and order some 4 layer boards
It just kind of sucks these are all QFN with a thermal pad for the heatsinking, makes it difficult to DIY. Seems like this is the sort of thing you really have to pick & replace + reflow.