Even a 0.5mm pitch QFN isn't that tough to dead bug. This took about 20 minutes and it's a 0.5mm pitch QFN24. Forgive the crappy iPhone photos.
I agree though, properly mounting the chips would be best. There's really no reason not to, other than the turnaround of a week raising the price of a PCB. Even buying a surfboard would be better (and easier).
EXCELLENT JOB! Now trick is to actually solder together VDD pins and put proper capacitors between GND pad and VDD pads connected. Then solder to central pad THICK wire - interesting how that could be done (as heat sink). Initially I thought that it must be done with hot air after capacitors soldered and chip is held.... wires would be soldered as last step as it would be hard to solder to thermal pad if you have thick wire there.
One of the ways how to do - take thick wire - say 16 sq.mm, solder it from one side thoroughly, cut (remove also insulation if any) - say leave 50mm of wire length... Then - heat wire first while holding it with pliers, then heat chip and wire togeher and connect them. Then you'll have to cool this with air and then spread copper wires and you'll get heatsink.
Yes, with how you laid out the pins it should actually be relatively easy. As you say, just use a bus for Vdd across the entire row of Vdd with a few 0402 capacitors to the thermal pad. You could either use a thick wire to connect Vss, or use an array of pins. I was planning on using maybe 4-6 of the pins from a 2mm header as the ground, since that would give you a decent bit of surface area that you could run a fan across them.
Great idea! Yeah - with pin layout - I did layout thinking of strings of chip assembly and did most of redistribution inside of chip, having in mind that for example it could fit on metal-core PCB when you don't have many layers. So wires should be straight there. If everything is wired correctly
I'm putting together a PCB for testing, but I'll have to see whether it's reasonable to get it fabbed and shipped to me at a reasonable cost by Thursday. What is the max SPI speed supported by the chip?
Well - with PCB take care of capacitor impedance. I doubt that thick 2-layer PCB will work better than capacitors you put there. I'll give you model:
1) Internal capacitance is about 50 nF
2) wirebond single VDD wire is about 1.5 - 1.8 nH
3) wirebond to GND is about 0.04 nH
total VDD+GND wirebond inductance is about 0.08 nH
resonant frequency of this internal LC-tank is about 70 Mhz.
Make at least ESL (serial inductance) to capacitors to about the same - of 0.08 nH
If you have 0402 and place it really well - it would have about 0.4 nH inductance - so put at least 5 of them there. But depends on your capacitors actually, they're a bit different.
Then if your power supply is far away (lab power supply) - I would put somewhere there 1 or 2 tantal caps and maybe some 0805 caps. But to calculate actual numbers - err - should do math - for frequencies up to say 100 Mhz here lumped circuit and it is pretty straightforward to calculate by hand using complex amplitudes... not slept too long, unfortunately will not do now :-)
The overall idea of power supply is to get |Z|(w) adequate low value, and rather flat without increasing peaks at specific frequencies that will be excited when chip average consumption changes a bit cycle to cycle (this is what I would like actually to see - how power consumption spectrum looks like). Also beware of parasitic resonances when different caps are placed (C - L - C) - that's why I offered such analysis.
Inside chip there's largest power consumption spike is 200-300 ps current risetime with target of about 8 amps, while average consumption is about 4 Amps for 0.8 V. It's pretty tought. As the more ripple on internal VDD ==> less clock you'll have or at low voltages flip-flops can loss data.
To sum up - I can't say if it will work as expected in say on 2-layer pcb with big homemade vias and large distances between caps and chip it will work as expected. Much more capacitors shall be installed with less efficiency.
Please note that small capacitor works as INDUCTOR at high frequencies... Not as capacitor... it shorts higher frequencies as small INDUCTOR would. INDUCTANCE IS PROPORTIONAL TO CURRENT PATH AREA (!!!). So - having larger distance between planes + larger distance for electrons to flow from your capacitors and they will flow without being happy and will do their job of calculating hashes lazily, so to keep them happy - reduce number of inductors on their way!
