Thanks asmi, that's perfect - I'll look at those suggestions in some detail over the next week or two as I work on the power supplies. Do you use EasyEDA at all? If so, I'm happy to share the project with you so you could give me more constructive feedback if you wish?
One of my commercial customers paid for my Altium Designer license a couple of years back (before the COVID), so that's what I'm using now. But I will be happy to help with your design as well, if not with doing the actual layout, but at least with feedback.
As far as the mezzanine board idea goes, I understand what you mean now - thanks for the links. I had a quick look on Mouser last night for those mezzanine/back-to-back connectors, but they don't seem to have a good supply of them (certainly not the 144-pin versions anyway), but I guess the whole layout/form-factor of the board (and whether I'll use a mezzanine for the FPGA itself) is something I can worry about a little later. Getting a good schematic sorted is my first priority, and now I've committed to the Artix A7-100T I'm keen to get moving on it - it's just a busy time of year with family commitments as I'm sure you'll understand! ![Smiley :)](https://www.eevblog.com/forum/Smileys/default/smiley.gif)
That's OK, there is no rush, especially since there is going to be a Chinese New Year coming, so enjoy your time with the family. I've lost my mother to a COVID two years ago, so now I know how important it is to spend as much time as you can with the family, because you never know how much of it you have left...
As for connectors, I know a good place where you can find all kinds of connectors always in stock. And you can sometimes even get some for free
![Wink ;)](https://www.eevblog.com/forum/Smileys/default/wink.gif)
But we will get there when we will get there, right now it's more important to plan your design thoroughly such that you won't have to do a redesign because of some small stupid thing you just forgot about, or didn't think hard enough.
Also, when you receive your FPGAs, please resist your urge to open them up. These things are moisture- and ESD-sensitive, so don't take unnecessary risks if you can help it. Or - if you can't resist - at least take out the 35T part as it's cheaper in case something bad happens
![Grin ;D](https://www.eevblog.com/forum/Smileys/default/grin.gif)
It looks like I'm going to need two DDR3 chips in the design too, so that's something I'll need to bear in mind, thanks to the conversation with BrianHG over in the GPU thread:
...We are beginning to enter the realm of a simple 3D accelerator and with an added texture reader prior to this writer, with proper design, and maybe a second DDR3 chip for a 256bit wide bus & 128x speed, we will pass the first Sony Playstation in rendering capability.
If you wish, you can implement two 32 bit DDR3 interfaces, or even up to 4 independent 16 bit DDR3 interfaces, or implement 4 x 8 bit interface instead of 2 x 16 bit one for higher capacity. There are a lot of possibilities. You just need to figure out what you need before you embark on a board design.
One of the elements of the PCB design that has caused me headaches with the (admittedly 0.8mm pitch) LFE5U FPGA was the decoupling capacitors underneath the board. I can solder 0402 confidently, but I don't feel confident at all going smaller than that. How did you solder the 0201 caps on your boards?
I use a stereo microscope (this one:
https://amscope.com/products/se410-xyz but you can find cheaper options) and under 10x magnification 0201's are not that hard to solder unless your hands are really shaky. I typically do a reflow, so I place all parts by hand on a solder paste under microscope, and then stuff it into the oven to reflow it all at once. But if neccessary I can solder them manually one-by-one. That said, I try to avoid them and stick to 0402 whenever I can, because 0402 are super easy to solder under the microscope - infact I even taught my wife to do it and she now does it just as good (if not better) than I do - despite her knowing exactly nothing about electronics
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/smiley.gif)
I highly recommend you consider buying such microscope - it makes microsoldering a breeze since your depth perception still works (thanks to stereoscopic image). My wife finds using it so comfortable that she even does her nails now under it
![Grin ;D](https://www.eevblog.com/forum/Smileys/default/grin.gif)
Make a good Christmas present for yourself
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/smiley.gif)
Also if you have small kids, they might also find it interesting looking at various things under magnification. You will also need a pair of good tweezers (search for "titanium alloy tweezers" on Aliexpress - they are quite good, and should last for a long time, just be careful to avoid punctures as the "business end" is super-sharp).
Finally, to make soldering BGAs (or anything really) easier you might want to consider getting some sort of preheater. It doesn't need to be very powerful because realistically you will only be preheating your board to like 100°C or so, so if you have some sort of hot plate which can reach such temperature - it's good enough. Just make sure you can comfortably work with a hot air gun above PCB while it's on a heater - otherwise it's just a matter of time until you accidentally make a wrong move and end up getting a burn. Trust me, it will eventually happen in any case
![Banging Head |O](https://www.eevblog.com/forum/Smileys/default/bangheadonwall.gif)
, but there is no reason to hasten that eventuality
![Wink ;)](https://www.eevblog.com/forum/Smileys/default/wink.gif)