Honestly, I wouldn't try to solder my own BGA's. I know this doesn't directly address your issues, but hear me out.
It takes a lot of work and effort to solder a BGA. There's a lot of trial and error. A lot of messed up test boards. But then it's soldered. Now what?
Now you have to prove that it's soldered correctly. For that you need one or more of the following: JTAG test (US$10k, never has 100% coverage), optical inspection (US$20k for the equipment), or X-Rays (US$500k). The cost of doing these tests is too much for the normal hobbyist, and is even beyond many small companies.
Skipping those tests, you proceed with debugging your PCB. And let's say that the BGA is a complex CPU. Inevitably you'll find a bug. The CPU will randomly crash. Is it your software, your electrical design, or the soldering on the BGA that's causing the problem? Debugging this, in light of some possibly problematic soldering, is going to be terrible. It will add a lot of time to your debug process, possibly months, and you'll loose a lot of hair on your head. And then you can repeat this for the next major bug.
Without confidence that your soldering is perfect, you will always have this dark cloud over your head. Every little bug that shows up "could be a BGA soldering problem". This is made worse if you have multiple engineers working on the same PCB since the software guy will be questioning the hardware guy, etc.
Then, even if the BGA soldering is perfect, did the chip get too hot? Did you destroy the chip by getting it too hot? Even on modern assembly lines this is an issue. But with the proper equipment you can adjust and measure the temperature profiles to at least get you in the right ballpark. On one board I did recently, the BGA's were being damaged. The solder balls looked great, but under a very nice X-Ray machine we could see that the gold bond wires melted from the heat.
I've been there. Not at the hobbiest level, but professionally as we were bringing up new boards while the assembly shop was learning to do BGA's. We had no JTag. No optical inspection. And the X-Rays were terrible. Our PCB had 11 BGA's on them. That was 2 years of hell I don't wish to repeat.
So, here's my recommendation:
Get someone who has the proper equipment, training, and experience to solder your BGA's. There are a lot of contract manufacturers that'll do a single BGA. It takes money, but that's way less than the time you'll spend trying to debug your own soldering.
If you must do it yourself, then you should get the proper equipment, training, and figure out how to get the experience required. For this to pay off in the end, you need to have a large enough company and need to justify the huge amount of time and money that you'll put into this.
But I would never try to just kludge something together. That's a recipe for, um, bad stuff.
You've already accepted an answer, but I'll add this:
Keep in mind that all but the smallest (number of balls) and crudest (ball pitch) BGA layouts are going to require expensive multilayer boards- 6 or 8 layers, often not even the relatively inexpensive 4-layer type. Costly per board in small quantities and high up-front NRE costs that get charged every time you make a change. Slower, too, unless you pay astronomical rush charges.
They will also likely require microvias, which also increase the cost and limit which suppliers you can use. Companies that act as front ends for offshore factories will typically use a different factory for such multilayer boards.
The iMx6 processors use 21 x 21mm, 0.8 mm BGA, which is not the highest density, but will still likely require microvias, 6 or 8 layers and fine pitch.
Mounting a BGA chip is actually not that difficult if you don't require X-ray inspection- print with a stencil (rework stencils are available) and a pass through a reflow oven will do it. If the process is right they'll almost always be okay.
If you have sufficient budget for that kind of board technology, it is not a particular problem, but keep in mind that multiple spins of even a small board can eat up many weeks and thousands of dollars. Be sure to read the recommendations carefully on BGA layout before doing it (or deal with a layout person who has done this before) as mistakes are unusually costly if you're used to dealing with 1-2-4 layer boards.
Best Answer
The Ironwood sockets work like this. They use an elastomer interposer with embedded wires. Depending on the type they’re good for hundreds to thousands of mating cycles. They use a slightly modified version of the BGA footprint, and are compatible with soldering down the BGA later.
The other BGA socket type uses pogo spring pins. These are more common for production test boards.
That said, it’s not feasible to just push the BGA down onto the board with a clamp. Something has to compensate for co-planarity as well as make a gas-tight contact. Not only that, but pushing the chip down with that much force will damage the solder balls, making it impossible to solder the chip later.