I'm experimenting with trying to reflow a 0.8mm BGA myself for prototypes/repairs.
I've solved the main problem: alignment. I've used my 3D printer to print custom board guides that align on large through-hole pads and guide the BGAs into place. So far, I'm 100% on alignment for the 4 BGAs I've done so far.
Now, I'm trying to reflow it with my hot air system. I've got a BGA tip that fits over the part, and I have followed some general advice from a tech who told me to set it to 450 degC and put the BGA head down just about on the PCB totally covering the BGA for no more than 20 seconds.
I'm noticing that even the outer row of pads (All I can examine) are not shiny. They've reflowed beautifully, but all the flux has not burned off. I notice that paste pads that have been under the hot air long enough go completely shiny, and many other pads never quite burn off the flux (I assume) and remain somewhat dull. Is this fine, or does that indicate it didn't reflow properly?
How well does the air from these hot air BGA heads penetrate to the inner pads of a medium sized (14mm square) BGA? Should I bump up to my maximum 480 degC and/or heat it longer… ?
After noticing the dull pads on my first board, I attempted to reflow it for a longer period (40 sec) and pretty much burned the board. So, I know how far NOT to take it.
Any advice on the actual reflow of these?
EDIT: I forgot to mention I am using an IR preheating unit. (I actually use the hot air gun with the board on the preheating unit) I leave the preheating unit at about 250 degC for a couple minutes before starting.
I am seeing some videos online showing the use of a hot air gun and sort of following a real reflow oven profile at lower temperatures. Should I be doing that? I was thinking the hot air was not going to be as efficient and needed to be somewhat higher.
EDIT 2: I've tried following a profile used on a Youtube video for reflowing an XBox chipset, and even the paste on the surface of the board doesn't reflow. I guess if I really want to do this right I need to get some thermocouples and measure this directly. I re-ran the Youtube profile with 460C instead of 360C, and it looks good visually. I'll complete that board and see if it works.
EDIT 3: It works! An i.MX283 ARM processor running full Linux @ 454Mhz. 0.5-1 watt w/Ethernet. I'll get these 6 BGAs (3 boards, 2 BGAs each) X-rayed and see how I did.
Best Answer
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.