Does anyone have experience about what is requied to reflow a BGA?
We had a very expensive BGA rework station (Weller WQB3000) at my last place of employment.
There are all sorts of problems with this, even if you have all the right equipment.
We all had a go at this, and even the sales rep for the equipment had real difficulty during a sales demo making it work.
First you need to fit the new chip to a jig that aligns it perfectly with the BGA pattern on the circuit board. This alignment is usually done with a small CCTV camera mounted to the jig.
Then you preheat both board and chip with a combination of infrared radiation and hot air from above and below.
The chip is then lowered onto the board, and as you say, surface tension in the molten solder "pulls" the chip into final position.
The first problem is heating the board. Too much heat for too long can delaminate a multilayer PCB, cause it to bulge and buckle under the BGA, and totally destroy the board. Too little heat and the process will not work, or work imperfectly.
The chip needs to be lowered onto the board dead square and dead on alignment. You only get one go, and it must be done fairly quickly because overheating will definitely destroy things.
Let a professional replace any BGA chips for you, and even then, don't be too surprised if your board never works ever again.....
It is a very hairy procedure at best, although someone doing it all day, every single day will get pretty good at it.
There is a vast difference in setting up a fully automated repetitive surface mount manufacturing process, to doing a one off repair job.
The automated process, you can afford to waste ten boards getting the times, positioning, and temperature profiles exactly right for that specific BGA chip size.
The automated machine then can do it a million more times with perfect success every single time.
A one off repair with one odd sized BGA chip is a whole different ball game, even with the very best equipment..