Well, the XuLA2 PCBs arrived last week and now they are moving through assembly. But before I could start that, I had to build up one of the boards to make sure it worked. (I wouldn't want to assemble a batch of boards at $60 a pop and then find out the PCB was wacked.)
The XuLA2 board has a 256-ball BGA on it. In the past, I've sent a single board and BGA to my assembler and had it mounted. Then I would assemble the rest of the board and test it. The problem with doing this is the delay:
Monday: I mail a PCB and BGA to the assembler. (They are forty miles away.)
Tuesday: The assembler receives the package and - if they jump right on it - mounts the BGA on the PCB.
Wednesday: The assembler mails the mounted BGA and PCB back to me.
Thursday: I receive it along with a bill for $50.
To avoid a three-day delay and $50 out-of-pocket, I wondered if I could mount the BGA myself. The total cost of the BGA and PCB was less than $35, so the potential loss was minimal if I screwed up. And I could always fall back on my assembler if I failed.
While I didn't have the temperature-controlled convection heater or the X-ray inspection machine like my assembler, I did have a $40 paint stripper that should heat the BGA enough to make it reflow. Surprisingly enough, I was able to successfully mount the BGA to the PCB using very simple tools and procedures. Here's a video that shows how I did it:
The first BGA I mounted was a failure, but every one since then has worked. I wouldn't employ this technique on a board I'd send to a customer or one with a large, expensive BGA, but I would use it for short-term prototypes with mid-size BGAs.