[danmatan]

And from a manufacturing/engineering point-of-view (which I am neither), I guess it's really hard to solve this problem.

You have some unpredictable 1/100 or 1/1000 defect that occurs long after production and sale.

Just how do you go about isolating the cause, and testing a solution? Make 5 changes, and put through a production batch of 1000 units, and then do accelerated testing? If 5 fail from one batch, and 2 from the rest, is there even enough statistical power to confirm that you've come across a solution? And you just burned through 5000 units.

Sounds like fun trying to solve this kind of problem.

[jmpe]

There are PCB design/layout rules that deal with BGA. I'm not saying it's a 100% guarantee, but (much like EMC/EMI design rules) there are a lot of solid pointers that remove 90% of the issues. The remaining 10% are (again, much like EMC/EMI) subject to the layouter's level of experience.

Currently on mobile, can't link a PDF right now but if you Google " BGA PCB layout guidelines" you'll get a ton of documents.

Lastly: PCBs go through several optimization cycles, some occur after release for high volume stuff. There are always revision numbers of the silkscreen, sometimes they catch an issue like this after x1000 devices in the wild and do an update.

[DanBC]

To add to what jmpe says:

In production you would profile the boards. You take a board and run it through the oven with some thermocouples. You'd then set the temperatures of the pre-heat, heat, and cool down sections. This would heat the solder to melting point without putting too much stress on the components.

This is from memory from a long time ago using a teeny tiny little pick and place machine that did a few thousand components per hour.

BGAs were always always horrible to do.

"Design for production" is really very important and it's hard to find much information about it. Some simple little things can make the difference between an operator having to plonk a component on the board by hand every time just before it goes into the oven or having the machine do it. (Again, from memory).