On Mon, Dec 2, 2019 at 3:23 PM Paul Boddie paul@boddie.org.uk wrote:
Hello again,
I saw the latest update when it was issued a few days ago, with these details being particularly important:
"PCBs are etched with acid, and when the tracks or pads are particularly close together (such as with BGA balls), not enough acid gets in to eat away the copper, and (in a very indirect way) the BGA pads end up being far larger than they should be. This, in turn, means that when the IC is put on the PCB and heated up, the BGA balls (which are made of solder) will spread out much farther, and potentially even spread so far that they contact each other and short out."
https://www.crowdsupply.com/eoma68/micro-desktop/updates/measurements-and-a-...
From what it says, it rather sounds like same (or a similar) problem is being encountered as the one which happened with the Ingenic JZ4775 boards:
yehyeh. except i didn't know about the PCBs not actually matching the gerber files, back then.
"When the first 6 samples were done, only one was found to be working: for some reason the DDR3 BGA solder balls had spread and caused short circuits. One of the samples was still with the factory, and that too was found to have shorts. Mike has been extremely helpful, and this is the first time that he's been involved with BGA, where his uncle's factory has been the one that assembled the samples."
http://rhombus-tech.net/ingenic/jz4775/news/EOMA68-jz4775_XRay_Photos/
At that point in time, I don't remember any more news about resolving the matter, and with the campaign being finalised the priority was no longer to get these boards working.
i did actually partly get them up and running, but i'd put a 24mhz XTAL on instead of 48mhz, and the SD/MMC wasn't having it. i tried fixing that in software (doubling the PLL frequencies for the SD/MMC) but couldn't get it up and running.
with it only being single-core 1ghz MIPS32 i dropped the investigation.
But perhaps one of these situations informs the
other, or maybe they inform each other somehow.
i'd forgotten about it, so thank you for the reminder.
Thanks in any case for keeping us updated!
no problem paul.
l.