On Mon, Dec 2, 2019 at 3:23 PM Paul Boddie <[email protected]> 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-hypothesis > > 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. _______________________________________________ arm-netbook mailing list [email protected] http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook Send large attachments to [email protected]
