[Arm-netbook] EOMA68 Computing Devices Update: Measurements and a Hypothesis
Luke Kenneth Casson Leighton
lkcl at lkcl.net
Mon Dec 2 20:05:55 GMT 2019
On Mon, Dec 2, 2019 at 3:23 PM Paul Boddie <paul at boddie.org.uk> wrote:
> Hello again,
> I saw the latest update when it was issued a few days ago, with these
> being particularly important:
> "PCBs are etched with acid, and when the tracks or pads are particularly
> 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
> they should be. This, in turn, means that when the IC is put on the PCB
> 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
> short out."
> From what it says, it rather sounds like same (or a similar) problem is
> 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
> One of the samples was still with the factory, and that too was found to
> shorts. Mike has been extremely helpful, and this is the first time that
> been involved with BGA, where his uncle's factory has been the one that
> assembled the samples."
> 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
> 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.
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