[Arm-netbook] EOMA68 Computing Devices Update: Measurements and a Hypothesis
paul at boddie.org.uk
Mon Dec 2 15:22:13 GMT 2019
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
>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:
"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."
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. But perhaps one of these situations informs the
other, or maybe they inform each other somehow.
Thanks in any case for keeping us updated!
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