[Arm-netbook] EOMA68 Computing Devices Update: Measurements and a Hypothesis

Paul Boddie paul at boddie.org.uk
Mon Dec 2 15:22:13 GMT 2019

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."


>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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